Shear-Dependent Rheological Behavior of Ecologically Improved Cements Containing Calcined Clays as Clinker Substitute

通过用火山灰材料替代熟料，可以大大减少水泥的二氧化碳足迹。煅烧粘土（CC）被认为是最有前途的替代材料，然而，取决于天然原粘土的组成，其总是呈现不同粘土矿物的混合物，在水泥中可能发生各种效果。本研究的目的是自行制备四种不同的纯煅烧粘土（Meta高岭土，Meta蒙脱石，Meta伊利石和Meta云母）的高火山灰活性通过煅烧，表征它们，并评估其对这些原始粘土或OPC-CC 70：30共混物的悬浮液的流变学的影响。此外，中央项目提供的煅烧粘土混合水泥将作为所有测试的参考材料。通过使用Couette型旋转粘度计，将特别确定它们的剪切相关粘度，并将捕获相应的流变关键参数，例如塑性和表观粘度、屈服应力、凝胶强度等，并应确定流体的总体行为（剪切稀化或剪切增稠）。此外，流变图将拟合到已知的流变模型，包括幂律，宾汉，赫歇尔-Bulkley等。此外，所有体系将与四种自行合成并表征的高效减水剂混合（=分散剂），即2种聚羧酸盐、1种聚磷酸盐-羧酸盐和1种缩聚物，为了理解煅烧粘土与这种分散剂的相互作用，并评估它们在实际应用中的行为，例如在混合、运输、泵送，与TU布伦瑞克（Lowke教授）合作，我们的OPC/CC复合水泥颗粒和SPP提供的低熟料复合水泥在添加超塑化剂后的时间和剪切速率依赖性解聚将通过使用FBRM仪器进行跟踪。从机理上讲，将通过ζ电位测量来确定CC颗粒表面上电化学双层的积聚，并将形成吸附等温线，其可以指示分散剂是优先吸附在水泥上还是在CC上。这项研究的总体目标是提供一个纯的，个人煅烧粘土在微观和纳米水平的剪切依赖性流变行为的理解，作为未来的研究在宏观层面（混凝土）进行的基础。此外，通过了解单个纯煅烧粘土的行为，可以更好地预测通常发生在由天然粘土沉积物制备的CC中的混合物的性质。

The significant CO2 footprint of cement can be reduced considerably through substitution of clinker with pozzolanic materials. Calcined clays (CCs) are considered as the most promising substitution material, however, depending on the composition of the natural raw clay which always presents a mixture of different clay minerals, various effects can occur in cement. This study aims to self-prepare four different pure calcined clays (meta kaoline, meta montmorillonite, meta illite and meta muscovite) of high pozzolanic activity via calcination, to characterize them and to evaluate their impact on the rheology of suspensions of these pristine clays or OPC-CC 70:30 blends. Furthermore, the calcined clay blended cement provided by the Central Project will be included as a reference material in all tests. By using a Couette-type rotational viscometer, especially their shear-dependent viscosity will be determined and corresponding rheological key parameters such as plastic and apparent viscosity, yield stress, gel strengths etc. will be captured and the overall behavior of the fluid (shear-thinning or shear-thickening) shall be ascertained. Moreover, the rheograms will be fitted to known rheological models including Power law, Bingham, Herschel-Bulkley etc. Furthermore, all systems will be admixed with four self-synthesized and well characterized superplasticizers (= dispersants), namely 2 polycarboxylates, 1 polyphosphate-carboxylate and 1 polycondensate, to understand the interaction of the calcined clays with such dispersants and to assess their behavior in practical applications such as during mixing, transport, pumping, in 3D printing etc. In cooperation with TU Braunschweig (Prof. Lowke) the time and shear rate dependent disagglomeration of our OPC/CC composite cement particles and of the low clinker composite cement provided by the SPP upon addition of superplasticizer will be tracked by employing an FBRM instrument. Mechanistically, the build-up of the electrochemical double layer on the surface of the CC particles will be determined via zeta potential measurements and adsorption isotherms will be developed which could indicate whether the dispersants preferentially adsorb on cement or on CC. The overall aim of the study is to provide an understanding of the shear-dependent rheological behavior of pure, individual calcined clays at the micro and nano level as a basis for future studies to be conducted at the macro level (concrete). Additionally, by understanding the behavior of individual pure calcined clays the properties in mixtures which typically occur in CCs prepared from natural clay deposits can be predicted better.