Here - Institute for Building Materials - ETH Zürich

Controlling building materials microstructure through the mixing stepHélène Lombois-BurgerLafarge – LCR (France)Mixing is a key step for the production of cement pastes or concretes. Indeed, eventhough very short this stage has a major influence on the quality of the microstructureof the mix and thus on the materials performances. Its impact extends on the wholematerial’s service life, from the rheology to the mechanical strength and even thedurability. These microstructural characteristics due to the mixing are the result of acomplex interplay between process and mix design parameters.Using several techniques to monitor the mixing extent in terms of homogenization,de-agglomeration of the fine particles, prevailing inter-particle forces, allows:(i) To unveil mixing mechanisms, and demonstrate the role of both processparameters (sequence for the introduction of the components, mixingtime/speed/energy, volume effects, etc) and mix design ones such as coarse aggregateproportion for instance. Mixing optimization consists then in obtaining the bestmicrostructure while shortening the process duration and required energy.(ii) To monitor mix design levers such as packing effects, water content, competitionbetween admixtures, etc39