Bond strength of the interface between normal concrete substrate and GUSMRC repair material overlay

Construction and Building Materials 216 (2019) 261–271

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Bond strength of the interface between normal concrete substrate and GUSMRC repair material overlay S.H. Abo Sabah a, M.H. Hassan a, N. Muhamad Bunnori a,b,⇑, M.A. Megat Johari a a b

School of Civil Engineering, Engineering Campus, Universiti Sains Malaysia, Nibong Tebal, 14300 Penang, Malaysia Department of Civil Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia

h i g h l i g h t s
We examine the bond characteristics between NC substrate and GUSMRC repair material.
The bond strength increases as the age of the NC/GUSMRC composite increases.
The sand blasting surface treatment enhances the bond strength more than the grinding treatment.
GUSMRC seems to be a very promising material for the repair and rehabilitation of RC structures.

a r t i c l e

i n f o

Article history: Received 14 November 2018 Received in revised form 23 April 2019 Accepted 30 April 2019 Available online 9 May 2019 Keywords: Ultra-high performance concrete Bond strength Repair material Concrete rehabilitation Normal concrete substrate

a b s t r a c t This study investigated the interfacial bond strength between a new Green Universiti Sains Malaysia Reinforced Concrete (GUSMRC) as a repair material and the existing normal concrete substrate (NC) using two methods of surface treatment: grooving and sandblasting. The bond strength was evaluated via the slant shear, splitting tensile, and pull-off strength tests at 7, 28, and 90 days. The results showed that the bond strength of the NC/GUSMRC composite was extremely high, especially with the sandblasting surface treatment. The slant shear results showed that the specimens with sandblasting surface treatment showed almost 1.5 times higher slant shear strength than the strength of those with the grooving surface treatment at the three tested ages. The splitting strengths of the sandblasted samples were 8.3%, 20.7%, and 18.5% higher than the strengths of the grooved samples at 7, 28, and 90 days, respectively. Similarly, the pull-off strengths of the sandblasted specimens were 2.3%, 10%, and 14.5% higher at 7, 28, and 90 days, respectively. The bond strength increased as the age of the composite increased. Therefore, GUSMRC has great potential in the rehabilitation of RC structures. Ó 2019 Elsevier Ltd. All rights reserved.

1. Introduction The first use of reinforced concrete (RC) dates back to the 1850s by the French industrialist François Coignet. Coignet stated that his concept of adding reinforcement to the concrete was not to enhance the concrete strength but to prevent the overturning of walls, especially in monolithic construction. Nowadays, it is extremely essential to develop adequate RC infrastructures to cater for the convenience of nations. The mere fact is that these infrastructures are always subjected to degradation as a result of harsh environments and external loads. Therefore, one of the major challenges currently faced by civil engineers is to propose solutions to rehabilitate and maintain these damaged structures. ⇑ Corresponding author at: Department of Civil Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia. E-mail address: [email protected] (N. Muhamad Bunnori). https://doi.org/10.1016/j.conbuildmat.2019.04.270 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.

The aging of existing RC structures has always motivated civil engineers to search for effective strengthening and repair remedies. The addition of a new cementitious material (repair material) to the old concrete (substrate) is the most common method used to rehabilitate old and damaged RC structures [1,2]. The thickness of the added repair layer usually varies from 20 mm to 100 mm and might be reinforced with fibers or steel bars if needed. Fig. 1 illustrates the rehabilitation concept of concrete structures [3]. For the past few decades, researchers have been making huge efforts to enhance the behavior of cementitious repair materials. One of these materials is the Ultra-High Performance Fiber Reinforced Concrete (UHPFRC). UHPFRC is a type of concrete that contains steel fibers to achieve ductile behavior in tension and eliminate the use of passive reinforcement. In other words, concrete alone cannot provide the flexibility needed, and, for this reason, steel reinforcing bars are used in the concrete to limit the crack width. These bars are known as passive reinforcement.

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Fig. 1. Addition of new concrete overlay to old concrete [3].

However, the use of steel fibers in UHPFRC can possibly eliminate the use of passive reinforcement. It is a preferred repair material due to its impressive mechanical properties. In addition, its permeability is extremely low, which prevents harmful substances, such as water and chlorides, from entering and damaging RC structures thereby making it suitable for use in aggressive environments [4– 8]. It possesses a compressive strength of more than 170 MPa, a flexural strength higher than 30 MPa, and a tensile strength in excess of 8 MPa [9,10]. In addition, its bond strength with normal concrete is superior; as indicated by Tayeh et al. [4]. Ghazy and Bassuoni [11] studied the performance of nanomodified fly ash concrete to repair concrete pavements and found that it can reduce shrinkage deformations. The use of calcium fly ash geopolymer mortars (GPM) with ordinary Portland cement as a repair binder was investigated by Phoo-ngernkham et al. [12]. Its performance was compared to the performance of five commercial repair (RM) binders: non-shrink grout mortar, high performance repair and finishing mortar, fiber-reinforced non-shrink mortar, multi-purpose non-shrink grout, and polymer modified repair mortar. The results showed that the shear bond and bending strength of GPM were higher than those of RM binders. In addition, Jamellodin et al. [13] combined fine-grained mortar made of waste material with textile fabrics (TFGM) to repair plain concrete prisms. TFGM was found to enhance the ductility and the ultimate load carrying capacity of the concrete prisms. Moreover, Geraldo et al. [14] employed alkali-activated mortar (AAM) to repair reinforced concrete beams. They concluded that AAM enhanced both the adhesion and the strength and they suggested it could be used as a repair material to reinforce concrete structures. The bond strength between the repair material and substrate plays a major role in the performance of the repaired structures. Beaupre [15], Momayez et al. [16], Mu et al. [17], and Bonaldo et al. [18] stated that the strength of the interfacial bond is always the main weakness in the repair chain as failure could occur in either the repair material or the substrate. The bond quality fundamentally relies upon several factors, such as friction, moisture content, bonding agent, aggregate interlock, and interface roughness [19]. Nowadays, epoxy resins are widely employed as the main bonding agent in repair work as they enhance the bonding strength [16]. Tayeh et al. [20] evaluated the interfacial bond strength between normal concrete and UHPFRC and found that UHPFRC can be an excellent repair material due to its significant bonding characteristics with normal concrete. To ensure a good bond strength in a repair system, consideration should be given to employing the proper surface treatment as it has considerable influence on the reliability and durability of the repair [21]. According to Halicka and Jabłon´ski [21], Courard et al. [22], Garbacz et al. [23], Hoła et al. [24], Courard et al. [25], and Garbacz et al.[22], surface preparation can significantly influence the surface roughness and substrate saturation thereby affecting the bond strength between the repair material and the concrete substrate. Kamada and Li [26] investigated the effects of surface preparation on the durability of an engineered cementitious composite/

