Efficiency of silica-fume content in plain and natural fiber reinforced concrete for concrete road

Construction and Building Materials 244 (2020) 118382

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Efficiency of silica-fume content in plain and natural fiber reinforced concrete for concrete road Mehran Khan a,b,⇑, Abdul Rehman b, Majid Ali c,⇑ a

Department of Civil Engineering, Dalian University of Technology, Dalian, China Department of Civil Engineering, University of South Asia, Lahore, Pakistan c Structural Materials Research Group (SMaRG), Department of Civil Engineering, Capital University of Science and Technology, Islamabad, Pakistan b

h i g h l i g h t s
Plain concrete (PC) and coconut fiber reinforced concrete (CFRC) are considered.
The detailed mechanical behavior is explored with development of empirical relations.
Different silica-fume (SF) contents (5%, 10%, 15% and 20%) are evaluated for both PC and CFRC.
The optimum SF contents (by cement mass) for PC and CFRC are 10% and 15%, respectively.
The SF and CF in concrete showed up to 8% reduction in road thickness.

a r t i c l e

i n f o

Article history: Received 28 June 2019 Received in revised form 1 January 2020 Accepted 6 February 2020

Keywords: Silica-fume Coconut fiber Concrete Mechanical properties Energy absorption Toughness index Concrete roads Thickness

a b s t r a c t The coconut fiber (CF) has the benefit of highest toughness among natural fibers. The abundant availability and low cost make it more convenient for its use in concrete composites. The thickness of concrete roads can be reduced with the use of natural fibers. In this study, the mechanical properties including energy absorption and toughness indices of silica-fume plain concrete (S-PC) and silica-fume coconut fiber reinforced concrete (S-CFRC) with addition of different silica-fume contents, i.e. 5%, 10%, 15% and 20%, by cement mass, are considered. Also, the reduction in thickness of concrete roads is evaluated using American concrete pavement association StreetPave thickness design software. It is found that S-CFRC has generally improved mechanical properties with 15% SF content, than that of their respective S-PC. Furthermore, the reduction in thickness of concrete road with optimal content of SF in CFRC is observed up to 12 mm. Thus, the enhancement in mechanical properties of S-CFRC favors its utility to be used in concrete roads for thickness reduction. Ó 2020 Elsevier Ltd. All rights reserved.

1. Introduction 1.1. Effect of silica-fume on cementitious composites Many researchers have considered the effect of silica-fume (SF) in concrete for structural applications [1–3]. This is due to enhanced mechanical properties than that of plain concrete (PC). Silica-fume concrete is made by addition of cementious material like silica-fume in PC. Gjørv [4] reported that the mineral admixtures are most of the time industrial by-products which make con⇑ Corresponding authors at: Structural Materials Research Group (SMaRG), Department of Civil Engineering, Capital University of Science and Technology, Islamabad, Pakistan (M. Ali). E-mail addresses: [email protected] (M. Khan), professor. [email protected] (M. Ali). https://doi.org/10.1016/j.conbuildmat.2020.118382 0950-0618/Ó 2020 Elsevier Ltd. All rights reserved.

crete less costly by reducing the required amount of cement and make environment more friendly. Banthia [5] stated that silicafume plain concrete (S-PC) has received greater attention due to its use in structural members. The addition of SF in concrete improves the mechanical properties as well as permeability, abrasion resistance and drying shrinkage [6–10]. The use of silica-fume concrete leads to design of small sections of structures [11]. As stated earlier, the incorporation of SF in concrete improves the mechanical properties and service life of structural applications. 1.2. Effect of short discrete fibers on concrete The natural fibers are inexpensive and abundantly available in developing countries. The coconut fiber have the highest toughness and its use in silica-fume concrete will further results in better per-

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formance of structural applications. Ali et al. [12] reported the effect of coconut fiber (CF) on properties of concrete. It was found that, CF with 5 cm length and content of 2% had improved mechanical properties than that of PC. The highest toughness among natural fibers was the reason for selection of CF in the previous studies [12–15]. The mechanical properties of coconut fiber reinforced concrete (CFRC) were also reported in the literature [15]. The incorporation of 2% CF, by volume fraction showed improved mechanical properties than that of PC. The outcomes of SF and coconut fiber in concrete are summarized in Table 1. Therefore, the CF along with inclusion of SF in concrete may result in improved mechanical properties. Nowadays, natural/artificial fibers with combination of mineral admixtures in concrete may enhance the properties of concrete [16–22]. The silica-fume with addition of different natural/artificial fibers showed improved mechanical properties as shown in Table 2. Therefore, the silicafume with incorporation of coconut fiber may result in enhanced mechanical properties for concrete roads. 1.3. Concrete roads and thickness design Concrete road pavements are more durable and require less maintenance as compared to that of flexible pavements [20]. The shear modulus and elastic modulus of concrete is much higher than that of bituminous material. Also, the flexible pavements are defenseless against folding, rutting and pushing due to heavy vehicular loadings and braking force. In concrete pavements, both compressive and flexure stress are produced under vehicular loadings. However, considering flexural stress, the effect of flexural strength is more in concrete pavement thickness design. The concrete pavement thickness design has two main parameters, i.e. elastic modulus and modulus of rupture [23,24]. The thickness of concrete roads can be reduced by improving these two parameters. Nowadays, natural fiber reinforced concrete is becoming an interesting construction material for concrete pavements [20,25]. A fiber reinforced concrete road is an efficient design choice due to its better performance as compared to that of plain concrete roads [26]. Recently, researchers are developing fiber reinforced concrete for the application of pavements [25–28]. The addition of natural fiber in concrete improves strength, toughness, energy absorption capacity and resistance against cracking as well as helps to reduce

the thickness of concrete roads [20,25,28]. StreetPave software is a latest thickness design technology by American concrete pavement association (ACPA) used for thickness calculation of concrete pavements [29,30]. The StreetPave software utilizes new engineering analysis for roadways to produce optimal concrete pavement thicknesses. The thickness design procedure of StreetPave software is based on methodology of American Portland Cement Association [30,31]. Therefore, keeping in mind the above discussion, the natural fiber reinforced concrete can be helpful to reduce the thickness of concrete roads ultimately results in saving the material. 1.4. Identified research gap for current work Limited work has been done on the combined use of silica-fume and coconut fibers in concrete [32,33]. The outcomes of these studies stated that investigated few properties had improvement up to some extent and needed to be explored further in detail. In addition, the use of short discrete fibers for better behavior and economical design of concrete roads is restricted. However, the usage of coconut fibers for concrete road application is still not explored yet. So, it is essential to predict and evaluate the mechanical behavior of coconut fiber reinforced concrete for its possible use in civil engineering applications especially in concrete pavements. To the author’s best knowledge, no detail study has been reported regarding thickness reduction of concrete roads with the coconut fiber reinforced concrete (CFRC) having different silica-fume content. Thus, an area that needs to be studied is the silica-fume coconut fiber reinforced concrete for the application of concrete pavements. The coconut fibers (CF) has many advantages, i.e. highest toughness compared to other natural fibers and inexpensive material [12–15]. Therefore, the current work is conducted for possible utilization of coconut fibers in concrete for the applications of roads. The advantage of this study is that the optimized mix proportion contents of all raw materials is readily available for immediate use in road application with specified considered conditions. Also, by working on similar lines, optimization of mix proportions for other materials can be done for concrete roads with any requirements. In current work, the strength properties, energy absorption and toughness indices of silica-fume plain concrete (S-PC) and silica-fume coconut fiber reinforced concrete (S-CFRC) are studied. Strength properties are used for the concrete

