Effect Of Recycled Concrete Aggregate Research Articles

Properties of recycled concrete aggregate under different curing conditions

Construction and demolition wastes are produced every day around the world. Thus the idea of using recycled concrete aggregate in new concrete production appears to be an effective utilization of concrete waste. This paper presents the results of an experimental study to evaluate the effects of recycled concrete aggregate (RCA) percentages under different curing conditions. The percentages of recycled coarse aggregate to dolomite were (0:100%, 25:75%, 50:50%, 100:0%) respectively. The concrete properties which were studied were the mechanical properties (compressive and splitting strength) and mass transport properties (ISAT and sorptivity). The concrete specimens were exposed to three different curing conditions, moist (standard), open-air, and painted specimens using the substance (Curassol 1). The coarse recycled concrete aggregates were obtained by crushing a laboratory produced primary concrete at age of 28days. The results showed that curing using paint material was the most efficient method of curing at all ages and percentages of recycling except at 100% recycling, where the maximum value of both compressive and tensile strengths was obtained using water curing. Also, in moist curing, full replacement of coarse aggregates gave the highest compressive strength at age of 28days. In all cases of recycled aggregate ratios, curing using water caused a decrease in the concrete permeability.

Study on thermal properties of recycled aggregate concrete and recycled concrete blocks

This paper investigated the thermal properties of recycled aggregate concrete (RAC) and recycled concrete block. Considering the effect of four factors, an orthogonal test was conducted to study the thermal conductivity of RAC. The thermal conductivities of large particle recycled aggregate concrete (LRC) and recycled brick concrete (RbC) were also tested at different replacement ratio of recycled aggregate. By defining an influence coefficient c, the effect of recycled concrete aggregate (RCA) on thermal conductivity of RAC was better explained. A modified formula was also proposed to calculate the thermal conductivity of RAC based on that of normal concrete. The thermal resistance of recycled concrete block was calculated, and an experiment on the heat transfer coefficient of recycled concrete block wall in practical engineering was conducted. The study shows that the recycled coarse aggregate has the greatest influence on thermal conductivity of RAC. There is a significant linear relationship between the influence coefficient c and the thermal conductivity of RAC. The results calculated from modified formula for thermal conductivity of RAC agreed basically with the test results.

Creep and Shrinkage of Normal-Strength Concrete with Recycled Concrete Aggregates

This paper describes an experimental investigation on the creep and shrinkage of normal-strength concrete with recycled concrete aggregates (RCA) as replacement for coarse natural aggregates (for example, crushed stone and gravel). Three RCA sources and two aggregate replacement levels were used; additional parameters were curing conditions, loading age, and axial stress level. It was found that RCA significantly increases the creep and shrinkage deformations of concrete, but this increase is smaller than the effect of RCA on the initial (that is, immediate mechanical) deformations. The creep compliance increases with increased loading age of RCA concrete, in a similar manner as for conventional concrete. Out of the three materials tested, the RCA producing the smallest concrete compressive strength resulted in the largest creep compliance. Adjustment factors were determined for code-based creep models to predict the creep deformations of RCA concrete. The use of these factors is intended to be similar to other code-based adjustment factors for “nonstandard” conditions (for example, loading age).

Behavior of Reinforced Concrete Beams with Recycled Concrete Coarse Aggregates

This paper investigates the flexural and shear behavior of reinforced concrete beams that use recycled concrete aggregates (RCA) as replacement for coarse natural aggregates (e.g., crushed stone, gravel). The experimental results from 12 twin pairs of normal strength concrete beam specimens are presented and compared with predictions from existing code methods and analytical models for conventional concrete. Each pair of beams is saw-cut from a single, longer member to investigate the inherent variability in the results, specifically focusing on locally available recycled materials with minimal processing and construction methods that are consistent with current U.S. practice. It is found that the use of RCA does not cause an observable change in the progression of nonlinear behavior and failure. The effect of RCA on the flexural and shear strength of the beams is also small; however, there is a considerable reduction in the initial stiffness and an increase in the ultimate flexural deflections as the amount of RCA is increased. In general, the predicted results are reasonably close to the measured trends, indicating that existing analytical models and code-based procedures for conventional concrete can also be applied to RCA concrete beams.

