Percentages Of Recycled Coarse Aggregate Research Articles

Experimental and analytical studies on recycled coarse aggregate concrete

Investigated properties of concrete made with recycled coarse aggregate (RCA) as partial replacement to natural coarse aggregate (NCA). A series of tests were performed to determine the fundamental strengths of the proposed concrete. NCA in concrete is replaced with 0, 25, 50, 75, and 100% of RCA. Results confirmed a gradual decrement in fundamental strengths with increment in the percentage of RCA. Finite element analysis (FEM) is performed by using ANSYS APDL 16.2 software to validate the results. Few Regression Analysis Models were deduced to estimate the strengths of RCAC.

The Dynamic Mechanical Properties for Recycled Aggregate Concrete under Tensile-Compressive States

The experiments under biaxial tensile-compressive (T-C) complex stress were carried out for two kinds of substitution percentages of recycled coarse aggregate (RCA) on biaxial proportional loading (α = σ1:σ3 =1:0, 0: −1, 0.05: −1, 0.1: −1, 0.25: −1, 0.5: −1, 1: −1 and−1: −1) and four loading deformation rates of 10−5/s, 10−4/s, 10−3/s, and 10−2/s. The research was completed in the static-dynamic true triaxial machine. The experimental phenomena indicate the tensile failure appears in these specimens of recycled aggregate concrete (RAC) under biaxial T-C stress states. The dynamic mechanical behavior for RAC under biaxial T-C loadings was affected by the strain rates, stress ratios and its substitution percentages of RCA. Accompanied by the increase of strain rates, its strength of RAC is improved. As the tensile stress increases, its compressive strength decreases. The T-C strengths for RAC under biaxial T-C states are less than its corresponding uniaxial T-C strengths at a certain identical strain rates, respectively. Considering the effect of loading rates, a new tensile-compressive failure criterion is established under complex stress states.

Evaluation of high-strength concrete made with recycled aggregate under effect of well water

In the present study, the influence of using recycled coarse aggregate (RCA) and well water (WW) on the mechanical characteristics of high-strength concrete were investigated. The reuse of devastated structures as recycled aggregate became an especially serious issue in Mosul City, Iraq, following the 2017 war. These events have also made it difficult to access drinking water. This study sought to determine the effect of the more readily available well water in Mosul City when combined with recycled aggregate on compressive, splitting, and flexural strengths of high-strength concrete. The mixtures were prepared using four different percentages of RCA, replacing 0 %, 25 %, 50 %, and 100 % natural coarse aggregate (NCA). In total, eight mixtures were designed, four mixtures cured by potable water (PW), and the other four mixtures cured by well water. The results showed the compressive strength decreases by about 16.0 % when using well water for concrete made with NCA. Also using WW caused drop about 13.2 %, 10.0 % and 8.5 % for concrete containing 25 %, 50 % and 100 % RCA, respectively. The flexural and splitting tensile strength also reduced when using well water. A regression analysis allowed the formulation of new material constitutive relationships for high-strength concrete, including the effects of WW and RCA.

Analysis on Mechanical Properties of Recycled Aggregate Concrete Members after Exposure to High Temperatures

In order to study the mechanical properties of recycled aggregate concrete (RAC) specimens after exposure to high temperatures, 120 RAC prism specimens, 57 reinforced recycled aggregate concrete (RRAC) specimens, and 56 steel reinforced recycled aggregate concrete (SRRAC) specimens were designed, involving two varying parameters such as recycled coarse aggregate (RCA) replacement percentage and temperature. The performance degradation of RCA materials, RRAC members, and SRRAC members after exposure to high temperatures was analyzed in depth. The research results show that after exposure to high temperatures the surface color of members may change from cinereous to gray-white. Some cracks may appear on surface of members and the mass of members may be lighter. With the increase of the experiencing temperatures, the bearing capacity (compressive, bending, and shearing) of RAC and its members are reduced, but their ductility and energy dissipation capacity have little effect on the change of high temperature. With the increase of the RCA replacement percentage, the mass loss ratio, ultimate bearing capacity, and peak deformation of each RAC and its members increase slightly, and the displacement ductility and energy dissipation capacity of the RRAC members decrease slightly. With the increase in replacement percentage of RCA, mechanical properties of RAC and their members have little effect after exposure to elevated temperatures, and the fluctuation range is within 20%.

