Clays for Low‐Carbon Cements: Overview, Progress, and Challenges

TL;DR

This paper reviews the use of activated clays as eco-friendly alternatives to traditional cement, aiming to reduce carbon emissions while maintaining strength and durability.

Contribution

The paper provides a critical overview and identifies key challenges for the widespread adoption of activated clays in low-carbon cements.

Findings

LC3-50 blends reduce CO2 emissions by ~40% compared to Portland clinker.

Activated clays show high compressive strength and good resistance to chloride and sulfate attacks.

Challenges include low early strength and workability loss, which are being addressed with admixtures and curing methods.

Abstract

The replacement of Portland clinker with supplementary cementitious materials is a key approach to reducing the embodied carbon content of concretes. In this context, a widely studied family is the “limestone calcined clay cements, LC3.” Within this eco‐friendly family of materials, one composition is gaining popularity, LC3‐50, a blend of ~50% of Portland clinker, 30% of activated clay, 15% of limestone and 5% of gypsum. This interest is due to a ~40% reduction of CO2 emissions compared to Portland clinker, together with high compressive strengths after 7 days and very good durability against chloride and sulfate attacks. However, limitations still exist, such as low strengths at 1 day, workability loss during the first 2 h and reduced carbonation resistance. These drawbacks are being overcome with tailored admixtures and curing approaches. Here, after introducing low‐carbon cements, pozzolans, and pozzolanic reactions, as well as phyllosilicate minerals, attention is given to recent progress in thermal and mechanical, aka mechanochemical, activations. Then, general correlations are established to assist in predicting compressive strength. This work concludes by highlighting the challenges that must be overcome for the widespread adoption of these classic rocks processed to yield advanced materials with the highest possible pozzolanic reactivity.

This review provides a critical overview of recent developments of activated clays to function as artificial pozzolans. After a thorough description of the clays that yield good pozzolanic performances, selected examples are given on thermal and mechanical activations. Chiefly, general correlations are extracted from reported data despite its scattered nature. Finally, key challenges are identified and discussed.

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