Influence of Metakaolin Content to the Microstructure and Strength in Hardened Lc3 Paste

Abstract

Low-grade kaolinitic clay has proven useful in manufacturing limestone calcined clay cement (LC3) but may lead to lower mechanical performance. This paper presents an in-depth investigation of the mechanical implications of varying metakaolin contents in LC3. Results show that the presence of metakaolin increases the cumulative heat release rate during hydration and significantly influences calcium hydroxide and calcium carbonate levels in the cement matrix. A specific threshold of 70% metakaolin content is necessary for optimizing pozzolanic activity, beyond which excess remains unreacted. The study reports a noticeable improvement in the compressive strength of LC3 containing calcined clay with 30% impurities. The addition of metakaolin refines pore structure, reduces large pores detrimental to strength, and promotes the formation of ettringite and other hydration products, thereby enhancing mechanical properties. This understanding of the role of metakaolin in LC3 supports its development as a commercially viable and eco-friendly alternative to OPC.

Keywords: Metakaolin, LC3, Hydration, Pozzolanic reaction, Mechanical properties