Table 1 Mechanical properties of concrete with silica-fume and coconut fiber. Concrete type

CS (%)

STS (%)

F.S (%)

Reference

PC S-PC (10%) CFRC (2%) CFRC (2%)

100 108 113 120

100 112 128 110

100 107 123 102

(–) Afroughsabet and Ozbakkaloglu [19] Baruah and Talukdar [15] Ali et al. [12]

Note: PC denotes plain concrete; S-PC means concrete prepared with silica-fume and CFRC represents coconut fiber reinforced concrete. The percentage in the bracket is the content by mass of cement.

Table 2 Mechanical properties of different fiber reinforced concretes with silica-fume. Concrete Type

Fiber Type

Fiber Length

Fiber Content

CS (%)

STS (%)

F. S (%)

Reference

PC CFRDSF (10%) S-SFRC (8%) S-PFRC (10%) S-SFRC (10%) S-SF-PF-FRC (10%)

(–) Coconut fiber Steel Polypropylene Steel Steel + Polypropylene

(–) 100 mm 60 mm 12 mm 60 mm 60 mm + 12 mm

(–) (0.09%) (1%) (0.45%) (1%) (0.85%) + (0.15%)

100 96.2 133 113 119 118

100 – 174 120 155 151

100 107 157 113 161 154

(–) Soleimanzadeh and Mydin [17] Nili and Afroughsabet [18] Afroughsabet and Ozbakkaloglu [19] Afroughsabet and Ozbakkaloglu [19] Afroughsabet and Ozbakkaloglu [19]

Note: PC denotes plain concrete; CFRDSF means concrete prepared with coconut fiber and dense silica-fume; S-SFRC represents silica-fume steel fiber reinforced concrete; SPFRC indicates silica-fume polypropylene fiber reinforced concrete and S-SF-PF-FRC designates silica-fume steel polypropylene fiber reinforced concrete. The percentage in the bracket of concrete type column is the content of silica-fume, by mass of cement; and the percentage in the bracket of fiber content column is by total volume friction.

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road applications. In addition to this, the thickness design calculation for concrete road is performed using American concrete pavement association StreetPave software. 2. Research motivation and significance The research motivation is to provide better sustainable and economical infrastructure to public with use of natural fibers. The handling of agricultural waste including plant fibers is the major issue nationwide for a sustainable development all over the world. And the use of plant fibers in construction industry will ensure more sustainable and greener development than that of synthetic fibers. Recently, the utilization of plant fibers gets inveterate and highlighted in many structural components [12–15,32,33]. The research significance of current work is the formulation of a procedure with the help of which the possible use of plant fibers in concrete with admixtures can be explored from material properties investigation to structure design for particular civil engineering structure application. Therefore, the coconut fiber and silica-fume are considered for its possible use in concrete roads. 3. Experimental program 3.1. Raw ingredients The raw ingredients were coconut fiber (CF), silica-fume (SF), cement, fine aggregate, coarse aggregate and water. The silicafume was bought from Sika company in Pakistan. The images of coconut fiber length, cross-section and surface are shown in Fig. 1(a)–(c), respectively. The maximum size of coarse aggregate was 12.5 mm. The diameter of CF ranges from 0.2 mm to 0.4 mm. A mature coconut has larger amount of CF embedded in soft material and hard skin known as husk. The husk is soaked into the water for soft material decomposition which is around the fibers and then the CF is extracted. This process is followed for the treatment of CF in developing countries and is known as retting [34]. 3.2. Experimental procedure and testing A total of five batches each for S-PC and S-CFRC were prepared with various silica-fume contents, i.e. 0%, 5%, 10%, 15% and 20%, by cement mass. The coconut fiber length was 5 cm and content were 2%, by cement mass. The reason is because many studies showed that the highest strength properties of concrete were achieved with addition of 5 cm coconut fiber length having 2% content [12,15,20–22]. The target strength of concrete was 20 MPa. The mix proportion of S-PC was 1, 2, 2 and 0.45 for cement, fine aggregate, coarse aggregate and water, respectively, with different silicafume contents. For the preparation of S-CFRC mix, the same design mix ratio with addition of coconut fibers and different percentages

Table 3 Slump of S-PC and S-CFRC. Silica-fume content (%)

PC W/C ratio: 0.45 (mm)

CFRC W/C ratio: 0.50 (mm)

0 5 10 15 20

95 40 20 5 0

90 35 15 0 0

of silica-fume were used. To make S-CFRC workable, a relatively high-water cement ratio of 0.50 was used. The S-PC and S-CFRC were prepared according to the layer’s procedure reported by Ali et al. [12]. The slump was calculated according to ASTM C143/ C143M-15a [35] and ACI544.2R [36]. The slump values of S-PC and S-CFRC are presented in Table 3. In S-PC mixes, the slump values are reduced due to the various contents of SF. The reduction in slump with addition of silica-fume in concrete is also reported by Suryavanshi et al. [37]. On the other hand, the slump is further reduced due to the inclusion of coconut fibers in S-CFRC as compared to that of S-PC mixes. Vijaya and Ajitha [32,33] also reported that addition of coconut fiber in silica-fume concrete resulted in decreased workability. The preparation and curing of samples were done according to ASTM standard C192M-16a [38]. The size of cylinders was 100 mm  200 mm for compressive properties, 100 mm  100 mm  400 mm beams for flexural properties and 100 mm  200 mm cylinders for splitting-tensile properties. The three cylinders, three beam-lets and three cylinders were cast for compressive strength, flexural strength and split-tensile strength testing, respectively. From each batch of S-PC0, S-PC5, S-PC10, SPC15, S-PC20, S-CFRC0, S-CFRC5, S-CFRC10, S-CFRC15 and S-CFRC20, a total of nine samples were cast. The subscript number of S-PC and S-CFRC denoted the silica-fume content percentage, i.e. 0%, 5%, 10%, 15% and 20%. The three samples of each batch were denoted as S-PC0, S-PC5, S-PC10, S-PC15, S-PC20, S-CFRC0, S-CFRC5, S-CFRC10, S-CFRC15 and S-CFRC20. The ASTM testing standards and studied parameters for compressive properties, flexural properties, split-tensile properties and thickness design are shown in Table 4. The American concrete pavement association (ACPA) StreetPave thickness design software is used to calculate the thickness of concrete roads. 4. Test results 4.1. Compressive properties Fig. 2 shows the stress-strain curves for S-PC and S-CFRC under compressive loading. It may be noted that S-PC10 and S-CFRC15 has the maximum load as shown in Fig. 2(a) and (b), respectively. The modulus of elasticity (MOE) of all silica-fume plain concrete and

Fig. 1. Images of coconut fiber: (a) length; (b) cross-section; (c) surface.

