Recycled Brick Aggregate Research Articles

Bond behavior of confined rebar in recycled brick aggregate concrete using bending pullout test

The pertinence of recycled brick aggregate (RBA) in concrete structures largely depends on their bonding ability with the rebars. Considering the practical detailing of concrete structures where main rebars are usually confined by stirrups, this study conducted bending pullout tests on 12 beam specimens to study the influence of concrete confinement on the bond behavior of rebar in RBA concrete. The investigated variables include RBA%, rebar diameter (d), embedment length (le), and the ratio of concrete cover to rebar diameter (c/d). Bond stress-slip relationships were acquired, analyzed, and average bond strengths were compared to the AS 3600, CEB-FIP codes, and existing MacGregor's model. The average bond strength of confined specimens was nearly double that of the unconfined specimens. A progressive increase in bond strength was noticed with the presence of RBA regardless of confinement. The confined specimens also exhibited higher deformability, ductility, and toughness values than those of the unconfined beams. At 15% RBA content, the maximum toughness value of the confined specimen was 3078.1 J, while the unconfined specimens reached a value of 278.1 J, only. Similarly, the ductility of the confined beam was found in a range of 1.21–1.60 whereas the value is only 1.04–1.10 for the unconfined cases. Moreover, the confined specimens exhibited a significant number of cracks during their failure, while the unconfined specimens experienced a split type brittle failure. Nevertheless, these findings may contribute to the further development of the bond behavior of rebar in RBA-based concrete structures and thus play a role in the sustainability of construction materials.

Mechanical Characteristics of Hardened Concrete with Different Types of Cement and Aggregate Available in Bangladesh

This paper presents the results of an investigation on the influence of aggregate and binding material type on the mechanical properties of hardened concrete. To perform this investigation, four different types of coarse aggregate (Brick Aggregate, Recycled Brick Aggregate, Black Stone and Shingles) and eight types of binding material [Ordinary Portland Cement (OPC), CEM Type II B-M, CEM Type II B-M-SL, 40% OPC – 60% Slag CEM IIIA, 80% OPC – 20% Slag(CEM II/A-S), 70% OPC – 30% Slag(CEM II/B-S), 30% OPC –70% Slag(CEM-IIIB), 15% OPC –85% Slag(CEM-IIIC)] have been used. Aggregates were collected and prepared according to grading requirements of ASTM C33-03. Several tests as specific gravity, absorption capacity, unit weight and abrasion resistance were performed for coarse aggregate. Cylindrical concrete specimens of diameter 100 mm and length 200 mm were made with different W/C ratio (0.45 and 0.5) and cement content (340 kg/m3 and 400 kg/m3). A total of 42 different cases were considered for testing. The specimens were tested for compressive strength, stress-strain curve and Young’s modulus at the age of 28 days. Non-destructive test as Ultrasonic Pulse Velocity (UPV) were also performed. To conduct UPV test Portable Ultrasonic Non-destructive Digital Indicating Tester (PUNDIT) were used. The major objective of this study was to investigate the mechanical characteristics of concrete for different types of aggregate and binding materials. The significance of those results is discussed here.

Ensemble machine learning models for compressive strength and elastic modulus of recycled brick aggregate concrete

This study delivers an in-depth analysis of predicting the compressive strength and elastic modulus of recycled brick aggregate concrete (RBAC). It assembles an extensive database of 633 compression test results and develops five ensemble learning models—random forest (RF), gradient boosting regression trees (GBRT), extreme gradient boosting (XGB), light gradient boosting machine (LGBM) and stacking (St). These models are evaluated against existing empirical formulas with respect to their effectiveness. The findings reveal that machine learning (ML) models outperform existing formulas: for compressive strength prediction, traditional models achieve a maximum determination coefficient R² of 0.38, whereas ML models attain an R² range of 0.91–0.94. For elastic modulus, the highest R² values are 0.44 for traditional models and 0.97 for ML models. Notably, the LGBM and St models excel in predicting compressive strength and elastic modulus, respectively. The study also identifies critical parameters influencing RBAC’s compressive behavior and highlights their impact trends. Remarkably, while the mass-weighted water absorption of coarse aggregates and the replacement ratio of recycled brick aggregates (RBAs) have less impact on compressive strength compared to the effective water-to-cement ratio, they become more influential for elastic modulus. Additionally, the decrease in elastic modulus due to higher RBA replacement ratios or increased mass-weighted water absorption of coarse aggregates exceeds the corresponding reduction in compressive strength. This research not only deepens the understanding of RBAC’s mechanical properties but also provides valuable predictive tools for civil engineering applications.

