Mechanical and micro-structural properties of blended fly Ash-slag based alkali activated concrete

Abstract

The production of cement, for example, has shown to be a significant source to the majority of net greenhouse gas emissions. Consumption of calcium-silica-alumina rich wastes is strongly recommended to reduce the environmental pollution danger posed by the building sector, such as carbon footprint reduction. This research work is primarily focused on completely replacing the conventional binder i.e., cement with a blended proportion of fly-ash (FA) and ground granulated blast-furnace slag (GGBS), using an alkali activator solution to form geopolymer concrete (GPC). A total of 5 types of blends with FA-GGBFS mix, with a control PCC mix have been prepared keeping other parameters of alkali concentration viz. molarity, alkali ratio, liquid to binder ratio as constant. As the binder portion of the mix is supposed to be a 100% replacement of cement, the percentage combination of FA & GGBFS is varied from 90 to 10 to 50–50. A Sodium Hydroxide (NH) and Sodium silicate (NS) mix is prepared to act as Alkali Activator for the proposed mix, with a definite NS-NH ratio and molarity of NH as 2.5 and 12 M respectively. Non-destructive tests (NDT) were performed on the prepared specimens, including the ultrasonic pulse velocity (UPV) and rebound hammer (RH) tests. Similarly, the compressive strength (CS) of 100 mm concrete cubes, split tensile strength (ST) of 100 mm Φ × 200 mm high concrete cylinders and the flexural strength of 100 × 100 × 500 mm size prisms were measured after 28 days. The blended proportion of 50% FA and 50% GGBFS turned out to be most effective, yielding a compressive strength of 52 MPa. Furthermore, the effect of replacing FA with GGBFS was investigated using scanning electron microscopy (SEM) for microstructural investigation.