The Effect of Silica Fume Addition on the Resistance of Concrete to Alkali Silica Reaction

Abstract

Concrete mix made of cement CEM I 42.5 R, silica fume, fine aggregate sand of 0/4 fraction and superplasticizer was tested. Five batches of specimens were made with different silica fume content, where up to 10 % of the binding material was replaced with silica fume. Compressive strength, water absorption, density and resistance to alkali silica reaction were tested in concretes modified with different amounts of silica fume addition. The effect of silica fume addition on the expansion of modified concrete conditioned in 1M NaOH solution for 56 days was tested. Concrete modified with silica fume at 10 % by weight of cement was found to be the most appropriate for structures exposed to alkaline environment. The control specimen without mineral addition had the expansion of 0.113 %, which exceeds the limit value by 0.1 %, whereas the expansion of specimens modified with 2.5 % of silica fume was equal to the limit value, i.e. 0.1 %. The expansion values reduced in specimens modified with 5 % and 7.5 % of mineral addition. After 56 days of testing, the expansion values of these specimens were 0.093 % and 0.082 % respectively. The lowest expansion value was obtained in specimens with the highest content of silica fume, i.e. 10 %. The expansion of these specimens was 0.07 % after 56 days of conditioning in 1M NaOH solution of 80 °C temperature. The tests revealed that concrete modified with silica fume replacing 10 % of cement had better resistance to alkali silica reaction and better durability characteristics and thus can be used as structural concrete.