Using Metakaolin as an Enhancing Component in Supersulfated Cement: A Comprehensive Evaluation.

Area of Science:

• Materials Science
• Civil Engineering
• Geochemistry

Background:

• Supersulfated cement (SSC) is a sustainable alternative binder.
• Enhancing the early strength development of SSC is crucial for practical applications.
• Metakaolin (MK) is a reactive supplementary cementitious material (SCM).

Purpose of the Study:

• To investigate the impact of metakaolin (MK) content on the hydration, rheology, and mechanical properties of supersulfated cement (SSC).
• To determine the optimal MK dosage for enhancing early strength and microstructure of metakaolin-supersulfated cement (MSSC).
• To elucidate the hydration mechanisms and phase evolution influenced by MK addition.

Main Methods:

• Systematic variation of MK content (0-30 wt%) in SSC formulations.
• Evaluation of hydration thermodynamics, flowability, and setting time.
• Comprehensive characterization using techniques like XRD, FTIR, TG-DTG, and SEM-EDS.
• Mechanical property testing, including compressive strength at early and later ages.

Main Results:

• MK addition accelerates early hydration by providing nucleation sites.
• Optimal MK content of 25 wt% yielded significant improvements in early and 28-day compressive strengths (up to 208.87% of control).
• MK's pozzolanic activity promotes the formation of ettringite (AFt) and C-(A)-S-H, refining the pore structure.
• Excessive MK (30 wt%) reduced strength due to limited portlandite availability.

Conclusions:

• 25 wt% MK is identified as the optimal dosage for enhancing SSC performance, particularly early strength.
• MK addition positively influences the hydration kinetics and microstructure of SSC.
• The findings support the use of MK as an effective SCM for sustainable cementitious materials with improved early strength.