Brick Aggregate Concrete Research Articles

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.

Study on performance deterioration and life prediction of reed straw-recycled brick aggregate concrete after freeze-thaw cycle

The current rate of carbon dioxide emissions poses a significant threat to global climate, making it increasingly important and urgent to lead the carbon-intensive construction industry to achieve carbon neutrality. Currently, the most practical method involves reusing waste materials. In this study, waste red bricks were used to replace 75 % of natural aggregates in concrete, and three different forms of reed stalks (including reed straw ash, reed straw strips, and reed straw powder) were added to prepare the recycled reed straw brick aggregate concrete (RSAC). Freeze-thaw tests were carried out for 25, 50, 75, and 100 cycles in water and sodium sulfate solution to establish a freeze-thaw deterioration model and perform life prediction. The results showed that the degree of freeze-thaw deterioration of the specimens in sulfuric acid solution was small, and the degree of deterioration of reed powder concrete (RSAC-F) and reed ash concrete (RSAC-H) was more serious than reed strip concrete (RSAC-T) and additive-free concrete (RSAC-0). After 100 water freeze-thaw cycles, the strength losses of the specimens were 21.55 %, 21.7 %, 18.71 %, and 20.54 %, and the relative dynamic elastic modulus losses were 6.11 %, 7.25 %, 4.39 %, and 5.79 %, and the mass losses were 1.79 %, 2.04 %, 1.4 %, and 1.5 %. The fitting results showed that the predicted values of the parabolic model and two-parameter Weibull distribution damage model were closer to the experimental values, and the fitting rates are both greater than 90 %. The life prediction results show that the freeze-thaw resistance of the four types of reed-brick aggregate recycled concrete can reach more than 80 years in southern China, meeting the durability requirements, and the RSAC-T and RSAC-0 group concrete could also be used in projects with lower frost resistance requirements in the north region of China.

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.

EVALUATING THE STRUCTURAL EFFICACY OF ANGLE AND CHANNEL SHEAR CONNECTORS IN BRICK AGGREGATE CONCRETE AND STONE AGGREGATE CONCRETE AND COMPARISON

Composite structure is becoming prominent for its economy, less time consumption, and higher stiffness-mass ratio. Composite action of the steel-concrete composite structure mainly depends on the connector's geometry and materials. Proper choice of shear connector could make steel beam and concrete slab cross-section minimal. This study carries out push-out tests to evaluate the structural efficiency of channel and angle shear connectors in brick aggregate concrete and stone aggregate concrete. It specifically looks at the failure mode, ductility, load-slip behavior, and energy absorption capacity. In brick aggregate concrete, results show that under monotonic loading, channel connectors have been found to have 15.27% more shear capacity & 28.38% more slip than angle connectors. Similarly, in stone aggregate concrete, channel connectors have been found to have 14% more shear capacity & 12.97% higher slip than angle connectors. On average, stone aggregate concrete has been found to have 34.84% higher shear capacity and 6.7% greater slip than brick aggregate concrete. Strain energy and plastic energy were found 78% and 17.6% less in brick aggregate specimens than those in stone aggregate specimens, respectively. Experimental results were slightly lower for both shear connectors than the empirical values.

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.

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.

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.

Mechanical properties and microstructure of brick aggregate concrete with raw fly ash as a partial replacement of cement

In response to environmental concerns, researchers explore fly ash as a cement replacement material, and crushed bricks as a cost-effective and load-reducing aggregate, particularly where stone chips are scarce. Therefore, this study investigates the mechanical properties and microstructure of brick aggregate concrete (BAC) with raw fly ash (FA) as a partial replacement of cement. The research involved casting raw FA based BAC (FBAC) cylinders (100 mm diameter and 200 mm height) and prism (100 × 100 × 500 mm) with varying levels of FA (0–25%) using a constant mix proportion by volume of 1:1.5:3 (cement : fine aggregate : coarse aggregate) with a water to binder (w/b) ratio of 0.50 and three curing ages (7, 28, and 90 days). Tests for mechanical properties, including compressive strength, split tensile strength, flexural strength, modulus of elasticity, and Poisson's ratio were conducted to assess the behavior of FBAC, and microstructure were then investigated at 28 days. The results indicated that increasing the FA content up to 15% led to gradual improvement in compressive strength and tensile strength values. At 28 days, the highest values of compressive strength and split tensile strength were observed at 10% FA, with 7.9% and 14.2% increase, respectively, compared to the control concrete. However, the flexural strength of FBAC decreased gradually with cement replacement. On the other hand, modulus of elasticity and Poisson's ratio increased gradually up to 20% and 25% cement replacement, respectively. Up to 15% FA enhanced a more uniform and compact microstructure than that of control concrete. Several equations have been developed to express relationship between compressive strength and other mechanical properties of FBAC. Hence, up to 15% raw FA as a partial replacement of cement improved the mechanical properties and microstructure of BAC.

