GEOPOLYMER CONCRETE

GEOPOLYMERCONCRETE

 Geopolymer is a new development in the world of concrete in which cement is totally replaced by pozzolanic materials like fly ash and activated by highly alkaline solutions to act as a binder in the concrete mix. For the selection of suitable ingredients of geopolymer concrete to achieve desire strength at required workability, an experimental investigation has been carried out for the gradation of geopolymer concrete and a mix design procedure is proposed on the basis of quantity and fineness of fly ash, quantity of water, grading of fine aggregate, fine to total aggregate ratio. Sodium silicate solution with Na2O = 16.37 %, SiO2 = 34.35 % and H2O = 49.28 % and sodium hydroxide solution having 13 M concentration were maintained constant throughout the experiment. Water-to-geopolymer binder ratio of 0.35, alkaline solution-to-fly ash ratio of 0.35 and sodium silicate-to-sodium hydroxide ratio of 1.0 by mass were fixed on the basis of workability and cube compressive strength. Workability of geopolymer concrete was measured by flow table apparatus and cubes of 150 mm side were cast and tested for compressive strength after specified period of oven heating. The temperature of oven heating was maintained at 60 °C for 24 h duration and tested 7 days after heating. It is observed that the results of workability and compressive strength are well match with the required degree of workability and compressive strength. So, proposed method is used to design normal and standard Geopolymer concrete.

Use of concrete is globally accepted due to ease in operation, mechanical properties and low cost of production as compared to other construction materials. An important ingredient in the conventional concrete is the Portland cement. Production of Portland cement is increasing due to the increasing demand of construction industries. Therefore the rate of production of carbon dioxide released to the atmosphere during the production of Portland cement is also increasing. Generally for each ton of Portland cement production, releases a ton of carbon dioxide in the atmosphere . The green house gas emission from the production of Portland cement is about 1.35 billion tons annually, which is about 7 % of the total greenhouse gas emissions . Moreover, cement production also consumes significant amount of natural resources. Therefore to reduce the pollution, it is necessary to reduce or replace the cement from concrete by other cementitious materials like fly ash, blast furnace slag, rice husk ash, etc. Fly ash is a by-product of pulverized coal blown into a fire furnace of an electricity generating thermal power plant. According to the survey, the total fly ash production in the world is about 780 million tons per year but utilization is only about 17–20 % . In India more than 220 million tons of Fly ash is produced annually . Out of this, only 35–50 % fly ash is utilized either in the production of Portland pozzolana cement, workability improving admixture in concrete or in stabilization of soil. Most of the fly ash is disposed off as a waste material that covers several hectares of valuable land. The importance of using fly ash as a cement replacing material is beyond doubt ,replacing cement by fly ash up to 60 % known as high volume fly ash concrete. But it was observed that the pozzolanic action of fly ash with calcium hydroxide formed during the hydration of cement is very slow. The particles of size less than 45 μm are responsible for pozzolanic reaction. Higher size particles present in fly ash acts as filler. Therefore for complete replacement of cement by fly ash and to achieve the higher strength within a short period of curing. Fly ash when comes in contact with highly alkaline solutions forms inorganic alumino–silicate polymer product yielding polymeric Si–O–Al–O bonds known as Geopolymer . To produce concrete of desired strength, various mix proportioning methods are used on the basis of type of work, types, availability and properties of material, field conditions and workability and durability requirements. As geopolymer concrete is a new material in which cement is totally replaced by fly ash and activated by alkaline solutions. Chemical composition, fineness and density of fly ashes are different from cement. Similarly, in cement concrete, water plays main role during hydration process while water come out during polymerisation process as in case of geopolymer concrete. Therefore it is necessary to develop a new mix design procedure for geopolymer concrete to achieve desired strength at required workability. So, in the present investigation, geopolymer concrete mix design procedure is proposed on the basis of quantity and fineness of fly ash to achieve desired strength , quantity of water to achieve required degree of workability , grading of fine aggregate  and fine-to-total aggregate ratio by maintaining solution-to-fly ash ratio by mass of 0.35 , water-to-geopolymer binder ratio of 0.35 , sodium silicate-to-sodium hydroxide ratio by mass of 1  and tested after oven heating at a temperature 60 °C for duration of 24 h and tested after test period of 7 days.

OVEN CURING OF GEOPOLYMER CONCRETE