Date This project started on 01 January 2005 and ended on 01 December 2008
Status This project is Finished
Organic admixtures form an essential part of all modern cementitious formulations. This is particularly true for superplasticizers. As far as the main lines of their rheological action are concerned, we may consider that our current knowledge is satisfactory.
The main mechanisms have been identiﬁed, though neither entirely nor quantitatively related to molecular structures yet. The picture is much less satisfactory when it comes to the speciﬁc character of their interaction with the different mineral phases or mineral components of cements.
The lack of knowledge on these speciﬁc interactions is a source of problems, fortunately not frequent but often unexpected and ill-mastered, which impede the robustness of formulations. It is generally admitted that the main source of problems comes from the interaction of the admixtures with the aluminate phases, mainly 3CaO.Al2O3, which is highly reactive and plays a key role in the fresh paste immediately after mixing. Adsorption, co-precipitation or even intercalation on or in the early hydrates have all to be considered as possible sources of undesired interactions, leading possibly to a loss of availability and a loss of ﬂuidity.
The NANOCEM Core Project 3 "Organo-Aluminate Interactions" is focused on the interaction of superplasticizers with the so-called AFm phases (C4AHx). Parallel work has demonstrated that, as expected from its crystal structure and its low speciﬁc surface area, C3A itself cannot be an important source of SP sequestration.
On the contrary, AFm phases, which are formed in the very early times after mixing, are a major potential source of SP sequestration, thanks to their swelling layered structure and their positive layer charge. AFm phases belong to the general family of Layered Double Hydroxides (LDHs), also called anionic clays.
The recent materials chemistry literature contains a wealth of examples showing that these layered minerals are able to form organo-mineral compounds with a wide variety of anionic organics, from simple molecules to large molecular weight polymers, including biopolymers. The formation mechanism may be true intercalation or co-precipitation or, more probably, templated crystal growth. Previous work has shown that super-plasticizers co-precipitated with AFm phases form quasi-amorphous organo-mineral compounds.
The aim of Core project 3 is to establish the structure of these organo-mineral compounds and to understand the conditions for their formation in molecular and cement chemistry terms. So far, the efforts have been focused on the detection of possible intimate interactions between the mineral and the organic molecules. NMR was used as the main tool, for its ability to detect short- and meso-range interactions, even in a disordered environment. This approach makes it possible to study the molecular and cristallochemical parameters of these interactions.
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