Mechanical Characterization of Hybrid (Organic-Inorganic) Geopolymers

The mechanical properties of geopolymers can be obtained through different kinds of experimental tests: this paper is focused on the compressive strength (i.e. in a direction parallel to the loading axis) for the case of uniaxial compression. The compressive strength of such materials is traditionally characterized by the 28th-day value, but their strength is expected to increase in time at a continuously decreasing rate. The knowledge of the strength vs. time law is of importance when a structure is subjected to a certain type of loading at a later age. In this work inorganic polymers from activated metakaolin (alumina silicate inorganic polymers, obtained from alkali activation of powders containing SiO2+Al2O3 > 80%(wt)) are reported. In order to improve their compressive strength a percentage of polyethylene glycol has been added, thus obtaining a hybrid (organic-inorganic) geopolymer. Many factors can influence significantly the compressive strength of such materials e.g. w/c ration, aggregate content, water curing period, polyethylene/glycol ratio. Afterwards experimental compressive tests (performed in a Zwick-Roell (R) testing machine) have been carried out varying the polyethylene/glycol ratio and the main dimensions of the samples.