Crack Development Research Articles

Nanodiamond reinforced self-healing and transparent poly(urethane–urea) protective coating for scratch resistance

ABSTRACT With increasing demand for scratch-resistant flexible electronics, the development of transparent coatings with good scratch resistance and self-healing properties has emerged as a key research topic. In this study, a high-strength self-healing poly(urethane – urea) (PUU)-based nanocomposite coating was prepared by introducing functionalized nanodiamond (ND) into a PUU matrix via solution blending. The PUU matrix had hard-segment repeating units and was constructed using isophorone diamine and isophorone isocyanate. The ND particles were modified using a silane coupling agent, 3-aminopropyltriethoxysilane, to obtain well-dispersed KH-ND nanoparticles. KH-ND promoted microphase separation in the PU matrix, inducing the formation of dense and homogeneous hard domains that dissipated stress, prevented further crack development, and improved the mechanical properties and scratch resistance of the coating. In addition, the coating exhibited excellent self-healing properties. Fourier-transform infrared spectroscopy, scanning electron microscopy, and atomic force microscopy were used to characterize the self-healing and hardening mechanisms of the coating. The environmentally friendly PUU/KH-ND coating is easy to prepare and has broad application prospects in transparent and anti-scratch coatings for flexible electronics, automobiles, and home appliances.

Effect of manufactured sand, micro silica, and GGBS on properties of high-performance concrete

The most often used building material for engineering constructions is concrete. The rapid urbanization has necessitated the need for High Strength (HS) and High -Performance Concrete (HPC) for specialized constructions, such as high rise/tall structure and other important structures. Greater cement content may be required for concrete with higher performance like strength and durability, but code does not permit it, because higher cement content increases the heat of hydration, which leads to the development of thermal cracks in concrete, reduces its structural performance and damage environment by producing CO2 during production of Ordinary Portland Cement (OPC). This study tries to replace OPC by Micro Silica (MS) and Ground Granulated Blast Furnace Slag (GGBS) by some percentage to find our effect of these materials on properties of concrete HPC.In this work, the influence of Manufactured Sand (M-Sand), Micro Silica (MS) and Ground Granulated Blast Furnace Slag (GGBS) on the mechanical and durability qualities of High - Performance Concrete (HPC) is examined experimentally. Ordinary Portland cement (OPC) is used to create the HPC mixtures and then 40%,45%, 50% by weight of OPC is replaced with GGBS and 2.5% and 5% by weight of OPC is replaced with MS respectively. Additionally, OPC is replaced by 40%GGBS+ 2.5% MS, 40% GGBS+5% MS, 45%GGBS+ 2.5% MS, 45% GGBS+5% MS, and 50%GGBS+ 2.5%MS, 50%GGBS+5% MS. For each percentage replacement workability test, compressive test at the age of 28,56 and 90 days, water permeability test at 28 days and 90 days, Scanning Elector Microscope (SEM) test after 90 days are carried out. The investigative study’s findings showed that partial replacement of OPC with GGBS, MS, and combinations of GGBS and MS produces more consistent outcomes for strength and durability when compared to control mix.

Detection of cracks in aircraft structures using digital image processing technology

Full-scale aircraft structural fatigue testing exposes structural weaknesses by simulating the use of the aircraft in service and monitoring the development and expansion of fatigue cracks to guide the optimisation of aircraft structural design, the determination of service life and the development of maintenance and repair programmes. If crack damage is not detected in time, the uncontrolled expansion of the crack may lead to structural damage and prolong the test cycle. Therefore, it is crucial to achieve accurate detection of early cracks in fatigue testing of aircraft structures. Digital image technology is a new technology supported by a number of technical and theoretical achievements. In practical application, it relies on the support of computer functions, by converting image information into two-dimensional digital signals, thus realising various operations. In this paper, digital image processing techniques are used to deepen the backbone feature extraction network structure and improve the prediction scale of small targets, thus improving the performance of the model in terms of feature extraction and small defect detection. Experimental results show that the method can achieve accurate detection of small cracks, providing an effective technical approach for the automatic detection of cracks in aircraft structural fatigue tests. The technique of detecting cracks in aircraft structures using digital image processing also provides a new idea for research into improving aircraft endurance testing, which can be further developed with the aid of image technology.

