Study on Assessment of Pozzolanic Activity: Slate Cutting Waste

The mining industry is responsible for various environmental problems, including the extraction of natural resources and the generation of a significant volume of waste. The use of such residues in the construction industry as supplementary cementitious material (SUM) is one possible solution to minimize its disposal and a way for both industries to improve their eco-efficiency. This research aims to study the pozzolanic potential of the residue generated in slate cutting, as well as to compare the current standard methods applied to verify the pozzolanic activity (strength activity index) and direct methods based on calcium hydroxide consumption. A milling study in a planetary ball mill was carried out to evaluate the effects of particle size distribution on reactivity. The pozzolanic activity was investigated based on current standard methods (strength activity index) and analytical evaluations. The results of calcium hydroxide consumption were obtained from simultaneous thermal analysis (thermogravimetric and thermal differential analysis) and X-ray diffraction. Conflicting results between the current standard and direct methods were observed. The tested specimens with low or inexpressive calcium hydroxide consumption presented a high -strength activity index, while the specimens that presented a higher calcium hydroxide consumption showed a strength activity index below the minimum values required by the current standards. The results pointed to the potential use of slate cutting waste and contributes to the discussions about the phenomena neglected by the current strength activity index standard.