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Materials 2018, 11(7), 1128; https://doi.org/10.3390/ma11071128

Effect of a Synthetic Nano-CaO-Al2O3-SiO2-H2O Gel on the Early-Stage Shrinkage Performance of Alkali-Activated Slag Mortars

1
Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing Tech University, Nanjing 210009, China
2
Guangdong Provincial Key Laboratory of Durability for Marine Civil Engineering, College of Civil Engineering, Shenzhen University, Shenzhen 518060, China
*
Author to whom correspondence should be addressed.
Received: 23 May 2018 / Revised: 27 June 2018 / Accepted: 30 June 2018 / Published: 3 July 2018
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Abstract

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. View Full-Text
Keywords: alkali-activated slag; C-A-S-H gel; drying and autogenous shrinkage; mesopore; microstructure alkali-activated slag; C-A-S-H gel; drying and autogenous shrinkage; mesopore; microstructure
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Liu, B.; Yang, J.; Li, D.; Xing, F.; Fang, Y. Effect of a Synthetic Nano-CaO-Al2O3-SiO2-H2O Gel on the Early-Stage Shrinkage Performance of Alkali-Activated Slag Mortars. Materials 2018, 11, 1128.

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