Structural properties and failure characteristics of granite after thermal treatment and water cooling

In a variety of fields such as exploitation of geothermal energy and the reconstruction of nuclear waste storage, both of high-temperature and cooling process change the physical and mechanical properties of granite. Uniaxial compression tests were performed on five groups of granite samples at 25 °C, 200 °C, 400 °C, 600 °C and 800 °C after water cooling, and CT scanning, acoustic emission(AE) monitoring and X-ray diffraction(XRD) scanning were used to investigate the structure properties and failure characteristics of granite. It is found that the proportions of pore volume greater than 106 μm3 and less than 105 μm3 with are positively and negatively correlated with the thermal treatment temperature respectively. The mechanical properties of granite are significantly deteriorated by temperature gradient shock, and crack development scale during failure process overall increases as implied by AE response. The failure intensity index η is proposed to characterize the failure severity of granite, and the value of η descends with the increase of thermal treatment temperature, indicating the failure severity of granite is alleviated. Three types of loading failure mode are classified for water-cooled high-temperature granite. The failure mode of granite at 200 °C and 600 °C is tensile failure and tensile-shear failure respectively, while the granite samples are dominated by shear failure at 25 °C, 400 °C and 800 °C.

A new method for machining RB-SiC with high efficiency and quality: Laser assisted ultrasonic grinding

Reaction Bonded Silicon carbide (RB-SiC) ceramic is preferred material for space mirrors in aerospace field. However, the high hardness, brittleness and inhomogeneous structure bring great challenges for high quality and efficient machining. In this study, laser ablation assisted ultrasonic grinding (LAAUG) process was proposed. The high efficiency of laser ablation and high quality of ultrasonic grinding were effectively combined. Laser pre-ablation experiments were carried out firstly, and then thermal damage layer was removed through ultrasonic grinding. The results show that RB-SiC ceramics transform into relatively loose and homogeneous ablation products (SiO2 and recrystallized SiC) by laser irradiation. Moreover, it is accompanied by cracks development. Compared with conventional grinding, the maximum reduction of grinding force and surface roughness is 34 % and 13.8 %, respectively. Abrasive grain wear is significantly restrained and the percentage of plasticity removal is improved. This study indicates that LAAUG is feasible and efficient method for machining RB-SiC ceramics.

Characteristics of strata movement and method for runoff disaster management for shallow multiseam mining in gully regions: A case study

Multiseam mining in gully regions has resulted in severe and complex disaster chains, including crack development, mountain landslides, river blockage, and intensified mine water inflow. To prevent and control water inrush disasters, it is imperative to investigate the characteristics and mechanizations of overburden failure under the combined effect of gully terrain and repeated mining in coal seams. This study takes multiseam mining within the gully region of the Xiqu Coal Mine as a case study. The comprehensive analytical method that integrates surface exploration, Interferometric Synthetic Aperture Radar (InSAR) measurement, numerical simulation, and rainfall-runoff analysis, is used to anatomize the entire process of overburden failure induced by downward multiseam mining and the accumulation process of runoff in the gully region. The results reveal that compared to single-seam mining activities, repeated mining and the occurrence of key stratum (KS) structure failure triggered the comprehensive subsidence of the interburden, producing a cutting-type fracture and stepped subsidence, while the overburden exhibited severe damage. Compared to gentle surface topography, gully slopes are prone to shear sliding under the effects of mining subsidence and gravity, resulting in the connection of the downward cracks of the slope and the upward cracks of the overburden. In addition, if the accumulation formed by gully landslides due to repeated mining blocks the river channel and forms a barrier lake during the flood season, it may cause a surge in underground water. High-precision terrain synthesized by UAV tilt photogrammetry is used to simulate the rainfall inundation range and time of different durations during the “100-year return period” rainstorm in the study area. This study proposes a zoning prevention and control method for surface runoff disasters based upon the characteristics of surface deformation and surface inundation time; this method involves filling surface cracks in runoff areas and submerged and crack development areas, implementing slope cutting and control in potential landslide areas, and strengthening the riverbed in submerged and maximum settlement areas.

