Although considerable research has been undertaken on alkali-activated binders for geopolymer concrete production, few of these studies have focused on clay based geopolymer concrete. This paper reports the results of an experimental investigation to optimize the mix design of geopolymer concrete prepared solely from clay material. Four Activator Modulus (AM); 1.0, 1.25, 1.5 and 1.75 for each of two Sodium Oxide (Na2O) dosages of 10% and 15% were selected for this investigation. A total of eight mix ratios comprising 72 specimens were tested. A comparison of physical behavior of clay based geopolymer mortar to that of fly ash based geopolymer mortar has been drawn throughout this paper. A Na2O dosage of 10% provided consistent strength for all AM tested, however the specimens prepared with Na2O dosage of 15% showed a reduction with time for all but the AM 1.0 specimens. Compressive strength of specimens prepared with AM of 1 for both of the Na2O dosage of 10% and 15% exhibited the superiority over other AM. The investigation showed potential for clay material to be an alternative to ordinary Portland cement (OPC).
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