Clay calcination technology: state-of-the-art review by the RILEM TC 282-CCL

Abstract

The use of calcined clays as supplementary cementitious materials provides the opportunity to significantly reduce the cement industry’s carbon burden; however, use at a global scale requires a deep understanding of the extraction and processing of the clays to be used, which will uncover routes to optimise their reactivity. This will enable increased usage of calcined clays as cement replacements, further improving the sustainability of concretes produced with them. Existing technologies can be adopted to produce calcined clays at an industrial scale in many regions around the world. This paper, produced by RILEM TC 282-CCL on calcined clays as supplementary cementitious materials (working group 2), focuses on the production of calcined clays, presents an overview of clay mining, and assesses the current state of the art in clay calcination technology, covering the most relevant aspects from the clay deposit to the factory gate. The energetics and associated carbon footprint of the calcination process are also discussed, and an outlook on clay calcination is presented, discussing the technological advancements required to fulfil future global demand for this material in sustainable infrastructure development.

Acid Activated Smectite Clay as Pozzolanic Supplementary Cementitious Material

“…The highest reactivity was observed in sample 8H90 which was subjected to 8 h of acid treatment. This also compares unfavourably to calcining where the treatments are usually conducted in <1 h [38]. The use of 5 M HCl is the greatest contributor to embodied carbon in this sample.…”

Bending Behavior of Fiberglass Textile-Reinforced Thin Geopolymer Mortar Panels

“…The current study adopted an endothermic procedure to change the kaolinites to metakaolins; this conversion process requires tremendous energy to remove the hydroxyls chemically-bonded ions by destroying the crystal structure kaolinites, producing amorphous silica and alumina phases having notable surface areas. According to previous studies [8], the optimal activation temperatures can range from 550 -850 °C; based on Snellings R. et al (2012), the temperature range is 650 -750 °C is considered the most likely to be used. The chemical components of MK are detailed in Table 1.…”

“…TRC reinforcement has recently resulted in innovative cementitious composites having a significant strength and ductility under static and dynamic loading. TRC displays closer, narrower and regular-spread cracks in tension and flexural due to the alignment of the fiber [8].…”

Designing Efficient Flash-Calcined Sediment-Based Ecobinders

“…As a matter of fact, this process includes dehydroxylation that activates the material with thermal excitation between 700 °C and 850 °C. For products containing undesirable non-active materials, complex calcium-based minerals, sulfur-rich phases [ 38 ], or phosphates [ 39 ], flash calcination can be considered to be more advantageous than traditional treatment methods such as rotary calcination. Flash calcination is also able to activate Muscovite, illite, phlogopite, and kaolinite, which are among the clay minerals that show pozzolanic activity after appropriate heat treatment and are generally present in sediment minerals.…”