Performance Evaluation of Geopolymer Concrete Developed Using Sillimanite Sand

Abstract

As the infrastructure industry continues to expand, the demand for cement is destined to rise. Cement producing industries are classified as extremally polluting industries. The primary pollutant that cement companies emit is carbon dioxide (CO2). The production of cement causes severe greenhouse gas emission into the earth atmosphere. This issue causes the researchers to develop a new type of concrete which is different from conventional concrete and is termed as Geopolymer Concrete. Geopolymer concrete not only lowers the dependency of conventional concrete but also lowers the amount of global warming without compromising the mechanical and durability properties. Geopolymer does not form Calcium Silicate Hydrates (C-S-H) for matrix formation, unlike ordinary portland cement. Rather it forms Sodium Alumina Silicate Hydrate (N-A-S-H) gel. The present dissertation work is performed to assess the impact by replacing natural sand with sillimanite sand in geopolymer concrete. Sillimanite sand contains high alumina and silica content and is used as a high-temperature refractory material. In geopolymer concrete, river sand has been replaced with sillimanite sand at 0, 25, 50, 75 and 100% replacement levels. Furthermore, the impact of molarities (8M and 16M) and curing type (ambient curing and steam curing) on the mechanical, durability, and microstructural characteristics of geopolymer concrete, are also evaluated. Based on trial and error, geopolymer concrete mix design is prepared by reviewing previous literature and existing observations as standard code for geopolymer concrete is not available. Tests were conducted at the age of 28 days according to the provision of Indian Standard (IS) and American Society of Testing and Materials (ASTM) guidelines. The various mechanical test results revealed that the steam curing sample has higher strength compared to the ambient curing samples. In addition to it, GP16 (16M) mix has excellent mechanical and durability properties compared to the GP08 (8M) mix. The 25 to 50 % replacement level indicates optimum replacement level leading to higher mechanical and durability characteristics in the context of percentage replacement. An increase in percentage replacement beyond 50% indicates a reduction in the effectiveness of both mechanical and durability properties, whereas control mix demonstrates minimal durability as compared to sillimanite contained mix. The SEM, EDS, and XRD analysis also indicate dense interconnection between the gel networks due to the presence of sillimanite sand.