While damage of concrete due to alkali-silica reaction (ASR) may not be the leading cause of the collapse of a constructed facility, it is a major factor in reconstruction. Nevertheless, a small expansion due to ASR can cause overall deterioration or technical problems when ASR is present in massive concrete construction such as dams (Bérubé et al. 1992). For instance, a minor expansion was reported to jam turbines or overflow valves (Bérubé et al. 1992). Many studies (Hobbs 1988, Diamond et al. 1992, Helmuth 1993) have been Helmuth published on the topic, and the major factors, related to the material used, contributing to ASR have been identified: water, hydroxide ions, other cations, and reactive silica. Related environmental factors that can play a significant role in ASR are the relative humidity (RH), the porosity of the concrete, and mineral admixtures in the concrete. The cations and other ions are released into the pore solution mainly by the cement, but can in principle be released from other concrete constituents as well (Bérubé et al. 1992).
The scope of this study was to determine the influence of the addition of silica fume, as a cement replacement, on the stresses generated by the specimen. Comparison was also made between cement replacement with silica fume and cement replacement with an inert silicon carbide powder. A parameter that could be useful for the engineer is the value of the stresses generated by the ASR reaction. Therefore, a device to measure the axial stresses on a confined mortar cylinder was designed (Ferraris et al. 1995, 1996, 1997).
The stress measured was a combination of any initial applied stress, loads generated by the ASR gel expansion, and loads generated by the expansion associated with water absorption that counterbalances self-desiccation shrinkage. To isolate the stresses due to the ASR expansion, reactive and non-reactive sand mortars were compared.
Using SEM observations, a tentative explanation of the results is given to determine the leading mechanisms for the mitigation effect of silica fume on ASR expansion and stresses. The cement content reduction alone does not reduce the expansion and stresses due to ASR. The addition of silica fume up to 15 % replacement of cement reduces, but does not eliminate, the deleterious effect of ASR.