Experimental Investigation into the Freeze-Thaw Resistance of Concrete Using Recycled Concrete Aggregates and Admixtures

This work investigates the effects of recycled concrete aggregates on the freeze-thaw resistance of the concrete. Taguchi orthogonal optimization technique was used in this investigation in order to minimize the number of samples required for each experiment. Therefore, only a few combination values of control factors required were chosen. Orthogonal table with three levels and four factors was used to prepare the mixing proportions. The results were analysis to check interaction among the factors. The results showed that in saturated Recycled Aggregate Concrete (RAC), the recycled aggregate has negative effects on its durability performance, therefore their use in structures exposed to severe climate is not strongly recommended. However, with the use of mineral and chemical admixtures, particularly air-entraining admixtures and fly ash, the recycled aggregate concrete could exhibit some level of durability.

Improvement of the durability of concrete with recycled aggregates in chloride exposed environment

Recycled aggregates concrete (RAC) becomes an important participant in recycled materials although there are still questionable properties of it, like chloride penetration and diffusion. An extensive experimental campaign was performed in order to evaluate the effect of recycled concrete aggregates (RCA) over some properties of concretes. Composition and mix design influence on the concrete were studied in mixes ranging from 0.45 to 0.60 w/c ratios, with 0%, 20%, 50% and 100% coarse aggregates replacement. Concretes were submitted to saline attack and the total chloride contents were determined as well as the chloride penetration profiles. Both new cement paste and RCA from different concrete mixes were analysed by XRD and SEM in order to evaluate the chlorides binding. A chloride binding phenomenon is detected in RAC which may compensate the RCA higher permeability. According to chloride diffusion results, high RCA content lead to an improvement of durability in RAC with sufficiently low w/c ratio, in terms of chlorides presence.

Evaluating Recycled Concrete Aggregate as Hot Mix Asphalt Aggregate

Abstract The use of recycled concrete aggregate (RCA) in asphalt mix is a sustainable construction practice, provided that the addition of RCA does not adversely affect the performance of the asphalt mix. In this study, the effects of RCA on the performance behavior of hot mix asphalt (HMA) were examined. The mixes were produced by blending RCA with virgin aggregate at six different percentages (0 %, 20 %, 40 %, 60 %, 80 %, and 100 %). The mix design results indicate that the RCA is highly absorptive, and that as the percentage of RCA in the mix increases, the optimum asphalt content increases significantly. In terms of performance behavior, the addition of RCA to the HMA mix reduced the modulus, resistance to rutting, fatigue, thermal cracking, and resistance to moisture damage of the asphalt mix. Considering the performance behavior and the need for a higher asphalt content, the use of RCA as HMA aggregate is not recommended, even though all the RCA mixes met the volumetric requirements. More important, the findings in this study indicate that the absorbed asphalt might play a significant role at high temperatures, likely because of expansion of the asphalt.

The effect of recycled concrete aggregate and steel slag on the dynamic properties of asphalt mixtures

A high percentage of asphalt mixtures (in terms of weight and volume) are composed of aggregates; thus, new aggregates are needed to build and maintain roads. The use of waste material as aggregates in the pavement industry can prevent the accumulation of waste material and environmental pollution and can reduce primary production costs. Thus, the objective of the present study was to determine the mechanical properties of asphalt mixtures with waste concrete and steel slag aggregates. Six different asphalt mixtures containing three types of aggregate (dacite, recycled concrete and steel slag) were used to prepare Marshall specimens and to determine the optimal asphalt binder content. The mechanical characteristics of the mixtures were evaluated by Marshall stability, indirect tensile resilient modulus, dynamic creep and indirect tensile fatigue tests. The results indicated that the optimal mixture contained steel slag coarse aggregates and recycled concrete fine aggregates.

Effect of Recycled Concrete Aggregate Properties on Mixture Proportions of Structural Concrete

This study focuses on characterizing several recycled concrete aggregate (RCA) sources, developing concrete mixture proportions that incorporate RCA as coarse aggregate, and investigating the effect of coarse aggregate properties on the main mixture proportion parameters [i.e., cement content, water demand, and water–cement (w/c) ratio]. Four aggregate types were investigated: one control virgin aggregate source and three RCAs produced from the crushing of hardened concrete. Numerous aggregate tests, including density, absorption, abrasion resistance, adhered mortar content, and crushing value, were performed. Fourteen mixture proportions were developed with the use of three mixture proportion scenarios (control, direct replacement, and strength based) and two compressive strength levels (40 and 60 MPa). The effect of RCA on compressive strength and workability was evaluated by replacement of natural coarse aggregate with RCA. Contrary to numerous studies, one of the RCA concretes (RCA-1) had compressive strengths up to 12% higher than the equivalent control mixture. Mixture proportions (water, cement, and w/c ratio) were later adjusted to ensure that the RCA concretes had compressive strength and slump values similar to the control concretes. Variations in water demand, cement content, and w/c ratio could then be directly attributed to the properties of the RCA source. RCA-1 concrete required less cement (and a higher w/c ratio) to achieve strengths and slumps similar to the control concrete. The findings and recommendations of this research will assist concrete producers, engineers, and field technicians involved in the selection of RCA sources in developing mixture proportions for structural-grade RCA concrete.