Acoustic emission characteristics of stainless steel reinforced geopolymer coral concrete beams under four-point bending

The fabrication of geopolymer coral aggregate concrete beams (GCACB) can effectively address the challenges associated with constrained concrete raw materials and structural erosion in island construction. Acoustic emission technology (AE) presents an appealing solution for non-destructive evaluation and structural health monitoring. In this study, 6 specimens were conducted to examine the flexural behavior of GCACB accounting for variation in the reinforcement ratios under the four-point bending test, simultaneously recording the corresponding AE data. Then, the effect of the AE parameters on crack development was analyzed. By utilizing the GMM algorithm, the crack pattern classification was investigated. Finally, the GCACB damage was evaluated based on two different AE b-value analysis methods. The findings indicate that the cracks within GCACB predominantly occur along the coral coarse aggregate with low strength and high brittleness. The presence of reinforcement ratio has an enhancement on both the flexural capacity and deformation capacity of GCACB while impeding the crack width. It seems that a positive correlation between increasing crack damage and cumulative hits and AE energy occurs. Based on the enhanced GMM model, the cracks are categorized into tensile crack, shear crack, and mixed crack, with tensile crack predominating. A probabilistic division line is established for the RA-AF relationship that progressively leans towards the AF axis as the reinforcement ratio increases. In contrast to the b-value obtained from the GBR method, the Aki method demonstrates enhanced predictive capability for GCACB damage.

Analysis of fracture characteristics of saturated sandstone based on infrared radiation variance

The use of infrared radiation technology for monitoring rock stability and failure has been a common practice. However, the presence of groundwater significantly compromises the precision of infrared monitoring. This study employs scanning electron microscopy technology and PFC simulation to examine the micro-fracture development and infrared radiation variance (IRV) characteristics in dry and saturated sandstone conditions, and establishes a direct relationship between the two. The findings of this research indicate the following: (1) Saturated sandstone exhibits a substantially weakened internal structure, with the number of cracks at peak strength is approximately twice that of dry sandstone，the strength, peak stress, and elastic modulus of the saturated samples decreased to 56% and 59%, respectively. (2) The surface IRV characteristics of saturated samples are notably more pronounced, with an IRV value 9.57 times that of dry rocks. (3) Two infrared radiation variance indicators have been introduced to delineate different fracture stages of sandstone: “slow fracture variance” (SFIRV) denotes the initial crack formation in sandstone, while “rapid fracture variance” (RFIRV) characterizes a rapid fracture stage marked by a significant increase in crack development, serving as a precursor to complete sandstone fracture. (4) The relationship between IRV and the quantity of internal fractures adheres to a power function. A mathematical model for Fracture-IRV has been established, demonstrating a high degree of consistency with actual experimental results. The outcomes hold valuable implications for infrared monitoring research in deep engineering that may encounter groundwater-related challenges, such as tunnel and coal mining.

Non-Destructive Testing Methods for In Situ Crack Measurements and Morphology Analysis with a Focus on a Novel Approach to the Use of the Acoustic Emission Method

This article presents a concise review of modern non-destructive testing (NDT) methods that allow the detection, tracking, and measurement of cracks in reinforced concrete structures. Over the past decades, the range of solutions available on the market has increased. This provides excellent opportunities when choosing and designing systems for diagnosing and continuously monitoring structures. Cracking affects the mechanical properties, durability, and serviceability of a structure or its elements. Therefore, there is a need to develop methods that would allow the determination of the moment of a destructive process’s formation, i.e., a crack’s appearance. At the same time, it is crucial to be able to track the development of cracks for the entire structure, not just selected locations. This work also presents the concept of combining selected NDT methods and creating a system for the continuous monitoring of structural integrity and predicting changes in the durability of existing and future buildings.

Shear cracking behavior of pre-damaged PVA-aggregate mixed ECC beams: Direct observation using DIC

Normal polyvinyl alcohol-engineered cementitious composites (PVA-ECC) exhibit high mechanical performance but are susceptible to shear cracking. It has been recently found that the shear resistance can be largely improved by including coarse aggregates. However, under complex stress conditions, the mechanism of shear movement and the contribution from coarse aggregate remain unclear. This paper presents an experimental investigation of the shear cracking behavior in pre-damaged PVA-ECC beams with a mixture that includes coarse aggregate. Symmetric and antisymmetric loading tests were carried out to examine the effects of coarse aggregate under different stress rotation fields. To clarify the shear cracking mechanism, digital image correlation (DIC) was applied to observe crack development and strain localization in the shear span of the PVA-ECC beams. The results obtained from DIC and conventional measurements showed good agreement, confirming the reliability of monitoring complex fracture processes using the DIC technique. The shear cracking mechanism of the PVA-ECC beam under complex stress conditions was analyzed. The collaboration of coarse aggregate was observed from the orientation of secondary cracks, which showed less dependence on the presence of precracks. Crack opening and sliding were significantly limited due to the reduced anisotropic effect of the predamage. Therefore, using the DIC technique, the positive effect of coarse aggregates was verified, and the shear cracking mechanism of pre-damaged PVA-ECC beams was revealed through direct observations.

