Prediction of the Maximum Compressive Strength Geopolymers Using the Method of Weighted Chemical Compositions of Binders

Geopolymers are composite hard materials made by mixing solid binders such as fly ash and slag, and alkaline liquid activators such as NaOH and sodium silicate. Geopolymers have recently been developed to be used as a replacement for portland cement concrete. Industrial by-products, such as fly ash, steel making slags and garbage melting furnace slags, can be used to create geopolymers in a process that emits less carbon dioxide than does cement making. This reduction in CO2 emission is important because CO2 is one of the substances known to contribute to global warming. In the future, further uses of these fly ashes and slags must be explored. The development of high compressive strength geopolymers using fly ash and slags will strongly contribute to the fields of construction, geotechnical engineering, and architecture. The compressive strength of geopolymers, qu, is generally considered to be a function of the weight ratio of activator to binder, w, and the weight ratio of NaOH to sodium silicate, η. The maximum compressive strength, qumax, is determined as the maximum value among the peak values of qu, which were obtained for various values of w and η. The values of w and η that yield the maximum compressive strength, qumax, are defined as the optimum values wopt and ηopt, respectively. When designing geopolymers, it is essential to establish a method to predict qumax using the chemical compositions of the binders only. This research first determines the chemical and physical properties of geopolymer materials by using scanning electron microscopy (SEM) and X-ray diffraction (XRD) observations, and then determines the mechanical properties of qumax, and finally devises a method to predict qumax by combining SiO2, Al2O3, and CaO in binders.