Abstract
The present study performs a detailed investigation on the chemical mechanisms of calcium carbonate precipitation for cement-based materials in different reactive environments, which is aiming to interpret the divergences in existing experimental studies. Subsequently, the mechanical influences of carbonation is evaluated for the integrity assessment of wellbore system adopted in the CO2 sequestration. Based on the experimental observation and numerical simulation, the presence of magnesium in the cement leaching system is demonstrated to protect the material from a chemical degradation by sealing the water/cement interface. In the absence of magnesium, the concentration of dissolved CO2 dominates the degradation rate by the pore-clogging effect of the calcium carbonate layer. The interplay of pH and CO2 concentration leads to the dissolution and re-precipitation of calcium carbonate, and consequently presents a shifting Ca-rich layer within the cement matrix. The precipitated calcium carbonate is incorporated with leached cement paste to evaluate the residual elastic moduli by a micromechanical model, which demonstrates that calcium carbonate can counteract the stiffness loss and even rise over the original stiffness. After the dissolution/precipitation of cement constituents, the flexural performance is evaluated with the updated stiffness to demonstrate the influence of carbonation on a cement paste beam. The reinforcement of calcium carbonate layer on the mechanical behaviour gradually is weakening along with the layer shifting inwards, which could further compromise the well integrity.
Published Version
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