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M. Khan et al. / Construction and Building Materials 244 (2020) 118382

Table 4 Testing standards and studied parameters. Tests

Standards

Parameters studied

Compressive properties

ASTM C39 [39]

Flexural properties

ASTM C78 [40] and ASTM C1609 [41] ASTM C496 [42]

Stress–strain curves, modulus of elasticity (MOE), compressive strength (C-S), compressive pre-crack energy absorption (CPE1), compressive post-crack energy absorption (CPE2), compressive total energy absorption (CTE) and compressive toughness indexes (CTI). Load-deflection curves, flexural strength (F-S), flexural pre-crack energy absorption (FPE1), flexural post-crack energy absorption (FPE2), flexural total energy absorption (FTE) and flexural toughness indexes (FTI). Strength-time curves, splitting-tensile strength (STS), splitting-tensile pre-crack energy absorption (SPE1), splitting-tensile post-crack energy absorption (SPE2), splitting-tensile total energy absorption (STE) and splittingtensile toughness indexes (STI). Thickness of concrete road.

Splitting-tensile properties Thickness design

ACPA StreetPave software

post-crack energy absorption of S-PC10 than that of S-PC0. The CPE2 of S-CFRC15 is increased by 56%, as compared to that of CFRC0. The CPE2 S-CFRC15 is 89% more as compared to respective S-PC specimen. The SD range of CPE2 for both S-PC and S-CFRC is up to ±0.001 MJ/m3. The compressive total energy absorption in S-PC10 is increased by 66%, as compared to that of S-PC0. The CTE S-CFRC15 is increased by 66%, as to that of S-CFRC0. The CTE of S-CFRC15 is 58% more than that of respective S-PC samples. The improvement in CTE is due to the addition of CF. The CTE SD range for both S-PC and S-CFRC is up to ±0.002 MJ/m3. The CTI of S-PC10 is 1.67 ± 0.05. The compressive toughness index of S-PC10 is increased by 11%, as compared to that of S-PC0. The CTI of S-CFRC15 is decreased by 2%, as compared to that of S-CFRC0. The CTI of SCFRC15 is increased by 89%, as compared to respective S-PC specimen. For S-PC and S-CFRC, the range of SD for CTI is ±0.06 and ±0.05, respectively. The comparison between compressive properties of all S-PC and S-CFRC samples are presented in Fig. 3. The enhancement in CPE1, CPE2 and CTE of S-PC samples is due to the incorporation of various SF content. Furthermore, the improvement in CPE1, CPE2 and CTE of S-CFRC is due to the inclusion of various percentages of SF as well as the presence of CF. The compressive energy absorbed and toughness index is increased by incorporation of fibers in concrete [12,44,45]. On the other hand, beyond the optimum content, the reduction in compressive pre-crack energy absorption, compressive post-crack energy absorption and compressive total energy absorption of S-PC and S-CFRC samples are due to higher SF content which caused the heterogeneity in the mix.

silica-fume coconut fiber reinforced concrete samples are shown in the Table 5. It is noted that the MOE of S-PC10 is 12% more as to that of S-PC0; whereas the MOE of S-CFRC15 is 9% greater as to that of SCFRC0. The standard deviation (SD) range for MOE of both S-PC and S-CFRC is up to ±1.4 GPa. The modulus of elasticity of silica-fume plain concrete is improved with inclusion of various percentages of SF. Shannag [3] reported that addition of different silica-fume content in mortar and concrete resulted in increased modulus of elasticity. Table 5 presents the compressive strengths of all silicafume plain concrete and silica-fume coconut fiber reinforced concrete samples. The compressive strengths (C-S) of S-PC10 is increased by 9%, as compared to that of S-PC0. There is an increase of 19% in S-CFRC15, than that of S-CFRC0. The C-S of S-CFRC0 and SCFRC15 are enhanced by 5% and 25%, respectively, as compared to that of respective S-PC samples. The SD range for C-S of S-PC and S-CFRC is up to ±1.3 MPa and ±1.6 MPa, respectively. Due to the presence of fibers in concrete, the C-S of S-CFRC may have decreased. This may be due to the voids caused by incorporation of low dense coconut fiber. The improvement in C-S is due to the inclusion of different SF content up to the optimum content in the S-PC and S-CFRC [18]. The increase in C-S due to coconut fiber addition in concrete is also reported by Ali et al. [12], Baruah and Talukdar [15] and Ramli et al. [43]. The compressive pre-crack energy absorption (CPE1), compressive post-crack energy absorption (CPE2), compressive total energy absorption (CTE) and compressive toughness index (CTI) are calculated according to the procedure reported by Khan et al. [44] and Zia and Ali [45]. The pre-crack energy absorption, post-crack energy absorption, total energy absorption and toughness indexes of S-PC and S-CFRC are shown in Table 5. The compressive precrack energy absorption of S-PC10 is 62% more, as compared to that of S-PC0. The CPE1 of S-CFRC15 is increased by 71%, as compared to that of S-CFRC0. The SD range for CPE1 of both S-PC and S-CFRC is up to ±0.001 MJ/m3. There is an increase of 20% in compressive

S-PC0

S-PC5

S-PC15

S-PC20

4.2. Flexural properties Fig. 4 shows the load-deflection curves of S-PC and S-CFRC samples under flexural loading. It may be noted that S-PC10 and SCFRC15 has the maximum load as shown in Fig. 4(a) and (b),

S-PC10

30

20 10 0

(a)

S-CFRC5

S-CFRC15

S-CFRC20

S-CFRC10

40 Stre s s (MPa)

Stre s s (MPa)

40

S-CFRC0

0

0.005

0.01

Strain (-)

0.015

30 20 10

0

(b)

0

0.005

0.01

Strain (-)

Fig. 2. Stress-Strain curves under compressive loadings (a) S-PC (b) S-CFRC.

