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The strength and stiffness of unbound pavement base and subbase layers built with recycled concrete aggregates (RCA) can increase due to the self-cementing properties of RCA. While the effect of different levels of self-cementing properties on resilient deformation behaviour has not been thoroughly studied. In this research, the self-cementing properties, microstructure and resilient deformation behaviour of two different RCA, NRCA (New RCA, crushed recently) and ORCA (Old RCA, crushed long time ago), showing significantly different levels of self-cementing properties, after curing for different times (1, 180, 360 and 720 days), were studied by calorimeter tests, mercury intrusion porosimetry (MIP) tests and repeated load triaxial tests (RLTT). The results indicate that long-term resilient behaviour is influenced by the level of self-cementing properties. For NRCA, showing strong self-cementing properties, the microstructure and resilient deformation behaviour were improved after curing for 720 days, which were comparable to those of lightly treated materials. On the contrary, for ORCA, showing negligible self-cementing properties, the resilient behaviour is not affected by curing. [ABSTRACT FROM AUTHOR]

To solve the problems on resource utilization and environmental pollution of waste concrete and waste polypropylene (PP) plastics, the recycling of them into asphalt pavement is a feasible approach. Considering the high melting temperature of waste PP, this study adopted a thermal-and-mechanochemical method to convert waste PP into high-performance warm-mix asphalt modifiers (PPMs) through the hybrid use of dicumyl peroxide (DCP), maleic anhydride (MAH), and epoxidized soybean oil (ESO) for preparing an asphalt mixture (RCAAM) containing recycled concrete aggregate (RCA). For the prepared RCAAM containing PPMs, the mixing temperature was about 30 °C lower than that of the hot-mix RCAAM containing untreated PP. Further, the high-temperature property, low-temperature crack resistance, moisture-induced damage resistance, and fatigue resistance of the RCAAM were characterized. The results indicated that the maximum flexural strain of the RCAAM increased by 7.8~21.4% after using PPMs, while the sectional fractures of the asphalt binder were reduced after damaging at low temperature. The use of ESO in PPMs can promote the cohesion enhancement of the asphalt binder and also improve the high-temperature deformation resistance and fatigue performance of the RCAAM. Notably, the warm-mix epoxidized PPMA mixture worked better close to the hot-mix untreated PPMA mixture, even after the mixing temperature was reduced by 30 °C. [ABSTRACT FROM AUTHOR]

Recycled Concrete Aggregate (RCA) of the chemical and biological effects must be understood to avoid potential adverse impacts to the bay's aquatic ecosystem. RCA application as a base material for oyster reefs did not adversely affect oyster spat growth and survival, or the surrounding environment. Evaluated RCA leaching for petroleum byproducts showed that RCA as a base material for oyster reefs did not leach any hydrocarbon chemicals, and no water extractable SVOC were detected. The research found potential RCA application to the Chesapeake Bay watershed as a bottom conditioning material for oyster aquaculture. Overall, the findings support the use of RCA for oyster aquaculture. [ABSTRACT FROM AUTHOR]

Recycled aggregate concrete (RAC) is not widely used in construction because of the concerns related to its quality. This paper investigates the effect of the replacement levels of recycled concrete aggregate (RCA) on bulk and hardened densities of RAC. The analysis of variance (ANOVA) was used to investigate the sensitivity of bulk and hardened densities of concrete to the replacement level of RCA. Predictive equations were developed to estimate the 3-day, 7-day, and 28-day compressive strength of RAC from its fresh properties, which are helpful for early quality control inspection of RAC. Furthermore, a predictive equation has been proposed to determine the flexural strength of RAC based on its 28-day compressive strength. The comparison of the predictive capability of the proposed and widely used code equations showed the incapability of the latter to estimate the flexural strength of RAC. In contrast, the proposed equation demonstrated a high level of prediction accuracy. [ABSTRACT FROM AUTHOR]

This study determines how untreated recycled concrete aggregates (URA), thermally treated recycled concrete aggregates (TRA), and recycled concrete aggregates developed through an integrated thermomechanical treatment process (TmRA) perform in concrete relative to each other. A concrete composed of 100% recycled aggregates (RCA) with Portland pozzolana cement has been successfully developed in the present study. The compressive strength, split tensile strength, flexural strength, fracture energy, and modulus of elasticity of TmRC is observed higher than URC by 18.62%, 8.20%, 40.72%, 24.18%, and 54.99%, and those TRC by 7.54%, 28.57%, 29.78%, 24.12%, and 34.35%, respectively. The split tensile strength, flexural strength, fracture energy, and modulus of elasticity of these concretes are strongly correlated with their compressive strength. TmRC material properties match NAC, standard requirements, and reported values closely. URC and TRC chloride-ion penetrations are around 3.51- and 2.42-times greater than TmRC. Among these concretes, only TmRC meets corrosion protection requirements like NAC. The abrasion resistance of TmRC is observed 52.03% greater than URC and 43.07% greater than that of TRC. TmRC has substantially lower sorptivity compared to URC and TRC and is close to NAC. TmRC has around 32.65% and 16.67% less weight loss in drying than URC and TRC, respectively. URC and TRC have around 1.99- and 1.82-times less abrasion resistance than TmRC. An optimal reduced adhered-mortar volume, the minimized porosity and microcracks, dense and uniform surface texture, strengthened interfacial transition zones leads the performance of TmRA superior to URA and TRA, and close to or superior to parent aggregates. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to use the data‐driven approach to predict and evaluate the mechanical properties of concrete made with recycled concrete aggregate (RCA), including compressive strength and elastic modulus. Using 358 data samples, including 10 input variables, 10 popular machine learning (ML) algorithms are introduced to select the best ML performance model for predicting RCA concrete's compressive strength and elastic modulus. Gradient Boosting and Categorial Boosting have the best performance in predicting the compressive strength of RCA concrete, with R2 = 0.9112, RMSE = 5.3464 MPa, MAE = 4.0845 MPa, and R2 = 0.9175, RMSE = 5.1520 MPa, MAE = 3.7567 MPa, respectively. Light Gradient Boosting and Categorial Boosting have the best performance in predicting the elastic modulus of RCA concrete, with R2 = 0.8775, RMSE = 2.3560 GPa, MAE = 1.8330 GPa, and R2 = 0.9300, RMSE = 2.3560 MPa, MAE = 1.2589 MPa, respectively. Based on the Shapley Additive Explanation analysis, the influence of main factors on compressive strength and elastic modulus of RCA concrete values has been analyzed qualitatively and quantitatively. RCA replacement level and cement/sand ratio slightly affect compressive strength but have a dominant influence on the elastic modulus of RCA concrete. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of quarry waste sand (QWS) on the physical and mechanical properties of recycled aggregates concrete (RAC). Two sets of concretes were made one with natural sand (NS) and another with QWS sand. Five mixes with replacement ratios of 20%, 40%, 60%, 80% and 100% of ordinary coarse aggregates (OCA) by recycled concrete aggregates (RCA) were produced for each set. Tests were performed to determine slump, compressive strength, flexural strength, water absorption by immersion and shrinkage. The results showed that the mixes produced with QWS sand exhibited slightly better fresh and hardened properties. The combination of QWS sand and RCA aggregates reduces the degradation often recorded and makes RAC concrete to have the same level of performance as concrete with ordinary aggregates. Some relationships were deduced to express each performance of QWS sand-based concrete with that of NS sand-based concrete. This makes the use of this sand very practical and its modifications easily quantifiable. [ABSTRACT FROM AUTHOR]

