Characterisation of vegetal compounds responsible for the setting delays in hydraulic binders

Abstract

Biobased materials, integrating vegetal compounds in their composition, are used for various civil engineering applications. However, mechanisms underlying the association between plants and mineral binders are not well known. Issues have been raised concerning the durability or strength performance, attributed as a consequence of the manufacturing process. Especially, during the setting phase of hydraulic binders. Indeed, some studies showed the implication of vegetal molecules acting as hydration retarders.These molecules come from the leaching of plants by water during mixing, which are also known as extractives. The main molecules identified to have a role are sugars and a few organic acids. However, several studies suggest that other molecules derived from plant material, such as polyphenols, have an influence on the setting of the hydraulic binder as well. Moreover, the chemical composition of plants is subject to great variability, as well as many other characteristics, depending on variety, growth conditions and seasons…

Here, we compare two types of raw material used in the fabrication of biobased materials. These materials have significative differences in strength performance correlated with a difference of hydration time found with calorimetric assays. The difference between the raw materials is also found in the chemical investigation, indeed the HPLC analysis on sugars showed a significative difference on certain molecules, especially on glucose, which is a well-known sugar acting as hydration retarders. Moreover, a focus on other compounds type was achieved, especially on polyphenols. By observation and UV-Vis analysis on crudes water extracts, quantitative and qualitative differences were found between raw materials. Roughly, polyphenols, particularly flavonoid-type molecules seem to be present in extracts, a consistent element correlated with calorimetric assays and literature. This is a relevant clue suggesting that a deeper analysis of these molecules could therefore shed some light on this topic.