Assessment of compressive strength, microstructure, thermal, and radiation shielding properties of Taal volcanic ash-based geopolymer mortar

This present study aims to assess the effect of mixing Taal volcanic ash (TVA) as an aluminosilicate material in geopolymer (GP) mortar. Specifically, it examines various mortar properties such as compressive strength, microstructure, thermal, and radiation shielding as an effective barrier for X-ray and gamma-ray energies. In this investigation, the mixed proportion of the samples includes an S/B ratio of 0.5, an A/B ratio of 1.0, and an SP/VA ratio of 0.02. Using an automatic compression tester, the recorded maximum compressive strength of 7.73 MPa from TVA-based GP mortar revealed that pre-curing of the samples resulted in an overall gain in the average compressive strength of the samples. Following the British Standards, the modes of failure showed hourglass-shaped from vertical crack propagation and brittle failure during post-compression. From the XRD, minerals of anorthite and albite from plagioclase feldspar series pre-dominated both TVA-based GP mortar and its precursor. In the FTIR, spectra the spectral band at 459572 cm- 1 was due to the presence of silicate in geopolymer samples, and at 1200 cm-1 denoted the anorthite mineral presented and identified also in diffractograms. The significant shift from TVA and GP mortar in this spectral band can be attributed to the extent of the chemical reaction during geopolymerization. Meanwhile, a maximum loss of 9.77 % can be accounted to the removal of -OH groups from the N-A-S-H gel product. The surface morphology images revealed a degree of geopolymerization, although not optimally, took place from the precipitate formed around the TVA which can be linked to the coarseness of the particles leading to low reactivity. This can be solved by extending the grinding and sieving process of TVA prior to mixing it in the GP. Regarding radiation shielding parameters interpolated and done by EpiXS software, MACs and LACs were seen the highest in favor of GP mortar, while the lowest thickness for both MFP and HVL. High Neff and Zeff values were also observed from GP mortar which was attributed to the presence of a high amount of Fe. Lastly, the EABF and EBF plots displayed higher values at 40 MFP occurred at the intermediate-energy region due to the photon absorption, Compton scattering, and secondary radiations. The results suggest that utilizing a TVA-based geopolymer provided good performance for radiation shielding applications, although compressive strength can still be improved further.