Ball Milling of Silica-Based Pyroclastic Scoriae: Measurement of Mechanochemical Reactivity by Radical Scavenging

The present work concerns the mechanochemical reactivity of Pozzolane Rosse, a historical constituent of ancient Roman mortars and concretes. Suitably sieved Pozzolane Rosse powders were subjected to mechanical activation. Chemical behavior was investigated both during and after the mechanical treatment using an ethanol solution containing a free radical scavenger. Experimental findings indicate that the mechanical processing induces a decrease in scavenger concentration. The scavenger consumption is significantly larger when Pozzolane Rosse is exposed to the ethanol solution during the mechanical treatment, due to fracturing processes resulting in the increase of specific surface area of Pozzolane Rosse powder and to frictional processes between particles. The surface density of active sites is indirectly evaluated, and the emerging mechanochemical effects are discussed. Kinetic effects of the mechanical processing on the reaction between Pozzolane Rosse and calcium hydroxide in water are also evaluated. The accurate measurements of experimental observables and their interpretation based on a reliable kinetic model allowed a quantitative assessment of the mechanochemical reactivity of the material.