0.015

5

M. Khan et al. / Construction and Building Materials 244 (2020) 118382 Table 5 Compressive properties of all silica-fume plain concrete and silica-fume coconut fiber reinforced concrete samples. Concrete Type

S-PC0 S-PC5 S-PC10 S-PC15 S-PC20 S-CFRC0 S-CFRC5 S-CFRC10 S-CFRC15 S-CFRC20

Parameters MOE (GPa)

C-S (MPa)

CPE1 (MJ/m )

CPE2 (MJ/m3)

CTE (MJ/m3)

CTI (–)

25.0 26.0 28.1 26.9 25.8 25.8 27.7 30.5 33.4 25.3

26.0 26.6 28.3 26.0 25.3 27.2 27.5 28.8 32.4 26.6

0.013 0.016 0.018 0.016 0.015 0.014 0.017 0.018 0.024 0.021

0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001

0.006 0.008 0.012 0.006 0.005 0.007 0.009 0.013 0.011 0.007

0.019 0.024 0.030 0.022 0.020 0.021 0.026 0.031 0.035 0.028

1.46 1.50 1.67 1.38 1.33 1.50 1.53 1.72 1.46 1.33

± ± ± ± ± ± ± ± ± ±

1.4 1.2 0.7 0.3 0.7 1.2 1.2 1.1 1.0 1.4

± ± ± ± ± ± ± ± ± ±

3

0.8 1.3 1.0 1.0 1.3 0.2 0.9 0.4 1.6 0.2

± ± ± ± ± ± ± ± ± ±

± ± ± ± ± ± ± ± ± ±

0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001

S-PC5

S-CFRC5

S-PC10

S-CFRC10

S-PC15

S-CFRC15

S-PC20

S-CFRC20

S-PC0

S-CFRC0

± ± ± ± ± ± ± ± ± ±

0.002 0.002 0.002 0.002 0.002 0.002 0.001 0.002 0.001 0.002

± ± ± ± ± ± ± ± ± ±

0.03 0.05 0.05 0.06 0.04 0.02 0.05 0.04 0.05 0.04

200% 150% 100% 50%

0% MOE (MPa)

C-S (MPa)

CPE1 (MJ/m3) CPE2 (MJ/m3) CTE (MJ/m3)

CTI (-)

Fig. 3. Comparison of compressive properties of S-PC and S-CFRC.

respectively. Also, the deflection is more in S-CFRC samples than that of S-PC due to the bridging effect of CF. The flexural strength of all silica-fume plain concrete and silica-fume coconut fiber reinforced concrete samples are shown in Table 6. The flexural strength (F-S) of S-PC10 is increased by 25%, than that of S-PC0. There is an increase of 34% in F-S of S-CFRC15, than that of S-CFRC0. The F-S of S-CFRC15 is improved by 38%, respectively, than that of respective S-PC specimen. The SD range for F-S of S-PC and S-CFRC is ±0.7 MPa and ±0.4 MPa, respectively. Due to the inclusion of the SF in the S-PC and S-CFRC enhancement in F-S is observed [18]. The flexural strength of S-CFRC is further improved due to bridging effect of coconut fiber [15,17,43]. The addition of higher silicafume percentage beyond optimum content results in heterogeneity of the mix ultimately reduces the flexural strength. The flexural pre-crack energy absorption (FPE1), flexural postcrack energy absorption (FPE2), flexural total energy absorption (FTE) and flexural toughness index (FTI) are calculated according to the procedure reported by Khan et al. [44] and Zia and Ali [45]. The pre-crack energy absorption, post-crack energy absorption, total energy absorption and toughness indexes of S-PC and S-CFRC are shown in Table 6. The flexural pre-crack energy absorption of S-PC10 is increased by 27%, as compared to that of S-PC0. The FPE1 of S-CFRC15 is increased by 43%, than that of S-CFRC0. The FPE1 of S-CFRC15 is increased by 105%, as compared to respective S-PC specimen. The SD range for FPE1 of S-PC and S-CFRC is ±0.25 J and ±0.24 J, respectively. There is no flexural post-crack energy absorption in S-PC because at first crack load, the S-PC samples are broken in two pieces. The FPE2 of S-CFRC15 is increased by 94%, than that of S-CFRC0. The SD range for FPE2 of S-PC and SCFRC is up to ±0.00 J and ±0.09 J, respectively. The flexural total energy absorption in S-PC10 is increased by 27%, as compared to that of S-PC0. The FTE of S-CFRC15 is increased by 37%, than that of S-CFRC0. The FTE SD range for S-PC and S-CFRC is ±0.25 J and

±0.26 J, respectively. The flexural toughness index of S-PC0, S-PC5, S-PC10, S-PC15 and S-PC20 are 1. The FTI of S-CFRC15 is increased by 3%, as to that of S-CFRC0. The FTI of S-CFRC15 is increased by 35%, as compared to respective S-PC samples. For S-PC and SCFRC, the range of SD for FTI is ±0.00 and ±0.02, respectively. The comparison of flexural properties of all S-PC and S-CFRC samples are presented in Fig. 5. The improvement in FPE1 and FTE of S-PC sample is due to the incorporation of different percentages of SF. Moreover, the FPE1, FPE2, FTE of S-CFRC samples are increased due to the inclusion of different SF contents and as well as of CF. The fibers provide bridging effect due to which the flexural postcrack energy absorption, flexural total energy absorption and flexural toughness index of fiber reinforced concrete are enhanced; and are also reported by Zia and Ali [45] and Khan and Ali [46].

4.3. Splitting-tensile properties The Strength-Time curves for S-PC and S-CFRC under splittingtensile loading are shown in Fig. 6. It may be noted that S-PC10 and S-CFRC15 has the maximum load as shown in Fig. 6(a) and (b), respectively. Also, the S-CFRC samples have the load carrying capability after the peak load due to CF bridging. Table 7 shows the split-tensile strength of all silica-fume plain concrete and silicafume coconut fiber reinforced concrete samples. The split-tensile strength (STS) of S-PC10 is increased by 19%, than that of S-PC0. There is an increment of 20%, in STS of S-CFRC15, as compared to that of S-CFRC0. The STS of S-CFRC15 is improved by 38%, than that of respective S-PC sample. The SD range for STS of S-PC and S-CFRC is up to ±0.3 MPa and ±0.4 MPa, respectively. In the S-PC and SCFRC, the improvement in STS is because of inclusion of the silica-fume up to optimal percentage [18]; beyond this the STS is reduced due to incorporation of higher silica-fume content which

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M. Khan et al. / Construction and Building Materials 244 (2020) 118382

S-PC0

S-PC5

S-PC15

S-PC10

S-PC20

Load (k N)

Load (k N)

9 6

S-CFRC20

5 0

0

0.3

S-CFRC10

10

3

(a)

S-CFRC5

S-CFRC15 15

12

0

S-CFRC0

0.6

0.9

Deflection (mm)

0

0.5

(b)

1

1.5

2

Deflection(mm)

Fig. 4. Load-Deflection curves under flexural loading (a) S-PC (b) S-CFRC.

