Experimentell investigations and microstructure-based modeling of the elastic and visco-elastic behavior of PCC depending on temperature

由于对工程结构的经济和生态要求越来越高，人们越来越需要优化建筑材料混凝土在各种荷载下的抗力。用热塑性聚合物对粘结剂进行改性，多年来一直是提高胶凝材料耐久性、耐化学性和粘接性能的一种公认的方法。因此，聚合物改性水泥砂浆和混凝土(PCC)的应用领域近年来得到了稳步扩大。为了在施工中也建立PCC，全面了解聚合物改性对力学行为的影响是基本的。特别是在弹性和粘性变形性能方面，PCC与常规砂浆和混凝土有很大的不同。然而，由于聚合物具有明显的温度依赖性，有必要将PCC的力学行为描述为温度的函数。该项目的目标是表征PCC的弹性和粘弹性特性的温度依赖性。为此，使用了相辅相成的跨尺度实验和分析方法。聚合物对水泥浆体、砂浆和混凝土的荷载-变形行为的温度依赖影响通过标准测量和新的实验活动来表征。后者包括短期蠕变试验，根据该试验，样品在生产后的第一周内每小时承受一次压力，持续三分钟。这种方法能够准连续地测定试件的弹性性能和蠕变应变。结果与长期蠕变试验相补充，从而可以全面地描述PCC的蠕变行为。分别在-20℃到+60℃的不同温度下进行研究，温度影响前后的微观结构研究也提供了关于单相形态变化的信息。研究结果被捆绑在基于连续细观力学方法的半解析多尺度模型中。通过自下而上的方法，使用特定的微观结构行为来确定宏观尺度上的均质属性。因此，由于温度影响而产生的微观结构变化可以直接与材料的宏观行为相关联。在考虑热孔弹性原理对现有的多尺度模型进行扩展后，PCC力学性能的温度依赖关系将是可预测的。

Due to increasing economic and ecological requirements regarding engineering structures, there is a growing need to optimize the resistance of the building material concrete against a wide variety of loads. The modification of the binder with thermoplastic polymers has been an established method for improving the durability, chemical resistance, and adhesive properties of cementitious materials for many years. The fields of application for polymer-modified cement mortars and concretes (PCC) have therefore been steadily extended in recent years. In order to establish PCC also in construction, a comprehensive understanding of the effects of polymer modifications on the mechanical behavior is fundamental. Particularly with regard to the elastic and viscous deformations properties, the PCC differ significantly from conventional mortars and concretes. However, due to the pronounced temperature dependence of the polymers, it is necessary to describe the mechanical behavior of PCC as a function of the temperature. The objective of the proposed project is to characterize the temperature dependence of the elastic and viscoelastic properties of PCC. For this purpose, cross-scale experimental and analytical approaches that complement each other are used. The temperature-dependent influence of the polymers on the load-deformation behavior of cement pastes, mortars, and concretes is characterized both by standard measurements and by novel experimental campaigns. The latter include short-term creep tests according to which the sample is subjected to a compressive force once every hour for three minutes during the first week after production. This procedure enables the quasi-continuous determination of the elastic properties and the creep strains of the samples. The results are complemented by long-term creep tests so that the creep behavior of PCC can be comprehensively described. The respective investigations are carried out at different temperatures between -20 and +60 °C. Microstructural investigations before and after the temperature influence also provide information on changes in the morphology of single phases.The results of the study are bundled in a semi-analytical multiscale model based on the methods of continuum micromechanics. By means of a bottom-up approach, homogenized properties at the macroscale are determined using the specific microstructural behavior. The microstructure changing as a result of the temperature influence can thus be directly correlated with the macroscopic material behavior. After extending an existing multiscale model by considering principles of thermo-poro-elasticity, the temperature dependence of the mechanical properties of PCC will be predictable.