Manuscript title: Development of strength prediction models for fly ash based geopolymer concrete

Abstract

Geopolymer concrete has progressively gained acceptance as one of the best alternative construction materials in civil and infrastructural engineering applications. The geopolymer binders have excellent mechanical properties and commercial potential, with lower environmental impact compared to ordinary Portland cement. In the past, most studies have focused on mixtures, properties, mixing and curing process, and micro-structure, etc., of the geopolymer binder. However, studies on structural member design using fly ash geopolymer concrete are still limited and do not have comprehensive coverage. Furthermore, some design parameters are rarely available, and this has slowed down the development of applications. The objective of this study was to evaluate and establish strength parameters of fly ash geopolymer concrete under flexural, shear and torsion loadings, utilizing prior experimental data and those from various standard design codes such as ACI, AS3600, CSA, and CIB-FIP. Models of modulus of rupture, elastic modulus, torsional strength, and flexural beam shear were developed in terms of compressive strength. In our experimental study, three different experimental sets were performed: 1) uniaxial compression and flexural beam test to evaluate modulus of rupture, 2) uniaxial compression and torsion test to determine cracking torsional strength, and 3) beam test (with shear span to effective depth ratio (a/d) ≈ 2) and uniaxial compression test to characterize shear strength. By using experimental data of the current and prior studies, the modulus of rupture model was developed in terms of an exponential function for the geopolymer concrete compressive strength, with acceptable accuracy. The modulus of elasticity in a power function was more accurate with 85% R2 for a board range of compressive strengths. The proposed cracking torsional strength model, based on thin-wall theory, was established with the critical stress 0.47√f'c. The proposed shear strength estimate having similar form as the original ACI equation is reasonably conservative and facilitates the practical use of geopolymer concrete in structural design.Finally, the interaction surface for combined loads, such as bending, shear and torsion was demonstrated for the quarter-parabola bending –shear and – torsion, and for the quarter - circle torsion and shear interactions, with the critical stresses: (fb = 0.815f′c), (fs = 0.11f′c) and (ft = 0.30f′c), respectively.