Recycled Aggregate Content Research Articles

Sulfate activation of wheat straw ash to enhance the properties of high-performance concrete with recycled aggregates and waste tire steel fibers.

A sustainable alternative to conventional concrete involves using recycled aggregates (RA) instead of natural aggregates (NA) and incorporating wheat straw ash (WSA) as a partial replacement for Portland cement. The demand for high-performance concrete (HPC) is rising due to the need for architecturally complex structures and long-span bridges, but HPC's low ductility necessitates reinforcement. Waste tire steel fibers (WTSFs) are gaining popularity for their tensile strength. However, WSA-RA concrete's low early strength is a challenge. Chemical activators like sodium sulfate can enhance early-age strength. This study evaluated the durability and strength of fiber-reinforced concrete with both inactivated and activated WSA. Tests included compressive strength, indirect tensile strength, modulus of rupture (MOR), acid attack resistance, chloride penetration, sorptivity, and water absorption. Activated WSA-RA concrete showed significantly improved early strength. The mixture with 30% RA, 40% WSA, WTSFs, and activator exhibited the highest strength at 90 days. At 60% RA content, activated concrete with 40% WSA and 2.5% WTSFs outperformed the control. Durability was enhanced with a 14-17% reduction in water absorption and sorptivity and a 25.2% decrease in chloride penetration. Acid resistance improved by 26%. X-ray diffraction (XRD) confirmed these findings with elevated hydration product peaks. This study demonstrates that chemical activation of WSA optimizes the engineering properties of WSA-modified HPC with WTSFs and RA, providing a sustainable solution to their challenges.

Examining the Influence of Recycled Aggregates on the Fresh and Mechanical Characteristics of High-Strength Concrete: A Comprehensive Review

This review examines the impact of recycled aggregates (RAs) on the fresh and mechanical properties of high-strength concrete (HSC). The results revealed that incorporating RAs can reduce the compressive strength of HSC by up to 25%, with strength values ranging from 40 to 70 MPa depending on the RA content. The addition of supplementary materials like silica fume, fly ash, and polycarboxylate ether significantly mitigated these negative effects, enhancing the compressive strength by approximately 15–20% compared with the control mixes without additives. Furthermore, the tensile strength was observed to decrease by up to 18% with increasing RA content, but fiber reinforcement improved this by 10%, demonstrating the potential of additives to offset mechanical weaknesses. The modulus of elasticity also declined by up to 30% with higher RA dosages, highlighting the critical impact of the adhered mortar quality on the overall stiffness of the concrete. According to the literature, it was noticed that, when the dosage of RCAs is increased, there is a drop in the strength activity index (SAI). When the substitute dosage exceeded 50%, the SAI decreased. These findings underscore the importance of using optimized additive combinations to improve the mechanical performance of RA concrete, making it a viable option for sustainable construction. Overall, the findings suggest that, although RAs may negatively affect certain physical traits of HSC, the use of appropriate additives can optimize its performance, making it a viable option for sustainable construction practices.

Tension stiffening and cracking behaviors in glass fiber reinforced polymer bar enhanced precast recycled aggregate concrete specimen

Glass fiber reinforced polymer (GFRP) bar-enhanced precast recycled aggregate concrete (PRAC) elements combine PRAC’s environmental benefits with GFRP’s corrosion resistance, making them ideal for coastal urban infrastructure. However, in-depth research on the tensile stiffness and cracking behaviors of this composite is lacking. The significant mechanical differences between GFRP bars (low modulus, high strength) and PRAC, as compared to traditional materials, raise safety concerns for widespread use. This study investigates the short-term load capacity, deformation and cracking characteristics of GFRP bar-reinforced PRAC tensile specimens through tests and analyses. The tests examine how variables like water-to-binder ratio, coarse aggregate type, recycled aggregate (RA) content and mixing methods affect the specimens' mechanical responses. Theoretical analyses, using existing equations and a partial interaction model, clarify stress-strain relationships and crack propagation under applied loads, revealing: (a) As RA content increases, PRAC shows a moderate decrease in workability and mechanical performance. The strength variability in PRAC generally falls between that of natural aggregate concrete (NAC) and conventional recycled aggregate concrete (CRAC) using RAs from construction and demolition waste, being closer to NAC. Additionally, the strength conversion relation seen in NAC applies similarly to PRAC. (b) During tension at both ends of the specimen, PRAC's resistance decreases by 24.3 % compared to NAC but is still 20.3 % higher than CRAC. (c) The number of cracks in the PRAC specimen decreases with higher RA content and basalt fibers, while the ratio of stabilized load to cracking load increases. (d) The CEB-FIP standard offers more accurate predictions of the specimen’s composite stress-strain relation, while the Chinese code excels in predicting crack width. The partial interaction model effectively predicts the specimen’s load, deformation and crack characteristics by accounting for the behaviors and bonding of both PRAC and GFRP bars.

