Potential applicability of calcium phosphate modified portland cement paste for geologic sequestration of CO2

In order to increase the integrity of the wellbore which is used to prevent the leakage of supercritical CO2, it is necessary to develop a concrete that is strongly resistant to carbonation. In an environment where the concentration of CO2 is exceptionally high, Ca2+ concentration in portland cement concrete drops significantly due to the rapid consumption of calcium hydroxide, which decreases the stability of the calcium silicate hydrate. In this work, it is hypothesized that if fairly large quantity of the hydration product becomes more thermodynamically stable than calcite, the damage caused by rapid carbonation will certainly be minimized. For this purpose, portland cement system was modified by monocalcium, dicalcium and tricalcium phosphates to produce hydroxyapatite in portland cement paste. According to the experimental results, addition of calcium phosphate produced hydroxyapatite. Among three different calcium phosphates, monocalcium phosphate showed the most significant impact on hydration. It caused faster stiffening and delayed calcium silicate hydration. Although cement pastes modified by calcium phosphates showed less compressive strength than plain cement paste, they showed an excellent durability after exposure to supercritical CO2. It is clear from the results that the potential applicability of calcium phosphate modification in portland cement for geologic sequestration of CO2 was successfully proven.