Behaviour of ambient cured prestressed and non-prestressed geopolymer concrete beams

One of the sustainable alternatives to Portland cement is geopolymer concrete consisting of industrial waste. Practical application of geopolymer concrete is restricted as it requires the use of high temperature to develop compressive strength. This study aims to develop a mixture design for geopolymer prestressed concrete specifically designed to take prestressing force using ambient curing technique and compare its performance with the same grade of Portland cement concrete mix. As ambient curing technique is used for geopolymer concrete hence a combination of blast furnace slag and fly ash is taken as source materials and due to ease of availability and economy, sodium hydroxide and silicate are chosen as activators. After several trial mixtures, M 40 grade of geopolymer concrete is developed using an equal proportion of fly ash and ground granulated blast furnace slag (GGBFS) as source material. GGBFS provides early strength at ambient curing in geopolymer concrete and hence was incorporated with fly ash. 3 ply of 3 mm diameter bars were used as pre-tensioning wire. Load v/s deflection graph for non-prestressed geopolymer concrete beams and beams with same grade Portland cement concrete show that the load-carrying capacity of both beams was at par. It was also observed that prestressed geopolymer concrete beams which were cured under ambient curing developed sufficient strength and were equally capable of carrying the load as compared to Portland cement concrete beams. Load carrying capacity increased in prestressed Portland cement concrete beams increased by 78% while in prestressed geopolymer concrete beams the increase was 83% and also the deflection of both prestressed beams was more compared to non-prestressed beams. This indicates that sustainable material can be effectively utilized in prestressing work without comprising on strength.