Investigation of the mechanism of failure of neat cement and mortar specimens

The problem of the investigation of the mechanism of failure in compression of neat cement and mortar specimens is considered in this thesis. The study was made on two hundred specimens of cement paste and mortar, of which approximately one half were tension briquets and the other half compression cylinders. The underlying theory which led to this study was that failure in compression in specimens with aggregate (mortar and concrete) is due to the wedging action of the particles of aggregate within the matrix of cement paste. Steam-curing was used to avoid delay in the hardening of cement. It was found that the cement used was of the type which continues hardening after being steam-cured. The importance of having the specimens at a constant temperature throughout their mass and at room temperature when the tests were performed was realized. An investigation of the effect of end conditions on test cylinders in compression was conducted. It is considered that the confined rubber end conditions used were an improvement on testing with lubricated ends only. Observations were made on the effect of the bursting action of water in compression tests of moist specimens. A study of the effect of stress concentration around voids was made on tension specimens. Compression specimens made of neat cement, mortar and cement with inclusions in the form of balls were studied. Inclusions were placed in cement cylinders to imitate the action of the aggregate in mortar and concrete specimens. Tests on compression specimens with inclusions were useful in the interpretation of results of tests on neat cement and mortar cylinders and in the study of the stress-strain curves. Transverse bending tests of cylinders were made with the purpose of investigating the presence of transverse cracks formed in the cylinders as a consequence of the application of compressive loads. They did not provide a good method of investigation but were very useful in that they were an aid to realizing the effect of the horizontal cracks in the stress-strain curves.Applied Science, Faculty ofCivil Engineering, Department ofGraduat