concrete repair system using both smooth and rough surface preparations. They found that the smooth surface system performed better than the rough surface system and was more durable. In contrast, many researchers reported that a rough surface is more beneficial for the repaired system bond strength [27]. Courard et al. [28] evaluated the concrete substrate surface preparation effect via measurement of the roughness, observation of micro-cracking near the surface layer, and the pull-off test. Using a multiple regression approach, they revealed that the substrate surface roughness and method of treatment are the main factors affecting the bond strength. In addition, they concluded that the surface roughness and the bond coat greatly affect the failure mode. Courard et al. [29] studied the effect of the texture of the concrete substrate on the adhesion properties of polymer cement concrete (PCC) repair mortar and analyzed the relationship between the surface roughness, propagation of stress wave, and adhesion strength. They concluded that the surface preparation technique affects the repair system rebound number value as well as the microcracking on the surface. In 2013, Aldahdooh et al. [30] produced a new ultra-high fiber reinforced concrete called ‘‘Green Universiti Sains Malaysia Reinforced Concrete” (GUSMRC) in which 34% of its content is ultrafine palm oil fuel ash (UPOFA). This UPOFA was originally produced by the treatment of palm oil fuel ash (POFA) via the procedure developed by Megat Johari et al. [31]. The mechanical properties of GUSMRC are significantly remarkable since it achieves a compressive strength of 156.72 MPa, a splitting tensile strength of 20.46 MPa, a flexural strength of 42.38 MPa, and a modulus of elasticity of 46.72 GPa at 28 days. The GUSMRC mix design proportions are presented in Table 1. The aforementioned studies and others have proposed several repair materials to rehabilitate damaged RC structures. However, the durability of most of the repair systems is of great concern to the owners of the structures who are not completely satisfied with the existing repair systems [32,33], especially the bond between the repair patch and the substrate, which is the weakest point. Therefore, it is essential to find a new repair system that can overcome this problem. Since GUSMRC is still a new cementitious material, it is of great importance to explore its suitability for use as a repair material. In this study, ‘‘Green Universiti Sains Malaysia Reinforced Concrete” (GUSMRC), of which 34% of its content is ultra-fine palm oil fuel ash (UPOFA), is used as a green repair material to rehabilitate reinforced concrete structures. The main aim of this study is to investigate the bond strength between a GUSMRC overlay and an existing normal concrete (NC) substrate using two methods of surface treatment: grooving and sandblasting to enhance the interfacial bond.

Table 1 GUSMRC mix proportions [30]. Components (k)

Quantity (Kg/m3)

Ordinary Portland cement (OPC) Densified silica fume (DSF) Ultra-fine palm oil fuel ash (UPOFA) Mining sand (MS) Water (W) Superplasticizer (SP) Steel fiber : Ɩ1 = 6 mm Ɩ2 = 13 mm Total binder (B) W/B SP/B P Summation of volume fractions V

360.25 214.25 290.52 1057.3 168.30 50.43 390.0 78.0 865.02 0.195 0.058 1

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2. Experiments 2.1. Materials and mix proportions Two types of concrete were employed: normal concrete (NC) substrate and GUSMRC (repair material). For the NC substrate, the mix proportion was designed to achieve grade 40 (G40) at 28 days. Table 2 presents the NC mix proportions used in this study. The specific gravities of ordinary Portland cement (OPC), natural river sand, and coarse aggregate were 3.16, 2.7, and 2.66, respectively. The slump value was between 150 mm and 180 mm with a water ratio (W/C) of 0.5. For GUSMRC, the same mix proportions as those used by Aldahdooh et al. [30] were employed; as presented in Table 1. Fig. 2. NC substrate samples.

2.2. Specimens preparation 2.2.1. NC substrate OPC, coarse aggregate, and natural river sand were thoroughly mixed in a concrete mixer. Water and superplasticizer were added slowly to the mixer for a duration of 4 to 5 min. The slump test was then performed before the pouring of the fresh concrete into the molds according to ASTM-C143/C143M [34]. The concrete was then poured into the molds in three layers; each layer was compacted using a vibrating table. After reaching 28 days, the samples were left to dry for two more months in order to be used as the old concrete [16]. The duration considered for the concrete to be old has varied among researchers from one to four months [16,19,35–38]. After that, the substrate surfaces were roughened using the grooving and sandblasting surface treatments. The dimensions of the specimens were different for each test, as will be explained later. Fig. 2 shows the old concrete substrate samples.

