Thixotropy and interlayer bond strength of self-compacting recycled concrete

Abstract

This work is focused on assessing the thixotropy of self-compacting recycled concrete (SCRC) and on evaluating the interlayer bond strength. To do so, four SCRC mixes with 0%, 20%, 50%, and 100% of recycled coarse aggregate (by volume) were studied. This aggregate was used in dry-state conditions and an extra quantity of water was added during mixing in order to compensate its absorption.Three testing methods were used to assess the degree of thixotropy of SCRC: structural breakdown curves at various rotational speeds, hysteresis loop flow curves and yield stress at rest. To evaluate the effect of the structural build-up at rest on SCRC interlayer bond strength, two methods were used: flexural tests and water permeability tests.The results indicate that the increase of thixotropy and interlayer bond strength with the replacement percentage is due to the difference in the effective w/c ratio, result of the non–compensated water absorption, to the higher amount of fines in the recycled aggregates and generated from the old adhered mortar and also to the higher internal friction of recycled aggregates. Moreover, as water absorption is compensated in the mixing protocol, changes over time in the effective w/c ratio are negligible. Therefore, the thixotropic changing rate is similar in all studied mixes.