Search

Destruction of old buildings generates waste concrete and powder. In addition, the city's drainage system is gradually struggling to keep up with the demands. Therefore, this study takes the recycled aggregate and powder generated from the crushing of waste C30 concrete as the research object, and investigates the impacts of both on the permeable mortar and summarizes the permeability mechanism and hydration mechanism of permeable mortar. Carbon emission reduction calculations and life cycle assessment were performed for both. The study’s findings demonstrated that the extent of volcanic ash reaction increases and then decreases with increasing grinding time. Considering the activity and economy, the regenerated powder with a grinding time of 5 min was selected, and its activity index was 83%. By exploring the performance of the two, the permeable mortar with 10% of recycled micronized powder and 50% of recycled aggregate has good mechanical properties and water permeability, and its permeability coefficient is about 1.57 mm/s, continuous porosity is 21.8%, and the compressive strength is 18.7 Mpa. The permeable mortar has a quality loss rate of 5.01% and a strength loss rate of 25.1% at the 17th freezing and thawing cycle. Recycled aggregates and recycled powders produce far fewer carbon emissions during production and transportation than natural sand and cement. Currently, permeable bricks are mainly used as construction materials for sidewalk pavements. Recycled permeable mortar is more convenient, environmentally friendly, and stronger than permeable bricks, so the research results will provide basic theoretical support for replacing permeable bricks with recycled permeable mortar. [ABSTRACT FROM AUTHOR]

Nowadays, special concrete-like self-compacting concrete (SCC) requires sustainability by introducing recycled aggregates as a partial replacement for natural aggregate. Technological development initiatives in the construction sector estimate the 28 days' concrete compressive strength before casting due to faster requirement; one method selected is an artificial neural network. From works of literature, 515 mixed design are collected and utilized for training, validation, and testing data to prepare models. Different applications of SCC require different strengths of concrete. Based on control mix compressive strength, the mix designs are grouped into three families as low, medium, and high strength, apart from a common family. The correlation between input and output variables for three different families is analyzed. ANOVA analyses are done for input parameters. Coefficient of relation (R2) is used for sensitive assessment and results for family I (R2 = 0.9299), family II (R2 = 0.824), family III (R2 = 0.8775), and family IV (R2 = 0.7991). Two further sensitivity analyses indicate that input parameters' influence varies for different families.

Several research studies have been conducted to investigate the hardened and durability characteristics of the normal aggregate concrete (NAC) and recycled aggregate concrete (RAC). Similarly, few studies have been done to examine the thermal behaviour of the NAC and RAC. However, the influence of elevated temperature on the RAC with treated recycled coarse aggregate (RCA) in the concrete still needs to be investigated. This study presents the comparative discussion on the thermal performance of NAC, RAC, carbonated recycled aggregate concrete (CRAC) and bio-deposited recycled aggregate concrete (BRAC) at various elevated temperatures of 25, 200, 500 and 800°C. The investigation involves the determination of residual compressive strength, tensile strength, elastic modulus and thermal conductivity with a series of concrete mixtures under elevated temperatures. The optimal residual strength was observed at 500°C, beyond exposure of it causes a reduction in the strength. The residual strength of NAC, RAC, CRAC and BRAC at optimal temperature was reduced by 30.10%, 7.06%, and 31.02%. The equivalence of the thermal expansion coefficient of RCA with cement paste improves the residual response of RAC, and higher porosity of RCA decreases the thermal conductivity of the RAC by 43.06% compared to control concrete. Furthermore, no concrete samples crumbled at 800°C, but the residual properties tend to decrease for all mixes.

The bond strength of tension lap splices in recycled-coarse-aggregate-reinforced concrete strengthened with hybrid (steel–polyolefin) fibers was experimentally investigated. This study was conducted with the help of twelve lap-spliced beam specimens. The replacement level of coarse natural aggregates with recycled concrete aggregate (RCA) was 100%. The following variables were investigated: various ranges of steel–polyolefin fibers—100–0%, 75–25%, 50–50%, 25–75%, and 0–100%—in which the total volume fraction of fibers (Vf) remains constant at 1%; and two lengths of lap splices for rebars of 16 mm diameter (db): 10 db and 15 db. The test results showed that the best range of steel–polyolefin fibers that gave the highest bond strength was 50–50%. The ductility of the fiber-reinforced recycled-aggregate (FR-RA) concrete was significantly improved for all the cases of various relative ratios of steel and polyolefin fibers. The bond strength was also predicted using three empirical equations proposed by Orangun et al., Darwin et al., and Harajli. This study showed that the Harajli equation gave a more accurate estimation of the bond strength of reinforcing bars embedded in FR-RA concrete than those proposed by Orangun et al. and Darwin et al.

