Influence of the addition of grinding dust to a magnesium phosphate cement matrix

Magnesium phosphate cement materials were prepared by reacting magnesium oxide with water-soluble phosphates such as mono-ammonium dihydrogen phosphate (ADP), which solidified at ambient temperature through the formation of hydrated phases in the material. Cylindrical specimens of magnesium phosphate cement were molded and varying amounts (0-40% weight) of grinding dust, waste generated in the clutch disc finishing process by grinding and polishing, were added to the ceramic matrices. The influence of the addition of grinding dust on the characteristics of the cement compositions was verified in terms of setting time, apparent porosity, density and leaching/solubilization tests. The setting time was analyzed according to NM 65 (the Vicat needle) and by indirect calorimetric measurements, the apparent porosity and density of the materials were analyzed by the water immersion method, based on the Archimedes principle. Using an Instron 5500R universal testing machine, various analyses were made to ascertain how the different waste contents in the compositions affected the mechanical strength (axial compression and tensile strength by diametral compression). The results obtained proved highly satisfactory for the application of this waste as an additive in magnesium phosphate mortars. The addition of grinding dust to the magnesium phosphate cement matrix did not affect the formation of new phases or the setting time to any appreciable extent, but an increase in grinding dust content led to an initial increase in strength up to a given limit (about 30% of waste). (C) 2009 Elsevier Ltd. All rights reserved.