Alkali-activated fly ash. Relationship between mechanical strength gains and initial ash chemistry

Abstract

Alkali-activated fly ash is the primary component of a new generation of high-strength, durable binders with excellent mechanical properties and durability (on occasion bettering traditional Portland cement performance). Moreover, development of these cements may contribute to mitigating CO2 emissions, since the base material is an industrial by-product. The present study was conducted to determine the effect of the composition of the initial materials (SiO2/Al2O3 and Na2O/Al2O3 ratios) on the mechanical properties, nature and composition of the reaction products. The results obtained indicate that there is no linear relationship between these ratios and mechanical strength, but rather a series of optimal values above and below which strength declines. In the specific case of the ratios studied in the present paper, these values were: SiO2/Al2O3= 4.0 and Na2O/Al2O3= 1.0 (molar ratios).

Keywords

• fly ash
• alkali activation
• alkaline cements
• high-strength cements
• zeolites