Table 6 Flexural properties of all silica-fume plain concrete and silica-fume coconut fiber reinforced concrete samples. Concrete Type

Parameters

S-PC0 S-PC5 S-PC10 S-PC15 S-PC20 S-CFRC0 S-CFRC5 S-CFRC10 S-CFRC15 S-CFRC20

F-S (MPa)

FPE1 (J)

FPE2 (J)

FTE (J)

FTI (–)

5.2 6.2 6.5 6.0 5.5 6.2 6.6 7.8 8.3 4.7

3.05 3.26 3.88 3.60 2.73 5.16 5.57 6.88 7.39 4.19

0 ± 0.0 0 ± 0.0 0 ± 0.0 0 ± 0.0 0 ± 0.0 1.61 ± 0.04 1.81 ± 0.03 2.54 ± 0.04 2.64 ± 0.06 0.88 ± 0.09

3.05 ± 0.12 3.26 ± 0.13 3.88 ± 0.25 3.60 ± 0.06 2.73 ± 0.20 6.77 ± 0.26 7.38 ± 0.13 9.42 ± 0.07 10.03 ± 0.03 5.07 ± 0.21

1 ± 0.0 1 ± 0.0 1 ± 0.0 1 ± 0.0 1 ± 0.0 1.31 ± 0.01 1.32 ± 0.01 1.37 ± 0.01 1.35 ± 0.01 1.21 ± 0.02

± ± ± ± ± ± ± ± ± ±

0.2 0.2 0.6 0.7 0.2 0.1 0.2 0.4 0.2 0.1

± ± ± ± ± ± ± ± ± ±

0.12 0.13 0.25 0.06 0.20 0.24 0.10 0.11 0.06 0.13

S-PC5

S-CFRC5

S-PC10

S-CFRC10

S-PC15

S-CFRC15

S-PC20

S-CFRC20

S-PC0

S-CFRC0

400%

300% 200% 100% 0% F-S (MPa)

FPE1 (J)

FPE2 (J)

FTE (J)

FTI (-)

S-PC0

S-PC5

S-PC15

S-PC20

S-PC10

4 3

2 1 0

(a)

0

15

Time (s)

30

45

Splitting te ns ile s trength (MPa)

Splitting te ns ile s trength (MPa)

Fig. 5. Comparison of flexural properties of S-PC and S-CFRC.

S-CFRC0

S-CFRC5

S-CFRC15

S-CFRC20

S-CFRC10

4 3 2

1 0

(b)

0

15

30

Time (s)

Fig. 6. Strength-Time curves under splitting tensile loading (a) S-PC (b) S-CFRC.

45

60

7

M. Khan et al. / Construction and Building Materials 244 (2020) 118382 Table 7 Splitting-tensile properties of all silica-fume plain concrete and silica-fume coconut fiber reinforced concrete samples. Concrete Type

Parameters

S-PC0 S-PC5 S-PC10 S-PC15 S-PC20 S-CFRC0 S-CFRC5 S-CFRC10 S-CFRC15 S-CFRC20

STS (MPa)

SPE1 (MJ/m .s)

SPE2 (MJ/m3.s)

STE (MJ/m3.s)

STI (–)

2.7 3.0 3.2 2.6 2.4 3.0 3.4 3.5 3.6 2.9

23.9 29.2 40.0 25.3 25.9 45.9 50.6 52.6 56.9 50.4

0 ± 0.0 0 ± 0.0 0 ± 0.0 0 ± 0.0 0 ± 0.0 35.7 ± 1.02 42.9 ± 1.53 47.9 ± 1.05 46.9 ± 2.23 27.8 ± 0.96

23.9 ± 1.1 29.2 ± 1.1 40.0 ± 1.31 25.3 ± 1.94 25.9 ± 0.70 81.7 ± 2.29 93.5 ± 3.15 100.6 ± 2.74 103.9 ± 3.12 78.2 ± 2.58

1 ± 0.0 1 ± 0.0 1 ± 0.0 1 ± 0.0 1 ± 0.0 1.77 ± 0.04 1.84 ± 0.01 1.91 ± 0.02 1.82 ± 0.05 1.55 ± 0.04

± ± ± ± ± ± ± ± ± ±

3

0.2 0.3 0.3 0.1 0.2 0.1 0.2 0.2 0.4 0.1

± ± ± ± ± ± ± ± ± ±

1.1 1.1 1.31 1.94 0.70 1.27 1.62 1.69 0.92 1.59

caused heterogeneity of the mix. The bridging effect of coconut fiber in concrete enhanced the split-tensile strength [12,15]. The splitting-tensile pre-crack energy absorption (SPE1), splitting-tensile post-crack energy absorption (SPE2), splittingtensile total energy absorption (STE), splitting-tensile toughness index (STI) are calculated. The splitting-tensile pre-crack energy absorption, splitting-tensile post-crack energy absorption, splitting-tensile total energy absorption and splitting-tensile toughness index are shown in Table 7. The splitting-tensile precrack energy absorption of S-PC10, is increased by 67%, than that of S-PC0. The SPE1 of S-CFRC15 is increased by 24%, as compared to that of S-CFRC0. The SPE1 of S-CFRC15 is increased by 126%, as compared to respective S-PC specimen. The SD range for SPE1 of S-PC and S-CFRC is up to ±1.94 MJ/m3.s and ±1.69 MJ/m3.s, respectively. There is no splitting-tensile post-crack energy absorption in S-PC samples because at first crack load the S-PC samples are split in two pieces. The SPE2 of S-CFRC15 is increased by 44%, as compared to that of S-CFRC0. The SPE2 of all S-CFRC specimen are 100% greater as to that of S-PC. The SD range for SPE2 of S-PC and S-CFRC is up to ±0.0 MJ/m3.s and ±2.23 MJ/m3.s, respectively. The splitting-tensile total energy absorption in S-PC10 is increased by 67%, as compared to that of S-PC0. The STE of S-CFRC15 is improved by 29%, as to that of S-CFRC0. The STE of S-CFRC15 is enhanced by 312%, as compared to respective S-PC samples. The STE SD range for S-PC and S-CFRC is ±1.94 MJ/m3.s and ±3.15 MJ/ m3.s, respectively. The STI of S-PC0, S-PC5, S-PC10, S-PC15 and SPC20 are 1 because SPE1 and STE are same. The STI of S-CFRC15 is increased by 4%, as compared to that of S-CFRC0. The STI of SCFRC15 is increased by 91%, as compared to respective S-PC specimen. For S-PC and S-CFRC, the range of SD for STI is up to ±0.00 and ±0.05, respectively. The comparison of splitting-tensile properties of all S-PC and S-CFRC samples are presented in Fig. 7. Moreover, the splitting-tensile pre-crack energy absorption, splitting-tensile post-crack energy absorption and splitting-tensile total energy

absorption of S-CFRC specimen are improved because of inclusion of coconut fiber and silica-fume. The bridging effect of fibers results in improved splitting-tensile post-crack energy absorption, splitting-tensile total energy absorption and splitting-tensile toughness index [44,45].

