Investigation of engineering properties of normal and high strength fly ash based geopolymer and alkali-activated slag concrete compared to ordinary Portland cement concrete

Fly ash-based geopolymer (FAGP) and alkali-activated slag (AAS) concrete are produced by mixing alkaline

solutions with aluminosilicate materials. As the FAGP and AAS concrete are free of Portland cement,

they have a low carbon footprint and consume low energy during the production process. This paper

compares the engineering properties of normal strength and high strength FAGP and AAS concrete with

OPC concrete. The engineering properties considered in this study included workability, dry density,

ultrasonic pulse velocity (UPV), compressive strength, indirect tensile strength, flexural strength, direct

tensile strength, and stress-strain behaviour in compression and direct tension. Microstructural observations

using scanning electronic microscopy (SEM) are also presented. It was found that the dry density

and UPV of FAGP and AAS concrete were lower than those of OPC concrete of similar compressive

strength. The tensile strength of FAGP and AAS concrete was comparable to the tensile strength of OPC

concrete when the compressive strength of the concrete was about 35 MPa (normal strength concrete).

However, the tensile strength of FAGP and AAS concrete was higher than the tensile strength of OPC concrete

when the compressive strength of concrete was about 65 MPa (high strength concrete). The modulus

of elasticity of FAGP and AAS concrete in compression and direct tension was lower than the

modulus of elasticity of OPC concrete of similar compressive strength. The SEM results indicated that

the microstructures of FAGP and AAS concrete were more compact and homogeneous than the

microstructures of OPC concrete at 7 days, but less compact and homogeneous than the microstructures

of OPC concrete at 28 days for the concrete of similar compressive strength.