Binary Supplementary Cementitious Material from Expanded Clay Production Dust and Opoka

Global warming is a critical issue driven largely by the extensive release of greenhouse gases, with the cement industry being one of the biggest contributors to CO 2 emissions. A sustainable solution involves the integration of supplementary cementitious materials (SCMs) into cement production, which can mitigate environmental impacts. This study focuses on the effects of binary SCMs, composed of calcined expanded clay kiln dust and opoka, on the hardening and hydration behavior of Portland cement. The analysis used methods such as X-ray diffraction, thermal analysis, calorimetry, and compressive strength testing. The tested dust was thermally activated at 600 °C and the opoka was dried and milled to evaluate its combined influence on the cement properties. Portland cement was substituted with a combination of these two additives. The findings revealed that the two-component mixture exerts a multifaceted impact on the hydration process of Portland cement. The activated expanded clay kiln dust triggers a pozzolanic reaction because of its high reactivity, while the opoka component promotes the development of monocarboaluminates. This binary supplementary cementitious material, derived from opoka and expanded clay kiln dust, proves to be a highly effective substitute, allowing up to 25 wt.% replacement of Portland cement without reducing its compressive strength.