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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.

Analyzing and validating the behavior of sustainable concrete mixes under near-realistic conditions is essential to advance their use. In this research, full-scale high-workability concretes, 0.5 m3 in volume, containing maximum amounts of sustainable raw materials and their response in cyclic wet-dry tests are studied. The mixtures contained Electric Arc Furnace Slag (EAFS) and Recycled Concrete Aggregate (RCA) as aggregates, and Ladle Furnace Slag (LFS) and Ground Granulated Blast-furnace Slag (GGBS) as binders. Each mixture underwent 30 wet-dry cycles with temperature variations between 20 °C and 70 °C. Throughout the cycles, the internal-damage level was assessed through (increasing) weight measurements, (decreasing) ultrasonic-pulse-velocity readings, thermal strain, hardened-property variations, and flexural deformability. Overall, all the mixes underwent initial internal damage, attributable to both the thermal shock that increased with each cycle and the aging of the cementitious matrix, which in turn resulted in shrinking that reduced their thermal deformability. A linear thermal expansion coefficient of 1.6·10-5 °C-1 was adequate for safely estimating all the maximum thermal strains. Internal damage was less relevant with the use of EAFS and GGBS that led to fewer strength decreases, which were only 15–20% compared to 25–30% in the RCA mixes. However, the combination of EAFS and LFS increased flexural deformability after the test, which resulted in compliance under bending stresses that was two times higher than in the other mixes. Under those conditions, the joint use of EAFS and GGBS was the most recommendable multi-criteria and multi-purpose option where any change in concrete composition significantly affected behavior.

Recycled concrete aggregate (RCA) presents several challenges such as irregular shape, high water absorption, high crushing value, and low apparent density, which restrict its application in concrete. Although carbonation technology offers a more effective solution, its effect on inferior RCA remains unclear. Compared to its common counterpart, inferior RCA is characterized by longer aging time, lower crushing value, and reduced carbonizable substances. This study focuses on low-quality RCA, employing a method of impregnation and carbonation with cement slurry to strengthen the properties of RCA. The investigation studied the carbonation system (hydration time + carbonation time), water–cement ratio of the cement paste, and carbonation effects and mechanisms via mercury injection, nanoindentation tests, X-ray diffraction, and scanning electron microscopy. The findings indicate that the optimal carbonation system involves hydration for 1 d and carbonation for 14 d (H1d + C14d). In this system, the water–cement ratio exhibits minimal influence on carbonation depth. After the impregnation–carbonation treatment, RCA displayed the best performance improvement at a water–cement ratio of 0.8 (0.8-RCA). This condition resulted in a 15.41% reduction in crushing value and an 18.00% decrease in porosity alongside a 21.42% increase in apparent density. Moreover, the interfacial transition zone (ITZ) between aggregate and mortar and the elastic modulus of adhesive mortar are improved after strengthening. Compared with the primitive RCA, the distribution of Ca2+ in the adhesive mortar of the strengthened RCA was more uniform and denser. The moderately fluid cement slurry penetrated the RCA pores easily, enabling CaCO3 produced by carbonation to efficiently fill defects.

Chloride migration poses a significant challenge to the long-term durability of concrete structures due to its potential to corrode reinforcement and deteriorate the structure. This study focuses on chloride migration in self-compacting concrete (SCC) made with pozzolans, namely silica fume (SF) and fly ash (FA), along with recycled concrete aggregate (RCA). Particularly, the effects of external electrical potential (power-on) duration and RCA content on the features of SCC were examined, alongside the influence of pozzolanic materials, focusing on the chloride migration coefficient and mechanical properties. Six groups of SCC mixtures were created with varying proportions of SF and FA, and different levels of RCA replaced the natural coarse aggregate. The findings reveal a multifaceted impact on SCC behaviour. The chloride migration coefficient exhibits a distinct pattern as the power-on duration increases from 12 to 36 h. Initially, the coefficient increases and then decreases, demonstrating a healing and sealing mechanism within the concrete matrix, which enhances resistance to chloride penetration. The chloride migration coefficient significantly decreased with adding SF and FA. With 15% SF and 30% FA, the coefficient decreased to 59.9% and 49.5%, respectively. Moreover, incorporating RCA in SCC mixtures significantly influences coefficient levels. RCA inclusion at 20% remarkably decreased the coefficient after 12 h by 16.17%. Subsequently, the levels decreased by 39.49% and 46.87% after 24 and 36 h, respectively, compared to the control mixture. This behaviour highlights the importance of RCA in enhancing the resistance of SCC to chloride ingress, a crucial factor for long-term durability. Additionally, mechanical properties such as splitting tensile strength, ultrasonic pulse velocity and surface hardness consistently improved with longer power-on durations and higher RCA and SF content. SCC with RCA and pozzolanic materials exhibits enhanced chloride resistance and superior mechanical performance, making it ideal for sustainable concrete production.

