Influence of alkali silica reaction (ASR) on mechanical properties of mortar

This experimental investigation deals with effects of ASR on the mechanical properties of cement-based materials. Two selected mortars, only differentiated by the chemical nature of the aggregates used (reactive and non-reactive) are investigated. After a maturation period of 28 days, triaxial compression tests with different confining pressures (0, 5, 15 MPa), bending tests, porosity and permeability measurements are carried out on a part of the samples in order to obtain a reference state as the sound material while the other part is stored in a controlled environment with temperature of 60 °C and relative humidity of 95% for ASR development. During this period of storage, the axial expansion of samples for the two mortars studied is monitored. After 100 days of storage in the controlled environment, the above cited tests and measurements are performed again in order to evaluate the effects of ASR. In addition, microstructural analyses are also carried out in order to better understand various phenomena which occur in mortars before and after storage of samples in controlled environment. It is found that the increase of mechanical strength under compression is more significant in the reactive mortar than in the non-reactive one. This can be attributed mainly to its more compact microstructure in the ITZ, shown by the microstructural analyses, compared with the non-reactive mortar. However, the ASR process induces a decrease of bending strength, which is directly related to tensile strength, in reactive mortar. Moreover, the elastic modulus and Poisson's ratio of the reactive mortar decrease due to the ASR process. These results indicate that the tensile strength and elastic properties are more significantly affected by the ASR expansion related microcracking than the compressive strength. The microcracking due to the ASR is also detected through the permeability and porosity measurements.