Optimizing foaming agent concentration and recycled fine aggregate content to enhance mechanical and durable properties of foam concrete mixes

This research explores the impact of using recycled fine aggregates from construction and demolition wastes (CD-RFA) through the replacement of natural sand in proportion of 0 %, 10 %, 30 %, 50 %, 70 %, and 100 % for making foam concrete mixes. Protein based foaming agent was diluted with water in ratios of 1:20, 1:40 and 1:60. It was found that with the increase in the proportion of recycled fines, the porosity, sorptivity and water absorption of foam concrete mixes increases significantly. At the same time, a downward trend in the mechanical characteristics was noted. However, the obtained values of compressive strength, flexural strength, and split tensile strength of 22.35, 5.68 and 2.27 MPa were found to be well within the ACI 523 R 2014 recommended ranges of 8–22, 3–6.4 and 1–2.2 MPa, respectively. Hardened density, abrasion resistance, and resistance to sulphates and chlorides attack showed perceptible decline. The present study recommends the replacement of natural sand up to 50 % with CD-RFA. The foam concrete mix prepared using recycled fines will help clearance of a large quantities of CD wastes, thereby benefiting the environment and ecology.

Influence of aggregate size on pervious concrete properties with and without construction and demolition waste

This research evaluates the impact of aggregate sizes on pervious concrete properties, comparing aggregates of 12.5 mm and 19 mm, as well as replacing natural aggregates with recycled aggregates set at 0% and 50%. Four types of pervious concrete were produced, and their properties were determined: density, porosity, permeability coefficient, compressive strength, flexural tensile strength, and abrasion resistance. The results indicate that water permeability is directly related to pore size and is influenced by aggregate size (90% of the variation in pervious concrete permeability) and, to a lesser extent, by recycled aggregate content (10% of the variation). Mixes with larger aggregates (19 mm) demonstrated higher permeability coefficients. Replacing natural aggregates with recycled aggregate did not significantly affect the mechanical properties of pervious concrete, highlighting the effectiveness of waste processing and mixing procedures, allowing for the incorporation of 50% of recycled aggregate. The concretes met the requirements of the American Concrete Institute, suggesting technically feasible conditions for sustainable practices in the construction industry.

Experimental Study of Recycled Concrete under Freeze-Thaw Conditions.

Recycled concrete is a new and environmentally friendly material for future construction. When applying recycled concrete to cold and severe regions, it is necessary to consider the freeze-thaw resistance of recycled concrete. Using an indoor freeze-thaw cycle test system, the rapid freezing method was used to conduct rapid freeze-thaw tests on recycled concrete specimens under set freeze-thaw cycle conditions. Relevant parameters (such as compressive strength, quality loss rate, rebound value) were tested on recycled concrete specimens that completed the set number of freeze-thaw cycles. The influence of various factors (freeze-thaw cycle number, replacement rate of recycled aggregates) on the compressive strength, quality loss rate, and rebound value of recycled concrete was analyzed. The results indicate that with the increase of freeze-thaw cycles and recycled aggregate content, the workability, rebound value, and compressive strength of the specimens decrease, and the quality loss rate increases. The changes in workability of concrete are sharp, with a slump difference of 21 mm between concrete with 100% recycled coarse aggregate and concrete using natural coarse aggregate. The rebound value of the specimen shows a decreasing trend overall, but the rebound value varies for different measuring points on the same specimen. The attenuation of compressive strength is significant. When fully using recycled aggregates to prepare concrete, the compressive strength after 30 freeze-thaw cycles decreases by 49.42% compared to the compressive strength after 0 freeze-thaw cycles. The overall quality loss rate shows a decreasing trend, but the quality loss is not severe.

