Recycled Coarse Research Articles

Effect of Superabsorbent Polymers and Presoaked Coarse Recycled Shale Lightweight Aggregates on Relative Humidity Development in Early-Age Concrete

Self-desiccation-induced shrinkage may result in cracking at an early age, which is averse to the durability of concrete. Internal curing (IC) agents, such as superabsorbent polymers (SAP), are normally used for moisture regulation and shrinkage reduction. In addition, the make-up of recycled shale lightweight aggregate (RSLA) results in a good absorbing capacity, which makes it a potential candidate for IC. In this paper, the synergistic effect of SAP and RSLA on the relative humidity (RH) variation in early-age concrete under sealed conditions is investigated experimentally in terms of the setting time, relative humidity, and autogenous shrinkage. The results indicate that adding SAP and presoaked RSLA can significantly postpone the initial and final setting times. The initial setting time of RSLA30 and SAP06 is delayed by 127 and 171 min, respectively, compared to the benchmark mixture. In addition, increasing the amounts of SAP and presoaked RSLA can effectively extend the duration of the vapour-saturated stage, reducing the decrease in RH and autogenous shrinkage at 28 days. When the RSLA dosage increases from 0 to 10%, 20%, and 30%, the duration of the vapour-saturated stage is extended by 2, 9.4, and 26 days, respectively. Moreover, due to different water desorption behaviours, more IC water released by RSLA during the initial stage can slow the water release of SAP and lead to a higher RH level at 28 days.

Enhancing the Mechanical and Durability Properties of Fully Recycled Aggregate Concrete Using Carbonated Recycled Fine Aggregates.

The global construction industry is increasingly utilizing concrete prepared from recycled aggregate as a substitute for natural aggregate. However, the subpar performance of recycled fine aggregate (RFA) has resulted in its underutilization, particularly in the structural concrete exposed to challenging environments, including those involving chlorine salts and freeze-thaw climates. This study aimed to enhance the performance of RFA as a substitute for river sand in concrete as well as fulfill the present demand for fine aggregates in the construction sector by utilizing accelerated carbonation treatment to create fully recycled aggregate concrete (FRAC) composed of 100% recycled coarse and fine aggregates. The impacts of incorporating carbonated recycled fine aggregate (C-RFA) at various replacement rates (0%, 25%, 50%, 75%, and 100%) on the mechanical and durability properties of FRAC were investigated. The results showed that the physical properties of C-RFA, including apparent density, water absorption, and crushing value, were enhanced compared to that of RFA. The compressive strength of C-RFC100 was 19.8% higher than that of C-RFC0, while the water absorption decreased by 14.6%. In a comparison of C-RFC0 and C-RFC100, the chloride permeability coefficients showed a 50% decrease, and the frost resistance increased by 27.6%. According to the findings, the mechanical and durability properties, the interfacial transition zones (ITZs), and micro-cracks of the C-RFC were considerably enhanced with an increased C-RFA content.

Influence of Pretreatment Methods for Coarse Recycled Aggregates on the Performance of Alkali-Activated Concrete

Influence of Pretreatment Methods for Coarse Recycled Aggregates on the Performance of Alkali-Activated Concrete

Analysis on the mechanical properties of recycled concrete

Recycled concrete consists of cement, water and aggregates as conventional concrete; however, the difference is that the former includes a certain percentage of recycled aggregates to achieve environmental friendliness and economic efficiency. This article would focus on the existed application of recycled coarse (RCA) and fine (RFA) aggregate in concrete manufacturing and observe the material properties, such as compressive strength, shear strength, and slump value with different proportion of recycled aggregate mixed during fabrication. Based on sample results from existed experiments, for different amount of recycled coarse aggregate applied for concrete making, the material property would be varied and the appropriate amount of recycled coarse aggregate applied is around 50% for aggregate proportion (could be different for different type of RCA applied). In RFA section, two main resources of RFA are introduced, which are the wasted bricks and concrete. By investigating related research articles, the conclusion of wasted concrete is better than wasted bricks in making RFA is obtained. Several researches are included in RFA replacement experiments, and the conclusion of RFA replacement is that the proportion should be less than 20% in fine aggregate part. Also, intermediate materials such as fly ash, slag powder and silica fume should be applied to guarantee the cohesive property of concrete product. This article illustrates the hurdles and benefits of recycled aggregate application in current stage, and the prospects of recycled aggregates application in concrete products can be more predictable by analyzing the available experiments

