Slant Shear Test 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.

Bond performance of fly ash-based geopolymer mortar in simulated concrete sewer substrate

Geopolymers have been extensively explored as a promising repair material for deteriorated Ordinary Portland Cement (OPC) concrete elements. However, knowledge of the adhesion performance of geopolymer to concrete substrates is limited. This study investigates the bond performance of low calcium fly ash geopolymer (FAGP) mortar and concrete for holistic acidic environmental conditions, such as in sewer rehabilitation. The bond evaluation was conducted by slant-shear test, performed at different substrate conditions, namely Rough-Dry, Rough-Saturated, Smooth-Dry and Smooth-Saturated, to simulate the in-service condition of a typical sewer pipe wall. The standard OPC repair mortar and a commercially available proprietary geopolymer repair product (P-GP) were evaluated and compared as controls to ascertain the viability of geopolymer for repair application. The shear bond strength of FAGP mortar was found to be in the order of 14 MPa, outperforming OPC and P-GP in all substrate conditions. Even though FAGP bond strength was insensitive to roughened substrate moisture levels, the synergistic effect of smoothness and moisture condition appeared detrimental. The testing of the prototype geopolymer-coated concrete pipe under line loading showed no sign of delamination at the bond plane. OPC and P-GP exhibited a distinct bond separation, which commenced at only 20 % of the ultimate load. The acid resistance and low permeability of FAGP mortar appeared to aid in preserving the repair bond.

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.

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.

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.

Analysis of Structural Parameters of Steel-NC-UHPC Composite Beams.

The cracking of the negative moment area of steel-normal concrete (NC) composite bridges is common owning to the low tensile strength of concrete. In order to solve the problem, Ultra High Performance Concrete (UHPC) is used to enhance the tensile performance of the negative moment area. This paper conducted interface experiments to study the bonding behaviour of the UHPC-NC interface. The design parametric analysis of steel-NC-UHPC composite bridges was carried out based on the interface experimental results. Firstly, slant shear tests and flexural shear tests were carried out to study the rationality of the interface handling methods. Then, the finite element model was used to analyze the state of every component in the composite beams based on experimental results, such as the stress of UHPC, concrete and steel plate. Finally, the calculation results of finite analysis were compared and summarized. It is concluded that (1) the chiseling interface can meet the utilization requirements of physical bridges. The average shear stress and flexural tensile strength of the chiseling interface are 10.29 MPa and 1.93 MPa, respectively. In the failure state, a slight interface damage occurs for specimens with a chiseling interface. (2) The influence on overall performance is different for changes in different design parameters. The thickness of concrete has a significant influence on the stress distribution of composite slabs. (3) Reliable interface simulation is conducted in the finite element models based on interface test results. The stress variation patterns are reflected in the change of design parameters.

Effect of GO-modified epoxy on the bond behavior of old-new concrete and comparison with different surface preparation techniques

The interface of old to new concrete is the weakest plane during retrofitting and repairing of concrete structures, resulting in the interface or adhesive failure of the composite formed. Various surface preparation techniques and adhesives have been used and reported in the literature to improve the bond behavior of concrete-to-concrete interface. Epoxy is a commonly used adhesive to bond existing concrete with new overlay concrete, as it provides high adhesion and chemical resistance; however, inadequate roughness and low strength negatively affect the epoxied concrete joints, causing poor bonding at the concrete interface. On the other hand, the use of graphene oxide (GO) in epoxy showed significant enhancement in its mechanical properties. Hence, in the present study, GO-modified epoxy has been proposed as an adhesive to improve the bond performance of the interface between existing and new concrete by conducting split tensile, bi-surface shear, and slant shear tests. Simultaneously, a comparison has been carried out with other frequently used surface preparation techniques such as grinding wire brushing (GW), grooves, and adding carbon and glass fiber laminate over the existing concrete with and without neat (plain) epoxy. The GO-modified epoxy has been prepared using three different GO concentrations; out of them, 0.05% by weight turned out to be the optimum concentration and performed best under all bond strengths and resulted in concrete failure instead of adhesive failure. Furthermore, scanning electron microscopy (SEM) revealed homogeneous dispersion of GO at 0.05% by weight and formation of the bond between GO and cement hydrates with both concrete interfaces. As a result, GO-modified epoxy turned out to be a high-strength adhesive to join existing concrete with fresh overlay concrete for strengthening, retrofitting, and repairing concrete structures and shows an effective composite action.