Reverse design for mixture proportions of recycled brick aggregate concrete using machine learning-based meta-heuristic algorithm: A multi-objective driven study

Construction and Demolition Wastes (CDW) have a significant impact on global waste streams. Brick waste stands out as a prominent type of CDW, and numerous studies have explored its recycling for the creation of environmentally-friendly concrete. Reverse design of recycled brick aggregate concrete (RBAC) mixture proportion is presented in this paper with a focus on four key objectives, that is: compressive strength, cost, and environmental elements (i.e., energy consumption and carbon emission). Based on compiled experimental datasets of 374 samples, the back propagation neural network (BP), random forest (RF), and four meta-heuristic algorithm optimization models were constructed to achieve the desired compressive strength objective. In all machine learning (ML) methods, the compressive strength of RBAC can be predicted with high accuracy, with the SSA-BP (optimized back propagation neural network model using the sparrow search algorithm) model achieving superior results (i.e., NSE=0.91, RPD=3.2). The SSA-BP is therefore used as the objective function for compressive strength. The economic objective is primarily influenced by material costs, and the objective functions of energy consumption and carbon emission are determined by various aspects of production, transportation, and their mixing processes. In order to obtain the optimal RBAC design, the Non-Dominated Sorting Genetic Algorithm (NSGA-III) was implemented considering imperative constraints. Results indicate that cement amount and recycled brick aggregate (RBA)-to-natural aggregate proportion have a positive impact on the compressive strength. The suggested design framework allows for the creation of RBAC composite designs with varying levels of RBA substitution rates and strength targets, providing valuable guidance for tackling the CDW challenge and optimizing RBA usage.

Bond behavior between geopolymer recycled brick aggregate concrete and steel bars after exposure to high temperatures

The use of recycled brick aggregate (RBA) as the replacement for natural coarse aggregate in geopolymer concrete is an effective method for waste recycling. When the formed geopolymer recycled brick aggregate concrete (GRBC) is employed in structures, it may encounter the risk of fire. Whether the steel bars and GRBC can work together after a fire is the basis for structural safety and analysis. However, previous research on the bond behavior between GRBC and steel bars after exposure to high temperatures is still lacking. In this paper, pull-out tests on 50 GRBC and 50 ordinary recycled brick aggregate concrete (ORBC) were conducted to investigate the effects of temperature (20 °C, 200 °C, 400 °C, 600 °C, and 800 °C), and RBA replacement ratio (0 %, 25 %, 50 %, 75 %, and 100 %). The test results show that the failure pattern of GRBC specimens changes from splitting-pull-out failure to pull-out failure as the heating temperature increases. The bond strength decreases with the increase of temperature or RBA replacement ratio. When the temperature rises from 200 °C to 800 °C, the bond strength of GRBC pull-out specimens decreases by 11.54 %–72.33 % compared with the specimens at room temperature, and the decrease rate is lower than that of ORBC. The bond strength of GRBC specimens with a 100 % replacement ratio decreases by 46.34 %–53.74 % compared with those without replacement. The peak slip of GRBC specimens generally increases with increasing temperature or decreasing RBA replacement ratio. Based on the post-temperature test results and the room temperature model, suitable models for the bond strength and peak slip of GRBC after high temperatures were established. The predicted results of bond stress−relative slip curves were in good agreement with the test results. The findings of this study can provide a foundation for the application of GRBC, and provide a basis for its structural analysis after high temperatures.

