Investigation of the mechanical, microstructural and mineralogical morphology of soundless cracking demolition agents during the hydration process

Soundless cracking demolition agents (SCDAs) have emerged as a potential method for underground rock fragmentation. However, the application of SCDAs in deep earth formations requires them to be modified to suit each application. Basic understanding of the hydration mechanism and the expansive pressure generation of SCDAs is of paramount importance in the process of adapting SCDAs to such applications. Therefore, the microstructural, mineralogical and mechanical morphology of SCDA during the hydration process was studied through a series of experiments (Uniaxial compressive strength (UCS), scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis) carried out on SCDA specimens at different degrees of hydration. Experimental results suggest that mechanical properties of hydrating SCDA are dependent on the confinement provided to the SCDA during the hydration process and the porosity of aging SCDA reduce during hydration if the volume expansion is restrained. The pressure generation mechanism was explained using a spherical expansion model, and SEM images obtained for hydrating SCDA confirm this hypothesis. XRD analysis of SCDA indicates that expansive pressure is generated by a combination of Ca(OH)2 and Ettringite formation in the system, although it is dominated by Ca(OH)2. The early strength gain in SCDA was found to be related to the calcium silicate hydrate formation in the compound. The relationships observed between the microstructure, mineralogy and the mechanical properties of SCDA with increasing expansive pressure aids to improve the current understanding of SCDA.