Multifunctional ultra-high performance fibre-reinforced concrete with integrated self-sensing and repair capabilities towards in-situ structure monitoring

Achieving continuous in-situ monitoring of repaired concrete structures has always been a great challenge. Ultra-high performance fibre-reinforced concrete (UHPFRC), featuring superior mechanical capacity, excellent erosion resistance, and long-life cycle, is expected to realize durable, cost-effective, and aesthetically pleasing repairs and possesses tremendous potential for intrinsic self-sensing. This paper presents the multifunctionality of UHPFRC with integrated self-sensing and repair capabilities using multi-walled carbon nanotube (MWCNT). An experimental evaluation on the bond performance and self-sensing properties, including the bond strength and failure patterns by the three-point bending, splitting tensile, and slant shear tests, electrical properties via alternating current impedance spectroscopy test, and electromechanical properties under three-point bending, was conducted through the designed composite layer between concrete substrate and UHPFRC. The microstructure of the interfacial zone was analysed to reveal the bonding mechanism. Results indicate that the addition of MWCNT improved the bond strength between concrete substrate and UHPFRC as MWCNT can enhance the adhesion and cohesion of the interfacial zone through inactive filling effect, as well as the frictional and mechanical interlocks through increased mechanical properties of repair UHPFRC. Moreover, the repair UHPFRC showed remarkable sensing capabilities for the initial cracking, deflection hardening or softening, and fibre pull-out and debonding processes of the composite layers. The optimal content of steel fibre and MWCNT in multifunctional UHPFRC should be 2 vol.% and 0.2 wt.%, respectively, considering the synergistic damage sensing and bonding properties.

3D-printed concrete shear keys: Design and experimental study

To incorporate 3D-printed concrete (3DPC) for modular construction of large-scale building and infrastructure, it is important to develop interlocks firmly connecting adjacent 3DPC modules and providing sufficient shear resistance to prevent inter-segment slippage. To develop guidelines for design and testing of 3DPC shear key interlocks, this paper proposes a fabrication method of such interlocks and studies various designs of 3DPC shear keys through push-off tests and slant shear tests for specimens with different shear key angles and shear joint inclinations. The experimental study focuses on the effect of these geometrical parameters on joint capacities and failure processes. The tests results showed that a smaller shear key angle slightly improved the shear capacity. The normalized shear stress of 3DPC shear keys was similar or slightly lower than precast concrete shear keys whereas shear capacity equations in the literature significantly underestimated the shear strength of 3DPC shear keys.

Evaluation of bonding performance of ultra high-performance concrete with fly ash content as overlay on normal strength concrete.

Ultra High-Performance Concrete (UHPC) has good mechanical strength and durability, so it can be the solution for an overlay material for old materials that need to be renewed. The problem with using UHPC as a construction material is the high price and sustainability, so a partial replacement for cement is required to reduce production costs, energy consumption, and CO2 gas emissions. Bonding performance is an important parameter and must be considered when applying UHPC as an overlay material. The bonding performance test of the UHPC consists of three tests: the slant shear test, splitting tensile, and direct tensile/pull-off test. The results of this study were compared with the standards of ACI 546R-14 and M.M. Sprinkel & C. Ozyildirim. Based on the test results, replacing 40% of cement with fly ash on UHPC is good to use as an overlay because it meets applicable standards. The test results showed an increase of 27% in the slant shear test and 37% in the splitting tensile test compared to the existing standard. Replacing cement with fly ash in UHPC can also increase workability, reducing the need for superplasticizers, reducing UHPC production costs by 18.4%, energy consumption, and CO2 emission problems.

Microstructure, tensile strength and shear strength of aggregate-mortar interface: Effect of aggregate mineralogy

This work aims to study the mechanical properties of the interfacial transition zone (ITZ) through both experimental tests and microstructural observations. The study considers a mortar with water-cement ratio of 0.58 and four types of aggregates: sandstone, granite, and two different types of limestone with varying water absorption coefficients. Chemical compositions, physical characteristics, and surface micromorphology of the four aggregates were evaluated using X-ray diffraction (XRD), thermogravimetric analysis (TGA), and water absorption measurements as well as SEM observations. Experimental setups were developed to investigate the bonding behavior of the aggregate-mortar interface. The bonding strength between granite and mortar through direct tensile test varied from 51% to 69% of tensile strength of mortar from young age to mature, while 61% to 74% for sandstone, 48% to greater than 90% and 81% to greater than 102% averagely for black and white limestone respectively. The fact of failure in the bulk mortar indicates ITZ adhesion for limestones may equal or exceed the mortar tensile strength generally from 28-day age. This conclusion is consistent with the results obtained by slant shear test. The significant difference of adhesion behavior of ITZ between two limestones due to their water absorption capability. High-water absorption turns out to be beneficial in forming a strong chemical bond at early age, however, the mineralogy remains the pivot under same surface condition. This chemical bond is evidenced by the failure pattern and morphology of the aggregate surface after failure and the presence of a dense accumulation of portlandite and C-S-H under SEM.