Prediction of the Compressive Strength from Resonant Frequency for Low-Calcium Fly Ash-Based Geopolymer Concrete

Abstract

Due to its usage in large quantity, the concrete industry contributes to 5% of the annual anthropogenic carbon production. The main reason is the production of traditional concrete binder materials, Ordinary Portland Cement (OPC), involves a high carbon emission. Therefore, finding a greener binder material has been considered as the most effective way to reduce the carbon footprint for the concrete industry. In recent years, fly ash, a waste material from power plants, has gained public attention owing to its similar binding properties as OPC. Therefore, this study focuses on using fly ash to produce a cement-free geopolymer concrete. Instead of using sodium-based activator, this study adopts potassium-based activator that consists of hydroxide and silicate, due to its better contribution on workability and strength. Under the heat curing condition, the effect of the constituent of activator was investigated in this study, by ranging the concentration of hydroxide (10M, 12M and 14M), the ratio of silicate to hydroxide (2.0, 2.5 and 3.0). The results have shown the compressive strength increases with the increasing hydroxide concentration and the decreasing silicate to hydroxide ratio. Besides, attempts were made to propose a non-destructive methodology for the prediction of compressive strength from resonant frequency. The dynamic elastic modulus was determined from resonant frequency test, following by compression test. The predictive equation was proposed by conducting a multiple regression analysis between dynamic elastic modulus and compressive strength. Given the relationship between resonant frequency and dynamic elastic modulus from ASTM Standard Code, the proposed equation was successfully correlated to the resonant frequency. The accuracy of proposed equation was then evaluated with experimental data and validated with previous work from another researcher.