Drying shrinkage, strength and microstructure of alkali-activated high-calcium fly ash using FGD-gypsum and dolomite as expansive additive

Abstract

This paper aims to investigate drying shrinkage, strength development, and microstructure of alkali-activated high-calcium fly ash (AAFA) paste by using FGD-gypsum 2 (FGD) and dolomite (DLM) as the expansive additive. The 10 molar of sodium hydroxide combined with sodium silicate solutions were used as liquid alkaline activation in all mixtures. The preparation of the AAFA paste was divided into 2 steps. First, the study was focused on the effects of expansive additive (FGD and DLM) and liquid/binder (L/B) ratio on the drying shrinkage of the AAFA paste. The FA was replaced by FGD and DLM at the dosages of 0%, 2.5%, 5.0%, 7.5%, and 10% by weight of binder. The AAFA paste with low drying shrinkage at the age of 90 days would be selected to further study. The other was to study setting time, compressive strength, and microstructure of the AAFA paste containing FGD and DLM. Test results indicated that the use of FGD and DLM as the expansive additive could improve the drying shrinkage of the AAFA paste. The increasing L/B ratio had adverse effects on its drying shrinkage. The setting time of the AAFA paste containing FGD and DLM had decreased, whereas its strength development had increased. However, the strength development of the AAFA paste incorporated with FGD tended to decline at the curing time of 120 days. These behaviors were consistent with the results of XRD, FTIR, and SEM/EDS analyses. The differences in reaction products were an essential factor in the strength development of the AAFA paste with expansive additive. It can be recommended that using DLM was advantages regarding the improvement of drying shrinkage and longterm strength in comparison with the AAFA paste with FGD.

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Long-term (2 years) drying shrinkage evaluation of alkali-activated slag mortar: Experiments and partial factor analysis

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