Recycled concrete aggregates are potentially interesting for the precast concrete industry as they provide a new use for high-quality waste from its products’ life cycle. In precast concrete structures, it is common to use headed bars in several connection types between structural members. This paper presents the results of experimental tests to investigate the impact of replacing coarse natural aggregates with coarse recycled concrete aggregates in the concrete breakout strength of cast-in headed bars embedded in slender structural elements. Results of 12 tests on 16 mm headed bars embedded in 500 × 200 × 900 mm concrete members with an effective embedment depth of 110 mm are presented. The percentage of replacement of natural aggregates by recycled concrete aggregates was 0%, 30%, and 100%, and the flexural reinforcement ratio of the structural elements varied from 0.5% to 3.5%. The behavior and strength of the tested specimens are discussed, and comparisons with theoretical strength estimates are presented. The results showed that the concrete breakout strength of the headed bars was not affected by the use of recycled concrete aggregates and that the flexural reinforcement ratio significantly impacts the load-carrying capacity of the headed bars as they control the crack widths before failure.

Despite extensive regulations, the systemic under-reporting of construction and demolition waste generation rates pervades the South African waste sector due to the extensive and active informal waste management practices that are typical of developing countries. This study merges the rapid development of high-technology 3D-printed concrete (3DPC) with the increasing pressure that the built environment is placing on both natural resource consumption and landfill space due to construction and demolition waste (CDW) by establishing an inventory of CDW that is suitable for use in 3DPC in South Africa. This is an essential step in ensuring the technical, economic, and logistical viability of using CDW as aggregate or supplementary cementitious materials in 3DPC. Of the methods considered, the lifetime material analysis and per capita multiplier methods are the most appropriate for the context and available seed data; this results in CDW estimates of 24.3 Mt and 12.2 Mt per annum in South Africa, respectively. This range is due to the different points of estimation for the two methods considered, and the per capita multiplier method provides an inevitable underestimation. In order to contextualise the estimated availability of CDW material for use in concrete in general, the demand for coarse and fine aggregate and supplementary cementitious material in South Africa is quantified as 77.9 Mt. This overall annual demand far exceeds the estimated CDW material (12.2–24.3 Mt) available as an alternative material source for concrete.

The literature shows that a circular economy can benefit some sectors such as the construction industry. This sector demands huge amounts of raw materials and produces waste when buildings and structures are demolished. This paper explores the possibility of manufacturing at industrial scale paving blocks using different types of construction and demolition wastes as aggregates, without modifying the commonly used industrial conditions. A total of four different recycled aggregates were used in this research. Both natural and recycled aggregates have been characterized. The dosages were optimized (three different formulations). Prefabricated tests have been carried out on the products manufactured in industrial plants and the evolution of mechanical properties over time has been analysed. The results obtained were analysed statistically by applying the principal component analysis (PCA) method. To ensure the security of the elements manufactured, the ionic leaching of the materials used as recycled aggregate and of the elements produced has been tested. The main implications of this research on the construction industry show that the majority of recycled aggregates used could replace 25% of the natural aggregate in manufactured precast concrete, that the properties of the aggregates should be taken into account in the different standards and that all paving blocks manufactured in this study can be considered environmentally safe (no risk of leaching) according to the Netherland Soil Quality Decree. Therefore, it is evident that it is possible to manufacture on an industrial scale paving blocks with mixed recycled aggregates, concrete and ceramic in nature, both with the fine and coarse fractions that meet the requirements of its reference standard UNE-EN 1338 and the Netherland Soil Quality Decree that evaluates environmental risks due to leaching.

With diminishing natural aggregate resources and increasing environmental protection efforts, the use of recycled fine aggregate is a more sustainable approach, although challenges persist in achieving comparable mechanical properties. Exploration into the incorporation of steel fibers with recycled aggregate has led to the development of steel-fiber-reinforced recycled aggregate concrete. This study investigates the shrinkage performance and compressive constitutive relationship of steel fiber recycled concrete with different steel fibers and recycled aggregate dosages. Initially, based on different replacement rates of recycled coarse aggregate and different volume contents of steel fiber, experimental results demonstrate that as the replacement rate of recycled coarse aggregate increases, shrinkage also increases, while the addition of steel fiber can mitigate this effect. An empirical shrinkage model for steel fiber recycled concrete under natural curing conditions is also proposed. Subsequently, based on the uniaxial compression test, findings indicate that with an increasing replacement rate of recycled fine aggregate, the peak stress and elastic modulus of concrete decrease, accompanied by an increase in peak strain, and the addition of steel fiber limits concrete crack development and enhances its brittleness while the peak stress and strain of recycled fine aggregate concrete are enhanced. However, the steel fiber volume percentage has a negligible effect on the elastic modulus. A constitutive relationship for concrete considering the effects of recycled fine aggregate and steel fiber is also proposed. This finding provides foundational support for the influence patterns of steel fiber dosage and recycled aggregate ratio on the mechanical properties of steel fiber recycled concrete.

