Análise experimental da resistência à punção em lajes lisas com substituição de agregados graúdos naturais por reciclados de concreto

Abstract

The popularization of the use of recycled concrete aggregates has increased due to socioeconomic aspects, but above all, as sustainability is being pursued and, in this context, some international standards have been published to facilitate and standardize the use of this material. Despite the constant evolution of studies on punching shear, there is a need for national and international regulatory adjustments in relation to the use of recycled concrete aggregates in flat reinforced concrete slabs. Two reasons explain the slight influence of the incorporation of recycled aggregates on the punching shear resistance of concrete slabs: lower mechanical strength and better bond between the cement paste and the recycled concrete aggregate due to the higher cement content, porosity, and roughness, when compared with natural aggregate. Thus, the punching shear strength is influenced by these properties of the aggregates along the shear plane of the cracks, the two effects offset each other, leading to a similar punching shear strength. This research carried out the experimental test of 6 flat slabs of reinforced concrete without shear reinforcement subjected to symmetrical loading, containing variations in the rate of flexural combat reinforcement (0.7% and 1.4%) and replacement rate of natural aggregate by recycled concrete aggregate (0%, 30% and 100%). The study evaluated the influence of these variables on the punching shear resistant capacity and analyzed the upper limits of resistance. The slabs were octagonal with 2500 mm of distance between parallel faces, sides of 1030 mm and thickness of 210 mm, molded with concrete with fck of 25 MPa and supported on columns of 300 mm of side. The standards used as a parameter for estimating resistant capacity were NBR 6118:2014, ACI 318:2019 and Eurocode 2:2004. The experimental results showed that the slabs with ARCO showed a maximum reduction of 6 % in the punching shear resistance when compared to the slabs with conventional coarse aggregates. The reinforcement rate was able to increase the cracking load at the service limit state (ELS) and the recycled concrete aggregate had little influence on the opening of cracks in the slabs with the highest rate of flexural reinforcement.