Performance evaluation of Ultrahigh performance fibre reinforced concrete – A review

Construction and Building Materials 232 (2020) 117152

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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

Review

Performance evaluation of Ultrahigh performance fibre reinforced concrete – A review Faiz Uddin Ahmed Shaikh a, Salmabanu Luhar b,⇑, Hasan Sß ahan Arel c, Ismail Luhar d a

School of Civil and Mechanical Engineering, Curtin University, Perth, Australia Institute of Mineral Resources Engineering, National Taipei University of Technology, Taipei, Taiwan c _ _ Faculty of Architecture, Izmir University, Izmir, Turkey d Shri Jagdishprasad Jhabarmal Tibrewala University, Rajasthan, India b

h i g h l i g h t s  Fibers might be wielded for the fabrication of Ultrahigh performance fibre reinforced concrete.  UHPFRC unveiling a higher compressive, tensile and flexural strengths.  UHPFRC is having higher ductility as well as admirable durability.  The article reviewed the mechanical properties, specimens size effect, as well as loading rate effect.  The article also reveals the effects of fıbre– type, geometry, length, volume and orientation on concrete attribute.

a r t i c l e

i n f o

Article history: Received 17 June 2019 Received in revised form 22 September 2019 Accepted 3 October 2019

Keywords: Ultrahigh performance fibre reinforced concretes (UHPFRC) Compressive strength Impact strength Bond behavior Steel fibre Tensile and flexural strengths Supplementary cementitious materials

a b s t r a c t Ultrahigh performance fibre reinforced concrete (UHPFRC) is a newfangled cement-based material unveiling a compressive strength of more than 150 MPa, higher tensile and flexural strengths, ductility as well as admirable durability. This review of the past researches on diverse influential features is vital in obtaining fundamental data for its viability for the application. Consequently, this study aimed to review the available literatures on UHPFRCs that examine the attributes of ideal UHPFRC, such as mechanical properties viz., compressive, tensile and flexural strengths; mixing proportions and environment friendliness; curing regimes; effect of specimens size on its compressive, flexural and tensile strength as well as loading rate; effects of fıbre properties – type, geometry, length, and volume fractions, orıentatıon and quantıty attrıbutes of UHPFRC is endeavoured along with relevant discussion. Subsequently, the best UHPFRC mixture was determined to be obtainable with 2% to 3% of steel fibre content and water/cement ratio of <0.2. Additionally, the UHPFRCs that were subjected to curing at 90 °C yielded compressive, tensile, and flexural strengths that were 49% better than the samples cured at 20 °C. The review elucidates the key points of producing environmental friendly UHPFRC material for future applications as the current UHPFRC contains about twice the amount of cement compared to ordinary concrete. Ó 2019 Elsevier Ltd. All rights reserved.

Contents 1. 2. 3. 4. 5. 6.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Ideal UHPFRC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Mix Proportion of UHPFRC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Sustainable UHPFRC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Curing Regimes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 UHPFRC Mechanical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 6.1. Compressive Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

⇑ Corresponding author. E-mail address: [email protected] (S. Luhar). https://doi.org/10.1016/j.conbuildmat.2019.117152 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.

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7. 8. 9. 10. 11. 12. 13.

6.2. Tensile and Flexural Strengths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3. Impact Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Effects of specimen size on mechanical properties of UHPFRC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Effects of fıbre geometry, length, and volume fractions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Effects of fıber orıentatıon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Effect of fıbre type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Effect of quantity of fıbres . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Applications and prospective recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusions and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Declaration of Competing Interest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1. Introduction Concrete is the utmost expansively employed building material owing to its widespread application and rewards despite its shortcomings, such as its moderately lower tensile strength or brittleness [1–4] and comprehensively employed construction materials on the earth which is an impetus of constructional and infrastructural development of any nation since Romans had initiated its use as ‘‘Opus Caementicium” [5,6]. However, an exigency of various performances by concrete has escalated with the increasing demands of today’s construction and infrastructure industries and has attained levels that traditional concrete cannot satisfy [7,8]. High-performance concrete (HPC) is preferential to conventional concrete on account of high strength and durability in engineering applications [9]. However, although it has greater strength, its brittleness is known be higher than that of traditional concrete. The use of HPC dates to the 1970s. HPCs with 62-MPa compressive strength were used for the Water Tower Place in Chicago in 1974, HPCs with 69-MPa compressive strength were utilized for the construction of Taipei 101 in Taiwan in 2004, and HPCs with a compressive resistance of 80 MPa were employed for the 126 floors of the Burj Khalifa in the United Arab Emirates, Dubai in 2009 [10]. Despite its frequent use, several disadvantages stand out. For instance, if high-performances and conventional concretes are subject to heat, high-performance concrete’s strength loss is higher than conventional concrete [11]. Ultrahigh-performance fibre-reinforced concrete (UHPFRC) is produced by combining HPC and fibre at 3 vol% or above [12,13]. UHPFRC is a form of concrete with a high compression intensity (150–200 MPa) (Fig. 1 demonstrations a compressive stress-strain curve), a lower water to concrete ratio of 0.2 or less, high bending strength, a ten-

Fig. 1. Typical compressive strength – strain curve [44].

10 14 14 18 20 21 23 23 24 25 25

sile strength of >7 MPa (Fig. 2 illustrations the tensile stress-strain curve), a maximum aggregate diameter of less than 1 mm, superior ductility in tension and bending, high fracture toughness and low maintenance. Despite its low water/concrete ratio, it has high workability (200 mm) and retains its pump ability [14–17]. UHPFRC has been an attractive alternative material for High elevation buildings, pre-stressed girders as well as long span bridges because of its superior compressive and tensile strengths and toughness performance [18,19]. Fig. 3 shows the SEM images of silica fume-substituted normal concrete (a), fibre-reinforced concrete (b), HPC (c), and ultra-HPFRC (d). 2. Ideal UHPFRC The strength of UHPFRC depends on three characteristics: cement paste pore structure, quality of the aggregate, and structure of the aggregate–matrix and fibre-matrix interfaces. The weakest among these characteristics is the interface area, which could be enhanced by reducing the water to cement ratio as well as custody the aggregate diameter below 1 mm. However, both methods have upper limits. Cementitious materials, such as fly ash, slag, and silica fume, not only lower the cost of production but also increase the strength [20,21]. The durability of highstrength concrete is determined as functions of full volume and the pore s. The quality of the aggregate directly affects the highstrength concrete [22–27]. UHPFRCs are not generally used when traditional concrete is productive because of its elevated manufacturing price, providing the required output. In this regard, researchers pointed out three main factors that can be reduced to lower the cost without compromising the quality of the product, namely, the high-strength fibre quantity added to the mix, the powder quantity, and the curing [28–30]. For the production of

Fig. 2. Uni-axial direct tensile stress – elongation curve [45].

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3

Fig. 3. SEM images of NC, FRC, HPC and UHPFRC concretes – a) [135], b) [136], c) [137,138], d) [139].

UHPFRC the mean particle size is frequently less than 1 mm, but aggregates are up to 8 mm to 15 mm. [31]. The reactive powder concrete (RPC) word can be used if the maximum total size is roughly 0.5 mm. The aggregate must be mechanically strength to ensure that the concrete is not fragile [32]. When coarse aggregates are added to the mortar, the cement content is decreased. coarse aggregates are not often used in UHPFRC, but can be used if the structural component size is greater than the aggregates thickness [33]. In UHPFRC, costly silica sands are usually used. However, natural sand can usually be substituted for silica sand and retain excellent mechanical efficiency and ductility. The use of natural sand does not have a significant impact on UHPFRC strength [34]. Depending on the concrete type and application, the fiber content can differ considerably. When it is important to workability attribute, the fibers in the concrete are usually a mixture of a large number of short fibers and a few lengthy fibres [35]. The fibers may be less than 12 mm and the complete quantity can be 11 percent [36]. Approximately 2.5% steel fibers with aspect ratio of 40 to 60 have however been demonstrated to produce the highest outcomes in terms of fresh and hardened concrete characteristics. The length of the fibers should be set to the maximum aggregate diameter in order to ensure low porosity. At least ten times the maximum overall diameter should be the length of the fiber. Unless high-performance plasticizers are added, the UHPFRC cannot workable, i.e. up to 5 percent by weight of a cement. The aspect ratio of fibers has a major impact on the fibers ’ facility to mix into the concrete and on the workability of the concrete. Workability reduces in particular with the increase in the aspect ratio [37]. UHPFRCs are sometimes undergoing heat therapy in order to enhance the concrete quicker (compressive and tensile resistance), decrease shrinking time and creep impacts and considerably enhance the concrete’s durability [38]. Heat treatment begins to produce more hydrates, leading to enhanced features [39]. The requisites to obtain maximum performance from UHPFRCs can be summarized into four: (1) improving the homogeneity using sand

with a grain size of 150 to 600 mm, (2) increasing the density by adding cement and silica fume, (3) improving ductility by adding steel fibres, and (4) implementing temperature treatment (90 °C) to improve the UHPFRC microstructure and increase early age durability [34,40,41].

3. Mix Proportion of UHPFRC The raw materials of UHPFRCs and concretes with normal fibres are the same, except the superplasticizer, aggregates and the mineral additives with different binding characteristics. The hydration process of the paste phase and the microstructure of the hydrated paste demonstrate variances because the water/cement or water/ binder ratios are low and high-range water reducers are employed in UHPFRCs. To achieve the required UHPFRC output: (1) the cement fineness should be high; (2) the quantity of C3S should be high; (3) C3A and C4AF quantities should be low; and (4) it should have a cubic polymorph structure, and the amount of alkali and alkaline sulfates should be limited. The UHPFRCs collapse when aggregates crack. Thus, an aggregate with low durability would cause the UHPFRC to have low durability as well. In UHPFRCs, the high-range water reducer rapport with the cement is highly important. Sufficient workability should be provided and not be exhausted in a short period. The purpose behind adding steel fibres to the cement is to establish a crack control and resistance to the pull-out force that the cement matrix cannot carry for a long time after the peak load. Bending strength addresses the fragility of the steel fibre, and the fibre amounts are the utmost imperative features in determining the characteristics of UHPFRCs. Preferably, the water/binder and water/cement ratios are maintained at approximately 0.16–0.2 in UHPFRCs [42,43]. The content of cement usually varies from 600 to 1000 kg/m3 having 3000 and 4500 cm2/kg of fineness shall be used. Ordinary Portland cement with low C3A content is suggested to use owing to its low water

4

Table 1 Research studies that examined the ideal mixture ratios of UHPFRCs at a wide range. References

Mix design (kg/m3)

Fiber

[46]

875 CEM I 52.5 R, 44 micro silica, 218.7 Microsand (0–1 mm), 202.1 water, 45.9 Superplasticizer, 1054.7 Sand (0–2 mm), 0.23 w/c, 0.19 w/b Proportions by weight 1.0 Portland cement, 0.3 Filler (crushed quartz with an average diameter of 10 lm and a density of 2600 kg/ m3), 1.1 Fine aggregate (sand with a diameter of < 0.5 mm), 0.02 Water-reducing admixture, 0.2 w/b

Short straight steel fibers (length of 13 mm and diameter of 0.2 mm), 2.5 (vol.%), Specific density 7800 kg/m3 Proportions by steel fibers, Diameter of 0.2 mm, lengths of 16, Diameter of 0.2 mm, lengths of 19 (Used together at weight 0.25 (volume of 1.5%) the same time) Steel fiber, 13 mm long with a diameter of 0.15 mm 0.2 (Proportions by and tensile strength of 2800 MPa weight)

[47]

[55]

[61] [145]

[146] [147] [148] [45] [149] [150] [144]

[88] [141] [151] [152] [44] [153] [154] [143]

[26] [60]

Steel fiber Short high strength 13  0.15 mm

steel fibers, 13 mm length and 0.16 mm diameter

160 kg (%2 by volume) 0.05 0.1 0.15 0.2 0.25 0.3 3%

steel fibers, straight (10 mm, 0.2 mm) Steel fiber (Lf = 10 mm, df = 0.2 mm),

470 157

Steel fiber (Lf = 10 mm, df = 0.2 mm),

90

Steel fibers 12 mm long with diameter of 0.18 mm

158

steel fiber 13 mm length and 0.2 mm diameter

157

straight high carbon steel with a tensile strength of 2000 MPa, 13 mm in length and 0.20 mm in diameter Steel fibers straight, lf/df = 13 mm/0.20 mm

%2 By volume

The steel fibers, 13 mm long and 0.18 mm thick with an aspect ratio of 72 steel fibers with a diameter of 0.2 mm and a length of 13 mm. yield strength of 2500 MPa. Steel fibers (1/d = 50)

192

Fibers metal Steel fiber, fibers are of type OL13 with 2000 MPa tensile strength, 13 mm length and 0.2 mm diameter Steel, straight, lf/df = 13 mm/0.2 mm

195 157 (2%)

(proportions by weight) Steel Fibers (13  0.15 mm)

microfibers and straight steel fibers (10 mm/0.2 mm) 13 mm steel fibers, 0.2 mm in diameter (%2 Steel fiber volumetric percentage) 13 mm steel fibers, 0.2 mm in diameter (2.5% Steel fiber volumetric percentage) 20 mm steel fibers, 0.3 mm in diameter (2.5% Steel fiber volumetric percentage) 235.5 Steel fibers (13/0.16 mm) 0.27 (proportions by weight) Fiber, Straight steel fiber, length/diameter = 13 mm/0.20 mm

Proportions by weight 0.25

2.0% 468

0.25, (2.5% by volume) 706.5 156 195 195

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[67]

