Microstructural, thermal, physical and mechanical behavior of the self compacting concrete containing SiO2 nanoparticles

In the present study, flexural strength, thermal properties and microstructure of self compacting concrete with different amount of SiO2 nanoparticles has been investigated. SiO2 nanoparticles with the average particle size of 15 nm were partially added to self compacting concrete and various behaviors of the specimens have been measured. The results indicate that SiO2 nanoparticles are able to improve the flexural strength of self compacting concrete and recover the negative effects of superplasticizer on flexural strength of the specimens. SiO2 nanoparticle as a partial replacement of cement up to 4 wt% could accelerate C–S–H gel formation as a result of the increased crystalline Ca(OH)2 amount at the early ages of hydration. The increased the SiO2 nanoparticles’ content more than 4 wt%, causes the reduced the flexural strength because of unsuitable dispersion of nanoparticles in the concrete matrix. Accelerated peak appearance in conduction calorimetry tests, more weight loss in thermogravimetric analysis and more rapid appearance of peaks related to hydrated products in X-ray diffraction results, all also indicate that SiO2 nanoparticles up to 4 wt% could improve the mechanical and physical properties of the specimens. Finally, SiO2 nanoparticles could improve the pore structure of concrete and shift the distributed pores to harmless and few-harm pores.