The microstructure and mechanical properties of cementitious materials comprised of limestone, calcined clay and clinker

Abstract

Limestone, calcined clay and cement (LC3) are one of the low carbon cement materials which are used as a partial substitution of clinker and Portland cement. In this study, the effects of limestone and calcined clay (LC2) on the mechanical properties and microstructure of mortars were studied under multi-scales. It could be concluded that the compressive strength decreased slightly with an increase in the LC2 content, but the flexural strength increased significantly due to the greater formation of crystalline aluminates in the LC3. The x-ray diffraction and thermal analysis results prove the pozzolanic activity of the calcined clay in the LC3 system which is in agreement with the results of the decreasing calcium hydroxide and the increasing ettringite content, and the LC2 could reduce the heat of the hydration of the LC3 significantly. Also, the formation of calcium hemicarboaluminate (3CaO·Al2O3·Ca[(OH)(CO3)0.5]·xH2O) and calcium monocarboaluminate (3CaO·Al2O3·CaCO3·xH2O), as well as the pozzolanic activity of the calcined clay contributed to the development of the mechanical strength.