Avaliação experimental da retração em concretos com substituição do agregado graúdo natural por agregados reciclados

Abstract

The construction segment is one of the biggest waste producers and, this waste, frequently are dispose on inappropriate places. Additionally, the construction activity requires along the all the product chain a lot of natural. In face of the necessity to reduce the natural impact caused by the construction activity, many researchers are committed to studying the impact of the replacement of natural aggregate for recycled aggregate. The academic community appoints the viability to use this material in structural concrete but, barely is known about these long-time concrete behaviors. The shrinkage and creep phenomenon are inherent of concrete and they made the concrete structures deform along the time. In opposite of the creep phenomenon, the shrinkage brings the concrete structure to strain even the structure is unloaded and, consequently, cracks may occur, and these cracks will compromise the structural durability. Thus, in face of this phenomenon importance, this researches goal is determining the autogenous and drying shrinkage magnitude in conventional concretes with 60MPa and 40MPa of compression resistance and concretes produced with coarse aggregate replacement for recycled concrete aggregates (RCA) and recycled masonry aggregate (RMA). Therefore, to study the shrinkage of theses concretes, an experimental tests were conducted in accordance by ABNT NM 131 (1997) and by ASTM C157 (2017) on concretes with resistance of 60 MPa confectioned with Brazilian cement CP II and CP V, concretes with resistance of 40 MPa with rate w/c 0,35 and 0,38 and concretes mix with 40 MPa of resistance with natural coarse aggregate replacement in proportion of 25%, 50%, 75% and 100% by RCA and RMA. The experimental results were compared with those values that was indicated by the Brazilian code NBR 6118 (2014) and the values indicated by the international codes CEB-fip (2010), Eurocode 2 (2004) and ACI 209.2R (2008). Subsequently, the recycled concretes results were compared with the values presented by Lye et al. (2016) and by Silva et al. (2015) and, the experimental results were compared with results obtained by Lye et al. (2016) equations. After this, a covariance analysis (ANOVA) was performed in different concretes groups intend to identify the differences among these concretes. This analysis permit identifies, for example, that the concrete resistance and the cement type influenced at the shrinkage magnitude, for the concretes which present w/c rate of 0,35 and 0,38, this difference did not result in significant differences. Using linear regressions analysis, equations ware developed to represents the autogenous and drying shrinkage for the produced concretes. Theses equations were used to determine the crack width in concrete slabs, through the calculus model proposed by Gilbert and Nejadi (2004). Through this analysis, were possible to determine the ideal reinforcement rate to be use in slabs to prevent the shrinkage cracks.