Stress–strain relationship of cement paste under triaxial compression

Understanding the stress–strain behaviour of cement-based materials is important for the performance modelling of concrete structures. This work studied the stress–strain behaviour of cement paste under a triaxial stress state with varying confining pressures. The influence of confining pressure on peak stress, peak strain and volume change was studied using the experimental results obtained from cement paste samples with compressive strengths of 28 and 35 MPa. The samples were tested under four confining pressures (0, 5, 10 and 15 MPa). A simple equation for the strain at peak compressive strength was developed from linear regression analysis of the test data and available results in the literature. The commonly used stress–strain model for concrete was adopted to model the behaviour of cement paste. A functional relationship for model parameters was developed and calibrated using the experimental results. As expected, the obtained results demonstrated that the strength and ductility of cement pastes are significantly improved due to confinement. The relationship between lateral and axial strains was found to be linear. Overall, the proposed model showed good agreement with the experimental results and can be used to numerically analyse structures with cement paste (e.g. oil wells).