Bond strength between corroded steel reinforcement and recycled aggregate concrete

This paper investigates the bond performance of recycled coarse aggregate (RCA) concrete with un-corroded/corroded reinforcing steel bars, with the main parameters being RCA content, corrosion level, bar diameter and embedment length. For this purpose, 60 pull-out specimens containing different percentages of RCA (i.e. 0%, 25%, 50% and 100%) and steel bars of two diameters (12 and 20 mm) and different embedment lengths were tested. In order to establish various levels of corrosion, specimens were exposed to an electrochemical corrosion for 2, 5, 10 and 15 days. The bond strength between RAC concrete and un-corroded/corroded steel are compared to current codes and equations proposed by other researchers.Experimental results showed that larger corrosion rate of steel bars was observed with the increase of the replacement level of RCA due to its high porosity and water absorption. The use of RCA had a slight influence on bond strength for un-corroded specimens compared to that obtained from conventional concrete. Furthermore, the bond strength of RCA concrete was strongly affected by corrosion products; bond strength slightly enhanced for up to about 2% corrosion rate, and then significantly decreased as the corrosion time further increased, similar to that of conventional concrete. However, the rate of bond degradation between RCA concrete and corroded steel bars was much faster than that observed in corroded conventional concrete.

Flexural Behavior of Corroded Reinforced Recycled Aggregate Concrete Beams

Recycling concrete not only reduces the use of virgin aggregate but also decreases the pressure on landfills. As a result, recycled coarse aggregate (RCA) is extensively recommended for new construction projects. However, the flexural behavior of corroded reinforced recycled aggregate concrete (RAC) beams is uncertain. The experimental research presented in this paper was performed to investigate the flexural behavior of corroded reinforced RAC beams compared to that of corroded reinforced natural aggregate concrete (NAC) beams and consequently explore the possibility of using RAC beams in corrosive environments. Four different percentages of RCA in total mass of coarse aggregate in concrete mixtures (0%, 33%, 66%, and 100%) and two different concrete strengths (C30, C60) were the governing parameters. The electrochemical method was adopted to accelerate steel corrosion. Full‐scale tests were performed on eight simply supported beams until the failure load was reached. Comparison of load‐deflection behavior, crack patterns, failure modes, ductility, and ultimate flexural capacity of corroded reinforced NAC and RAC beams was made based on the experimental results obtained. The comparison results show that the flexural behavior of corroded reinforced RAC beams with an appropriate percentage of RCA is satisfactory compared to the behavior of NAC beams.

Development of sustainable concrete using recycled coarse aggregate and ground granulated blast furnace slag

The present investigation aims to use recycled coarse aggregate (RCA) and ground granulated blast furnace slag (GGBFS) as replacement of natural coarse aggregate (NCA) and ordinary Portland cement (OPC) for developing sustainable concrete. Sixteen numbers of concrete mixes are prepared with 0%, 25%, 50% and 100% replacement of NCA by RCA for each 0%, 20%, 40% and 60% replacement of cement by GGBFS. The effects of RCA and GGBFS on fresh and hardened concrete properties such as workability, compressive strength, split tensile strength, flexural strength, rebound number, density, water absorption and volume of voids are experimentally investigated. The test results obtained in the present investigation show that the workability increases with the use of RCA or GGBFS or both of these two. The compressive, split tensile and flexural strength decrease with increase in the percentages of RCA or GGBFS or both. The reduction in split tensile and flexural strength of the concrete mixes containing RCA or GGBFS or both RCA and GGBFS is less pronounced unlike its compressive strength. The values of rebound number obtained from non destructive test (NDT) show the similar trend with the results of compressive strength. Water absorption and volume of voids of the concrete mixes increases with increase in RCA content. However, the use of GGBFS improves the quality of the concrete mixes by improving the ITZ and bond between mortar and RCA. The concrete mix with 50% RCA and 40% GGBFS achieves values of these properties closer to those of the concrete mix without RCA and GGBFS. Finally, the concrete mix with 50% RCA and 40% GGBFS is considered as the optimum mix which is satisfying the target mean strength of the mix design and producing sustainable concrete by saving 40% of cement and 50% of NCA and utilizing maximum waste products such as GGBFS and RCA.