Investigation On Microstructure Changes Of Cementitious Materials In The Carbonation Reaction

Carbonation reaction of alkaline substances from internal concrete is an important reason which affect concrete durability. The existing quantitative forecast models about carbonization contain few microstructural parameters, which have not discuss the relationships of between the microstructure parameters. In order to predict concrete structure durability, it is necessary to deeply research the differences of microstructural changes between complete carbonation area and part carbonation area.This paper focus on the partition of carbonated cement paste and mortar with different water cement ratio, admixtures, CO₂ concentration, blending load and so on. The microstructure evolution （solid phase composition and pore phase structure） during carbonation reaction process are determined using modern experimental test equipment, XRD, TG-DSC,MIP and BET, respectively. The carbonation model based on microstructure parameters will be built.The carbonization test shows that, no matter cement paste or mortar, the length of part carbonation area and the length of complete carbonation area are both increased with water to blinder ratios increased. With the same water to blinder ratios, the complete carbonation area length of cement paste is bigger than mortar and the length is increasing with time extension. The length of part carbonation area got by DG-TSC is bigger than pH test. The porosity of carbonated sample decreases with depth, but the pore water saturation increases. The porosity and the pore water saturation of cement paste is higher than mortar.With different CO₂ concentration, the partition of cement paste with 0.53 water to blinder ratio. When the CO₂ concentration is higher, the length of complete carbonation area and the length of part carbonation area are the bigger, the porosity in the two area will be decreased.Compared to cement paste, admixture has a few influence in carbonation tests,no matter it is 30% fly ash or 50% blast. There is no part carbonation area appears in this experiment. And they have more big pore after carbonation, whose pore radius at least 434nm.Carbonization loading experiments show that, compression will inhibit carbonization while tension will promote the carbonization; When the stress ratio is +0.4, the part carbonation area is the longer; When the stress ratio is -0.4, the part carbonation area is the shorter.