Effect of curing conditions on freeze-thaw resistance of geopolymer mortars containing various calcium resources. (27th December 2021)

• Record Type: Journal Article
• Authors: Jiao, Zhenzhen; Li, Xueying; Yu, Qinglin
• Is Part Of: Construction & building materials. Volume 313(2021)
• Publication Date: 2021-12-27
• Subjects: Geopolymer mortar -- Curing conditions -- CaO content -- Freeze-thaw resistance -- Microstructure; Building materials -- Periodicals; 624.18
• DOI: 10.1016/j.conbuildmat.2021.125507
• Languages: English
• ISSNs: 0950-0618

Abstract

Highlights: Various calcium resources were used as raw materials of geopolymer mortars. Standard and steam curing conditions for geopolymer mortars were investigated. Mechanical properties and freeze-thaw resistance of geopolymer were studied. The relationship between macro and micro properties were established. CF35-S and SC35C100-C geopolymer exhibited excellent freeze-thaw resistance. Abstract: This study focused on the effects of curing conditions (standard and steam curing) on the freeze–thaw resistance of geopolymer mortars containing Class C fly ash, Class F fly ash, slag, and Ca(OH)2 . Geopolymer mortar specimens were prepared with water-to-Class C fly ash ratios of 0.35 and 0.40, and CaO contents of 45% and 100% with different compositions. The specimens were subjected to freeze–thaw cycles until the mass loss exceeded 5% or the relative dynamic elastic modulus was below 60%. The reaction hydrates and pore structures were analyzed using scanning electron microscopy with energy-dispersive spectrometry and mercury intrusion porosimetry, respectively. In terms of mechanical performance, steam curing condition was better than standard curing condition for the early-age strength of geopolymer mortars. The compressive strength of the geopolymer mortars at 2 d and 28 d was increased 2.2–5.1 times and 0%-40%, respectively, under steam curing condition compared with standard curing condition. The experimental results indicated that Class C fly ash geopolymer mortar (CF35) under steam curing condition and Class F fly ash-slag geopolymer mortar with 100% CaO content (SF35C100) under standard curing condition exhibited remarkable freeze–thaw resistance with a freeze–thaw resistance grade of F300 at the lowest. Moreover, the water-to-ash ratio was critical for the freeze–thaw resistance under both standard and steam-curing conditions. The mass loss of specimens with water-to-ash ratios of 0.35 and 0.40 under standard curing condition were 4.67% and 8.79%, respectively, at 25 freeze–thaw cycles, whereas that of specimens with water-to-ash of 0.35 under steam curing condition was 3.03% at 300 freeze–thaw cycles. In addition, the freeze–thaw resistance of geopolymer specimens with different compositions had a direct relationship with the microstructure of the geopolymer mortars. Furthermore, the experimental results verified that a higher compressive strength did not necessarily indicate a better freeze–thaw resistance.