Thermal, chemical and mechanical characterization of recycled corundum powder in metakaolin-based geopolymer binder

In this study we report on the addition of a waste, a real spent corundum abrasive powder collected after testing, to a metakaolin-based alkali activated binder. The waste has been chosen as representative of spent grits produced by industrial blasting processes. In this model system based on metakaolin, the effect of corundum powder in the environment of high alkaline media was investigated in terms of 3D reticulation of the aluminosilicate amorphous structure of the consolidated geopolymeric mixes. A number of microstructural techniques (FT-IR, XRD, TGA/DTA) have been used in combination with less conventional one, such as the ionic conductivity measurements of the eluate produced after 24 h of immersion of the sample in water. The overall 3D aluminosilicate frame typical of MK-based geopolymer is retained also after 50 wt% addition of recycled corundum, as shown by FT-IR, XRD, and TGA/DTA. The traces of ceramic materials abrasion present in the waste showed good reactivity, as shown by the disappearance of their characteristic peaks in the XRD patterns. Ionic conductivity of the eluates evidenced the most extended reactivity of the alkaline activator solution in the case of 10 and 20 wt% addition of the waste. While the role of 20, 30 and 40 wt% addition of the waste to the MK-based matrix produced the highest compressive strength in the consolidated mortars after 28 days comparable to those of Ordinary Portland cement concretes. It was proved that, when produced using a partially reactive waste with well-formulated mix designs, metakaolin alkali-activated binders or mortars are an important aluminosilicate source for room temperature produced construction materials.