Experimental investigation on mechanical properties of fiber recycled concrete filled-square steel tube columns under pure flexural based on acoustic emission technique

Currently, global countries are actively focusing on carbon emission reduction. Utilizing recycled aggregate concrete (RAC) is expected to realize global carbon neutrality objectives. However, due to its inherent mechanical limitations, its application in structural contexts is restricted. This study aimed to enhance the mechanical attributes of RAC and expand its utility beyond low-strength applications. By employing recycled aggregates, steel fibers, and ordinary Portland cement, a novel eco-friendly composite filler was developed for steel- tube filling. A comprehensive study on 16 concrete mix ratios and 23 steel-tube recycled concrete columns was conducted. The parameters included the recycled aggregate volume, steel fiber content, and steel pipe thickness. The results revealed that reasonable mix design enabled RAC to exhibit flexural performance similar to that of conventional steel-tube concrete. Moreover, while increasing the recycled aggregate content deteriorated the overall mechanical properties, incorporating steel fibers extended the elastic stage and enhanced the flexural characteristics. Optimal results were achieved with 1.2 % steel fiber addition and 75 % recycled aggregate. The comparison between the derived equation and the experimental data demonstrated a high level of agreement, confirming the accuracy of the equation. Furthermore, acoustic emission technology was employed in this experiment to monitor the failure progression of steel tube recycled concrete columns subjected to a pure bending load. The findings revealed a triphasic failure process: elastic, elastic-plastic, and strengthening stages. The analysis demonstrated a consistent correlation between acoustic emission parameters and waveform characteristics with the failure process of the specimen. Empirical evidence demonstrated the efficacy of acoustic emission technology in effectively monitoring the damage severity and failure chronology in recycled concrete steel pipe columns during bending.

Experimental study and analytical modeling of tensile performance of ultra-high-performance concrete incorporating modified recycled aggregates

Incorporating recycled aggregates (RA) into Ultra-High-Performance Concrete (UHPC) is pivotal for the sustainable development of high-performance construction materials. This study investigates the enhancement of RA through two methods: low-concentration acid treatment and sodium silicate treatment, focusing on improving physical properties and microstructural integrity. Experimental designs encompassed varying types of modified RA (URA, T1RA, T2RA), RA replacement rates (0%, 25%, 50%, 100%), and two steel fiber shapes (SSF and HSF), resulting in twenty-one distinct axial tensile specimen formulations. The study reveals substantial improvements in modified RA's physical properties, effectively mitigating internal microcracks and pores. Modified RA significantly bolstered UHPC-RA's tensile strength, notably when chemically strengthened, underscoring its efficacy in enhancing RA quality. However, escalating RA content correlated with diminished mechanical indices like tensile strength and toughness, attributed to reduced specimen quality. Digital Image Correlation (DIC) accurately forecasted crack locations, highlighting the minimal influence of modified RA and fiber bridging on specimen failure modes. A comprehensive theoretical model incorporating RA deterioration and hooked steel fiber anchorage predicted tensile behaviour, offering vital insights for designing UHPC-RA systems.

Elucidating the role of recycled concrete aggregate in ductile engineered geopolymer composites: Effects of recycled concrete aggregate content and size

Utilizing recycled fine aggregate (RFA) as silica sand replacement for ductile engineered geopolymer composites (EGC) provides a high value-added approach to recycling concrete waste and reduces the needs for high-cost silica sand. RFA contains abundant active alkaline substances which can promote the secondary geopolymerization of EGC. Substituting RFA for silica sand can improve EGC micro-characteristics, and the micro-structure of RFA-EGC is further refined with the decreased RFA size. The compressive/flexural strength of EGC is elevated as RFA is incorporated, and the decreased RFA size further enhances the compressive/flexural strength of RFA-EGC. Attributed to the micro-pores and micro-cracks in RFA, including RFA benefits the formation and development of crack, leading to an enhancement in the uniaxial tensile behavior of EGC. The tensile strength and tensile strain capacity of 100 % RFA blended EGC are 5.7 % and 8.6 % higher than those of 100 % silica sand blended EGC. The decreased RFA size can enhance the tensile strength, and an appropriate increase in RFA size improves the tensile strain capacity of RFA-EGC. When RFA size is 0.15–0.3 mm and 0.3–0.6 mm, the tensile strain capacity of 100 % RFA blended EGC is 8.6 % and 12.9 % larger than the reference EGC with 100 % silica sand (0.15–0.3 mm). A moderate increase in silicate modulus can further improve the tensile behavior, and the RFA-EGC with 1.5 M shows the best tensile behavior; besides, the longer fiber length results in the higher tensile strength of RFA-EGC. By optimizing the replacement rate and size of RFA, adjusting the silicate modulus and fiber characteristics, one can achieve a sustainable high-ductility RFA-EGC with exceptional mechanical behavior.

