Quantitative kinetics of pozzolanic reactions in coal/cofired biomass fly ashes and calcium hydroxide (CH) mortars

• TGA provided convenient and accurate measurements of reaction extent of CH.
• The chemically combined CH gram CH/g fly ash is approximated 30/70, with 20/80 deficient and 40/60 excess of CH.
• The first order respective to CH and fly ash fitted the data very well with R2 as high as 0.93–0.96.
• The low activation energy, 1.59–30.7 kJ/mol confirmed it diffusion control for all fly ashes.
• Revisit of the ASTM C 618 for inclusion of cofired biomass fly ash in concrete is necessary.

This document comprehensively studies the quantitative kinetics of pozzolanic reactions of class C and F and cofired biomass fly ashes with Ca(OH)2 (CH) under carbonation free conditions. The grams of chemically combined CH per gram of fly ash increase with the CH mixing ratio, curing temperature and curing days. The chemically combined mass ratio is approximated at 30/70 (CH/fly ash), although it varies slightly from ash to ash. The quantitative kinetics shows that class C and F, cofired biomass and pure biomass fly ashes share the diffusion mechanism. Therefore, the cofired biomass fly ash needs reevaluation in rather than exclusion by ASTM C 618 from concrete for its “noncoal” origin.