2.2.2. GUSMRc GUSMRC was mixed according to the procedure of Benson and Karihaloo [39]. OPC, DSF, UPOFA, and mining sand were mixed in the concrete mixer. The 13 mm long steel fibers were added to the dry mix in proportions of 25%; each 25% of fiber was distributed uniformly for 2 min before the addition of the next 25%. Then, the 6 mm long fibers were added in the same way. Next, SP was mixed with water, added to the dry mix, and thoroughly mixed for about 6 min. To produce the NC substrate/GUSMRC composite, the GUSMRC mixture was poured on the top or the side of the NC substrate depending on the type of layering condition required. The specimens were cast on a vibrating table and left for one day to harden. After de-molding, they were steamed for 48 h at a temperature of 90° C, as done by [4,40–43]. Steam curing is currently practiced in the pre-stressed and precast industry sectors [44,45]. Uchida et al. [46], and Graybeal [47] recommended steam curing to UHPFC to accelerate its strength development, especially in cold environments [48] where the strength gain rate is slow. This will shorten the rehabilitation period and be an advantage when dealing with structures requiring fast repairs, such as bridges.

2.2.3. Surface treatment preparation As mentioned earlier, two methods of treatment were employed: grooving [23,24,30,37,49] and sandblasting [16]. These treatments were applied to the surfaces of NC substrates prior to bonding to enhance adhesion. For the grooving treatment, first, a gridline of 50 mm  50 mm was sketched on the NC substrate surfaces using a marker. Next, an angled diamond wheel grinder was utilized to create the gridlines; as shown in Fig. 3(a). Finally, according to EN 1504 [50], the substrate needs to be sound, clean, rough-textured, and dry after the surface preparation; thus, the treated grooved surface area was cleaned using an air compressor to remove the existing dust. In addition, any concrete or mortar left on the surface was also removed. For the sandblasting treatment, the samples had to be sent to the factory at Simpang Ampat Tasik, Pulau Pinang, Malaysia. Sand particles ranging in size from 300 mm to 2.36 mm were blasted onto the NC surfaces using a long nozzle sandblasting machine at an applied pressure of 1000 kPa. Fig. 3(b) depicts a specimen after being treated with the sandblasting method. 2.3. Engineering properties of monolithic samples of NC substrate prior to repair The compressive strength, modulus of elasticity, splitting tensile strength, and flexural strength were tested prior to repair to evaluate the mechanical properties of the NC substrate and GUSMRC.

Table 2 NC mix proportions. Materials

Quantity (kg/m3)

Ordinary Portland cement (OPC), Type 1 Coarse aggregate (Maximum size 10 mm) Natural river sand (Fineness Modulus 3.1) Water Superplasticizer (Glenium ACE 309) W/C = 0.5

400 930 873 200 4 Fig. 3. Surface treatments: (a) grooving; (b) sandblasting.

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2.3.1. Compressive strength test The compressive strength test was performed on the monolithic samples of the NC substrate according to BS EN 12390-3 [51] with a loading rate of 0.30 MPa/s. A minimum of three specimens 100 mm  100 mm  100 mm in size were tested using the 3000 kN Automatic Concrete Compression Machine at the ages of 3, 7, 14, 28, and 90 days. 2.3.2. Modulus of elasticity test The modulus of elasticity of the monolithic NC substrate samples was tested according to ASTM C469 [52] using the Shimadzu UH-F Universal Testing Machine with 1000 kN capacity and a loading rate of 0.30 MPa/s. The samples had a diameter of 50 mm and a height of 100 mm height cored from a 400 mm  100 mm  100 mm prism and tested at 7, 28, and 90 days. After the coring process, and to ensure equal loading distribution during testing, the top surface was leveled using a diamond grinder. Fig. 4 shows the modulus of elasticity experimental set-up of the NC substrate sample. 2.3.3. Splitting tensile test The splitting tensile test was performed on the cylinder samples of monolithic NC substrate at the ages of 7, 28, and 90 days using the Shimazu UH-F 1000 kN Universal Testing Machine. The diameter and height of the samples were 100 mm and 200 mm according to ASTM C496 [52], respectively. 2.3.4. Flexural strength test NC substrate samples having dimensions of 100 mm  100 mm  400 mm were tested for flexural toughness based on ASTM C1018 [53] using the 100 kN AG-X Shimadzu Universal Testing Machine at 7, 28, and 90 days. 2.4. Test methods for composite NC substrate/GUSMRC 2.4.1. Slant shear test The slant shear test was performed at 7, 28, and 90 days to assess the bond strength of the NC/GUSMRC composite using the Shimadzu UH-F 1000 kN Universal Testing Machine. The composite specimen- with a slant plane inclined vertically at an angle of 30° was employed as stated in ASTM C882 [34] (Fig. 5(a)). The overall prism dimensions were 100 mm  100 mm  300 mm. First, the NC substrate was cast occupying half of the prepared mold and cured for 28 days; it was then removed from the water tank and left to dry for two months; as explained in Section 2.2.1. After that, and prior to the casting of the GUSMRC repair material, the grooving surface treatment was applied to the NC surfaces; as explained in Section 2.2.3. Then, the GUSMRC mix (Section 2.2.2)

Fig. 4. Modulus of elasticity experimental set-up for the NC substrate.

Fig. 5. (a) Geometry of the slant shear specimen; (b) slant shear experimental set-up.

was poured over the NC substrates that had been placed in the prepared molds. A steel plate was used to create a 30° angled inclination. The specimens were cast on a vibrating table and left for one day to harden and then de-molded. After that, they were steamed for 48 h at a temperature of 90 °C. Finally, the samples were put back into the water to cure. The slant shear test was performed at 7, 28, and 90 days. Fig. 5(b) shows the slant shear test set-up for the composite specimens. 2.4.2. Splitting tensile test This indirect tension test was conducted to evaluate the bonding characteristics between NC substrate and GUSMRC repair material through subjecting the load along the composite line between the substrate and the repair material until tension failure occurred. The test was conducted at 7, 28, and 90 days according to ASTM C496 [52]. GUSMRC was cast over the old concrete (NC substrate) in a cylindrical mold. The specimens had a diameter of 100 mm and a height of 200 mm; the test was performed at a loading rate of 0.015 MPa/s using the Shimadzu UH-F 1000 kN Universal Testing Machine. The grooving surface preparation for the splitting test specimens is depicted in Fig. 6 using the same method mentioned in Section 2.2.3. 2.4.3. Pull-off test This test was the third test employed to assess the bond strength of the NC/GUSMRC composite interface. First, NC substrate slabs having dimensions of 300 mm  300 mm  70 mm were cast. After being cured for 28 days, the slabs were left for two months before adding the GUSMRC overlay. The surfaces of the slabs were then treated and cleaned. After that, a 10 mm thick GUSMRC overlay was cast on the NC slab to form the composite. The samples were cured again via steaming for 48 h at a temperature of 90 °C. When the specimens reached 7, 28, and 90 days, the

Fig. 6. The grooving surface treatment for the splitting tensile test specimens.

