The Impact of the High-Energy Grinding of Wood Ash on Its Pozzolanic Activity

Wood ash is a promising supplementary cementitious material (SCM) due to its inherent pozzolanic properties. Intensive grinding has been shown to enhance this aspect and reduce the negative effects of variability in the chemical composition. This study investigated the influence of grinding through ball milling on the pozzolanic properties of wood ash. Four different types of wood ash were studied, each subjected to grinding durations of 10 and 20 min. Coal fly ash was used as a reference material. The pozzolanic activity of raw and ground wood ashes was evaluated using the strength activity index (SAI), the Frattini test, the R3 test, thermogravimetric analysis (TGA/DTG), X-ray diffraction (XRD) analysis, and scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS). The results indicated that both 10 min and 20 min grinding durations enhanced the reactivity and compressive strength. However, the 10 min grinding duration showed better overall performance than 20 min grinding, likely due to reduced agglomeration and more effective particle refinement. For calcium-rich wood ashes, the reactivity was linked to the hydraulic properties rather than the pozzolanic properties.