Mechanical Performance of Concrete with Graphene-Oxide-Treated Recycled Coarse Ceramic Aggregates: Effects on Aggregate Water Absorption and Workability

This study investigated the mechanical performance and durability of concretes produced with varying proportions of recycled coarse aggregate from construction and demolition waste (CDW), ranging from 0% to 100% replacement of natural coarse aggregate, using recycled aggregates derived from crushed concrete and mortar debris, characterized by lower density and high water absorption (~9%) compared to natural aggregates. A key contribution of this research lies in the inclusion of intermediate replacement levels (20%, 25%, 45%, 50%, and 65%), which are less explored in the literature and allow a more refined identification of performance thresholds. Fresh-state parameters (slump), axial compressive strength (7 and 28 days), total immersion water absorption, sorptivity, and chloride ion penetration depth (after 90 days of immersion in a 3.5% NaCl solution) were evaluated. The results indicate that, up to 50% CDW content, the concrete maintains slump (≥94 mm), characteristic strength (≥37.2 MPa at 28 days), and chloride penetration (≤14.1 mm) within the limits for moderate exposure conditions, in accordance with ABNT: NBR 6118. Water absorption doubled from 4.5% (0% CDW) to 9.5% (100% CDW), reflecting the higher porosity and adhered mortar on the recycled aggregate, which necessitates adjustments to the water–cement ratio and SSD pre-conditioning to preserve workability and minimize sorptivity. Concretes with more than 65% CDW exhibited chloride penetration depths exceeding 15 mm, potentially compromising durability without additional mitigation. The judicious incorporation of CDW, combined with optimized mix design practices and the use of supplementary cementitious materials (SCMs), demonstrates technical viability for reducing environmental impacts without significantly impairing the structural performance or service life of the concrete.

Optimal utilization of low-quality construction waste and industrial byproducts in sustainable recycled concrete

Introduction: Construction and Demolition Waste (CDW) constitutes a major portion of solid waste and presents a significant environmental challenge. This study aims to evaluate the transformation of CDW into a Recycled Aggregate (RA) as a sustainable strategy to mitigate environmental pollution. Methods: The research assesses the mechanical properties and economic benefits of RA concrete, which is made by substituting natural aggregate with RA. Results: Results indicate that RA has lower density, higher water absorption, and reduced crushing strength compared to natural aggregates. However, RA concrete achieves optimal strength with a 40% replacement rate, marking a critical threshold for material efficiency. An economic analysis confirms the financial viability of using recycled concrete, indicating a favorable investment return. Advances in the research and application of RA suggest its expanding role in engineering applications. Conclusion: A lifecycle assessment of carbon emissions from concrete production to site transportation was conducted. It revealed that the primary source of emissions in recycled concrete is the raw materials, accounting for about 85% of total emissions. This finding underscores the need to optimize raw material usage to enhance the sustainability of recycled concrete.

Construction activities are booming in and around the cities with development and modernization. As a result of these constructions, natural aggregates are being extracted. Simultaneously, there is a significant amount of construction and demolition waste (CDW) generated due to the demolition of structures either due to the structure attaining service life or fashion and the ongoing trend of reconstruction. Therefore, recycling coarse aggregate from CDW in concrete is one of the sustainable solutions to prevent a serious threat to the environment due to the extraction of virgin aggregates and landfilling. This paper presents the results of a study undertaken to examine the influence of recycled concrete aggregate on the properties of new concrete and its life cycle cost (LCC) analysis. It is clear from the test that the strength of RAC is much lowered than natural aggregate concrete (NAC). In order to achieve the optimum strength, the natural aggregate is replaced by recycled aggregate within a range of 0% to 100%, in intervals of 10%. Additionally, to enhance its strength further, reinforcing RAC with new and recycled polypropylene (PP) fiber is done in percentages ranging from 0.25% to 2% by weight of cement with an interval of 0.25%. For analysis, compression, and split tensile strength tests were performed at the end of 28 days of the curing period. The result revealed that 40% replacement of natural aggregate with recycled aggregate achieves the ideal percentage replacement without compromising the strength. Moreover, incorporating 1.5% of new PP fiber or 1.25% of recycled PP fiber in the RAC provides optimum strength. For LCC analysis, the initial investment cost, operations, and maintenance cost, and salvage cost of all the alternatives are compared. Through this analysis, it was determined that the LCC of concrete manufactured using recycled aggregate as concrete ingredients is the lowest. Consequently, incorporating recycled aggregates in concrete production reduces the LCC compared to using natural aggregates.

