Analysis of rheological behaviour of self-compacting concrete made with recycled aggregates

Abstract

This research focuses on studying the fresh state behaviour of self-compacting recycled concrete (SCRC) using rheology as a fundamental tool. For said purpose, a reference self-compacting concrete (SCC) was designed and it was modified to obtain other two SCCs with different water to cement ratios. Lastly, the natural coarse aggregate of each SCC was replaced with recycled aggregate using three different replacement percentages, 20%, 50% and 100% (by volume). At 15min from the contact time of water with cement (reference time), two different tests were carried out with a rheometer: a stress growth test and a flow curve test.The results show that the specificity of SCRC design lies in the quantity of extra water necessary to compensate the recycled aggregate absorption during the mixing protocol and in the intrinsic characteristics of this particular aggregate. Mainly the rough texture when both natural and recycled coarse aggregates are crushed-shaped and the fines content in the recycled aggregate and generated during mixing by the wear of old adhered mortar change the baseline mortar.All these singularities lead to different “rheological variations – (w/c)ef” curves in a SCRC compared to a SCC. The SCRC curves present higher slope than the SCC ones, so they predict higher rheological variations, especially when the w/c ratio is low.