Hydration and thermal properties of alkaline hybrid cements based on waste clay and solid alkaline activators

Abstract

The cement industry is actively pursuing sustainable alternatives to reduce CO₂ emissions and combat climate change. This study focuses on replacing Portland cement (PC) with rotary kiln flue dust (RFD), a byproduct of metakaolin production. The research investigates the viability of using moderately alkaline activators, including Na₂SO₄, Na₂CO₃, K₂SO₄, and K₂CO₃, to achieve alkali activation without the need for high-temperature calcination, which consumes a lot of energy. The experimental mixtures, comprising 75% RFD, 20% PC, and 5% alkaline activator, exhibit promising results in terms of compressive and flexural strengths. Na₂SO₄ enhances the mechanical properties of the binder. Synergic effect of alkaline activator and PC accelerate reaction original raw material, leading to the formation of ettringite. Conversely, carbonate activators extend the setting time and delay reactions, impacting the early age properties of the binder. The study also explores the thermal stability of the binders, demonstrating a notable impact of alkaline activators on the expansion and contraction behaviors during heating. The findings contribute with valuable insights into the design and optimization of eco-friendly alkali-activated binders, addressing the need for sustainable construction materials with enhanced performance and durability. This research represents a significant step toward developing environmentally preferable cementitious materials, paving the way for the construction industry to adopt more sustainable practices and reduce its ecological footprint.