In this study, the performance of recycled concrete aggregate (RCA/RSA) available in Agartala, Tripura (north-eastern regions of India), was studied in reinforced concrete members subjected to a severe artificially induced corrosive environment. The performance test was based on the non-destructive and destructive parameters of concrete. Due to the scarcity of normal stone aggregate (NSA) in this region, studying the effect of using such type of aggregate in reinforced concrete members help not only to mitigate the demand but also assists in waste management. The study also presents an innovative application of micro-bend opticalfibre sensors for corrosion monitoring and validated using other non-destructive instruments. The study presents an effective application of the micro-bend optical fibre sensor to predict the initiation of corrosion (de-passivation) and initiation of cracking (critical stress) due to corrosion in reinforced concrete specimens. Later, the results were validated using half-cell potentiometer and electrical strain gauge values. The specimen also presented different mechanical and durability properties with varying RCA percentages. A regression model to predict mechanical properties and corrosion amount (hoop strain) in reinforcement for different RCA-replaced concrete has been presented. The sorptivity and other porosity-related results were also presented for different RCA replacement percentage specimens. [ABSTRACT FROM AUTHOR]

Abstract This study investigated the mechanical properties of fibre-reinforced concrete (FRC) by varying fibre content and incorporating supplementary cementitious materials into M20 grade concrete. The research focused on the effects of four types of fibres—hooked end steel, chopped glass, PET fibres from recycled bottles, and jute fibres—introduced at volume fractions of 0%, 1%, 2%, and 3%. Additionally, 30% of the cement was replaced with fly ash, and 25% of the coarse aggregate was substituted with recycled concrete aggregate (RCA) to enhance sustainability. The primary aim of this study was to evaluate the impact of these fibres on the compressive strength, flexural strength, and split tensile strength at various fibre dosages. The results provide valuable insights into optimizing FRC formulations for sustainable construction, emphasizing the benefits of using recycled materials and diverse fibre types to improve concrete performance and durability. The study concluded that the optimal fibre dosage is 3% for steel fibres and 1% for glass fibres. PET fibres improved compressive and split tensile strengths at a 1% dosage but led to a decrease in flexural strength with increasing fibre content. In contrast, jute fibres were found to reduce strength as fibre content increased, supporting previous findings that suggest the optimal dosage for jute fibres is below 1%.

In this study, Recycled Concrete Aggregate (RCA) was employed as a sandwich technique around the geogrid to enhance the pullout resistance of the geogrid in clayey backfills. Large-scale pullout tests were conducted on three configurations: geogrid-reinforced clay, geogrid-reinforced RCA, and geogrid sandwiched between layers of RCA, aimed at investigating pullout resistance and deformation. The experiments encompassed two different geogrid types (designated as G1 and G2), varying normal pressures ranging from 10 to 50 kPa, and RCA layers with thicknesses of 40, 80, 160, and 320 mm. Results from the experiments revealed that the inclusion of RCA layers around the geogrid substantially enhanced pullout resistance, with improvements ranging from 1.5 to 3 times compared to clay specimens. Optimal RCA thicknesses were determined in order to enhance soil-geogrid bonding and pullout resistance. For G1 geogrid, a thickness of 160 mm (equivalent to replacing 25% of clay volume with RCA) was identified as optimal, while for G2 geogrid, an 80 mm thickness (equivalent to replacing 15% of clay volume with RCA) was found to be sufficient. These thicknesses were established to achieve over 80% of the pullout force compared to full RCA specimens. • Large-scale pullout tests were performed on two types of geogrids. • Recycled Concrete Aggregate (RCA) was utilized at various thicknesses within a sandwich technique to enhance geogrid pullout resistance in clayey backfills. • The optimum thickness of RCA layer in sandwich technique was determined. [ABSTRACT FROM AUTHOR]

Recycled Concrete Aggregate (RCA) of the chemical and biological effects must be understood to avoid potential adverse impacts to the bay’s aquatic ecosystem. RCA application as a base material for oyster reefs did not adversely affect oyster spat growth and survival, or the surrounding environment. Evaluated RCA leaching for petroleum byproducts showed that RCA as a base material for oyster reefs did not leach any hydrocarbon chemicals, and no water extractable SVOC were detected. The research found potential RCA application to the Chesapeake Bay watershed as a bottom conditioning material for oyster aquaculture. Overall, the findings support the use of RCA for oyster aquaculture.

