Confined-Direct Electric Curing of NaOH-activated fly ash based brick mixtures under free drainage conditions: Part 1. Factorial experimental design

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.