The Durability of Concrete with the Participation of Hydrophilic and Hydrophobic Nanosilica Without and Within the Presence of Silica Fume and New Generation Superplasticizer

Abstract

In the paper the research was undertaken in order to determine the impact of hydrophilic nanosilica used in a form of aqueous colloidal solution with admixture of nano-silver, as well as hydrophobic nanosilica dissolved in ethanol and isopropanol on properties of the concrete without and with presence of silica fume and polycarboxylate based superplasticizer. Tests were conducted for concrete mixture (slump test, Vebe test, density, air content by the water column method) and hardened concretes (compressive strength after 1, 7, 14 and 28 days of curing, density, depth of penetration of water under pressure, water absorption, frost resistance). For mixture and hardened concrete without participation of silica fume, Portland cement 42.5 R was used in an amount of 549.7 kg/m³ for obtaining BWW high-quality concretes. Nano-additives were used in the amount of 0.5 and 1.5% in relation to the mass of cement. The silica fume was additionally added to concretes in the amount of 8% by mass. While as a chemical admixture in the amount of 2% in relation to the cement mass, a 40% solution of a superplasticizer based on a polycarboxylic ether (SP) was used. Pebble aggregate consisting of two fractions with a grain size of 2–8 and 8–16 mm was used and sand with a grain size of 2 mm. Properties of fresh concrete and hardened concrete were tested in the accredited Construction Material Laboratory of the Faculty of Civil Engineering and Architecture at the Opole University of Technology. Whereas the increase of nanoadditive amount to 1.5% by mass contributed to better improvement of concrete physical properties in the presence of hydrophobic nanosilica than in the presence of hydrophilic nanosilica. In that case particularly beneficial properties were demonstrated by “nano-concrete”, which apart from nanosilica also contained the silica fume and the superplasticizer, which to the most extent had the impact on the improvement of concrete properties, including its reduced absorptivity, higher compressive strength or higher freeze-thaw resistance compared to other concretes tested.