Study on the influence of aggregate on rheological properties of recycled aggregate asphalt mixture using microstructural quantification

Recycled aggregate (RA) is generated through the crushing process of Construction and Demolition Waste (CDW). Although there has been extensive research on the mechanical properties of recycled aggregate asphalt mixture (RAAM), the impact of recycled aggregate (RA) on its rheological characteristics remains underexplored. This paper aims to assess the rheological properties of recycled aggregate asphalt mixture (RAAM) during the processes of mixing and compaction. Firstly, different percentages of recycled aggregate (RA) were utilized in the design of the recycled aggregate asphalt mixture (RAAM), and rheological behaviors of RAAM during the mixing and compaction stage were characterized by mixing torque and compaction energy, respectively. Then, high-precision three-dimensional models of RA were reconstructed utilizing CT images, and four indices were established to quantitatively assess the macro shape and micro-morphology of RA particles, utilizing the spatial model data for precise measurements. Finally, a correlation was found between rheological properties of RAAM and RA morphology through a comprehensive analysis of laboratory test results and spatial model indicators. Results show that aggregate particles’ microstructural morphology significantly influences asphalt mixture’s rheological behavior during mixing and compaction. Additionally, the 3D spherical degree and Needle-flake index performed more significant correlations with mixing and compaction than the 3D angular index and 3D texture index. As opposed to natural aggregate, RA exhibits more intricate morphological characteristics stemming from its porous cement mortar composition. Increasing the RA content causes more energy consumption and increases the thickness of asphalt mortar film during the compaction process. In general, methods established in this study offer an efficient mean of quantifying the morphological characteristics of aggregate particles, thereby enabling the assessment of the impact of RA on the rheological properties of asphalt mixtures.

Research on Macroscopic Mechanical Behavior of Recycled Aggregate Concrete Based on Mesoscale.

Recycled concrete is a heterogeneous composite material, and the composition and volume fraction of each phase affect its macroscopic properties. In this paper, ANSYS APDL was used to construct a two-dimensional numerical model of recycled aggregate concrete with different replacement rates of recycled aggregate (0%, 25%, 50%, 75% and 100%), and a uniaxial compression test was carried out to explore the relationship between recycled aggregate content and its macroscopic mechanical behavior. On this basis, the numerical simulation of different strain rates (0.1 s-1, 0.05 s-1, 0.01 s-1, 0.005 s-1 and 0.001 s-1) was carried out. It was found that with the increase in the recycled aggregate replacement rate, the peak stress decreases first and then increases, and the peak strain increases continuously. When the replacement rate of recycled aggregate exceeds 50%, the overall damage area of the material increases rapidly. The strain rate will change the path of the micro-crack initiation and expansion of recycled concrete, as well as the process of damage accumulation and evolution. As a result, the unit area and shape of recycled concrete are different at different strain rates, and the damage degree of each phase material is also different.

Mathematical modeling of mechanical and physical properties of ecological pervious concrete containing recycled aggregates

The proper treatment of river slopes is a tough issue regarding ecological and environmental governance. Ecological pervious concrete (EPC) that alleviates soil erosion and promotes plant growth thereafter is proposed to solidify the river slope. Herein, 31 groups of EPC with varied water-to-binder ratios (w/b), recycled aggregate (RA) dosages, aggregate particle sizes, and admixtures were prepared to investigate the effects of these factors on the compressive strength, continuous porosity, and pH value. Results show a w/b of 0.24 and an RA content of 25 % enables EPC to achieve a compressive strength of 13.2 MPa and a continuous porosity of 24.7 % when the aggregate size composition is 35 % 10–16 + 65 % 16–20 mm. The EPC exhibited the highest strength under the 5–25 mm aggregate size, yet the resulting continuous porosity was only 22.6 %. Moreover, GBFS exerts a critical role in compressive strength and continuous porosity, with 15 % of GBFS resulting in higher compressive strength in EPC. Upon further optimization of the EPC, GBFS contributes most significantly to both continuous porosity and compressive strength. A 15 % incorporation of GBFS leads to a higher compressive strength of the EPC. The aluminum potassium sulfate contributes 73.64 % to the pH value, neutralizing alkalinity in EPCs. In addition, a 5-11-1 GA-BP neural network is established to model the experimental data, yielding an R2 value of 0.98 and a mean absolute error (MAE) of 1.35 MPa.