Considering the seismic conditions of Iran and the many damages that occur as a result, it is necessary to change the current performance of structural design to achieve better performance in the seismic system. On the other hand, environmental concerns have prompted civil engineers to identify appropriate methods of reusing construction waste. The purpose of this research is to investigate the behavior of concrete made with recycled materials as a wide foundation, which has the role of seismic isolation for low- or medium-height buildings. In this research, the effect of crumb rubber and recycled concrete aggregate on concrete was examined in a laboratory. The design basis of its resistance is 30 MPa. The first mixture, as a control mixture, does not contain rubber granules, Forta fibers and recycled concrete aggregate. In the other three mixtures, the difference in the amount of recycled concrete aggregate is 40%, 50%, and 60% instead of coarse aggregate. Also, the percentage of rubber granules is constant, about 15% of the total volume, and the amount of Forta fibers is about 0.5% of the total volume. Compressive strength, Flexural strength, and Shear strength tests were performed on the 4 mentioned mixtures at the age of 28 days in a laboratory. The results of the compressive strength test showed that the addition of recycled concrete aggregate, rubber granules, and Forta fibers significantly reduced the compressive strength value. The results of the flexural strength test indicated that the additives cause a noticeable reduction in flexural strength, and this reduction intensifies with the change in recycled concrete aggregate percentage. The results of the shear strength test represented a considerable increase with the increase in the percentage of recycled concrete aggregate. Based on the test results, it is concluded that this type of composition material can be used as a foundation isolator, which showed a favorable shear behavior.

This research investigates the potential of utilizing recycled concrete aggregate (RCA) and recycled sand (RS), derived from crushed concrete cubes, as sustainable alternatives in construction materials. The study comprehensively evaluates the properties of RCA and RS, focusing on workability, impact resistance, abrasion resistance, and compressive strength to determine their viability as substitute construction materials. A notable finding is RS’s enhanced fire and heat resistance when used as a fine aggregate in mortar blends, mixed with cement and Sinicon PP in a 3:1 ratio. The experimental analysis included thorough assessments of uniformity, durability, and curing time, alongside Scanning Electron Microscopy (SEM) for structural examination. Results show that RCA has an Aggregate Impact Value (AIV) of 5.76% and a Los Angeles Abrasion Value (LAA) of 21.78%, demonstrating excellent strength of the recycled aggregates. The mortar mix was also prepared using recycled sand, cement, and Sinicon PP, and its stability was confirmed through soundness tests, which resulted in a 0.53 mm expansion and a satisfactory consistency level of 44%. Ultrasonic pulse velocity (UPV) tests also indicated high-quality concrete formation using RCA and RS. SEM imaging corroborated this by revealing a bond between the cement paste and the aggregates. Incorporating RS and RCA in concrete mixtures impressively yielded a compressive strength of 26.22 N/mm2 in M20-grade concrete. The study concludes that using RCA and RS waste materials in the construction sector underlines that sustainable practices can be integrated without compromising material quality. This approach aligns with sustainable development goals and fosters a more environmentally friendly construction industry.

Abstract Research on concrete recycling has led to the discovery of many processes for recycled concrete aggregate (RCA) treatment, each with its pros and cons on quality improvement, resource requirements, or scalability. This study aimed to propose a technique that combines two methods (mechanical grinding and acidic soaking) for mortar removal and improves the quality of RCA so as to realize a zero-waste, highly efficient, few-hours-long single-step process which we call acid milling. A quantitative comparison of aggregate and final concrete quality has been performed between each separate method. The proposed method shows about 57% relative improvement of aggregate quality for water absorption and density, while the concrete experiment shows up to 10% relative improvement for the compressive and flexural strengths compared with the untreated RCA concrete. This study paves the way for an efficient and sustainable concrete recycling process to be applied on a large scale.

Using recycled concrete aggregates (RCAs) in concrete is a promising approach to minimise the environmental impacts associated with construction and demolition waste while simultaneously enhancing the sustainability of concrete. Improving the quality of RCAs is crucial for promoting confidence among materials suppliers and systematic utilisation of RCAs in construction. Pristine graphene (PG) suspensions (0.1% and 0.2% concentrations in water) were investigated for improving the properties of RCAs and thereby improving the mechanical and durability properties of concretes made with 100% RCAs as coarse aggregates. Two PG treatment methods were used – spraying and soaking. Nano-silica (NS) suspensions of the same concentrations were also used for comparison. Tests for axial compressive, splitting tensile and flexural strengths were performed; water absorption and drying shrinkage were also assessed. Microanalysis was conducted using scanning electron microscopy and micro computed tomography. PG was found to be more effective than NS for increasing strength properties and reducing water absorption and drying shrinkage of concrete due to its lower porosity. For a given nanomaterial concentration and type, concretes made with soaked RCA exhibited higher strengths and lower water absorption and drying shrinkage than concretes with sprayed RCA. The concretes made with soaked RCA also had lower porosity and fewer microcracks. The results are promising and indicate that treating RCAs reduces their water absorption, thereby improving concrete performance. [ABSTRACT FROM AUTHOR]

In today's environment, where energy is desired to be used more efficiently, it has been understood that the interest in the use of lightweight concrete with superior performance in terms of thermal insulation properties has increased. On the other hand, it has been stated that construction waste increases rapidly, especially after severe earthquakes. In this context, encouraging the use of recycled concrete waste and efficient disposal of construction and demolition waste is of great importance for the European Green Deal. It is also known that pollutants such as COx and NOx stick to facades over time, causing environmental pollution and visual deterioration. It has been reported that materials with photocatalytic properties are used in lightweight concrete facade elements to prevent such problems. This study examines the effect of using recycled concrete aggregates on the thermal properties of self-cleaning lightweight concrete mixtures (SCLWC). For this purpose, an SCLWC containing 1% TiO2 and 100% pumice aggregate was prepared. By replacing pumice aggregate with recycled concrete aggregate at the rates of 15%, 25%, 35%, 45% and 50%, four different SCLWCs with self-cleaning properties were produced. High-temperature resistance, thermal conductivity performance, microstructure analysis and photocatalytic properties of the produced mixtures were examined. It has been understood that the unit volume weight loss of SCLWC mixtures exposed to high temperatures generally decreases due to the increase in the recycled concrete-aggregate substitution rate. However, it was determined that the loss of compressive strength increased with the increase in the amount of recycled concrete-aggregate replacement. Additionally, it was determined that the thermal-conductivity coefficient values of the mixtures decreased with the use of pumice. After SCLWC mixtures were exposed to 900 °C, small round-shaped crystals formed instead of C–S–H crystals. [ABSTRACT FROM AUTHOR]

