STRENGTH, POROSITY, AND RESISTIVITY OF COARSE RECYCLED CONCRETE AGGREGATE SELF-COMPACTING CONCRETE CONTAINING FLY ASH

Abstract

This article was a study of the possibility of using recyclable waste concrete in high strength self-compacting concrete. The waste concrete was cylindrical specimens with 150 mm diameter and 300 mm height, and 150 mm cubes which were aged 1-2 years. The waste concrete was crushed into a 20 mm maximum nominal size to use as a coarse aggregate. Self-compacting concrete with water to binder ratio of 0.35 was used as controlled concrete (PC), in which the target compressive strength of 100 mm cubes was 70 MPa at the age of 28 days. The PC concrete mixture was replaced crushed limestone with crushed recycled concrete aggregate, and the cement was partially replaced by class C fly ash at the dosage of 0%, 20%, 40%, and 60% by weight of the binder to produce concrete (CA, 20FA, 40FA, and 60FA concrete, respectively). The slump flow was controlled in the range of 650-750 mm. The compressive strength, porosity, electrical resistivity, and non-steady state chloride migration were investigated. From the experimental results, it was found that the compressive strength of CA concrete was lower than that of PC controlled concrete but higher than the target compressive strength. The CA concrete had higher the porosity and the chloride diffusion coefficient and lower the electrical resistivity than that of PC controlled concrete at the age of 28 days. The compressive strength of concrete containing fly ash was higher than the target compressive strength at the age of 90 days, except the 20FA concrete was higher at the age of 28 days.  The chloride penetration resistance of concrete containing fly ash was higher than that of PC control concrete. The tendency of the chloride penetration resistance increased with containing the fly ash increased at the age of 90 days.