PCE-based superplasticizers for composite cements containing calcined clay

Global cement production currently amounts to about 4.4 billion tons per year. Unfortunately, this comes with a huge CO2 emission which represents approximately 7 % of total anthropogenic CO2 output. A major source (~ 60 %) of the CO2 emission in cement manufacture is the decarbonation of limestone. Hence, a more eco-friendly binder is required.

Thermally activated (calcined) clays (CCs) have been identified as a very promising approach to reducing the clinker factor in cement and to reducing its CO2 footprint. A typical example of such an eco-friendly binder is LC3, which contains 50 % clinker, 30 % CC, 15% limestone powder and 5 % gypsum.

The problem of using calcined clays lies in the huge variation of natural deposits with respect to their clay composition. Depending on the type of clay, different calcination temperatures are required. Moreover, CCs containing high amounts of calcined kaolin (metakaolin) are favorable with respect to early strength development, but significantly increase the water demand which necessitates the addition of dispersing polymers (superplasticizers) to such cements. On the other hand, meta illites and smectites do not impact the water demand much, but they provide relatively poor early strength which prompts the need for hydration accelerators.

This paper highlights the progress made so far with respect to the problems mentioned above and addresses potential solutions based on specifically designed polycarboxylate comb polymers. Their chemistry, molecular properties, and physico-chemical interaction with cement and CC will be presented.

It is concluded that calcined clays of broad variation relative to their composition can be used successfully in blends with Portland cement clinker, provided that they are applied in combination with superplasticizers tailored to their specific surface chemistry. This way, in cement production potential savings of approx. 1 to 1.3 billion tons of CO2 seem to be achievable, thus making cement “greener”.

Related articles:

Issue 2018-02 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 2017-02 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 2020-02 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 2014-02 New additions to concrete

Effective alternatives for precast concretes –

Problem statement Precast concretes are subject to demanding materials-related parameter requirements as well as to commercial and ecological aspects. The importance of these factors will further...

Issue 2013-02

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...