INFLUENCE OF CURING TEMPERATURES ON DRYING SHRINKAGE CHARACTERISTICS OF PORTLAND CEMENT MORTAR WITH HIGH DOPING OF FLY ASH

The drying shrinkage of portland cement mortars with different fly ash dosages after curing at 20 ℃ and 60 ℃ before drying was investigated. The hydration degree of cements, the pore structure and the pore size distribution of hydrated cement mortars were analyzed by chemical binding water and mercury intrusion porosimetry(MIP). Effects of curing temperatures on the drying shrinkage of the portland cement mortars with and without doping of fly ash were discussed. Results show that after curing at 20 ℃ and before drying, drying shrinkage values of cement mortars with higher mass of fly ash are lower than that of the cement mortars without or with lower mass of fly ash. After curing at 60 ℃ and before drying, the drying shrinkage values of the cement mortars with higher mass of the fly ash are greater than that of the cement mortars without or with lower mass of the fly ash. However for the cement mortars with the same fly ash dosage when the curing temperature increases from 20 ℃ to 60 ℃, the drying shrinkage of the cement mortars are remarkably decreases. When the dosage of the fly ash is lower (0-20%) the drying shrinkage of the cement mortars cured at higher temperature is lower than that of the cement mortars cured at lower temperature, while the fly ash dosage is higher, the result is just reverse. The drying shrinkage values at all stages of cement mortars with fly ash, no matter cured at 20 ℃ or 60 ℃ before drying, are lower and the stabilized period are shorter than that of portland cement mortars cured at 20 ℃ before drying. For the portland cement without the fly ash, curing temperature mainly affects the microstructure of CSH gel phase and consequently affects the drying shrinkage. For the portland cement with the fly ash curing temperature mainly affects hydration rate of system and pore size distribution of the hydrated cement mortars and consequently affects the drying shrinkage.