Effect of different activation techniques on the engineering properties of cement-free binder containing volcanic ash and calcium carbide residue

This study developed a cement-free binder using volcanic ash (VA) and calcium carbide residue (CCR) as an alternative binder to cement. First, the optimal proportions of VA and CCR were determined to achieve superior flow, compressive strength, and bulk electrical resistivity. After that, various activation techniques, namely physical (sieving the CCR on sieve No. 325), chemical (adding 1 % NaOH by binder mass to the paste), and thermal (curing the paste in an oven at 65℃ for 24 h), were used either exclusively or synergically to enhance the performance. The results show that the optimum VA:CCR was 95:5. The flow increased by chemical activation but decreased with physical activation. Using subsequent physical and chemical activation led to a slight increase in flow. Binders subjected to physical activation followed by thermal activation had the highest compressive strength of 31.2 MPa at 28 days of curing. In contrast, subsequent combined chemical and thermal activation produced superior bulk resistivity of 193 Ω.m at the same age compared to other activation techniques. Nevertheless, all activation techniques improved the strength and bulk resistivity. The calorimetric analysis confirmed that the emitted heat increased with different activation methods compared to the mix without activation, which agreed with compressive strength results. X-ray diffraction (XRD) analysis showed that the reaction products were calcium-silicate-hydrate and calcium-aluminate-silicate-hydrate gels. Scanning electron microscope (SEM) images confirmed that different activation techniques resulted in a denser microstructure than the inactivated VA-CCR paste. This cement-free binder contributes to the ongoing efforts to reduce the carbon footprint of cement-based materials by finding sustainable alternative binders to cement.