This paper explores the new potential strategy of using fine recycled aggregates (fRA) derived from waste 3D printed concrete (3DPC) as a substitute for cement in additive manufacturing. This study hypothesizes that fRA can optimize mixture design, reduce cement content, and contribute to sustainable construction practices. Experimental programs were conducted to evaluate the fresh and hardened properties, printability window, and buildability of 3DPC mixes containing fRA. Mixes with replacement rates of cement with fRA by 10 vol%, 20 vol%, 30 vol%, 40 vol%, and 50 vol% were produced. A comprehensive experimental protocol consisting of rheological studies (static and dynamic yield stress), dynamic elastic modulus determination (first 24 h of hydration), flexural and compressive strengths (2 d and 28 d), and an open porosity test was performed. The obtained results were verified by printing tests. In addition, an economic and environmental life cycle assessment (LCA) of the mixes was performed. The results indicate that up to 50 vol% cement replacement with fRA is feasible, albeit with some technical drawbacks. While fRA incorporation enhances sustainability by reducing CO2 emissions and material costs, it adversely affects the printability window, green strength, setting time, and mechanical properties, particularly in the initial curing stages. Therefore, with higher replacement rates (above 20 vol%), potential optimization efforts are needed to mitigate drawbacks such as reduced green strength and buildability. Notably, replacement rates of up to 20 vol% can be successfully used without compromising the overall material properties or altering the mixture design. The LCA analysis shows that reducing the cement content and increasing the fRA addition results in a significant reduction in mix cost (up to 24%) and a substantial decrease in equivalent CO2 emissions (up to 48%). In conclusion, this study underscores the potential of fRA as a sustainable alternative to cement in 3D printed concrete.

In road engineering, road construction requires a large amount of natural aggregate; its substitution with recycled construction-solid-waste aggregate not only saves resources but also reduces the burden on the environment. The main components of construction solid waste are concrete blocks and brick slag; the breakability of the latter can affect the performance of mixed recycled aggregate, which hinders the use of construction solid waste in road engineering applications. To analyze the applicability of recycled construction-solid-waste aggregate containing brick slag aggregate in the subgrade layer, the effect of brick aggregate content on the CBR (California bearing ratio) and crushing value of mixed recycled aggregates was evaluated based on laboratory tests, and the field compaction quality of the recycled aggregates was analyzed. The results show that the 9.5–19 mm mixed recycled aggregate samples were crushed to a higher degree during the compaction process. A brick aggregate content less than 40% had little effect on the performance of mixed recycled construction-solid-waste aggregate. It is recommended to use a 22 t road roller for five passes (two weak vibrations + two strong vibrations + one weak vibration) at a speed of 3 km/h in the main compaction stage of the subgrade filling.

The reasonable and effective application of waste tires and discarded concrete in concrete is an important branch of green concrete development. This paper investigates the effects of the inorganic modification mode on the basic mechanical properties of rubber recycled concrete based on indoor tests. Inorganic modification, such as water washing, acid washing, and alkaline washing modification, was mainly used to treat and modify rubber particles. The factors affecting the compressive strength, the splitting tensile strength, the flexural strength, the axial compressive strength, and the modulus of elasticity of modified rubber recycled concrete were analyzed. The study results show that the incorporation of recycled aggregates and rubber reduced the mechanical properties of concrete, with the compressive and splitting tensile strengths showing the greatest reductions of 27.36% and 27.24%, respectively. Three modification methods significantly improved the mechanical properties of rubber recycled concrete. The alkali washing modification method was the most effective, maximally improving the mechanical properties of rubber recycled concrete by 7.53–15.51%. The effects of the three modifications on the mechanical properties of concrete were ranked as follows: alkali washing > acid washing > water washing. This study provides a data basis for the practical application of rubber recycled concrete in engineering and a test basis for the development of green concrete.

Abstract RCC using hematite as an aggregate has interesting characteristics for use in massive structures or structures for radiation shielding. In Brazil, there is a considerable amount of hematite ore tailings without practical use, which makes this material an environmental problem and a matter of public safety. Thus, the search for alternatives to use these tailings is a priority environmental concern. An RCC containment dam with hematite aggregate was constructed to protect the basin of the Barao de Cocais River, including the city of Barao de Cocais in the State of Minas Gerais in Brazil, from a possible rupture of the Sul Superior tailings dam in the Congo Soco iron mine. Approximately 150,000 m3 of RCC was deposited in three months. In this article, the results of the technological control tests during the construction of the containment are presented and compared with the results of the cores extracted after the construction, showing their coherence and strength performance compared with RCC using conventional aggregate. Also, studies related to the performance of radiation shielding of this RCC are presented. An attenuation of 10% of 1.6 MeV gamma radiation in relation to conventional concrete was observed.

