Abstract
Drying shrinkage of alkali-activated slag concrete (AASC) is significantly greater than that of concrete made with ordinary Portland cement (OPC). It limits the large-scale application of AASC in field engineering. This study investigates the effect of early age-curing methods, including water curing, curing in elevated-temperature water, and CO2 curing, on drying shrinkage of AASC. Scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric (TG-DTG), and mercury intrusion porosimetry (MIP) were carried out to analyze the composition and microstructure of hydration products, to provide deeper understanding of drying shrinkage of AASC. The results show that water curing decreased drying shrinkage of both C30 and C50 AASC moderately compared to air curing, while it was more effective for C30 AASC. Curing in water of elevated temperature and CO2 curing were very beneficial to mitigate drying shrinkage of AASC. Heat curing decreased drying shrinkage of AASC up to 80%. SEM and TG-DTG results show that denser microstructure formed because of the accelerated hydration, resulting in lower porosity and lower proportion of pores smaller than 25 nm that contributed to the reduction of drying shrinkage. In addition, under high-temperature curing, most autogenous shrinkage of AASC occurred in the first few days because hydration was accelerated. After measurement of drying shrinkage was started, recorded autogenous shrinkage of AASC cured in elevated-temperature water should be much less than that of AASC cured at normal temperature. It is another important reason for the reduction of drying shrinkage. Carbonation occurring in the CO2 curing period led to the decalcification of C-(A)-S-H gel; it coarsened the pore-size distribution and decreased the total porosity. Therefore, drying shrinkage of C30 and C50 AASC was declined by 49% and 53% respectively.
Highlights
Alkali-activated slag (AAS) cement is a novel type of clinker-free binder material prepared by blast furnace slag and alkaline solution, such as sodium hydroxide and water glass
The embodied energy and CO2 emission could be reduced significantly due to the use of AAS as an alternative to ordinary Portland cement (OPC) [1,2,3,4,5], much attention has been paid to the properties of AAS in recent decades
Under the same curing condition, C50 activated slag concrete (AASC) showed lower drying shrinkage but higher drying shrinkage sensitivity to moisture loss than C30 concrete. This result was due to the lower total porosity and finer pore size of C50 AASC caused by the lower w/b
Summary
Alkali-activated slag (AAS) cement is a novel type of clinker-free binder material prepared by blast furnace slag and alkaline solution, such as sodium hydroxide and water glass. Compared to OPC, AAS cement exhibits lower hydration heat and faster hydration rate [6,7,8]. Alkali-activated slag concrete (AASC) has high early strength, good resistance to permeability, chemical attack, and freeze-thaw cycles. It is a green building material of energy-saving, waste-eliminating and environmentally friendly [9,10,11,12]. It is widely reported that drying shrinkage of mortars and concretes made with AAS cement was considerably higher than that of OPC. Atişe et al [13] found that drying shrinkage
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