Optimisation of Using Low-Grade Kaolinitic Clays in Limestone Calcined Clay Cement Production (LC3)

Area of Science:

• Materials Science
• Civil Engineering
• Sustainable Construction

Background:

• Limestone calcined clay cement (LC3) is a promising low-carbon alternative to Portland cement.
• Optimal LC3 performance requires a minimum kaolinite content in calcined clays.
• Local clays may have insufficient kaolinite, necessitating performance enhancement strategies.

Purpose of the Study:

• To evaluate the use of low-kaolinite clay from Valencia, Spain, for LC3 production.
• To investigate enhancing the performance of LC3 made with this clay by incorporating metakaolin.
• To analyze the impact of metakaolin addition on the mechanical properties and hydration of LC3.

Main Methods:

• Physico-chemical characterization of raw materials.
• Microstructural analysis of cement pastes (isothermal calorimetry, thermogravimetry, XRD).
• Mechanical testing of mortar compressive strength at various curing ages.

Main Results:

• LC3 mortars with higher calcined kaolinite content (achieved via metakaolin addition) showed increased compressive strength.
• Metakaolin additions accelerated LC3 hydration kinetics, promoting AFm phase formation (monocarboaluminate, hemicarboaluminate).
• Significant strength improvements were observed: 6% metakaolin enhanced 90-day strength, 10% surpassed control at 28 days, and 15% exceeded control at 7 days.

Conclusions:

• Metakaolin effectively enhances the mechanical performance of LC3 made with low-kaolinite clay.
• The addition of metakaolin improves hydration kinetics through nucleation effects and AFm phase formation.
• Combining less reactive local clays with highly reactive metakaolin is a viable strategy for sustainable cement production.