IJCT (2017) 1–13 © JournalsPub 2017. All Rights Reserved Page 1 International Journal of Concrete Technology Vol. 3: Issue 1 www.journalspub.com Effect of Colloidal Nanosilica on High Strength Rice Husk Ash Concrete Rajendra B. Magar, Afroz Khan*, Vipin Gupta, Vinay Gupta, Khalil Sayed Anjuman-I-Islam’s Kalsekar Technical Campus, Mumbai University, Maharashtra, India ABSTRACT Nowadays, supplementary cementitious materials (SCMs) are used in concrete because it reduces CO 2 emission during. The husks, which are production of cement, reduces cement contents, improve workability, increase strength and enhance durability. Pozzolanic reaction takes place when siliceous or aluminous material comes in contact with calcium hydroxide in the presence of moisture to form compounds possessing cementitious properties approximately 50 percent cellulose, 30 percent lignin and 20 percent silica, are incinerated by controlled combustion leaving behind an ash that predominantly consists of amorphous silica. Rice husk ash is highly pozzolanic due to its extremely high surface area (50,000 to 100,000 m 2 /kg). The colloidal nano silica (CNS) which is nano material and behaved not only as a filler to improve cement micro-structure (porosity decrease), but also as a promoter of pozzolanic reaction used in cement for accelerating pozzolanic action due to which the cement sets faster than conventional mix. In the present study, the mineral admixture, rice husk ash (RHA) was used as 5, 10, 15% replacement for OPC in M60 grade of concrete. The 10% RHA was taken as optimum dose on the basis of workability and compressive strength. To this 10% RHA concrete, effect of 1, 2, 4, and 6% CNS addition were experimentally studied with various properties like workability, compressive strength and split tensile strength. Keywords: colloidal nano silica, compressive strength, ordinary Portland cement, rice husk ash, split tensile strength *Corresponding Author E-mail: afroz.nk@gmail.com INTRODUCTION AND LITERATURE REVIEW Nanotechnology has attracted considerable scientific interest due to the new potential uses of particles in 1–100 nm scale [1]. At the nanoscale, physical, chemical, and biological properties vary from the properties of individual atoms and molecules of bulk matter. Therefore, it provides opportunity to develop new classes of advanced materials which meet the demands from high-tech applications [2]. Thus, industries may be able to re-engineer many existing products that function at unprecedented levels. A quickly growing range of applications of nonmaterial’s in many fields has been observed in recent years [2]. Among them, nanosilica is a widely used nanomaterial with applications in polymer, adhesives, fiber optic strands, sealants, inks, paints, coatings, cosmetics, food additive and in cement-based building materials [3]. Concrete is a highly heterogeneous material produced by mixture of finely powdered cement, aggregates of various sizes and water with inherent physical, chemical and mechanical properties. A reaction between the cement and water yields calcium silicate hydrate, which stretches concrete strength and other mechanical properties of concrete,