Geopolymers are composite hard materials made by mixing binders, such as fly ash and slags, and activators, such as NaOH and sodium silicate. The chemical mechanism for hardening composite materials, aluminosilicate binders, with alkaline activators is known as a geopolymer reaction. 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 made into geopolymers in a process that emits less carbon dioxide than in the cement making process. 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 ash 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.
So far, ground blast furnace slag has yielded the highest compressive strength geopolymer among various kind of binders such as fly ash, ground stainless steel-making slag, and garbage melting furnace slags. A potential use for the poor binders, yielding low compressive strength geopolymers, is to combine it with a richer binder to create stronger products. This paper examines the characteristics for improvement of compressive strength of geopolymers for the binders in various mixture ratios of poor binders and the ground blast furnace slag.