In recent decades the problem of construction and demolition waste has been receiving more attention due to possible ecological and economic damage caused by them. This is because they are produced in large quantities and often receive inadequate disposal, being deposited illegally in vacant lots, public places and even in areas of environmental preservation. The practice of recycling of construction and demolition waste (CDW) by construction is an alternative that minimizes the amount of waste generated and the impacts caused by them. Moreover, the introduction of alternative materials might reduce the production costs of construction. In Brazil, there is great availability of lateritic concretions. This material, according to some studies, proved to be a viable alternative to be used as coarse aggregate in concrete production. In this study, it is used the CDW as a filler to replace 10% of Portland cement and, as coarse aggregate, lateritic concretions. Tests of physical properties of coarse and fine aggregates and determination of the mechanical strength of hardened concrete were made. The construction and demolition waste used as filler to replace the mass of cement in the mixture proved to be a viable alternative.

This research aims to study the utilization of waste from power plants, construction and demolition, and agriculture by varying the ratios of flue-gas desulfurization (FGD) gypsum, construction and demolition waste (CDW), and oil palm trunks (OPT) in concrete production. This research used these as the raw materials for the production of concrete bricks of 15 × 15 × 15 cm. There were 12 ratios of concrete brick, fixing 5.5 wt% of FGD gypsum to replace Portland cement and substituting coarse sand with 0 wt%, 25 wt%, 50 wt%, or 75 wt% of CDW, and gravel with 0 wt%, 0.5 wt%, and 1 wt% of OPT. The initial binder:fine aggregate:coarse aggregate ratio was 1:2:4 and the water to cement ratio was 0.5, curing in water at room temperature for 28 days. Then, all concrete brick specimens were tested for compressive strength and water absorption. From the experiment, it was found that the highest compressive strength of concrete brick specimens was 45.18 MPa, which was produced from 5.5% gypsum without CDW and OPT, while 26.84 MPa was the lowest compressive strength obtained from concrete bricks produced from 5.5% FGD gypsum, 75% CDW, and 1% OPT. In terms of usage, all proportions can be applied in construction and building work because the compressive strength and water absorption were compliant with the Thai Industrial Standard TIS 57-2530 and TIS 60-2516.

Influence of graphene oxide properties, superplasticiser type, and dispersion technique on mechanical performance of graphene oxide-added concrete

Construction and demolition wastes (CDW) are generated at a large scale and have a diversified potential in the construction sector. The replacement of natural aggregates (NA) with CDW recycled aggregates (RA) in construction materials, such as mortars, has several environmental benefits, such as the reduction in the natural resources used in these products and simultaneous prevention of waste landfill. Complementarily, CDW have the potential to capture CO2 since some of their components may carbonate, which also contributes to a decrease in global warming potential. The main objective of this research is to evaluate the influence of the exposure of CDW RA to CO2 produced in cement factories and its effect on mortars. Several mortars were developed with a volumetric ratio of 1:4 (cement: aggregate), with NA (reference mortar), CDW RA and CDW RA exposed to high levels of CO2 (CRA). The two types of waste aggregate were incorporated, replacing NA at 50% and 100% (in volume). The mortars with NA and non-carbonated RA and CRA from CDW were analysed, accounting for their performance in the fresh and hardened states in terms of workability, mechanical behaviour and water absorption by capillarity. It was concluded that mortars with CDW (both CRA and non-carbonated RA) generally present a good performance for non-structural purposes, although they suffer a moderate decrease in mechanical performance when NA is replaced with RA. Additionally, small improvements were found in the performance of the aggregates and mortars with CRA subjected to a CO2 curing for a short period (5 h), while a long carbonation period (5 d) led to a decrease in performance, contrary to the results obtained in the literature that indicate a significant increase in such characteristics. This difference could be because the literature focused on made-in-laboratory CDW aggregates, while, in this research, the wastes came from real demolition activities, and were thus older and more heterogeneous.