Rising environmental awareness has prompted in‐depth studies on how the concrete industry affects the environment. Using recycled concrete aggregates (RCAs) and supplementary cementitious materials (SCMs) in concrete manufacturing provides advantages for sustainability. However, the broader chemical composition of SCMs and the inferior qualities of RCAs compared with natural aggregates (NAs) often lead to a decrease in concrete mechanical strength. The difficulty lies in foreseeing how the inclusion of SCMs and RCAs will affect the concrete compressive strength. The artificial neural network (ANN) approach presented herein can precisely forecast the recycled aggregate concrete (RAC) compressive strength, even when incorporates SCMs. The analysis employing the connection weight approach (CWA) determines how input variables influence compressive strength. Results indicate silica fume contributes most to compressive strength, followed by cement content, silica modulus, fine natural aggregate dosage, and coarse natural aggregate. Additionally, the amount of water utilized, the water/cement ratio, and the presence of RCA are all detrimental to compressive strength. The adverse effect of the cementitious materials' alumina modulus can be attributed to increased water demand during their reaction. Performance metrics of the final ANN model on the testing data subset include R2 = 0.94, and RMSE = 3.11, utilizing 834 data observations after outlier treatment for training and validation purposes. In summary, the ANN‐based approach demonstrates its efficacy in predicting concrete compressive strength when incorporating SCMs and RCAs, shedding light on the influential factors in concrete performance. [ABSTRACT FROM AUTHOR]

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This research aims to develop sustainable high-strength concrete (SHSC) by replacing 100% fine and/or coarse aggregates with fine recycled aggregate (RA) and/or coarse RA. Due to the high surface water absorption of coarse RA, a surface treatment method was adopted, consisting of immersing it in a cement and silica fume slurry. Moreover, to improve the performance of the produced SHSC, steel fibers were employed at a relatively low volume fraction (0.5%). Eleven blends were cast and tested in this experimental study. A control SHSC mix (without RA) and ten other mixtures, including fine natural and RA, treated and untreated coarse RA, with and without steel fibers, were prepared. Compressive, splitting, and flexural strengths, water absorption, density, and ultrasonic pulse velocity (UPV) of the resulting SHSC were conducted. The results indicated that the use of RA in SHSC resulted in an average drop of 25% in its mechanical properties and an increase of about 30% in water absorption. However, using treated RA compensated the compressive and tensile strength reductions in SHSC by 9% and 7%, respectively, compared to mixes containing untreated RA. On the other hand, adding fibers helped improve compressive, flexural, and splitting tensile strengths by about 8%, 23%, and 31%, respectively, compared to the corresponding control mix. Consequently, the results showed that it is possible to produce durable SHSC made from 100% RA and 0.5% steel fibers with a reduced density and improved mechanical performance to a comparable level or even superior to high-strength concrete (HSC) with only natural aggregates (NAs). [ABSTRACT FROM AUTHOR]

In order to enhance the utilization rate of recycled concrete aggregate (RCA), this paper proposes a method of ionic precipitation (MIP) to treat RCA by using a saturated solution of sodium bisulphate and calcium hydroxide combined with ultrasonic waves and organosilicon hydrophobes. The effects of MIP on the micro-morphology and physical properties of RCA, as well as the oil/stone ratio and road performance of asphalt mixtures, were analyzed. The test results show that the MIP resulted in the surface of RCA covered by a layer of alkaline cementitious materials. Moreover, the pores of RCA are filled with gypsum, calcium hydroxide and ettringite. Consequently, the crushing index, wear value and water absorption rate of RCA are reduced greatly. MIP treatment significantly reduces the optimal asphalt content of RCA-asphalt mixture and enhances interface adhesion, water stability and high-temperature stability. In addition, according to the test results, the replacement of 60% (mass fraction) original coarse aggregates by using of MIP-RCA can construct an asphalt mixture with excellent road performance and a low optimal asphalt content. [ABSTRACT FROM AUTHOR]

This research investigates the potential of utilizing recycled concrete aggregate (RCA) and recycled sand (RS), derived from crushed concrete cubes, as sustainable alternatives in construction materials. The study comprehensively evaluates the properties of RCA and RS, focusing on workability, impact resistance, abrasion resistance, and compressive strength to determine their viability as substitute construction materials. A notable finding is RS's enhanced fire and heat resistance when used as a fine aggregate in mortar blends, mixed with cement and Sinicon PP in a 3:1 ratio. The experimental analysis included thorough assessments of uniformity, durability, and curing time, alongside Scanning Electron Microscopy (SEM) for structural examination. Results show that RCA has an Aggregate Impact Value (AIV) of 5.76% and a Los Angeles Abrasion Value (LAA) of 21.78%, demonstrating excellent strength of the recycled aggregates. The mortar mix was also prepared using recycled sand, cement, and Sinicon PP, and its stability was confirmed through soundness tests, which resulted in a 0.53 mm expansion and a satisfactory consistency level of 44%. Ultrasonic pulse velocity (UPV) tests also indicated high-quality concrete formation using RCA and RS. SEM imaging corroborated this by revealing a bond between the cement paste and the aggregates. Incorporating RS and RCA in concrete mixtures impressively yielded a compressive strength of 26.22 N/mm2 in M20-grade concrete. The study concludes that using RCA and RS waste materials in the construction sector underlines that sustainable practices can be integrated without compromising material quality. This approach aligns with sustainable development goals and fosters a more environmentally friendly construction industry. [ABSTRACT FROM AUTHOR]

AbstractA sustainable and reliable methodology to strengthen the mortar adhered to recycled concrete aggregate (RCA) is crucial for optimizing its utilization in construction. This research proposes a mortar strengthening method by soaking RCA in different dosages (weight percentages) of pozzolanic slurries, i.e., fly ash and silica powder (F-S), fly ash and cement (F-C), cement and silica powder (C-S) for various durations. The influence of each slurry dosage and soaking duration on RCA's physical and mechanical properties and surface morphology were examined. Further, a modified two-stage mixing approach (M-TSMA) was employed to produce recycled aggregate concrete (RAC) incorporating 100% untreated and surface-treated RCA. The impact of M-TSMA and treated RCA on concrete was demonstrated regarding its mechanical and durability properties, such as compressive strength, ultrasonic pulse velocity, rebound hammer, sorptivity, and resistance to chloride ions. Results show that soaking RCA in 30% C-S slurry for 6 h enhances RCA's overall properties by increasing the calcium silicate hydrate (C-S-H) content. Moreover, employing M-TSMA and incorporating treated RCA improves the mechanical and durability properties of RAC by reducing microcracks and densifying the microstructure. Overall, the proposed surface treatment and M-TSMA can potentially enhance RAC performance with complete RCA utilization. [ABSTRACT FROM AUTHOR]