This study performed laboratory experiments to evaluate the performance of porous asphalt mixtures (PAMs) containing recycled concrete aggregate (RCA). One open aggregate gradation with Class C fly ash as the filler, granite aggregate, two binder types (PG 67–22 and PG 76–22), and four RCA contents (0%, 10%, 20%, and 30% by mass of aggregates in the sieve size range of 4.75 to 9.5 mm) were included in the experiments. The mixture properties evaluated include permeability and air-void content, Marshall stability and flow, indirect tensile strength, moisture susceptibility, Cantabro abrasion loss, macrotexture, and sound absorption coefficient. The study found that using a blend of granite and RCA in a PAM led to better performance in terms of indirect tensile strength, stiffness, moisture resistance, and resistance to raveling. This was particularly confirmed for PAMs with an unmodified PG 67–22 binder. The mixture that contained 30% RCA performed the most satisfactorily, with an indirect tensile strength of 0.81 MPa and a Marshall stability of 23 kN at 25 °C. These values were 37.5% and 15%, respectively, higher than the control mixture. Based on these results, the study recommends the use of 30% RCA in PAMs for the friction course of a highway pavement or the porous surface of a porous pavement.

Construction and demolition waste is produced in large quantities and constitutes an overlooked resource with significant potential for recycling and reuse. In fact, recycled concrete aggregate (RCA) has a high resource value, although it is also the case that RCA has characteristics that complicate its reuse. This research study looks at the efficacy of producing green self-compacting concrete (SCC) using uniform in-situ prestressed concrete pile waste (RCA) as a replacement for natural aggregate and fly ash (FA) as a replacement for Type 1 Portland cement (OPC). In accordance with the European standard, the workability characteristics of the SCC mixtures were assessed using slump flow, T500 time, J-ring flow, L-box, and V-funnel tests. The hardened properties of compressive strength at 7, 28, and 91 days as well as pulse velocity, Young's modulus, and surface resistivity were also tested. Based on this study, it is possible to produce SCC with both RCA and FA that has better workability and hardened properties than does RCA and also to reduce the negative effects of the latter. SCC produced without coarse natural aggregates showed compressive strength above 50 MPa and maximum compressive strength above 74 MPa at 91 days. SCC produced in this way is, therefore, viable for industrial use.

Influence of Bacillus Subtilis (B. Subtilis) bacteria on the strength characteristics of 100% recycled concrete aggregate (RCA), incorporating silica fume (SF) as a substitution of cement, has been investigated in this study. Two groups of mixes (A for w/c=0.3 and B for w/c=0.35) were prepared using two different cement contents in each (400 and 450 kg/m3). The cement was partially substituted by weight with 5%, 7.5%, and 10% SF, with a constant concentration of bacterial culture (105 cfu/ml). All specimens were tested after a curing period of 7, 28, and 90days. The best results were observed by replacing cement with 7.5% SF via all mixes, with the best mix being A/2. At 90 days, the compressive strength (CS) of concrete in mix A/2 increased from 29.62 to 33.64 MPa for 5% SF, from 29.62 to 37.3 MPa for 7.5% SF and from 29.62 to 34.04 MPa for 10% SF with the addition of B. Subtilis bacteria. Similarly, for splitting tensile strength (STS) at 90days, the strength increased from 2.73 to 3.24 MPa for 5% SF, from 2.73 to 3.35 MPa for 7.5% SF, from 2.73 to 3.26 MPa for 10% SF. Calcite precipitation upon addition of B. Subtilis bacteria is considered the reason for the improved CS and STS of concrete, and SEM and EDS analysis confirmed this. Thereby, the formation of new C-S-H products and CaCO3 crystals in voids made the concrete denser. Incorporation of B. subtilis led to a 12 ± 1.5% increase in CaCO3 formation in concrete’s mortar after 7days of curing compared to specimens without bacteria. Moreover, the effect of atomic Ca/Si and Al + Fe)/Ca ratios was studied, and the results showed that the highest CS and STS were associated with the values Ca/Si = 0.17 and Al + Fe)/C = 2.95. Meanwhile, it is noteworthy that according to the Indian specifications (IS-10262–2009), based on the strength of the concrete, the findings of this work fulfill the requirements of lean, ordinary grade, and standard grade concrete. An economic study of all mixes has also been carried out. Additionally, using response surface methodology, a regression equation was developed to accurately predict the CS and STS and validate the data in this experimental work with a minimum range of error.

Understanding the effects of recycled concrete aggregate (RCA) and polymer impregnation on the properties of self-compacting concrete (SCC) is crucial for the construction industry's efforts to reduce environmental impact and utilise recycled materials. This study aims to examine the impact of RCA inclusion and polymer impregnation on the properties of SCC, in response to the urgent demand for sustainable construction practices. Two different methods of polymer impregnation were evaluated to assess their impact on the workability and hardened characteristics of SCC. The SCC mixtures were prepared using river sand (natural fine aggregate (NFA)), natural crushed limestone (natural coarse aggregate (NCA)) and a polymer impregnation level of 0.05 wt% of the water content, with a water-to-cement ratio of 0.34. RCA was used as a complete replacement for NFA and NCA, adhering to the American Society for Testing and Materials (ASTM) C33 standards for recycled fine concrete aggregate (RFCA) and recycled coarse concrete aggregate (RCCA)The workability of the SCC mixtures was evaluated based on the criteria set by the European Federation of National Associations Representing for Concrete (EFNARC). Among the hardened properties, the compressive strength of the hardened properties was tested at four different time intervals (1, 3, 7 and 28 days), and the integrity of the SCC specimens was assessed using ultrasonic pulse velocity. The polymer impregnation process resulted in a slower compressive strength development rate compared to that observed in the control concrete. However, combining polymer impregnation type 1 with either RFCA and NCA or RCCA and NFA significantly increased the 28-day compressive strength by 5.02% and 1.80%, respectively. These findings provide valuable insights into the behaviour of SCC incorporating RCA and polymer impregnation. Optimising the selection and combination of materials can enhance the performance and sustainability of SCC in construction applications.