(Proportions by weight) 1.00 CEM I 52.5R, 0.25 Silica fume, 0.25 Glass powder, 0.22 Water, 0.031 high-range water reducer (Sika SVC 20 Gold) , 0.019 high-range water reducer (Sika ViscoCrete 20He), 0.42 Fine sand (0.1/0.6 mm), 0.8 Fine sand (0.3/0.8 mm), 0.176 w/b 800 CEM I 52.5R, 176 water, 40 high range water reducers, 336 fine sand (0.1/0.6 mm), 640 fine sand (0.3/0.8 mm), 200 silica fume, 200 glass power 0.95 Fine sand (0.3/0.8 mm) (proportions by weight) 1.00 Cement I 52.5 R, 0.22 water, 0.05 high range water reducer, 0.42 Fine sand (0.1/0.6 mm), 0.25 Silica 0.90 Fine sand (0.3/0.8 mm), 0.85 Fine sand (0.3/0.8 mm) fume, 0.22 w/c 0.80 Fine sand (0.3/0.8 mm) 0.75 Fine sand (0.3/0.8 mm) 0.70 Fine sand (0.3/0.8 mm) 657 CEM I 52.5 N, 418 Ground Granulated Blast Furnace Slag, 119 Silica fume, 1051 Silica sand, 59 Superplasticizers, 185 Water, 0.15 w/b 1050 CEM I 52.5 N, 730 Quartz sand (Diameter < 500 lm), 275 Silica Fume (spec. surf. 12 m2/g), 35 Superplasticizer, 0.14 w/b 768 OPC (Type 1, 42.5R), 1140 Mining sand (Diameter < 1180 lm), 192 Silica fume (23.7 m2/g), 40 Superplasticizer (PCE-based), 144 Water, 0.15 w/b 825 OPC (Type 1, 42.5R), 1140 Mining sand (Diameter < 1180 lm), 181 Silica fume (23.7 m2/g), 45 Superplasticizer (PCE-based), 174 Water, 0.17 w/b 1011 Blast furnace slag cement III/40, 58 Silicate fume, 79 Sílica flour (18 lm), 60 Aggregates (150–300 lm), 823 Aggregates (425– 600 lm), 76 Micro fibers de wollastonite, 50 Plasticizer PA, 162 Water, 3.75 Air (%), 0.19 w/b 657 CEM I 52.5 N, 418 Ground Granulated Blast Furnace Slag, 119 Silica fume, 1051 Silica sand (average size 0.27 mm), 40 Superplasticizers, 185 Water, 0.15 w/b 657 CEM1 52.5 N, 418 Ground Granulated Blast Furnace Slag, 119 Silica fume, 1051 Silica sand (average size 0.27 mm), 40 Superplasticizers, 185 Water (Proportions by weight) 1.00 Cement PC Type I (3930 cm2/g Blaine value), 0.25 Silica fume (very low carbon content (0.3%) and a median particle size of 1.2 lm), 0.25 Silica powder (median particle size 1.7 lm) , 0.22 Water, 0.0054 Superplasticizer (Solid content), 0.26 Fine sand 1 (max. grain size 0.2 mm), 1.03 Fine sand 2 (max. grain size 0.8 mm), 0.22 w/b 960 CEM II/A-L 42.5 R, 240 Silica fume (specific surface area of about 18 m2/g), 24 Superplasticizer, 960 (Sand well-graded very fine natural sand was used with particle size up to 100 lm), 227 Water, 0.24 w/c, 0.19 w/b (Proportion of materials by weight ratio), 1.0 ordinary Portland cement, 0.25 silica fume, 0.3 filler, 1.1 fine aggregate (diameters<0.5 mm), crushed quartz with an average diameter of 10 lm, 0.02 Water-reducing admixture, 0.2 w/c 1051 CEM I 52.5, 273 silica fume, 733 Sand (dmax = 0.5 mm), 165 Water, 35 Superplasticizer, Air content 4% of total volume, 0.14 w/b 2349 Premix EIFFAGE B1M2, 195 Water, 50 Superplasticizer Glenium G51, 1.9 void ratio (%) 657 cement, 418 Ground Granulated Blast Furnace Slag, 119 Microsilica (silica fume), 1051 Silica sand, 40 Superplasticizers, 185 Water Proportions by weight, 1.0 Cement PC Type I, 0.25 Silica Fume, 0.25 Quartz Powder, 0.22 Water, 0.0054 Superplasticizer (solid content), 0.26 Fine sand A (max. grain size 0.2 mm), 1.03 Fine sand B (max. grain size 0.8 mm), 1410.2 CEM I 52.5, 366 Silica Fume, 80.4 Fine Sand (maximum size of 0.5 mm), 200.1 Water, 44.1 Superplasticizer, 0.13 w/b 2195 (Premix = Proprietary mixture designs, including inert and cementitious constituents), 30 High-range water-reducing admixture, 130 water 2161 (Premix = Proprietary mixture designs, including inert and cementitious constituents), 29 High-range water-reducing admixture, 128 water 2296 (Premix = Proprietary mixture designs, including inert and cementitious constituents), 50 High-range water-reducing admixture, 190 water 1277.4 CEM III/B (66–80% high percentage of blast furnace slag), 95.8 Silica fume, 664.6 Sand, 42.3 Superplasticizer, 198 Water, W/ C = 0.155 (proportions by weight), 1.00 Cement, 0.25 Silica fume, 0.25 Glass powder (Median particles size is 1.7 lm), 0.19 Water, 0.011 Superplasticizer, 0.28 Sand A (Maximum grain size is 0.2 mm), 0.64 Sand B (Maximum grain size is 0.8 mm),

Table 1 (continued) References

Mix design (kg/m3)

Fiber

[155]

(Proportion by weight), 1.00 Cement 52.5 ordinary Portland cement, 0.41 high strength fine aggregate (size ranging from 1 to 3 mm), 0.3 Silica flour (size between 0.1 mm and 0.3 mm and surface area ranging from 20 to 28 m2/g), 0.32 Silica fume (average size of 0.04 mm), 0.19 water, 0.19 W/C 795.4 CEM I 52,5R HS-NA Cement, 168.6 sika silicoll uncompact, 24.1 sika viscocrete, 198.4 fine quartz, 971 sand quartz (0.125/ 0.5), 0.255 w/c, 0.210 w/b 1.00 Type 1 Portland cement, 0.25 Water, 0.25 Silica fume, 1.10 Sand (grain size lower than 0.5 mm), 0.30 Silica four (2 lm diameter, including 98% SiO2), 0.018 Superplasticizer, 0.2 w/b 1.00 Cement, 0.25 Water, 0.25 Silica fume, 1.10 Sand (grain size smaller than 0.5 mm), 0.30 Silica flour (2 lm diameter, including 98% SiO2), 0.018 Superplasticizer, 0.2 w/b 855 cement, 470 quartz sand (9–300 lm), 470 quartz sand (250–600 lm), 214 microsilica, 188 water, 28 Superplasticizer, 0.22 water/cement, 0.18 water/binder Percentage by Weight (%),28.6 Cement, 9.3 Silica Fume, 8.5 Ground Steel Fibers, diameter of 0.2 mm and a nominal length of Quartz, 41.1 Fine Sand, 0.5 Superplasticizer, 5.6 Water 12.7 mm. Its yielding stress is 3150 MPa and ultimate stress is 3250 MPa. Relative weight ratios to cement, 1.00 Type I Portland cement, 0.25 Water, 0.25 Silica fume (200,000 cm2/g Specific surface), 1.10 Sand (grain size smaller than 0.5 mm and 2-lm-diameter), 0.30 Silica flour (98% SiO2), 0.016 Superplasticizer, 0.2 w/b

short straight steel fiber, 6 mm long, diameter of approximately 0.2 mm (The tensile strength and Young’s modulus for the steel fibers were reported to be 1.2 GPa and 210 GPa) 79.31 steel fiber (1%) 160.25 steel fiber (2%) 2% Steel Smooth fiber, 0.2 Diameter, 13 Length, 2500 Tensile strength (MPa)

[68] [156] [62] [157] [64]

[158]

[160] [59] [142]

[66]

Ductal Premix (consist of Portland cement, silica fume, quartz sand with a maximum particle diameter of 1.2 mm and very fine powder composed mainly of quartz as the mineral admixture), w/c 0.22, 155 water, 25 superplasticizer DuctalÒ (712 kg/m3 Portland Cement, 1020 Fine Sand, 231 Silica Fume, 211 Ground Quartz, 30.7 high-range water-reducing admixture, 30 Accelerator, 109 Water), 0.22 w/c (Relative weight ratios to cement), 1.00 Type I Portland cement, 0.25 water, 0.25 silica fume, 1.10 sand (grain size smaller than 0.5 mm), 0.30 silica flour (2 lm-diameter, 98% SiO2) , 0.016 superplasticizer, 0.2 w/b 654 type I Portland cement, 109 silica fume (specific surface area 2200 m2/kg), 109 fly ash (specific surface area 686 m2/kg), 218 slag (specific surface area 766 m2/kg), 1090 sand, 32.7 superplastizer, 0.16 w/b 880 Standard Portland pozzolan cement with a strength category of 52.5 N/mm2, 220 Undensified silica fume with 97% purity in SiO2, 475 Calcareous Sand 125–250 lm, 358 Calcareous Sand 250–500 lm, 172 Water, 67 Polycarboxylate polymer based superplasticizer, 0.20 Water/cement, 0.16 Water/binder

(390 kg, 0.16 mm diameter, 6 mm long), (78 kg, 0.16 mm diameter, 13 mm used together at the same time Percentage by Weight (%) 6.4

0.2 mm Diameter, 13.0 mm Length, 7.8 g/cm3 Density, 2500 MPa Tensile strength

Short straight steel fiber, diameter 0.2 mm, 15 mm long Short straight steel fiber 1%, 2%, 3%

1% 2% 3% 4% 157 kg/m3, (%2)

2% Steel fiber, 0.2 mm Diameter, 13.0 mm Length, 2500 MPa Tensile strength Cold drawn low carbon steel fiber, 13 mm length, 0.175 mm diameter, tensile strength 1800 MPa

2% 3% 4% 401 Brass Coated Steel Fibers 6 mm and 0.16 mm diameter, 80 Brass Coated Steel Fibers 13 mm and 0.16 mm diameter used together at the same time

F.U.A. Shaikh et al. / Construction and Building Materials 232 (2020) 117152

[159]

2% Steel Smooth fiber, 0.2 Diameter, 13 Length, 200 Tensile strength (GPa)

5

6

F.U.A. Shaikh et al. / Construction and Building Materials 232 (2020) 117152

Table 2 Curing regimes. References

Curing type

[46] [54]

