Component additive approach to predict Cement paste Rheology considering Secondary Cementitious Materials and their special effect on thixotropy and concrete de-airing behaviour

新拌混凝土的和易性和脱气性能主要是其中所含新拌水泥浆的流变性能的函数。膏体的流动行为受含水量、颗粒库存、水化行为、温度和作用于膏体的剪切（以及其他因素）的影响。通过采用二次胶凝材料（SCMs），如煅烧粘土或石灰石粉末，混凝土的环境足迹可以显著改善，但会导致流变特性的显著变化。然而，到目前为止，这些新粘合剂对流变性的影响还非常未知。例如，已知煅烧粘土会显著增加混凝土的触变性，这将对通风行为产生不利影响。提议的项目CONCERT-CCair的目标一方面是将项目资助期I开发的流变模型从普通波特兰水泥（OPC）扩展到煅烧粘土和石灰石粉末。这需要广泛了解水化对颗粒相互作用行为和流变学的影响。另一方面，研究膏体流变对新拌混凝土脱气性能的影响。在这方面，需要进行广泛的实验研究，以了解脱气机理并模拟该过程。为了解决上述开放性的科学问题，在第一步，研究了煅烧粘土和石灰石粉末（与OPC结合）的粒子相互作用行为。该结果将允许通过纳入二次胶凝材料显着扩展在资助期I开发的表面络合模型。然而，这项工作只能成功地预测流变性能，当颗粒的水化作用-即溶解和沉淀-被彻底描绘出来。因此，将对煅烧粘土的水化行为进行广泛的研究。所有这些研究都伴随着流变试验，通过流变试验，可以量化水化，颗粒相互作用等对膏体流动行为的影响。综合结果将产生一个流变性模型，在该模型中，水泥浆被理想化为胶体宾厄姆体的混合物，其中较大的粘结剂颗粒悬浮在其中，并影响胶体盐水的流变性能。在此模型的基础上，在最后一步，研究了胶结膏体的流变特性对脱气行为的影响。这是与FP I的（可能的）合作伙伴一起完成的（这种合作将非常有帮助，但不是必要的先决条件）。这部分项目的目标是研究和模拟气泡与膏体库存的相互作用行为，并在此基础上根据流变标准预测脱气行为。

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.