Desert sand-high calcium fly ash-based alkali-activated mortar: Flowability, mechanical properties, and microscopic analysis

Abstract

In this study, the reaction mechanism of desert sand-high calcium fly ash-based alkali-activated mortar under different influencing factors has been investigated. Different properties of the developed desert sand-high calcium fly ash-based alkali-activated mortar, such as flowability, compressive and flexural resistance, micro-morphological attributes, and reaction mechanism, were studied for alkali admixture (Na2O/b), sodium silicate modulus, and ground granulated blast-furnace slag (GGBS) content. The results indicate that too low and too high Na2O/b (2%, 10%) and sodium silicate modulus (0.4, 2.0) lead to poor flowability and compressive strength. The compressive strength of the specimens could reach more than 70 MPa for Na2O/b and sodium silicate modulus in the range of 5%–8% and 1.0–1.5, respectively. With the increase in GGBS content, the flowability of the fresh paste continued to decrease, whereas the compressive strength increased. Under the effect of alkali activation, the desert sand was partially dissolved, promoting the formation of C(N)-A-S-H gel to some extent. It is also found in this study that the iron ions in the high calcium fly ash partially dissolved and formed a rice-grain iron-rich gel, effectively filling the matrix pores.