Milling as a pretreatment method for increasing the reactivity of natural zeolites for use as supplementary cementitious materials

This work examined the effects of milling using a gravity ball mill on the reactivity of natural zeolites used as supplementary cementitious materials (SCMs). Six different particle size distributions of zeolites, created by milling the as-received zeolite in a ball mill for a specified amount of time, were characterized using x-ray fluorescence, quantitative x-ray diffraction, particle size analysis, pore size distribution and surface area analysis. Following material characterization, the pozzolanic reactivity of the zeolites was determined by measuring the quantity of calcium hydroxide in paste after 28 or 90 days and by tracking the compressive strength of zeolite-cement mortars. Results showed that a critical milling time exists, corresponding to a d50 of 7–9 μm, after which reductions in particle size can no longer be achieved and zeolite performance can no longer be improved through ball milling.