Enhancing energy dissipation in mortar utilizing recycled brick fine aggregate impregnated with polymer emulsion under uniaxial cyclic load

Optimizing the damping properties of materials can enhance the energy dissipation capacity of structures and mitigate the negative effects of dynamic loads on building components. This study investigated the effects of the polymer emulsion-impregnated recycled brick fine aggregate (PRBFA) replacement rate, emulsion-impregnation treatment method, and emulsion solid content on the dynamic damping properties of PRBFA-prepared mortar (PBM). Combined with microscopic tests, the enhanced damping mechanism of PBM was discussed. The results show that under the same stress amplitude, the equivalent damping ratio and loss modulus of PBM increase with the PRBFA replacement rate and emulsion solid content. The drying treatment of PRBFA demonstrates superior damping characteristics of PBM, with the equivalent damping ratio and loss modulus increased by 84.9%–129.4 % and 71.0%–117.2 %, respectively, compared to those of PBM with undried PRBFA. The damping enhancement of PBM is attributed to the weak interface between the aggregate and cement matrix, which facilitates slippage and friction. The damping layer formed between the high viscoelastic emulsion and the aggregate, or between the emulsion and the cement matrix, is conducive to energy dissipation. The optimal PRBFA replacement rate for balancing the mechanical and damping properties of PBM is between 38% and 60 %.

Strength and microstructure of geopolymer recycled brick aggregate concrete after high temperatures

Geopolymer recycled brick aggregate concrete (GRBC), as a new environmentally friendly material, exhibits excellent mechanical performance at ambient temperature, but its properties after exposure to high temperatures are not clear. In this paper, the strength and microstructure of GRBC after high temperatures were investigated and compared with ordinary recycled brick aggregate Portland cement concrete (ORBC) through compressive strength, splitting tensile strength, and microscopic tests. The main parameters varied in the strength tests were temperature (20 °C, 200 °C, 400 °C, 600 °C, and 800 °C) and recycled brick aggregate (RBA) replacement ratio (0 %, 25 %, 50 %, 75 %, and 100 %). The results indicated that the strength of GRBC decreased less than that of ORBC after high temperatures. The compressive strength retention rate of GRBC after exposure to 800 °C was 0.359−0.456, and the tensile strength retention rate was 0.415−0.442. The strength of GRBC with 50 % RBA replacement ratio was about 0.70 that of the case without RBAs. The microscopic test results showed that the structure of GRBC was denser than that of ORBC, and the interfacial transition zone (ITZ) between matrix and RBAs was less affected by the temperature. The first weak zone after high temperatures was RBA itself for GRBC, but ITZ between matrix and RBAs for ORBC. The X-ray diffraction analysis indicated that the phase composition of GRBC and ORBC after high temperatures was basically similar to that at ambient temperature. The strength of GRBC was mainly provided by the N-A-S-H and C-A-S-H gels, while the strength of ORBC was mainly relied on the C-S-H gel.

Comparative analysis of ternary blended cement with clay and engineering brick aggregate for high-performance 3D printing

Utilising recycled brick aggregate in cementitious mixtures can decrease the overdependency on limited natural resources and improve the sustainability of concrete. This paper presents a potential solution to lower the amount of waste being landfilled and increase the sustainability of 3D concrete printing technology by combining low-carbon ternary blended cement with recycled aggregates. Hence, the effect of incorporating two types of recycled brick aggregate - clay brick (CBA) and engineering brick (EBA) on the properties of 3D printable ternary blended cement were investigated. The natural aggregate in a pre-existing 3D printable blend was substituted by up to 50 wt.-% with two varieties of recycled brick aggregates available throughout Europe. The recycled brick aggregates underwent characterisation to determine their properties. The fresh property evaluation using the green strength test was used to assess the effect of aggregate replacements on the mixture's shape stability. The mechanical performance of mixtures containing CBA and EBA, both cast and 3D printable mixes, was evaluated and compared to that of the control sample. The results indicated that incorporating recycled brick aggregate enhances green strength and Young's modulus significantly. Mechanical strength performance showed significant enhancement when incorporating RBA, which reached up to 67% and 55% for both cast and 3D printing methods, respectively. The suitability of the developed mix formulations for 3D printing was assessed by printing cylindrical objects.

Investigation of Axial Tensile Fracture Performance of Recycled Brick Coarse Aggregate Concrete Using a Cohesion Model.

