This paper investigates the effects of different levels of expansion resulting from alkali-carbonate reaction (ACR) on mechanical properties of concrete at different ages. Concrete prisms and companion cylinders were cast with three aggregates that are non-reactive, marginally-reactive and highly-reactive, and cured under the same conditions. The concrete prisms showed 1-year expansion values of 0.021 %, 0.042 % and 0.271 % for the non-reactive, marginally-reactive and highly-reactive aggregates, respectively. In general, the results showed a reduction in mechanical strengths of concrete with increasing the expansion. However, the mechanical properties and permeability of concrete made with non-reactive and marginally-reactive aggregates were very close. It was concluded that up to 1 year of accelerated testing at 38°C, or up to an expansion value of about 0.04 %, the mechanical performance of concrete made with marginally carbonate reactive aggregates is not adversely affected.