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Fig. 7. (a) Coring pull-off test specimens; (b) gluing cored specimens to a circular steel disc.

specimens for the pull-off test were cored out of the slabs. The coring process started from the top to a depth of 25 mm (10 mm of GUSMRC + 15 mm of NC); as shown in Fig. 7(a). The specimens were then glued to a steel disc with a 50 mm diameter using a high strength epoxy glue (2 Ton Epoxy-Clear); as depicted in Fig. 7(b). The bonded samples were left for 24 h before being tested according to ASTM D4541 [54] using the pull-off instrument at the concrete laboratory.

3. Experimental results and discussion 3.1. Engineering properties of monolithic samples of NC substrate prior to repair 3.1.1. Compressive strength As presented in Table 3, the NC substrate was designed to achieve grade 40 (G40) at 28 days; however, the results show that at 7 days the compressive strength was already 40 MPa. The compressive strength kept increasing as age increased until it reached 50.76 MPa at the age of 90 days. Fig. 8 shows the monolithic NC specimen after the compression test. Table 3 also presents the average compressive strength of GUSMRC which also increased with the curing age. According to EN 1504 [55], the compressive strength of the repair material for a structural purpose should be more than 25 MPa. In this study, GUSMRC achieved a minimum compressive strength of 144.8 MPa at 7 days which is higher than the minimum specified compressive strength. From Table 3, it is clear that the compressive strength was more than 25 MPa at the other ages as well. Based on EN 1504 [56], the surface strength of the substrate before repair must be at least 1.5 MPa. In their book, Raupach and Büttner [50] provided a graph (Fig. 9) to evaluate the surface strength of the substrate using compressive strength. Based on the results obtained at 28 days, the compressive strength was

49.2 MPa; thus, the surface strength is about 2.3 MPa, which is higher than 1.5 MPa indicating that the substrate was in good condition. 3.1.2. Modulus of elasticity Fig. 10 presents the results of the average modulus of elasticity of the NC substrate at the test ages of 7, 28, and 90 days. The average modulus of elasticity for NC substrate at 28 days reached 36.57 GPa, and increased to 43.35 GPa at 90 days and prior to repair. 3.1.3. Splitting tensile strength As illustrated in Fig. 11, the average splitting tensile strength of NC substrate reached 3.18 MPa and 3.62 MPa at 28 and 90 days, respectively. The tensile strength increased as the age of the concrete substrate increased. 3.1.4. Flexural strength The results of the flexural strength of the NC substrate showed that it increased with time and that it reached 5.28 MPa prior to repair (90 days). At the ages of 7 and 28 days, the flexural strengths were 4.44 MPa and 5.17 MPa, respectively. Fig. 12 illustrates the NC specimen failure under the flexural test. 3.2. Tests results of composite NC substrate/GUSMRC 3.2.1. Slant shear strength The slant shear strength of the NC/GUSMRC composite was obtained by dividing the maximum load by the area of the slant shear. Table 4 presents the slant shear strengths and modes of failure for both the grooved and sandblasted specimens. From Table 4, it can be seen that the dominant failure mode for both treatment methods was the substratum failure with good interface (D) signifying that the failure took place in the NC substrate (old concrete)

Table 3 Average compressive strength of NC substrate and GUSMRC. Test age (days) Compressive strength (MPa)

NC substrate GUSMRC

7

28

90

39.9 146.60

49.20 152.82

50.76 153.64

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Fig. 11. Average splitting tensile strength of NC substrate.

Fig. 8. Failure of NC substrate under compression.

Fig. 12. NC substrate specimen under flexural load.

Fig. 9. Evaluation of surface strength of substrate based on compressive strength [50].

Fig. 10. Average modulus of elasticity of NC.

and not in the GUSMRC (repair material); as shown in Fig. 13(a). The specimens with sandblasting surface treatment showed almost 1.5 times higher slant shear strength than the strength of those with the grooving surface treatment at the three tested ages;

as shown in Fig. 13(b). This could be due to the fact that grooving caused the destruction of the substrate superficial zone and created stress at the edges of the grooves which led to lowering the slant shear strength of the grooved specimens. The average slant shear strengths for both the grooving and sandblasting surface treatments are higher than the minimum acceptable bond strength range provided in the ACI Concrete Repair Guide [57] (presented in Table 5) at 7 and 28 days. In addition, Fig. 13(b) shows that the slant shear strength increased as the age of the composite increased for both treatment methods. In this paper, the same NC mix proportion was similar to that used by Tayeh et al. [20] with the difference being in the repair materials. In this study, GUSMRC was used as a repair material while Tayeh et al. [20] employed UHPFC. When comparing the average slant shear strengths in both studies for the grooved and sandblasted specimens at 7 days, it can be seen that the results of this study are superior to those in [20]. For the grooving surface treatment, the average slant shear strength at 7 days was 23.27 MPa, while it was only 13.89 MPa in [20]. Similarly, for sandblasting surface treatment, the slant shear strength in this study was higher by 50.4% than that in [20] (34.6 MPa and 17.17 MPa, respectively). The types of failure obtained in this study were (D) for both surface treatments, as shown in Table 4, while Tayeh et al. [20] reported (C) and (D) failures for grooving and sandblasting treatments, respectively. Table 6 presents the results obtained by Tayeh et al. [20]. 3.2.2. Splitting tensile strength Based on ASTM C496 [52], the splitting tensile strength was calculated using the following Equation:

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S.H. Abo Sabah et al. / Construction and Building Materials 216 (2019) 261–271 Table 4 Slant shear strength and failure modes of composite NC substrate/GUSMRC specimens. S.T. Sample No.