Currently, microscopic research on the tensile fracture properties of recycled brick coarse aggregate concrete has mainly adopted microscopy techniques, which can clearly observe the actual damage situations of each phase material but are unable to individually analyze the effect of a specific material factor on the tensile properties of recycled concrete. This brings much uncertainty to the practical application of recycled concrete. Therefore, this study proposes a cohesive zone model (CZM) for simulating the tensile fracture of recycled brick coarse aggregate (RBCA) concrete. To this end, the study explores the effects of various critical factors on the fracture mode and bearing capacity of recycled brick aggregate concrete, including the replacement rate of recycled brick coarse aggregate, pore structure, interfacial transition zone (ITZ) strength, mortar strength, and volume fraction of brick aggregate. The results indicate that, when the minor to major axis ratio of elliptical pores is 0.5 ≤ K < 1, the following order of influence can be observed: random convex polygonal pores, circular pores, and elliptical pores. Moreover, excessively strengthening the ITZ and mortar does not significantly enhance the tensile performance of RBCA concrete. The distribution location of aggregate has a significant impact on the crack shape of recycled concrete, as does the pore structure, due to their randomness. Therefore, this article also discusses these. These findings contribute to a comprehensive understanding of the tensile properties of recycled brick coarse aggregate and provide insights into optimizing its behavior.

Study on the mechanical properties of recycled brick coarse aggregate concrete based on finite element modeling

In recent years, the use of recycled materials in concrete production has garnered significant attention due to their environmental and economic benefits. To promote the application of recycled aggregates, this study focuses on investigating the utilization of Recycled Brick Coarse Aggregate (RBCA) as a substitute for natural aggregate. This paper presents the development of stochastic convex polygonal RBCA through the utilization of a custom-programmed algorithm and proposes a finite element model designed to simulate the behavior of RBCA concrete under compression and splitting tensile. Numerical simulations were conducted to investigate the effects of brick aggregate Replacement Rate (RR) and porosity on the compressive and splitting tensile properties of RBCA concrete. A strong correlation was found between the Concrete Damage Plasticity (CDP) model developed in this study and experimental results, indicating high reliability. The results indicate that the replacement rate of brick aggregates has a more significant impact on the compressive strength than on the splitting tensile strength of concrete. Furthermore, the distribution of coarse aggregates and pores has a minor influence on the mechanical properties and ultimate failure mode of RBCA concrete but significantly affects the crack distribution pattern. The sequence of damage initiation in RBCA concrete was found to be: pores, old Interfacial Transition Zone (ITZ), old mortar, new ITZ, new mortar, RBCA, and Natural Coarse Aggregate (NCA). These findings contribute to a comprehensive understanding of RBCA's performance and offer valuable insights for optimizing its behavior.

Fabrication and characterization of recycled construction waste bricks modified with sisal fibers

The study presents an investigation into the preparation and characterization of modified hemp fiber reinforced recycled construction waste bricks for ground and road applications. By incorporating 1 % hemp fiber and a 70/30 ratio of recycled concrete aggregate to recycled brick aggregate, the optimal combination was identified, resulting in a maximum compressive strength of 36.2 MPa, a 38.7 % improvement over the control bricks. The addition of 2 % hemp fiber increased the flexural strength by 85.7 %, while the thermal conductivity decreased by 41.5 % with the inclusion of 2 % hemp fiber and 100 % recycled brick aggregate. Scanning electron microscopy and X-ray diffraction analysis confirmed the compatibility of hemp fibers with the cement matrix and their role in enhancing the microstructure of the bricks and hydration process. These findings highlight the potential of hemp fiber-reinforced recycled waste bricks as environmentally friendly high-performance materials for sustainable ground and road construction.

