Steam-cured Fly Ash Concrete

With the development of national economy, the contradiction about the railway carrying capacity and the passenger and goods transports amounts increasing need is increasingly obvious. So our country must accelerate a railwaying. The railway prestress concrete should have a better function to fit in with the development of direction of the railway freight heavy load and the passenger transport high speed.This paper mainly presents the study on the some problems of steam-cured concrete containing fly ash for railway prestress concrete sleeper. By testing chemically combined water and compressive strength of hardened pastes and SEM, the influence of fineness and content of fly ash, waterbinder ratio,admixture and cured regime on hydration characteristics of cement fly ash composite binders on steam curing condition was study. The mortar experiment showed the fly ash was activated by adopting the mechanical grind and different chemical activators on steam curing condition. Meanwhile, by testing compressive strength of steam-cured concrete containing fly ash at different ages, the excellent steam-cured regime was selected. Finally, the influence of content of fly ash on penetration of chloride ions into concrete by ASTM C1202 and RCM on steam curing condition was study.The main conclusions of this paper are as following:(1)The steam curing increases the hydration velocity of cement fly ash composite binders;(2)On steam curing condition, the fineness of fly ash does not influence the early hydration and the late hydration velocity increases with the rise of fineness of fly ash; the early hydration velocity decreases with the rise of content of fly ash, and the late hydration degree with the suitable content of fly ash is higher than the hydration degree of cement; the addition of fly ash facilitates the hydration of cement and the hydration velocity of cement increases with the rise of content of fly ash;(3)On steam curing condition, the excellent method of activating fly ash is mechanical grind and there are respective optimal contents when six chemical activators activate fly ash. (4)The steam-cured regime with procuring time for 2h, heating-up time for 2h, maximum temperature for 60℃, temperature holding time for 8h and cooling time for 1h is suitable on the concrete containing fly ash;(5)The fly ash drops obviously the porosity of concrete and improves greatly chloride ions resistance of concrete. The porosity of concrete on steam curing condition is greater than the porosity of concrete on standard curing condition.