Liu Bao, Yang Jingbin, Li Dongxu, Xing Feng, Fang Yuan
Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing Tech University, Nanjing 210009, China.
Guangdong Provincial Key Laboratory of Durability for Marine Civil Engineering, College of Civil Engineering, Shenzhen University, Shenzhen 518060, China.
Materials (Basel). 2018 Jul 3;11(7):1128. doi: 10.3390/ma11071128.
The relatively high shrinkage of the alkali-activated slag (AAS) has restricted its application as a widely-used building material. This research attempts to study the effect of a hydrothermally synthesized C-A-S-H gel, which has a similar composition to that of the main AAS product, on the shrinkage performance of the AAS. The C-A-S-H nano-particles were mixed into AAS mortars in a proportion ranging from 1 wt % to 5 wt % using two different methods, and the drying and autogenous shrinkage ratio of modified AAS mortars were measured at various ages. The effect of C-A-S-H on their microstructures was also characterized. Results obtained indicated that the addition of C-A-S-H gel to AAS mortars had reduced their drying and autogenous shrinkage, with the addition of 3 wt % reaching the maximum reduction. However, the added amount was not directly proportional to the decrease of shrinkage; the proportion of early-stage drying shrinkage of AAS mortars was greater than that of autogenous shrinkage; the dispersion method was slightly better than the dry mixing method in both shrinkage reduction. MIP results suggested that the addition of C-A-S-H gel had reduced the total porosity and the average pore size of AAS mortars, optimized their pore structure distribution, and significantly reduced the volume of mesopores (<0.05 µm) which resulted in high shrinkage, while the adding method had no significant effect on the pore size distribution of AAS mortars. SEM results showed that the addition of C-A-S-H gel can reduce the crack width of mortars, obtain a dense and uniform matrix structure, increase the density, and effectively suppress both shrinkage deformation of the system, whereas the adding method has no obvious effect on the crack width of the mortar. This research provides a novel approach of the AAS shrinkage reduction and structure refinement, shedding lights on nano-material modification of the AAS.
碱激发矿渣（AAS）相对较高的收缩率限制了其作为广泛使用的建筑材料的应用。本研究试图研究水热合成的C-A-S-H凝胶（其组成与主要AAS产物相似）对AAS收缩性能的影响。采用两种不同方法将C-A-S-H纳米颗粒按1 wt%至5 wt%的比例混入AAS砂浆中，并在不同龄期测量改性AAS砂浆的干燥收缩率和自收缩率。还表征了C-A-S-H对其微观结构的影响。结果表明，向AAS砂浆中添加C-A-S-H凝胶可降低其干燥收缩率和自收缩率，添加3 wt%时降低效果最大。然而，添加量与收缩率的降低并非直接成正比；AAS砂浆早期干燥收缩率的比例大于自收缩率；在降低收缩率方面，分散法略优于干混法。压汞法结果表明，添加C-A-S-H凝胶降低了AAS砂浆的总孔隙率和平均孔径，优化了其孔隙结构分布，并显著减小了导致高收缩率的中孔（<0.05 µm）体积，而添加方法对AAS砂浆的孔径分布没有显著影响。扫描电子显微镜结果表明，添加C-A-S-H凝胶可减小砂浆的裂缝宽度，获得致密均匀的基体结构，提高密度，并有效抑制体系的收缩变形，而添加方法对砂浆的裂缝宽度没有明显影响。本研究为降低AAS收缩率和细化结构提供了一种新方法，为AAS的纳米材料改性提供了思路。
