Relationship Between Engineering Properties, Mineralogy, and Microstructure in Cement-Based Hydroceramic Materials Cured at 200°-350°C

Cement‐based materials used to seal geothermal or deep oil wells are exposed to severe conditions. Optimizing engineering properties such as strength and permeability is therefore very important. We have synthesized hydroceramic materials for such applications based on the CaO−Al2O3−SiO2−H2O (CASH) system and cured them over a range of temperatures (200°–350°C). Depending on initial composition and curing temperature, hydroceramics of complex and diverse mineralogy and microstructure are formed. The minerals found include portlandite, jaffeite, xonotlite, gyrolite, 11 Å tobermorite, truscottite, hydrogarnet, and calcium aluminum silicate hydrate. These cement‐based hydroceramic materials develop complicated pore structures, which strongly affect bulk properties. We report the compressive strength and permeability of these materials and show how these bulk engineering properties are related to microstructure. The compressive strength was found to be in the range 2–52 MPa and the intrinsic permeability in the range 0.5 × 10−17 to 3300 × 10−17 m2. Scanning electron microscopy (SEM) was used for imaging the hydroceramic microstructures. Further, we have computed the intrinsic permeability from 2‐D SEM images by using the Stokes equation solver, Permsolver, applied to reconstructed 3‐D images and the results are shown to be in good agreement with experimentally determined values.