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.

Failure investigation of steel and brick aggregate concrete composite construction with angle and channel shear connectors

ABSTRACT This investigation focuses mainly on the failure behaviour and performance of angle and channel shear connectors in composite structures made with steel and brick aggregate concrete. It was observed that both angle and channel shear connectors did not fail themselves. However, in some specimens, localised connector yielding was observed in channel shear connectors. In both cases, concrete strata failed as either concrete crushing and shearing, combined splitting and bending, or complete splitting mode of failure. Crushing and shearing failure was noticed in specimens having smaller web and flange and were brittle in nature as compared to the failure of specimens with larger web and flange. Other parameters, such as shear resistance, energy absorption, and load-slip behaviour, were also investigated. Web height and flange width of both connectors significantly affected the ultimate shear capacity and slip of the brick aggregate concrete specimen. Channel connectors were found more flexible and carried more shear than angle connectors. Channel connectors had an average of 32.41% and 116.17% more ultimate load and slip capacity than the angle connectors in brick aggregate concrete, respectively. The load-carrying capacity, slip, and failure behaviour of the brick aggregate concrete were found similar to those of stone aggregate concrete.

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.

Study on the mechanical properties and microstructure of recycled brick aggregate concrete with waste fiber

Abstract Recycled concrete technology can promote the sustainable development of the construction industry, but the insufficient mechanical properties of recycled concrete have become a key constraint on its development. By adding waste fibers, the mechanical properties of recycled concrete can be improved, and the problem of disposing of waste polypropylene fibers can be solved. In this article, the effects of recycled brick aggregate content and waste fiber content on the mechanical properties and microstructures of recycled brick aggregate concrete through macroscopic mechanical experiments and microstructure experiments are investigated. The results show that the addition of recycled brick aggregate reduces the mechanical properties of concrete; when the content of recycled brick aggregate is 100%, the compressive strength and splitting tensile strength decrease by 22.04 and 20.00%, respectively. The addition of waste fibers can improve the mechanical properties of recycled brick aggregate concrete, but it is necessary to control the contents of waste fibers in a certain range. When the content of waste fibers is 0.08%, the best improvement effect on the mechanical properties of concrete is achieved; the compressive strength of concrete with a 50% (100%) recycled aggregate replacement rate increases by 6.06% (8.90%), while the splitting tensile strength of concrete with a 50% (100%) recycled aggregate replacement rate increases by 2.30% (6.16%). Through microstructural analysis, the mechanism by which waste fiber improves the mechanical properties of recycled brick aggregate concrete is revealed. The addition of waste fibers has the effect of strengthening the framework inside the recycled brick aggregate concrete, forming a good structural stress system and allowing the recycled brick aggregate concrete to continue to bear loads after cracking. In this study, waste brick aggregate and waste fiber are effectively utilized, which can not only reduce pollution to the environment but also realize the sustainable utilization of resources.

Review of Fracture Properties and Research Methods of Fiber Recycled Concrete

Aiming at the background of the application of fracture mechanics in fiber recycled concrete as well as the shortcomings of the current research, the relevant results and progress are summarized from three aspects, namely, the basic theory of fracture mechanics of fiber recycled concrete and the research progress of the fracture properties of fiber recycled concrete as well as the testing methods of the fracture of fiber recycled concrete, respectively. The development history of the application of fracture mechanics in concrete is described, three fracture forms, fracture process zones and three softening curve models of concrete are introduced, and it is proposed to combine the bilinear softening curve and the virtual crack zone model to construct the ontological relationship of the whole process of concrete cracking. The current research status of recycled brick aggregate concrete and polypropylene coarse fiber concrete is introduced. The incorporation of recycled brick aggregate adversely affects the workability, basic mechanical properties and fracture properties of concrete. The reinforcing effect of polypropylene fibers on concrete can effectively improve the adverse effects of brick aggregate on concrete, which opens up the research prospect of green concrete and has high research value. The applications of three-point bending test, four-point bending test and DIC technique in the study of concrete fracture characteristics are introduced.

