Mix Design Formulation and Stress-Strain Relationship of Fly Ash-Based Workable Geopolymer Concrete: an Experimental Study

Geopolymer concrete is known as a concrete made by one of cementitious materials in order to reduce carbon dioxide (CO₂) emissions for sustainable development purposes. Instead of using Portland cement for a mortar matrix, mineral residues as a result of power plant processes so-called fly ash are used to replace completely the existence of cement in a concrete structure. A large amount of chemical compounds such as silicon dioxide or silica (SiO₂), aluminum oxide (Al₂O₃) and iron(III) oxide or ferric oxide (Fe₂O₃) contained in fly ash can substitute Portland cement as a chemical binder in concrete materials. Fly ash Class F which contains more than 70% of SiO₂, Al₂O₃ and Fe₂O₃ in total with less than 10% of calcium oxide (CaO) has been investigated yielding compressive strengths similar to or even higher than the conventional concrete using Portland cement. In order to obtain a strong chemical binder between aggregates and fly ash, an activator containing a mixture of sodium hydroxide (NaOH) and sodium metasilicate (Na₂SiO₃) is applied here, where two types of Na₂SiO₃ (Be52 and Be58) are employed. Further, workability is investigated by comparing Na₂SiO₃ type Be52 and Na₂SiO₃ type Be58, with maintaining an acceptable compressive strength. Then the results of proportional mix design variations for geopolymer concrete are analyzed in terms of the modulus of elasticity and the Poisson’s ratio as well as its stress-strain relationship compared to the conventional concrete.