Mixture ratio optimization of basalt fiber recycled aggregate concrete based on RSM

In this paper, the effects of W/B ratio, recycled aggregate (RA) content and basalt fiber (BF) dosage on the compressive strength, splitting tensile strength and slump of concrete were investigated and a regression model was developed for analysis and prediction, and the regression model was validated using ANOVA and confidence analysis. Statistical analysis revealed that W/B ratio, RA content and BF dosage had significant effects on all properties of concrete. The established regression model fits the experimental data well and can accurately predict the properties of concrete. It was also found that there was a significant interaction between W/B ratio and BF dosage, as well as RA content and BF dosage, which suggests that the combination of these factors should be considered in the design of concrete mixture ratio to achieve optimum performance. The predicted values of compressive strength, split tensile strength and slump of concrete under optimum proportioning were in good agreement with the experimental values. Therefore, optimizing the concrete proportion by response surface methodology can improve the testing efficiency and obtain basalt fiber recycled aggregate concrete that meets the design requirements and has better overall performance.

Damage-fracture mechanism analysis of steel-polypropylene fiber reinforced recycled concrete based on acoustic emission and digital image correlation

The engineering application of recycled aggregate concrete is significant for resource conservation and environmental protection. However, the applied range of recycled aggregate concrete is greatly limited due to microscopic defects such as microcracks in recycled aggregate. Steel-polypropylene fiber reinforced recycled concrete (SPRAC) makes up for the defects brought by recycled aggregate to a certain extent due to the action of hybrid fiber. To further promote the practical application of SPRAC, it is crucial to evaluate its damage-fracture mechanic's response mechanism under different hybrid fiber admixtures and recycled aggregate replacement rates. For this purpose, the following work is carried out in this paper: firstly, SPRAC beam specimens with different substitution rates of hybrid fiber and recycled aggregate were prepared; and the damage-fracture process of specimens under four-point bending load was monitored in real-time by using acoustic emission and digital image correlation techniques to analyze the influence of hybrid fiber and recycled aggregate on the flexural properties and damage-fracture characteristics of SPRAC; the inherent relationship between the acoustic emission rise time/amplitude (RA) and the average frequency (AF) is utilized to classify the crack type of SPRAC in the course of the data analysis; the b-value is also analyzed to assess the crack evolution process in SPRAC, and the corresponding warning thresholds are given.; strain and displacement fields on the specimen surface are analyzed using the digital image correlation; finally, the microscopic results of SPRAC are also given to better understand the damage-fracture evolution mechanism of SPRAC. Results show that the flexural strength and fracture toughness of SPRAC decreased nonlinearly with the increase of recycled aggregate content; on the contrary, the addition of hybrid fiber improved the mechanical properties of SPRAC. The study in this paper provides a new method to characterize the damage-fracture mechanism of SPRAC under bending loads quantitatively. It provides a reference for the engineering application of SPRAC.

Macroscopic and Microscopic Investigation of Gypsum Slag Cement-Stabilized Recycled Aggregate Base Layers.

The purpose of this study is to investigate the macro and micro properties of stabilized recycled aggregate base layers using gypsum slag cement (GSC) and compare them with ordinary Portland cement (OPC). To achieve this, four levels of recycled aggregate content (0%, 50%, 60%, 70%) and three levels of binder materials (3.5%, 4.5%, 5.5%) were designed, where the binding materials included OPC and GSC. When GSC is used as the binding material with 0% recycled content, two scenarios for the ratio of slag to activator are considered: 4:1 and 4:2. For recycled content of 50%, 60%, and 70%, only the 4:1 ratio is considered. The macro-mechanical properties of the composite material were studied through compaction tests, unconfined compressive strength tests, and indirect tensile strength tests. Microscopic properties were investigated through X-ray diffraction (XRD) and scanning electron microscopy (SEM). Macroscopic test results indicate that, at an equal binder content, GSC exhibits a higher moisture content and maximum dry density compared to OPC. Moreover, the unconfined compressive strength and indirect tensile strength of GSC are higher than those of OPC. Microscopic test results reveal that the hydration products of both binding materials are essentially similar; however, under identical curing conditions, the hydration products of GSC are more abundant than those of OPC.