5. Discussions 5.1. Optimization of silica-fume content The optimization of silica-fume content for S-PC and S-CFRC is shown in Table 8 and Fig. 8. The MOE, C-S, CTE, CTI, F-S, FTE, FTI, STS, STE and STI of suggested S-PC10 are increased by 12%, 9%, 66%, 5%, 25%, 27%, 0%, 19%, 67% and 0%, respectively, as compared to that of S-PC0 (refer Fig. 8(a)). In comparison to S-CFRC0, the MOE, C-S, CTE, F-S, FTE, FTI, STS, STE and STI of suggested S-CFRC15 are increased by 28%, 19%, 66%, 34%, 37%, 3%, 20%, 29% and 4%, respectively (refer Fig. 8(b)). The MOE, C-S, CTE, F-S, FTE, FTI, STS, STE and STI of suggested S-CFRC15 are increased by 19%, 14%, 17%, 28%, 158%, 35%, 13%, 160% and 82%, respectively, as compared to that of S-PC10. The Comparison of current study with Vijaya and Ajitha [32,33] study is shown in Table 9. In this current study, the mix design ratio for S-CFRC is 1:2:2 (C:S:A) with 0.50 w/c ratio. The coconut fiber content is 2% and fiber length is 50 mm. Vijaya and Ajitha [32,33] studied the S-CFRC with mix design ratio of 1:1.17:2.22:0.32 (C:S:A:W); while the coconut fiber content is 2% and fiber length is 40 mm. The silica-fume content is 0%, 5%, 10%, 15% and 20%, by replacement of cement and total batches was five; while in present study, the same content of silica-fume is added, by mass of cement, and total batches are ten. The specimen’s size for C-S was 150 mm  150 mm  150 mm and for STS 150 mm  300 mm in Vijaya and Ajitha [32] study; and for F-S the size was 600 mm  150 mm  150 mm [33]. In present study,

S-PC5

S-CFRC5

S-PC10

S-CFRC10

S-PC15

S-CFRC15

S-PC20

S-CFRC20

S-PC0

S-CFRC0

400% 300% 200% 100%

0% STS (MPa)

SPE1 (MJ/m3.s)

STE (MJ/m3.s)

Fig. 7. Comparison of splitting tensile properties of S-PC and S-CFRC.

STI (-)

8

M. Khan et al. / Construction and Building Materials 244 (2020) 118382

Table 8 Optimization of silica-fume content in S-PC and S-CFRC. Concrete Type

MOE (GPa)

C-S (MPa)

CTE (MJ/m3)

CTI (–)

F-S (MPa)

FTE (J)

FTI (–)

STS (MPa)

STE (MJ/m3.s)

STI (–)

PCs with minimum values PCs with maximum values Recommended PC (10%) CFRCs with minimum values CFRCs with maximum values Recommended CFRC (15%)

25.0 ± 1.4 (0%) 28.1 ± 0.07 (10%)

25.3 ± 1.3 (20%) 28.3 ± 1.0 (10%)

0.019 ± 0.002 (0%) 0.030 ± 0.002 (10%)

1.46 ± 0.03 (0%) 1.67 ± 0.05 (10%)

5.02 ± 0.2 (0%) 6.5 ± 0.06 (10%)

2.73 ± 0.2 (20%) 3.88 ± 0.25 (10%)

1 ± 0.0 (0%) 1 ± 0.0 (10%)

2.4 ± 0.2 (20%) 3.2 ± 0.3 (10%)

23.9 ± 1.1 (0%) 40.0 ± 1.31 (10%)

1 ± 0.0 (0%) 1 ± 0.0 (10%)

28.1 ± 0.07

28.3 ± 1.0

0.030 ± 0.002

1.67 ± 0.05

6.5 ± 0.06

3.88 ± 0.25

1 ± 0.0

3.2 ± 0.3

40.0 ± 1.31

1 ± 0.0

25.3 ± 1.4 (20%)

26.6 ± 0.3 (20%)

0.021 ± 0.002 (0%)

1.33 ± 0.04 (20%)

4.7 ± 0.1 (20%)

5.07 ± 0.21 (20%)

1.21 ± 0.02 (20%)

2.9 ± 0.1 (20%)

78.2 ± 2.58 (20%)

1.55 ± 0.04 (20%)

33.4 ± 1.0 (15%)

32.4 ± 1.6 (15%)

0.035 ± 0.001 (15%)

1.72 ± 0.04 (10%)

8.3 ± 0.2 (15%)

10.03 ± 0.03 (15%)

1.37 ± 0.01 (10%)

3.6 ± 0.4 (15%)

103.9 ± 3.12 (15%)

1.91 ± 0.02 (10%)

33.4 ± 1.0

32.4 ± 1.6

0.035 ± 0.001

1.46 ± 0.05

8.3 ± 0.2

10.03 ± 0.03

1.35 ± 0.01

3.6 ± 0.4

103.9 ± 3.12

1.82 ± 0.05

Note: Percentage with in the bracket is the content of silica-fume by mass of cement.

200%

S-PC5

S-PC10

S-PC15

S-PC20

S-PC0

150%

100%

50%

0%

MOE

C-S

CTE

CTI

F-S

FTE

FTI

STS

STE

STI

(a) S-CFRC5

S-CFRC10

S-CFRC15

S-CFRC20

S-CFRC0

200%

150%

100%

50%

0%

(b)

MOE

C-S

CTE

CTI

F-S

FTE

FTI

STS

STE

STI

Fig. 8. Optimization of silica-fume content (a) in S-PC (b) in S-CFRC.

the size of specimen is 100 mm  200 mm for compressive properties, 100 mm  100 mm  400 mm for flexural properties and 100 mm  200 mm for splitting-tensile properties. Vijaya and Ajitha [32] considered two parameters, i.e. C-S and STS for optimization; and consider F-S in another study [33]. In this research, a total of 16 parameters are considered, i.e. MOE, C-S, CPE1, CPE2, CTE, CTI, F-S, FPE1, FPE2, FTE, FTI, STS, SPE1, SPE2, STE and STI. In this study, it is found that the optimized silica-fume content for S-PC is 10%, by mass of cement; and optimized silica-fume content for SCFRC is 15%, by cement mass, with the 2% CF content for achieving better mechanical properties. The optimized content reported by Vijaya and Ajitha [32,33] is 10% silica-fume, by replacement of

cement and with addition of 2% coconut fiber. Furthermore, in this study, an empirical equation is developed for CTI, FTI and STI from experimental results of C-S, F-S and STS, respectively. Also, the conducted study focuses the thickness design of concrete road. 5.2. Empirical equations between toughness indexes and strengths Fig. 9 shows the comparison of S-CFRC experimental and empirical equations values. The empirical equations (i.e. Eqs. (1)–(3)) have been established with the help of average experimental data. The R2 range of is 0.86–0.99 for numerically predicting the compressive toughness index (CTI), flexural toughness index (FTI)

