Cracking Resistance of Steam-Cured Precast Concrete Using High Alite Cement with Modified Fly Ash

Cement with fly ash has rarely been used in Japan, mainly because its strength development is slower than ordinary Portland cement. In this research, the effect of the new type of fly ash (which was modified by the electrostatic belt separation method) with high alite (C3S) cement on cracking resistance of precast concrete prepared by steam curing was studied. The mechanical and shrinkage properties of the proposed fly ash concrete were compared with those of concrete made using OPC cement without fly ash. In order to study the cracking tendency of precast concrete with the proposed cement with fly ash, thermal stress analysis was conducted, taking into consideration the experimental data of concrete properties with the different concrete mix proportions. A standard precast concrete box culvert model was used in this 3D FEM analysis, and the distribution of temperature and relative humidity in the cross-section and induced restraint stress during and after steam curing were discussed. Steam-cured concrete with fly ash and high alite cement developed higher compressive strength on the first day of age than concrete with OPC. The proposed fly ash concrete developed high cracking resistance in the early days. On the other hand, the results showed that the drying shrinkage at later ages was the main cause of cracking.