Properties of high-workability concrete with recycled concrete aggregate

This study presents the effects of recycled concrete aggregate (RCA) on the key fresh and hardened properties of concrete. RCA was used to produce high-workability concrete substituting 0-100% natural coarse aggregate (NCA) by weight. The slump and slump flow of fresh concretes were determined to ensure high workability. In addition, the compressive, flexural and splitting tensile strengths, modulus of elasticity, and permeable voids of hardened concretes were determined. The test results revealed that RCA significantly decreased the workability of concrete. RCA also affected the compressive strength, modulus of elasticity, and permeable voids of concrete. At the age of 28 days, the concrete with 100% RCA provided 12.2% lower compressive strength and 17.7% lesser modulus of elasticity than the control concrete. Also, 100% RCA increased the permeable voids of 28-day old concrete by 8.2%. However, no significant negative impact of RCA was observed on the flexural and splitting tensile strengths of concrete.

Effects of recycled concrete aggregate on the fresh properties of self-consolidating concrete

Concrete wastes are generally delivered to the landfill sites for disposal. Due to increasing charges of landfill and scarcity of natural coarse aggregate (NCA), recycled concrete aggregate (RCA) derived from concrete wastes is growing interest in construction industry. In the present study, RCA was used as partial and full replacements of NCA to produce self-consolidating concrete (SCC). Different SCC mixes were produced with RCA substituting 0%, 30%, 50%, 70%, and 100% NCA by weight. The water to cement (W/C) ratio and high-range water reducer (HRWR) dosage were kept the same for all concretes. The effects of RCA on the key fresh properties such as filling ability, passing ability, and segregation resistance of SCC were investigated. The test results revealed that the filling ability and passing ability of SCC were improved for 30% and 50% RCA. The SCC mixes with 30% and 50% RCA also possessed adequate segregation resistance. In addition, strong correlations were observed for filling ability, passing ability, and segregation resistance. The overall test results suggest that RCA can be used to produce SCC substituting up to 50% NCA without affecting the key fresh properties of concrete.

Evaluation of Effects of Recycled Concrete Aggregate on Volumetrics of Hot-Mix Asphalt

Each year around 200 million tons of demolition wastes are produced from aging U.S. infrastructures. Of that amount, 100 million tons are portland cement concrete debris. Disposal of these wastes in landfills has been a traditional solution, but environmental regulations, costs, and a lack of landfill areas have hindered safe disposal. These problems have led to a search for alternate ways of reusing demolition wastes by recycling. Recycling the concrete waste not only reduces the waste disposal problem but also reduces the quarrying of virgin aggregate. The incorporation of recycled concrete as a hot-mix asphalt (HMA) aggregate can be a viable option in terms of costs and environmental considerations. This use of recycled concrete aggregate (RCA) as an HMA aggregate can be beneficial for constructing low-volume roads. RCA differs from virgin aggregates in that there is cement paste on the surface of the recycled concrete. In this study, 5% RCA was evaluated as an HMA aggregate. Mix designs were conducted, and the effect of RCA on the volumetrics of HMA was evaluated. The mix design results indicated that RCA is absorptive, and that as the percentage of recycled concrete increased in the mix, the optimum asphalt content increased linearly. The statistical regression model showed that RCA had significant effects on the volumetrics of the mix.

Effects of recycled concrete aggregates on properties of asphalt concrete

Recycled concrete aggregates (RCA) are produced by crushing demolished concrete elements. RCA differ from fresh aggregates due to the cement paste attached to the surface of the original natural aggregates after the process of recycling. This highly porous cement paste and other contaminations contribute to the lower particle density and higher porosity, variation in the quality of the RCA and the higher water absorption. This paper presents some of the results of an investigation on the possible application of RCA in asphalt concrete. It was found that all the volumetric properties (except the percentage of air voids), resilient modulus and creep values of asphalt specimens containing RCA as coarse aggregates were relatively lower compared with the values found for similar specimens made with only fresh aggregates. Some of these measured properties were within the acceptable recommended limits, for the RCA sample used in this study.