This research aims to study the effect of adding nanosilica (NS) on the properties of sustainable high-strength concrete (SHSC). The SHSC was produced using recycled aggregates from concrete debris as a 100% alternative to coarse aggregate, and industrial waste was used as supplementary cementitious materials at 50% and 75% of Ordinary Portland cement (OPC) weight. A total of 25 mixes, including control mix (The first mix was made as the reference by using only cement without replacement materals), binary mixes (OPC and fly ash (FA)), ternary mixes (OPC, FA and ground-granulated blast-furnace slag (GGBS)) and quaternary mixes (OPC, FA, GBFS and silica fume (SF)) were developed. The dosage of NS was 0%, 1%, 3% and 5% by binder ratio. The fresh properties of SHSC were evaluated by slump test, and the mechanical properties were assessed by testing the compressive strength, splitting tensile strength, flexural strength and modulus of elasticity. The transport properties were evaluated by water permeability, water sorptivity and chloride permeability tests. Results showed that compared with the reference mixture, the SHSC containing 75% of the quaternary blends with 3% NS achieved enhanced mechanical properties at 28 and 91 days, indicating that this mixture can achieve the highest sustainability performance. The SHSC mixture containing 3% NS and 50% quaternary mixtures achieved the highest performance of 80.7, 6.46 and 10.09 MPa for compressive strength, split tensile strength and flexural strength, respectively, at 28 days. This SHSC mixture also achieved water permeability; chloride permeability was 2.54 × 10−11 (cm/sec) and 1370 coulombs at 28 days.

The requirement of the construction sector pushes researchers and academicians to determine the 28-day concrete compressive strength due to less consumption of natural products and reduced cost. One recommended method to reduce the cost and simultaneously adopt sustainability is introducing recycled aggregates in concrete. Most typical structures require concrete, which is self-flowable and compactable; specific structures require concrete, which is self-flowable and compactable; one such concrete is self-compacting concrete (SCC). 515 mix design samples for SCC with recycled aggregates are collected from the literature and used for training, validation, and testing to create the model using machine learning techniques (Extra Gradient (XG) Boosting, Ada Boosting, Gradient Boosting, Light Gradient Boosting, Category Boosting, K Nearest Neighbors, Extra Trees, Decision Trees, Random Forest, and Support Vector Machine). The correlation between input and output variables is analyzed using ANOVA and is indicated that data can be used to develop machine learning models successfully. Sensitive analysis and error assessment are performed to choose the best machine learning methods, and it found that CB, KNN, and ERT have the highest R2 value and lowest MSE.

Abstract This study aimed to identify the influence of replacing coarse natural aggregate with coarse recycled concrete aggregate on the thickness and volume of the cementitious paste under the variation of the water/cement ratio in the fresh and hardened properties of pervious concrete. The determined theoretical paste thickness was inefficient for pervious concrete dosage. However, it was found that the paste volume was the parameter that was best related to the mechanical and permeability properties of the studied material. Pervious concrete with natural aggregates showed higher compressive strength than concrete with recycled aggregates, although both met the regulations. All the concretes produced, except one with recycled aggregate of w/c ratio 0.25, reached the tensile strength in the minimum design bending. Pervious concrete with recycled aggregates showed more significant mass loss by abrasion and more porosity than concretes with natural aggregates. Finally, all pervious concretes presented permeability coefficients greater than the lower limit determined by the standard.

Enzyme induced carbonate precipitation (EICP) which applied to improve the quality of recycled aggregates (RA) is a novel technology in the field of civil engineering. The urease was extracted from soybean, and the factors including soybean powder concentration, temperature and pH value on urease activity were investigated. Then the EICP reaction kinetics was carried out to obtain the most suitable reaction environment. A spraying method instead of soaking method for modifying RA was proposed, and the physical and mechanical properties of RA were evaluated by water absorption, hardness, apparent density and crushing index. The results show that the optimum pH value of soybean urease is 8.0, the concentration of soybean power is 40 g/L, and the urease activity increases with temperature in the range of 10–50 °C. Spraying method was better than soaking method in water absorption reduction rate of RA with different particle sizes. When the concentration of the chemical solution is 0.5 mol/L, the improvement in the water absorption characteristics of the RA is most significant. And the modified RA have also undergone substantial improvements in terms of hardness and apparent density. On the 7-day of modification, the crushing index of the RA reaches the peak. Through microscopic observation, the pore volume of the modified RA is significantly reduced, and the content of CaCO3 is significantly increased, and the main crystalline form of CaCO3 are calcite and vaterite.