Mechanical Damage and Freeze–Thaw Damage of Concrete with Recycled Brick Coarse Aggregate

The influence of different recycled brick coarse aggregate (RBA) substitution rates on the mechanical performance and frost resistance of concrete was observed. The test findings revealed that RBA deteriorated the compressive and flexural properties in concrete and improved the tensile properties and plasticity in concrete to some extent. The frost resistance of concrete can be effectively improved by adding RBA. The influence degree of the RBA concrete frost resistance factor was quantified by gray entropy correlation theory, and the gray entropy correlations between freezing and thawing cycles, natural coarse aggregate substitution rate, recycled brick aggregate substitution rate, and freezing and thawing damage value (DN) were 0.9979, 0.9914, and 0.9876, respectively. Moreover, the freezing and thawing damage model about GM(1, 1) theory was developed (R2 &gt; 0.87), which can better predict the freezing and thawing damage of RBA concrete. The damage mechanism of RBA concrete during freezing and thawing was revealed.

Study of recycled concrete properties and prediction using machine learning methods

This paper is divided into two parts, with the first part examining the influence of recycled brick aggregate (BA) ratios on physical properties of blended coarse aggregate (BNA). These properties include apparent density (SSD), water absorption (WA), and crushing value (CV). The compressive strength of recycled concrete (RAC) prepared with BNA was tested. The tested results show that when SSD decreases from 2700 kg/m3 to 2000 kg/m3, the compressive strength of the corresponding RAC decreases by 40.5 %. Moreover, when the WA increases from 5 % to 10 %, the compressive strength of the concrete decreases by 15.9 %. Furthermore, as the CV rises from 9 % to 37 %, the compressive strength of the concrete decreases by 38.4 %. And the second part explores the application of machine learning models to predict the concrete compressive strength, incorporating parameters such as BA replacement rate, SSD, WA, CV, water-to-cement ratio (W/C), and blended coarse aggregate to cement ratio (BNA/C). To improve model accuracy, we integrated data from our own experimental tests with an additional 128 datasets sourced from literature, resulting in a combined dataset of 133 entries for training and testing the machine learning models. Three machine learning models were proposed and compared: the BP neural network, GA-optimized BP (GA-BP) neural network, and convolutional neural network (CNN) model. Compared to the other two models, the CNN model exhibits the highest prediction accuracy and generalization ability, as evidence by its training accuracy of 0.969 and test accuracy of 0.927. The CNN model proved capable of facilitating intelligent RAC mix design in engineering applications. A case study was presented to illustrate the utilization of the CNN model in predicting the W/C and BNA/C ratios for 11 different BA ratios, ensuring the targeted RAC strength is achieved with specific type of BNA.

Compression and Splitting Tensile Strength Model of Recycled Seawater and Sea Sand Concrete after Seawater Freeze–Thaw Cycles

Using seawater, sea sand, and recycled bricks to make concrete for nearshore and marine engineering can save resources and protect the environment. Therefore, this article studies the mechanical degradation law and failure mechanism of recycled seawater and sea sand concrete (SSC) after seawater freeze–thaw (SFT) cycles. Using the replacement rate of recycled brick coarse aggregate as a variable, the mass loss rate, relative dynamic elastic modulus, compression and splitting tensile strength, and microstructure changes of specimens under different SFT cycles were tested, and a mechanical performance degradation model was established. The results indicate that the SFT failure of recycled brick coarse aggregate SSC results from the action of physical SFT and chemical crystallization. Friedel’s salts without cementitious properties and ettringite with expansive properties are generated inside the concrete due to the chloride and sulfate ions in the internal concrete and external seawater reacting with cement hydration products. The formation of harmful crystals leads to the loosening of the concrete, especially in the interface area between brick aggregates and cement. The calculated results of the mechanical model established in this article agree with the test results. The compression and splitting tensile strength decrease linearly with the increase in SFT cycles.

Bond behavior of deformed rebar in concrete containing recycled brick aggregate and waste rubber

The reuse of aggregates and crumb rubber (CR) in concrete is gaining interest globally for reducing the adverse effects on the environment and maintaining construction sustainability. The bond strength of reinforcing rebars in such concrete is one of the key issues to be addressed before their practical application, particularly in structural elements. Pull-out tests were performed on 80 specimens to assess the bond performance of deformed rebars in rubberized recycled brick aggregate concrete (RRBAC). After investigating the strength properties of RRBAC, pull-out tests were performed on two sizes of cylindrical specimens. RBA%, CR%, rebar diameter (d), embedment length (le), and concrete cover-to-rebar diameter ratio (c/d) were among the test variables in this bond behavior investigation. Bond stress-slip relationships were obtained, examined, and average bond strengths were compared with the available codes. Concrete split failure was observed in 79% of the tested specimens, whereas rebar fracture was not seen in any of the tests. The bond strength was found to be decreased with the inclusion of RBAs and CRs though relative improvement was observed for higher percentage RBAs. Additionally, regression analysis was performed on the experimental data to produce a closed-form equation for forecasting the bond strength for RRBAC. With a strong coefficient of determination (R2 = 0.97) and low values of error terms, the predicted bond strengths were seen to be a good agreement with the test results.

