Strength and elastic properties of low-fine self-compacting concretes designed with nano SiO₂

Self-compacting concrete (SCC) is increasingly takes place in construction applications due to its excellent self-compacting characteristic. It is known that, in order to achieve self-compacting feature, it is necessary to use high volume of fine materials in the mix design with effective superplasticizers. Using high volume of fine materials causes a decrease in the amount of total coarse aggregates. Coarse aggregates have an important role on the strength and elastic properties of concretes. This paper presents the results of an experimental study which investigated the strength and elastic properties of SCC mixtures modified with nano-SiO₂. Nano-SiO₂, having 35nm average particle size, was used with the aim of reducing the total fine material in SCC designs. Five different nano-SiO₂ percentages (0.5%, 1.0%, 1.5%, 2.0% and 2.5%) were utilized and the total fly ash content used in the reference mixture was gradually reduced. The volumetric emptiness occurred by the fly ash reduction was filled by aggregates. Successful mixtures which exhibited desired SCC properties were subjected to compressive tests at 28^th and 120^th days. Moduli of elasticity of concrete specimens were also measured. Results have shown that with increasing W/Cm ratio, compressive strengths were decreased. The use of nano-SiO₂ in reduced-fly ash content mixtures could not compensate the strength decrement. However, the use of nano-SiO₂ combined with fly ash has prominently enhanced the elastic modulus of nano-modified SCC mixtures.