The prisms are demolded approximately 24 h after casting and then cured in water at about 21 °C. The samples were de-molded after 24 h. Thereafter, the recommended curing treatment for the UHPFRC (steaming at 90 °C and 100% relative humidity for 48 h) was applied. The samples were then cured in water at 27 °C ± 2 °C until the testing day. The specimens were then covered with damp hessian and polythene sheeting. After one day, they were de-molded and cured in water either at 20 °C or at 90 °C. The heat cured specimens were stored in a hot water bath from an age of 1 day until 7 days. These specimens were then stored in air at room temperature until testing. The 20 °C cured specimens were kept in a standard curing tank until testing. Thermal treatment for 5 days with a constant temperature of 90 °C, water curing for 5 days with a constant temperature of 20 ± 2 °C, Subsequently the specimens were kept in the temperature 20 ± 2 °C and relative humidity 60 ± 5% until testing The concrete samples underwent 5 days of moist curing followed by dry curing under ambient conditions, with the concrete properties determined on the day of the column tests The cylindrical test specimens were cured by steam curing at a temperature above 90 °C for 48 h, and then they cured at room temperature for 60 days until testing Specimens were removed from molds after 24 h and subsequently placed in water tanks for another 27 days The specimens were cured in a steam curing tank at 90 °C for 3 days. The evolution of the relative humidity in the material was recorded in a sealed specimen under isothermal conditions at T = 20 °C. The relative humidity was constant at 100% until 32 h after the addition of water and then decreased monotonically The specimens were covered with a damp cloth and a polythene sheet in their molds for 24 h before being demolded and cured for 28 days in a fog room with a controlled environment of 100% relative humidity and 23 ± 1 °C. Specimens mixes were covered with damp hessian and polythene sheets, and kept at laboratory temperature 20 °C for 24 h. After all the specimens were checked for initial set, demolding took place at approximately 24 h. All the specimens were placed in a curing tank in an elevated temperature of 90 °C for the next 48 h and finally kept at laboratory temperature until the testing day All the samples were cured after casting under approximately 20 °C for the first 24 h, followed by a hot water curing tank at 90 °C for the next 48 h and finally dry cured at laboratory temperatures until testing After casting, the specimens were covered with plastic sheets and stored at room temperature for 24 h. Then they were taken out of their molds and stored in a water tank at 20 °C for an additional 25 days. All specimens were tested at the age of 28 days after being removed from water and left to dry in the laboratory environment for 48 h. Three prismatic specimens (40 by 40 by 160 mm) were manufactured for each mixture and for each curing time in order to evaluate mechanical behavior of the seven UHPFRC mixtures. they were soft cast in steel forms (vibrated for 30 s after casting), then wet cured at 20 °C (standard curing) for compressive strength measurements. Cast in 50  200  500 mm3 molds. No thermal treatment was applied. After 3 days in sealed conditions, the specimens were removed from molds and exposed to wet curing until 28 days (Table 2). Afterwards, specimens were stored in a room at 20 ◦C and 50% relative humidity. The specimens were submitted to tensile tests after at least 1 month of storage and brought back to the room. No thermal treatment was applied. After 3 days under sealed conditions, the specimens were removed from molds and exposed to wet curing until 28 days. All test specimens were covered with plastic sheets just after concrete casting and cured at room temperature for the first 48 h prior to demolding. After demolding, heat curing (90 ± 2 °C) was carried out for 3 days, and then the specimens were stored in the laboratory with room temperature until testing. The temperature evolution of the UHPFRC, extrapolated from semi-adiabatic tests, showed a dormant period of more than 24 h. The final adiabatic temperature was 115 °C. The specimens were cured by steam curing for 48 h at a temperature of 90 °C and 100% relative humidity, and subsequently cured in water maintained at room temperature of 27 ± 2C until the testing day. The specimens were left for one day after casting without curing, apply curing treatment includes steaming the UHPFC at 90 °C for 60 h. Specimens were then cast in molds under a frequency vibrator for<1 min. They were then covered with a polyethylene sheet and allowed to harden at laboratory temperature (20 °C) for one day. All the specimens were then taken out of the molds and were placed in a special curing tank at 90 °C for 2 days. After casting, the specimens were covered with plastic sheets and stored at room temperature for 24 h. Then they were taken out of their molds and stored in a water tank at 20 °C for an additional 25 days. All specimens were tested at the age of 28 days. Steam treatment curing at 90 °C (194°F) and 95% humidity for 48 h, Laboratory curing The specimens underwent a curing regimen. Placed the specimens in a constant 22 °C temperature and 100% humidity room, and performed demold 24 h later. 48 h later, specimens were submerged in a water bath maintaining 90 °C for 24 h. Finally, put the concrete specimens to the autoclave, raised the autoclave temperature from the room temperature to 200 °C within 2.5 h. Kept 1.1 MPa autoclave pressure and 200 °C temperature for a moment. Then, naturally cooled down the specimens to the room temperature. After demolding, the specimens were steam cured at a high temperature of 90 ± 2 °C for 3 days and then stored at room temperature again until testing. All test specimens were demolded after 24 h and immediately sealed with aluminum adhesive tape. The shrinkage measurement began just after UHPFRC casting and was performed in a room with a temperature of 23 ± 1 °C and a humidity of 60 ± 5%. After casting, the specimens are covered and stored at room temperature for 24 h. Afterward they are removed from their molds and stored in a water tank at 20 °C for additional 25 days. All specimens are then tested at 28 days. About 48 h prior to testing the specimens are removed from water and left to dry in the laboratory environment. About 24 h prior to testing, a spray coating is applied on the surface of the middle portion of each specimen for better crack detection. The specimens were covered with plastic sheets and stored at room temperature for 48 h prior to demolding. Water curing with high temperature (90 ± 2 °C) for 3 days after demolding was carried out. All specimens were tested in dry conditions for 21 days. Two to three layers of polyurethane were sprayed on all surfaces of the specimens after drying to facilitate crack detection. Specimens were heated to a maximum temperature of 90 °C from the room temperature of about 25 °C. Each 24-h thermal cycle consisted of a gradual temperature rise period of 30 min, followed by a dwell period of 8 h and ending with a slow temperature drop. This thermal cycle mimics a summer’s day in arid hot climate when the temperature of exposed concrete surface is known to reach the chosen maximum temperature. The number of thermal cycles varied from 0 to 90 cycles. After the requisite number of thermal cycles, the specimens were tested at room temperature. The mixes can be cured at ambient temperature for 28 days or at the elevated temperature of 90 °C for just 7 days with no noticeable difference in the mechanical properties. Ice cubes are added during the casting to control the mixing temperature and working properties and are necessary if the environmental temperature is higher than 25 ◦C. The test specimens were cured at room temperature for the first 48 h prior to demolding. After demolding, heat curing (90 ± 2 °C) was performed for 3 days. After their removal from the molds, all specimens were cured at 90 °C for 2 days The specimens were stored in the condition of 20 °C and 95% relative humidity for 24 h, and then removed from the molds and cured in the same condition for 90 days. After curing, the hardened UHPCC were cut and ground into smooth cylinder specimens with thickness of 35 mm and diameter of 75 mm.

[34]

[56] [57] [47] [145] [67] [146] [45] [149]

[150] [144]

[88]

[151]

[105] [161] [162] [147] [148] [44] [153] [143] [155]

[156] [62] [65]

[163]

[157]

[140] [64] [158] [159] [142]

F.U.A. Shaikh et al. / Construction and Building Materials 232 (2020) 117152

consumption. This is preferably due to the very small water/binding proportion of UHPFRC. Silica fumes (SF) consist of very lower particles (around 1/100) than cement particles. Its tiny size makes SF very effective as filler and improves the density of packing. A large amount of silica fumes of about 10 to 30 percent of the cement mass are required to fill the voids between cement particles.

4. Sustainable UHPFRC The mixture ratios, fibre characteristics, and material attributes obtained from various studies of UHPFRCs are outlined in Table 1. The table shows that silica fume is mixed with immense amounts of cement in most study (>80 percent) in the blend that makes UHPFRC carbon footprint and its price very high. This highperformance material, which reduces its extensive implementation in many nations in infrastructure, has the disadvantages of high price and high carbon footprint. A number of researchers have soughed to assess the effects of different additional cementitious materials (SCM), for instance, slag, palm oil ash, fly ash, as a replacement of cement in the UHPFRC binder to tackle the high carbon footprint and high costs of the UHPFRC. Mahmud et al. [44] A research indicated where slag was used to substitute cement with 35 percent by mass. In this research, compression strength with approximately 150 MPa and uniaxial tensile strength with approximately 9 MPa are noted. Toledo-Filho et al. [45] reported that a compressive strength of 160 MPa, 11 MPa tensile strength and an ultimate tensile strain of 0.25%, in which 52% of blast furnace slag mixed to cement to produce UHPFRC. The effects of slag, fly ash and limestone powder as partial (30% each) substitution of Cement on mechanical characteristics of the UHPFRC were assessed in other research by Yu et al. [46]. The results indicate a decrease in UHPFRC compressive strength with 30% slag relative to UHPFRC control and less decline in fly ash and limestone powder composites. In the event of flexural resistance similar findings are also noted. In another research the compressive strength of

7

UHPFRC has also been decreased because palm oil fuel ash has been added as part of a cement substitution by Aldahdooh et al. [47]. In their research, the palm oil fuel ash was used to replace cement as 30%. Yu et al. [48] also used as a partial substitute of cement as municipal waste bottom ash (20 wt%) in UHPFRC. Lampropoulos et al. [49] developed UHPFRC containing 35% slag, 10% silica fume, 55% cement and 3% steel fibres which unveiled compressive strength-164 MPa, tensile strength as well as strain capacities are 12 MPa and 0.35%, respectively. Hasan et al. [50] and Hasan and Jones [51] also developed UHPFRC using similar mix proportions of Lampropoulos et al. [49] however, with steel fibres content of 2% which revealed analogous compressive strength164 MPa but considerable inferior tensile strength of 7.4 MPa. Makita and Bruhwiler [26] reported fatigue behaviour of UHPFRC made by low heat cement containing about 66–80% slag and 8.5% silica fume as addition to cement in their composite. Shaikh et al. [52] recently evaluated the impact of the different fly ash content of 20% to 50% as part of a cement substitution on the UHPFRC compressive strength and tensile stress strain behaviour. Their outcome showed approximately 4–14% less compressive strength, approximately 14–19% less ultimate tensile strength, about 10– 37% fewer ultimate tensile strain and about 22–48% less energy consumption during strain hardening than the control UHPFRC. Their findings indicate that their tensile strength is lower. Their findings have shown that UHPFRC with 40 percent fly ash has a significantly greater ultimate tensile strain, higher ultimate tensile strength, and energy absorption capacities than the one with 30 percent fly ash whereas the former has a slightly reduced CO2 emission about 15% than the latter.

5. Curing Regimes UHPFRCs might not display significant changes in terms of mechanical characteristics after 28 days. Although the lengthening of the curing process yields a certain amount of increase in the mechanical characteristics, the increase in the mechanical charac-

Fig. 4. Studies with compressive strength between 150 and 170 MPa.

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F.U.A. Shaikh et al. / Construction and Building Materials 232 (2020) 117152

Fig. 5. Studies with compressive strength between 170 and 190 MPa.

Fig. 6. Studies with compressive strength between 190 and 300 MPa.

teristics after one year is not significantly different from those of the 28-day-old samples. In fact, the samples that were cured in air and contained silica fume displayed time-dependent strength retrogression. Two types of heat treatments are applied in UHPFRCs [39]. (1) Autoclaving takes place at a moderate 65 °C temperature because greater temperatures affect the threat of delayed ettringites formation at elevated humidity. In particular, this method decreases the early setting time. (2) Concrete was

paced where the temperature gradually increased to around 85° C to 90° C. The cement is maintained at relative moisture of almost 100% over 1 to 2 days at this temperature. This therapy is implemented after the concrete is settled [38]. The characteristics of the concrete material are affected by this kind of therapy owing to more hydrates in the concrete. Subsequent to the treatment, certain aspects of the concrete’s durability are improved, the longterm performance is better; shrinkage as well as creep are reduced.

F.U.A. Shaikh et al. / Construction and Building Materials 232 (2020) 117152 Table 3 Compressive strengths and specimen sizes. References

Specimen size and Comp. Strength at 28 day (MPa)

[46] [34]

UHPFRC is cast in molds with the size of 40 mm  40 mm  160 mm and compacted on a vibrating table, 156 MPa The compressive strengths of the samples that were cured below 20 °C were not noted due to the yielded strengths being below 150 MPa For the samples that were cured at 90 °C; 50 mm cubes, when using silica sand 170 MPa, fine ordinary sand type I 177 MPa, Fine ordinary sand II 175 MPa, recycled glass cullet 153 MPa 100 mm concrete cubes (With the 637.9 cement, 173 MPa), (With the 700 cement, 175 microsilica fume, 175 MPa), (With the 700 cement, 250 microsilica fume 176.9 MPa), (With the 850 cement, 265.5 microsilica fume, 160 MPa), (With the 850 cement, 212.5 microsilica fume, 173 MPa), (With the 850 cement, 159.5 microsilica fume, 170 MPa), (With the 850 cement, 175 microsilica fume, 150 MPa), With the (720.49 cement, 181.41 MPa) 70  70  70 mm cubes, thermal treated 181.2 When 100 mm  200 mm cylinders, 4% steel fiber is used 153Mpa. When 6% steel fiber is used 165 MPa Cylindrical test specimens with a diameter of 100 mm and a height of 200 mm 166.9 Flexural strength was evaluated on 40  40  160 mm prisms and compressive strength was determined on the halves of these prisms 151.7 following Cylinders with 100 mm diameter and height of 200 mm 151.7 Cylinders were 200 mm high with diameter of 100 mm. When 0.5% fiber is used 154 MPa, when 1% fiber is used 149 MPa, when 1.5% is used 149 MPa, when 2% fiber is used 164 MPa, when 2.5% fiber is used 159 MPa, when 3% fiber is used 148 MPa Cube compressive tests (100 mm side) 164 Compressive strength was determined on cylindrical specimens (£ 11 cm, length 22 cm) 168 100 mm cube 170 100 mm cube 172 50  100 mm cylindrical specimens 156 100 mm cube 151 100 mm cube 164.3 100 mm cube, Steel fibers straight, lf/df = 13 mm/0.20 mm, Proportions by weight steel fiber 0.25 201 prismatic specimens (40 by 40 by 160 mm) 156 cylindrical specimens with a diameter of 100 mm and a height of 200 mm 194 cast in 50  200  500 mm3 molds 168 Nine standard 110  220 mm control cylinders were cast 170 The compressive strengths were determined on 11/22 cm cylinders. 192.4 Cast horizontally in 50  200  500 mm3 molds. 168 Cylindrical specimens with a dimension of u 100  200 mm were used. Relative weight ratios to cement is 0. When shrinkage reducing admixture was used 200.14 MPa, when 0.01 shrinkage reducing admixture was used 186.75 MPa, when 0.02 shrinkage reducing admixture was used 194.85 MPa Cylinders (16 cm, length = 32 cm) 168 Cylindrical, 50 mm diameter  100 mm 150 Prism shaped specimens with a slenderness of 2 (50  50  100 mm) 201 11/22 cm cylinders 190 All of these values were calculated from tests on cast cylinders, with cylinders with a diameter of 76 and 110 mm, The result of steam curing at 2195 kg premix was 220 MPa, the result of lab curing at 2195 kg premix was 192 MPa, the result of steam curing at 2161 kg premix was 212 MPa, the result of 2296 kg premix was 213 MPa prisms with a section of 40 mm  40 mm and a length of 160 mm were cast 56 daily 217 250 150 mm cube 300 1% fiber, a diameter of 100 mm and a height of 100 mm (cube) 176.27 1% fiber, a diameter of 100 mm and a height of 200 mm (cylinder) 178.28 2% fiber, 100 mm  100 mm  100 mm (cube) 178.03 2% fiber, 100 mm  100 mm  100 mm (cylinder) 178.35 The length and width of the tested tunnel lining segments were 1000 mm and 500 mm respectively, while their thickness was 100 mm. The crown height of the tested segment was 100 mm from the horizontal surface. This was intended to represent a segment taken from a tunnel having a diameter of 1.9 m. When 8 mm length fiber is used 1% result is 156 MPa, when it is used 3% result is 164 MPa, when it is used 6% result is 171 MPa When 12 mm length fiber is used 1% result is 158 MPa, when it is used 3% result is 166 MPa, when it is used 6% result is 173 MPa When 16 mm length fiber is used 1% result is 159 MPa, when it is used 3% result is 165 MPa, when it is used 6% result is 170 MPa three cylindrical specimens of diameter 100 mm and length 200 mm were prepared and tested according to ASTM C 39 197.3 Three cylindrical specimens with a dimension of u 100 200 mm 201.8 cylinder u 100  200 mm 196.4 0 thermal cycle 200 MPa, 30 thermal cycle 224 MPa, 90 thermal cycle 225 MPa When 0.5% of 6 mm and 2.5% of 30 mm fibers are used together 167.1 MPa, when 1.0% of 6 mm and 2.5% of 30 mm fibers are used together 171.7 MPa, when 1.5% of 6 mm and 2.5% of 30 mm fibers are used together 176.9 MPa, when 2.0% of 6 mm and 2.5% of 30 mm fibers are used together 182.4 MPa The compressive test was carried – out on cube specimens (100 * 100 * 100 mm) and cylinders with (100 mm diameter and 200 mm height) after 28 days curing (1%, length of 30 mm and a diameter of 1.0 mm and steel fibers, cube 151 MPa, cylinder 137 MPa), (1%, length of 50 mm and a diameter of 1.0 mm and steel fibers, cube 154 MPa, cylinder 141 MPa), (2%, length of 50 mm and a diameter of 1.0 mm and steel fibers, cube 163 MPa, cylinder 147 MPa), (2%, length of 30 mm and a diameter of 1.0 mm and steel fibers, cube 160 MPa, cylinder 145 MPa), (3%, length of 50 mm and a diameter of 1.0 mm and steel fibers, cube 169 MPa, cylinder 154 MPa), (3%, length of 30 mm and a diameter of 1.0 mm and steel fibers, cube 166 MPa, cylinder 151 MPa) The compressive tests were conducted on 7 cm diameter, 14 cm long cylinders with both ends ground. Mean strength of 228 MPa was recorded, giving a characteristic value of 197 MPa with 95% confidence. The design strength is set at 180 MPa accordingly. Dimension of 100  200 mm, with 1% fiber 195 MPa, with 2% fiber 200 MPa, with 3% fiber 209 MPa, with 4% fiber 183 MPa 214.7 MPa Cylinders 100  200 mm. With 1% fiber 154.8 MPa, with 2% fiber 162.4 MPa, with 3% fiber 158.7 MPa Dimension of 100  200 mm, 152 MPa Dimension of 100 mm  100 mm  100 mm. With 2% fiber 151 MPa, with 3% fiber 177 MPa, with 4% fiber 194 MPa 173.0 MPa

