A large variety of mix design variables and environmental conditions in which alkali activated concretes (AAC) are cured, influences the nature and intensity of the binder formed. Equations developed for OPC-based concrete in various codes and published work may not accurately predict engineering properties of these AAC. AAC in this study was synthesized utilizing natural pozzolan (NP) in the presence of alkaline activators. Nano-SiO₂ was added for enhancing the strength development at room temperature curing as NP is a low calcium precursor material. Development of compressive strength, flexural strength and modulus of elasticity were investigated. Using the data generated, two constitutive models, relating the compressive strength to flexural strength and modulus of elasticity were developed and compared with the equations specified in international codes for OPC-based concrete and previous studies in the area. The results show that the ACI 318, underestimates the flexural strength and overestimates the modulus of elasticity of alkali activated concrete. However, constitutive models developed in this study are in good agreement with the equations proposed in the previous works for AAC. Only the limited data available to date on the engineering properties of AAC cannot be used to establish robust constitutive relationships and more research is required in this area.