粉煤灰-水泥水化的核磁共振定量分析

利用高分辨固体核磁共振仪结合去卷积技术,定量分析了粉煤灰水泥浆体中水泥和粉煤灰的水化程度以及C-S-H凝胶中硅氧-铝氧链平均长度,同时研究了粉煤灰火山灰反应对C-S-H结构的影响。结果表明:水化3 d时,系统中约47%的水泥和14%的粉煤灰参与了水化反应,C-S-H平均链长为3.2;水化120d时,水泥和粉煤灰的水化程度分别为89%和33%,C-S-H平均链长约为3.8,远大于纯水泥浆体中C-S-H的平均链长(为2.7)。水化3 d时粉煤灰玻璃相结构中的Si—O—Si,Si—O—和Al—Al共价键断裂,形成了单体硅酸根和单体铝酸根,这些单体结构桥连体系中的二聚体单元进而提高了C-S-H平均链长。粉煤灰掺入并不会因为C-S-H聚合度提高以及ACL增加就能促进粉煤灰水泥浆体强度。

QUANTITATIVE ANALYSIS OF FLY ASH-CEMENT HYDRATION BY 29Si MAS NMR

The hydration degree and average chain length (ACL) of SiO4 and/or A1O4 tetrahedra in calcium silicate hydrate (C-S-H) for fly ash-cement (FC) paste were quantitatively analyzed with high resolution solid-state 29Si magic angle spinning nuclear magnetic resonance spectroscopy d deconvolution technique. The effect of pozzolanic reaction of fly ash (FA) on the C-S-H structure was also investigated. The experimental results indicate that the cement of 47% and the FA of 14% can react in the paste in the presence of FA of 30% in mass and the ACL of C-S-H was 3.2 at 3 d. At 120 d, the cement of 89% and the FA of 33% could react, and the ACL of C-S-H was 3.8, which was higher than that in the plain cement paste (ACL was 2.7). After the covalent bonds of Si-O-Si, Si-O-Al and Al-O-Al in the structure of FA were broken at 3 d, monosilicate Si-OH and Al-OH groups formed, leading to a polymerization of C-S-H dimers and an increase in ACL of C-S-H. Although the addition of FA increased the polymerization of C-S-H and the ACL value, the mechanical strength of hardened FC paste could not be improved.