Superposing particle interactions and hydration effects on the rheology of cementitious systems in the presence of different ions in the aqueous phase – (SPHERE DOS)

混凝土技术的未来挑战要求在浇注和早期硬化过程中具有量身定制的流变性。坍落度保持时间和凝结时间的单独调整在即时制造、预拌混凝土、喷射混凝土、干拌砂浆和3D打印等技术中发挥着重要作用。高效减水剂通过吸附作用影响流变性，而促进剂则通过影响水化反应来影响水化反应。除高效减水剂外，所使用的外加剂会影响孔溶液化学以及颗粒的形态和相互作用，从而使本已复杂的高效减水剂效果复杂化；取决于化学和剂量，所有这些都在几分钟内发生。由于高效减水剂的效果很大程度上依赖于水泥的水化反应，因此在浇注过程中，快速水化已经引起了显著的流变性变化。对随时间变化的粘度变化的错误估计可能在宏观上导致填充不当、气孔含量变化、粘结性差、冷连接问题、纤维分布不均匀等方面。然而，离子浓度的快速变化、颗粒间的相互作用、颗粒形态和固体体积分数的快速变化，进而影响了颗粒间的分散力和高效减水剂的效果，这是微观上的根本原因。SPHERE项目旨在从介观到宏观的不同维度上了解流变性效应。总体目标是了解加速胶凝体系在从浇注到凝结的关键加工步骤中的流变性。为了了解流变学变化的基本机制，需要从颗粒相互作用和相互作用的水化效应的角度来研究该体系。最终，需要了解和评估观察到的效应与应用级别的相关性，这意味着必须进行从粒子界面到大规模具体应用的提升。直接粒子相互作用将主要使用原子力显微镜在简化的模型系统上进行各种条件下的研究。这些结果将有助于理解由于孔溶液化学变化以及离子和聚合物在颗粒表面的吸附而引起的流变现象的变化。将利用X射线衍射仪、扫描电子显微镜、原子力显微镜、超声、差热分析等技术来研究形貌变化和物相演变的影响。从溶液水平到浆体、砂浆和混凝土流变仪，以及通过应用技术，如喷涂、大规模浇注和标准新拌混凝土技术，将在不同的尺度上检测流变性响应。

The future challenges of concrete technology demand for tailored rheological properties during the casting and early hardening process. The individual adjustment of slump retention and setting time plays a major role for technologies such as just-in-time manufacturing, target slump delivery of ready-mixed concrete, sprayed concrete, dry-mixed mortar and 3D-printing. While superplasticizers affect the rheology due to adsorption, accelerators are used to influence the hydration reaction. The employed admixtures beyond superplasticizers complicate the already complex superplasticizer effects by affecting the pore solution chemistry, as well as the morphology and interactions of the particles; depending upon the chemistry and dosage all happening within minutes. Since the effect of superplasticizers strongly depends upon the cement hydration reaction, rapid hydration causes significant rheology changes already during the casting process. A false estimation of the time dependent viscosity change can result macroscopically in improper filling, varied air pore content, poor bond, cold joint problems, inhomogeneous fibre distribution and other aspects. However, the root cause can be found on the microscopic scale in rapid changes of the ionic concentration, particle interactions, changes of the morphology and the solid volume fraction, which furthermore affect the dispersing forces between particles and the effectiveness of superplasticizers.The SPHERE project aims at understanding the rheological effects on different dimensional scales; from mesoscopic to macroscopic. The general objective is to understand the rheology of accelerated cementitious systems during the critical steps of processing from casting until setting. In order to understand the fundamental mechanisms underlying the rheological changes, the system needs to be studied from the perspective of particle interactions as well as from hydration effects that mutually interact. Eventually, the observed effects need to be understood and evaluated on their relevance for the application level, which means an upscaling from the particle interface to the large scale concrete application has to be conducted.Direct particle interactions will mainly be studied using atomic force microscopy in various conditions on simplified model systems. The results will support understanding changes of rheological phenomena induced by changes in the pore solution chemistry as well as by adsorption of ions and polymers on particle surfaces. Effects of changed morphology and phase evolutions will be studied using XRD techniques, SEM, AFM, US, DTA, etc. The rheological response will be examined on various scales from solution level up to paste, mortar and concrete rheometry as well as by using applied technologies such as spraying, large scale casting and standard fresh concrete technologies.