•Pressure swing cycling increases 100th cycle utilization to 27.7% at 20barg.•The kinetic rate of the fast regime exhibits a similar decay to calcium utilization.•Initial loss of reactivity attributed to pore coarsening.•Grain boundary loss due to sintering causes increased surface area and utilization.•Increased carbonation pressure increases reaction-controlled carbonation rate. CO2 capture by means of CaO cycling represents a cost effective, immediate solution to rising CO2 emissions. The mechanism of loss of utilization efficiency and associated change in carbonation kinetics of CaO particles was examined by conducting calcination/carbonation cycling of 150–250μm Strasburg limestone precursor, by swinging the pressure from atmospheric (for calcination) to 5, 10 and 20barg (for carbonation) at constant temperatures of 975–1025°C and a flow of pure CO2. Increased carbonation pressure led to an increase in utilization over 100 cycles from 0.128±0.005 to 0.271±0.035 for 5 and 20barg respectively. Samples were examined by scanning electron microscopy and BET. The carbonation kinetics were determined by plotting the rates of reaction for both the kinetically controlled and diffusion controlled carbonation stages. Sintering, grain boundary formation and elimination, and changes in particle surface area are found to all play important roles in causing the initial rapid loss in surface reaction-controlled rate, followed by partial recovery over multiple cycles. The loss of grain boundaries due to sintering caused an increase in the reaction-controlled rate and residual calcium utilization due to a shift in the dynamics of carbonation/calcination nucleation and molecular volume contraction. The rate of the reaction-controlled regime was found to be a function of carbonation pressure. The diffusion-controlled rate is independent of pressure and temperature.