Research on concrete recycling has led to the discovery of many processes for recycled concrete aggregate (RCA) treatment, each with its pros and cons on quality improvement, resource requirements, or scalability. This study aimed to propose a technique that combines two methods (mechanical grinding and acidic soaking) for mortar removal and improves the quality of RCA so as to realize a zero-waste, highly efficient, few-hours-long single-step process which we call acid milling. A quantitative comparison of aggregate and final concrete quality has been performed between each separate method. The proposed method shows about 57% relative improvement of aggregate quality for water absorption and density, while the concrete experiment shows up to 10% relative improvement for the compressive and flexural strengths compared with the untreated RCA concrete. This study paves the way for an efficient and sustainable concrete recycling process to be applied on a large scale. [ABSTRACT FROM AUTHOR]

Rheology of Self-Compacting Concrete (SCC) containing selected silica fume dosages (0% (control mix), 5%, 10% and 15%) in a binary binder has been investigated using the flow-curve test protocol implemented on a co-axial cylinder rheometer. At each silica fume dosage, coarse recycled concrete aggregate volumetric replacement levels were 0%, 50% and 100%. Calibration of selected flow models with the measured flow data showed that rheology transitioned from shear thickening to shear thinning as the silica fume dosage increased from 0% to 15%, other mix constituents remaining unchanged. Similar flow behaviour was noted in the SCCs made with the recycled concrete aggregates (SCRACs) across all replacement levels though for a given silica fume dosage, degree of shear thinning decreased with increasing contents of the coarse recycled aggregates. The experimental results have been used to propose a workability box containing bounds for acceptable rheology of the SCCs and the SCRACs. [ABSTRACT FROM AUTHOR]

Regarding the traditional Hot Mix Asphalt (HMA), Warm Mix Asphalt (WMA) with Recycled Concrete Aggregate (RCA) contents (WMA-RCA) requires lower production temperatures and diminishes the consumption of natural aggregates (NAs). Nonetheless, these environmental benefits may be counteracted by the higher optimal asphalt binder demanded by the WMA-RCAs. In this regard, this research develops a computational model to optimize the WMA-RCA design. In order to build a sufficiently accurate and adaptable model, it was decided to employ Artificial Neural Networks (ANNs). The ANN implementation was based on the postulates of the statistical learning theory, i.e., preferring to generate learning through low-complexity models. Also, a representative case study of the northern region of Colombia was assessed. In this scenario, the optimal coarse RCA content was 10%, and the sustainability savings were maintained up to an RCA's hauling distance of 200 km. [ABSTRACT FROM AUTHOR]

Recycled coarse aggregate concrete enables the creation of environmentally friendly and cost-effective mixes. It helps address the disposal problem of demolition concrete waste, meeting demand while improving product functionality and reusability. The abundance of obsolete buildings in cemeteries contributes to Construction and Demolition waste. Recycled Concrete Aggregate (RCA) from demolished structures can be utilized as aggregates, albeit with concerns about its impact on compressive strength due to absorption issues. This review aimed to study and develop the different Artificial Intelligence (AI) model for the prediction of the compressive strength of concrete with varying RCA content and natural coarse aggregate content as input parameters while compressive strength as output parameter. The range of the input parameters is 0 % to 100 % while the range output parameter is 28 MPa to 70.3 MPa. Experimental data from literature articles used to train and validate the model development. Engineers and researchers can utilize these models to predict compressive strength by changing the input parameters. XGBoost Regression Model performed well with R2 0.93594 followed by Random Forest Model with R2 0.92766, and Gradient Boosting Model with R2 0.90616 respectively. Ridge Regression, Lasso Regression, and Linear Regression Models were not performed well in predicting the compressive strength of RCA concrete with R2 0.57657, 0.57558, 0.57675 respectively. ANN also performed significant in prediction of RCAC compressive strength with R2 0.8039. Future research could focus on optimizing the mechanical properties of concrete containing RCA using AI models. Furthermore, the study extends its analysis to explore the application of AI in predicting the strength of various types of concrete, highlighting the versatility and potential of AI-driven approaches in enhancing concrete mix design.

This data article presents details on the assessment of fracture parameters of laboratory asphalt mixtures produced using both natural and recycled concrete aggregates. The gap-graded stone matrix asphalt (SMA) is created by incorporating Trinidad Lake Asphalt (TLA) binder with carefully calibrated mixtures of recycled concrete aggregates (0 %, 10 %, 35 %, and 50 %) and natural aggregates (limestone and dust filler). The dataset variables were chosen based on the specifications of the single-edge notched beam (SENB) and semi-circular bending (SCB) tests, which are currently used for quality control and assurance (QC & QA) assessment of asphalt concrete mixtures. The data parameters provided include air void content, voids in mineral aggregates, voids filled with asphalt, density, Marshall Stability, Flow, test temperature, peak loads, RCA content, and notch depths. The fracture resistance of the mixes was studied by analysing the fracture energy, tensile strength, and fracture toughness for the collected dataset. The data shows that incorporating up to 10 % of RCA into SMA mixes, similar fracture properties can be achieved compared to traditional SMA mixtures. This presents a sustainable and environmentally advantageous option, however, it is important to exercise caution as the RCA content increases.

