Hydration and mixture design of calcined clay blended cements: review by the RILEM TC 282-CCL

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.

Section: Microstructuresupporting

confidence: 72%

Section: Reactivitymentioning

confidence: 98%

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

Thienel,

Scherb,

Beuntner

et al. 2023

“…The synergy between calcined clay and limestone prompts for an optimal molar ratio, which is normally 2/1 [7,12]. However, these proportions can be changed according to the conditions of the supply of raw materials.…”

Section: Product Formulationmentioning

confidence: 99%

“…When calcined clays are used in combination with limestone in a Portland cement system the alumina phases will further react with it and form carboaluminates (hemi or mono), which are reaction products capable of filling out porosity, and thus moving the boundaries for clinker substitution further, thus enabling reduction of 25-40% of carbon emissions associated with cement manufacture. [6][7][8] This extended abstract presents the accumulated experience in the investigation of the new cementitious system and the introduction at the industrial level.…”

Section: Introductionmentioning

confidence: 99%

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

Martirena

2023

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.

“…These differences primarily result in a large extent of the mineralogy and content of the included clay minerals (other than metakaolin). Investigations using such common clays show that below 30 mass percent of kaolinite content in the clay, the reactivity of clay minerals like illite, smectite or mixed-layer minerals becomes highly significant [20][21][22].…”

Section: Introductionmentioning

confidence: 99%

Influence of calcined clay on micromechanical properties and creep of hardened cement paste

Deiters,

Rozanski,

Schack

et al. 2023

A highly interesting approach to lower CO2 emissions in cement and concrete industry is to reduce the cement clinker content while using supplementary cementitious materials (SCMs) such as calcined clays. Whereas for classical Portland cement clinker, comprehensive studies are already available on the microstructural development during hydration as well as on the resulting macromechanical properties such as compressive strength or long‐term deformation behavior, such understanding is missing for calcined clays. In this paper, systematic micromechanical investigations using microindentation of hardened cement pastes with various amounts of calcined clay at ages up to 28 days are presented. The micromechanical results indicate a faster strength development as well as a lower overall porosity of the classical clinker system compared to mixtures containing calcined clay. Looking to creep, the indentation creep modulus is higher for pure OPC mixtures compared to calcined clay systems up to seven days, indicating less pronounced creep. Beyond this age, however, the differences in creep behaviour became less pronounced. The outcomes suggest that the reactivity of the calcined clay seems to be decisive when it comes to mechanical properties and creep behaviour rather than the rate of substitution.