Experimental Study on Mechanical Performance of Recycled Fine Aggregate Concrete Reinforced With Discarded Carbon Fibers

With the development of technology in every field, it is necessary to recommend an eco-friendly material to be utilized in the construction industry. Recently, using waste/recycled materials in the concrete as a substitute is a trend to bring sustainability to the construction industry, but the recycled/waste materials has poor mechanical properties, thus to enhance these poor properties, this research studies the mechanical performance of sustainable concrete incorporating waste materials as aggregates, the study is performed in the three stages. In the first stage, the natural sand was substituted with recycled sand in the percentage of 0, 35, 70, and 100%, and all the tests i.e. compressive strength, split tensile strength and flexural strength were performed on concrete which was cured in water for 28 days. As the 35% substitution of natural sand with recycled fine aggregate presented the optimum mechanical performance, it was selected for the third stage of the research. In the second and the third stages, the discarded carbon fibers were utilized in concrete with 2, 4, and 6% by weight. A total of 90 samples were prepared for this research, in which 30 samples were cubes, 30 samples were cylinders and 30 samples were beams, all the samples were tested at 28 days. Comparative analysis was performed to validate and verify the results of this paper with the relevant literature. The SEM test was also performed on a fractured concrete surface to study its microstructure. The outcome of tests revealed that the utilization of discarded carbon fibers in concrete enhances compressive, split tensile and flexural strength by 27.8, 17.8, and 35.9% and acts as a crack bridging and also restrain the propagation of the first cracks. Fibers also helped the concrete to improve its energy absorption capacity and ductility.

Feasibility Studies on Demolition Recycled Fine Aggregate and Sea Sand as Partial Preplacement to Natural Fine Aggregate in Concrete

In this research work, an attempt is being made to partially replace the natural fine aggregate with sea sand and recycled fine aggregate obtained from demolished concrete waste in varied proportions to concrete mix and subject the specimens to mechanical strength tests for short and long durations of 7, 28, 56 and 90 days curing. The compressive strength, split tensile strength and flexural strength results of 30% mix proportion (15% Sea sand + 15% demolished waste sand) were found to be 58.3 N/mm2, 3.53 N/mm2 and 4.71N/mm2 respectively. All the three strength test results obtained were found to yield 15% higher strength than the control specimens. Finally, it can be concluded that partial replacement of natural fine aggregate by sea sand and demolition recycled fine aggregate in construction industry, not only eliminates the waste management problems and impacts on environment, but also leads to the sustainable development by reducing the consumption of natural resources.

Time-Dependent Shrinkage Model for Recycled Fine Aggregate Thermal Insulation Concrete

In this study, the shrinkage performance of recycled aggregate thermal insulation concrete (RATIC) with added glazed hollow beads (GHB) was investigated and a time-dependent shrinkage model was proposed. Two types of recycled fine aggregate (RFA) were used to replace natural fine aggregate in RATIC: RFA from waste concrete (RFA1) and waste clay brick (RFA2). Besides, the mechanical properties and thermal insulation performance of RATIC were also studied. Results showed that the pozzolanic reaction caused by RFA2 effectively improved the mechanical properties of RATIC; 75% was the optimal replacement ratio of RATIC prepared by RFA2. Added RFA decreased the thermal conductivity of thermal insulation concrete (TIC). The total shrinkage strain of RATIC increased with the increase of the replacement ratio of RFA. The 150d total shrinkage of RATIC prepared by RFA1 was 1.46 times that of TIC and the 150d total shrinkage of RATIC prepared by RFA2 was 1.23 times. The addition of GHBs led to the increase of early total shrinkage strain of concrete. Under the combined action of the higher elastic modulus of RFA2 and the pozzolanic components contained in RFA2, the total shrinkage strain of RATIC prepared by RFA2 with the same replacement ratio was smaller than that of RATIC prepared by RFA1. For example, the final total shrinkage strain of RATIC prepared by RFA2 at 100% replacement ratio was about 18.6% less than that of RATIC prepared by RFA1. A time-dependent shrinkage model considering the influence of the elastic modulus of RFA and the addition of GHB on the total shrinkage of RATIC was proposed and validated by the experimental results.