In the Netherlands, yearly 20 Mt Construction- and Demolition waste (CDW) is being produced mainly consisting of concrete and masonry rubble. This is two third of the yearly production of concrete (33 Mt). Currently, less than 1 Mt/year of the 20 Mt/year CDW is recycled in new concrete (mainly as coarse recycled concrete aggregates). This preliminary study being part of a larger study, is aiming to increase that amount, amongst others by focusing on use of the fine recycled concrete aggregates. Fine recycled concrete aggregates (fRCA) appear promising for (partial) replacement of natural fine aggregates (sand) and cement in new concrete. Nevertheless, they can be expected to have adverse properties and components that may reduce the performance of the concrete. Their physical, chemical and mechanical properties, which thus may significantly differ from that of natural sand, are still far from being fully investigated. The present paper focusses on characterization of physical properties of fRCA for finding the most critical indicators for fRCA quality. The tests include particle size distribution, morphology, BET surface area, solid density and water absorption of individual and total fractions (0–0.25 mm, 0.25–4 mm and 0–4 mm). The tests are performed on three fRCAs with different origin. Natural river sand with 96 wt.% of SiO2 was also studied to provide a baseline for comparison. Experimental results showed that, on the one side, the particle size distribution, surface area and amounts of individual fractions of fRCAs are significantly different from that of natural sand and that there is a large difference between each other. This is caused by variations of the parent concrete properties and by the type of recycling technique and processes (one step or multiple steps crushing). On the other side, fRCAs have comparative solid densities, which were still lower than that of natural sand. It was also shown that difference in water absorption between fractions 0.25–4 mm and 0–4 mm is very small in all three fRCAs groups. The results of this study will be used for future correlations between investigated properties of fRCAs with properties of concretes with fRCAs. This will be investigated in the next stage of the project, such that these correlations can enable production of durable concretes with fRCAs and assist recyclers in optimization of their production processes based on quality control of fRCAs.

The main objective of this study was to evaluate the use of construction and demolition waste (CDW) from the Passo Fundo region of Rio Grande do Sul (RS), Brazil, in the development of aerated foamed concrete. This waste had not yet been characterized or even reused. CDW was processed (sieved only), characterized, and used as an aggregate, completely substituting natural sand. The influence of CDW granulometry and the amount of foam upon compressive strength, wet and dry bulk density, water absorption, and the air voids of concrete blocks were determined. Results showed that CDW has regular characteristics for the development of aerated foamed concrete. Compressive strength and density decreased as the amount of foam increased, while water absorption and air voids also increased. Also, CDW that was classified as coarse showed higher compressive strength. On average, CDW medium-sized particles had a higher air void content, while water absorption showed little variation with respect to granulometry. CDW residue from the region of study can be used as aggregate for the development of aerated foamed concrete. However, it must characterized before being used to guarantee the quality of the final product.

The construction industry is responsible for the intensive consumption of natural resources and the generation of large volumes of construction and demolition waste (CDW), which are often disposed of improperly. This research developed concrete blocks using recycled CDW aggregates, promoting sustainability and circular economy by reusing these materials in urban infrastructure. Waste was collected from a recycling plant over five months, selecting Brita 1, Brita 0, and Pó de Brita to compose the concrete mixes. Particle size distribution, bulk density, and specific gravity tests were performed, and blocks and specimens were molded with 100% replacement of natural aggregates by CDW. The compressive strength tests were carried out at 14 and 28 days, while the abrasion test was performed only at 28 days. X-ray fluorescence (XRF) and Scanning electron microscopy (SEM) were used to characterize the products. The results indicated a compressive strength of 34.3 MPa at 28 days, close to the minimum required by the standard (35 MPa). XRF analysis showed a predominance of SiO₂, CaO, Al₂O₃, Fe₂O₃, MgO, SO₃, and K₂O oxides, all within normative limits. Leaching and solubilization tests, conducted according to NBR 10005 and NBR 10006, classified the waste as non-hazardous and non-inert. This study demonstrates that using CDW in concrete block production is a viable and sustainable alternative, contributing to waste reduction, material reuse, and the development of sustainable urban infrastructure.

