Properties and occurrence of clay resources for use as supplementary cementitious materials: a paper of RILEM TC 282-CCL

The acceleration of the impact of climate change prompts the cement industry for swift and effective solutions to reduce a large part of the carbon dioxide associated with cement manufacture. The use of Supplementary Cementitious Materials, SCM, such as fly ash and slag have enabled so far, the possibility of partially replacing clinker, the most energy intensive and main responsible component in cement for carbon emissions. However, reserves of both SCM are declining and their price is increasing, and replacing more than 30% clinker with these SCM can compromise early strength. In recent years a global team of scientists from Switzerland, Cuba and India have proven the possibility of dropping clinker content in cement down to 50% or even less through the combined use of calcined kaolinitic clays and limestone, both cheap and abundant materials, to produce a new cement called “LC3”. The resulting cement matches the properties of a CEM I (EN‐197) at all ages, and carbon emission reduction is reportedly around 25‐40%, depending on the cement to compare with. This paper presents the accumulated experience in the investigation of the new cementitious system and the introduction at the industrial level. Issues like the choice of the right clay, calcination technology, product formulation, standardization and economic feasibility will be discussed. The information in this paper is intended to encourage industrial partners to invest in the new technology.

Section: 1mentioning

confidence: 99%

Practical experiences in the use of a combination of calcined clay and limestone as clinker substitute in cement

Martirena

2023

“…2:1 clay minerals like illite, smectite and montmorillonite as well as 2:1:1 chlorite are rather formed in cold regions as in the northern or southern hemisphere [8,9]. Alujas Diaz et al [10] provide a comprehensive overview on the global occurrence of clay minerals. Maier et al [11] highlight the domination of 2:1 clay minerals in Germany in their view on local availability of the different clay types.…”

Section: Availabilitymentioning

confidence: 99%

“…At the same time they transform into inert high temperature phases at lower temperatures than kaolinite [15]. As a result, their temperature window for thermal activation is narrower and pozzolanic reactivity is lower [10]. Figure 2 summarizes some practical production temperatures (upper x-axis) and the corresponding CO2 emission originating from the raw material and the fuel used for production [16] with data from [14].…”

Section: Productionmentioning

confidence: 99%

1:1 or 2:1 ‐ Does it matter for calcined clay as supplementary cementitious material?

Thienel,

Scherb,

Beuntner

et al. 2023

Self Cite

Calcined clays are the most promising future supplementary cementitious material which are capable of replacing fly ashes and blast furnace slag on the long run due to their potential to achieve high cement replacement levels and their global availability. In the last decade most research has focused on calcined clays rich in the 1:1 kaolinite. Clay with less than 20 to 25 % kaolinite were seen as worthless. Even the content of 2:1 phyllosilicates in the kaolinitic clays was neglected and not even mentioned although especially these clays are dominant in areas like central and northern Europe. Here, highly kaolinitic clays are rare or used by other industries leading to high prices. This paper is based on published works and highlights whether information obtained for calcined 1:1 dominated clays can be applied for calcined 2:1 dominated clays or not and where further research is needed.

“…Clays can be activated through calcination at about 800 °C for 1-2 hours for static calcination and a few seconds for flash calcination, albeit at a higher temperature. This process turns kaolinite into metakaolin which is highly amorphous and has great potential for pozzolanic activity [3,4]. The combined use of calcined clay and limestone in cement guarantees a number of physical and chemical interactions between the SCMs and clinker.…”

Section: Introductionmentioning

confidence: 99%

Influence of clay impurities on the performance of calcined clay‐limestone cements

Matschei,

Muzenda,

Georget

2023

The use of blended cements including novel supplementary cementitious materials is the most powerful lever to cut down the carbon footprint of cementitious materials. This has led to an increased interest in research on calcined clay limestone cement (CCLC) over the last years. In this study, we investigate the fresh and early hydration properties of CCLC using kaolinitic clays with a wide range of chemical and mineralogical compositions, which are all of industrial origin. Results show that early performance of calcined clays is not only dependent on kaolinite content but that the total specific surface area of the raw and calcined clays plays a key role in the onset and evolution of rheological properties as well as early hydration and reactivity. Further analysis indicated that among secondary mineral impurities, iron phases affect the physiochemical properties of calcined clays. This is shown by the high specific surface area of these clays. It appears possible that by causing higher kaolinite structure disorder, iron phases also impact hydration.