Study on Coarse Recycled Concrete Aggregate

The use of recycled concrete aggregate (RCA) is one of the best solutions to mitigate the problem of ecological instability created by concrete waste. RCA has less crushing strength, impact resistance, specific gravity, and more water absorption capacity than the natural aggregate (NA). To overcome the compromised properties of RCA, a comprehensive study supported by the experimental investigation is required. This paper prescribes a methodology based on experimental investigation for the use of coarse-RCA (C-RCA) of size (4.75-20mm) as 100% replacement of coarse-NA in fresh concrete. A

Characterization of Coarse Recycled Aggregates Produced from Concretes with Different Strength Levels

With the acceleration of Urban Renewal Program, particularly in large cities of Turkey, the problem of finding land-fills and eliminating construction waste with the least environmental pollution necessitates its value-added recycling. However, the presence of adhered weak mortar layer, comprising 20-70% of recycled concrete aggregate (RCA), limits the use of RCA or lowers its inclusion level in concrete mixtures. Within the scope of this study, limestone- and basalt-bearing RCA obtained from 6 different concrete mixtures with three different water/cement ratios (0.45, 0.60, 0.70) were prepared and their water absorption, specific gravity, dense and loose unit weight, flatness indices, Los Angeles degradation values were determined. The results showed that, increasing w/c ratio of the parent concrete increased water absorption of the resultant RCA. However, the specific gravity, unit weight, abrasion resistance and flakiness index of RCA were decreased by increasing w/c ratio of the parent concrete.

Effects of recycled aggregate combinations and recycled powder contents on fracture behavior of fully recycled aggregate concrete

This paper studied the fracture behavior of fully recycled aggregate concrete (FRAC), which was prepared with 100% recycled coarse and fine aggregates (RCA and RFA) and partial recycled powder (RP). Three-point bending tests on center-notched beams were conducted to evaluate the effects of aggregate combinations and RP contents on the meso-scale fracture mechanism and macro-scale fracture parameters of FRAC. It was found that the FRAC mostly presented transgranular or intergranular failure with RCA or RFA, respectively. The RCA substitution had little effect on the critical crack opening displacements, but the RFA and RP substitution increased and decreased them, respectively. Only the incorporation of RFA led to a reduction of the initial cracking toughness of FRAC. The employment of RAs, especially RCA, reduced the fracture energy Gf and unstable fracture toughness KIcun, while the use of RP had a limited impact. The results of the characteristic length showed that RAs made the fracture behavior of concrete more brittle while RP played an opposite role. Both Gf and KIcun reduced with the decrease of tensile strength. The former was remarkable in FRAC due to the variation of aggregate combination whereas the latter was more likely associated with the aggregate size.

The Feasibility of Hydroxypropyl Methylcellulose as an Admixture for Porous Vegetarian Concrete Using Coarse Recycled Aggregates

In this paper, hydroxypropyl methylcellulose (HPMC) is used as a new additive for porous vegetarian concrete (PVC) to improve its void structure and strength. The effect of the HPMC on the fluidity of the mortar was first investigated by a viscosity test. Then the cement hydration process was determined for analyzing the effect of the HPMC on the strength and durability of the hardened PVC. Subsequently, experiments to investigate the mass transport and compressive strength characteristics, as well as the vegetarian properties, of the concrete were carried out. The results show that the bonding forces between the recycled aggregates and packing layer are elevated by viscosity improvement. The viscocity and flowability are significantly related to the dosage of HPMC from 0.0‰ to 0.3‰. The harden time is also delayed while the content of HPMC increases.The segregation phenomenon caused by the recycled aggregate powder in porous concrete could also be relieved by adding HPMC. The durability of PVC in the wetting–drying cyclic test is significantly improved by incorporating HPMC. The results of the vegetarian test also prove that, with HPMC mixing, sufficient space would be created in porous concrete, which is more suitable for plant growth due to a large number of existing pore channels.

