Activated clay – Grinding makes all the difference

Calcined clays will soon present an attractive opportunity to produce concretes that are optimized in both environmental and engineering terms. This will provide the construction industry with a versatile yet sophisticated material for a wide range of applications in concrete technology. Critical to the successful use of calcined clays is their processing, which includes calcination and grinding. To date, only a few studies have been conducted that investigated the effects of grinding on the properties of calcined clays. This is, in part, attributable to the fact that there are hardly any industrial production facilities for clay calcination. As a result, materials are not available in the quantities required for industrial-scale grinding tests. However, the grinding process has a significant impact on the reactivity and performance of calcined clays. The first part of this presentation refers to tests carried out on calcined clay granules at a pilot plant of Gebr. Pfeiffer using a vertical roller mill (VRM). In addition to the findings obtained for the grinding process (specific power consumption, wear rate of grinding parts), the results related to the material (fineness, physical characteristics, and reactivity) will be discussed and compared with empirical values established for conventional supplementary cementitious materials. The second part of the presentation provides in-depth insights into the option of thermomechanical activation (i.e. grinding and calcination merged into a single-stage process), which was tested for different clays in a ZIM project conducted jointly with research partners Gebr. Pfeiffer, Institut für Werkstoffe des Bauwesens and TBS Transportbeton. Incomplete dehydroxylation of the phyllosilicates contained in the clays proved to be a critical parameter affecting both the performance and the durability of the concretes and producing properties not previously known from calcined clays.


Related articles:

Issue 02/2020 A challenge for concrete technology?

Reduction of CO2 emissions by means of calcined clays

Calcined clays offer the opportunity to fulfil environmental requirements, to counteract the shortage of resources and to provide the market with high-performance binders, in synergy with other...

Issue 02/2017 New aspects of concrete technology pertaining to their use

Calcined clays as alternative supplementary ­cementitious materials

High-performance supplementary cementitious materials (SCMs) will be required to improve the technical and environmental characteristics of concrete. These SCMs will substitute conventional binders to...

Issue 02/2018 Cement manufacturing

Innovative superplasticizers for thermally activated (calcined) clays

The use of thermally activated (calcined) clays as supplementary cementitious materials (SCMs) in cement represents a promising optimization step for ordinary Portland cement in terms of environmental...

Issue 02/2013

Calcined clays in modern construction materials – Fundamentals and application potentials

The use of calcined clays as additions in mortars and concretes goes back to antiquity. In the context of current sustainability discussions – as well as due to the increasingly greater demands...

Issue 06/2023

Calcined clays in CO2-reduced cements – challenges ranging from raw materials to concrete

The climate protection aims of the German government call for fast and effective action for conversion to CO2-neutral production methods. For the industrial area of action, amendment of the German...