Development of Supplementary Cementitious Materials by Mechanochemical Activation Using Raw Materials from Hungary

Abstract

Supplementary cementitious materials (SCMs) are currently at the forefront of research due to the demand for cement in the rapidly growing construction industry and strict environmental regulations. Their application can efficiently reduce the energy required for production and CO₂ emissions. Trass and thermally activated kaolin (metakaolin) exhibit pozzolanic reactivity because of their high active silica and alumina content. Their application reduces the amount of cement clinker and the energy required for cement production, while providing beneficial properties to concrete. As a viable alternative to thermal activation for the production of SCMs, mechanochemical activation (MCA) is currently the subject of extensive research. In this work, MCA was performed by high-energy dry grinding mixtures of locally available kaolin and trass in the mass ratios of 25:75, 50:50, 75:25 and 100:0.
X-ray diffraction, thermal analysis, infrared spectroscopy, scanning electron microscopy and specific surface area measurements were used to examine the structural as well as morphological changes that occurred during MCA. To characterize the pozzolanic reactivity, the compressive strength of binders was studied, in which 10% w/w of Ordinary Portland Cement (OPC) was replaced by activated mixtures. It was found that the addition of 25, 50 and 75% w/w of trass reduced the grinding time of the complete amorphization of the kaolinite from 90 mins to 75, 45 and 30 mins, respectively. Meanwhile, almost complete (~90%) amorphization was achieved for all mixtures by halving the grinding times. The 28-day-long compressive strength of the binders containing activated mixtures reached that of the OPC reference. Overall, it was concluded that the addition of trass positively reduced the grinding time and energy required for the amorphization of kaolinite, moreover, that SCMs with good levels of pozzolanic reactivity can be produced with 90% amorphization from local raw materials.