M. Khan et al. / Construction and Building Materials 244 (2020) 118382

9

Table 9 Comparison of current study with Vijaya and Ajitha [32,33] study. Parameters

Vijaya and Ajitha [32,33]

Current Study

Mix design Water-cement ratio Fiber length Fiber content Silica-fume content

1: 1.17: 2.22 0.32 40 mm 2%, by mass of cement 0%, 5%, 10%, 15% and 20%, by replacement of cement 150 mm  150 mm  150 mm (cube) 600 mm  150 mm  150 mm (beam) 150 mm  300 mm (cylinder)

1: 2: 2 0.50 50 mm 2%, by mass of cement 0%, 5%, 10%, 15% and 20%, by addition of cement

Only C-S, STS [32] and F-S [33]


MOE, C-S, CPE1, CPE2, CTE and CTI
F-S, FPE1, FPE2, FTE and FTI
STS, SPE1, SPE2, STE and STI Ten (five for S-PC and five S-CFRC) 90, i.e. 30 for compressive properties, 30, for flexural properties and 30 for splittingtensile properties Developed for CTI, FTI and STI from C-S, F-S and STS, respectively Thickness design for concrete road

Specimen Sizes

Compression Flexural Splittingtensile Optimization aspects

Total batches Total samples for 28 days testing Empirical equations Application

Five (one for PC and four for S-CFRC) 30, i.e. 15 for CS and 15 for STS only [32]. 15 for F-S only [33] (–) (–)

100 mm  200 mm (cylinder) 100 mm  100 mm  400 mm (beam) 100 mm  200 mm (cylinder)

and splitting-tensile toughness index (STI) of S-CFRC. Thus, empirical equations of CTI, FTI and STI from the experimental data of C-S, F-S and STS, respectively, shows satisfactory outcomes for S-CFRC. The highest percentage variance between numerical and experimental values is up to 3.4% (refer Fig. 9).

CTISCFRC ¼ 0:0426 ðC  SÞ2 þ 2:5347 ðC  SÞ    35:946 R2 ¼ 0:99

ð1Þ

FTISCFRC ¼ 0:0122 ðF  SÞ2 þ 0:1999 ðF  SÞ þ 0:5386 ðR2 ¼ 0:98Þ ð2Þ STISCFRC ¼ 1:4493 ðSTSÞ2 þ 9:7467 ðSTSÞ  14:487 ðR2 ¼ 0:86Þ ð3Þ whereas, the experimental values of C-S, F-S and STS are in MPa. 5.3. Thickness design of concrete road The thickness design of concrete road is presented in Table 10. The elastic modulus and rupture modulus are the two important parameters in the thickness design [20,23,24]. The rupture modulus of S-PCs and S-CFRCs are increased as compared to that of S-PC0 and S-CFRC0, respectively. The concrete road thickness of S-PC10, SPC15, S-CFRC5 and S-CFRC10 are decreased by 6 mm as compared to that of S-PC0 and S-CFRC0. It may be noted that the S-CFRC15 has maximum reduction of about 12 mm in concrete road thickness.

S-CFRC0

S-CFRC5

S-CFRC10

S-CFRC15

S-CFRC20

Experimental

Percentage

105 100 95 90

CTI (Eq. 1)

FTI (Eq. 2)

STI (Eq. 3)

Fig. 9. Comparison of S-CFRC experimental and empirical equations values.

The reduction in thickness of concrete roads is up to 4% and 8% for S-PC and S-CFRC, respectively, as compared to that of their respective control mixes. The thickness of concrete roads was also reduced up to 12 mm by use of hair and wave polypropylene fiber [20]. Altoubat et al. [47] stated that the performance and structural capacity of concrete roads is improved due to addition of fibers. Thus, the S-CFRC15 can be helpful in reducing thickness, enhancing structural capacity and performance of concrete roads. Also, the fibers are surrounded by adhesive contact of paste which improves the strength of concrete from stress transfer mechanism between matrix and reinforced fibers. Moreover, a part of tensile stresses is taken by fibers generated due to applied loading, thus resist crack growth and help to retain compact microstructure [48]. In fiber reinforced concrete, the uniformly distributed fibers in concrete are responsible for transfer of stress from matrix. The discontinuous randomly distributed fibers in concrete controls and delays the tensile cracking throughout the matrix. The strength of concrete is improved due to the inclusion of fiber which results in delaying and controlling the shear and flexural cracks [17]. Ramli et al. [43] found that use of optimize coconut fiber benefits in long-term strength and durability in aggressive environment. Thus, the S-CFRC with optimal SF content may control the cracking ultimately enhance the structural capacity and performance of concrete roads as well as helpful in material saving.

5.4. Microstructural mechanism The SEM images show the microstructure of silica-fume and coconut fiber in Fig. 10. The micro-structure of the matrix is enhanced due to high pozzolanic activity of silica-fume (refer Fig. 10(a)). The pozzolanic effect means that the C-S-H gel is formed by silica-fume reacting with Ca (OH)2 during hydration under alkaline environment. These formed C-S-H gel can fill the pores and reduce the porosity of cement hydration products ultimately increase the strength of matrix. The silica-fume react with Ca (OH)2 because it cannot hydrate directly with water. Also, an adverse effect on interfacial and microstructure properties can be occur due to orientation and crystallinity of Ca (OH)2. The addition of silica-fume up to certain extent enhance the strength but the higher amount of silica-fume may result in heterogeneity of the mix and can be the basis of low bond strength. However, the fiber debonding can be occurred due to the low bond strength of matrix as shown in Fig. 10(b). The incorporation of coconut fiber lead to new interfaces in the matrix which result in weak link between coconut fiber and the matrix. This indicates that the interfacial

10

M. Khan et al. / Construction and Building Materials 244 (2020) 118382

Table 10 Thickness design of concrete road. ‘Concrete type

Modulus of rupture (MPa)

Modulus of elasticity (GPa)

Thickness (mm)*

Remarks

Plain concrete Hair fiber reinforced concrete Wave polypropylene fiber reinforced concrete S-PC0 S-PC5 S-PC10 S-PC15 S-PC20 S-CFRC0 S-CFRC5 S-CFRC10 S-CFRC15 S-CFRC20

3.07 3.57 3.61

16.7 17.7 17.65

190.5 178 178

Khan and Ali (2018)

