Abstract
To mitigate autogenous shrinkage that may cause early-age cracking of alkali-activated fly ash-slag (AAFS) concrete, internal curing using superabsorbent polymers (SAP) is employed in this study. AAFS pastes with different SAP dosages (0–0.5%) and slag replacement ratios to fly ash (15–30%) are investigated. Experimental results indicate that with the addition of SAP workability of fresh paste is improved while compressive strength is comparatively reduced. As SAP dosage increases from 0.2% to 0.5%, chemical shrinkage and autogenous shrinkage of AAFS pastes are reduced by around 18% to 45% and 76% to 85%, respectively. Internal curing of SAP is found to lower the heat peak and shift the peak to the right. This indicates the slower hydration rate corresponding to the lower chemo-mechanical deformation (chemical shrinkage), which contributes to the mitigation of autogenous shrinkage. Therefore, internal curing by means of SAP is an efficient method for mitigating autogenous shrinkage in AAFS pastes.
Highlights
Ordinary Portland cement (OPC) concrete is the most widely used construction material due to its high performance in terms of workability, compressive strength and cost [1]
Setting time of alkaliactivated fly ash-slag (AAFS) pastes increases with the addition of superabsorbent polymers (SAP), while the compressive strength is reduced with increasing SAP dosage due to the additional water incorporated in the mixtures with SAP
The compressive strength is decreased by 20% when 0.2% SAP is added into the mixture and tends to be stable when the SAP dosage is in the range between 0.2% and 0.4%
Summary
Ordinary Portland cement (OPC) concrete is the most widely used construction material due to its high performance in terms of workability, compressive strength and cost [1]. The growing demand of OPC poses great challenges to concrete industry because of its large carbon emissions [2] This motivates researchers for seeking suitable alternatives to OPC, and alkali-activated concrete is considered as a potential alternative by utilising industry by-products such as fly ash (FA) and ground granulated blast-furnace slag (GGBS) [3,4,5]. The common types of shrinkage consist of chemical and autogenous shrinkage in early age and drying shrinkage in the long term. To avoid early-age and long-term cracking, taking curing methods to mitigate various types of shrinkage of AAFS pastes, where there is still a lack of systematic studies, is in urgent need
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