Experimental Study on Preparation and Characteristics of Concrete Modified by Construction Waste

With the advancement of urbanization construction, the proportion of construction waste to the total urban waste continues to increase, especially waste concrete. The treatment and reuse of waste concrete is a major trend that poses enormous pressure on environmental protection. This article focuses on the problems in the preparation of recycled aggregates from waste concrete, which has important practical value. This article presents a new type of recycled concrete prepared through surface modification of recycled coarse aggregate and design experiments to change the replacement rate of coarse aggregate. The physical properties of recycled coarse aggregate, workability of fresh concrete, and mechanical properties of recycled concrete are analyzed. The research results indicate the following: (1) Through surface modification, recycled concrete can improve the workability of fresh concrete at a fixed water cement ratio, which can meet the requirements of mixing, transportation, and pouring of fresh concrete. (2) By modifying the surface of recycled aggregates, the strong water absorption performance of recycled aggregates caused by old mortar and surface defects has been reduced. And the modification effect of recycled aggregate improves the hydration process of recycled concrete, making the surface structure dense and further enhancing the strength of recycled concrete. (3) The compressive strength of recycled concrete specifications from construction waste shows a decreasing trend with the increase in coat aggregate replacement rate. The final ratio is as follows: modular dose of 12%, modification time of 90 min, and 20% recycled aggregate content.

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.

Correlation between mechanical properties and pore structure deterioration of recycled concrete under sulfate freeze-thaw cycles: an experimental study

Concrete is subject to the combined erosive effects of physical and chemical activities in cold, salty soil regions. In this work, durability tests of recycled concrete (RC) subjected to sulfate freeze-thaw cycles were conducted. The macroscopic performance deterioration law of RC under the influence of the replacement rate (0%, 50%, 100%) and the moisture content of coarse recycled concrete aggregate (CRCA) (0%, 50%, 100%) was investigated by analyzing the change characteristics of apparent damage, mass loss rate, and Relative dynamic modulus of elasticity (RDME) of RC during the erosion process. At the same time, nuclear magnetic resonance (NMR) and microhardness testing equipment were used to examine the multi-parameter evolution features such as porosity, pore distribution, interfacial transition zone (ITZ) width, and strength. The findings indicate that the main cause of the variation in the degree of damage to the RC surface layer is the variance in the effective water-cement (w/c) ratio of the mortar due to replacement rate and moisture content. The strength and area of erosion damage increase when the CRCA replacement rate rises due to the easier inward penetration of the sulfate solution. CRCA with a 50% moisture content could increase the strength of the mortar by decreasing the mortar's effective w/c ratio. The rate and effectiveness of salt solution replenishment inward were simultaneously slowed down by the improved ITZ performance. In erosive situations, the fractal dimension of RC reduces to varying degrees. This is due to the expansion of the pore structure. The porosity/fractal dimension is employed as the comprehensive pore parameter η in this research so as to take into account the integrity of the pore structure and the specificity of the pore distribution. The improved microstructure damage variables can reflect the erosive microstructure deterioration process of RC.

Effect of High Recycled Aggregate Content in Hot Mix Asphalt on Volumetric and Skid Resistance Characteristics

Effect of High Recycled Aggregate Content in Hot Mix Asphalt on Volumetric and Skid Resistance Characteristics

The influence of recycled aggregate on the properties of geopolymeric recycled concrete: A comprehensive review

This paper offers a comprehensive review of geopolymeric recycled concrete (GRC) research, particularly focusing on mechanical properties, durability, microstructure, and the interfacial transition zone (ITZ). The study emphasizes the influence of recycled aggregate (RA) content on GRC performance. Findings indicate that higher RA content leads to a gradual reduction in GRC’s compressive, tensile, and flexural strengths, elastic modulus, and toughness. The elastic modulus is most affected, followed by compressive strength, while tensile strength experiences the least decline. Moreover, increased RA content is associated with elevated water absorption, decreased resistance to chloride ion permeability, sulfate corrosion, acid, frost, and carbonization in geopolymer concrete. The integration of RA creates more intricate ITZs in geopolymer concrete, resulting in reduced bonding strength and a looser, more porous microstructure. However, the use of geopolymers can mitigate these effects by enhancing bonding in ITZs. The paper also presents a statistical analysis of compressive strength test results from various studies and proposes a preliminary method for estimating the compressive strength of geopolymer concrete with different RA replacement rates.