An Experimental Study on Geopolymer Concrete Using Low Calcium Fly Ash

Abstract

Concrete is the widely used building material and cement is the main constituent in the manufacturing of concrete. In concrete production, ordinary Portland cement (OPC) is conventionally used as primary binder to produce concrete. In production of cement burning of lime stone take place which results in emission of carbon dioxide (CO2) gas into the atmosphere. So, it is important to find substitutes binders which have less carbon foot-print than cement, less natural resource depletion, less energy consumer and better strength. From many alternatives geopolymer binder is best alternative. In geopolymer concrete, a by-product material rich in silicon and aluminum such as low calcium fly ash, is chemically activated by a high- alkaline solution such as NaOH and Na2SiO3 to form a paste that binds the loose coarse and fine aggregates, and other unreacted in mixture. In this study, fly ash sample is collected from Ayka Addis Textile and its oxides composition investigated in the laboratory of Dangote Cement factory Enterprise and physical properties (unity weight, specific gravity, water absorption, moisture content, fineness modulus and silt content) of coarse and fine aggregate, workability of fresh geopolymer concrete, density and compressive strength geopolymer concrete tests are conducted in laboratory of Jimma Institute of Technology. Experimental laboratory sample test has been made in this research work, C-25 with 0.5 of water to fly ash ratio and the slump of 25 to 50mm are used in geopolymer concrete mix design. Geopolymer Concrete cubes of size 150*150*150mm are prepared and placed in ambient temperature for a maximum of 28 days. Six different geopolymer concrete samples with ratio of 0.5 and 1.5 Na2SiO3 to NaOH and sodium hydroxide solution with concentration of 10M, 13M and 16M are prepared to make a concrete samples and one control OPC concrete. For each variable three sets of specimens are prepared for compressive strength tests conducted at the age of 7, 14 and 28 days. Test results revealed that the slump value of the geopolymer concrete with low calcium fly ash had shown a slight reduction as concentration of NaOH and ratio of Na2SiO3 to NaOH increases. In addition to that, density of the test specimens increased with an increase in concentration of NaOH but, less density than control OPC concrete and also the compressive strength of geopolymer concrete have shown improvement over the control OPC concrete with concentration of NaOH 10M, 13M and 16M and ratio of Na2SiO3 to NaOH of 1.5 at 28 day age. But, lesser compressive strength at age of 28 days with concentration of NaOH 10M, 13M and 16M and ratio of Na2SiO3 to NaOH of 0.5. So, geopolymer concrete with NaOH 10M, 13M and 16M and ratio of Na2SiO3 to NaOH of 1.5 suitable as construction material in construction industry