Statistical analysis of the carbonation coefficient in open air concrete structures

In recent years, the number of reinforced concrete structures with anomalies associated with reinforcement corrosion problems has significantly increased. One of the causes is concrete carbonation which occurs when carbon dioxide (CO2) penetrates the concrete’s porous system to create an environment with lower pH around the reinforcement in which corrosion can proceed.Several analytical models describe the relationship between carbonation depth and concrete age, of which the most frequently used results from Fick’s first law: x=Kt, where K is the carbonation coefficient. This coefficient depends on environmental conditions such as CO2 concentration and humidity and concrete characteristics like w/c ratio, type of cement, and so it varies significantly from one structure to another.A statistical study is presented in this paper to enable a better evaluation of K in open air concrete structures. The study is based on the results of over 100 measurements taken on existing structures up to 99 years old. The results were statistically analysed to obtain correlations between K and factors such as structure age, the effect of painting, concrete compressive strength and exposure conditions. This analysis allowed recommendations for the covering of reinforcing bars to be made at design level.

▸ Analysis of carbonation prediction models. ▸ Data from real reinforced concrete structures. ▸ Compressive strength as input parameter for carbonation prediction models. ▸ Recommendations for covering of rebars at design level. ▸ Scatter makes carbonation evolution very hard to predict.