This paper presents an experimental investigation on the mechanical properties and microstructure of geopolymer concrete mixed using class F fly ash (FA), ground granulated blastfurnace slag (GGBS) and high-magnesium nickel slag (HMNS). An optimal combination of FA, GGBS and HMNS was determined using the compressive strength tests of geopolymer (GP) pastes mixed with various different replacements of FA with GGBS and/or HMNS. It was found that the replacement of FA with 20% of GGBS and 10% of HMNS in GP concrete increases the 28-day compressive strength by 100% and the 28-day splitting tensile strength by 58%. The microstructure analysis of the GP concrete using SEM, XRD, and FTIR showed the formation of aluminosilicate amorphous phase in a three-dimensional network. The SEM images revealed a fully compact and cohesive geopolymer matrix, which explains the reason why the mechanical properties of the FA based GP concrete with both GGBS and HMNS are improved.

This investigative study aims to study the mechanical and morphological properties of fly ash (FA)-based geopolymer paste as a repair material when applied on ordinary Portland cement (OPC) overlay concrete. The first part of this study investigates the optimal mix design of FA-based geopolymer paste with various NaOH concentrations of 8, 10, 12, and 14 M, which were used later as a repair material. The second part studies the bonding strength using a slant shear test between the geopolymer repair material and OPC substrate concrete. The results showed that a shorter setting time corresponds to the higher NaOH molarity, within the range of 53 and 30 min at 8 and 14 M, respectively. The compressive strength of FA-based geopolymer paste was found to reach 92.5 MPa at 60 days. Also, from the slant shear test results, prism specimens with 125 mm length and 50 mm wide have a large bond strength of 11 MPa at 12 M. The scanning electron microscopy/energy-dispersive X-ray (SEM/EDX) analysis showed that the OPC substrate has a significant effect on slant shear bond strength, where the presence of free cations of Ca2+ on the OPC substrate surface contributed to the formation of calcium alumina-silicate hydrate gel (C-A-S-H) by building various cross-links of Ca-O-Si.

This paper presents a review on fly ash as prime materials used for geopolymer. Due to its advantages of abundant resources, less in cost, great workability and high physical properties which lead to achieve high mechanical properties. Fly ash is considered as one of the largest generated industrial solid wastes or so-called industrial by products, around the world particularly in China, India and USA. The characteristics of fly ash allow it to be a geotechnical material to produce geopolymer cement or concrete as an alternative of Ordinary Portland cement. Many efforts are made in this direction to formulate a suitable mix design of fly ash based-geopolymer by focusing on fly ash as the main prime material. The physical properties, chemical compositions and chemical activation of fly ash are analysed and evaluated in this review paper. Reference has been made to different ASTM, ACI standards and other researches work in geopolymer area.

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