This paper studies the fresh and mechanical properties of high-strength concrete (HSC) by incorporating recycled concrete aggregates (RCA) of varying sizes and concentrations. The recycled aggregate concrete (RAC) was prepared by partially replacing RCA with natural coarse aggregate (NCA) at 0%, 15%, 30%, and 45%, with aggregate sizes ranging from 5 to 12 and 12–20-mm. Fresh concrete properties, such as slump, Kelly ball, compacting factor, K-slump, and fresh density, were tested to determine the influence of RCA size and concentration. In addition, the mechanical properties were studied through the execution of compressive, split-tensile, and stress-strain tests. The test results revealed that increasing the RCA concentration declines the fresh and hardened properties of HSC. In the fresh concrete experimentation, the 12–20 mm aggregate size RAC mixes exhibited greater workability than the 5–12 mm aggregate mixes. On the contrary, 5–12 mm aggregate mixes RAC had higher compressive and split-tensile strength and a higher modulus of elasticity than 12–20 mm aggregate mixes concrete. When it comes to sustainability, the study found that the smaller size range of RAC produces inferior embodied CO2 (eCO2) and provides a cost-effective and sustainable solution for the construction industry.

ABSTRACTKenaf fiber (KF) has been applied in concrete to compensate for the weak tensile strength. Similarly, recycled concrete aggregate (RCA) is applied to reduce problems associated with waste concrete materials. However, both KF and RCA reduce the compressive strength (fck) of concrete. This study involves addition of calcite-producing bacillus subtilis bacteria to recycled aggregate concrete (RAC) incorporated with KF. The bacteria is added to concrete with varying proportions of RCA and KF to produce bio-fibrous recycled concrete (BFRC). The proportions of RCA are 0%, 25% 50% and 75% replacement of coarse aggregate, while KF are 0.2%, 0.5% and 1% of concrete. W/C of 0.45, 0.5, and 0.6 are applied to evaluate the effects of different w/c ratios. The properties evaluated are the fck and the flexural strength (ft) of the concrete samples at 28 days. The results showed that 0.2% KF in bio-concrete (BC) increases the fck by 12%; however, increasing above 0.2% decreases fck. KF in BC increases ft by 60%. Furthermore, 0.5% KF content resulted in highest ft of BRC. Increasing RCA content in bio-recycled concrete and BFRC decreases fck by 30% and 33%, respectively, as well as ft by 13% and 18%, respectively.

To reduce the environmental impact of concrete, recycled aggregates are of significant interest. Recycled concrete aggregate (RCA) presents a significant resource opportunity, although its performance as an aggregate in concrete is variable. This study presents a meta-analysis of the published literature to refine the understanding of how the moisture content of RCA, as well as other parameters, affects the compressive strength of concrete. Seven machine learning models were used to predict the compressive strength of concrete with RCA, including linear regression, support vector regression (SVR), and k-nearest neighbors (KNN) as single models, and decision tree, random forest, XGBoost, and LightGBM as ensemble models. The results of this study demonstrate that ensemble models, particularly the LightGBM model, exhibited superior prediction accuracy compared to single models. The LightGBM model yielded the highest prediction accuracy with R2 = 0.94, RMSE = 4.16 MPa, MAE = 3.03 MPa, and Delta RMSE = 1.4 MPa, making it the selected final model. The study, employing feature importance with LightGBM as the final model, identified age, water/cement ratio, and fine RCA aggregate content as key factors influencing compressive strength in concrete with RCA. In an interaction plot analysis using the final model, lowering the water–cement ratio consistently improved compressive strength, especially between 0.3 and 0.4, while increasing the fine RCA ratio decreased compressive strength, particularly in the range of 0.4 to 0.6. Additionally, it was found that maintaining moisture conditions of RCA typically between 0.0 and 0.8 was crucial for maximizing strength, whereas extreme moisture conditions, like fully saturated surface dry (SSD) state, negatively impacted strength. [ABSTRACT FROM AUTHOR]

Mineral carbonation provides a way to increase the recycling of concrete waste in added-value products, and contributes to the principles of the circular economy. At present, most concrete waste is still downcycled. The high water absorption of recycled concrete aggregates, among other factors, impedes their recycling in the concrete industry. The quality of coarse recycled concrete aggregates (RCA) can, however, be enhanced by carbonation. Even when starting with high-grade RCA obtained from a selective demolition process, the carbonation process can decrease the water absorption of the RCA to as low as 3.0%. Concrete with a 50% replacement rate of carbonated RCA can be produced without a significant compressive strength reduction. The research further shows that carbonation can be performed at atmospheric pressure and low CO2 concentrations (e.g., 10%). The recycled concrete fines (RCF, 0–4 mm) in combination with 25% stainless steel slag were used to make zero-cement hollow blocks (39 × 19 × 9 cm) by carbonation curing without using any hydraulic binder. The hollow blocks have a compressive strength of 15.4 MPa at the lab scale. Both technologies were demonstrated on a pilot scale. In both processes, CO2 is immobilized in the resulting construction product. The developed production processes use less primary raw materials and cause less greenhouse-gas emissions than the production of traditional concrete products. [ABSTRACT FROM AUTHOR]

This study aims to predict the final‐age compressive strengths of sustainable concrete series produced using different aggregate types with high accuracy using an artificial intelligence model and to reduce environmental degradation and conserve rapidly decreasing natural resources within the scope of sustainable development and circular economy goals. For this purpose, 45 different sustainable concrete series containing all‐natural, recycled, natural, and recycled concrete aggregates were produced and subjected to compressive strength tests at 7 and 28 days. In addition, this study also considers whether deep neural network models, which have gained popularity in recent years but have high time and resource costs, or shallow models are more suitable for determining the compressive strength values with high accuracy. For this purpose, a method is proposed that can automatically generate the optimal neural network model using a metaheuristic approach that eliminates the human factor. For this purpose, the proposed method was extensively compared with different classical machine learning algorithms. The proposed method predicted the 7 and 28‐day compressive strength with a coefficient of determination of 0.999 and presented better compressive strength predictions than all other algorithms. Considering the number of buildings to be constructed after earthquakes, the widespread use of concrete, and the importance of compressive strength, the proposed method will likely provide significant gains within sustainable development, circular economy, and disaster risk reduction. [ABSTRACT FROM AUTHOR]

