Retracción por secado en hormigones con árido grueso reciclado

Abstract

The main goal of this research is to analyze the shrinkage strain of concrete with different recycled coarse aggregates content, and to determine the suitability of mathematical expressions proposed by different standards and codes for theoretical prediction of this kind of strain. Firstly, two conventional concretes were designed, one of them with water-to-cement ratio of 0.65 and another one 0.50, and their respective recycled concretes with 20%, 50% and 100% of recycled 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. With the aim of analyzing shrinkage strain, prismatic specimens of 10x10x60 cm were made for each concrete, and so, cylinder specimens of 15x30 cm and cubic ones of 10x10x10 cm in order to determine the mechanical properties of these concretes. All of them were placed and tested under air temperature-humidity conditions of laboratory. Shrinkage strain was determined by an embedded gauge placed into the cross section of prismatic specimens. In this way, deformations without loading (free shrinkage) were monitored continuously during a time period of 1000 days. The main component of measured shrinkage is the drying shrinkage due to environmental variations of air temperature-humidity conditions. The obtained results show an increase of shrinkage with the replacement percentage of aggregate. This increase can be attributed to the reduction on mechanical properties of recycled concretes and to the presence of recycled aggregate in its own right. In order to analyzing the influence of this last parameter, theoretical values of shrinkage were calculated according to different standards and taking into account the experimental fc of each concrete. The obtained results noted that it is necessary to provide a correction factor for the standards equations, in order to keep the same ratio “experimental shrinkage/theoretical shrinkage” in conventional concretes and recycled concretes with different replacements percentage.