Performance of High-Workability Mortars Incorporating Metakaolin as a Partial Cement Replacement

Area of Science:

• Materials Science
• Civil Engineering
• Sustainable Construction

Background:

• Portland cement (CEM I) production has significant environmental impacts.
• Supplementary cementitious materials (SCMs) are explored to mitigate these impacts.
• Metakaolin (MK) is a pozzolanic material with potential as an SCM.

Purpose of the Study:

• To investigate the effects of metakaolin (MK) as a partial replacement for CEM I in high-workability mortars.
• To evaluate fresh-state properties, mechanical performance, microstructure, and carbon footprint.
• To determine optimal MK replacement levels for performance and sustainability.

Main Methods:

• Mortars prepared with 0-50% MK replacement of CEM I.
• Constant water-to-binder ratio and superplasticiser dosage.
• Assessment of fresh-state behaviour, mechanical properties (compressive/flexural strength), durability indicators (water absorption, capillary uptake), and microstructural analysis (SEM, TGA, XRD).
• Comparative carbon footprint analysis.

Main Results:

• Increasing MK content reduced flowability but maintained high workability up to 20% replacement.
• MK replacement up to 10% retained 90-95% of control strength; higher levels reduced strength.
• Moderate MK (20-30%) improved durability indicators by refining pore structure.
• Microstructure showed portlandite consumption and C-A-S-H formation at moderate MK levels; unreacted MK at excessive levels.
• MK incorporation proportionally reduced embodied CO2 emissions.

Conclusions:

• Metakaolin (MK) can be effectively used as a supplementary cementitious material in mortars.
• Replacement levels of 10-20% offer the best balance of mechanical properties, durability, and reduced carbon footprint.
• MK contributes to the development of low-carbon, high-workability construction materials.