Role of Al in the crystal growth of alkali-activated fly ash and slag under a hydrothermal condition

Abstract

The present study investigates the role of Al in the evolution of the crystalline phases of an alkali-activated binder. Samples were synthesized corresponding to the binder composition with various Al2O3/Na2O and MgO/binder ratios in a hydrothermal condition. Thermodynamic modelling was carried out to predict the effect of the Al content in the binder composition on the formation of Al-bearing phases. The test results showed that an increasing Al content led to the alteration of the predominant zeolite phases in the alkali-activated binder. In addition, MgO incorporation enhanced the reaction degree of hydration in the alkali-activated system and the crystal growth, specifically hydrotalcite-like phase. Consequently, the formed reaction products had a great effect on the pore characteristics of the alkali-activated binder given their variations in the crystal structure.