Slant Shear Research Articles

A comparative study on the bonding performance of an admixed repair mortar and high-strength flowable micro-concrete with substrate: Considerations on the physico-mechanical compatibility

The physical and mechanical properties of repair mortar (RM), incorporating a multipurpose hybrid admixture and a high-strength concrete matrix phase known as micro-concrete (MiC), have been experimentally investigated. The flexural and compressive strengths, as well as the modulus of elasticity of each mixture, were tested at 7 and 28 days. The dimensional stability of prismatic bar specimens under dry and water-saturated conditions was monitored over a period of 56 days. The thermal coefficient of expansion for each repair material was determined, and the risk of thermal cracking was evaluated. Additionally, the bonding performance of admixed repair mortar and micro-concrete with substrate mortar (SM) was assessed using a modified slant shear test setup. The influence of surface roughness on slant shear strength was also studied. The compatibility of each mix design with substrate mortar was quantified and compared using a “physico-mechanical compatibility” based proximity comparison criterion. The proposed methodology can be used to monitor the compatibility and bonding potential of a repair material for a given substrate. Test results and analysis indicated that the admixed RM, with lower compressive/tensile strength ratio, performed better than MiC in terms of substrate compatibility.

Repair of ordinary concrete using basalt fiber reinforced geopolymer: High temperature resistance and micro structure evolution of adhesive interface

Good bonding properties in the interfacial transition zone (ITZ) between the substrate and the repair material are critical to the success of the repair, and a good repair material can act as a protective layer to reduce the impact of fire on the structure. In this paper, Ordinary concrete (OP), geopolymer mortar (GP), and basalt fiber reinforced geopolymer mortar (GPb) were poured as the three repair materials on the roughened surface of the old substrate. The bonded specimens were exposed to temperatures of 23 °C, 200 °C, 400 °C, 600 °C and 800 °C for 1 h. The interfacial bond strength of the bonded specimens was tested by slant shear test, and the physical phase change of the repair material and the microstructure of the ITZ were analyzed by microscopic test. The results showed that the mechanical properties and high temperature resistance of ITZ were best when the old substrate interfaces were grinded and grooved and GPb was used as the repair material. Compared with S-OP, the bond strength of S-GPb was 26.92 %, 27.43 %, 46.50 %, 44.26 %, and 97.02 % higher at different temperatures. The increase in interfacial bond strength can be attributed to three mechanisms: (1) Mechanical interlocking with the old substrate with a rough surface. (2) The increase in temperature accelerates the volcanic ash reaction, and the formation of hydration products further fills the voids at the ITZ, maintaining the strength and compactness of the ITZ. (3) The addition of basalt fibers can form an anchoring effect at the interface, reducing the risk of interfacial spalling and cracking caused by material shrinkage in the ITZ.

Evaluation of Bonding Behavior between Engineered Geopolymer Composites with Hybrid PE/PVA Fibers and Concrete Substrate.

Engineered geopolymer composites (EGCs) exhibit excellent tensile ductility and crack control ability, making them promising for concrete structure repair. However, their widespread use is limited by high costs of reinforcement fiber and a lack of an EGC-concrete interface bonding mechanism. This study investigated a hybrid PE/PVA fiber-reinforced EGC using domestically produced unoiled PVA fibers to replace commonly used PE fibers. The bond performance of the EGC-concrete interface was evaluated through direct tensile and slant shear tests, focusing on the effects of PE fiber content (1%, 2%, and 3%), fiber hybrid ratios (2.0:0.0, 1.5:0.5, 1.0:1.0, 0.5:1.5, and 0.0:2.0), concrete substrate strength (C30, C50, and C70), and the ratio of fly ash (FA) to ground granulated blast furnace slag (GGBS) (6:4, 7:3, and 8:2) on interface bond strength. Results showed that the EGCs' compressive strength ranged from 77.1 to 108.9 MPa, with increased GGBS content significantly enhancing the compressive strength and elastic modulus. Most of the specimens exhibited strain-hardening behavior after initial cracking. Interface bonding tests revealed that a PE/PVA ratio of 1.0 increased tensile bond strength by 8.5% compared with using 2.0% PE fiber alone. Increasing the PE fiber content, PVA/PE ratio, GGBS content, and concrete substrate strength all improved the shear bond strength. This improvement was attributed to the flexible fibers' ability to restrict thermo-hydro damage and deflect and blunt microcracks, enhancing the interface's failure resistance. Cost analysis showed that replacing 50% of the PE fiber in EGC with unoiled PVA fiber reduced costs by 44.2% compared with PE fiber alone, offering the best cost-performance ratio. In summary, hybrid PE/PVA fiber EGC has promising prospects for improving economic efficiency while maintaining tensile ductility and crack-control ability. Future optimization of fiber ratios and interface design could further enhance its potential for concrete repair applications.

