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

新拌混凝土的工作性和除气性能主要取决于其中所含的新拌水泥浆体的流变性。糊状物的流动行为受水分含量、颗粒含量、水化行为、温度和作用于糊状物上的剪切力等因素的影响。通过使用二次胶凝材料(SCM)，如煅烧粘土或石灰石粉，可以显著改善混凝土的环境足迹，但会导致混凝土流变性的显著变化。然而，到目前为止，这些新的粘结剂对流变学的影响是非常未知的。例如，已知的煅烧粘土会显著增加混凝土的触变性，这将对干燥行为产生不利影响。拟议的项目Concert-CCair的目标一方面是将项目第一阶段开发的流变模型从普通波特兰水泥(OPC)显著扩展到煅烧粘土和石灰石粉。这需要广泛了解水化作用对颗粒相互作用行为和流变学的影响。另一方面，应研究浆体流变性对新拌混凝土干燥性能的影响。为解决上述悬而未决的科学问题，首先研究了煅烧粘土与石灰石粉(结合OPC)的颗粒相互作用行为。这一结果将允许通过纳入二次胶凝材料来显著扩展在资金阶段I中开发的表面络合模型。然而，这项工作只有在对颗粒的水化--即溶解和沉淀--进行彻底描绘的情况下，才能成功地预测其流变性。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，利用这些试验可以量化水化、颗粒相互作用等对浆体流动行为的影响。综合结果将产生一个流变模型，在该模型中，水泥浆体被理想化为胶体宾汉体的混合物，其中较大的粘结剂颗粒被悬浮在其中，并衡量胶体盐水的流变性。在该模型的基础上，在最后一步中，研究了粘结剂浆体的流变性对干燥行为的影响。这是与FP I的(可能的)合作伙伴一起完成的(这样的合作将非常有帮助，但不是必要的先决条件)。该项目这一部分的目标是调查和模拟气泡与膏体库存的相互作用行为，并在此基础上基于流变学标准预测脱气行为。

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.