The Effect of Polypropylene Fiber and Glass Fiber on the Frost Resistance of Desert Sand Concrete

To study the influence of polypropylene (PP) fibers and glass fibers on the frost resistance of desert sand concrete (DSC), the fast-freezing tests were carried out to investigate the freeze-thaw damage law using the apparent damage, mass loss, and relative dynamic elastic modulus as indicators; Based on the mercury intrusion method (MIP) and scanning electron microscopy (SEM), the microstructure evolution was analyzed to reveal the mechanism of fiber frost resistance enhancement. Fit the freeze-thaw damage process of fiber reinforced DSC (FRDSC) and predict the frost resistance life. The results show that fibers can greatly improve the freezing resistance of DSC. The hybrid fiber had the highest enhancing effect, followed by PP fiber and glass fiber. The dynamic elastic modulus of the DSC with 0.15% PP fiber and 0.05% glass fiber is as high as 95%. The pore distribution ratio of FRDSC changes faster, but it is still better than that of reference DSC after freeze-thaw. PP fiber and glass fiber can play a full role in the micro and macro stages of crack development of DSC respectively. The freeze-thaw damage model has high fitting accuracy and the DSC mixed with fibers can significantly improve the service life of buildings in northern China.

Experimental study on ice breaking by a cavitating water jet in a Venturi structure

Ice breaking by a cavitating water jet based on Venturi structure is studied experimentally. Systematic researches of cavitating water jet interacting with ice are carried out by doing indoor experiments, where the cavitating jet is generated by a tailor-made device through Venturi nozzle and the circular fresh-water ice plates are made of boiled water in a cryostat. The whole evolution of cavitating jets and ice plates is recorded by two high-speed cameras from two views simultaneously. Pressure loads on the rigid wall of cavitating water jet is compared with that of conventional non-cavitating water jet and the change is analyzed. Among two typical structural parameters of Venturi cavitating nozzles selected in this paper, the ratios of throat length to diameter ε (1; 1.5; 2) and the diverging angles α (8°; 10°; 12°), the nozzle withε = 1 andα = 12° is found to be the best in terms of loads on wall. On this basis, the responses of ice plate, including crack generation, crack development and fracture, are studied under the cavitating jet loads, mainly involving the compressible pressure P1 and cavitation pressure Pc. According to the main cause and propagation sequence of cracks, the failure mechanisms of ice under Venturi cavitating jet can mainly be divided into three types: shock waves failure, overall strength failure and local strength failure, along with six damage patterns roughly. Furthermore, the effects of ice plate thickness, cavitating water jet strength and boundary conditions are also investigated.

Constitutive Model of Bond-Slip between Rubber Granule–Basalt Fiber Composite Modified Concrete and Rebar

The bonding properties between rubber granule–basalt fiber composite modified concrete (RBFC) and rebar greatly impact the load-carrying capacity, stiffness, and crack development of RBFC structures. In this paper, the effects of rebar diameter, bonding length, and concrete type on the bonding properties between RBFC and rebar were investigated using center pull-out tests. The bond stress–slip curve as well as the bond strength and its influencing factors were discussed in detail, and a semi-theoretical and semi-empirical model of RBFC with rebar was established. According to the findings, when rubber granules were added to concrete, its bond strength with rebar decreased. At a dosage of 5%, the bond strength was reduced by approximately 4% compared to ordinary concrete (OC) under the same conditions. It was shown that the addition of small amounts of rubber granules did not significantly reduce the bond strength. On the other hand, the incorporation of an appropriate amount of basalt fibers had a positive effect on the bond strength. An admixture of 4.56 Kg/m3 of fibers increased the bond strength by 3% compared to OC under the same conditions. The bond strength of RBFC with these two additions was improved by approximately 2% compared to OC under the same conditions. When the bonding length was 60 to 100 mm, the ultimate bond strength decreased with increasing bonding lengths. The bond strength decreased by 13.91–16.72% for every 20 mm increase in bonding length. When the rebar diameter was 12 to 16 mm, the ultimate bond stress decreased as the rebar diameter increased. The bond strength decreased by 3.96–5.94% for every 2 mm increase in rebar diameter. The segmental bond–slip constitutive model between RBFC and rebar, established using the results of the center pull-out test, can provide a reference basis for engineering applications of RBFC.