Grooving

Test results at 7 days 1 2 3

Test results at 28 days 1 2 3

Test results at 90 days 1 2 3

Sandblasting

P (kN)

S (MPa)

F.M.

P (kN)

S (MPa)

F.M.

542.00 472.00 382.00 Mean 23.27

27.10 23.60 19.10 S.D. 4.01

D D D COV 17.23

764.00 590.00 722.00 Mean 34.60

38.20 29.50 36.10 S.D 4.54

D D D COV 13.12

472.00 394.00 568.00 Mean 23.90

23.60 19.70 28.40 S.D. 4.36

D D D COV 18.24

570.00 746.00 794.00 Mean 35.20

28.50 37.30 39.70 S.D. 5.89

D D D COV 16.73

568.00 396.00 594.00 Mean 25.90

28.40 19.80 29.70 S.D 5.38

D D D COV 20.77

620.00 824.00 724.00 Mean 36.13

31.00 41.2 36.20 S.D. 5.10

D D D COV 14.12

S.T. = Surface treatment; P = Maximum applied load (kN); S = Slant shear bond strength (MPa); F.M. = Failure mode; COV = Coefficient of variation (%); S.D. = Standard deviation; Failure mode A = Interface failure; Failure mode B = Interface failure and substrate cracks; Failure mode C = Interface failure and substrate fracture; and Failure mode D = Substratum failure with good interface.

NC GUSMRC

(a)

(b)

Fig. 13. (a) Failure mode D; (b) average slant shear strength for the different types of substrate surface at different ages.

r¼

Table 5 Acceptable bond strength range for slant shear test according to ACI Concrete Repair Guide [57]. Days

Bond Strength (MPa)

1 7 28

2.76–6.9 6.9–12.41 12.41–20.68

2P

ð1Þ

pA

where r is the splitting tensile strength (MPa), P is the maximum applied load (kN), and A is the area of the bond plane (mm2). It can be inferred from Table 7 that the average splitting tensile strengths for both grooved and sandblasted samples were higher than 2.1 MPa, which can be classified as excellent according to the classification of Sprinkel and Ozyildirim in Table 8 [58].

Table 6 Slant shear strength and failure modes of composite NC and UHPFC specimens [20]. Surface preparation

Sample no.

Max. force (kN)

Compressive stress (MPa)

(s) Shear stress (MPa)

Grooved

GR1 GR2 GR3

296.69 292.22 244.52

29.67 29.22 24.45

SB

SB1 SB2 SB3

322.66 370.06 337.61

32.27 37.01 33.76

s Average (MPa)

Standard Deviation (MPa)

COV (%)

Failure mode

Percentage of NC substrate

14.83 14.61 12.23

1.45

10.41

C C C

73.11

16.13 18.50 16.88

1.21

7.06

D D D

90.38

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Table 7 Splitting tensile strength and failure modes of composite NC substrate/GUSMRC specimens. S.T Sample No.

Grooving

Test results at 7 days 1 2 3

Test results at 28 days 1 2 3

Test results at 90 days 1 2 3

Sandblasting

P (kN)

T (MPa)

F.M.

P (kN)

T (MPa)

F.M.

157.50 138.92 128.84 Mean 4.5

5.00 4.41 4.09 S.D. 0.46

C C C COV 18.24

160.34 155.29 148.68 Mean 4.91

5.09 4.93 4.72 S.D. 0.19

C B C COV 10.22

203.18 208.85 214.20 Mean 6.63

6.45 6.63 6.80 S.D. 0.18

C C C COV 2.17

256.73 264.92 269.64 Mean 8.37

8.15 8.41 8.56 S.D. 0.21

C C B COV 2.51

212.00 225.23 219.56 Mean 6.95

6.73 7.15 6.97 S.D 0.21

C C C COV 3.02

2.58.62 268.70 278.78 Mean 8.53

8.21 8.53 8.85 S.D 0.32

C C C COV 3.75

S.T. = Surface treatment; P = Maximum applied load (kN); T = Splitting tensile bond strength (MPa); F.M. = Failure mode; COV = Coefficient of variation (%); S.D. = Standard deviation; Failure mode A = Pure interface failure where no cracking; Failure mode B = Interface failure combined with partial substrate failure; and failure mode C = Substratum failure with good interface.

Table 8 Quantitative bond quality in terms of bond strength [58]. Bond quality

Bond strength, T (MPa)

Excellent Very good Good Fair Poor

2.1 1.7–2.1 1.4–1.7 0.7–1.4 0–0.7

Fig. 14(a) shows the observed failure modes in the grooved samples, which can be classified as a substratum failure with good interface (C). That is to say, the failure occurred in the NC substrate. The majority of specimens with the sandblasting treatment experienced a substratum failure (C) (Fig. 14(a)); however, two specimens at 7 and 28 days experienced interfacial failure with a partial substratum failure (B); as shown in Fig. 14(b). For both grooving and sandblasting treatments, the average splitting tensile strengths increased as the age of the composite increased; as depicted in Fig. 15. The sandblasted samples strengths were higher than those of the grooved samples at all ages. The reduction in the splitting tensile strength of the grooved specimens was also due to the grooving surface treatment which caused the substrate superficial zone destruction and stress accumulation at the edges of the grooves. The percentage differences between the grooved and the sandblasted samples strengths at 7, 28, and 90 days were 8.3%, 20.7%, and 18.5%, respectively.

Fig. 14. (a) Substratum failure with good interface (C); (b) interfacial failure with partial substrate surface (B).

