Effect of aggregate clay content on concrete mechanical properties and its bond with reinforcement

In this study, the effect of clay content of aggregate on mechanical properties and reinforcement-concrete bond strength of conventional and self compacting (SCC) concrete was studied. In this regard, compressive strength, tensile splitting strength, pull-out, four-point bending and beam bending tests were performed. A CEM I 42.5 R type cement and two different w/c ratios, namely 0.40 and 0.42 were used in the study. Clay content of aggregate was determined by means of methylene blue test and three different aggragates with different methylene blue values were used in the experiment. In order to adjust viscosity, different types of water-reducing admixtures were used in conventional and SCC mixtures. The compressive strength tests were carried out on 1,7 and 28-day age specimens. The flexural strength, splitting tensile strength, pull-out and Belgium hinged beam bending tests were applied to 28-day age specimens. According to the results, both the compressive strength and flexural strength values of traditional and self-compacting concrete decreased with increasing the clay content of the aggregate. However, the viscosity, T50 value and Vfunnel values of SCC mixtures were improved by increasing clay content of the aggregate. Besides, visual inspection reveated that increasing the aggregate clay content increased the stability of the concrete mixtures in terms of segregation resistance. From rebar-concrete bond point of view, SCC mixtures showed superior results than those of conventional concrete. However, the pull-out and flexural strength of both concrete types reduced with increasing the methylene blue value of the aggregate.