低热水泥复掺粉煤灰体系的强度放热与水化演变研究

Study on strength exothermic and hydration evolution of low heat cement mixed with fly ash

进行低热水泥复掺粉煤灰材料的放热、强度与水化过程研究。考虑粉煤灰掺量、水胶比与养护时间对复掺体系的放热、力学性能影响,研究复掺体系的优势与不足。随后,借助XRD、扫描电镜、热重试验,从水化产物与微观结构角度研究粉煤灰在低热水泥中的作用机理。主要结论如下:随粉煤灰掺量增加,基体强度略有下降,但后期强度增长率有所提高,同时,复掺材料早期放热降低,增加水泥诱导期,进而推迟了C3S的早期快速反应的时间。随水胶比降低(0.5、0.42、0.34),基体后期的强度有所增加,早期放热增加(3 d为147.8、155.2、157.4 J/g)。由CH含量与化学结合水的结果可得:粉煤灰在水化7 d后具有水化活性的硅铝玻璃体被碱环境激活,与CH发生二次水化,形成大量C-S-H凝胶,这也是掺30%的粉煤灰后期强度增长率较大的原因。此外,低热水泥复掺粉煤灰的大体积混凝土是可行的,可降低基体的温度裂缝,增加体积稳定性,但改变水胶比时需谨慎。

It studies the heat release,strength and hydration process of low heat cement mixed with fly ash.Considering the effects of fly ash content,water binder ratio and curing time on the exothermic and mechanical properties of the composite system,the advantages and disadvantages of the composite system are studied.Then,with the help of XRD,SEM and thermogravimetric test,the action mechanism of fly ash in low heat cement was studied from the perspective of hydration products and microstructure.The main conclusions are as follows with the increase of fly ash content,the matrix strength decreases slightly,but the later strength growth rate increases.At the same time,the early exothermic of the compound material decreases,increases the cement induction period,and then delays the early rapid reaction time of C3 S.With the decrease of water binder ratio(0.5,0.42 and 0.34),the strength of the matrix increased in the later stage and the early heat release increased(147.8,155.2 and 157.4 J/g in 3 days).The results of CH content and chemical bound water can be obtained the hydration and activity of the silicon aluminum vitreous body activated by fly ash after 7 days of hydration is activated by alkali environment,and the hydration of CH occurs with the two times,resulting in a large number of C-S-H gels.This is also the reason for the increase of the strength of the 30% fly ash at later stage.In addition,the mass concrete with low heat cement mixed with fly ash is feasible,which can reduce the temperature crack of the matrix and increase the volume stability,but care should be taken when changing the water binder ratio.