The management of material flows in societies is complex yet crucial for the sustainable coexistence of humans and materials. While industrial ecology (IE) has long examined material flows, studies acknowledging their sociomaterial nature are scarce. Consequently, the existing IE research has not yet answered why materials flow in societies as they do. This study therefore examines human–material interaction (HMI) in material flows. We build on the IE and sociomateriality literature and empirical findings from a qualitative multiple‐case study of two material flows (recycled concrete aggregate; biogas and recycled nutrients) where humans interact with materials to advance material flows in society more sustainably. We identify and conceptualize 11 HMI elements (adaptability, general acceptance, public interest, regulation, compatibility, consistency, degradability, availability and continuity, intensity, proximity, and re‐utilizability) that further divide into three categories (human‐driven, material‐driven, and equally driven HMI elements) to explain in detail the manifestations of HMI in societal material flows. Together, these HMI elements explain material flows as the physical movement of materials motivated by goal‐oriented humans who engage with materials, a process that leads to humans and materials becoming constitutively intertwined in spatiotemporal practice. To visualize our findings on this complex yet pivotal HMI phenomenon, we employ DNA as a conceptual metaphor. The study contributes to IE by uncovering the dynamic HMI in material flows and guiding practitioners on how to manage material flows in societies, acknowledging both human and material perspectives. [ABSTRACT FROM AUTHOR]

A detailed laboratory study is carried out to evaluate the engineering properties of the Recycled Concrete Aggregate (RCA) coming from the construction and demolition waste to be used in the stabilized subbase of the flexible pavement. The index properties such as impact test, abrasion test, specific gravity, water absorption, and pH test were carried out on the RCA material. The RCA was blended with the natural aggregate (NA) in 20% to 100% with an increment of 20%. The cement was added in the 3%, 4%, 5%, and 6% to the RCA and NA material blend to make a bound subbase layer. On the combination of RCA, NA, and cement proctor tests, the Unconfined compressive strength (UCS) test, durability test, and Repeated load triaxial (RLT) test were carried out. The results support the use of RCA material in the subbase layer of flexible pavement with UCS of more than 1.5 MPa, which is the Indian standard requirement. Even the durability under wet and dry cycles was satisfied by all combinations except combinations having 100% RCA + 3% Cement. From the RLT test, the resilient modulus (Mr) was found for different fifteen stages of confining pressure and deviator stresses. The Mr values increase with the increment in deviator stress and confining pressure. The combinations showed better performance in terms of strength with natural aggregate added in RCA to be used in the bound subbase layer of the flexible pavement. [ABSTRACT FROM AUTHOR]

Product sustainability has moved beyond being an elective preference to becoming a certain necessity. However, earthquakes in different regions, particularly Türkiye–Syria, Afghanistan, and Morocco, have produced a substantial amount of construction waste and debris. In the context of green urban initiatives and environmental preservation, theeffective management and reduction of environmental impact (EI) are imperative. This urgency underscores the significance of the study's focus on a ten-story reinforced concrete (RC) dormitory building in Győr, Hungary, chosen as a case study. The research delves into the incorporation of three distinct concrete compositions through seismic design, aligning with the innovative approach of emphasizing recycled aggregate-based concrete to mitigate the EI. Utilizing AxisVM X7 and Revit software, the study meticulously created and analyzed a detailed building model, revealing a significant percentage (35%) and amount (1519.89 tons) of concrete waste that could be incorporated into construction. The results also showed a reduction in both total carbon emissions and the price of materials by falling 27.5% and 9.13%, respectively. We propose an eco-friendly way to effectively reuse debris from earthquakes, focusing on the case study of the 2023 Türkiye–Syria earthquake and encouraging resource efficiency while also addressing the construction waste problems that arise after an earthquake. [ABSTRACT FROM AUTHOR]

The world is moving towards the use of sustainable concrete due to its ability to reduce environmental pollution caused by the presence of waste arising from the demolishing of old buildings or those collapsed as a consequence of earthquakes. The combined effects of fine recycled concrete aggregate (RF), light expanded clay coarse aggregate (LECA), and steel fibres (SF) on the properties of concrete were investigated in the present study. The evaluated properties were slump test, compressive strength, flexural strength, splitting tensile strength, density, and water absorption. The prepared concrete specimens were also evaluated, considering non-destructive tests through ultrasonic pulse velocity and rebound hammer tests. Findings indicated that the inclusion of RF with LECA as a partial and full replacement of gravel in both fibrous and non-fibrous concrete resulted in a drop in compressive, splitting, and flexural strength by an average of 17%, 22%, and 25%, respectively when 50% LECA was used. Furthermore, when 100% LECA was used, the drop became more pronounced, with decreases of 39%, 42%, and 45%, respectively. However, the use of hooked steel fibre at 0.75% compensated for this adverseness, and the strengths of the mixes were generally higher than those of the reference mix, which was produced with normal-weight aggregates. [ABSTRACT FROM AUTHOR]

The present study focuses on the innovative technique for making rectangular and circular hollow concrete blocks using fly ash (FA) and recycled concrete aggregates (RCA). The feasibility of employing RCA in conjunction with fly ash as a substitute for natural aggregates and cement in a proportion ranging from 30%–90% and 15%–45%, respectively, is tested in the laboratory. According to current standards, the tests comprise the slump test, compressive strength test, water absorption test, and structural efficiency evaluation. An empirical quantitative technique is used for the cost–benefit analysis of a 100-square-foot model built with recycled concrete hollow blocks. The study suggests that employing recycled concrete aggregate and fly ash as replacements for conventional materials would result in a minimum cost savings of 17%. The quantity of greenhouse gases produced in CO2 equivalents during concrete production is calculated using the Inventory of Carbon and Energy database. According to research findings, the utilization of recycled concrete aggregates and fly ash reduced carbon dioxide equivalent emissions by 30%–40%. It was also confirmed that cement has a major effect on greenhouse gas emission generation throughout the concrete manufacturing phase, regardless of the use of RCA over virgin aggregates. This study intends providing a significant understanding of how RCA and FA can not only contribute to environmental conservation but also offer economic benefits. Finally, the research intends to encourage the adoption of ecologically responsible and economically viable sustainable practices in the construction industry. [ABSTRACT FROM AUTHOR]