The main problem of our cities is the lack of treatment and final disposal of construction and demolition waste (CDW), which, accompanied by a lack of knowledge, becomes a major problem. Likewise, a city in the north of Peru (Cutervo) is not immune to the problematic reality experienced in the country and worldwide, since the lack of CDW management projects has generated the formation of informal dumps. The main objective of this research is to determine the technical and economic feasibility of using CDW for the production of pedestrian pavers, given that it includes measurements of the physical and mechanical characteristics to be analyzed. It is concluded that the use of CDW in the production of paving stones is feasible, from the economic and technical aspects, incurring a reduction in cost.

This study investigates the potential of metakaolin as a mineral admixture to enhance the performance of concrete mixtures with varying proportions of recycled aggregates (RA). Sixteen distinct concrete combinations were formulated by substituting natural aggregates (NA) with RA at 0 %, 50 %, 75 %, and 100 % and incorporating metakaolin at 0 %, 5 %, 10 %, and 15 % as a replacement for cement. Experimental investigations were conducted to evaluate the effects of metakaolin (as a cement replacement) and RA (as a replacement for NA) on key concrete characteristics, including density, water absorption, compressive and tensile strength, and acid resistance. The results revealed that an increase in RA reduced mechanical properties, such as compressive strength, tensile strength, and dry density. Additionally, RA-based concrete mixtures exhibited higher water absorption and void volume than those with natural aggregates. However, including metakaolin in RA-based concrete significantly reduced the void volume and water absorption. The optimal proportion of metakaolin substitution was 15 %, resulting in the best overall performance for RA-based concrete mixtures. Notably, the highest compressive and splitting tensile strength (41.6 MPa and 4.3 MPa, respectively) were observed at 90 days in mixtures with 0 % RA and 15 % metakaolin. Similarly, the highest hardened density and lowest water absorption (2494.7 kg/m3 and 4.7 %, respectively) were recorded in samples with 0 % RA and 15 % metakaolin. Furthermore, concrete mixes containing 15 % metakaolin and 50 % RA demonstrated comparable qualities to conventional concrete, indicating that sustainable concrete can be produced by utilizing a significant quantity of waste concrete (15 % metakaolin and 50 % RA) without compromising strength criteria. This study sheds light on the potential of incorporating metakaolin and recycled aggregates as environmentally friendly alternatives in the construction industry, contributing to sustainable and eco-conscious practices.

Recycled aggregate concrete (RAC) typically suffers from inferior properties due to old mortar on the surface of recycled aggregate (RA), and the practical application of two proposed treatment methods, microbial-induced carbonate precipitation (MICP) and enzyme-induced carbonate precipitation (EICP), has encountered challenges in determining optimal culture medium and precipitation regimes. This study initially aimed to address these challenges by establishing the feasibility of using chloride-free cultivation medium to avoid introducing chloride ions that could damage the steel reinforcement. The optimal Ca concentration in the precipitation culture medium was determined as 0.3 mol/L for MICP and 0.5 mol/L for EICP. Furthermore, the optimal precipitation regimes for MICP and EICP treatments were identified as I-S (5 cycles) and M-S (3 cycles), respectively. The quantitative evaluation of the above factors enabled the direct practical application of these optimal treatment regimes. The performance of RAC was significantly improved after both MICP and EICP treatments compared to untreated RAC, with EICP treatment demonstrating superior performance. The precipitated CaCO3 formed during MICP treatment consisted mainly of spherical vaterite crystals, while the precipitation formed during EICP treatment comprised vaterite, calcite, and aragonite. These differences in phase and mechanism between MICP and EICP treatments could explain the variations in the performance of RAC.

The main problem of our cities is the lack of treatment and final disposal of construction and demolition waste (CDW), which, accompanied by a lack of knowledge, becomes a major problem. Likewise, a city in the north of Peru (Cutervo) is not immune to the problematic reality experienced in the country and worldwide, since the lack of CDW management projects has generated the formation of informal dumps. The main objective of this research is to determine the technical and economic feasibility of using CDW for the production of pedestrian pavers, given that it includes measurements of the physical and mechanical characteristics to be analyzed. It is concluded that the use of CDW in the production of paving stones is feasible, from the economic and technical aspects, incurring a reduction in cost. [ABSTRACT FROM AUTHOR]