Influence of Metakaolin and Silica Fume on the Mechanical and Durability Performance of High-Strength Concrete Made with 100% Coarse Recycled Aggregate

There is a strong need for a sustainable and ecofriendly approach from the construction industry toward mitigating climate change, as it is one of the critical sectors accountable for exploiting natural reserves and generating greenhouse gases. In order to resolve this issue, various supplementary cementitious materials (SCMs) and artificial aggregates are now in use. The use of recycled aggregate (RA) also seems to be a possible alternative to natural aggregate. However, the practical utilization of RA is rare. The amount of porous attached mortar and the source of the RA determines the quality of RA concrete (RAC). In this study, efforts were made to improve the quality of high-strength RAC, made with 100% RA, by incorporating metakaolin (MK) and silica fume (SF) using the well-known two-stage mixing approach (TSMA). In addition, DIN standards were followed to obtain the maximum particle packing of the aggregate. In total, 10 types of RAC were mixed––two comprising RACs at water-to-binder (w:b) ratios of 0.25 and 0.35, and eight mixes for obtaining a high-strength RAC. Both MK and SF were incorporated into those eight mixes at 10% and 15% replacement levels and w:b ratios of 0.25 and 0.35. The synergistic effects on fresh and hardened RACs, and their durability performance, considering DIN standards, the TSMA, and SCMs, were addressed. In this context, a comparative analysis showed positive results for using SF and MK in RAC, bearing in mind its mechanical and durability performance.

Characterization of PVA Fiber-Reinforced Pervious Concrete with Blended Recycled Ceramic Aggregates and Natural Aggregate

Effective industrial waste management is one of the important challenges facing modern society. Ceramic wastes occupy an important proportion of industrial waste. The utilization of waste of ceramics is becoming more and more attractive for many researchers to alleviate the environmental impact of industrial waste. As a low-impact development method, pervious concrete (PC) received more and more attention from researchers in recent years. However, the relatively low strength compared with ordinary concrete restricts the application of pervious concrete. This research used recycled ceramic coarse aggregates (RCCA) to partially replace natural coarse aggregates (NCA) to prepare recycled ceramic coarse aggregate pervious concrete (RCCAPC) and fiber-reinforced RCCAPC incorporating polyvinyl alcohol (PVA) fibers, and the effect of the replacement rate of RCCA and the amount of PVA fiber on the mechanical properties and permeability was investigated. The results show that RCCA can improve the mechanical properties of PC at a low substitution rate, as well as PVA fiber, and when the PVA content is about 0.3%, the enhancement effect is the best. Both RCCA replacement rate and PVA fiber content have little effect on the permeability coefficient of PC. Based on described studies, using RCCA to partially replace NCA at a low substitution rate is suitable for the preparation of PC, and PVA fibers can enhance the strength of PC, which may help to broaden the application scenarios of PC.

Effect of Coarse Recycled Aggregate and Rice Husk Ash on Concrete: A Factorial Design Approach

Effect of Coarse Recycled Aggregate and Rice Husk Ash on Concrete: A Factorial Design Approach

Water-Washed Fine and Coarse Recycled Aggregates for Real Scale Concretes Production in Barcelona

The use of recycled aggregate to reduce the over-exploitation of raw aggregates is necessary. This study analysed and categorised the properties of water-washed, fine and coarse, recycled aggregates following European Normalization (EN) specification. Because of their adequate properties, zero impurities and chemical soluble salts, plain recycled concrete was produced using 100% recycled concrete aggregates. Two experimental phases were conducted. Firstly, a laboratory phase, and secondly, an on-site work consisting of a real-scale pavement-base layer. The workability of the produced concretes was validated using two types of admixtures. In addition, the compressive and flexural strength, physical properties, drying shrinkage and depth of penetration of water under pressure validated the concrete design. The authors concluded that the worksite-produced concrete properties were similar to those obtained in the laboratory. Consequently, the laboratory results could be validated for large-scale production. An extended slump value was achieved using 2.5–3% of a multifunctional admixture plus 1–1.2% of superplasticiser in concrete production. In addition, all the produced concretes obtained the required a strength of 20 MPa. Although the pavement-base was produced using 300 kg of cement, the concrete made with 270 kg of cement per m3 and water/cement ratio of 0.53 achieved the best properties with the lowest environmental impact.

