Análise teórica da retratação por secagem do concreto com agregado reciclado

Abstract

The construction industry is considered a major cause of environmental degradation, thus, the sector has turned to sustainable development in order to reduce environmental impacts. One of the measures adopted is the reuse of construction waste, through the production of recycled aggregate. The construction waste are materials of great heterogeneity in their composition, which, consequently, affects the properties of the recycled aggregates derived from them. The variability of recycled aggregates causes uncertainties about their use in concrete, since it directly affects the behavior of concrete in both fresh and hardened states. However, the use of recycled aggregates in concrete is feasible, since it is possible to obtain concrete with recycled aggregates with mechanical properties similar to those of conventional concrete. Nevertheless, studies indicate that the shrinkage of concrete with recycled aggregate is higher than that of concrete with natural aggregate, due to the higher porosity and high absorption rate of recycled aggregates. Shrinkage is a time-dependent phenomenon that causes cracking in concrete, affecting the durability and service life of concrete structures. To enable the use of concrete with recycled aggregate, it is important to predict its behavior over time, through models capable of estimating its deformation. The deformation due to drying shrinkage depends on several factors, including those associated with the aggregate; but in spite of that, many of these factors are not considered in the numerical models that predict the behavior of conventional concrete. This study evaluated the shrinkage prediction models of NBR 6118 (2014), Model II (1978), Model B3 (1995), Model B4 (2015), CEB-FIP Model (1990), CEB-FIB Model (2010), Gardner Model (2004), ACI Model (1978), ACI Model (1992), Eurocode 2 (2008) developed for concrete with natural aggregate, in which through a parametric study and statistical analysis it was analyzed if they were able to predict the shrinkage of concrete with recycled aggregate. The theoretical values obtained with the models were compared with the experimental results of concrete with recycled coarse and fine aggregate, verifying that the models are not adequate to describe the shrinkage behavior of this type of concrete. Therefore, new adjustment proposals were developed to predict the shrinkage of concrete with recycled coarse aggregate and another for concrete with recycled coarse aggregate, as well as a new formulation for the models of NBR 6118 (2014), Model II (1978), CEB-FIB Model (2010), Eurocode 2 (2008), being validated with experimental data. The results show that knowing the value of the experimental shrinkage up to 90 days of conventional concrete it is possible to estimate the shrinkage by drying of concrete with recycled aggregate for the indicated models using the proposed correction coefficient Kc. The new proposal for the models CEB-FIP (1990), CEB-FIB (2010), NBR 6118 (2014) and Eurocode 2 (2008) presents behavior that is expected for the theoretical curves through a Kr coefficient that uses values of the shrinkage of concrete with recycled coarse aggregate.