Early Hydration and Setting Process of Fly Ash-blended Cement Paste under Different Curing Temperatures

A specially developed ultrasonic measurement apparatus (UMA) was used to in situ monitor the setting process of fly ash blended cement paste.Combined with the results of Vicat Needle tests,isothermal calorimetric measurement,XRD analysis,SEM morphology and compressive test,the influence of curing temperature (20,40,60,and 90 ℃) and fly ash content (0,10%,20% and 30%) on the setting and hydration process of fly ash blended cement paste was analyzed.The results show that setting and hardening process of fly ash blended cement paste at elevated temperature can be clearly identified into three stages including dormant stage,acceleration stage and deceleration stage.The increasing of curing temperature greatly accelerates the setting and hardening process.However,the content of fly ash does not have significant effect on the setting in condition of 90 ℃.Besides,the initial and final setting time of cement paste is correspondent with the time of duration of dormant stage and the time of UPV value is 1 500 m/s (T1500),respectively.Thus,the UMA can be used to determine the initial and final setting time of cementitious material under different curing temperatures.The compressive test results indicate that the paste with 20% fly ash presents higher compressive strength than the plain paste at curing temperatures of 90 ℃.Therefore,appropriate amount of fly ash is beneficial for concrete in the high temperature curing conditions.