Interpretable machine learning models for predicting the bond strength between UHPC and normal-strength concrete

Ultra-high-performance concrete (UHPC) boasts superior mechanical properties and durability, rendering it a viable material to repair and reinforce pre-existing concrete structures. The complexity of the bond behavior between UHPC and normal-strength concrete (NC) presents a challenge to make precise predictions of the interfacial bond strength. This study employed four machine learning algorithms, namely artificial neural network, random forest, adaptive boosting, and categorical gradient boosting, to predict the interfacial bond strength of UHPC-NC. A database of 95 samples of slant shear tests was collected from existing literature. The input variables for modeling include joint angle, compressive strength of NC and UHPC, surface treatment, interfacial moisture, curing age, and curing method. The impact of each feature on the slant shear bond strength was assessed using SHapley Additive exPlanations and Partial Dependence Plots. Results show that the categorical gradient boosting model performed the best on the testing set, achieving an R2 of 0.948, RMSE of 1.408, and MAE of 1.028. The accuracy of all four machine learning models surpassed that of two empirical models (AASHTO LRFD 2014 and Eurocode 2). The top three features influencing the interfacial bond strength were identified as the surface treatment, joint angle, and compressive strength of NC, while the impact of the curing method and the interfacial moisture were comparatively limited. The proposed machine learning model exhibits potential as a valuable tool for assisting structural retrofitting and rehabilitation with UHPC.

Effect of adsorption interactions of Arabic gum with cement

This study seeks to investigate the influence of cement and Arabic gum on the physico-mechanical and microstructural properties of cementitious composites. The influence of varying quantities of Arabic gum on the hydration, fluidity, mechanical performance and microstructure of cement paste was investigated. The influence of Arabic gum on slant shear performance and capillary water absorption was also investigated. The results indicate that the workability of cement was diminished as a result of the ability of Arabic gum to make the cement paste cohesive. It is evident that when the gum Arabic concentration increases from 147 to 174 mm, the resultant slump value for various w/b ratios drops. The adsorption characteristics showed that for a 15 mg g−1 dosage at 60, 45, 30, and 15 min, respectively, 1.43, 1.32, 1.25, and 1.03 mg g−1 are achieved. For 1% gum Arabic substitution, the highest flexural strength percentage growth is achieved at 38.46%, 23.74%, and 17.29% at 7, 14, and 28 days, respectively. In addition, the inclusion of Arabic gum improved the slant shear strength of cement composite, making it ideal for use as a building repair material with significant application potential. Experiments on the bonding behavior of the produced cementitious composite with the old mortar reveal that the shear bond strength was greatly increased, demonstrating the compatibility between the old and new cement composites. The microstructure and the porosity of the cement matrix also showed denser and compact matrix making them durable to attain better service life.

The mechanical performance of reinforced bituminous interfaces with paving fabric under freeze-thaw conditioning

The application of paving fabric at the interface of bituminous layers as a rehabilitation strategy has proved its effectiveness in extending the pavement service life by delaying the manifestation of reflective cracking on the surface. However, this enhanced performance relies on the adhesion bond supplied at the interface, which in the case of debonding, the structural benefits provided by the interlayer can be compromised. Gaining authentic knowledge about the bonding condition at a reinforced interface exposed to different conditioning impacts helps to improve the reliability of the input data, which has not been adequately considered in the mechanistic-based design methods proposed for reinforced bituminous structures. This research was dedicated to understanding the mechanical behavior of double-layer bituminous layers composed of two different hot mixtures and reinforced with paving fabric when subjected to freeze-thaw cycling. To attain this objective, the initial step involved determining the optimal dosage of bitumen for use as a tack coat at the interface of the paving fabric, which was established as 0.0014 m3/m2 through asphalt retention tests. Subsequently, the results from the shear test, conducted using the slant shear device, were utilized to establish three comparative criteria at the interface, aimed at elucidating distinctions when compared to unreinforced cases. These criteria include the energy absorbed by the interface during shearing, shear stiffness, and the coefficient of interface bonding (CIB). This study revealed that by increasing the number of freeze-thaw cycling, the reinforced interface keeps the shear stiffness and the CIB values unchanged. However, in terms of energy absorption capabilities, the unreinforced interfaces showed better performance. This study showed that using the CIB value to quantify the bonding strength at the interface and energy dissipation and initial shear stiffness to quantify the evolution of interface bonding over number of F-T cycles are all proper representatives to include into mechanistic-empirical design methods for reinforced structures in order to present realistic models.