3.2.3. Pull-off bond strength The Pull-off strength was calculated according to ASTM C1583 [59] using Eq. (2):

Pull  off bond StrengthðMPaÞ ¼

Tensile load at failureðkN Þ Area of test specimenðmm2 Þ

ð2Þ

Table 9 shows that the specimens with the sandblasting surface treatment exhibited higher pull-off bond strengths than the specimens with the grooving surface treatment at all ages. The sandblasting treatment improved the bond strength of the composite more than the grooving treatment at 7, 28, and 90 days by 2.3%,

Fig. 15. Average splitting tensile strength for grooved and sandblasted specimens.

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S.H. Abo Sabah et al. / Construction and Building Materials 216 (2019) 261–271 Table 9 Pull-off bond strength and failure modes of composite NC substrate/GUSMRC specimens. S.T Sample No.

Test results at 7 days 1 2 3

Bond quality Test results at 28 days 1 2 3

Bond quality Test results at 90 days 1 2 3

Bond quality

Grooving

Sandblasting

Tensile load (kN)

Bond strength (MPa)

F.M.

Tensile load (kN)

Bond strength(MPa)

F.M.

8.90 10.3 9.3 Mean 2.15 Exc.

2.01 2.33 2.10 S.D. 0.17

Sub. Sub. Sub. COV 7.91

8.20 10.40 9.00 Mean 2.20 Exc.

1.86 2.35 2.40 S.D. 0.30

Sub. Sub. Sub. COV 13.64

11.30 10.10 9.20 Mean 2.31 Exc.

2.56 2.29 2.08 S.D. 0.24

Sub. Sub. Sub. COV 10.39

12.60 10.70 10.80 Mean 2.57 Exc.

2.85 2.42 2.44 S.D. 0.39

Sub. Sub. Sub. COV 15.17

17.50 12.10 11.20 Mean 2.64 Exc.

3.96 2.74 2.53 S.D 0.15

Sub. Sub. Sub. COV 5.68

22.50 12.70 12.50 Mean 2.85 Exc.

5.09 2.87 2.83 S.D 0.03

Sub. Sub. Sub. COV 1.05

S.T. = Surface treatment; F.M. = Failure mode; COV = Coefficient of variation (%); S.D. = Standard deviation; Sub. = Substrate; Exc. = Excellent. Bond quality based on ACI Concrete Repair Guide [57,58].

10%, and 7.4%, respectively. At 7 and 28 days, the variability in the bond strength evaluated via the coefficient of variation (COV) was higher when the concrete specimens were treated using the sandblasting technique by 5.73% and 4.78%, respectively while the COV of the grooved specimens was higher by almost 4.63% at 90 days. This is due to the fact that the sandblasting surface treatment enhanced the adhesion between the NC substrate and GUSMRC overlay whereas the influence of the grooving treatment at 90 days maybe was not so effective because the coring size was small. In other words, the specimens were cored out of the composite slab and the coring may not have been exactly across the grooves causing a slight inconsistency in the results. Thus, to ensure the accuracy of the results, the results in Table 9 at 90 days for the grooved and sandblasted samples were based on set 2 and set 3 data only; set 1 data was not taken into account as the values

Fig. 16. NC substrate failure (A: GUSMRC; B: NC substrate).

are extremely different from the average. This variation may be caused by the rare existence of grooves in the cored samples. All specimens experienced failure in the NC substrates, as shown in Fig. 16; similar results were reported by Momayez et al. [16]. This indicates that the bonding between the substrate and the repair material is extremely strong [16,18]. Furthermore, according to Table 8, the bonding is classified as excellent. 4. Conclusion This study examined the bond strength between normal concrete (NC) as substrate and GUSMRC as a repair material using the grooving and sandblasting surface treatments. For bond strength assessment, the slant shear, splitting tensile, and pulloff tests were conducted. From the results, the following conclusions can be drawn: i) The results of the slant shear showed that the bond strength between the NC substrate and GUSMRC repair material was extremely high and that it increased as the age of the composite increased. The sandblasting surface treatment improved the bond strength more than the grooving surface treatment. The failure mode was classified as substratum failure with good interface (D), which means that the failure occurred in the NC substrate. ii) For the splitting tensile test, the results indicated that the bond strengths of the specimens treated with sandblasting were higher compared to those for the specimens with the grooving surface treatment. Most of the failures for both methods took place in the NC substrate. iii) The pull-off test results showed that the sandblasting treatment enhanced the bond strengths of the specimens slightly higher than the grooving treatment at 7, 28, and 90 days by 2.3%, 10%, and 7.4%, respectively. Since the sizes of coring and the groove were the same, this might have affected the pull-off strength of the grooved specimens as it was hard to observe whether the grids of the grooves existed in the cored specimens or not. This might have caused a slight