Material obtained from the demolition of concrete structures and milling of flexible pavements has the highest potential for recyclability. This study aimed to evaluate the performance of hot mix asphalt with the concurrent use of recycled asphalt pavement (RAP) and recycled concrete aggregate (RCA). Contents of RAP and RCA were varied from 0% to 50% by fixing the total recycling materials percentage to 50%. Penetration grade 40/50 virgin binder and waste engine oil (WEO) as rejuvenator were used in the present study. A series of tests, such as Scanning electron microscopy (SEM), Marshall stability, indirect tensile strength test, IDEAL CT, uniaxial compression test, and resilient modulus test, were carried out to assess the performance of the prepared recycled asphalt mixtures. SEM images revealed the presence of the medium to fine particles on RCA indicating the rough surface texture. Except RAP10 (10% RAP plus 40% RCA) and RAP50 (50% RAP) mixes, all mixes had Marshall stability value greater than the control mix, the highest for RAP40 (40% RAP plus 10% RCA) mix followed by RAP0 (50% RCA) mix. In the case of resilient modulus, the effect of RAP is more pronounced till 40% resulting in an almost linear increase in values. Also, RAP40 exhibited the highest rutting and fatigue resistance. As far as moisture sensitivity is concerned, all the mixes performed satisfactorily as the tensile strength ratio (TSR) was greater than 80%. Overall, the major factors affecting the performance of recycled mixes were surface roughness, stiffness of the aged binder and rejuvenator.

This study focuses on treating Acid Mine Drainage (AMD) using Recycled Concrete Aggregate (RCA) as a cost-effective and environmentally friendly material. RCA is utilized, considering its availability at low cost, to reduce heavy metal and sulfate concentration in AMD and neutralize its acidity in batch experimental mode. To that end, the adsorptive properties of RCA were characterized before and after adsorption by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), elemental mapping, Brunauer-Emmett-Teller (BET) surface area measurements, and X-ray Diffraction. Furthermore, the organic functional groups of the tested materials were identified by Fourier Transform Infrared Spectroscopy (FT-IR). Adsorption parameters such as dosage, contact time, the grain size distribution of adsorbent particles, and the solution pH, were optimized for enhancing the removal performance. The pH point of zero charges for the RCA sample was defined. The results revealed that RCA is a potential eco-friendly material for AMD treatment. The concentration of sulfate in the tested AMD water was reduced by approximately 84%, while that of the metal elements declined as follows: iron 100%, manganese 95%, copper 66%, zinc 97%, and lead 76%. Also, the pH value of AMD water increased rapidly and reached neutral by using small quantities of RCA (≤1g/L).

The construction industry in general is, through minor low-cost processing methods, converting several of its by-products into viable materials; furthermore, some siderurgic sector by-products are likewise of use. In this context, large-scale batches (mix volumes over 0.5 m3) of good quality structural concrete are proposed, in which two kinds of binder and two kinds of aggregate (steel slag and recycled concrete) are used to perform four concrete mixtures, containing more than 80 % in mass of good-quality recycled materials. A batch of tests, both in the fresh and in the hardened state, are performed, covering on-site placement and long-term properties, to guarantee the suitability and the quality of the mixtures as structural concretes. Most of the results were encouraging, mainly depending on the aggregate and the binder types that were used. The fresh-state workability of all the test mixtures was good. All the results in terms of hardened properties, strength (42 MPa in type I cement mixtures, and 32–38 MPa in type III cement mixtures), stiffness, long-term shrinkage, and microstructural state (porosity, permeability) were acceptable, their quality depending on the type of each component. The good results of the mixtures based on the slag-based binder deserve attention. Some weak points found were the slightly higher specific weight of the slag aggregate mixes (amounting to more than 2.7 Mg/m3), plastic shrinkage rates (in some cases greater than 1.2–1.5 thousand), and loss of resistance against chlorine penetration in recycled concrete mixes. However, drawbacks of that sort are no obstacle to their use in most structural applications.

Some techniques, such as removing the adhered mortar particles and surface modification of recycled aggregates, have been investigated in an attempt to improve their quality. This study intends to evaluate the performance of concrete containing recycled concrete aggregate (RCA) subjected to Portland cement treatment and grinding, as partial replacement of coarse crushed aggregates at 20 % and 50 %. It became evident that using RCA in the mix of new concrete has a negative impact on its properties. However, it was found that the use of treatments such as mechanical grinding and a two-stage mixing approach (TSMA) with 25 % Portland cement in the mix were viable technical alternatives for improving these aggregates. The test results indicated that, due to the efficiency of the grinding treatment (T1), the CRCA50-G mix presented a higher compressive strength than CRCA20-G and, when treatment TSMA (T2) was used, both the CRCA20-G-TS25 and CRCA50-G-TS25 mixes outperformed the conventionally mixed concrete, resulting from a superposition of effects. The splitting tensile strength results were satisfactory when replacing up to 50 % and the use of treatment T2 in concrete with varying RCA did not present a significant effect on this property. The two-stage mixing method applied together with grinding aid in the densification of the porous microstructure, which improved concrete resistance against carbon dioxide diffusion and chloride ingress, beyond improvements in water absorption by capillarity, which enabled greater use of RCA. It was concluded that the use of treatments like these improves the mechanical properties and durability of concrete produced by RCA, mainly when these treatments are used simultaneously. In general, using a properly prepared RCA can be produced concrete with physical and mechanical properties besides performance characteristics.

