Conditions for Carbonation of Silica Fume Concretes

This article outlines an experimental and numerical study on the pozzolanic interaction limits for carbonation of silica fume concretes. For this purpose cylinders of 8 types of High-Performance Concrete were cast. Carbonation and weight losses were studied parallel. An indirect method was used to measure carbonation; i.e. carbonation shrinkage was observed. The age of concrete at start of carbonation was defined in relation to the weight increase of the specimen. Parallel studies on the effect of w/c, silica fume and age on shrinkage of silica fume concretes were performed. Internal relative humidity and strength were investigated on cubes from the same batches of concretes that were used in the studies of carbonation. After 5-6 years (in 1997-1998) the carbonation depth was detected, which showed good correlation with the carbonation shrinkage. With low w/c ratio and sufficient amount of silica fume no carbonation shrinkage and no carbonation was observed. The results also indicate well-correlated relationships between shrinkage, w/c and RH. The type and amount of silica fume affected shrinkage. Sufficiently long sealed curing at water-cement ratio 0.30 and 10% silica fume content, prevented carbonation for at least 5 years. The study was performed at Lund University in 1992-1998.