[54]

[56] [57] [47] [55] [61] [145] [67] [146] [147] [148] [45] [149] [150] [144] [88] [141] [151] [152] [164] [105] [161]

[162] [44] [153] [154] [143]

[26] [60] [155] [68]

[165]

[63] [156] [62] [157] [140] [58]

[64] [158] [159] [160] [156] [142] [66]

9

10

F.U.A. Shaikh et al. / Construction and Building Materials 232 (2020) 117152

Fig. 7. UHPFRC sample after the compressive strength experiment– [39,140].

The heat curing is an expensive and energy-consuming approach to improve the material characteristics of UHPFRC. It restricts UHPFRC manufacturing to precast sector, and thus restricts the use in the cast in situ implementation of this material [34]. Developing UHPFRCs without heat treatment or pressure treatment would encourage use of the product, but because of all the influencing parameters it was a long time quite difficult [53,54]. Table 2 represents the curing regimes that were applied in various UHPFRCs in the literature. It can be seen that about 2/3rd of the studies presented in that table applied heat treatment during first few days of their curing periods.

be between 700 and 1050 kg/m3, and that of superplasticizer should be between 30 and 50 kg/m3. The water/binder ratio should be < 0.18 and the water/cement ratio < 0.2. The samples should be subjected to 90 °C heat curing. Quartz should be used as the sand type (specific surface area, 20,000–25,000 m2/kg), and the steel fibre volume should be between 2% and 4%. The preferred sand type should have a homogenous matrix. Thus, internal structure and geometric shape are the determinants of compressive strength and are necessary to avoid aggregate types, such as bottom ash or recycled glass. Yang et al. [34] reported that fine sand aggregate is an important factor in compressive strength of UHPFRC and recycled glass cullet due to its weak internal structure and its decreasing effect on the compressive strength compared to ordinary fine sand. Yu et al. [47] reported that when approximately 20% of quartz powder is used instead of cement, the hydration of the cement and the compressive strength improves due to the nucleation effect of the fine particles. Aldahdooh et al. [54] discovered that the capillary porosity increases with the amount of binder. They reported that compressive strength can decrease due to the bleeding and segregation that occur with the usage of an over the optimum dose of superplasticizer. Lim and Hong [55] reported that the compressive strength after 28 days of curing without using fibre is 2.5% and 6% higher than those using polypropylene and steel fibres, respectively. The crack that occurs due to the compressive strength is shown in Fig. 7. Magureanu et al. [56] informed that the highest compressive strength is obtained through the samples made of hybrid fibres and 4% nano-silica mixture. They also suggested that polypropylene fibre do not contribute to the compressive strength that causes a statistically significant change. Aoude et al. [57] noted that the application of steel fibers has an impact on elastic modulus and compressive strength pre-cracking values, but has an significant impact on post-cracking and failure mechanisms. Eldin et al. [58] described that compressive strength is higher in the samples containing 3% fibre than those with 1% and 2%; the samples that are produced with aspect ratio of 50, have higher compressive strength than those with 30. Othman and Marzouk [59] reported that increasing the fibre content of UHPFRCs to 3% further enriches the impact strength compared to 1% and 2%. 6.2. Tensile and Flexural Strengths

6. UHPFRC Mechanical Properties 6.1. Compressive Strength According to Association Française de Génie Civil (AFGC)’s recommendations [39], cylinders with sizes of 7  14 cm or 11  22 cm should use to determine UHPFRC compressive strength. In accordance with Eurocode 2, the compressive strength can also be measured on cubes, provided that the coefficient for switching from cylinders to cubes is validated in design or test suitability. The compressive strength as well as ration of water to cement relations of the studies that yielded values of 150– 170 MPa, 170–190 MPa, and 190–300 MPa are depicted in Figs. 4– 6, respectively. The relationship between the specimen size and the compressive strength after curing of 28 days is shown in Table 3. Table 3 and Figs. 4–6 demonstrate that with the decrease of the ratio of water to cement, the compressive strength increases. The increase of the cement content with the compressive strength does not yield a positive trend. The main reason behind this situation is assumed to be the increase in capillary porosity. This situation is not dependent on one variable when the studies reach >170 MPa of compressive strength. The total amount of binder should be between (cement + SF) 850 and 1000 kg/m3, that of sand should

For UHPFRCs, tensile and flexural strengths are also essential mechanical characteristics along with the compressive strength [33]. The compatibility of the fibres with the matrix and their sizes influence tensile behavior as shown in Fig. 26. Table 4 shows the tensile strength values in accordance with the sample sizes, fibre content, and type in the studies reviewed. Table 5 shows the flexural strength values. Steel fibres have an important role in the flexural and tensile strengths of UHPFRC. While samples type ‘‘dog-bone” were mostly used to measure the tensile strength (Fig. 8 shows the samples of the tensile strength experiments of Graybeal and Baby [60]), different sizes of prisms were used in flexural strength measurement (Fig. 9 shows the 40  40  160 mm prismatic sample used in the flexural strength experiment of Magureanu et al. [56]). When the studies were evaluated, the highest tensile strengths were observed and showed the following hierarchy: twisted fibres > long smooth fibres > hooked fibres > straight fibres. The common data show that the samples of twisted fibres with 2% to 3% cured at 90 °C yielded higher flexural and tensile strengths compared to the other fibres. The addition of 1% to 3% percent of shrinkage reducing additive to the mixture increased the flexural strength values further. Flexural strength is directly affected by the homogenous spread of the aggregate in the mixture and the

11

F.U.A. Shaikh et al. / Construction and Building Materials 232 (2020) 117152 Table 4 Tensile strengths and specimen sizes. References

Specimen size

Tensile Strength at 28 day (MPa)

[56]

100  100  100 mm cube samples

[65]

Shape dog-bone, Length 178 mm, width 51 mm and depth of constant area 25 mm

[163]

The section of tensile specimens used is 50  100 mm, the gage length of the specimens is 175 mm

(thermal treatment, 5 days, 90 °C, 20.4 MPa), (water curing regime, 5 days, water, temperature 20 ± 2 °C, 12.6 MPa) (when there is 22% Straight steel 15 MPa), (when there is 2.5% Straight steel 16.5 MPa), (when there is 3% Straight steel 17.8 MPa), (when there is 1.5% Hooked steel 12.4 MPa), (when there is 2% Hooked steel 14.7 MPa), (when there is 3% Hooked steel 19.3 MPa), (when there is 1.5 Twisted steel 11.1 MPa), (when there is 2% Twisted steel 14.2 MPa), (when there is 3% Twisted steel 19.6 MPa) When long smooth, steel is used 0.5% 11.419 MPa, when used 1.0% 13.305 MPa, when used 1.5% 13.217 MPa When hooked A uses 0.5% 10.895 MPa, when uses 1.0% 12.249 MPa, when uses 1.5% 13.842 MPa When hooked B, uses 0.5% 10.310 MPa, when uses 1.0% 11.331 MPa, when uses 1.5% 12.014 MPa When twisted uses 0.5% 13.498 MPa, when uses 1.0% 14.772 MPa, when uses 1.5% 18.560 MPa

[144]

It is pointed out that the small dimensions of the specimen in height (25.4 mm) and width (50.4 mm)

[157]

–

[46]

–

[58]

Cylindrical specimens with diameter 100 mm and height 200 mm were cast

[164]

Un-notched dog-bone specimens of 70 cm length and 10  5 cm2 cross section The tensile properties were determined with a uniaxial tensile test on notched plates having a cross-section of 20*5 cm2 and a reduced crosssection of 16*5 cm2 at the notches The limit of the hydraulic wedge grip mouth opening led to the selection of a prismatic specimen with a 50.8 mm square cross section for all tests. The tapered aluminum plates affixed to two sides of each end of each specimen were nominally 4.76 mm thick and linearly tapered to 1.0 mm thick over a 50.8 mm length. Two different specimen lengths, with corresponding changes in instrumented gauge lengths, aluminum plate dimensions, and grip lengths, were tested within the program. ‘‘Long” refers to a 431.8 mm total length prism, while ‘‘short” refers to a 304.8 mm total length prism. In all cases, the specimens were single-point cast in prismatic molds, allowing the UHPFRC to flow along the length of the form. 196.4 cm  4 cm  16 cm prisms To measure the direct tensile strength, dog bone-shaped specimens with a testing section length of 80 mm and cross section of 16 mm  30 mm were used. Test specimens had an overall width of 125 mm, a height of 300 mm, and a thickness of 25 mm, but an effective width and a height are 75 and 150 mm, respectively. The splitting tensile strength was measured on 100  100  100 mm cubes

[146]

[143]

[64] [54]

[47]

[56] [55]

[145]

Direct tensile tests were carried out on dog-bone shaped specimens without a notch. The length of the specimens was 330 mm and the crosssection of the narrowed part was 30  30 mm. Uniaxial tensile strength was determined on dog-bone shaped specimens where the cross-section of the gauge section had a square shape with a side length of 30 mm. Length of the gauge section was 80 mm and total length of the dog-bone specimen was 330 mm.

When straight steel, diameter 0.2 mm, length 13 mm, tensile strength 2600 MPa, uses 1.5% 8.3 MPa, when uses 2% 11.3 MPa, when uses 2.5% 14.2 MPa When hooked steel, diameter 0.38 mm, length 30 mm, tensile strength 2900 MPa, uses 1% 9.4 MPa, when uses 1.5% 11.7 MPa, when uses 2% 14.0 MPa When high twisted steel, diameter 0.3 mm, length 30 mm, tensile strength 2100 MPa uses 1% 8.0 MPa, when uses 1.5% 11.6 MPa, when uses 2% 14.9 MPa When low twisted steel, diameter 0.3 mm, length 30 mm, tensile strength 3100 MPa uses 1.5% 3.3 MPa Indirect tensile strength, 0 thermal cycle 27 MPa, 30 thermal cycle 31 MPa, 90 thermal cycle 31 MPa When 0.5% of 6 mm and 2.5% of 30 mm fibers used together 21.1 MPa, 1.0% of 6 mm and 2.5% of 30 mm fibers used together 23 MPa, 1.5% of 6 mm and 2.5% of 30 mm fibers used together 23.7 MPa, 2.0% of 6 mm and 2.5% of 30 mm fibers used together 26.6 MPa (1%, length of 30 mm and a diameter of 1.0 mm and steel fibers, 12.73) (1%, length of 50 mm and a diameter of 1.0 mm and steel fibers, 15.4 MPa) (2%, length of 50 mm and a diameter of 1.0 mm and steel fibers, 17.45 MPa) (2%, length of 30 mm and a diameter of 1.0 mm and steel fibers, 15.59 MPa) (3%, length of 50 mm and a diameter of 1.0 mm and steel fibers, 19.10 MPa) (3%, length of 30 mm and a diameter of 1.0 mm and steel fibers, 17.82 MPa) Age 90, Uniaxial tensile strength 14 MPa 11 MPa

2% steel fiber at Long specimen and steam curing is 11.20 MPa, 2% steel fiber at Short specimen and steam curing is 10.29 MPa, 2% steel fiber at Long specimen and lab. curing is 9.18 MPa, 2% steel fiber at Short specimen and lab. curing is 8.56 MPa, 2.5% steel fiber at Long specimen and steam curing is 11.56 MPa, 2.5% steel fiber at Short specimen and steam curing is 11.36 MPa, 2.5% steel fiber at Short specimen and lab. uring is 10.53 MPa

The corrected characteristic tensile strength is 8.1 MPa In the one with 720.49 cement, on the 28th day, the average strength still increased by up to 12.49 MPa. 11.5 MPa

Thermal treated (5 days, 90 °C) 20.4 MPa, water curing regime (5 days, water, temperature 20 ± 2 °C) 12.6 MPa 10.4 MPa

When 0.5% fiber is used 7.5 MPa, when 1% fiber is used 7.8 MPa, when 1.5% is used 9.9 MPa, when 2% fiber is used 164 MPa, when 2.5% fiber is used 8.9 MPa, when 3% fiber is used 10.9 MPa (continued on next page)

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Table 4 (continued) References

Specimen size

Tensile Strength at 28 day (MPa)

[67]

direct tensile tests of 6 dog-bone specimens with dimensions of 40 mm, 150 mm and 13 mm were carried out

The experimental results indicate a variation of the tensile strength between 11.74 MPa and 14.20 MPa. An average stress–strain curve was calculated and the average strength was found equal to 12 MPa

[45]

for the uni-axial tensile behavior 50  12x 200 mm prisms

[149]

two unnotched dog-bone specimens of slightly different geometries, each with an overall length of 200 mm, were prepared. The cross section of the specimens starts with 50  50 mm and changes to a prismatic shape of 26  50 mm after either 25 or 50 mm away from each ends of the specimens

An average first-crack stress of 9.2 MPa and was reached at a deflection of about 0.026 mm. The maximum post-cracking stress was about 11.1 MPa and was achieved at an elongation of about 0.213 mm. Note that the elongation at maximum stress is about 8 times higher than that observed at first crack. 9.07 MPa

[162] [158]

cast in 50  200  500 mm3 moulds

11 MPa Relative weight ratios to cement, when 0 shrinkage reducing admixture is used is 13.38 MPa, when 0.01 shrinkage reducing admixture is used is 12.5 MPa, when 0.02 shrinkage reducing admixture is used is 11.2 MPa

[162]

A uniaxial tensile test is developed for UHPFRC. Prismatic specimens with a cross-section of 20  5 cm2 are built-in the testing machine by applying the principle ‘‘gluing without adherence”

In tension the UHPFRC was characterized by a nearly linear-elastic stress increase until the first cracking strength 9.1 MPa (at 28 days), followed by strain-hardening until a strain of 0.28% at the tensile strength 11.0 MPa (at 28 days). 9 MPa 18 MPa

The length and width of the tested tunnel lining segments were 1000 mm and 500 mm respectively, while their thickness was 100 mm. The crown height of the tested segment was 100 mm from the horizontal surface. This was intended to represent a segment taken from a tunnel having a diameter of 1.9 m.