The behavior of Self-Compacting Concrete (SCC) is very sensitive to the use of by-products in replacement of conventional cement or finer aggregate fractions. The high proportions of these raw materials in SCC can in great part explain this performance. 18 SCC mixes of slump-flow class SF3 were prepared for a thorough evaluation of different sustainable materials and for the prediction of their effects as binder or fine/powder aggregate on the mechanical properties of SCC. The mixes incorporated 100% coarse Recycled Concrete Aggregate (RCA); different amounts (0%, 50% or 100%) of fine RCA; CEM I ordinary Portland cement and CEM III/A (with 45% ground granulated blast furnace slag); and more sustainable powders compared to conventional limestone filler

Warm Mix Asphalts (WMAs) are asphalt concretes produced at lower temperatures than traditional Hot Mix Asphalts (HMAs). Nonetheless, the above is not enough to diminish the environmental impacts associated with the road infrastructure industry. Accordingly, incorporating Recycled Concrete Aggregate (RCA) as a partial replacement for Natural Aggregates (NAs) in WMA design has been gaining notoriety in the literature as a viable alternative to increase sustainability. However, the eco-friendly manufacturing of WMA with RCA contents (WMA-RCA) is not easy to obtain satisfactorily because the RCA causes alterations in the mix design. Thus, this research proposes three (3) methods to determine the optimal design conditions (coarse RCA content) that minimize the environmental burdens caused by WMA-RCA production. The first method is a mathematical model based on Multiple Linear Regression (MLR), which is used as a benchmark for the other two methods. The second and third methods are computational models based on Artificial Intelligence (AI), i.e., Artificial Neural Networks (ANNs) and Genetic Algorithms (GAs), respectively. Notably, the Life Cycle Assessment (LCA) was employed as the theoretical framework to support all the proposed models. Consequently, this study concludes that: (i) all the proposed methodological alternatives achieve results with a great accuracy; (ii) the GAs model is the most precise method in terms of error minimization; (iii) the MLR model is the fastest method in terms of execution time; and (iv) the ANNs model is the method that requires the longest time of running, and its exactness is at a midpoint concerning the other models.

Concrete in service is unpredictably exposed to fire attack, while the properties of recycled concrete aggregate (RCA) and recycled concrete powder (RCP) from demolishing fire-damaged concrete have received little consideration until now. This work investigates the effects of fire-damaged concrete waste on the properties of its preparing RCA, RCP and newmade concrete. The results show that the water absorption of RCA from 300 to 800 °C fire-damaged concrete is 39.1–169.5% higher than that of ordinary RCA from waste concrete without induced damage. The properties of concrete decrease as RCA incorporates, and decrease following the growth of undergoing temperature on the fire-damaged concrete and its RCA. The compressive strength of concrete including 100% RCA from 300 to 800 °C fire-damaged concrete is 11.4–41.4% lower than that of concrete with 100% ordinary RCA, and the transport properties of concrete including fire-damaged RCA are higher than those of concrete with ordinary RCA. There is no obvious difference in the mineral composition of RCP made from 20 to 600 °C fire-damaged concrete, but new active components appear in RCP made from 800 °C fire-damaged concrete. The activity indexes of ordinary RCP and the RCP from 800 °C fire-damaged concrete are 72.6% and 90.4%. The properties of concrete decrease as RCP incorporates, while the properties of concrete incorporating RCP from fire-damaged concrete are better than those of concrete incorporating ordinary RCP. The compressive strength and absorption coefficient of concrete including 30% RCP from 800 °C fire-damaged concrete are 20.9% higher and 24.9% lower relative to concrete with 30% ordinary RCP.

Concrete is the most often used material in the building sector. The use of ground-granulated blast-furnace slag (GGBFS) and recycled concrete aggregates (RCA) in concrete reduces its negative environmental impact. However, increasing the number of ingredients in concrete complicates the prediction of its compressive strength. This research aims to develop a machine learning model for predicting the compressive strength of eco-friendly concrete using Multivariate Adaptive Regression Splines (MARS). MARS is a well-known technique for creating predictive modeling equations using experimental data. A data set of 161 concrete specimens was obtained to train and evaluate the machine learning algorithms for this work. The findings of the MARS prediction algorithm were compared to those of the Support Vector Machine and the Random Forest regression algorithms (black-box models) using the training set. A hyperparameter tuning procedure was applied to find the optimal MARS, RF, and SVM model parameters. The results of 5-fold cross-validation indicate that the MARS optimal model has the highest coefficient of determination (R2), with a value equal to 0.889, and the lowest Root Mean Squared Error (RMSE) measure, with a value equal to 4.110 MPa. For our case, the performance metrics measures proved the superiority of the MARS model when compared with RF and SVM. The final MARS optimal prediction equations were built using a full training set and were then evaluated using unseen data (testing set). Our model has the potential to help civil engineers in designing durable infrastructures.