Study on Seismic Performance of Concrete Columns and Beams Containing Recycled Brick Aggregate

In order to study the reinforced concrete beam and column components composed of natural concrete (NC), recycled aggregate concrete (RAC), recycled brick grain concrete (RBGC) and recycled brick aggregate concrete (RBC), the reinforced columns under the axial tension and compression cyclic load and the horizontal cyclic load and the simply supported beam under concentrated mid-span cyclic load are simulated respectively. The transient time history analysis is conducted to analyze their failure characteristics, hysteretic performance and energy dissipation performance. The results show that the damage of the column under horizontal cyclic loading is more obvious than that under vertical cyclic loading, and the energy dissipation is better, while the energy dissipation capacity of the beam is not as good as that of the column due to local concentration. The seismic performance of reinforced concrete columns and beams composed of RBGC and RBC materials is lower than that of NC and RAC materials. The materials of RBGC and RBC are more suitable for beam members.

Effect of polypropylene fiber and nano-silica on the compressive strength and frost resistance of recycled brick aggregate concrete

Abstracts Wasted clay bricks as coarse aggregate of recycled concrete is an effective solution to save energy and reduce CO2 emissions in the construction industry. However, the mechanical properties and frost resistance of recycled brick aggregate (RBA) concrete are inferior to those of ordinary concrete, which limits its widespread application. In this research, the effects of RBA, polypropylene fiber (PPF) and nano-silica (NS) on the mechanical properties and frost resistance of concrete were investigated. The effect of RBA, PPF, and NS on the compressive strength was quantitatively analyzed, and microstructural analysis and fractal dimension calculation of the concrete were performed. The results show that the concrete compressive strength decreased with the increase in RBA replacement rate, and it was effectively improved by adding PPF and NS (PPF-NS). The compressive strength first increased and then decreased with the increase in PPF and NS. The improvement effect of 0.12% PPF and 2% NS on the compressive strength of 50% replacement rate of RBA concrete was most effective. The gray relational degrees between the compressive strength and RBA, PPF, and NS were 0.6578, 0.8297, and 0.5941, respectively. The frost resistance of PPF-NS modified concrete was better than that of ordinary concrete, mainly manifested in its superior apparent phenomena, mass loss, and strength loss. Compared with normal concrete, the microstructure was denser and the fractal dimension of the cross-section was higher for RBA concrete modified with PPF-NS before and after freeze–thaw cycles.

Frost resistance and life prediction of recycled brick aggregate concrete with waste polypropylene fiber

Abstract Due to recycled aggregate concrete technology, sustainable resource utilization can be achieved, but the weak frost resistance of this type of concrete affects its application in cold regions. Using waste polypropylene fibers as reinforcing materials can improve the mechanical properties and durability of concrete. This study explores the influence of waste polypropylene fiber on the frost resistance durability and microstructure of recycled brick aggregate (RA) concrete. The results show that with the increase in freeze–thaw cycles, the mass of the concrete first increases and then decreases, while its relative dynamic elastic modulus and compressive strength gradually decrease. After 60 freeze–thaw cycles, the maximum mass loss, maximum relative dynamic elastic modulus loss, and maximum compressive strength loss of the RA concrete are 1.73, 45.1, and 73.7%, respectively. Waste fiber (WF) can improve the frost resistance of concrete, as demonstrated by the obvious reduction in mass loss, relative dynamic elasticity modulus loss, and compressive strength loss, which are 0.11, 33.0, and 64.0%, respectively, after 60 freeze–thaw cycles. The action mechanism of WF on the frost resistance of RA concrete is revealed, and the life prediction model of RA concrete with WF under freeze–thaw conditions is established.