Shrinkage Behavior of Stabilized Earth Bricks Reinforced with Wheat and Barley Straw

Due to its ecological and financial benefits, earth building has gained global attention, with earth bricks being extensively used. Shrinkage and crack development have a considerable impact on the performance and quality of earth bricks. This study employs laboratory experiments to examine the shrinkage behavior of earth bricks reinforced with wheat and barley straw. In addition to this, the impact of cement and gypsum additives is examined. The obtained results indicate that increased fiber content reduces crack formation effectively. However, higher levels of cohesive soil have been shown to have a negative influence on shrinkage behavior. In general, higher fiber contents contribute to the improvement of earth brick performance. These findings offer useful insights for improving the composition and characteristics of reinforced earth bricks, resulting in enhanced performance and quality in sustainable construction practices.

Time-dependent response of continuous steel-concrete composite beams under sustained loading

Although the long-term behavior of composite beams raises critical concerns in their application, only a few investigations have been conducted on the time-dependent response of continuous composite beams (CCBs). Herein, long-term tests were conducted on four two-span CCBs with different loading ages. The shear stiffness and time-slip relationship of flexible shear connectors were evaluated by carrying out short-term and long-term push-out tests. The experimental results revealed that loading age substantially affected the development of deflection, interface slip, crack, and internal force redistribution of CCBs under sustained loads. A finite element model (FEM-2) of test specimens was developed, considering the damage evolution, creep and shrinkage of concrete slab, and stiffness degradation of connectors. After the FEM results were verified against the experimental data, the developed FEM-2 model was implemented to further investigate the influences of loading age and loading level on the long-term performance of CCBs.

Study on instability mechanism of soft rock roadway and pressure-relief bolt-grouting support technology

Aiming at the engineering problem of roadway deformation and instability of swelling soft rock widely existed in Kailuan mining area, the mineral composition and microstructure of such soft rock were obtained by conducting scanning electron microscopy, X-ray diffraction experiments, uniaxial and conventional triaxial tests, and the law of softening and expanding of such soft rock and the failure mechanism of surrounding rock were identified. The combined support scheme of multi-level anchor bolt, bottom corner pressure relief and fractional grouting is proposed. The roadway supporting parameters are adjusted and optimized by FLAC3D numerical simulation, and three supporting methods of multi-layer anchor bolt, bottom corner pressure relief and fractional grouting are determined and their parameters are optimized. The study results show that: the total amount of clay minerals is 53–75%, pores, fissures, nanoscale and micron layer gaps are developed, providing a penetrating channel for water infiltration to soften the surrounding rock; the three-level anchor pressure-relief and grouting support technology can control the sinking amount of the roof within 170 mm, the bottom drum amount within 210 mm, the bolts of each level is evenly distributed in tension, and the maximum stress and bottom drum displacement in the pressure relief area are significantly reduced; the pressure-relief groove promotes the development of bottom corner cracks, accelerates the secondary distribution of peripheral stress, and weakens the effect of high stress on the shallow area. Using time or displacement as the index, optimizing the grouting time, filling the primary and excavation cracks, blocking the expansion and softening effect of water on the rock mass, realizing the dynamic unity of structural yielding pressure and surrounding rock modification, has guiding significance for the support control of soft rock roadway.

The impact of post-treatments on the brittleness and wear resistance of borided 8 % Cr steel

The implementation of post-treatments for the enhancement of the mechanical behavior of boride layers has been conducted in recent years. For this reason, the borided 8 % Cr steel underwent austempering-interrupted treatment and austempering-interrupted + cryogenic treatments. Resulting microstructures have been characterized using light optical microscopy, scanning electron microscopy and energy dispersive X-ray spectrometry, and X-ray diffraction. The brittleness grade and dry sliding wear resistance of the borided steel with and without post-treatments were achieved through a Vickers microindentation approach (at various loads of 2 N, 3 N, and 5 N) and the ball-on-flat wear test (at a constant load of 20 N for 100 m). In addition, a non-borided material (hardening + tempering) was tested employing the ball-on-flat wear test to demonstrate the improvement of the boride layers.As expected, the wear resistance of the 8 % Cr steel subjected to conventional boriding was 8 times greater than that of the non-borided material due to the surface hardening achieved through the thermochemical treatment. On the other hand, the austempering-interrupted treatment conducted after conventional boriding resulted in a 1.2 times improvement in wear resistance. This enhancement was attributed to the transformation of the FeB–Fe2B dual-phase layer into a Fe2B single-phase layer, which reduced the brittleness grade of the boride layer from 4 to 3.1. Nonetheless, the Fe2B single-phase layer achieved the highest wear resistance, which was 1.3 times greater, after undergoing austempering-interrupted + cryogenic treatments (resulting in a slight decrease in the material's brittleness grade from 3.1 to 2.9) compared to the borided steel treated with austempering-interrupted alone.Grooving and debris were observed on the entire wear tracks for both non-borided material (ductile) and boride layers (brittle). Additionally, brittle layers exhibited the development of cracks and spalling, while ductile non-borided steel showed plastic deformation.