Deformation properties of concrete containing 100 % recycled aggregate Through the use of demolition material in the form of broken concrete or masonry as aggregate in the concrete, enormous amounts of the construction waste can be reused, so that a disposal of these material flows is not necessary. On the other hand, primary raw materials for the production of concrete components can be saved, which effectively counteracts the global shortage of sand and gravel. The procedural technical methods for the processing of such demolition materials have been continually developed in recent years and the range of recycled aggregate is far from exhausted. In Germany, the application areas of recycled concrete are defined acc. to normative regulations and the recyclate quantities are limited to a maximum of 45 % of the coarse aggregate depending on the exposure class. With the help of this study, the deformation behavior of R‐concretes with 100 % recycled aggregate will be characterized more detailed. [ABSTRACT FROM AUTHOR]

The utilization of recycled aggregates and various industrial by-products is considered a sustainable strategy in the concrete industry. In this study, the effect of the maximum size of recycled coarse aggregate and the cementitious binder content on fresh and hardened properties of self-compacting concrete was investigated. Self-compacting concretes with maximum aggregate sizes of 9.5 mm, 12.5 mm, and 19 mm were prepared at water-to-binder ratios of 0.39, 0.42, and 0.45, respectively. For all mixtures, 100% recycled aggregate was used as coarse aggregate and 60% of cement was replaced by industrial by-products, i.e., fly ash and ground granulated blast furnace slag. The tests included slump flow, air content, hardened density, compressive strength, elastic modulus, and splitting tensile strength. The results showed that the increase in maximum aggregate size and binder content tended to improve both fresh and hardened properties of self-compacting concrete. [ABSTRACT FROM AUTHOR]

The utilization of recycled materials in the concrete industry has become one of the most essential environmental needs today, and more technical and economic studies are being performed every day in this subject. The effect of recycled materials on the shear behavior of geopolymer concretes was investigated in this work, along with a comparison to conventional recycled concretes and the effect of recycled aggregates on both concrete groups. For this purpose, ten mixing designs with recycled aggregate replacement percentages of 0, 25, 50, 75 and 100 were made in two groups of ordinary concrete and geopolymer concrete, as well as mechanical tests such as compressive strength, modulus of elasticity, and pull-off test. A reinforced beam without shear element was also created for each mixing design to study the effect of this type of aggregate on the shear behavior of the beam. The findings revealed that increasing the percentage of recycled aggregates causes a loss in mechanical characteristics in the designs and a reduction in beam bearing capacity, indicating that geopolymer concrete has a higher replacement capacity than regular concrete. [ABSTRACT FROM AUTHOR]

With the world's population increasing, the issue of energy consumption has become increasingly prominent, particularly during the building operation phase, where substantial energy is required for heating and cooling. Presently, the energy necessary for buildings is sourced mainly from the combustion of fossil fuels, leading to not only energy scarcity but also severe environmental pollution and ecological damage. Furthermore, rapid urbanization has generated a lot of construction and demolition waste. To address these challenges, one promising approach is the incorporation of phase-change materials in recycled aggregate from construction and demolition waste to replace the raw materials of concrete. In this study, the phase-change material suitable for the thermal comfort requirements of buildings was selected and combined with recycled aggregate to replace the natural aggregate in concrete. All the materials used were characterized and three compositions were prepared. From the results, the workability of concrete increased with the phase-change materials added. Regarding water absorption performance, the incorporation of functionalized recycled aggregate presented a small water absorption performance. However, the mechanical performance decreased with the phase-change materials used. This work provides data for the application of phase-change materials in green concrete. [ABSTRACT FROM AUTHOR]

In this study, the feasibility of utilizing locally produced coarse recycled aggregate (RA) from demolition waste in the UAE for structural applications was investigated. A comprehensive literature review on the subject showed that the shear and flexural responses of reinforced beams utilizing aggregate from concrete demolition waste are greatly dependent on the aggregate replacement ratio and the quality of the recycled aggregate. The experimental program in this study consisted of three phases. Phase I focused on the evaluation of the physical and mechanical characteristics of the RA, Phase II addressed the mix design and fresh and hard properties of the concrete, and Phase III dealt with the flexural and shear behavior of structural members. The research involved twelve 150 mm × 300 mm reinforced concrete beams with a length of 1500 mm or 2000 mm that were made with 0% (control), 50%, or 100% recycled coarse aggregate, replacing natural coarse aggregate (NA). Two target concrete compressive strengths, 25 and 35 MPa, were considered in the investigation. The results showed that the recycled aggregates had lower crushing and LA abrasion values by 40% and 18–28%, respectively, whereas the absorption capacity was 40–300% higher compared to the natural aggregate. In addition, the mechanical properties of the concrete made with different replacement ratios (R%) of RA were either similar or slightly less than those of the control mix. The shear beam tests with f c ′ = 25 MPa showed that the 50%- and 100%-replacement-ratio beams demonstrated closely matched normalized shear strength values that exceeded their corresponding NA beam by 12.5%, while the shear beam tests with f c ′ = 35 MPa showed that the NA beam exhibited normalized shear strength surpassing the 50% RA and 100% RA beams by 12.5% and 17.5%, respectively. In the flexural beam tests, the flexural strength exhibited minimal disparities for the beams that shared the same RA% but differed in their compressive strength targets, and overall, the variation in the RA% had a marginal impact on the flexural strength of the beams. Further, an increase in the RA% corresponded to an increase in the shear ductility index, which was in contrast with the findings on the flexural ductility index. Furthermore, predictions of flexural strength using the ACI318-19 code and shear strength using the strut-and-tie model yielded comparable results to the experimental ones. [ABSTRACT FROM AUTHOR]

