Developing High-Strength Geopolymer using Least Activator and Pressure-Applied Casting: Techno-Enviro-Economic Performance

This work is designed by coupling fly ash (FA) with dune sand (DS) for high-strength geopolymer activated in an alkaline environment under pressure-applied casting. Initially, the proportion of FA and DS is optimized with the least activator dosage to obtain higher than the compressive strength of 50 MPa. A uniaxial pressure is applied on a semi-dry mixture containing the least activators and immediately demolded, involving rapid production for the industrialization purpose of the paving blocks. The experimental study revealed that the FA-DS proportion of 1:1, with a liquid-to-solid ratio of 0.16, achieved a compressive strength of 54.4 MPa. Consequently, the coupling of DS provides an occupying effect and reduces the required activator quantity. The strength gain mechanism is discussed at the molecular level by analyzing Fourier-transform infrared. Finally, the technical performance of the strength and the density is evaluated on the real size 203 × 101 × 80 mm prism and compared with the commercially available conventional concrete blocks. Besides, the enviro-economic performance in terms of CO₂ emissions and the cost are analysed as well. It is concluded that the developed block is a more environmentally sustainable and economically viable alternative to conventional concrete blocks.