When 8 mm length fiber is used 1% 17.6 MPa, when used 3% 21.9 MPa, when used 6% 39.8 MPa When 12 mm length fiber is used 1% 15.8 MPa, when used 3% 16.6 MPa, when used 6% 17.3 MPa When 16 mm length fiber is used 1% 13.9 MPa, when used 3% 18.9 MPa, when used 6% 33.8 MPa

[44] [60]

[165]

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Specimen size

[63]

Tensile Strength at 28 day (MPa) 11.4 MPa

[62]

Direct tensile test, A dog-bone shaped specimen was fabricated with a cross section of 50  100 mm in the middle

7.4 MPa

[160]

Cylinders 100  200 mm

When there is 1% fiber 7.3 Pa, when there is 2% fiber 11.1 MPa, when there is 3%fiber 14.0 MPa

Table 5 Flexural Strengths of Studies. Researchers

Specimen size

Flexural Strength at 28 day (MPa)

[54]

In the one with 720.49 kg cement 30.31 MPa

[55] [45]

For the bending tensile strength measurement, four-point bending tests were conducted. The beams used to measure the bending tensile strength had a length of 279 mm, cross section of 51 mm  51 mm, upper loading span of 76 mm, lower support span length of 229 mm, and crosshead loading rates of 0.1 mm/min. The flexural strength was investigated by performing a 3-point bending test using 40  40  160 mm and 100  100  300 mm prismatic specimens. The specimens were thermal treated Flexural strength was evaluated on 40  40  160 mm prisms 100  12x 400 mm plate specimens

[143,144] [34]

50  50  200 mm prisms

[56]

[88] [141] [161]

[44]

[63]

[156]

[48,157] [58]

[156] [159] [160]

Three prismatic specimens (40 by 40 by 160 mm) A three-point bending test, The prism specimen had a height of 100 mm, a width of 100 mm, a span of 300 mm and a length of 400 mm three-point flexure test was performed using 100  100  400 mm sized beam specimens with a 10-mm notch at mid-length Fifteen beams of similar geometry with depth varying from 30 mm to 150 mm are tested under 3-point bending, width b = 150 mm and span l = 500 mm 100  100 mm and length of 400 mm were fabricated by placing concrete at the corner of the beam. three-point flexure tests were performed as per JCI-S-002–2003 for the beams with a 30-mm notch at the mid-length three-point bending test was performed according to a previous study. Three 100  100  400-mm-sized beams with a 10-mm notch at the midlength were fabricated and tested. 100  100  500 mm beam 100  100  500 mm prism

In the one with dimensions of 40  40  160 mm 22.30 MPa, in the one with dimensions of 100  100  300 mm 16.6 MPa 40.1 From the results we obtained, a mean bending tensile strength at the first crack of 18.2 MPa at a deflection of about 0.08 mm. The maximum postcracking strength reached at a maximum bending strength level of 23.0 MPa at a deflection of about 0.4 mm. Furthermore, a four-point bending test for 12 mm thick specimen and span of 300 mm showed a peak capacity of 35.0 MPa and for a specimen thickness of 100 mm the capacity was 23.0 MPa. lf/df = 13 mm/0.20 mm, Proportions by weight steel fiber 0.25, 30 MPa The compressive strengths of the samples that were cured below 20 °C were not noted due to the yielded strengths being below 150 MPa. Because it does not provide an opportunity to compare the flexural strength values of the samples that were cured at 20 °C’ were not written In the samples that were cured at 90 °C’ de; when using silica sand 24 MPa, fine ordinary sand type I 23 MPa, Fine ordinary sand II 25 MPa, recycled glass cullet 21.5 MPa 38 MPa 30.5 MPa Relative weight ratios to cement, when using 0 shrinkage reducing admixture is 36.72 MPa, when using 0.01 shrinkage reducing admixture is 38.39 MPa, when using 0.02 shrinkage reducing admixture is 31.88 MPa In the samples with a depth of 30 mm it is 22.32 MPa, with a depth of 60 mm it is 21.00 MPa, with a depth 90 mm it is 20.48 MPa, with a depth of 120 mm it is 20.11 MPa, with a depth of 150 mm it is19.76 MPa 31.6 MPa

32.6 MPa

up to 30 MPa (1%, length of 30 mm and a diameter of 1.0 mm and steel fibers, 16.8 MPa) (1%, length of 50 mm and a diameter of 1.0 mm and steel fibers, 18.4 MPa) (2%, length of 50 mm and a diameter of 1.0 mm and steel fibers, 20 MPa) (2%, length of 30 mm and a diameter of 1.0 mm and steel fibers, 19.2 MPa) (3%, length of 50 mm and a diameter of 1.0 mm and steel fibers, 22.4 MPa) (3%, length of 30 mm and a diameter of 1.0 mm and steel fibers, 21.6 MPa) When there is 1% fiber 23 MPa, when there is 2% fiber 33 MPa, when there is 3% fiber 41 MPa, when there is 4% fiber 44 MPa

Three-point flexure test, 100  100  400 mm sized beam specimens with a 10 mm notch at mid-length were fabricated and tested. 40 MPa Three point flexural strength test, 100  100  400 mm prisms with a clear span of 300 mm, when there is 1% fiber is 8.5 Pa, when there is 2% fiber is 19.2 MPa, when there is 3% fiber is 28.3 MPa

13

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Fig. 9. The 40*40*160 mm prismatic sample used in the studies of Magureanu et al. [142].

Fig. 10. Flexural strength – fiber content correlation. Yo et al. [143].

compared to UHPC without steel fibre, and by 67 percent for UHPFRC with a 3 percent stainless steel fibre fiber quantity. The UHPFRC samples have a tensile strength 2.2 times greater than those in the UHPC, reported by Magureanu et al. [56]. Wille et al. [65] reported that increased use of smooth fibers partially mitigates the need for additional mechanical bonds in hooked and twisted fibre. 6.3. Impact Strength

Fig. 8. Tensile strength experiment samples of Graybeal and Baby’s studies [141].

porosity and fibre content (as the fibre quantity increased, flexural strength also increased). Fig. 10 shows the link between fibre and flexural strength. The type of sand, rather than the amount of sand used, resulted in significant changes in the flexural strength values, and the best results were obtained with quartz sand compared to fine ordinary sand type I. Magureanu et al. [56] indicated that UHPFRCs exhibit higher flexural strength compared to UHPCs by 150% to 165%, the specimen sizes have an effect on flexural strength, and smaller-sized specimens yield higher flexural strengths. Máca et al. [61] reported that the highest flexural strength is obtained when a 3% fibre volume is used. They also indicated that specimens exposed to 90 °C temperature have higher flexural strength than those exposed to 20 °C. Yoo et al. [62] reported that bending-related deflection decreases with the increase in shrinkage reducing admixture content, and the highest benefit is obtained when 1% of the shrinkagereducing admixture is used. Mahmud et al. [44] indicated that until a depth of 150 mm, the beams do not have a significant effect on the flexural strengths. Yoo et al. [63] claimed that unlike conventional concrete and FRC beams, only very thin flexural microcracks occur in beams of the UHPFRC up to the peak load owing to strain hardening features. Farhat et al. [64] specified that the observed flexural failures were typically characterized by a single flexural crack in the middle third of the beam extending upwards to the top fiber of the concrete between the load points as well as downwards via the repair material. Eldin et al. [58] reported that steel fibres have a very important effect on flexural strength, and samples that have steel fibres show 40% higher flexural strength than those without steel fibres. Also, the same authors reported further that fibres have a very important effect on tensile strength and the samples that contain fibres have 55% more tensile strength. The report showed a rise in tensile strength by 34 percent in the UHPFRC, with a 1 percent stainless steel fibre fiber quantity,

The impact strength of concrete leads to elevated localized strain rates. High strain rates trigger enhanced tensile and compressive strengths (See Table 6). UHPFRCs has high energy absorption capacity and, with their high-strain, has the ability to control structural defects [37]. Several studies examined the behaviors of UHPFRCs against dynamic impact effect when concrete is replaced by fly ash, silica fume and slag, as well as when the concrete is mixed with different fibre contents [66]. Máca et al. [61] suggested that high-strength fibres improve the impact behavior in terms of penetration depth of UHPFRC compared to normal concrete. However, they reported that fibres that are added with 1% have no significant effect. They determined that the optimum ratio is 2%, and fibres that are added in this ratio improve the impact load resistance. Fig. 11 shows the impact effect of slabs that were applied in the examinational studies by Maca et al. [61]. Researchers unearthed that a bullet could not penetrate into the UHPFRC slabs and hence, it bounces back. Sovják et al. [67] reported that having more than 2% of steel fibres in the UHPFRC mixtures have no positive effect in terms of penetration depth. Feng et al. [68] indicated that short and straight fibres have a positive effect on impact resistance. Zhang et al. [66] suggested that steel fibres have a significant effect on dynamic strength, deformation, and energy absorption. The presence of these fibres improves dynamic strength, energy absorption, and deformation. 7. Effects of specimen size on mechanical properties of UHPFRC There exist two most extensively adopted rules for research investigations on ‘‘size effect” for researchers. A deterministic and powerful law for size effect was suggested by Bazant [69] which states that larger specimens release more stored energy to the front of the fracture than narrower samples. Furthermore, for the first moment Weibull [70] implemented a Statistical Size Effect law, which states that bigger samples are much more likely to fail than lower samples. The size impact of concrete is therefore quite important if material evaluation results for the structural layout are agreed upon because the sizes of the specimen used for material testing and structural components are generally different. With that in mind, numerous researchers [43,70–75] have investigated

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Table 6 Studies that examine impact strength of UHPFRCs. References

Impact strength

[55]

Rectangular slabs with dimensions 300  400 mm and thickness of 50 mm, the weight of the projectile was 124 grains (8.04 g) and the average muzzle velocity was 710 m/ s. In total 18 slabs were tested for impact loading, panel was punched but the projectile bounced back, Rectangular slabs with dimensions of 300  400 mm and thickness of 50 mm and 45 mm, The weight of the both steel jacketed projectiles was 8.04 g. The length of the deformable and non-deformable projectile was 23.2 mm and 26.6 mm, respectively. Yield strength of the mild-steel core was determined by compressive tests as 550 MPa. Distance to the slab was 20 m.

[145]

(Specimen number 1, 692 Muzzle velocity [m/s], 80 Crater diameter-front side [mm], 19 Penetration depth [mm], 63 Mass loss [g], 63 Spalling [g]), (Specimen number 2, 706 Muzzle velocity [m/s], 68 Crater diameter-front side [mm], 21 Penetration depth [mm], 44 Mass loss [g], 44 Spalling [g]) crater diameter, (300  400 mm large and 50 mm thick slab) penetration depth (300  400 mm large and 50 mm thick slab) Debris fragment mass (300  400 mm large and 50 mm thick slab) Debris fragment mass (300  400 mm large and 45 mm thick slab)

[155]

The ogival nose projectile was characterized with diameter of 10.8 mm, caliber-head-radius of 3.0 and amass of 30 g; while the geometry of the 44.5 g conical nose projectile was featured by 6 mm diameter, 13 mm nose height and 91 mm total height. The UHPFRC targets were casted as 104 mm diameter cylinder with depth of about 50 mm and 100 mm, respectively.

[159]

I section, 200 mm depth, 150 mm width, 1700 mm length, 3 deformed bar with diameter 13 mm, effective depth 170 mm, 400 kg hammer, radius 90 mm, beam was supported over a span of 1200 mm.

[142]

All tests were conducted under the condition that air pressure in the high-pressure steel bottle was about 3.4 MPa. Under this condition, the projectile speed was roughly 8.9 m/s. Then, the specimen was impacted repeatedly by the projectile with speed of 8.9 m/s until the specimen was broken into pieces.

