Hardening Properties of Fly Ash Blended Cement Cured at Elevated Temperatures

　Recently, fly-ash produced in Japan contains much carbon and less vitreous components compared with previous ones due to the lowering of combustion temperature of coal to prevent NＯx generatio. There are many reports on effect of quality change on hardening properties of fly-ash blended cement in the case of curing at room temperature, but a few on curing at elevated temperatures, such as steam and autoclave curing.
　The present study was carried out to fill in the latter gap and to clarify the suitability of carbon rich fly-ash for curing at elevated temperatures.
　CONCLUSIONS
　Hardening properties of fly-ash blended cement were investigated using fly-ash rich in unburnt carbon content by changing mixing ratios of fly-ash in the range from 10 to 70% and curing temperatures from 40゜ to 180 ℃.
　The results are summarized as follows:
　(1) As curing temperatures increased, bulk densities tended to increase.
　(2) Increase of curing temperature was effective to improve strength. Steam curing below 80℃ was effective for fly-ash content from 20 to 40%. By autoclave curing above 120℃, strengths of compacts containing fly-ash under 30% were improved remarkably. However, for fly-ash rich compacts over 40%, curing above 160℃ was required to obtain high strength.
　(3) As crystallin reaction products, monosulfate was formed nuder steam curing conditions. Above 100℃, the formation of hydrogarnet was observed. 11angstrom tobermorite was formed above 120℃ and its formation increased remarkably up to 180℃.
　(4) The reaction of Ca(OH)₂ liberated by the hydration of cement and fly-ash was remarkable at temperatures above 160℃, which resulted in the formation of 11angstrom tobermorite and the remarkable increase of the strengths of fly-ash rich compacts over 40%.