Rates of carbonation and reinforcement corrosion in high alumina cement concrete

High alumina cement (HAC) concrete was used extensively in the UK from the 1950s to the early 1970s in the manufacture of precast, prestressed concrete beams. Long-term durability problems have now begun to affect these elements, the most important of which is reinforcement corrosion due to carbonation of the cover concrete. A ten-year programme of research, funded by the DETR, was initiated at the Building Research Establishment in 1993 to provide data on the rates and mechanisms which control carbonation and reinforcement corrosion in HAC concrete. This paper reviews data obtained over 5 years. Carbonation depths and rates for the HAC concretes studied were found to be influenced by water/cement ratio, curing and exposure conditions, in a similar manner to Portland cement (PC) concretes. The carbonation rates appeared to be the same as those for PC concretes with 28-day compressive strength properties similar to the fully converted (minimum) strength of the HAC concrete. The majority of the steel in specimens exposed in natural conditions was still in uncarbonated concrete after five years' exposure. The risk of reinforcement corrosion in these specimens was therefore low. However, electrochemical measurements taken on fully carbonated specimens illustrate the strong relationship between the availability of moisture, concrete resistance and the rate of corrosion.