Preparation and properties of cementitious composites for geothermal applications

Three fiber-reinforced cement composites were prepared and cured in an autoclave for up to 168 h at 2 MPa of steam pressure in order to investigate the effect of hydrothermal curing on the alteration of pore structure, density, and formation and stability of hydrated products with time. Compressive strength was reviewed in connection with sample porosity. It was found that the time of autoclaving plays a crucial role in objective assessment of the durability of composites as potential candidates for geothermal applications. A mercury intrusion porosimeter Quantachrome Poremaster 60GT was used for the estimation of the pore structure parameters of composites. The thermal analysis method was used to identify different temperature ranges of cured samples?? thermal decomposition and to characterize the nature of hydrated products. Two kinds of products were formed. The first group consisted of calcium-silicate-hydrate (C-S-H), calcium-silicate-aluminate-hydrate (C-S-A-H), calcium-aluminate-hydrate (C-A-H), and calcium-carbonate (C-C) as a product of carbonation. The second group are chemically bond products, e.g. hydroxyapatite (Ca₅(PO₄)₃(OH)) and gibbsite (Al(OH)₃). These two hydroceramic products formed under hydrothermal conditions act also as binders and they can be useful as geothermal cement binders.