Effect of curing on carbonation of Portland Pozzolana cement concrete.

Abstract

Pozzolana cement concrete (PPC) hydrates slowly compared to ordinary Portland cement (OPC) concrete, the slow hydration process delays the formation of hydration products that fill up the pores in the matrix, this could eventually allow the ingress of harmful substances like carbon dioxide leading to carbonation if improper curing takes place. Good curing and the development of a well-developed microstructure are key if the concrete is to perform at its full potential. Curing is even more important with the increasing use of pozzolana cement whose reaction is slow. The effects of improper curing, compromise durability, but may not become visible for many years. As a result, three curing methods were employed to study the extent of carbonation front upon the three curing regimes namely; Air curing, spraying curing and submerged curing. This was studied at different curing periods including; 3 days, 7 days, and 28 days of curing for each of the above-mentioned methods. The carbonation chamber was constructed using steel plates (1.3m x 0.92m x 0.35m in size). The chamber was supplied with 4% concentration of carbon dioxide gas from a cylinder through a pipe. The experimental research also looked at the degree of hydration of concrete for the same curing regime. It was found that the submerged curing regime exhibited the highest resistance to carbonation of only 1.5 mm at 28 days as compared to the spraying and air curing for PPC concrete. Submerged curing also had a higher degree of hydration of 71% compared to spraying of 57% and air curing of 47% at 28 days. These findings have shown that the curing method and period have such an influence on the carbonation front, it has further demonstrated that there exists a relationship between Curing, carbonation resistance and the degree of hydration of the cement.