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inconsistency in the obtained results, especially at 90 days. All the failure modes occurred in the substrate and achieved an excellent bonding according to the ACI Concrete Repair Guide. Moreover, the pull-off test results showed that the tensile strength of the substrate was increasing with time. iv) Both grooving and sandblasting surface treatments achieved significant results; however, the sandblasting treatment was slightly superior since it enhances the bond strength more. v) Since most of the failures occurred in the substrate, this indicates that the bonding characteristic is significantly high and that GUSMRC can be used as a repair material for the rehabilitation of RC structures. Conflict of interest I don’t have any issue or conflict of interest with any researchers related to my paper and research. Acknowledgments This study was funded under the Ministry of Higher Education Malaysia via Fundamental Research Grant Scheme (FRGS), account number (203/PAWAM/6071365). The authors would also like to express their gratitude to Universiti Sains Malaysia (USM) and University of Malaya (UM). References [1] P.-W. Chen, X. Fu, D. Chung, Improving the bonding between old and new concrete by adding carbon fibers to the new concrete, Cem. Concr. Res. 25 (1995) 491–496. [2] A.D. Espeche, J. León, Estimation of bond strength envelopes for old-to-new concrete interfaces based on a cylinder splitting test, Constr. Build. Mater. 25 (2011) 1222–1235. [3] E. Brühwiler, E. Denarié, Rehabilitation of concrete structures using ultra-high performance fibre reinforced concrete, The Second International Symposium on Ultra High Performance Concrete, 2008. [4] B.A. Tayeh, B.A. Bakar, M.M. Johari, Y.L. Voo, Evaluation of bond strength between normal concrete substrate and ultra high performance fiber concrete as a repair material, Procedia Eng. 54 (2013) 554–563. [5] S.H. Park, D.J. Kim, G.S. Ryu, K.T. Koh, Tensile behavior of ultra high performance hybrid fiber reinforced concrete, Cem. Concr. Compos. 34 (2012) 172–184. [6] R. Toledo Filho, E. Koenders, S. Formagini, E. Fairbairn, Performance assessment of ultra high performance fiber reinforced cementitious composites in view of sustainability, Mater. Des. 36 (2012) 880–888. [7] B.A. Tayeh, B.A. Bakar, M.M. Johari, Y.L. Voo, Mechanical and permeability properties of the interface between normal concrete substrate and ultra high performance fiber concrete overlay, Constr. Build. Mater. 36 (2012) 538–548. [8] T.L.V. Voort, Design and Field Testing of Tapered H-Shaped Ultra High Performance Concrete Piles, Iowa State University, 2008. [9] P. Ambily, C. Umarani, K. Ravisankar, P.R. Prem, B. Bharatkumar, N.R. Iyer, Studies on ultra high performance concrete incorporating copper slag as fine aggregate, Constr. Build. Mater. 77 (2015) 233–240. [10] M.A. Al-Osta, Exploitation of ultrahigh-performance fibre-reinforced concrete for the strengthening of concrete structural members, Adv. Civ. Eng. (2018). [11] A. Ghazy, M. Bassuoni, Shrinkage of nanomodified fly ash concrete as repair material, ACI Mater. J. 114 (2017). [12] T. Phoo-ngernkham, V. Sata, S. Hanjitsuwan, C. Ridtirud, S. Hatanaka, P. Chindaprasirt, High calcium fly ash geopolymer mortar containing Portland cement for use as repair material, Constr. Build. Mater. 98 (2015) 482–488. [13] Z. Jamellodin, H.M. Saman, S.H. Adnan, N.S. Mohammad, W.Y.W. Yusof, TFGM a New Composite Material with Palm Oil Fuel Ash, Springer, InCIEC, 2016. [14] R.H. Geraldo, O.G. Teixeira, S.R. Matos, F.G. Silva, J.P. Gonçalves, G. Camarini, Study of alkali-activated mortar used as conventional repair in reinforced concrete, Constr. Build. Mater. 165 (2018) 914–919. [15] D. Beaupré, Bond strength of shotcrete repair, Shotcr. Mag. 1 (1999) 12–15. [16] A. Momayez, M. Ehsani, A. Ramezanianpour, H. Rajaie, Comparison of methods for evaluating bond strength between concrete substrate and repair materials, Cem. Concr. Res. 35 (2005) 748–757. [17] B. Mu, C. Meyer, S. Shimanovich, Improving the interface bond between fiber mesh and cementitious matrix, Cem. Concr. Res. 32 (2002) 783–787. [18] E. Bonaldo, J. Barros, P. Lourenco, Bond characterization between concrete substrate and repairing SFRC using pull-off testing, (2005). [19] P.M. Santos, E.N. Julio, Correlation between concrete-to-concrete bond strength and the roughness of the substrate surface, Constr. Build. Mater. 21 (2007) 1688–1695.