[66]

1000  1000  50 mm, the two identical vertical walls had a thickness of 25 cm and were reinforced on both faces with dense steel mesh. The vertical walls were fixed on a 50-cm reinforced slab, with top and bottom reinforcement mesh. Two different types of projectiles were used, namely ‘‘Solid Round’’ projectiles 12.7 mm and ‘‘Anti-tank Explosive Shells’’ 40 mm. (Initial velocity: 120 m/s, Maximum (impact) velocity: 300 m/s, Total projectile mass: 2250 g, Mass of hollow charge: 900 g, shooting distance: 90 m), (Maximum velocity: 820 m/s, Bullet mass: 116 g., Bullet diameter: 12.7 mm., Shooting distance: 300 m)

(deformable projectile, when 1% fiber is used is 85 mm, when 2% fiber is used is 74 mm, when 3% fiber is used is 73 mm), the panel was punched but the projectile bounced back (deformable projectile, when 1% fiber is used is 20 mm, when 2% fiber is used is 20 mm, when1% fiber is used is 19 mm), the panel was punched but the projectile bounced back non-deformable projectile, when 2% fiber is used is 60 g, other fiber ratios were not measured

Non-deformable projectile, when 0.5% fiber is used is 295 g, when 1% fiber is used is 99 g, when 1.5% fiber is used is 109 g, when 2% fiber is used is 98 g, when 2.5% fiber is used is 126 g. The projectile passed through the slab entirely Impact velocity-Residual Non-deformable projectile, when 0.5% fiber is used is 705 m/s-226 m/s, when 1% fiber is used is 703 m/s-228 m/s, velocity (300  400 mm when 1.5% fiber is used is 712 m/s-161 m/s, when 2% fiber is large and 45 mm thick used is 720 m/s-71 m/s, when 2.5% fiber is used is 711 m/sslab) 47 m/s Ogival nose projectile (UHPFRC cylinder thickness 51 mm, 817 m/s striking velocity, 1.5 mm depth of penetration), (UHPFRC cylinder thickness 50.5 mm, 823 m/s striking velocity, 10 mm depth of penetration), (UHPFRC cylinder thickness 52 mm, 816 m/ s striking velocity, 0 mm depth of penetration) Conical nose projectile (UHPFRC cylinder thickness 50.5 mm, 1382 m/s striking velocity, 28 mm depth of penetration), (UHPFRC cylinder thickness 98.4 mm, 1360 m/s striking velocity, 24 mm depth of penetration), (UHPFRC cylinder thickness 95.7 mm, 1380 m/s striking velocity, 17 mm depth of penetration), (Maximum load at Heights 0.8 m; 238.77 kN, ultimate load 128.17 kN, ultimate midspan deflection 16.8 mm) (Maximum load at Heights 1.0 m; 241.3 kN, ultimate load 128.36 kN, ultimate midspan deflection 16.9 mm) (Maximum load at Heights 1.2 m; 243.4 kN, ultimate load 128.52 kN, ultimate midspan deflection 17.0 mm) (Maximum load at Heights 1.4 m; 254.23 kN, ultimate load 128.67 kN, ultimate midspan deflection 17.1 mm) (Maximum load at Heights 1.6 m; 246.83 kN, ultimate load 128.79 kN, ultimate midspan deflection 17.1 mm) (impact times/absorption energy/average strain rate/dynamic compressive strength) (when 2% fiber is used; 1/0.770/24.8/154.1, 2/0.682/20.8/156.4, 3/0.682/21.9/154.7, 4/1.1/ 39.1/141.7, 5/1.41/85.6/111.1, 6/0.753/129.5/33.3) (when 3% fiber is used; 1/0.786/30.5/146.3, 2/0.788/27.8/148.9, 3/1.069/42.5/138.3, 4/ 1.365/95.5/88.2, 5/1.802/124.6/40.6, 6/0.594/125.8/32.1, 7/0.155/142.1/13.2) (when 4% fiber is used; 1/0.633/25.1/157.5, 2/0.663/29.6/154.2, 3/0.672/28.0/147.4, 4/ 0.839/30.5/145.8, 5/1.382/45.8/126.2, 6/1.522/51.8/116.9, 7/1.640/79.7/98.2, 8/1.075/ 111.4/46.1, 9/0.349/138.4/20.5) (Average results for Solid Round projectiles 12.7 mm; 63.3 cm3 Crater volume, 0.17 kg Mass loss) (Average results for Anti-Tank Explosive Shells 40 mm; 490 cm3 Crater volume, 1.29 kg Mass loss)

the effect of size for UHPFRC at both type of load i.e. quasi-static as well as impact loads. For most part, laboratory examinations are carried out by means of reduced scale, and therefore, simplifications must be prepared for real structures. This is the core reason why a number of researchers have paid attention to investigate the size effect of elements in the context of UHPFRC [70,76–80]. A research lab analysis has been put to trial for the size effect of elements on the compressive strength of UHPFRC employing heterogeneous fibre dosages by An et al. [75]. In that event, four cubic

samples of incongruent sizes possessing side lengths of 50 mm, 70.7 mm, 100 mm, as well as 150 mm were considered. The cubic samples enjoying generously proportioned size have demonstrated inferior compressive strengths in comparison with those of diminutive size. Also, the samples lacking in fibres have got the nod on the same line of action with regard to the effect of size on the compressive strength in comparison with high-strength and standard concrete. While, the quantity of fibre is escalating, the size effect is also turning out to be more momentous. By dint of three and

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Fig. 11. Impact effect of UHPFRC slab – [40].

four-points bending analyses, Mahmud et al. [44] also Wille and Parra-Montesinos [70] have conducted experiments for effect of size of specimen on the flexural strength performance of UHPFRC. The upshots have driven them to ultimate conclusion that the effect of size of samples on the attribute of flexural strength in UHPFRC is inconsequential which trails the yield measure as it is highly ductile. Also, Spasojavic et al. [76], have proven that the impact on size in small flexural UHPFRC employees was not a large thing. Lepech and Li [81], have likewise uncovered that engineered cementitious composites has put on show no high-flying modification with respect to flexural strength in accordance with the size of sample owing to it’s ductility. What’s more to add, Nguyen et al. [73] have portrayed about the flexural output of UHPFRC with a higher tensile ductility is less sensitive to the size impact than UHPFRC with a lower ductility, namely the flexural strength, normalised deflection plus toughness. Conversely, their results were near linear elastic fracture mechanics (LEFM) as opposed to the yield criterion [44,70], that was contradictory to the end results of other preceding investigations of Mahmud et al. [44]. Analogously, Kazemi and Lubell [78] have expressed that smaller UHPFRC specimens were found with higher compressive and flexural strengths, along with direct shear strengths, in comparison with bigger specimens. Conspicuously, a boosted size consequence on the shear strength had attained with more quantity of fibres. Also, Frettlohr et al. [80] have headed that when the sample size

improved, the uni-axial tensile and flexure strengths of UHPFRC decreased idiosyncratically, and that a better flexural resistance impact was controlled than for the uni-axial tension testing [79]. The mutually conflicting results can be due to the reality that although the flexural strength after cracking is mainly affected by the fiber bridging ability instead of the matrix strength [82], nevertheless, when the size impact was tested, they did not indicate the fiber orientation. Not only have that, the placement methods used in such research have not been described. Consequently, Yoo et al. [83] accounted that the divergences in the outcomes of size consequence attained from preceding researchers [44,70,73] were the result of dissimilar fibre orientation attributes. Their study evidenced an effect of clear size in beams prepared with UHPFRC, despite of application of matching placement techniques owing to various flow velocity gradients for varying sizes of specimens that escorts to various fiber distribution attributes. Their [83] verification indicated that when identical fiber allocation characteristics such as the fiber orientation, and number per unit area were acquired, the resulting size impact on UHPFRC beams was immaterial [83]. Accordingly, different fibre-distribution characteristics were mainly the effects of size in UHPFRC beams. Moreover, Yoo et al. [83], of late, carried out several flexural testing of UHPFRC fiber distribution attributes (i.e., fiber orientation and fiber dispersion) with distinct dimensions and performed image analysis, along with amount of fibers per unit area at the local cracks. Parallel to the findings achieved by Nguyen et al. [73], UHPFRC beams produced from the positioning of concrete on one end and allowing it to flow were noticeably reduced in flexural performance, as the sample size increased despite the fibre aspect ratio 65 to 100 or fiber forms [79]. Nevertheless, the divergent characteristics of fiber distribution were the primary foundation for the size impact in UHPFRC beams. The larger beams have a low fiber orientation with less fibre. Yoo et al. [71] had made sure that when analogous for all test beams with unlike dimensions, characteristics of fiber distribution were obtained in contrast to the dissimilar properties, which are considerably less sensitive to the size impact on flexural strength, as given away in Figs. 12 and 13. In view of that, finally, it was summarized that the size consequence in UHPFRC beams is predominantly on account of the different fibre distribution characteristics; as a consequence, by guaranteeing analogous fibre distribution attributes, a trivial dimension effect on the flexural resistance could be achieved for

Fig. 12. Crack patterns on surface; (a) Beams of small size, (b) Beams of medium-sized and (c) Beams of large-sized. [71].

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Fig. 13. Cracking effect; (a) number of cracks and (b) average crack spacing. [71].

Fig. 14. Effect of specimen size on compressive performance of concrete [75].

Fig. 15. Effect of quantity of fibres per unit area on the specimen size [72].

UHPFRC incorporating steel fibres about 2%. Size effect on compressive strength properties is demonstrated in Fig. 14. The impact of rate of load on the size impact and the fracture behavior of the concrete was researched by Bazant and Gettu [81]. The dimension effect on the concrete fracture was significantly strengthened by the time to failure escalation and by the declined effective process area length the fragilities augmented by trimming down the loading rate. Krauthammer et al. [84] of axial (compressive) impact tests using cylindrical samples further described the insinuation of the rate of loading for the dimension effect of high-strength concrete. Tran et al. [43] examined the impact of sample size on UHPFRC dynamic tensile. Their findings

Fig. 16. Torex twisted triangular and square steel fibre [86].

represented that the strength of the tensile after cracking enhanced as the sample dimension boosted, whereas the strain competence and hardening declined. The sample size did not influence the scores of cracks. In accordance with them [43], the ground for the boosted strength of tensile post-cracking is the inertial impact of the sample itself. The inferior capacity of strain as well as toughness were met with bigger samples owing to the enhanced sample dimension resulted in a more possibility of attaining more

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closed by Yoo and Banthia [72]. The impact of sample size and impact of the UHPFRC fiber content proportion are displayed in Fig. 15.

8. Effects of fıbre geometry, length, and volume fractions

Fig. 17. Bending behaviour of torex and hooked based UHPFRC [86].

Fig. 18. Load-displacement curves with different fiber content [131].

Fig. 19. Effect of fibre geometry on pullout behaviour of UHPFRC matrix [144].

substantial imperfections, piloting to poorer crack linking capability. Also UHPFRC beams, dimensions effect with a wide range of (straight and twisted) steel fibers under impact loads have dis-

‘‘Torex fibre” is a novel kind of twisted steel fibre that has been developed by Naaman [85] in 1990 which is portrayed in Fig. 16. It is made out of high-strength steel cable and has a polygonal transversal geometry, which allows for a twist on the axis. The original thought after defining its transversal geometry was based on the Fibre Intrinsic Efficiency Ratio (FIER). FIER is strongly allied to the strength of composites in post-cracking stage. When the cross-sectional area is constant, the triangular and square-shaped fibres are 28 percent and 12 percent more efficient, respectively at augmenting the FIER value as compared to fibre having circular-shaped [86]. When FIER value was augmented, the bonding of fibres with matrix like adhesion as well as the friction was also improved. The twisting of the fibres has brought about improvement in the mechanical bond. The archetypical fibre stress, slip curves of straight, hooked-end, as well as twisted steel fibres incorporated in the UHPFRC matrix are evaluated by Wille and Naaman [87]. Wille and Naaman [87] articulated that twisted addition of hooked at end steel fibre, which was discovered to be three times greater than short straight-line fiber of steel, achieved peak fibre stress. On the basis of enhanced fibre pull-out capability, the strength for tensile and strain of post-cracking competence of UHPFRC were correspondingly augmented to a large extent through employing the deformed (twisted plus hooked-end) steel fibres, in comparison with the short straight-line fibers of steel [88]. The tensile strength of 2 percent of twisted steel fiber was 14.9 MPa, and its strain capability of 0.61%; the values of tensile steel were approximately 32 and 205% greater, respectively compared to those with 2 percent of brief metal fibres. Bending behaviour of torex and hooked end steel fibres reinforced UHPFRC are depicted in Fig. 17 [86]. Fig. 17 shows comparison between UHPFRC specimen with torex fibres and commercially available hooked steel fibres. Fig. 17 clearly indicate that torex fibres exhibit good performance compare to hooked steel fibres. More to add, Yoo and Yoon [82] recorded that UHPFRC beams with twisted steel fibers have a flexural approximately 1.7 times higher than beams with short steel fibers. The squeezing deportment, like the compressive strength, elastic modulus, as well as strain capacity were also enhanced through the addition of twisted steel fibres as compared to short straight line steel fibres. However, the enhancement was comparatively of no consequence in comparison with monitored value for the tensile performance. In recent times, Yoo et al. [89,90] proposed one additional method for increasing UHPFRC’s flexural efficiency under uniaxial as well as biaxial stress and its capacity of fracture by using lengthy straight steel fibres. By increasing the fiber length, UHPFRC flexural resistance, deflection ability and robustness were significantly improved. UHPFRC panels showed an increase in flexural strength by only approximately 26 percent and 13 percent and an increase in deflection capabilities by 153 percent and 67 percent compared to those with medium and short steel fibres. Not only that but also application of longer sized steel fibres the fracture energies were almost 121 percent and 35 percent greater in comparison with medium and short steel fibres [90]. Employing longer steel fibres boosts the bond area among the fibre as well as the matrix that escorts to higher fibre pullout load carting competence and capacity of slip [91]. What is more to add, the number of crack surface fibers that is a major factor affecting the tensile behavior post-cracking has been modified in the same diameter trivially with fiber length. For illustration, the fiber count

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Fig. 20. Fibre distribution (a) Conventional concrete, (b) High strength concrete [98].