Preliminary investigation and life cycle assessment of artificial reefs with recycled brick-concrete aggregates

An economical and environment-friendly artificial reef concrete using fully recycled brick-concrete aggregate as raw material was proposed. This study investigates the mechanical properties, drying shrinkage, chloride ion penetration, and biological adaptability of the reef. A comparative analysis is conducted on the environmental impacts (EI), carbon emission impact and cost efficiency of artificial reefs, considering natural aggregate concrete and recycled brick-concrete aggregate concrete at the material level. The results indicate that the use of recycled brick-concrete aggregates can achieve service performance equivalent to that of natural aggregates. Field investigations involving samples immersed in seawater for six months reveal the positive trapping effects of recycled materials on aquatic organisms. The Life Cycle Assessment (LCA) results reveal that achieving a 100 % replacement rate of recycled brick concrete aggregate (RBCA) creates a positive feedback loop for carbon emissions when appropriately incorporating industrial waste materials like fly ash and silica fume. In comparison to ordinary concrete, the utilization of recycled materials can significantly reduce construction costs, up to 63.7 %, thereby presenting notable economic advantages.

Strengthening Effect of Nano-materials on the Compressive Strength and Microstructure of Recycled Brick Aggregate Concrete

To investigate the strengthening effect of different nano-materials on recycled brick aggregate concrete, this paper considered the influence of different nano-materials, different mixing amounts, and different mixing methods on the compressive strength and microstructure of recycled brick aggregate concrete. The results show that the 7-day, 14-day, and 28-day compressive strengths of recycled brick aggregate concrete increase to different degrees after adding nano-materials, but the improvement in early compressive strength is more obvious. The cubic compressive strength prediction model of three nanomaterial-reinforced recycled brick aggregate concretes is established using the compressive strength as the index. The optimum contents of nano-SiO2, nano-CaCO3, and nano-Al2O3 are 3 %, 2 %, and 3 %, respectively. Double-mixed nano-materials have a lower improvement effect on the compressive strength of recycled brick aggregate concrete at different ages than single-mixed nano-materials. The nanomaterials can not only promote the hydration reaction of cement but also fill the microcracks and micropores inside the concrete, making the structure denser and thereby improving the mechanical properties of recycled brick aggregate concrete. The 28-day compressive strength of recycled aggregate modified with nano-materials (nano-SiO2 and nano-Al2O3) concrete is higher than that of recycled aggregate concrete mixed with nano-materials. The early compressive strength of recycled aggregate modified with nano-Al2O3 concrete is lower than that of recycled aggregate concrete mixed with nano-Al2O3.

Optimal utilization of low-quality construction waste and industrial byproducts in sustainable recycled concrete

Construction and demolition waste (CDW) contains abundant low-quality recycled brick aggregates (RBA) that can potentially substitute natural aggregates (NA) in concrete production. However, recycled brick aggregate concrete (RBAC) shows inferior mechanical and durability performance compared to natural aggregate concrete (NAC), posing barriers to RBAC widespread adoption. This study investigates the combined influence of supplementary cementitious materials (SCMs) derived from industrial byproducts and hooked-end steel fibers (HSF) on properties of concrete with 0%, 50% and 100% RBAs from CDW as replacement for natural coarse aggregates (NCA). Addition of 0.5% HSF and 20%, 10%, and 30% fly ash (FA), silica fume (SF), and ground granulated blast furnace slag (GGBS) as cement replacement, respectively, were considered. Effect of different SCMs and HSF on compressive strength, splitting tensile strength, flexural strength, ultrasonic pulse velocity (UPV), water absorption (WA), freeze-thaw (FT) and acid attack resistance of concrete were studied. Results indicated that individual incorporation of HSF showed more contribution towards mechanical performance while combined incorporation of SCMs and HSF enhanced both mechanical and durability properties, along with reduction of up to 15.6% in embodied carbon of RBAC. Microstructural examination showed pore refinement and interfacial transition zone densification in RBAC with SCMs and HSF. This study demonstrates that sustainable RBAC with excellent mechanical and durability requirements could be produced using demolished brick waste and industrial byproducts.

