Penetrability of Lightweight Aggregate Concrete

Abstract

A study on the parameters affecting the sorption of water, chloride ingress, permeability of water and carbonation into lightweight aggregate concrete, normal weight concrete and recycled aggregate concrete was carried out. The parameters being studied are effect of water-cement ratio, aggregate type, initial moisture content of lightweight aggregate, size of lightweight aggregate, density of lightweight aggregate, volume of lightweight aggregate, varying temperatures of (1?C to 40?C), high pressure of 30MPa and the mineral admixture silica fume. Experimental programme series were designed to look into the effects of these parameters on the penetration of water and free chloride ions into lightweight aggregate concrete by water sorption under capillary action in unsaturated concrete, chloride diffusion under a constant concentration gradient, water permeability under a constant pressure gradient and carbonation. From this research, it was found that variations in water-cement ratio, size of lightweight aggregate, density of lightweight aggregate and volume of lightweight aggregate has reasonable effects on penetrability properties of lightweight aggregate concrete. The effect of initial moisture content in lightweight aggregate on properties of lightweight aggregate concrete was not obvious from this research. When comparing trends for normal weight granite concrete and lightweight aggregate concrete (atmospheric pressure versus 30MPa pressure), pressure did not have any significant effect on chloride ingress. The mineral admixture silica fume at (10% replacement level to cement content), showed negligible effect in reducing water sorptivity and chloride ingress and effect of temperature is more significant at higher temperatures (> 30?C) as compared to lower temperatures (<20?C) for chloride ingress into lightweight aggregate and normal weight concrete.

For recycled aggregate concrete, results show that increasing concrete strength for higher grades G60 and G80 for replacement percentage of 20%, will decrease the chloride diffusion depth. Trends of water absorption coincide with that of chloride diffusion. However, results show that using a lower grade of concrete with a higher replacement levels will increase the water absorption significantly. There is a resistance to carbonation for higher strength recycled aggregate concrete. Carbonation depth was reduced for the higher grades of concrete i.e: G60 and G80. Using lower grade concrete with higher replacement percentage of 50% and 100% will increase the carbonation penetration depth from 5.3-6.0%.