Behaviour of sustainable slag enriched concrete: Effect of fully replacement of natural coarse aggregate with construction waste

In construction domain and especially making concrete, the wise exploitation of natural resources along with the incorporation of recycled construction waste are solutions for making concrete an environmentally friendly construction material. This investigational study examines the performance of recycled aggregate concrete (RAC) made fully from recycled coarse (RC) aggregate. Only one mix made with natural coarse (NC) aggregate was prepared as a control for comparison purposes. The fresh concrete workability, the hardened concrete mechanical properties and the dynamic modulus of elasticity (Ed) were investigated. The impact of utilizing ground granulated blast furnace slag (GGBFS) as a replacement of cement at contents of 5%, 10%, 15%, and 20% on RAC performance was evaluated as well. Six mixes (two with no GGBFS and four with GGBFS) were prepared for measuring RAC behaviour. The findings of this study disclose that the workability (slump test values) decreases when GGBFS partially replaced cement in the mixes made fully with RC aggregate. A reduction of 26% in slump was observed when NC aggregate fully replaced with RC aggregate keeping cement without replacement and also in case of replacing only 5% of cement by GGBFS. Further reduction in slump was noticed when cement replacement by GGBFS increases in which the reduction reaches 43% for 20% replacement. Nevertheless, GGBFS can make a significant enhancement in concrete compressive strength as it almost reached 97% of NC aggregate concrete strength when 20% of cement replaced with GGBFS in the mix. The same positive effect of replacing cement with GGBFS was noticed in Ed results of concrete as well as resulted in slight enhancement in the density of the RAC.

Upgrading of demolition concrete into new construction concrete

In Morocco, buildings, road and urban infrastructure are ageing relatively quickly and often require renovation or demolition work. The large amount of demolition rebus generated is a considerable challenge that will have to be buried or reused. The reuse of these materials is an important aspect of their management, especially as regulations concerning landfill sites are becoming increasingly restrictive. Another challenge facing the construction industry is the reduction of natural aggregate sources due to the high demand for raw materials. The use of demolition concrete as recycled aggregates in new concrete is a promising solution in the current context of sustainable development. However, it should be noted that the properties of recycled aggregate concrete are different from those with natural aggregates, mainly their porosity, density and resistance. These differences are attributed to the cement mortar that adheres to natural aggregate particles, constituting an aggregate in itself.This work aims to study the influence of using a combination of Fine Recycled Aggregates (FRA) and Coarse Recycled Aggregates (CRA), with Natural Aggregates (NA). Since the use of the recycled coarse fraction in the production of new concrete may have revealed good performance in recycled concrete, the use of the recycled fine fraction remains still very limited, due to its absorptive capacity by reference to previous bibliographic studies. In order to improve the quality of Recycled Concrete (RC), this work also seeks to study a new crushing alternative that favours less adhered mortar.

A Comparative Study of the Mechanical Properties of Presoaked Coarse Recycled Concrete Aggregates Modified with Na2sio3 and Na2co3 Solutions

A Comparative Study of the Mechanical Properties of Presoaked Coarse Recycled Concrete Aggregates Modified with Na2sio3 and Na2co3 Solutions

Effect of Coarse Recycled Aggregate on Failure Strength for Asphalt Mixture Using Experimental and DEM Method

Coarse aggregate is the major part of asphalt mixture, and plays an essential role in mechanical performance of pavement structure. However, the use of poor-quality coarse recycled aggregate (CRA) reduces the strength and stability of the aggregate skeleton. It is a challenge to predict accurately the influence of CRA on the performance of asphalt mixture. In this study, both a uniaxial compression test and a direct tensile test were carried out to evaluate the failure strength of asphalt concrete with four CRA content. The discrete element method (DEM) was applied to simulate the specimen of asphalt concrete considering the distribution and properties of CRA. The results showed that temperature and loading rate have a significant influence on failure strength, especially when the CRA content was more than 20%. With the increase of CRA content, both cohesion force and internal friction angle were gradually weakened. The proposed model can be used to predict the failure strength of asphalt mixture, since both experimental and simulated results had a high consistency and repeatability. With the decrease of CRA strength, the nominal cohesion force of the specimen decreased, while the internal friction angle increased.