5.2 6.2 6.5 6 5.5 6.2 6.6 7.8 8.3 4.7

25 26 28.1 26.9 25.8 25.8 27.7 30.5 33.4 25.3

152 152 146 146 152 152 146 146 140 152

Current study

Note: * Using Design life = 30 years, ACI 330 Category A Traffic Load Spectrums, k = 130 psi/in, Design Lane Distribution = 100%, Directional distribution = 50% and Traffic Growth Rate = 2% per year. The same parameters for thickness design of concrete road were considered by Khan and Ali [20].

gets inveterate and highlighted in many structural components but the studies are still limited for concrete road applications. In this study, the possible utilization of coconut fibers in concrete with silica fume is explored from composite material properties to concrete road design using American concrete pavement association StreetPave software. Silica-fume plain concrete (S-PC) and silicafume coconut fiber reinforced concrete (S-CFRC) with different silica-fume contents of 5%, 10%, 15% and 20%, by cement mass, are investigated. The main emphasis is the optimization of SCFRC for energy absorption capacity, toughness and thickness design of concrete roads which is not considered yet. Therefore, in current study, the best S-PC and S-CFRC are selected based on number of increased parameters. Following conclusions are drawn:

Fig. 10. SEM images: (a) Silica-fume and matrix interface; (b) Coconut fiber and matrix interface.

and microstructure properties of S-CFRC still needs improvement which can be a new direction for future work.


The modulus of elasticity, compressive strength, compressive total energy absorption and compressive toughness index of S-PC10 are increased by 4%, 9%, 66% and 5%, respectively, than that of S-PC0. Compared to S-PC0, the flexural strength and flexural total energy absorption of S-PC10 are enhanced by 25% and 30%. In comparison to S-PC0, the splitting-tensile strength and splitting-tensile total energy absorption of S-PC10 are more by 19% and 67%, respectively.
There is an increment in modulus of elasticity, compressive strength, compressive total energy absorption of S-CFRC15 by 29%, 19% and 31%, respectively, than that of S-CFRC0. For SCFRC15, there is an enhancement of 34%, 64% and 3% in flexural strength, flexural total energy absorption and flexural toughness index, respectively, as compared to that S-CFRC0. The splitting-tensile strength, splitting-tensile total energy absorption and splitting-tensile toughness index of S-CFRC15 are improved by 20%, 29% and 4%, respectively, as compared to that of S-CFRC0.
The reduction in thickness of concrete road is observed up to 4% and 8% for S-PC10 and S-CFRC15, respectively, than that of their respective control samples.
The high pozzolanic activity of silica-fume improved the microstructure of the matrix up to certain extent and the heterogeneity of the mix result in low bond strength due to higher amount of silica-fume content.
S-PC10 and S-CFRC15 shows over all best properties and optimal silica-fume content for S-PC and S-CFRC are 10% and 15%, respectively.

6. Conclusions The use of natural fibers in concrete can provide better sustainable and economical infrastructure. Recently, the use of plant fibers

Thus, CFRC with optimized silica-fume content can be used for thickness reduction of concrete roads. The enhanced mechanical properties of S-CFRC may result in better performance and struc-

M. Khan et al. / Construction and Building Materials 244 (2020) 118382

tural capacity of concrete roads. However, the long-term durability of coconut fibers (being organic fibers) is still a matter of concern which needs to be considered in future. Also, it would be of great interest to study the chemical reaction analysis with in depth mechanism for S-CFRC. CRediT authorship contribution statement Mehran Khan: Conceptualization, Methodology, Software, Formal analysis, Writing - original draft, Writing - review & editing, Supervision. Abdul Rehman: Investigation, Formal analysis, Writing - original draft. Majid Ali: Conceptualization, Methodology, Writing - review & editing, Supervision. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgement The authors are thankful to Mr. Zeeshan Liaqat and Mr. Umair Aziz Khan for their kind support during the lab work. Also, thankful to Engr. Waqas Ahmad for helping in SEM analysis of coconut fibers. The careful review and constructive suggestions by the anonymous reviewers are gratefully acknowledged. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.conbuildmat.2020.118382. References [1] H.A. Toutanji, Properties of polypropylene fiber reinforced silica fume expansive-cement concrete, Constr. Build. Mater. 13 (4) (1999) 171–177, https://doi.org/10.1016/S0950-0618(99)00027-6. [2] R. Siddique, Utilization of silica fume in concrete: review of hardened properties, Resour. Conserv. Recycl. 55 (11) (2011) 923–932, https://doi.org/ 10.1016/j.resconrec.2011.06.012. [3] M. Shannag, High strength concrete containing natural pozzolan and silica fume, Cem. Concr. Compos. 22 (6) (2000) 399–406, https://doi.org/10.1016/ S0958-9465(00)00037-8. [4] O. Gjørv, High strength concrete, Developments in the Formulation and Reinforcement of Concrete, pp. 79–97, 2008. [5] N.P. Banthia, S. Mindess, A. Bentur, J.C. Maso, Durability Constr. Mater. (1987) 1033–1040. [6] B. Sabir, High-strength condensed silica fume concrete, Mag. Concr. Res. 47 (172) (1995) 219–226. [7] H. Toutanji, T. El-Korchi, Tensile and compressive strength of silica fumecement pastes and mortars, Cem. Concr. Aggregates 18 (2) (1996) 78–84. [8] M. Haque, Strength development and drying shrinkage of high-strength concretes, Cem. Concr. Compos. 18 (5) (1996) 333–342, https://doi.org/ 10.1016/0958-9465(96)00024-8. [9] J. Cabrera, P.A. Claisse, Measurement of chloride penetration into silica fume concrete, Cem. Concr. Compos. 12 (3) (1990) 157–161, https://doi.org/ 10.1016/0958-9465(90)90016-Q. [10] A.A. Bubshait, B.M. Tahir, M. Jannadi, Use of microsilica in concrete construction: reviews state-of-the-art silica fume concrete and discusses the influence silica fume has on the various properties of concrete and the effect on the bond between parent concrete and new concrete, Build. Res. Inf. 24 (1) (1996) 41–49, https://doi.org/10.1080/09613219608727497. [11] ACI, A. 363R-92, State-of-the-art report on high-strength concrete (reapproved in 1997). American Concrete Institute, 1997. [12] M. Ali, A. Liu, H. Sou, N. Chouw, Mechanical and dynamic properties of coconut fibre reinforced concrete, Constr. Build. Mater. 30 (2012) 814–825, https://doi. org/10.1016/j.conbuildmat.2011.12.068. [13] S.S. Munawar, K. Umemura, S. Kawai, Characterization of the morphological, physical, and mechanical properties of seven nonwood plant fiber bundles, J. Wood Sci. 53 (2) (2007) 108–113. [14] M. Ali, X. Li, N. Chouw, Experimental investigations on bond strength between coconut fibre and concrete, Mater. Des. 44 (2013) 596–605, https://doi.org/ 10.1016/j.matdes.2012.08.038.

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