This paper studies the fresh and mechanical properties of high-strength concrete (HSC) by incorporating recycled concrete aggregates (RCA) of varying sizes and concentrations. The recycled aggregate concrete (RAC) was prepared by partially replacing RCA with natural coarse aggregate (NCA) at 0%, 15%, 30%, and 45%, with aggregate sizes ranging from 5 to 12 and 12–20-mm. Fresh concrete properties, such as slump, Kelly ball, compacting factor, K-slump, and fresh density, were tested to determine the influence of RCA size and concentration. In addition, the mechanical properties were studied through the execution of compressive, split-tensile, and stress-strain tests. The test results revealed that increasing the RCA concentration declines the fresh and hardened properties of HSC. In the fresh concrete experimentation, the 12–20 mm aggregate size RAC mixes exhibited greater workability than the 5–12 mm aggregate mixes. On the contrary, 5–12 mm aggregate mixes RAC had higher compressive and split-tensile strength and a higher modulus of elasticity than 12–20 mm aggregate mixes concrete. When it comes to sustainability, the study found that the smaller size range of RAC produces inferior embodied CO 2 (eCO 2) and provides a cost-effective and sustainable solution for the construction industry. [ABSTRACT FROM AUTHOR]

The accumulation of huge amounts of rubble and the worn-out tires that resulted from the severe damage to Syrian facilities because of the current war in Syria poses a serious environmental problem. In this research, therefore, asphalt mixtures containing recycled concrete aggregates and an asphalt binder modified with tire rubber crumbs were designed. It also determines the loading cycles until failure on fatigue and rutting of these mixtures by following numerical modeling and using the 3D-Move Analysis program. The results showed an increase in the optimal asphalt ratio, the proportion of air voids and flow with the increase in the proportion of recycled concrete aggregates in the asphalt mixture. Contrastingly, it showed a decrease in both volumetric density and stability with the increase in the proportion of these aggregates in the mixture. With modifying these mixtures with tire rubber crumbs, both of the percentage of air voids and stability increase, while the volumetric density and flow decrease. The results also showed an increase in the fatigue strength of the asphalt mixture with an increase in the proportion of recycled concrete aggregates, while the rutting resistance increased when the mixture was modified with tire rubber crumbs. [ABSTRACT FROM AUTHOR]

Recycled concrete aggregate (RCA) can be used in landfill and slope cover systems, where its unsaturated hydraulic properties play an important role. The hydraulic behavior of RCAs can be potentially controlled through mixing coarse and fine aggregates by a pre-determined proportion, which lacks experimental validation. In this study, water retention curve (WRC) and permeability function (PF) of RCAs with different fine aggregate contents (fc) were investigated. Experiments on 9 RCAs with different gradations reveal that when fc is between 20% and 30%, a second air entry value appears, and the shape of both WRC and PF becomes bimodal, which is probably resulted from an uneven dual-peak pore size distribution. With an increasing fc, the first air entry value and the residual water content increases. The unsaturated coefficient of permeability decreases with the increasing fc for a low suction level (<0.1 kPa), but increases with the raise of fc for high suction (>10 kPa). Overall, adopting a properly mixed RCA with fc value of less than 10% or over 40%, instead of a narrowly graded RCA, is recommended for coarse- and fine-grained layers in a capillary barrier, respectively. [ABSTRACT FROM AUTHOR]

The objective of this research is to develop an innovative methodology for evaluating the quality of coarse aggregate mixes that incorporate recycled concrete aggregate for use in structural concrete. The proposed approach consists of three steps: measuring the packing density, quantifying the adhered mortar, and characterizing the mechanical resistance of the aggregate mixes containing both natural and recycled concrete aggregate. Comprehensive practical recommendations for each step are discussed in detail to facilitate the broader future utilization of recycled concrete aggregate in structural concrete. The mechanical resistance of aggregate mixes is significantly influenced by both packing density and the quantity of adhered mortar. Predictive models are used to illustrate the mechanical resistance of aggregate mixes based on packing density and adhered mortar amount, recognizing the direct correlation between these properties. [ABSTRACT FROM AUTHOR]

The replacement of virgin aggregate with recycled concrete aggregate (RCA) in concrete mixtures offers an eco-strategy to mitigate the environmental limitations linked with traditional recycling techniques of RCA. However, the inferior properties of RCA, in contrast to virgin aggregate, present an obstacle to efficiently proceeding with this approach. Therefore, the aim of this study is to enhance the characteristics of concrete that contains RCA using nano-ZnO particles. Virgin aggregate was replaced with RCA in 30 wt.% and 50 wt.% ratios, followed by the addition of 0.5 wt.% nano-ZnO. The performance of concrete mixtures was evaluated in terms of their physical, mechanical, and durability properties. The addition of nano-ZnO particles to concrete with RCA resulted in refining its pore structure and reducing its water absorption, where the impermeability of concrete with 30 wt.% and 50 wt.% treated RCA decreased by 14.5% and 18%, respectively. Moreover, nano-ZnO treatment increased the compressive strength of mixtures with 30 wt.% and 50 wt.% RCA by 2.8% and 4%, respectively. All mixtures underwent a reduction in their 28-day compressive strength after exposure to a 5% sulphuric acid solution, where concrete with 30 wt.% and 50 wt.% RCA showed 20.2% and 22.8% strength loss, respectively. However, there was a 17.6% and 19.6% drop in the compressive strength of concrete with 30 wt.% and 50 wt.% RCA and treated with nano-ZnO. [ABSTRACT FROM AUTHOR]

Sustainable waste management aims to reduce the consumption of raw materials by reusing as many RCA materials as possible. This research aims to evaluate the influence treated and untreated recycling coarse aggregate on the hot asphalt mixture’s properties using asphalt grade (40-50) modified with 3% Polyphosphoric Acid (PPA). RCA was used in different proportions (25%, 50%, 75%, and 100%) as a substitute for raw coarse aggregate; the effect of treatment on improving the RCA’s quality was tested. Volumetric properties associated with the Marshall test for asphalt concrete were tested. Tensile strength ratio (TSR) and index of retained strength (IRS) measurements were used to assess the moisture effect. The study findings indicated that 25% RCA is the maximum amount of RCA from concrete that should be added to asphalt mixtures. This percentage recorded the highest values for TSR and IRS, with the ideal modified asphalt content of 4.86%. Based on the results of this study, asphalt concrete's durability will generally grow with RCA use, while its susceptibility to moisture will increase. However, treated RCA improved the results compared to untreated RCA. Using asphalt modified with polyphosphoric acid remarkably improved the asphalt mixtures’ performance and reduced the asphalt consumption rate.