Performance of Recycled Coarse Aggregate Concrete Incorporating Metakaolin

The civil engineering industry is currently facing significant challenges of how to be an eco-friendly industry. The thoughtful utilization of natural resources in construction practices and the usage of recycled materials in the production of concrete can be a solution. In this experimental study, the behavior of recycled aggregate concrete (RAC) incorporating 100% recycled coarse (RC) aggregate is examined. It investigates the workability and mechanical properties of concrete after total replacement of natural coarse (NC) aggregate with RC aggregate. The influence of using Metakaolin (MK) at contents of 4, 8, 12, 16, and 20% on RA concrete performance is assessed. In total six mixes (one without MK and five included MK). A reference mix made with NCA was also prepared for comparison reasons. Workability, mechanical properties, water absorption (WA), and dynamic modulus of elasticity (Ed) were determined. The obtained results reveal that MK reduces the workability of the RAC. However, MK results in compressive strength enhancement and dynamic modulus of elasticity improvement, and lower water absorption of recycled aggregate concrete.

Eurocode Shear Design of Coarse Recycled Aggregate Concrete: Reliability Analysis and Partial Factor Calibration.

This paper contributes to the definition of design clauses for coarse recycled aggregate concrete. One of the main reasons for scepticism towards recycled aggregate concrete is the perceived notion that the heterogeneity of recycled aggregates may increase the uncertainty of the behaviour of concrete. Therefore, the paper uses structural reliability concepts to propose partial factors for recycled aggregate concrete’s design for shear failure. The paper builds upon a previous publication by the authors, in which the model uncertainty of recycled aggregate concrete elements designed for shear, with and without shear reinforcement, was compared with that of natural aggregate concrete elements. In that paper, the statistics of the model uncertainty for recycled aggregate concrete shear design were indeed found to be less favourable than those of natural aggregate concrete. Therefore, a partial factor for recycled aggregate concrete design is needed to ensure safety. This paper presents partial factors calibrated with explicit reliability analyses for different cases of design concerning beams (in the case of shear design of elements with shear reinforcement) and slabs (for the design of elements without shear reinforcement). For full incorporation of coarse recycled concrete aggregates and the design of elements without shear reinforcement, the calibrated partial factor reduces the design value of shear resistance by 10% (design with EN1992) or 15% (design with prEN1992) in comparison to natural aggregate concrete’s design. For the shear design of elements with shear reinforcement, the partial factor decreases resistance by 5% but a sensitivity analysis showed that the reduction might be, under pessimistic expectations, of up to 20%.

Improving the Durability Properties of Self-Consolidating Concrete made with Recycled Concrete Aggregates using Blended Cements

The paper evaluates the durability properties of Self-Consolidating Concrete (SCC) containing fine and coarse recycled concrete aggregates. The SCC mixtures were made with 0%, 25%, 50%, 75% and 100% substitution of Fine Natural Aggregates (FNA) with Fine Recycled Concrete Aggregates (FRCA) whereas Coarse Natural aggregates (CNA) were partially substituted (50%) with Coarse Recycled Concrete Aggregates (CRCA). Ordinary Portland Cement (OPC) was blended with 30% of Fly Ash (FA) which is further substituted with 10% of Metakaolin (MK). The durability parameters of SCC mixtures were evaluated using tests such as, Initial Surface Absorption Test (ISAT), Water Penetrability Test, Rapid Chloride Penetrability Test (RCPT), and Capillary Suction Test (CST). The Compressive strength test and Ultrasonic Pulse Velocity (UPV) test was also conducted on SCC mixtures. The durability and compressive strength properties of the SCC mixtures were found to deteriorate with the replacement of both CNA and FNA. At 120 days of curing, an increase of the order of 17.5%, 18.7%, 7.1% and 26.7% was observed in the results obtained in ISAT, RCPT, CST and Water Penetrability Test respectively with the substitution of FRCA with FNA and CRCA with CNA. However, the introduction of MK in the concrete matrix proved very effective as the values of ISAT, RCPT, CST and Water Penetrability Tests were observed at par with the control mix even with 75% FRCA and 50% CRCA content. In case of compressive strength, 9.3% drop was observed with 100% FRCA and 50% CRCA content. However, the presence of MK has been found to compensate this to 4.5% only. Moreover, all SCC mixtures with CRCA and FRCA and MK can be classified in the excellent category on the basis of their UPV values.

Effect of Fly Ash, GGBS, and Metakaolin on Mechanical and Durability Properties of Self-Compacting Concrete Made with 100% Coarse Recycled Aggregate

Abstract In developing country such as India, due to the significant boom in the infrastructure development the virgin aggregates (VAs) resources are diminishing at a high pace and thus creating an...