Fig. 21. Binary images of fibre orientation at center of UHPFRC beam; (a) Lf = 13 mm, (b) Lf = 16.3 mm, (c) Lf = 19.5 mm and (d) Lf = 30 mm. [90].

per unit area for short fibres was 34,00/cm2, the medium fiber 33,12/cm2 and the long one 35,79/cm2 [90]. The root cause of the incongruous change in the number of fibers per unit area, although the actual number of fibers incorporated into the mixture decreases with the same fiber longitudinally. The option is that fibers can increase with the fiber length on crack surfaces depending on their volume content. Because the fibers are included in the mixture. In brief, The shorter the length of the fibre, the faster the mixing, hence the greater the amount of fibers on the crack area. The post-cracking flexural strength and resistance parameters were more or less linearly reinforced with an increase in the fiber volume fraction in the three linear (or bi-linear) tensioning curve. Otherwise, The fibre volume fraction was trivially affected by the first cracking flexural strength and the corresponding deflection [92–94]. Approximately 64 MPa, which is nearly seven times greater than the flexural strength without fibers after cracking with short straight line steel fibers at a volume fraction of 5 percent [93]. A greater number of steel fibers and elastic modules up to a fiber volume fraction of 3 percent negligibly improve the compressive resistance [94]. Since the compressive strength has a major impact on fiber dispersion homogeneity, the optimal fiber volume fraction producing a maximum compression force is different for various scientists. Prabha

et al. [94] have found out that UHPFRC fibers have a maximum compressive strength of up to a fiber volume fraction of 3 per cent with 2 vol% 13 mm long steel fibers. While on the other hand, Yunsheng et al. [92] described that the compressive resistance improved constantly by up to 4% increase in fiber quantity-a compressive force 30–50 MPa greater that without fiber showed the 4 vol% steel fiber sample. In addition, by combining up to 2 vol% of steel fiber in the matrix, the fiber extraction performance was improved [94]. In this order both the strength of the tensile fibers and the stress capacity of UHPFRC were amplified by increasing their fiber volumes from 8 to 14 MPa, and from 0.17 to 0.24 percent, as well as for straight steel fibers from 8 to 15 MPa, and in this order, from 0.33 to 0.61 percent. Nevertheless, the tensile resistance of the UHPFRC increased with an accelerating fiber quantity from 9 to 14 MPa for hooked end steel fibers, whereas the stress capacity was continuous at about 0.46% [94]. Loaddisplacement curves concerning fibre volume ratio and impact of fibre geometry on pull-out strength of embedded in UHPFRC matrix are shown in Figs. 18 and 19. Fig. 18 demonstrate the load displacement curve for diverse fibre volume ratios. It is clear that, as the fiber content increases, original rigidity does not alter substantially, while the load in the softening portion is gradually increasing to fragile behaviour. While the struc-

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Fig. 22. Fibre orientation and dispersion parameters; (a) fibre dispersion coefficient, (b) number of fibre in the unit area, (c) packing density and (d) fibre orientation coefficient. [90].

tural ductility rises with the FRC content of fiber, there is no apparent trend in displacement at peak load with the UHPFRC fiber volume ratios. Fig. 19 illustrates fibre stress along with slip curves for hooked end steel fibre, twisted steel fibre as well as straight steel fibre in UHPFRC. From the figure, it could be seen that the pull-out stress of twisted steel fibre is three times higher than straight steel fibre [93]. Twisted as well as hooked end steel fibres are enhanced the pull out resistance as compared to straight steel fibres [93].

9. Effects of fıber orıentatıon The UHPFRC is used to manufacture structures with various positioning methods [95–97]. Boulekbache et al. studied [98] that fiber is rotated with various flow rates of fiber-reinforced concrete that can be flowing. The fibres, which exert strength and moments on the fibres, are vertically lined up in radial flow and parallel to the flow direction in shear flow. The manufactured UHPFRC steel bar beams by Kang et al. [99] were putting concrete using two different placement methods (i) allowing for one end of form to flow to another end or (ii) the center agreeing to flow to both ends. Their experiment results revealed a peak load that was about 15% greater than when cement was put at the center of the concrete beams. Due to UHPFRC’s flow capacity, more fibers are oriented towards the longitudinal direction of the beam. The rectangular slabs, unlike positioning processes, were also made by Ferrara et al [95] and Kwon et al. [96] and examined how fiber orientation affects UHPFRC flexural performance. The case of placing concrete

on a short edge of the mould and allowing for its flow [95] showed poor flexure in comparison to the parallel beams positioned as perpendiculars to the flow direction. The perpendicular arrangement of the fibers was ascribed to the beam length as shown in Fig. 20. Fig. 21 illustrates fibre orientation and dispersion in the middle of the UHPFRC beams on the cutting plane. Likewise, the beams paralleled with the flow direction showed a much lower load capacity in the situation where the concrete is placed in the center (radial flow) [96] compared to the beams in other areas. They also proved an unusual behaviour in flexural for UHPFRC, which is softening of deflections. They showed Mechanical and structural performance under tension as well as flexure are influenced by the fiber orientation. Consequently, a lot of investigations [15,70,96–98] have been carried out to quantifiably estimate how the fibre orientation features affect the mechanical attributes of UHPFRC and pencil in a few valuable upshots. Fibre orientation and dispersion parameters are shown in Fig. 22. The effects of casting methods, namely layer casting plus middle-casting, casting speed and the flexural behaviour of uniaxial UHPFRC beams, were investigated by Wille and ParraMontesinos [70]. It was noted that a snake-like flow pattern could be prevented when casting velocity increased and a thinner layer could be made with a preferable fiber layer in the beam axis to increase flexural efficiency. In addition, the beams cast in the center show a transitional flexural resistance between the beams cast in layers which have a high as well as low casting speed. Likewise, Yoo et al. [97] also supervised that the center beams contributed to greater flexural strength than the edge beams. The energy of the

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Fig. 23. Compressive strength (a) and Flexural strength (b) under quasi-static loading [106].

fractures was nevertheless somewhat influenced by the casting method since the benefit of the greater strength resistance compensated for a rapid decrease in stress after peak. They also submitted image analysis and verified that more steel fiber is positioned in the center for beams cast in the center (at peak time region) than the beams cast on the edge to evaluate the experiment results realistically. The flexural efficiency of UHPFRC panels under a biaxial stress condition was examined by Barnett et al. [15] and Yoo et al. [96]. However, various methodologies were employed-the method of the newly fetched biaxial flexural testing (BFT) suggested by Zi et al.[100]. However, similar testing findings had been achieved. The UHPFRC panel cast in the center showed significantly greater flexing forces than the panels cast using various placing techniques, i.e. casting around, casting arbitrarily and casting around the perimeter of the panel on a number of points. Yoo et al. [97] used binary images on the crack surfaces instead to work on picture analyses, which were changed by a highresolution camera with RGB pictures. The information from the analyses showed that, the rise in the flow speed in the other panels with varied positioning methods, a larger amount of stainless-steel fibers in the center panels were lined up at a correct angle to the flow direction. The aforementioned improved fiber arrangement led to a greater flexural strength and strength in the center of the panels than in the others. The fiber movement was evaluated arithmetically by Kang and Kim [101], based on the Jeffery equation [102], assuming that there were no fiber interactions. They described that the fibers were switched more parallel to the direction of the stream (for shear flow) and more vertical to the direction of the stream (for the radial flow). The actual findings from shear and radial fluxes that have been tested by Yoo et al. [97] have been unsurpassed by these statistical findings. According to Yoo et al. [97] and Lee et al. [103], the fiber orientation distribution Probability Function (PDF) for both UHPFRC and Engineered Cementitious Composites (ECC) showed completely poles apart from the behavior of suppositions for two and three dimensional. Nevertheless, the use of a 2-D arbitrary fiber orientation is more worthwhile in simulating the flexural behavior of uniaxial UHPFRC beams than the 3-D random fiber orientation, based on analysis based on micro-mechanics [87] it can be significant. The findings of quite a number of previous studies [70,73,90,99] show that the fiber distribution characteristics of fibre orientation and number per unit region are considerably influenced by the tensile or flexural efficiency of UHPFRC at virtually static stresses. This

occurred because its post-cracking characteristics are more influenced than matrix strength by the fiber bridge ability. The fiber distribution features are therefore also intended to affect the tensile or flexural conduct at elevated load rates of UHPFRC. However, only a tiny amount of investigators [97] studied the impact of fiber orientation on UHPFRC impact resistance. Yoo et al. [97] have lately experimentally studied for the first time how the rate based UHPFRC flexural features are affected by fibre orientation. Investigations were carried out successfully; [97] the fiber orientations in the UHPFRC beams were intentionally good and poor, with two different dimensions. A correct fiber orientation is the case that the fibers are mostly well aligned in the direction of tensile load, while the poor fiber orientation suggests that most fibers are arbitrary or tend to tensile loads. Based on the image analysis, quantitatively explored the characteristics of fiber distribution, together with fiber orientation, dispersion and unit number in the unit region. When correct fibre orientation was authorized-fibers are aligned in a more tensile stress direction-the fibre orientation significantly affected the flexural performance in UHPFRC at impact load and increased impact strength, i.e. improved flexural strength and energy absorption ability. Despite the potential energy and sample size, UHPFRC beams with correct fiber orientation showed greater resistance to flexural impacts. The findings of Xu et al. [104] on single fiber pull out tests are supported by the finding that the increased fiber pull-out strength is achieved if it tends slightly in the direction of load. Ideal alignment in the casting direction is almost impossible because interaction between fiber to fibre, with the fiber concentration is generated and stress applied by a fluidspeed trimmer in the fiber is reduced when the fiber structure approaches the flow direction. Consequently, the fibre-friendly beam may be more fibre-friendly with a slightly tendency toward the stress than its counterpart beam, with an increase in impact resistance under flexure. It has been noted as a whole that appropriate fiber aligning with the tensile load requires excellent shock or blast resistance to be achieved in UHPFRC components.

10. Effect of fıbre type The effect of a type of fiber on the tensile behavior of UHPFRC at quasi static and impact loads has been demonstrated by research tests by Tran et al. [43]. The highest impact resistance in the postcracking strength, stain capabilities and toughness were

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demonstrated in UHPFRC dog-bone samples with lengthy and straight steel strain range from 5 to 24/s. Although the use of twisted steel fibers demonstrated maximum tensile resistance at quasi-static loads, the strain capabilities and toughness at high tensile rates were found to be substantially below both longer and short steel fibers due to fiber splintering. Also, analogous findings of comments have been recorded by some additional investigators [44,58]. Wille et al. [105] pointed out that twisted steel fibers, due to their limited strain state resistivity tolerance, led to lower tensile strength at elevated load rates than straight steel fibres. Not only that, Yoo et al. [106] have pointed out that the UHPFRC beams have been controlled with a greater flexure resistance and energy absorption ability after cracking than those with short twisting and straight-driven steel fibers as shown in the Fig. 23. The mixing proportions, straight stainless-steel fiber type and mechanical static characteristics of the sample S65 are much closer to commercial UHPFRC [90]. It can therefore be concluded that using long straight or twisted steel fibre improves commercial UHPFRC impact strength. In addition, the improved impact strength with lengthy straight steel fibers compared to twisted fibers was supervised in the UHPFRC. This was allocated to the lower stress sensitivity to DIF, shown by the twisted steel fibers, for postcracking strength, which leads to a reduced increase in strength at an accelerating stress rate. The clarifications are in line with the results collected by Tai et al. [107] that show that twisted steel fibers have a reduced rate sensitivity to impact fiber pull out than straight steel fibers. Nevertheless, it is controversial that although single, twisted fiber in UHPFRC displays a high bond strength and dissipating energy capabilities at impact pull-out loads, UHPFRC-composites containing numerous twisted fibers arbitrarily oriented to the provision of an expanded weak effect resistance, as opposed to straight fibres [107]. In addition, due to the wonderful fiber bridging ability, the deflection-hardening behavior of UHPFRC has been recorded at impact loads. [97]. In addition, Pyo et al. [108] conducted an impact test for UHPFRC using a customized Strain Energy Frame Impact Machine. The investigations of the UHPFRC with twisted steel fibres, though, witnessed for higher impact resistance in the context of postcracking strength and ability to absorb energy in comparison with straight steel fibres having a variety of aspect ratios. The preceding testing upshots were divergent to this work creating an inconsistency among them. This might be owing to the variations in testing equipment and fibre characteristics, like dispersion, aspect ratio,

Fig. 24. Pressure-deflection relationships for UHPFRC slabs obtained under static uniformly distributed loading. [122].

