Abstract
The autogenous shrinkage of alkali-activated slag (AAS) is significantly higher than that of ordinary Portland cement (OPC). The higher risk of concrete cracking due to autogenous shrinkage is a critical drawback to wider use of this promising alternative binder. The effect of CaO content on the autogenous shrinkage of AAS mortar was investigated. The autogenous shrinkage of AAS mortars was determined by comparator. The pore structure of the pastes was determined by mercury intrusion porosimetry. The hydration products of the pastes were determined by Fourier transform-infrared, thermogravimetric analysis, X-ray diffraction, and 29Si solid-state magic-angle spinning nuclear magnetic resonance. The results show that the amount of portlandite increases as CaO content increases. CaO in the paste causes the partial replacement of C-S-H(I) (low stiffness) by C-S-H(II) (high stiffness). The hydration reaction of AAS is inhibited by the addition of CaO. The increase of polymerization degree of C-(A-)S-H and rearrangement of C-S-H(I) during hydration are inhibited by the addition of CaO, and micropores closure is also inhibited. Therefore, the autogenous shrinkage of AAS mortar decreases with the increase of CaO content.
Highlights
Ground granulated blast furnace slag (GGBFS) is a byproduct of iron smelting
activated slag (AAS) concretes are prone to significant shrinkage due to selfdesiccation and have a high risk of cracking [2]. ere have been various studies over the past decade aimed at determining the influence of formula on autogenous shrinkage of AAS base material
We investigated the effect of CaO on the autogenous shrinkage of AAS mortar, using NaOH (Na2O% 4% by mass of slag) as an activator
Summary
Ground granulated blast furnace slag (GGBFS) is a byproduct of iron smelting. Alkali-activated GGBFS is a replacement for Portland cement in concrete. Allahverdi et al [3] studied the effect of conditioning AAS mortar with liquid sodium silicate (LSS) on autogenous shrinkage. Neto et al [4] studied the effect of adding LSS on the autogenous shrinkage of AAS mortar and reached the same conclusion. Cartwright et al [2] studied the effects of conditioning AAS mortar with NaOH and varying the LSS modulus on autogenous shrinkage. Neto et al [6], Allahverdi et al [3], and Lee et al [5] all attributed the larger autogenous shrinkage of AAS or AFS mortar to its finer structure. We investigated the effect of CaO (at proportions of 3%, 6%, 9%, and 12%) on the autogenous shrinkage of AAS mortar, using NaOH (Na2O% 4% by mass of slag) as an activator
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