Recycling of the product of thermal inertization of cement-asbestos in geopolymers

Recycling of secondary raw materials has become a priority of waste handling in the worldwide environmental agenda. A novel secondary raw material of great importance is the product of the thermal transformation of cement-asbestos, which is chemically comparable to a Mg-rich clinker. Recently, this secondary raw material called KRY•AS has been successfully used for the production of concrete. In this work it has been used for the production of geopolymers. Geopolymers represent a class of synthetic alumino-silicate based materials potentially used in several industrial fields, and in particular in substitution of cements or mortars, with the positive advantage of reducing the emissions of carbon dioxide developed during the clinkering phase. Geopolymers are the result of a reaction of an alumino-silicate, usually metakaolinite, activated with an alkaline silicate solution at room temperature. In the present work, geopolymers obtained from alumino-silicate natural materials mixed with KRY•AS were prepared and characterized. The composition with 2.5 wt.% of KRY•AS presents the best physical and mechanical properties. The presence of KRY•AS introduces about 30 wt.% of amorphous phase in the system. The crystalline component of KRY•AS decomposes in strong basic conditions releasing elements such as calcium and silicon that promote the formation of calcium precipitates and/or minor paracrystalline silicate hydrates. These are responsible for the improved technological performances.