Influence of Surface Roughness on Durability of New-Old Concrete Interface

The bond zone between old and new concrete is greatly affected by environmental factors. This study investigates the impact of surface roughness on durability using as-cast surface (CS), drilled holes surface (DS), and grooved surface (GS). After a 28-day water-curing, specimens undergo a 5% NaCl solution immersion for 30 and 60 days; exposure to temperatures of 200 ℃ and 500 ℃; and a water permeability test. Slant shear and splitting tensile tests assess durability. Results show that CS exhibits the greatest decrease in resistance to sodium chloride solution and temperature, while DS and GS show less pronounced effects. At 500 ℃, CS and DS specimens fail, whereas GS retains 50% and 75% of its shear and tensile strengths, respectively. GS has the lowest water permeability (7 × 10-11 m/s), followed by DS (1.2 × 10-10) and CS (1.5 × 10-10). Overall, surface roughness enhances durability and mitigates environmental effects.

Influence of thermal fatigue cycles on concrete cold joints

Mass concrete structures in northern climates experience extreme oscillations in temperature each year. These fluctuating conditions incur large thermal stresses, which are of particular concern at cold joint locations. To better understand the behaviour of cold joints subjected to these thermal fatigue cycles, an experimental program was conducted at the University of Manitoba, focusing on the performance of concrete cylinders with concrete-to-concrete interfaces. Specimens were prepared with joints oriented either horizontally to evaluate direct tensile performance or at a 35°, 40°, or 45° angle for slant shear. These cylinders were then installed in specially designed vertical translation-restricting frames and placed in an environmental chamber, where they were subjected to temperatures cycling between −25 °C and 40 °C. Static testing after 50, 150, and 250 cycles was performed to ascertain remaining bond strength. An increase in performance of approximately 20 % was observed in direct tension after 50 cycles, followed by a subsequent decrease. In general, the thermal fatigue cycles did not appear to detrimentally impact bond strength after 250 cycles in both direct tension and slant shear. Additionally, interface friction demonstrated no meaningful trend between specimens that had experienced zero to 250 cycles, remaining relatively consistent with their corresponding roughness level defined in the Canadian Design of Concrete Structures code, and bond cohesion appeared to follow a similar trend to mean direct tensile bond strength results.

Projecting the resiliency of nano-modified cementitious composites with hybrid BFP/PVA fibers in shear key joints

Effective bond strength at the interface between conventional concrete (CC) and high-performance fiber-reinforced cementitious composites (HPFRCC) is vital for applications like shear key for bridge joints. This study investigated the suitability of HPFRCC incorporating various constituents (cement, slag, as well as nano-silica), with only basalt fiber pellets (macro-BFP) or hybrid fiber systems including macro-BFP and micro-polyvinyl alcohol (PVA) fibers. BFP is a new emerging class of basalt fiber strands protected by a polymer coat. Experimental results (slant shear, pure shear, rebar pull-out, etc.) were used to develop modeling [homogenization/finite element modeling (FEM)] components to evaluate the effect of HPFRCC mixture design parameters on the mode of failure and bonding capacity with CC and steel rebar. After verification, these model components were integrated in a full-scale shear key joint model to project the field performance of the developed HPFRCC. The results revealed that nano-silica had a significant effect at improving the HPFRCC bonding strength capacity with CC and steel reinforcement. Whilst increasing BFP dosage (4.5%) in the nano-modified composites resulted in reduction of the interfacial bonding with CC, it significantly improved the rebar interfacial bonding and ultimate shear key capacity of the joint. Comparatively, the inclusion of 1% micro-PVA fibers in the nano-modified composites comprising macro-BFP resulted in the highest increase in shear resistance force, interfacial bonding with precast CC and shear reinforcement dowels, and ductility which suggests their promising potential to be employed in shear key jointing applications.