Characterizations and quantification of freeze-thaw behaviors of recycled brick aggregate concrete

The use of recycled brick aggregates (RBAs) in concrete could provide sustainable solution in construction industry by reducing the consumption of natural resources and protecting the environment by saving landfill sites. However, the use of RBAs is uncommon due to limited available research studies investigating its mechanical and durability behavior, especially the freeze-thaw (FT) behavior. Despite a few studies on FT resistance of RBA concrete (RBAC), the FT deterioration mechanism in RBAC is not fully understood, particularly at the microscale. This lack of understanding hinders the widespread adoption of RBAC in sustainable construction practices, particularly in cold regions. Therefore, this study investigates the FT deterioration mechanism in RBAC using macro and microscale experiments and proposes a Weibull damage model to accurately describe the damage variation in RBAC. RBAC specimens with different water-cement (w/c) ratios of 0.65, 0.5 and 0.35 and RBA replacement levels of 0%, 25%, 50% and 100% were produced and tested under rapid FT cycles. Surface scaling, mass loss, relative dynamic modulus of elasticity, and compressive strength reduction were evaluated. X-ray computed tomography (XCT) was used to characterize pore structure and microcracking alterations during FT cycles. The results showed that the deterioration of RBAC increased with the increase in RBA replacement level. XCT revealed increased porosity and microcracking within the RBA particles, which was linked to the significant damage observed in RBAC compared to reference concrete. Quantitative analysis of pore size distribution before and after FT cycling revealed a substantial increase in small pores (<1 mm3) in RBAC. The proposed Weibull distribution damage model accurately described the damage variation in RBAC with different w/c ratios. This study provides new insights into multiscale FT deterioration mechanisms affecting RBAC, aiding in optimizing RBAC mix designs to balance sustainability and durability.

Study on Mechanical Properties and Microscopic Mechanism of PVA-Modified Recycled Brick Aggregate Concrete

This paper addresses a range of environmental issues stemming from the improper disposal of construction waste and its low recycling rate by examining the effects and mechanisms of polyvinyl alcohol (PVA) solution in modifying recycled aggregates. Basic physical properties, energy-dispersive spectroscopy (EDS), X-Ray diffraction (XRD), and scanning electron microscopy (SEM) were employed to study these effects and mechanisms. Tests on basic mechanical properties were performed to assess the impact of aggregate modification and the brick-concrete ratio on recycled brick-aggregate concrete’s mechanical characteristics. Nuclear magnetic resonance and microhardness tests were performed to analyze the influence exerted by PVA modification on the interfacial transition zone (ITZ), microstructure, and pore structure, thus exploring the connection between modified recycled-brick-aggregate concrete’s microstructure and its icromechanical properties. The findings show that the water absorption and crushing index of recycled aggregates (RA) immersed in a 10% PVA solution for 24 h decrease significantly, while the apparent density increases most notably. This phenomenon can be ascribed to the development of a PVA coating on the exterior of the reused aggregates. The optimal mechanical properties for recycled brick aggregate concrete (RAC) occur when the replacement rate is 30% and the brick-concrete ratio is 1:1. The compressive strength is 44.2 MPa, the bending strength is 15.6 MPa, and the splitting tensile strength is 3.85 MPa. Additionally, the modification with PVA results in a higher percentage of transition pores, while simultaneously reducing the percentage of macropores. There is an uptick in the frequency of harmless and less harmful pores, and a declining proportion of harmful and more harmful pores. The ITZ’s structural morphology in the RAC is effectively improved by the coating structure formed through the bonding of the polymer with cement hydration products, and PVA modification reduces the thickness of this zone.