Project Details
Projekt
Component additive approach to predict Cement paste Rheology considering Secondary Cementitious Materials and their special effect on thixotropy and concrete de-airing behaviour
Applicants
Professor Dr.-Ing. Michael Haist; Professor Dr.-Ing. Horst-Michael Ludwig; Professor Thorsten Schäfer, Ph.D.
Subject Area
Construction Material Sciences, Chemistry, Building Physics
Term
since 2021
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 452020613
The workability and the de-airing behaviour of fresh concrete are primarily a function of the rheological properties of the fresh cement paste contained therein. The flow behaviour of the paste is influenced by the water content, the particle inventory, the hydration behaviour, the temperature and shear acting onto the paste (among others). By employing secondary cementitious materials (SCMs) like calcined clays or limestone powders, the environmental footprint of concrete can be significantly improved, however leading to pronounced changes in the rheological properties. The influence of these new binders onto rheology however is vastly unknown so far. Calcined clays e.g. are known to significantly increase the thixotropy of the concrete, which will have detrimal effect on the de-airing behaviour.The goal of the proposed project CONCERT-CCair is on the one hand, to significantly extend the rheological model, developed in funding period I of the project, from Ordinary Portland Cement (OPC) to calcined clays and limestone powders. This required extensive knowledge on the effect of hydration on the particle interaction behaviour and onto rheology. On the other hand, the influence of paste rheology onto the de-airing behaviour of fresh concrete shall be studied. Here, extensive experimental investigations shall be carried out in order to understand the de-airing mechanisms and model the process.In order to solve the open scientific questions described above, in a first step, the particle interaction behaviour of calcined clays and limestone powder (in combination with OPC) is studied. The results will allow to significantly expand the surface complexation model developed in funding period I by incorporating secondary cementitious materials. This work, however, can only be successful in predicting the rheological properties, when the hydration of the particles – i.e. the dissolution and precipitation – are thoroughly pictured. Thus, extensive investigations on the hydration behaviour of calcined clays will be carried out. All of these investigations are accompanied by rheological tests, with which the influence of hydration, particle interaction etc. can be quantified onto the pastes flow behaviour. The combined results will yield in a rheological model, in which cement paste is idealized as a mixture of a colloidal Bingham body, in which larger binder particles are suspended and which scale the rheological properties of the colloidal brine.Based on this model, in a final step, the influence of the rheological properties of the binder paste onto the de-airing behaviour is investigated. This is done with (possible) partners from FP I (such a collaboration would be extremely helpful but is not an essential prerequisite). It is the goal in this part of the project to investigate and model the interaction behaviour of the air bubbles with the paste inventory and – based on that – to predict the de-airing behaviour based on rheological criteria.
DFG Programme
Priority Programmes
