Study on the impact of different CaO contents in fly ash on the stability and crack resistance of cement paste

Abstract

The impact of varying CaO concentrations in fly ash on the stability and crack resistance of cement paste was studied. Four kinds of fly ash with CaO content of 3.42%, 16.22%, 10.35% and 20.89% were selected for comparative analysis. The findings reveal that, as the CaO content and its proportion in the mix increase, the stability expansion value measured by Ray's clip method exhibits a slight upward trend. Notably, all four fly ash varieties exhibit excellent volume stability within a 40% dosage range.Furthermore, after 28 days, it was observed that all cement mortars underwent shrinkage. However, interestingly, as the CaO content rose, the degree of shrinkage decreased marginally.When comparing cementitious materials with identical cement types and fly ash dosages, it was evident that the initial cracking time was significantly shorter for the fly ash containing 20.89% CaO compared to the other three types. Conversely, the cementitious material with 3.42% CaO content exhibited the longest initial cracking time.

Keywords

high calcium ash / calcium oxide content / stability / crack resistance