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

考虑二次胶凝材料及其对触变性和混凝土脱气行为的特殊影响的组分添加剂方法预测水泥浆流变性

• 批准号: 452020613
• 负责人: Professor Dr.-Ing. Michael Haist
• 金额: --
• 依托单位: Institut für Baustoffe
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/452020613?language=en
• 关键词: Component; additive; approach; predict; Cement

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.

新拌混凝土的和易性和脱气性能主要取决于其中所含新拌水泥浆的流变性能。糊剂的流动行为受水含量、颗粒存量、水合行为、温度和作用于糊剂上的剪切（以及其他因素）的影响。通过采用二次胶凝材料（SCM），如煅烧粘土或石灰石粉，混凝土的环境足迹可以显着改善，但导致流变性能的显着变化。然而，到目前为止，这些新的粘合剂对流变学的影响还很不清楚。例如，众所周知，煅烧粘土会显著增加混凝土的触变性，这将对脱气行为产生不良影响。CONCERT-CCair项目的目标是，一方面，显著扩展在项目第一阶段开发的流变模型，从普通波特兰水泥（OPC）到煅烧粘土和石灰石粉末。这需要对水合作用对颗粒相互作用行为和流变学的影响有广泛的了解。另一方面，应研究浆体流变性对新拌混凝土脱气行为的影响。在这里，我们需要进行大量的实验研究，以了解脱气机理并对脱气过程进行建模。为了解决上述公开的科学问题，我们首先研究了煅烧粘土和石灰石粉（结合OPC）的颗粒相互作用行为。结果将允许显着扩展的表面络合模型，在资金周期I通过纳入二次胶凝材料。然而，这项工作只能在预测流变性能方面取得成功，当颗粒的水合作用-即溶解和沉淀-被彻底描绘时。因此，煅烧粘土的水化行为将进行广泛的调查。所有这些研究都伴随着流变学测试，通过这些测试，可以量化水化、颗粒相互作用等对膏体流动行为的影响。结合的结果将产生在一个流变模型，其中水泥浆被理想化为一个胶体宾汉体的混合物，其中较大的粘合剂颗粒悬浮和缩放的胶体brine. Based的流变性能的盐水，在这个模型的基础上，在最后一个步骤，对脱气行为上的粘合剂浆的流变性能的影响进行了研究。这项工作是与第一个方案计划的（可能的）伙伴进行的（这种合作将非常有帮助，但不是一个必要的先决条件）。该项目这一部分的目标是调查和模拟气泡与浆料库存的相互作用行为，并在此基础上根据流变学标准预测脱气行为。