Structural, thermal and acoustic aspects of crack propagation in titanium alloys

The aim of this work was to investigate the correlation between structural, acoustic emission and thermal characteristics of the fatigue crack growth in titanium alloys. Cluster analysis of the acoustic emission signals revealed two different types of signals recorded during the development of a fatigue crack. It has been shown experimentally that the evolution of the stored energy tends to an asymptotic value at the final stage of fatigue crack growth and it correlates with the intensification of the twinning process in titanium alloy Ti Grade 2. A correlation was assumed between the stages of change in the heat flux, the cumulative energy of the first cluster of AE signals and the crack length.

Cracking mechanisms and effect of extensive preheating in CM247LC and IN713LC Ni-base superalloy processed by Laser Powder Bed Fusion

Laser powder bed fusion processing of non-weldable γ’-strengthened Ni-based superalloys is challenging due to various cracking mechanisms that occur during the solidification and cooling stages of the materials. The current study offers an insight into the failure mechanisms of the CM247LC and IN713LC alloys, identifying the pre-heating temperatures which can mitigate cracking phenomena during processing. The adopted methodology involved the alloy processing by a standard Laser powder bed fusion system followed by microstructural characterization. It was confirmed that the development of cracks with a length in the range of 100–500 µm became evident in both alloys. High-temperature preheating strategies were then investigated using a simplified approach based on single laser track remelting. At pre-heating levels up to about 900 °C, corresponding to measured cooling rates of the order of 104 °C/s, hot cracks were still observed in the alloys due to γ’ precipitation and segregation of carbide former elements at the cell boundaries according to both microstructure observations and thermodynamic predictions. Preheating conditions at higher temperatures targeting levels above the γ’-solvus temperature, exceeding 1200 °C could promote slower cooling rates, leading to full suppression of cracks in the investigated γ’-strengthened alloys.

Performance-based alkali-activated seawater sea-sand concrete: Mixture optimization for mechanical, environmental, and economical objectives

This study aims to explore the viability of employing alkali-activated materials (AAMs) as alternatives for ordinary Portland cements (OPCs) in seawater sea-sand concretes, thereby promoting the sustainable utilization of marine resources in island-based constructions. Artificial seawater, sea-sand, coral coarse aggregate (CCA), normal limestone aggregate (NLA) and slag-based AAMs incorporating with 15 wt% fly ash and 5 wt% silica fume were mixed to prepare performance-based alkali-activated seawater sea-sand concrete (ASSC). The L9 (33) Taguchi orthogonal method was employed to analyze the influences of the replacement ratio of CCA for NLA, cementitious material content and water-to-binder ratio on the workability, compressive strength, splitting tensile strength, carbon dioxide equivalent (CO2-e) emission, energy consumption and cost of ASSC. Three standardized evaluation indexes and the Gray-Technique of Ordering Preferences by Similarity to Ideal Solution (TOPSIS) model were proposed to estimate the influence degree of each factor, and the suggested optimal mixture for ASSC was determined to be a replacement ratio of CCA for NLA of 50%, a cementitious material content of 440 kg/m3 and a water-to-binder ratio of 0.45. Then, the microstructure characteristics of the interfacial transition zone (ITZ) between the matrix and aggregate of ASSC for the optimal mixture were observed by scanning electron microscopy (SEM). It can be concluded that the main hydration products of ASSC had dense surface pores and internal pores of CCA, reducing the length, width and number of micro-cracks in ITZ. The substrate effect and micro-pump of CCA generate a high dense ITZ between the aggregate and matrix, which can inhibit the crack development of ASSC.