Any variation in temperature alters the dimensions of a concrete structure and provokes thermal stress. Moreover, the propagation of micro-cracking decreases the strength of concrete that is exposed to sub-zero temperatures (freezing), to heat phenomena (heating), or to cyclical thermal variations, especially when prepared using Recycled Concrete Aggregate (RCA). A reference self-compacting concrete (SCC) mix made with 100% coarse and fine natural aggregate and three SCC mixes containing 100% coarse and/or fine RCA in replacement of natural aggregate were tested in this study of the thermal performance of SCC and the related effects of RCA. The mixtures were subjected to five thermal tests designed with positive and negative, and both constant and cyclical, extreme-ambient temperature variations, reaching temperatures of − 15 °C and 70 °C. Stiffness, weight, compressive strength, thermal deformability, and internal damage of the SCC mixtures were monitored throughout suitable testing. Internal damage, hygroscopicity, and loss of strength increased at temperatures below 0 °C, especially in the mixtures containing 100% coarse RCA, although the SCC manufactured with simultaneous additions of fine and coarse RCA fractions showed the worst performance. Overall, RCA performed better under positive temperature variations. The test results lead to the recommendation of a linear thermal expansion coefficient of 1.2·10−5 °C−1 in calculations for SCC containing RCA under those extreme environmental conditions.

The paper is focused on the eco-efficiency calculations of recycled aggregate concrete (RAC) consisted of ordinary Portland and blast-furnace slag cements with three fine-grained wastes: quartz powder (Q), limestone powder (L) and fly ash (F). The characteristics of concrete mixes (slump and air content) and hardened concrete properties: 28- and 90-day compressive strength, water absorption as well as the depth of the carbonation (after the accelerated carbonation in the chamber) were examined. In order to parameterize the third feature of contemporary concrete, which is (next to the strength and durability) its sustainability potential, the binder intensity (bi) and carbon intensity (ci) indexes were calculated, taking into account CO2 emissions from cement production and technological processes related to preparation for use of other ingredients. The comparison of the effect of limestone powder and fly ash showed some advantages of the fly ash (taking into account the results of strength tests). However, limestone powder turned out to be more favorable in influencing other properties (especially resistance to carbonation). Nevertheless, the use of fly ash proved to be the most effective in terms of eco-efficiency factors. The pozzolanic properties of F increased the strength of the concrete, reducing both bi and ci values. Furthermore, the presence of F canceled out the negative effect of quartz powder. The use of F together with cement containing ground-granulated blast-furnace slag (GGBS) was most beneficial. Although quartz powder due to technological reasons occurred to be the worst option, its use may be beneficial when CO2 sequestration by concrete carbonation is taken into account. Lower strength and resistance to carbonation of concrete with Q allow CO2 to penetrate deeper into the structure, especially in concrete made of GGBS cement. In this way, the later uptake of CO2 from the atmosphere allows for a partial reduction of the ci value, making RAC more eco-efficient.

In this experimental study, the impact of using waste materials such as ground granulated blast furnace slag (GGBFS), waste rubber powder (WRP), and recycled concrete aggregate (RCA) were evaluated on the compressive, tensile and, flexural strengths and durability test of rapid chloride migration test (RCMT) of concrete. It was observed that the mechanical properties of concrete decreased by raising the proportions of recycled materials in all replacement ratios. Because of the adverse effects of the WRP and RCA on the cement matrix and the interfacial transition zone, the reduction of the mechanical properties is higher for the concrete specimens with both recycled materials. In the case of durability, the migration rate of chloride ions in concrete is reduced by increasing the WRP rates due to the blockage of micro-pores connections. However, adding the RCA has a negative effect on the durability performance of concrete. Regarding the simultaneous effect of slag, rubber powder, and recycled aggregate on the migration of chloride ions, it can be derived that durability of samples containing 20% slag, 2.5% rubber powder, and 25% recycled aggregate at the age of 7 days on average is 14.8% higher compared to the reference sample. As the age of the samples increases to 28 days, the migration of chloride ions in the samples reduced 9.5% compared to 7 days.

The combined use of recycled concrete aggregate (RCA) and glass fiber reinforced polymer (GFRP) reinforcement in reinforced concrete (RC) structures is deemed plausible to achieve sustainable construction. This paper aims to examine the effect of such a combination (RCA + GFRP reinforcement) on the shear behavior of RC beams. Six medium-scale RC beams (150 × 260 × 2200 mm) critical in shear were tested under three-point loading until failure. The test variables were the aggregate type (natural/recycled) and the shear reinforcement (steel/GFRP/none). The failure modes, cracking patterns, load-carrying capacities, deformational and strain characteristics were analyzed and compared among the tested specimens. It was found that using 100% RCA in the concrete mix reduced the shear strength of RC beams (by 12% on average). Minor effects were observed on the shear strength of the beam specimens (∼2%) with altering the transverse reinforcement (GFRP versus steel). Theoretical load-carrying capacities of the tested beams were obtained as per contemporary design guides and compared with the experimental results.

The effects of using recycled concrete aggregate (RCA) as coarse aggregate on the equivalent substrate stiffness and mechanical properties of sustainable alkali-activated concrete were investigated in this paper. High-calcium fly ash (HFA) and commercial silica fume (SF) were used as the precursors for producing the alkali-activated high-calcium fly ash concrete (AAHFAC). Sodium hydroxide (SH) and sodium silicate (SS) solutions were used as alkaline activator solutions with the constant SS/SH ratio of 1.0 and liquid-binder (L/B) ratio of 0.50. The natural coarse aggregate (NCA) used in this study was crushed limestone and replaced with RCA at the rates of 0%, 20%, 40%, 60%, 80%, and 100% by volume. The setting time, compressive strength, elastic modulus, Poisson’s ratio, and bond strength obtained by pull-out tests of AAHFAC and Portland cement concrete (NC) were investigated. Experimental results showed that the use of RCA to replace NCA resulted in reducing the setting time of concrete. Also, the setting time of the AAHFAC with and without SF were shorter than that of NC mixes for all of RCA replacement level. The use of RCA had a positive effect on the mechanical properties of alkali-activated binder; however, they declined at NC mixes. Therefore, the use of RCA in alkali-activated binder concrete is an excellent alternative for sustainable concrete since it allows for the substitution of natural resource components while somehow producing low CO2 emissions.

