Abstract
In this study, the strength development and microstructure evolution of alkali-activated fly ash (AAF), granulated blast furnace slag (AAG), and metakaolin (AAM) mortars under standard curing, steam curing, and oven curing conditions were investigated. The results show that 80 °C steam curing was more suitable for AAF mortar. Although oven curing was not as good as steam curing under the same temperature, the water evaporation increased the volume density of the N-A-S-H gel and refined the pore structure. For AAG mortar, the strength developed according to a Boltzmann function with time under steam curing conditions, which increased rapidly in the first 8 h, but grew little after about 15 h. Moreover, the strength development was severely limited by steam curing at 60 °C, and decreased under oven curing conditions due to the formation of microcracks that were induced by temperature stress and chemical shrinkage. For AAM mortar, the strength developed according to an Allometric power function with time under steam curing conditions, and the N-A-S-H gel formed in AAM had a higher polymerization degree and denser structure compared to that in AAF. The compressive strength of AAM mortar was 31.7 MPa after 80 °C steam curing for 4 h, and the standard curing time required to reach the same strength was less than 24 h, indicating that the standard curing was more suitable.
Highlights
Alkali-activated material is a new type of cementitious material that has gained much attention in recent years [1,2]
The y-intercept of the fitting line of FB was negative, indicating that its initial compressive strength is extremely low, and it began to produce strength after 40 h standard curing based on the function calculation, and the compressive strength at 3 d is only 1.3 MPa due to the low activity of fly ash [25]
The y-intercept of the fitting line of FB was negative, indicating that its initial compressive strength is extremely low, and it beg4aonf 1to3 produce strength after 40 h standard curing based on the function calculation, and the compressive strength at 3 d is only 1.3 MPa due to the low activity of fly ash [25]
Summary
Alkali-activated material is a new type of cementitious material that has gained much attention in recent years [1,2] It is made of silica-rich aluminum minerals (i.e., metakaolin, fly ash, slag, etc.) and alkali solution [3,4,5]. Some studies have found that the strength of alkaliactivated fly ash (AAF) concrete at 80 ◦C steam curing is higher than that in 50 and 65 ◦C environments [16]. Fly ash (FA), granulated blast furnace slag (GBFS), and metakaolin (MK) were used to prepare AAC in this work, and the strength development and the relationship between them under standard curing, steam curing, and oven curing were studied, in addition to the evolution of their microstructure. The results obtained are expected to provide some theoretical guidance for the curing production of AAC
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