Integrating push-out test validation and fuzzy logic for bond strength study of fiber-reinforced self-compacting concrete

This study offers a comprehensive analysis of Fiber-Reinforced Self-Compacting Concrete (FRSCC) with a focus on shear bond strength influenced by specific compositions of microsilica, zeolite, slag, and polypropylene fibers. Twenty distinct FRSCC mixes underwent extensive testing, including 28-day compressive strength, tensile strength assessments, and push-out and slant shear tests. A significant outcome is the strong correlation between the push-out and slant shear test results, exemplified by an R² value of 0.88, confirming the push-out test as a viable and practical alternative for bond strength assessment. Experimentally, fibers were found to enhance tensile strength, with the inclusion of 15% microsilica and slag further amplifying this effect, highlighting the critical role of precise pozzolan selection in achieving optimal mechanical performance and workability in FRSCC. Furthermore, the study introduces a fuzzy logic system for predicting shear bond strength, achieving high predictive accuracy with R² values reaching up to 0.96, depending on the t-norms utilized. This research not only validates the push-out test as a reliable method for evaluating shear bond strength in FRSCC but also demonstrates the efficacy of the fuzzy logic approach, representing a groundbreaking contribution in both computational analysis and practical methodology for concrete structural integrity.

Interface Shear Failure Behavior Between Normal Concrete (NC) and Ultra-High Performance Concrete (UHPC)

Ultra-high performance concrete (UHPC) with excellent mechanical properties and durability is a promising material for reinforcement of existing normal concrete (NC) structures. In this paper, the shear failure behavior of the NC–UHPC interface was studied by the slant shear test and the SEM (scanning electron microscope) visualization test, considering influence of the substrate strength and the interface roughed treatment. As the NC substrate and the UHPC overlay are tightly combined at the interface transition zone (ITZ), the interface exhibits good slant shear performance, and the measured interfacial shear strength could reach 19.4 MPa with C40 substrate and 21.8 MPa with C50 substrate. In addition, the microstructure and composition of the ITZ, the possible interfacial failure modes, and the load-carrying mechanism of the interface under compression–shear force are revealed. The high interface roughness and the substrate strength have positive influence on the shear strength, and greatly affect the prone failure mode and the load-slip characteristic.

Development of a novel and specialised cementitious matrix overlay for anode embedment in impressed current cathodic protection (ICCP) systems for reinforced concrete bridges

Impressed Current Cathodic Protection (ICCP) is a widely utilised method for safeguarding reinforced concrete (RC) structures, including bridges, in marine environments. However, certain ICCP systems encounter degradation of the backfill mortar caused by acid formation at the anode. The acid produced reacts with the anode backfill mortar, compromising the functioning of the cathodic protection system. Rectifying the acidification issue typically involves replacing the backfill mortar and, in some cases, even the anode when it is negatively impacted by acid attack. This paper presents, for the first time, a specialised sustainable cementitious matrix that exhibits excellent acid resistance, intended for use as the anode's backfill material in ICCP systems. The proposed mortar effectively mitigates the effects of acidification around the anode, significantly enhancing the durability of the mortar and, consequently, the service life of bridges equipped with ICCP systems. The mechanical and durability performance of the mortar in an acidic environment is evaluated through various tests, including gravimetric analysis, dimensional changes, diffusion depth, compressive strength, direct tension, slant shear, impact resistance, and interface integrity assessments. Additionally, scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques are employed to investigate the material's performance. Subsequently, the specialised mortar is applied to cover Mixed Metal Oxide (MMO) activated titanium mesh anodes of the ICCP system in a reinforced concrete bridge, while its performance is continuously monitored. The results demonstrate that the proposed mortar effectively eliminates acidification issues and improves the performance and longevity of ICCP systems in harsh marine environments.

Microstructural damage characterization of NC-UHPC composite under salt freeze-thaw cycles based on ex-situ X-ray computed tomography

In the harsh environment of extreme salt-freezing conditions, concrete structures face secondary durability issues after undergoing repairs, making it a critical yet challenging topic. This paper employs a novel ex-situ X-ray computed tomography approach to explore the mechanism of damage evolution in normal concrete (NC) to ultra-high performance concrete (UHPC) composites under salt-freezing conditions. For the first time, we consider evolution in both external and internal pores to quantitatively assess the damage. Additionally, slant shear tests, Mercury Intrusion Porosimetry (MIP) were also employed to validate the damage mechanism of NC-UHPC. Finally, empirical formulas summarizing the bond strength and pore changes in NC-UHPC were derived. The results reveal a crucial factor influencing the progression of damage in the NC-UHPC composite: the presence of external pores that directly interact with the salty solution. Damage initiation primarily occurs within the NC-UHPC composite due to these external pores located in the NC region, subsequently extending into the overlay transition zone (OTZ) and UHPC sections. Remarkably, the resistance of the OTZ, previously identified as the weakest zone in the NC-UHPC composite, surpasses that of the NC. This exceptional performance can be attributed to the higher porosity of the OTZ, offering additional space for the dissipation of pressure caused by freezing. What's even more important is that this highlights the consistent origin of damage in the NC-UHPC composite, emphasizing that it always begins within the NC. Considering this perspective prompts the question of whether the exceptionally high strength and durability of UHPC may lead to an excess of repair capabilities?

