RESEARCH ARTICLE The effect of SiO 2 nanoparticles derived from hydrother- mal solutions on the performance of portland cement based materials Ismael FLORES-VIVIAN a , Rani G.K PRADOTO a , Mohamadreza MOINI a , Marina KOZHUKHOVA a , Vadim POTAPOV b , Konstantin SOBOLEV a* a Department of Civil Engineering and Mechanics, Advanced and Nano Cement-Based Materials Laboratory, University of Wisconsin-Milwaukee, Milwaukee 53211, USA b Geotechnological Research Center, Far East Branch of Russian Academy of Science, Petropavlovsk-Kamchatsky 683002, Russia * Corresponding author. E-mail: sobolev@uwm.edu © Higher Education Press and Springer-Verlag Berlin Heidelberg 2017 ABSTRACT The nanoparticles of SiO 2 were used in cement systems to modify the rheological behavior, to enhance the reactivity of supplementary cementitious materials, and also to improve the strength and durability. In this research, low-cost nano-SiO 2 particles from natural hydrothermal solutions obtained by membrane ultrafiltration and, optionally, by cryochemical vacuum sublimation drying, were evaluated in portland cement based systems. The SiO 2 -rich solutions were obtained from the wells of Mutnovsky geothermal power station (Far East of Russia). The constant nano-SiO 2 dosage of 0.25% (as a solid material by weight of cementitious materials) was used to compare the cement systems with different nanoparticles against a reference mortar and a commercially available nano-SiO 2 . Nanoparticles were characterized by X-Ray Diffraction (XRD), BET Surface Area, Scanning Electron Microscope (SEM) and Fourier Transform Infrared (FTIR) spectroscopy techniques. It was demonstrated that the addition of polycarboxylate ether superplasticizer and the dispersion treatment using an ultrasound processor can be used to facilitate the distribution of nano-SiO 2 particles in the mixing water. The effect of nano-SiO 2 particles in portland cement mortars was investigated by evaluating the flow, heat of hydration and compressive strength development. It was demonstrated that the use of nano- SiO 2 particles can reduce the segregation and improve strength properties. KEYWORDS ultrafiltration, cryochemical vacuum sublimation drying, nanoparticles, portland cement, heat of hydration, surface area, compressive strength 1 Introduction There is an ongoing quest to improve the properties of concrete which can be achieved at different scale levels (Fig. 1). At a macroscale, the optimization of aggregates is used to reduce the consumption of cementitious materials [1–5] and also to improve the performance of concrete mixtures [6,7]. The addition of air entraining admixtures and engineering of specific air-void structure are com- monly used to enhance the resistance of concrete against freeze-thaw damage. At a sub-micro- and micro- scale, the addition of supplementary cementitious materials was used to improve the long-term mechanical response and durability of cement based materials [8,9]. At nanoscale, nanoparticles of SiO 2 were used in cement composites to modify the rheological behavior, to enhance the reactivity of supplementary cementitious materials, as well as to improve the strength and durability [4]. The nanoparticles of SiO 2 were extensively used to increase the strength and durability of concrete [1–3,10]. Björnström et al. investigated the effects of colloidal silica Article history: Received Mar 1, 2016; Accepted Jul 18, 2016 Front. Struct. Civ. Eng. DOI 10.1007/s11709-017-0438-2 1 5 10 15 20 25 30 35 40 45 50 55 1 5 10 15 20 25 30 35 40 45 50 55 FSC-17438-IFV.3d 12/6/017 16:50:6