Corrosion of reinforcement in concrete containing wet-stored fly ash

Abstract

The study described was concerned with moistened fly ash as a cement component in concrete and its influence on carbonation and chloride-induced corrosion. Five laboratory-moistened fly ashes (10% by mass) and samples from two power station stockpiles (moistened at 10–30% by mass) were examined, with several material/storage variables investigated. Initial tests quantified moisture effects, which indicate agglomeration of fly ash and a tendency for this to increase with free lime content, storage period and temperature. Concretes were compared at equal slump (75 mm) and 28 day (cube) strength. Air (intrinsic) permeability and water absorption were slightly greater (high free lime, 0.9%), or lower (low free lime < 0.1%) with moistened fly ash in concrete (compared to that with dry material), and where there were benefits, these increased with longer storage. For carbonation and chloride diffusion, moistening of low free lime fly ash generally gave similar or slightly enhanced results. In the case of high free lime fly ash, wet-storage lead to little change in carbonation but increased chloride diffusion. These seemed to be due to the effects that wet storage has on fly ash properties (agglomeration, reduced fineness/reactivity) and their influences on concrete and the durability processes. Carbonation tended to reduce with low storage temperature, while chloride diffusion gave little change. Reinforcement corrosion associated with these was similar between dry and moistened low free lime fly ash concretes. While paste experiments suggest some differences in chemistry between dry and wet-stored fly ash systems and their response to carbon dioxide and chloride exposures, these didn't seem to have a noticeable effect on concrete resistance to the processes.