Performance Evaluation of Hybrid Fiber‐Reinforced Inorganic Mortar for Textile‐Reinforced Mortar Applications

The need to improve existing structures has led to extensive research on strengthening techniques. Textile‐reinforced mortar (TRM) systems, which involve the integration of high‐strength fibers with inorganic matrix, have emerged as a highly promising and viable alternative. The objective of this research is to investigate the mechanical characteristics of inorganic mortar by examining different compositions involving sand, fibers, and cementitious materials. Various combinations were tested to evaluate their compressive strength, split tensile strength, and flexural strength. The findings indicated that a composite mixture (sample 12) comprising microsilica, silica sand, and optimized fibers demonstrated enhanced strength in all three assessments. Research highlights the significance of accurate mixing, additional components, and appropriate fibers to achieve intended performance of the mortar. The compatibility of the mortar is checked with substrate surface and textile sheet. Mortar is evaluated for splitting bond strength, slant shear test, direct pull‐off bond strength, and pull‐out strength. These results provide information about the strength and bonding characteristics of the mortar in different test scenarios. Values indicate how well the mortar performs with the substrate surface and the textile sheet under various types of stresses and loading conditions.

Performance Of Concrete-To-Concrete Bond Strength in Wetland Area

One of the techniques of building rehabilitation methods is repairing. Repair is a rehabilitation process to restore the initial capacity of damaged structures on structural components. A fairly popular repair technique is concrete-to-concrete. The strength of this bonding depends on several factors. The mixture used to repair the material affects the bond strength, as does the surface treatment and curing conditions. The study analysedanalysed the influence of strong bonds on surface treatment and curing conditions. Surface preparations were performed with four methods: as cast, drill holes, grooving, and bonding agent. The curing cycle applied two conditions: normal and wet-dry, and the test objects were compressive strength tests, slant shear tests, tensile tests, and flexural tests. The study results showed that the influence of wet-dry environmental conditions was lower than normal environmental conditions, and the highest bond strength values were found in grooving treatments, drill holes, as cast and bonding agents.

Tension and bond characteristics of foam concrete for repair applications

In this study, foam concretes (FCs) were developed, and their tension, shear, and bond properties were investigated for potential repair applications. Seven FC mixtures with varying combinations of ground granulated blast furnace slag (GGBS) and fly ash (FA) were prepared, along with one M25-grade conventional concrete mixture. The tension properties of both types of concrete were assessed through split tensile strength, flexural strength, and a pull-off test while the shear and bond strength (with reinforcing bars) were determined using the slant shear test and pull-out test, respectively. The results indicated that the compressive strength of the FC mixtures at 28 days ranged from 21.98 to 40.08 MPa, satisfying the requirements of IS 456: 2000 for M15 to M30-grade concrete. Furthermore, the split tensile strength of FC was in the range of 2.21 MPa to 2.83 MPa, while M25-grade concrete showed a strength of 2.24 MPa. Shear strength for FCs ranged between 6.67 MPa and 8.08 MPa while that of the M25-grade concrete was 5.49 MPa. Additionally, the tensile bond strength of FCs fell within the range of 0.67 MPa to 1.46 MPa while that of the M25-grade concrete was 1.12 MPa. The bond strength obtained from the pull-out test for FCs was observed to vary within the range of 11.87 MPa to 23.26 MPa while that of the M25-grade concrete was 14.14 MPa. FCs exhibited superior bond strength compared to M25-grade concrete with both the concrete substrate and reinforcing bars. It was also noted that the tension and bond strength of FC were linearly correlated with its compressive strength. Microstructure analysis indicated that macropores were isolated and discontinuous in all FC mixtures. The improvement in mechanical and bond properties was attributed to enhancements in the microstructure, and the ability of GGBS and FA particles to fill pores in the cementitious paste regions. In conclusion, FC developed using the GGBS and FA as substitutes for cement and sand, respectively showed promise as an alternative concrete repair material, with comparable or superior tensile and bonding properties compared to M25-grade concrete.

