碱对低热水泥早期水化进程和微结构的影响

Influence of Alkali on Early-Age Hydration Process and Microstructure of Low-Heat Cement

通过外掺Na_2SO_4的方式,将低热水泥中的碱含量(质量分数,下同)提高至0.80%,1.20%和1.60%.利用微量热仪研究了以硫酸盐形式存在的碱对低热水泥早期水化进程的影响,并通过水化动力学模型具体分析了碱对低热水泥各水化阶段的影响,最后利用29Si和27Al固体魔角核磁共振技术,研究了碱对低热水泥水化产物中含Al相和含Si相组成结构的影响.结果表明:碱能促进低热水泥的水化,但在一定碱含量范围内,低热水泥的水化并不随着碱含量的增加而显著增加,这种促进作用主要是由于碱提高了水泥结晶成核和晶体生长速率,并延长了相边界反应阶段;此外,碱在一定程度上促进了低热水泥中的Al向C-S-H链中转移,但随着碱含量的增加,Al在C-S-H链中的相对含量降低,更倾向于向六配位的AFt中转移.

The alkali content(by mass,the same below)of low-heat cement was adjusted to 0.80%,1.20%and 1.60%by adding Na 2SO 4.Isothermal calorimetry test was used to investigate the influence of alkali on early age hydration process of low-heat cement.The influence of alkali on the hydration stage of low-heat cement was analyzed by the hydration kinetic model.The structure of silicon phase and migration form of the aluminum phase in low-heat cement hydration products were observed by 29 Si and 27 Al magic angle spinning nuclear magnetic resonance.The results show that alkali can promote hydration process of low-heat cement,but the hydration process does not increase with the increment of alkali content in certain content.The promotion effect of alkali on low-heat cement is mainly due to increase of nucleation and crystal growth rate of low-heat cement and the stage of interaction at phase boundaries is prolonged.Besides,alkali is more likely to increase aluminum substitution ratio in calcium silicate hydrate(C-S-H)chain and the degree of polymerization of C-S-H.However,with the increment of alkali content,aluminum tends to shift to ettringite(AFt)rather than to C-S-H chain.