Constitutive model for self-compacting geopolymer mortar based on fly ash content

Abstract

Accelerated development of infrastructure has necessitated the use of sustainable binding materials with a low carbon footprint. This study aims to investigate the impact of fly ash content on the mechanical properties of a self-compacting geopolymer mortar (SCGM). The SCGM properties such as dry density, compressive strength, stress–strain relationship, Young’s modulus, and Poisson’s ratio are investigated. The results show that an increase in the fly ash to sand ratio (FA/S) with a decrease in the volume of water to a volume of powder ratio (Vw/Vp) and the superplasticizer to powder ratio (Sp/P) positively affected the compressive strength of SCGM. The maximum 28 d compressive strength of the SCGM mix was 39 MPa with an FA/S of 1.0, Vw/Vp of 0.94, and Sp/P of 2%. The stress–strain relationship shows that the NaOH molarity and FA/S had a strong influence on the stiffness and compressive strength of the SCGM. A conservative mathematical expression is proposed to predict the Young’s modulus of the SCGM based on the compressive strength, and it ranged from 5.63 GPa to 10.20 GPa, which is lower than the ordinary Portland cement (OPC) concrete proposed by the ACI 318; however, Poisson’s ratio is within the range of OPC concrete. The stiffness of the SCGM ranged from 25% to 55% at the ultimate strain compared to the initial stiffness. The increase in the FA/S ratio from 0.5 to 1.0 resulted in an increase in the SCGM strain, indicating an increase in flexibility. A mathematical model to predict the total stress for SCGM is proposed based on the initial stiffness and the corresponding total strain with the formulation of fracture parameters based on the concept of the elastoplastic fracture model of OPC concrete.