Establishing an effective method to enhance the adhesion of mortar on recycled concrete aggregate (RCA) is key to the utilization of RCA. In this paper, a novel and simple approach for strengthening the mortar layer of RCA by treatment with a crystallizing agent (CA) was proposed, and the effects of different treatment regime on the density, water absorption, mineral composition, and microstructure of RCA were determined. Moreover, the performance of CA-treated RCA in recycled aggregate concrete (RAC) was investigated, and its mechanism of the treatment was explored at both the microscopic and macroscopic levels. The results showed that CA treatment significantly improved the overall performance of RCA by increasing the density and calcium silicate hydrate (C–S–H) content, which enhanced the properties of the new and old interfacial transition zones and enhanced the mechanical properties of the RAC. The improvements were attributed to the reaction of CA with calcium-rich hydration products in the mortar layer of RCA, which formed C–S–H precipitates. The newly-formed C–S–H filled the pores of RCA and blocked cracks, which improved the compactness of the RCA.

Vinasse is the main by-product of the sugar and alcohol industry. For each liter of ethanol produced from sugarcane, approximately 12–18 L of vinasse are generated. Being such, its use as a hydration agent in concretes may be useful to save drinking water. This work analyzed the compressive strength of concrete manufactured with vinasse and recycled concrete aggregates (RCA), as a substitute for water (100%) and sand (50 and 100%), respectively. At the initial periods (7 and 14 days), the compressive strength of specimens hydrated with water was higher than those hydrated with vinasse due to the delay in hydration of the cement caused by the sucrose present in the vinasse. Therefore, in these stages, the hydration agent is the main contributor for the differences in the compression strength (p

Recycled aggregate concrete (RAC), mainly made from recycled materials such as construction and demolition waste (CDW), has emerged as a sustainable alternative to natural aggregate concrete (NAC). While RAC offers potential benefits in waste reduction and resource conservation, a comprehensive understanding of its environmental impact and sustainability compared to NAC has been lacking. This study addresses this gap by conducting a thorough review and analysis of comparative Life Cycle Assessment (LCA) studies between RAC and NAC. This paper synthesizes current literature to evaluate the environmental impact of both materials throughout their life cycles, from raw material extraction to disposal. It examines key factors such as energy consumption, greenhouse gas emissions, and resource depletion to provide a thorough comprehension of the effects on the environment of each concrete type throughout their life cycles. Challenges in using RAC as a sustainable concrete option, such as sourcing and quality control, are also discussed, along with recommendations for future research and industry practices. The findings indicate that the environmental impact of RAC compared to NAC is significantly influenced by transport distances and modes. In addition, the choice of functional units in LCAs substantially affects the comparison between RAC and NAC, with strength reliability offering a clear benefit by addressing concrete property variability and better reflecting real-world conditions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Construction and demolition activities generate numerous waste that could be reutilized as recycled aggregates. The replacement of natural aggregate with recycled aggregate generally has negative impact on the performance of conventional concrete. This impact is found to be less significant in self-compacting concrete (SCC), owing to the better quality of binder which modifies the interfacial transition zone and lesser amount of coarse aggregates used. Considering the wide sources of recycled aggregates such as concrete, bricks and blocks, few studies were conducted on comparing the performance of SCC incorporating different types of recycled aggregates. In addition, since SCC is more commonly used in high-rise buildings which may experience fire risks, it is important to ascertain the corresponding high temperature resistance. In this paper, three different types of recycled aggregates are considered, namely recycled concrete aggregate (RCA), recycled brick aggregate (RBA), and recycled concrete block aggregate (CBA). 100 % replacement is feasible for SCC-CBA and SCC-RCA because of the minor strength reductions. The results also showed that the RBA and CBA concretes outperformed the NA concrete at high temperature (400 °C and 600 °C). RBA is suggested to partially replace natural aggregate, since it gives inferior performance at room temperature, but it is more recommended to be used in high temperature environments.

The use of waste materials in the concrete mixture can help human beings to preserve the environment and achieve environmentally-friendly concrete. In this study, the influences of simultaneous replacements of cement by waste rubber powder (WRP) and coarse aggregate by recycled concrete aggregate (RCA) on the mechanical properties and durability of concrete were investigated experimentally. To do so, concrete specimens containing the WRP with the replacement ratios of 0 %, 2.5 %, and 5 % by weight of cement, and the RCA with the replacement levels of 0 %, 25 %, and 50 % of coarse aggregate were prepared. Moreover, different water to binder ratios and binder content were used. Mechanical properties of the concrete specimens consisting of compressive, flexural, and tensile strengths and the durability test of rapid chloride migration test (RCMT) were carried out at different ages. It was observed that the mechanical properties of concrete decrease by raising the proportions of recycled materials in all replacement ratios. Because of the negative effects of the WRP and RCA on, respectively, the cement matrix and the interfacial transition zone, the reduction of the mechanical properties are higher for the concrete specimens with both recycled materials. In the case of durability, the migration rate of chloride ions in concrete reduces by increasing the WRP rates due to the blockage of micro-pores connections. However, adding the RCA has a negative effect on the durability performance of concrete. Finally, four equations were proposed and evaluated for the compressive, tensile, flexural strength reduction and durability factors of concrete containing the WRP and RCA using the genetic programming.