The early bonding performance of geopolymer for repair: Effect of mix proportion of cement substrate

AbstractGeopolymer can be potential Portland cement alternatives or supplement for concrete repair. In order to understand the bonding mechanism of geopolymer repairing materials, the effect of the mix proportion of cement mortar substrate on the early bonding performance was studied. For repaired composites by geopolymer, with the increase of sand‐to‐cement ratio of cement substrate from 1.5 to 2.5, the trends in the interfacial flexural‐tensile strength and slant shear strength were the same, both decreasing, which may be explained by the combined effect of surface porosity and the amount of surface cement pastes. And with the rise of the water‐to‐cement ratio of cement substrate from 0.4 to 0.5, the interfacial flexural‐tensile strength also increased mainly because of the increase in the surface porosity of the substrate, while the slant shear strength decreased resulting from the impact of compressive strength of the substrate. This indicates that the interfacial flexural‐tensile test is more suitable for the evaluation of the bonding performance than the slant shear test when the mix proportions of substrate vary.

Adhesive characteristics of novel greener engineered cementitious composite with conventional concrete substrate

Engineered cementitious composite (ECC) is a high-graded advanced construction material that can be used to strengthen and repair structural composites owing to its high mechanical and durability properties. Nevertheless, the ability of ECC to strengthen and repair concrete surfaces depends on the interfacial bond between the conventional concrete (CC) substrate texture and ECC overlay. It ensures sufficient adhesive or bonding ability over a lifetime under various loading and environmental conditions. The present study investigates the bond strength between CC substrate and modified ECC with agro-industrial by-products, such as ground granulated blast furnace slag (GGBS), bagasse ash (BA), and rice husk ash (RHA). The bond strength is determined using three types of tests, namely the slant shear, split cylinder, and split prism tests. A mathematical model has also been developed to predict the bond strength of the different ECC mixtures. The results indicate that incorporating 40% GGBS, 10% BA, and 10% RHA in ECC helps in attaining the maximum interfacial bond strength with cross-hatched textures under all types of testing. According to the ACI standard, ECC with agro-industrial by-products ranging from 10% to 55% achieved the required bond strength in all three tests. Correspondingly, the outcomes of the present research are compared with those obtained from previous studies to gain further insights into various applications, which are highly relatable. Furthermore, the experimental outcomes were strongly correlated with the mathematical modeling with great accuracy.

Bond performance between cementitious grout and normal concrete subjected to freeze–thaw damage

Owing to the increasing application of cementitious grout in strengthening projects in cold regions, the freeze–thaw durability of the bond between cementitious grout and concrete has attracted attention. This study investigates the bond performance of a cementitious grout–normal concrete interface after FTCs through splitting tensile and slant shear tests at different angles. The microstructure of the cementitious grout–concrete interface is observed via backscattered electron (BSE) microscopy. The results show that FTCs rapidly reduce the splitting bond strength and slant shear bond strength of the interface. After 240 FTCs, the splitting and slant shear bond strengths decrease by 40.7%–72.4% and 46.1%–57.3%, respectively. An increase in substrate strength significantly enhances the interfacial bond strength, particularly the slant shear bond strength. Freeze–thaw damage to the substrate reduces the interfacial bond strength and frost resistance. The slant shear strength increases significantly with the slant shear angle. The effects of FTCs on the interfacial shear strength parameters are reflected through a rapid decrease in cohesion, whereas the interface internal friction angle remains relatively unaffected. Empirical formulas for calculating the interface bond strength are obtained from experimental data and validated. The BSE images show that cracks begin to appear at the cementitious grout–normal concrete interface as the number of FTCs increases, thereby decreasing the interfacial bond strength.

Evaluation of the Bond Shear Strength and Corrosion Resistance of Concrete with Setting Retarder

In this study, the bond shear strength and corrosion resistance of concrete with setting retarders were evaluated. For this, slant shear, bi-surface, and accelerated corrosion tests were conducted. The variables considered included the proportion of the setting retarder (0 and 1%), surface treatments of concrete (as-cast, chipping, and brushing), curing hours (8, 16, and 24 h), and concrete cover depths (20, 30, and 45 mm). Consequently, the bond shear strength of concrete with the retarder showed a higher value than that of normal concrete. Moreover, an increase in curing hours resulted in a higher value of the bond shear strength. Furthermore, the addition of a retarder in concrete increased corrosion resistance. Based on the test results, the addition of a setting retarder is believed to be a suitable solution to address the bond shear strength and durability issues that may arise at the interface of delayed concrete placement.