Performance evaluation on bond, durability, micro-structure, cost effectiveness and environmental impacts of fly ash cenosphere based structural lightweight concrete

Mechanical and durability performance of concrete produced with recycled aggregates from Greek construction and demolition waste plants

The recycling of construction and demolition waste (CDW) for the extraction of recycled concrete aggregates (RCAs) to be used to produce recycled aggregate concrete (RAC) is widely acknowledged internationally. However, CDW not only contains concrete debris but may also contain burnt clay bricks. The recycling of such CDW without the segregation of different components would result in recycled aggregates having different proportions of concrete and brick aggregates. The utilization of these aggregates in concrete requires a detailed investigation of their mechanical and durability properties. In this regard, the present study focused on investigating the mechanical and durability properties of hybrid recycled aggregate concrete (HRAC) made by the 100% replacing of natural aggregates with recycled brick (RBAs) and RCA in hybrid form. The partial replacement of cement with fly ash was also considered to reduce the corban footprint of concrete. An extensive experimental program was designed and carried out in two phases. In the first phase, a total of 48 concrete mixes containing coarse RBA and RCA in mono and hybrid forms were prepared and tested for their compressive strength. The test results indicated that the compressive strength of HRAC is greatly affected by the proportion of coarse RBA and RCA. In the second phase, based on the results of the first phase, eight concrete mixes with the most critical proportions of RBA and RCA in hybrid form were selected to evaluate their mechanical and durability performance. In addition, four mixes with natural aggregates were also prepared for comparison purposes. To evaluate the mechanical properties of the concrete mixes, compressive strength and modulus of rupture (MOR) tests were performed, while for the evaluation of durability properties, water absorption and behavior after exposure to aggressive conditions of acidic and brine solutions were studied. The results revealed that a 20% replacement of cement with fly ash resulted in acceptable mechanical and durability properties of HRAC intended to be used for making concrete bricks or pavers.

Construction and demolition waste (CDW) refers to the waste generated from demolished structures in the construction industry. This waste can include concrete and brick materials. In this study, the focus is on evaluating the physical and mechanical properties of coarse aggregates derived from CDW, as well as the compressive strength of non-structural concrete made by mixing CDW aggregates with natural aggregates (NA) in different proportions. The study involved preparing different mix proportions of concrete using various combinations of CDW coarse aggregates, natural coarse aggregates, and brick aggregates. The mix proportions were categorized into three groups:100% natural coarse aggregate,CDW concrete coarse aggregate mixed with natural aggregate in three proportions: (90% NA, 10% CA), (80% NA, 20% CA), and (60% NA, 40% CA) and Mixtures of natural coarse aggregate, CDW concrete aggregate, and brick aggregate in four proportions: (90% NA, 5% CA, 5% BA), (80% NA, 10% CA, 10% BA), (60% NA, 20% CA, 20% BA), and (80% NA, 30% CA, 30% BA). The physical and mechanical properties of the different mix proportions were analyzed, and it was found that all proportions, except (80% NA, 30% CA, 30% BA), met the specified limits. In terms of compressive strength, the concrete mixture with a proportion of (90% NA, 10% CA) exhibited the highest value (27.04 MPa), while the mixture with a proportion of (60% NA, 20% CA, 20% BA) had the lowest value (17.19 MPa). The mixture with a proportion of (80% NA, 30% CA, 30% BA) did not meet the targeted strength of 15 MPa. Conclusion: Based on the analysis of the test results, it can be suggested that CDW aggregates can be used as a replacement for natural aggregates up to a maximum of 40%. Additionally, a combination of CDW concrete and brick aggregates in equal proportions (20% - 20%) can be used as a replacement for natural aggregates to achieve a concrete strength of 15 MPa.