The use of Recycled concrete aggregate (RCA) obtained from construction and demolition waste not only reduces the need for virgin aggregates but also solves the problems associated with the disposal of construction and demolition (C&D) waste. Despite being a promising prospect, field utilization of RCA in bituminous mixes is limited due to the problems like lower strength and higher moisture susceptibility. To solve these issues present study aims at examining the effect of lime filler on RCA incorporated bituminous mixes. In the present study, RCA was obtained by mechanically treating C&D waste in a Los Angeles abrasion machine. Bituminous mixes were prepared by using 10%–50% of RCA. Additionally, 2% lime was added to the RCA incorporated mixes, and the parameter like optimum bitumen content, Marshall stability, Marshall quotient, Indirect tensile strength, Retained Marshall stability and Tensile strength Ratio were compared with the control mix to examine the effect of RCA and lime on mix properties. The inclusion of RCA was found to adversely affecting the properties of the mix whereas the inclusion of lime improved the properties. To provide a clear understanding of the environmental and economic benefits of utilizing RCA in bituminous mixes, economic and environmental assessment was also done. Based on different test results and analysis it was concluded that with the use of lime fillers it is possible to produce economical and environmentally friendly RCA incorporated bituminous mixes having properties comparable/better than conventional hot mix asphalt (HMA).

Conventional stone aggregates are becoming scare and costly because of huge infrastructure activities going on since last three decades in India. On the other hand, wastes such as that resulting from old concrete constructions are abundantly available. Many attempts have already been made to utilise these wastes referred to as recycled concrete aggregate (RCA) in various constructions including in bituminous paving layers. All types of bituminous binders commonly used in paving mixes in India may not be compatible with RCA. This experimental study aims to study the influence of binder type on the performance of dense graded bituminous mixtures containing RCA replacing the coarse fraction of conventional stone aggregates. In order to achieve this main objective, dense bituminous macadam (DBM) mixtures as per the relevant Indian specifications were prepared using three different types of bituminous binders commonly used in India, namely conventional VG 30 and VG 40 bitumens, and crumb rubber modified binder (CRMB). Separate Marshall samples were prepared using RCA and natural aggregate (NA) and either of the above three binders. As per the main scope of this study, the mixtures thus prepared were evaluated in terms of their engineering properties such as Marshall characteristics, indirect tensile strength, moisture susceptibility characteristics, resilient modulus and rutting resistance. It is observed that all mixtures considered in this study, in general satisfy the requirements in terms of Marshall and moisture susceptibility characteristics. Considering all engineering properties studied, the CRMB/VG40 bitumen offer superior and satisfactory results for mixtures containing either NA or RCA, with NA showing slightly better result as compared with RCA in the mixtures.

The eastern oyster (Crassostrea virginica) is a keystone species in the estuaries of the mid-Atlantic of the United States. Its population experienced drastic declines in the last century due to overfishing, habitat loss, and disease. Much interest has been focused on restoring this important commercial and ecological species. This research focused on evaluating the suitability of using recycled concrete aggregate (RCA) from road projects as an alternative bottom conditioning material for oyster restoration and aquaculture in the Chesapeake Bay. Three types of substrate (RCA, natural oyster shell, and RCA with a veneer of oyster shell) were used as bottom conditioning materials and tested their impacts on benthic epifaunal community and oyster recruitment at two sites in the Chesapeake Bay over the summer and fall of 2013. The diversity and abundance of the epifaunal community, and oyster spat density associated with these bottom conditioning materials were sampled. The results showed there was no significant difference across substrate type (RCA, oyster shell, and RCA with oyster shell) in terms of their impacts on benthic community diversity and oyster recruitment, demonstrating that RCA, as an alternative material, was generally similar to natural oyster shell with regards to ecosystem services provided, and could be a potential source for much needed bottom substrate for oyster restoration and aquaculture.

Carbon emissions from landfill construction and management have become a global concern. Life cycle analysis (LCA) has been widely used to assess the environmental impacts of engineered infrastructures over their lifetimes. LCA has also been applied to landfill leachate and gas management, but rarely to landfill final cover systems. This paper reports the results of an LCA of the following landfill final cover systems: compacted clay cover, geomembrane cover, cover with capillary effects (CCBE), dual capillary barrier cover, three-layer landfill cover system using natural soils, three-layer cover using recycled concrete aggregate (RCA) and biochar-amended three-layer landfill cover system using RCA. The LCA assessment of landfill cover considers the cost, carbon emissions and carbon sequestration during the production, construction and operation phases. The effects of landfill cover on global warming, freshwater eutrophication, terrestrial ecotoxicity, freshwater ecotoxicity, marine ecotoxicity and fossil resource scarcity are also evaluated. In addition, the sensitivities of cost and carbon emission to the use of electric-powered machines and transportation distance are analysed. It is revealed that the three-layer cover system using RCA and biochar has the lowest unit cost and carbon emission of all of the covers, up to 88 % and 66 % lower, respectively, than those of the other six covers. In addition, this cover system has the highest carbon sequestration rate, with a value of 47.9 kg CO 2 /(y·m 2 ), four times higher than that of the compacted clay cover. Finally, this sustainable cover mitigates global warming and reduces adverse environmental impacts by up to 82 %. Therefore, the biochar amended three-layer cover system using RCA without geomembrane offers the greatest economic benefits, performs effectively in terms of the pursuit of carbon neutrality and promotes sustainable development., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

