Mechanical and bond behaviour of high volume Ultrafine-slag blended fly ash based alkali activated concrete

Abstract

The development of Geopolymer concrete (GPC) mixes by employing large volume of ultrafine ground granulated blast furnace slag (UBFS) blended with Fly ash (FA) and activated by sodium hydroxide (SH) has been presented in this study. Several GPC mixes has been prepared to investigate the effect of varying alkali content, fine aggregate to total aggregate ratio (s/a) and molar concentration (M) of alkali activator on the fresh and hardened characteristics, including the bond strength with Portland cement concrete (PCC). The properties of the GPC mixes are assessed by workability test, compressive strength test, split tensile strength test and slant shear test, including the microstructure through FESEM (Field Emission Scan Electron Microscopy) and X-ray diffraction (XRD). The test result shows that s/a ratio is a crucial factor in controlling segregation and bleeding in GPC. However, an ideal GPC mix with s/a ratio 0.41 provides a better packing resulting in improved mechanical properties. Application of high volume UBFS in the GPC exhibits better reaction products as shown by the microstructure at a relatively lower alkali concentration which ultimately leads to higher strength. Superior bond strength is achieved between the GPC and old PCC substrate; however, the molarity of SH significantly affects the adhesion property of GPC.