Understanding workability of low carbon cements through advanced water detection techniques

Area of Science:

• Materials Science
• Sustainable Construction Materials
• Cement Chemistry

Background:

• Limestone Calcined Clay Cement (LC3) offers a sustainable alternative to Ordinary Portland Cement (OPC), reducing CO₂ emissions.
• The impact of calcined clay on the fresh-state workability of cementitious materials remains incompletely understood.
• Understanding these mechanisms is crucial for optimizing LC3 applications in construction.

Purpose of the Study:

• To investigate the effect of varying calcined clay content on the workability and early hydration of LC3 pastes.
• To elucidate the mechanisms behind the observed changes in rheology and water demand.
• To correlate fresh-state properties with long-term mechanical performance.

Main Methods:

• Formulation of LC3 cements with diverse calcined clay proportions.
• Utilized ¹H Time-Domain Nuclear Magnetic Resonance (TD-NMR) to quantify free water content.
• Employed Differential Scanning Calorimetry (DSC) for early hydration analysis.
• Conducted rheological measurements (mortar flow-table tests, rheometer) to assess workability and paste behavior.

Main Results:

• Increased calcined clay content led to accelerated free water consumption.
• Higher calcined clay content significantly increased superplasticizer demand and altered paste rheology (yield stress, viscosity).
• Early hydration analysis confirmed rapid water depletion in the presence of calcined clay.

Conclusions:

• Calcined clay plays a dual role, influencing both fresh-state workability and long-term strength development in LC3.
• Rapid water consumption by calcined clay explains the increased rheological challenges and superplasticizer requirements.
• LC3 formulations demonstrate competitive, and in some cases superior, 28-day mechanical performance compared to OPC CEM I, highlighting its viability as a sustainable cementitious material.