Effect of supplementary cementitious materials on autogenous shrinkage of ultra-high performance concrete

Ultra-high performance concrete (UHPC) not only presents ultra-high compressive strength but also exhibits ultra-high durability, due to its extremely dense structure and consequently highly reduced porosity. However, high dosages of silica fume (SF), typically adopted in UHPC, also lead to high autogenous shrinkage. This phenomenon, occurring at early ages, induces high internal stresses that, in turn, cause microcracking and increase permeability and, therefore, reduce the durability of concrete structures. The experimental study was conducted aiming to replace SF by another fine supplementary cementitious materials (SCMs), such as fly ash (FA) or ground granulated blast furnace slag (GGBS), in order to reduce the amount of autogenous shrinkage. The adopted approach involved partial or total replacement of SF by SCMs. Results indicate that the amount of fine pores in UHPC is a predominant factor that can highly affect the autogenous shrinkage. A strong correlation between the natural logarithm of autogenous shrinkage and the total porosity of UHPC mixtures was established. It was found that reducing the amount of fine pores in specimens containing FA or GGBS leads to a reduction of the autogenous shrinkage.