The Beauharnois dam is located near the city of Montreal (Quebec, Canada). The water intake and the powerhouse are founded directly on a quarzitic sandstone rock mass. The coarse aggregate used in the concrete to build the dam originates from these rocks and has a high reactivity to cement alkalis. This reactivity called alkali-aggregate reaction (AAR) is a slow reaction that causes the concrete to swell. Regarding the foundation, swelling of the concrete led to the transfer of stresses to the rock foundation. The intact rock is of high resistance and the rock mass of good quality. The dam foundation is stable to sliding despite the sub-horizontal bedding of the sandstone and the transferred stresses. However, it is shown that, locally, depending on the intensity and orientation of the stresses, they can contribute to the vertical opening of discontinuities near the concrete-rock interface.
The Beauharnois dam turbines a large part of the waters of the St. Lawrence River (see Figure 1). This large run-of-river power station is 1,397 m long, houses 36 turbine-generator units and is backed by a water intake with 74 passes. The particularity of Beauharnois generating station lies in its construction in three phases. Work for phases 1, 2 and 3 began in 1928, 1948 and 1956 respectively with the commissioning of each phase in 1948, 1953 and 1961.
The concrete aggregates from the Beauharnois power station were obtained by crushing excavation products from the Potsdam sandstone on the development site. The cement used for the construction of the three phases was of the ordinary Portland type. The first signs of concern about the swelling of concrete came in 1940 following the observation of cracks in the concrete of phase 1 of the construction. Several investigation campaigns were carried out to conclude that the swelling was caused by a reaction between the cement alkalis and the aggregates (Bérubé et al. 2000). Nowadays, this type of reaction, called alkali-aggregate reaction (AAR), is well known (Sims & Poole 2020).
