UK: A study by the University of Dundee has dispelled the myths of substantial performance differences between concretes made with cement containing dry or wet-stored fly ash, with comparable reinforcement corrosion between the two.
Vertical News has reported that the research, whose backers included the Department for Environment, Food & Rural Affairs and Heathrow Airport Holdings, was aimed at “quantifying moisture effects, which indicate agglomeration of fly ash and a tendency for this to increase with free lime content, storage period and temperature.”
Researchers tested five moistened fly ashes and samples from two power station stockpiles, and further investigated different material and storage variables, comparing the concretes at 75mm slump and 28 day strength. Air permeability and water absorption of moistened fly ash proved greater with high free lime (up to 0.9%) and lower with low free lime (to under 0.1%). What benefits there were improved with longer storage. The moistening of low-free-lime fly ash generally yielded similar, or slightly higher, carbonation and chlorine diffusion. The moisture caused little change in high-free-lime ash’s carbonation, while increasing chloride diffusion. Furthermore, high storage temperature equated to greater carbonation.
In spite of these intriguing chemical differences, the study concluded, "these didn't seem to have a noticeable effect on concrete resistance.”