fibre tensile strength, number of twists and fibre orientation. Therefore, advance research work should be put in execution to pencil in unambiguous conclusions concerning the effectiveness of the use of UHPFRC twisted steel fibers for loading provisions. The inferior quality impact resistance of the UHPFRC with the massive quantity of twisted steel fibers can indeed be allocated to the fact that twisted steel fiber has increased its bond strength because the fiber splitting rate is more likely to result in tension or fiber pulling at elevated stress rates. Therefore, the significantly decreased output energy of twisted steel fibers at greater strains has given the implementation of straight steel fibers a lower impact strength. Yu et al. [109] have shown that UHPFRC’s impact strength in place of the short fibers is controlled by the lengthy steel fibres. The impact resistance of UHPFRC was degraded, according to [109], with the constant content of the fiber volume increasing the substitution rate for long fibers to short fibres. Nevertheless, the improved impact strength and static flexural efficiency of UHPFRC in lengthy fibres have been accomplished based on the previous trial results by Tran and Kim [104] and Yoo et al. [110]. In consequence, fusion of long or medium-length steel fibres, both static and impact loads were promoted to improve the tensile or flexural performance of UHPFRC. Millard et al. [111] studied UHPC containing an amalgam of both short as well as long steel fibres and found it displaying inferior strain-rate sensitivity, signalling lesser dynamic increase factor at equal strain-rate, in comparison with that embracing merely the single short fibres. The core reason behind this was the reality that the mixture of fibres is greater effectually governs the formation of lateral crack development than its corresponding part. The pitiable fibre distribution in UHPFRC has been attained often when malformed steel fibres were incorporated. Predominantly, when the hooked steel fibre was integrated with UHPFRC mix, deficient separation of fibres was monitored on account of its bundles, escalating crises for constructability and cracking of matrix at close to the fibre end hook [112]. For that reason, a depreciated pull-out capacity of the hooked fibre took place resulting in the weak flexural performance of UHPFRC in comparison with one those containing straight steel fibres. Long straight steel fibers demonstrated maximum rate sensitivity after cracking when the short straight steel fibers showed the greatest strain and peak resistance sensitivity [43]. On the other hand, one more study by [113], straight steel fibres aspect ratio had not displayed any obvious impact on the dynamic increase factor of the post-cracking resistance to flexural. These scientists have significantly tracked the remaining flexure strength and toughness significantly increased by the use of lengthy stainless-steel fibers following impact damage in comparison with small stainless steel fibers. Long, straight fibers of steel are therefore effective reinforcements to improve the strength of UHPFRC following impact harm after cracking and residual loads. Yoo et al. [89,106] has already demonstrated the effectiveness of using lengthy straight steel fibers in UHPFRC in quasi-static loading states. The collective application of micro steel as well as Basalt fibres piloted to enhanced resistance to the impact and Trinitrotoluene (TNT) blast [114,115], resultant of the synergistic impact among the fibres. On the basis of the testing findings [114], little permeation depth of UHPFRC was attained by repetitive impact on utilizing both – steel as well as basalt fibres. On relying preceding comparative pull-out behaviours of steel and polymeric fibres entrenched in control or high-strength cement matrix, In addition, polymeric fibres are advantageous to contribute pull-out behaviour as slip-hardening in comparison with steel fibres. Although, the inferior tensile resistance of most of polymeric fibres, narrowed their use in UHPFRC owing to the fibre fracture prior to absolute pull-out. Recently, Polyethylene (PE) fibres displaying the extre-

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mely high tensile performance of roughly around 2700 MPa are developed, and they were productively employed to the cement matrix with the sky-scraping compressive strength of more than 150 MPa [116]. Given the fact that the polymeric fibres by and large offer enhanced pull-out behaviour than steel fibres, the use of PE fibres in UHPFRC mix may provide an enhancement in the context of impact resistance. Of late, Ranade et al. [117] have compared the resistance against impact of high strength concrete possessing PE fibres and UHPFRC along with steel fibres- hooked type and reported that the PE fibres demonstrated flexural behaviour more ductile in nature along with dispersed manifold micro size cracks than the UHPFRC on subjecting to impact loads dropweight type. 11. Effect of quantity of fıbres Rong and Sun [113] performed tests with various amounts of short straight steel fibers on the UHPFRC dynamic tensile behaviour with the help of a SHPB test machine and concluded considerably based on their test results. They specifically indicated that the tensile strength of UHPFRC increased, supported by the upshots of Yunsheng et al. [118], by an rise in stress rates and fiber volume content. In contrast to UHPC without any fiber, UHPFRC’s low strain rates achieved 2 and 2,5 times greater tensile strengths with stainless steel fibres of 3 and 4 vol%. Also, the direct tensile behavior of UHPFRC was calculating by Pyo et al. [119,120], with various amounts of fiber of steel. Parallel to Rong and Sun [113], they advocated that the tensile performance, strain capacity to absorb energy be increased by increased twisted steel fibers amount at high strain rates [119], while the strain hardening response was monitored through the use of the Strain Energy Frame Impact Machine. Therefore, Pyo et al. [120] and Yoo et al. [121] studies were used to determine UHPFRC strain and deflection-hardening behavior in respect of impact loads. Beyond the debates, it is important to think that UHPFRC’s dynamic tensile performance is improved in straight and deformed steel fiber instances with a greater content of fibre. Mao et al. [122] were also along the same lines as UHPFRC panels improve their blast resistance, with fiber volume content increasing up to 6%. With a rise in fiber content from two to six volumes percent at matching explosive charges and standby distance, the maximum 1/4 deflection of UHPFRC panels was significantly decreased. On the other side, the optimized fibre-volume content of UHPFRC to decrease local smashing was suggested as about 2 vol% on the basis of an previous research conducted by Máca et al. [61,123]. Their experimental findings however have improved the effect strength of UHPC panels by integrating short stainless steel fibres, while further increases in fiber content beyond 1 vol% and 2 vol% showed no noticeable insinuations on the penetration depth and crater diameter of UHPFRC panels by effect of projectile impact accordingly. Finally, the discussion leads to the conclusion that the massive breakdown of UHPFRC elements is improved by an increase in the fiber content up to 6% while the increase in the resistance to local damage by the projectile impact is limited to the fiber content and is discovered to be around 2% of its optimum quantity. The tensile strength of UHPFRC increases, without a doubt, when the amount of steel fibers is increased, because more fibers are bridging the splits and restricting the further spreading and amplification of the splits. But increasing the fibers has also resulted to disadvantages such as reduced downflow ability, greater porosity, more fiber alignment, fiber ball phenomenon and so on, and therefore, a linear rise in tensile strength with the fiber amount has not been achieved. Also, Yoo et al. [110] noted, because of numerous shortcomings, a non-linear increase in the post-cracking flexural strength of UHPFRC with a fibre refractory index.

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As the steel fibres cover a momentous portion of the entire cost of fabrication for UHPFRC, it is more methodically carrying great weight to put forward an optimum quantity of steel fibres, contributing adequate impact resistance, in comparison with explain that elevated impact resistance is attained at more fibre volume contents, which is rather expected, in the context of being economical. Tai [124] accounted that, while flat end projectile was utilized, harsher smash up was monitored for the UHPFRC panels lacking fibre scabbing larger area in comparison with standard strength concrete panels, because of their brilliant fragility. The failure mode of UHPFRC panels with no fibre was switched from fragile to pseudo plastic through incorporating steel fibres: on an adding up of 1 vol% steel fibres, around 50% slighter scabbing area was occupied [124]. Fascinatingly, Millard et al. [111] noted that the increase of UHPFRC flexural strength by elevated rate of load, i.e. loading rate sensitivity, can be reduced by increasing the fiber content between 0% and 6%. In accordance with their description [111], the effects of a greater loading rate are allocated to the decline, because fibers bridge the cracks in low resistance areas are reduced to lateral crack growth. Pressure deflection relations for UHPFRC slab loaded with a uniform static load and the relation between the quantity of the fiber and the critical scale size of the slab are indicated in Figs. 24 and 25. 12. Applications and prospective recommendations The strength and lightness of the structural elements have the power over the bulk of the applications whereas the rest of the utilizations consider the belligerent resistance, sustainability, and durability of the material to safeguard chiefly the existing or newfangled structures. Quite a lot of applications like anchor prestressing are erected primarily and essentially on compressive strength for columns or extremely stressed features. Also, UHPFRC has been found fitting to apply in architectural constructions. The erection of copious prototype structures have been made for UHPFRC in so many countries such as New Zealand, Japan, Germany, USA, Canada, South Korea, Australia, France, Malaysia, etc. In 1997, UHPFRC was applied for the first time ever for a UHPFRC-infilled steel tube composite to build footbridges in the city named Sherbrooke, in southern Quebec, Canada [125]. This was the era of commencement of UHPFRC to draw attention of universal researchers, concrete technologists, academicians, engineers, several departments and authorities of government, etc. The eye-catching illustration to implement UHPFRC structurally was during the period of 1997–98 in France, whereby the replacement of beams for Civaux and Cattenom cooling towers was performed displaying how it can be employed in aggressive conditions of the environment. One more example can be cited from the city of Seoul, South Korea during the year 2002 whereby the first footbridge of 120 m was built totally

Fig. 25. Fibre volume and critical scaled distance of slab relation [122].

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of substandard bridge substructures, and blast mitigation and safekeeping utilizations. The elevated-capacity UHPFRC projects for infrastructures are highlighted by accomplished projects of bridge viz., the Seonyu Footbridge of South Korea; the Sherbrooke Footbridge of Canada; Shepherds Gully Creek Bridge of Australia; the Bourg Les Valence Bridge of France; Gärtnerplatz footbridge in 2007 at Kassel, Germany; Seonyu footbridge in the year 2002, Seoul, Korea); and Sakata-Mirai footbridge of 2002, in Japan as well as roofing panels for silo in the year 2001, Joppa, Illinois USA; Cattenom nuclear power plant in 1997–1998, France; Shawnessy station in 2005, Calgary, Canada; and roof of Millau Viaduct tollgate during 2004, France. Recommendations are necessary to suggest for healthier understanding of the potential of UHPFRC. So far, the majority of the investigations were carried out on RC beam elements in context of UHPFRC but studies on other structural elements such as walls and columns are quite essential. Moreover, the durability performances of strengthened RC members such as resistance to attack of chemicals, namely, acid, sulphate as well as chloride ion attacks should also be examined and studied in detail to offer the requisite fortification against infiltration by such deteriorating factors creating a concern for durability and sustainability. Not only have that, there is quite a significant call for study the performances of UHPFRC under diverse conditions of environments including those of aggressive kind.

13. Conclusions and Discussion The following findings can be taken on the basis of a review of previous literature from UHPFRC and conversations:

Fig. 26. Tensile behaviour of UHP-FRC using twisted steel fibres with increasing volume content and same fibre aspect ratio [120].

with UHPFRC in the world as reported by Deem [126]. Subsequently, the VSL road bridge of Shepherds Gully Creek in Australia was built and launched in 2005 for public use. However, the pressing UHPFRC beams built with standard concrete, but the dimensions of element were significantly declined along with desirable durability and lightness [127–129]. UHPFRC can be employed in an extensive range of utilizations for highway infrastructures thereby offering a longer period of design, slender overlays, shelves and claddings on account of its enhanced durability as well as higher compressive and tensile strengths. Hitherto, the examples of highway bridges built with UHPFRC are a comparatively limited in quantity available in more often than not in Canada [130–132] and USA. The key investigations have been carried out in France, with significant development on the topic of bridges made up with UHPFRC. In Australia and Italy certain applications are also available [133,134]. What’s more, a lot of uses of UHPFRC are regarded as significant e.g. In the precast concrete piles, thin-bound overlays of degraded decks, the seismic retrofit

 The best mechanical characteristics in most UHPFRCs were obtained with water to cement ratio less than 0.20, steel fibre 3 percent of volume, steel fibre length of about 13 mm hook end type in the UHPFRC mixtures. The highest mechanical characteristics were obtained with the specimens exposed to thermal curing at 90 °C. The compressive performance of the samples that were exposed to thermal curing was higher than those exposed to water curing.  The most imperative factors that affect the behaviour of the UHPFRC were identified to be the fibre type, fibre geometry, fibre volume fractions, the distribution as well as orientation of the fibres in the concrete, and the matrix of the UHPFRC. Twisted steel fibres reinforced UHPFRCs exhibited much higher mechanical properties than those reinforced by hooked end steel fibres followed by those reinforced by smooth straight steel fibres. Increasing the fibre length does not effect after 13 mm.  UHPFRCs showed about 2.2 times higher tensile and flexural strengths than their counterpart ultrahigh strength concrete. The impact resistance performance of UHPFRC was better than static load, and impact resistance improved with the boost in fibre content up to 2%. UHPFRC was capable of dissipating higher absorbed energy by impact than traditional concrete with fibres. Steel fibres contents of >2% showed no positive effect in terms of penetration depth of UHPFRC due to impact.  Although the mixtures with long fibres exhibited a slight enhanced in flexural strength of UHPFRC compared to those with short fibres, however, UHPFRCs reinforced by short steel fibre yielded the same compressive strength values. Short fibres are preferred because long fibres pointedly inferior the workability of the mixes.  Using lengthy straight UHPFRC steel fibers was generally more efficient than the twisted and rounded steel fibre in terms of enhancing the bond strength and energy dissipation capabilities

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and displaying the greatest impact resistance, with postcracking strength and energy absorption capabilities. UHPFRC has also shown very high stress sensitivity. The twisted steel fibers were, however, the most efficient way to improve energy dissipation at quasi-static and dynamic concentrations. A decrease in diameter increased the UHPFRC straight steel fiber rate sensitivity.  Larger UHPFRC specimens contributed to inferior mechanical strengths to smaller samples. In addition, a higher size impact for bending strength was achieved than the strengths obtained by uni axial test. The magnitude of the flexural resistance was mainly because of discrepancies in the characteristics of fibre allocation, i.e. bigger samples escorted to a weak fiber direction and fewer fibres.  At greater stress rates, a substantial improvement in UHPFRC’s mechanical properties was achieved. The content of the fiber quantity has no significant effect on rate of strain sensitivity. The use of twisted steel fibers reduced tensile strength, compared to straight steel fibers, by approximately 10 percent, at a elevated strain rate of 10–1/s in UHPFRC. The strength of flexure resistance is twice and dissipated energy of three or four times more than standard fiber-reinforced concrete (FRC).  While more studies reported static and dynamic mechanical properties of conventional UHPFRCs containing cement as well as silica fume as the binder, relatively fewer studies reported mostly static mechanical performance of UHPFRCs comprising various supplementary cementitious materials. The application of supplementary cementitious materials for diverse scale substitution of cement as well as silica fume could considerably diminish the materials cost of UHPFRC and carbon footprint of this material. In an estimate, 40 percent fly ash in the UHPFRC shows approximate 35 percent lower CO2 emissions than the control UHPFRC. It is also shown that UHPFRC incorporating suitable quantity of supplementary cementitious materials could attain mechanical properties which are slightly lower than the conventional UHPFRC.

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