Experimental Investigation and Yield Line Prediction for Ultimate Capacity of Recycled Aggregate Concrete Slabs

Abstract

The present investigation was conducted to evaluate the influence of recycled aggregates on structural behaviour of reinforced concrete (RC) slabs. Concrete mixtures of 0.6 and 0.4 water/cement ratios were used to produce normal strength concretes and high strength concretes, respectively. Various concrete mixtures were prepared by replacing 19 mm natural coarse aggregates with 0, 25, 50, 100% recycled coarse aggregate (RCA) then used to cast RC slabs of size 500 x 300 x 100 mm thick, and 100 mm cubes. The two-way concrete slabs were reinforced orthotropically with Y12 steel bars. Workability, compressive strength, and split tensile strength properties of concrete were measured, while the RC slabs were subjected to monotonic loading until failure. The experimental results obtained were compared with theoretical failure loads predicted using the yield line theory. It was found that the use of RCA in concrete generally leads to reduction of workability and concrete strength in proportion with the RCA content incorporated into the mixture. The yield line method gave a conservative and accurate theoretical prediction of the actual ultimate loads for control concretes, predicting 10% lower values, but it exhibited loss of prediction accuracy for RCA concretes of normal strengths basically overestimating their failure loads. Accordingly, it would be unsafe to employ the yield line method for design of RCA concrete slabs of normal strengths. Generally, the adverse effects of RCA on concrete properties and structural behaviour can be mitigated significantly by adjusting mixture designs to higher strengths or by employing high strength concretes