In the current green concrete structures, recycled concrete aggregate is used as recycled concrete waste. In this process, concrete waste is collected and crushed using a recycling procedure in order to produce crushed concrete which is then used in structural concrete where it replaces natural aggregate which is coarse. The recycled aggregate concrete is a sustainable concrete waste which in the long term can replace the demand for natural aggregate, a process which would, in turn, lead to its preservation. However, most concrete industries have been observed to be reluctant in the production of recycled aggregate concrete and utilization in its maximum potential. Industries are yet to embrace it not only due to its uncertain material performance but also due to its unexplored manufacturing plant operations which are yet to be established. This research aims to use of a cost-benefit analysis model of the production of ready-mixed high-performance concrete made with recycled concrete aggregate in Thailand. The model focuses on the evaluation of the financial effects which favor the recycled aggregate concrete manufacturing operations instead of the ordinary concrete. Research findings indicate that regardless of the manufacturing plant used, the price of recycled concrete aggregate cannot decrease below the price of natural aggregate concrete. The key result of this research is that recycled concrete aggregate manufacturing set-ups can be used in the industrial-scale manufacture of recycled concrete and at low prices. In addition, overhead bin type and front-end loader type of plants can be used to lower the incremental costs of recycled concrete aggregate. However, the demand and supply factors and the pricing effects of recycled concrete pose various difficulties which are hardly accounted for.

This paper presents an analytical approach to calculate the effective diffusion coefficient of chlorides in concrete with both natural and recycled concrete aggregates. In the approach the concrete is treated as a composite consisting of three phases, namely mortar, natural aggregate plus interfacial transition zone, and recycled concrete aggregate plus interfacial transition zone. The effective diffusion coefficient of chlorides in the composite is calculated through two steps. The first step is to calculate the effective diffusion coefficients of chlorides in the natural aggregate plus interfacial transition zone and in the recycled concrete aggregate plus interfacial transition zone by using multilayer spherical approximation, the results of which provide the information about the quality of recycled concrete aggregate in terms of chloride penetration resistance. The second step is to calculate the effective diffusion coefficient of chlorides in the three-phase concrete composite by using effective medium approximation, the results of which provide the information about the influence of recycled concrete aggregate on the diffusivity of recycled aggregate concrete. The analytical expression of the effective diffusion coefficient is derived and carefully compared with the results obtained from both the experiments and numerical simulations, which demonstrates that the present analytical model is rational and reliable. The analytical expression presented can be used to predict the service life of recycled aggregate concrete exposed to chloride environment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)

The coronavirus (COVID-19) pandemic has not only created a global health crisis, but it is also now threatening the environment. A multidisciplinary collaborative approach is required to fight against the pandemic and reduce the environmental risks associated with the disposal of used personal protective equipment (PPE). This paper explores an innovative way to reduce pandemic-generated waste by recycling the used face masks with other waste materials in civil constructions. In this research, for the first time, a series of experiments, including modified compaction, unconfined compression strength and resilient modulus tests, were conducted on the blends of different percentages of the shredded face mask (SFM) added to the recycled concrete aggregate (RCA) for road base and subbase applications. The experimental results show that RCA mixed with three different percentages (i.e., 1%, 2% and 3%) of SFM satisfied the stiffness and strength requirements for pavements base/subbase. The introduction of the shredded face mask not only increased the strength and stiffness but also improved the ductility and flexibility of RCA/SFM blends. The inclusion of 1% SFM to RCA resulted in the highest values of unconfined compressive strength (216 kPa) and the highest resilient modulus (314.35 MP). However, beyond 2%, increasing the amount of SFM led to a decrease in strength and stiffness., Competing Interests: Declaration of competing interest We hereby confirm that there are no conflicts of interest associated with our paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

The prevalence of construction and demolition (C&D) waste and the concurrent demand for construction aggregate presents the opportunity to recycle C&D waste materials as substitutes for virgin aggregate. Commonly, recycled concrete aggregate (RCA) is used as base course in pavement construction. Environmentally responsible applications of RCA must consider the high pH leachate and trace element leaching risks reported in the literature. This review presents the methodology, results, and limitations of existing laboratory and field investigations of RCA leachate chemistry. Long-term highway field studies of RCA leachate illustrate that an initially high leachate pH approaches neutral within approximately one to two years of construction. Conversely, laboratory investigations of RCA leachate pH using batch reactor leaching tests and column leaching tests measure consistently high leachate pH (pH > 10). The discrepancies between field and laboratory measurements of RCA leachate pH suggest that the current laboratory methodology inadequately describes leachate conditions in the field. The authors recommend that future laboratory investigations consider intermittent wetting and drying cycles, eliminate particle abrasion, employ relevant contact times, and consider additional environmental processes that reduce leachate pH such as soil acidity and carbonation., (Copyright © 2019 Elsevier B.V. All rights reserved.)