Recycled aggregate refers to crushed concrete, mortar, bricks, or asphalt derived from construction debris and repurposed in other building projects. It is obtained by crushing demolished waste to reclaim the aggregate. Over the past few decades, the abundance of Construction and Demolition Waste (C&DW) has increased significantly, leading the concrete industry to incorporate it, thereby reducing the cost of aggregates. The use of C&D waste in construction not only decreases carbon emissions but also facilitates the expansion of the concrete industry without causing harm to the environment. The objective of this study is to analyze the mechanical properties such as compressive strength, splitting tensile strength, flexural strength, and durability properties such as resistance to chloride, carbonation, freeze, and thaw of concrete utilizing recycled aggregate. It is observed that the mechanical and durability behavior of Recycled Aggregate Concrete (RAC) is inferior to that of standard concrete. However, by employing different admixtures and mixing approaches, the desired properties can be achieved. Furthermore, the study indicates that the improvement of mineral admixtures contributes more to enhancing the performance of recycled aggregate than it does to the characteristics of natural aggregate. [ABSTRACT FROM AUTHOR]

Increasing construction and demolition waste (CDW) and the large amount of energy consumption in the building operation process are high-profile issues at present. In the construction industry, recycled aggregated (RA) from CDW can be reutilized in construction, along with green materials, for example, as a road base layer, as aggregate in concrete, etc. Phase change materials (PCM) are often used as building materials due to their good latent heat storage properties. With the use of RA as a matrix to absorb PCM, a thermal performance aggregate can be obtained. This work studied the physical properties of RA from Portugal and combined PCM with RA to prepare a green thermal aggregate through two methodologies using a vacuum and atmospheric pressure. The green aggregate was used in concrete to observe its effect on the compressive strength of concrete. The results showed that the amount of PCM absorbed by the RA mainly depends on the porosity of the matrix material. At the same time, the volume expansion coefficient of PCM was 2.7%, which was not enough to destroy the RA. Ultimately, as the amount of green thermal aggregate increases, the compressive strength of concrete decreases. Green thermal aggregate prepared under vacuum conditions has a greater negative impact on the compressive strength of concrete. [ABSTRACT FROM AUTHOR]

In this study, the bullet projectile performance of repaired projectile bullet damaged recycled aggregate (RA) or natural aggregate (NA) RC beams using carbon fiber reinforced polymer (CFRP) sheets in conjunction with RA or NA concrete was experimentally investigated. The experiment consists of a total of six subjected to projectile bullet loading. The effect of the type of material used in combination with the CFRP sheet was studied. According to the test findings, utilizing the CFRP sheet demonstrated a much higher load capacity than the control beams, but a decreased level of ductility. Therefore, CFRP sheet is a viable repair technique of projectile bullet damaged RA or NA RC beams. Besides, the results show that the repaired damaged RC beams with CFRP combined with the NA layer had a higher load compared to the repaired damaged RC beams with CFRP combined with the RA layer. However, CFRP in combined with RA shows a good enhancement in load capacity (115.6–117.8%). The repaired beams with CFRP and NA layer showed debonding failure while using RA with CFRP showed debonding with cover separation in repairing RA beam. [ABSTRACT FROM AUTHOR]

This article focuses to study some properties of recycled aggregate concretes (RAC) according to the equivalent water absorption of aggregates and the parent concrete strength of RCA and thus new relationships were deduced. The results indicated that 1% increase of the equivalent water absorption induced 0.12% increase in superplasticiser dosages. The hyperbolic model seems to be more adequate to estimate compressive strength and shrinkage of RAC when the parent concrete strength and the equivalent water absorption were introduced. According to the obtained results, the parent concrete strength of RCA must not be less than 10 MPa than that of the reference concrete to avoid the drop in compressive strength. For high equivalent water absorption, the ultimate shrinkage became higher and slower. [ABSTRACT FROM AUTHOR]

