Comportamiento deformacional de los hormigones reciclados bajo carga axial sostenida

Abstract

Deformational behavior of recycled concrete under sustained compressive load within its elastic branch (≤0.4fc) is analyzed in this study, with the aim of determining strain-time curves, specific creep values and creep coefficient referred to each kind of concrete according to replacement percentage of recycled aggregate. In order to carry out the research, two control concretes were made, one with w/c ratio of 0.65 and another one with 0.50, and their corresponding recycled concretes, with 20%, 50% and 100% replacement percentages of coarse aggregate for each series. Thereby, eight different concretes were obtained, which were named as H65-0, H65-20, H65-50, H65-100, H50-0, H50-20, H50-50 and H50-100. Regarding load mode, a pulley system was designed in order to transmit the sustained compressive load to both cylinder specimens were arranged in a metal frame in series. Longitudinal and transversal strain gauges and metal discs DEMEC were placed over these specimens. Experimental strains were recorded through a data acquisition system during a testing period of 1000 days after load. The performed measures allow distinguishing three different strain-stress states. A first phase without load during the 42 early days, in which only the shrinkage strain is produced. A second step in which sustained load is applied and the elastic instantaneous strain produced by that load is identified. And finally, a branch with long-term concrete strains consisting mainly of creep and drying creep. This latter is due to environmental thermo-hygrometric conditions of laboratory in which tests were carried out. In general, the obtained results show an increase of creep in recycled concretes compared to conventional ones. However, the monitored strain produced by sustained load does not show a clear trend of behavior related to replacement percentage of recycled aggregate in a concrete, as there are many factors independent from the kind of aggregate used, which have a significant influence in this phenomena.