Role of nano silica in enhancing the properties of aerated concrete

Abstract

Infrastructure development has witnessed the use of new construction materials in the Industry. One such material is the Lightweight concrete which can be classified as cellular concrete and lightweight aggregate concrete. This concrete can be customized as low strength concrete having density less than 800 kg/m3, medium strength concrete with density ranging from 800 to 1200 kg/m3 and structural concrete with density from 1200 to less than 2000 kg/m3. The objective of this study is to optimize a mix proportion for structural light weight concrete incorporating Nano materials for improved strength and durability. Nano silica is a pozzolanic material extracted by annealing rice husk ash. Addition of very small percentage of nano silica in concrete and mortar has shown good strength enhancement and improved durability properties due to increased reactivity, pozzolanic reaction forming additional hydration products and filler effect thereby reducing the porosity and improving the durability properties. This work is based on examining the role of nano silica in enhancing the properties of aerated concrete which is a form of cellular concrete. Also the product has been aimed at making a sustainable construction material using foundry sand from automobile industry which is a waste material and dumped in valuable lands causing land pollution. Aluminium powder is used as an aerating agent and foundry sand was used as sand replacement. Gypsum was used up to 5% in order to enable the strength gain in non-autoclaved aerated concrete. Nano silica was found to be effective up to 7.5% addition beyond which there was not much improvement in terms of strength and durability. The resulting concrete had a density of 1180 to 1620 kg/m3 which is very less compared to the conventional concrete. This a major advantage of this material which can reduce the dead load of the structure. The compressive strength and flexural strength achieved was 25.2 MPa and 1.4 MPa respectively. Durability tests were conducted by sorptivity and Rapid chloride penetration tests to understand the permeability of concrete. Also microstructure investigations with SEM and XRD were done to find the hydration products.