Influence of Basalt Aggregate on Concrete Durability

Basalts are the major source of aggregate for concrete and roadmaking in Melbourne, Australia. Although they have generally performed satisfactorily, some green basalts which contain secondary clay minerals have failed in roadways and concern has been expressed about their possible poor performance in structural concrete. As a consequence, research was undertaken to assess the influence of aggregate instability of stone from a new quarry at Deer Park and other basalts from the Melbourne area on concrete durability. The mineralogy of the basalts is described and results are reported on the behavior of the aggregates with regard to cycles of wetting and drying. Concrete testing provided data on compressive and tensile strength, dimensional movement, and modulus of elasticity of specimens for practical strength grades exposed to cyclic conditions for 3 years. The investigation established the durability in concrete of the altered basalt from Deer Park while showing that aggregate instability can seriously affect the long-term durability of concrete. The reliability of current specifications used in Victoria for detecting unstable aggregates for concrete is questioned. It is proposed that durability should be determined by shrinkage measurements of aggregate and concrete.