Improving class G cement carbonation resistance using nanoclay particles for geologic carbon sequestration applications

The hydrated products of Portland cement drastically change after exposure to CO ₂ rich brine, compromising the cement physical properties, especially, the compressive strength. This phenomenon is known as strength retrogression which occurs when the Ca/Si ratio of the cement hydrated products is close to 2.0. Previous studies showed that the use of silica flour enhances the cement resistance to the strength retrogression because of the formation of long silica chains. In this work, the influence of modified montmorillonite nanoclay (NC) particles which are nanoparticles of layered mineral silicates, on the strength retrogression resistance under carbonation process was evaluated. Two cement slurries with 0% and 1.0% NC were prepared and tested for the change in their different properties of compressive and tensile strengths, porosity and permeability with the carbonation time for 20 days of reaction into 0.5 M NaCl solution at 95°C and 10 MPa. After 7 days of preparation, the properties of the samples were tested, then samples were immersed into the CO ₂ saturated brine, after 5, 10, 20 days of reaction some samples represent each specimen were collected and tested for the same properties mentioned earlier. The results revealed that incorporating the NC particles enable to decrease the decline in the compressive strength from 12.62% to 2.13%, and the tensile strength reduction reduced from 8.21% for the base samples to 1.72% for the NC-based samples after 20 days of reaction. The porosity decline was also reduced to be 6.49% compared with 17.58% for the base samples (i.e. without NC), while the permeability reduction changed from 19.51% for the base cement to 8.70% for the NC-based cement. The permeability reduction, as well as the chemistry of the NC particles which enables them to accelerate the hydration process, are the main mechanisms which enhance the cement resistance to the carbonation.