养护龄期对粉煤灰混凝土抗碳化性能影响研究

Study on the Effect of Curing Period on Carbonation Resistance of Fly Ash Concrete

本文基于快速碳化环境通过试验研究水胶比为0.35、0.42、0.50,粉煤灰等质量替代水泥0%、30%、60%,标准养护28 d、56 d、90 d混凝土试件碳化规律,根据水泥-粉煤灰体系非蒸发水含量、粗骨料界面过渡区扫描电镜(SEM)图像对养护龄期影响混凝土抗碳化性能机理进行深入剖析。结果表明:水胶比和粉煤灰含量一高一低时,界面过渡区密实程度对其影响占主导地位,可使粉煤灰混凝土抗碳化性能明显提高;当粉煤灰含量为60%、水胶比为0.35时,B、C条件下混凝土28 d碳化深度增加值仅分别为A条件的66%和38%;粉煤灰含量和水胶比均较高或较低时,延长养护龄期对其界面过渡区改善作用并不明显,早期养护56 d或90 d均不能有效提高粉煤灰混凝土抗碳化性能;对于含掺合料混凝土,当水胶比较大时,无论掺合料掺量大小,即使延长养护时间至90 d亦不能使其抗碳化性能明显提高。

Based on the rapid carbonization environment,the carbonation law of concrete specimens with water binder ratio of 0.35,0.42 and 0.50,fly ash replacing cement by 0%,30%and 60%,and standard curing for 28,56 and 90 days was studied.According to the non-evaporating water content of cement-fly ash system and the SEM of concrete coarse aggregate interface transition zone,the mechanism of curing age affecting the carbonation resistance of concrete was deeply analyzed.The result shows that the water binder ratio and fly ash content are high and low,the compactness of the interface transition zone plays a dominant role,which can significantly improve the carbonation resistance of fly ash concrete;when the content of fly ash is 60%and the water binder ratio is 0.35,the increase of 28 d carbonation depth of concrete under B and C conditions is only 66%and 38%of that under A condition,respectively;when the fly ash content and water binder ratio are high or low,the improvement effect of prolonging the curing age on the interface transition zone is not obvious,and the carbonation resistance of fly ash concrete can not be effectively improved by early curing for 56 or 90 days;for concrete containing admixtures,when the water binder ratio is large,no matter the amount of admixture,even extending the curing time to 90 days can not significantly improve its carbonation resistance.