Confined-direct electric curing of NaOH-activated fly ash based brick mixtures under free drainage conditions: Part 1. Factorial experimental design

Abstract

The utilisation of fly ash is a global concern. Under conditions of mass production and rapid turnover in automated plants, a reduction in the curing duration of alkali-activated fly ash based mixtures is sought-after. An alternative accelerated curing technique, confined–DEC (Direct Electric Curing), with the binding mechanism of NaOH activation of fly ash was investigated for the rapid manufacture of fly ash based bricks. This concept is a potentially viable alternative solution for high–volume fly ash utilisation. The investigation revealed that the confined–DEC technique shows great promise in the rapid accelerated curing of NaOH-activated fly ash based brick mixtures. The best induced design conditions, a mixture consisting of 4.1% NaOH, 9% water and 86.9% fly ash by weight, simultaneously subjected to a confining pressure of 10 MPa and a voltage gradient of 0.8 V/mm, obtained a compressive strength of 11.5 MPa in 7 min and the mixture continued to increase in compressive strength after the application of confined-DEC, acquiring a compressive strength of 20.1 MPa at 28 days. The investigation also revealed the limitations of confined–DEC under free drainage conditions.