Limestone calcined clay cement (LC3) is one of the most promising ways to further reduce the clinker factor as it provides satisfying mechanical and durability properties compared to other (blended) cements. Clays are as well abundant, widely available, and don’t result in CO₂ emissions during their activation process besides the energy required to calcine and mill them. Moreover, cement composed with such materials doesn’t require high grade clay material and can therefore tolerate rather high amounts of impurities.

On the other hand, such materials usually come with very high specific surface area resulting in challenging rheological properties.

One of the goals of this work was to study and understand the reasons for the pronounced issue of loss of workability observed in the case of LC3 type of binders. It has been found that the intrinsic reactivity of the calcined clays leads to the formation of early aluminate hydrates, most presumably ettringite, and appears to be a major factor for the loss of workability.

At clinker replacement levels up to 30%, traditional superplasticizers are sufficient to extend the slump life. However, these superplasticizers prove much less effective for replacement levels reaching 50% and above, where the loss of workability is particularly distinct.

Nonetheless we found some carbohydrate derivatives being able to control the formation rate of these early hydrates, resulting in extended workability without dramatically affecting the strength development. Such approaches would enable the broader use of such novel binders and help decarbonize the construction sector.