Properties of recycled aggregate concrete (RAC) are influenced by the composition and particle size distribution of recycled coarse aggregate (RCA). The study herein designed seven distinct groups of RACs with varying aggregate fractal dimensions (D) and one group of natural concrete (NAC). The impact of D on the workability, compressive strength, resistance to chloride ion penetration, and carbonation resistance of RAC was measured. It was found that an increase in the D value led to a decrease in the slump and slump flow, with the compressive strength and chloride ion penetration increasing and then decreasing, and carbonation gradually declined. The optimal fractal dimension was thereby determined to be 2.547 by a strength model accommodating two parameters of D and the curing age. Additionally, the mass percentage of each particle size for the corresponding gradation was presented. The compressive strength and chloride permeation resistance of RAC (D = 1.0) relative to RAC (D = 2.5) was increased by 16.7% and 13.3%, respectively. Furthermore, the carbonation depth of RAC (D = 2.5) was comparable to that of NAC. Additionally, the carbonation resistance of RAC was influenced by both the size distribution and the degree of natural carbonation of RCA, resulting in four distinct features relative to NAC. It is thereby feasible to enhance RAC performance through the manipulation of RCA's fractal dimensions. [ABSTRACT FROM AUTHOR]

Several research studies have been conducted to investigate the hardened and durability characteristics of the normal aggregate concrete (NAC) and recycled aggregate concrete (RAC). Similarly, few studies have been done to examine the thermal behaviour of the NAC and RAC. However, the influence of elevated temperature on the RAC with treated recycled coarse aggregate (RCA) in the concrete still needs to be investigated. This study presents the comparative discussion on the thermal performance of NAC, RAC, carbonated recycled aggregate concrete (CRAC) and bio-deposited recycled aggregate concrete (BRAC) at various elevated temperatures of 25, 200, 500 and 800°C. The investigation involves the determination of residual compressive strength, tensile strength, elastic modulus and thermal conductivity with a series of concrete mixtures under elevated temperatures. The optimal residual strength was observed at 500°C, beyond exposure of it causes a reduction in the strength. The residual strength of NAC, RAC, CRAC and BRAC at optimal temperature was reduced by 30.10%, 7.06%, and 31.02%. The equivalence of the thermal expansion coefficient of RCA with cement paste improves the residual response of RAC, and higher porosity of RCA decreases the thermal conductivity of the RAC by 43.06% compared to control concrete. Furthermore, no concrete samples crumbled at 800°C, but the residual properties tend to decrease for all mixes. [ABSTRACT FROM AUTHOR]

This research investigates the physical, mechanical, thermal conductivity, and fire-resistant properties of mortar incorporating with auto glass waste (AGW). The crushed AGW was used as fine aggregate to substitute natural sand (NS) from 0 to 100% by volume. The 40% replacement with AGW was optimum, with a slight increase in the 28-day compressive strength. The 90-day compressive strength of 100% AGW increased by 33% compared to NS mortar (without AGW) due to the increased pozzolanic reaction. The replacement of sand with AGW resulted in improvements in thermal insulation properties and fire resistance of mortars. The 100% replacement with AGW decreased the thermal conductivity coefficient by 63%, while the density decreased by only 2.8% compared to the NS mortar. The residual compressive strength increased with incorporating AGW after exposure to elevated temperatures. The 100% replacements with AGW showed a maximum compressive residual mortar strength of 66 MPa (126%) after exposure to high temperatures at 300°C. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering (17264073) is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Builder (1896-0642) is the property of PWB MEDIA Zdzieblowski sp.j. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In view of the problems of high energy consumption, poor ecological restoration and rational utilization of waste concrete in the practical application of acid mine wastewater treatment methods. Based on the water purification characteristics of pervious concrete, waste concrete, cement and other materials are used to develop water purification reclaimed aggregate pervious concrete (ZSCR), combined with diatomite and swelling. The performance and practical application prospect of different ZSCR were studied by modifying the clay and red mud. The recycled aggregate and ore were analyzed by XRD, SEM and other testing methods, Effect of material admixture on its water purification performance. The results show that: compared with ordinary pervious concrete, recycled aggregate has less influence on the water purification performance of pervious concrete. The water purification performance of ZSCR was obviously enhanced after the modification of the admixture. The addition of diatomite and other materials improved the pore structure of the specimen and produced a lot in the gel layer. The unhydrated mineral phase gel particles enhanced the adsorption performance of ZSCR to heavy metal pollutants. When the hydraulic retention time is 12 h and the red mud content is 30%, the red mud reclaimed aggregate pervious concrete can effectively intercept heavy metal ions in surface water of mining area, it can be used as reaction medium in water ecological restoration technology such as constructed wetland and biological filter to treat acid mine wastewater. [ABSTRACT FROM AUTHOR]