Improving drying shrinkage and strength development of alkali-activated high-calcium fly ash using commercial-grade calcium sulfate as expansive additive

• Main Authors: Chudapak Detphan, Patthamawadee Kaeorawang, Borwonrak Injorhor, Khattiya Chompoovong, Sakonwan Hanjitsuwan, Tanakorn Phoo-ngernkham, Prinya Chindaprasirt
• Format: Article
• Language: English
• Published: Khon Kaen University 2022-01-01
• Series: Engineering and Applied Science Research
• Subjects: alkali-activated high-calcium fly ash; commercial-grade calcium sulfate; strength development; shrinkage compensation
• Online Access: https://ph01.tci-thaijo.org/index.php/easr/article/download/245209/166734/

The effect of using commercial-grade calcium sulfate (CS) in alkali-activated high-calcium fly ash (AAHFA) paste on the drying shrinkage and strength is reported. Five different fly ash (FA): CS ratios of 100:0, 97.5:2.5, 95:5, 92.5:7.5, and 90:10 were investigated. A constant Na2SiO3:10 M NaOH ratio of 1.0, liquid alkaline activator/binder (L/B) ratio of 0.40, and ambient curing temperature (~25 °C) were used for all mixes. The results clearly showed a reduction in the setting time for the AAHFA incorporating CS. The compressive strength of the AAHFA paste increased with increasing CS content up to an optimum level. In addition, the use of a mixture of FA and CS to produce AAHFA could improve its drying shrinkage. The use of 2.5% CS or 5% CS is recommended to realize significant improvements in both the drying shrinkage and strength development of AAHFA paste.