[20] B.A. Tayeh, B.A. Bakar, M.M. Johari, Characterization of the interfacial bond between old concrete substrate and ultra high performance fiber concrete repair composite, Mater. Struct. 46 (2013) 743–753. [21] A. Halicka, Ł. Jabłon´ski, Shear failure mechanism of composite concrete Tshaped beams, Proc. Inst. Civ. Eng. Struct. Build. 169 (2015). [22] L. Courard, F. Michel, D. Schwall, A. Van der Wielen, T. Piotrowski, A. Garbacz, F. Perez, B. Bissonnette, Surfology: concrete surface evaluation prior to repair, WIT Trans. Eng. Sci. 64 (2009). [23] A. Garbacz, L. Courard, B. Bissonnette, A surface engineering approach applicable to concrete repair engineering, Bull. Polish Acad. Sci.: Tech. Sci. 61 (2013) 73–84. [24] J. Hoła, Ł. Sadowski, J. Reiner, S. Stach, Usefulness of 3D surface roughness parameters for nondestructive evaluation of pull-off adhesion of concrete layers, Constr. Build. Mater. 84 (2015) 111–120. [25] L. Courard, J.-F. Lenaers, F. Michel, A. Garbacz, Saturation level of the superficial zone of concrete and adhesion of repair systems, Constr. Build. Mater. 25 (2011) 2488–2494. [26] T. Kamada, V.C. Li, The effects of surface preparation on the fracture behavior of ECC/concrete repair system, Cem. Concr. Compos. 22 (2000) 423–431. [27] B. Bissonnette, L. Courard, A. Garbacz, Concrete Surface Engineering, CRC Press, 2015. [28] L. Courard, T. Piotrowski, A. Garbacz, Near-to-surface properties affecting bond strength in concrete repair, Cem. Concr. Compos. 46 (2014) 73–80. [29] L. Courard, A. Garbacz, D. Schwall, T. Piotrowski, Effect of concrete substrate texture on the adhesion properties of PCC repair mortar, Polym. Concr. (2006) 99–110. [30] M. Aldahdooh, N.M. Bunnori, M.M. Johari, Development of green ultra-high performance fiber reinforced concrete containing ultrafine palm oil fuel ash, Constr. Build. Mater. 48 (2013) 379–389. [31] M.M. Johari, A. Zeyad, N.M. Bunnori, K. Ariffin, Engineering and transport properties of high-strength green concrete containing high volume of ultrafine palm oil fuel ash, Constr. Build. Mater. 30 (2012) 281–288. [32] G. Tilly, J. Jacobs, Concrete Repairs: Observations on Performance in Service and Current Practice CONREPNET Project Report, IHS BRE Press, Watford, UK, 2007. [33] S. Matthews, CONREPNET: performance-based approach to the remediation of reinforced concrete structures: achieving durable repaired concrete structures, J. Build. Appraisal 3 (2007) 6–20. [34] ASTM C143/C143M-15a, Standard Test Method for Slump of HydraulicCement Concrete, ASTM International, 2015. [35] G. Li, H. Xie, G. Xiong, Transition zone studies of new-to-old concrete with different binders, Cem. Concr. Compos. 23 (2001) 381–387. [36] G. Li, A new way to increase the long-term bond strength of new-to-old concrete by the use of fly ash, Cem. Concr. Res. 33 (2003) 799–806. [37] E.N. Julio, F.A. Branco, V.t.D. Silva, Concrete-to-concrete bond strength. Influence of the roughness of the substrate surface, Constr. Build. Mater. 18 (2004) 675–681. [38] P. Santos, E. Júlio, Development of a laser roughness analyser to predict in situ the bond strength of concrete-to-concrete interfaces, Mag. Concr. Res. 60 (2008) 329–337. [39] S. Benson, B.L. Karihaloo, CARDIFRC-development and mechanical properties. Part 1: development and workability, Mag. Concr. Res. 57 (2005) 347–352. [40] M.-G. Lee, C.-T. Chiu, Y.-C. Wang, The study of bond strength and bond durability of reactive powder concrete, J. ASTM Int. 2 (2005) 1–10. [41] F.A. Farhat, D. Nicolaides, A. Kanellopoulos, B.L. Karihaloo, Behavior of RC beams retrofitted with CARDIFRC after thermal cycling, J. Mater. Civ. Eng. 22 (2009) 21–28. [42] B. Graybeal, Fatigue response in bridge deck connection composed of field-cast ultra-high-performance concrete, Transp. Res. Rec. (2011) 93–100. [43] C. Wu, D. Oehlers, M. Rebentrost, J. Leach, A. Whittaker, Blast testing of ultrahigh performance fibre and FRP-retrofitted concrete slabs, Eng. Struct. 31 (2009) 2060–2069. [44] P. Mangat, D.G. Catley, A novel low voltage heating system for curing and protection of early age concrete, Concr. Plant Int. Concr. Technol. Sect. 4 (2005) 106–112. [45] T. Erdem, L. Turanli, T. Erdogan, Setting time: an important criterion to determine the length of the delay period before steam curing of concrete, Cem. Concr. Res. 33 (2003) 741–745. [46] Y. Uchida, J. Niwa, Y. Tanaka, M. Katagiri, Outlines of ‘Recommendations for design and construction of ultra high strength fiber reinforced concrete structures’ by JSCE, Proceedings of International RILEM Workshop on High Performance Fiber Reinforced Cementitious Composites in Structural Applications, RILEM Publications SARL, 2006. [47] B.A. Graybeal, Compressive behavior of ultra-high-performance fiberreinforced concrete, ACI Mater. J. 104 (2007) 146. [48] S. Kosmatka, W. Panarese, B. Kerkhoff, Design and Control of Concrete Mixtures Skokie, Portland Cement Association, IL, 2002. [49] A. Garbacz, M. Górka, L. Courard, Effect of concrete surface treatment on adhesion in repair systems, Mag. Concr. Res. 57 (2005) 49–60. [50] M. Raupach, T. Büttner, Concrete Repair to EN 1504: Diagnosis, Design, Principles and Practice, CRC Press, 2014. [51] B. EN, 12390-3, Testing Hardened Concrete–Part 3: Compressive Strength of Test Specimens, European Committee for Standardization, Brussels, Belgium, 2009. [52] ASTM C496, Standard Test Method for Splitting Tensile Strength of Cylindrical Concrete Specimens, ASTM International, 2011.

S.H. Abo Sabah et al. / Construction and Building Materials 216 (2019) 261–271 [53] ASTM C-1018, Standard Test Method for Flexural Toughness and First-Crack Strength of Fiber-Reinforced Concrete (using beam with third-point loading), ASTM International, 1997. [54] ASTM D4541, Standard Test Method for Pull-Off Strength of Coatings using Portable Adhesion Testers, ASTM International, 2009. [55] B. EN, 1504-3, Products and Systems for the proTection and Repair of Concrete Structures-Definitions, Requirements, Quality Control and Evaluation of Conformity. Site Application of Products and Systems and Quality Control of the Works, British Standard European Norm, London, UK, 2005. [56] B. EN, 1504-10, Products and Systems for the Protection and Repair of Concrete Structures-Definitions, Requirements, Quality Control and Evaluation

271

of Conformity. Site Application of Products and Systems and Quality Control of the Works, British Standard European Norm, London, UK, 2003. [57] G. Chynoweth, R.R. Stankie, W.L. Allen, R.R. Anderson, W.N. Babcock, P. Barlow, J.J. Bartholomew, G.O. Bergemann, R.E. Bullock, F.J. Constantino, Concrete Repair Guide, ACI Committee, Concrete Repair Manual, 1996, pp. 287–327. [58] M.M. Sprinkel, C. Ozyildirim, Evaluation of High Performance Concrete Overlays Placed on Route 60 over Lynnhaven Inlet in Virginia, Virginia Transportation Research Council, 2000. [59] ASTM C1583, Standard Test Method for Tensile Strength of Concrete Surfaces and the Bond Strength or Tensile Strength of Concrete Repair and Overlay Materials by Direct Tension (pull-off method), ASTM International, 2004.