Basis for the purposeful design of the bond between high-modulus polymer fibres and cement-based matrices

新型建筑材料的开发是土木工程创新的重要推动力。新型水泥基纤维增强复合材料，如具有短聚合物纤维的应变硬化水泥基复合材料（SHCC），显示出巨大的潜力。其机械性能，尤其是其显著的延展性，决定性地取决于纤维和水泥基基质之间的物理和化学相互作用。本提案的目标是研究具有不同表面功能的高模量合成聚合物纤维（PVA，HDPE）与水泥基基质之间的相互作用，以及了解这些相互作用所基于的工作机制。最后，将制定一个有目的地设计这些互动的概念。通过改变纤维表面和基质成分，纤维-基质界面将在分子和微观水平上成形。这些措施应允许纤维增强水泥基复合材料（材料设计）的宏观性能的准确控制。该提案包括两个分项目。首先，PVA和HDPE纤维的表面将被系统地修改，以提供不同的和明确定义的功能，用于将互连转向水泥基基质。将实现碱性和酸性表面功能以及不同等级的疏水性。计划对HDPE纤维进行低压等离子体活化，作为后续化学改性的基础。改性步骤中的一个具体挑战是保持本体材料的高度结晶含量，从而保持本体材料的强度。纤维将通过专门适用的方法进行表征，以评估化学形态、流动电位、表面形貌和表面能。在第二个子项目中，将通过将有目的地功能化的PVA和HDPE纤维嵌入各种水泥基基质中，产生具有不同微观结构和纤维与基质粘合模式的界面。单纤维拔出试验将阐明界面形态对纤维-基体粘结的影响。所有界面相的形态和矿物学将根据纤维的表面性质以及基质的微观结构和化学特征进行表征和解释。将通过使用不同的储存条件来研究键特性的性质的发展。为了更好地理解粘结行为，将建立一个流变统计材料模型。基于所有的结果和见解的纤维和水泥基基质之间的相互作用的有目的的设计的概念将被编译。

Development of new construction materials is the crucial driving force for innovations in civil engineering. Novel cement-based, fibre-reinforced compounds such as strain-hardening cement-based composites (SHCC) with short polymer fibres suggest outstanding potential. Their mechanical performance, above all their pronounced ductility, is decisively determined by physical and chemical interactions between the fibres and the cement-based matrix. The target of the present proposal is to investigate the interactions between high-modulus synthetic polymer fibres (PVA, HDPE) with different surface functionalities and cement-based matrices as well as to understand the working mechanisms on which these interactions are based. Finally, a concept for the purposeful design of these interactions is to be developed. The fibre-matrix interphase will be shaped on the molecular and microscopic levels by modifying the fibres surfaces and by varying matrix compositions. These measures should allow unerring control of the macroscopic properties of fibre-reinforced cement-based composites (material design). The proposal consists of two subprojects. In the first, the surfaces of PVA and HDPE fibres will be systematically modified to provide different and well-defined functionalities for steering the interconnection to cement-based matrices. Basic and acid surface functionalities as well as different grades of hydrophobicity will be implemented. Low pressure plasma activation is scheduled for HDPE fibres as a basis for subsequent chemical modifications. A specific challenge in the steps of modification is the preservation of the highly crystalline content of and, hence, the strength of the bulk material. The fibres will be characterised by specifically adapted methods to assess the chemical morphology, streaming potential, surface topography, and surface energy. In the second subproject, interphases with different microstructures and modes of fibre bonding to the matrix will be created by embedding the purposefully functionalised PVA and HDPE fibres in various cement-based matrices. Single-fibre pullout tests will illuminate the effects of interphase morphology on the fibre-matrix bond. Morphology and mineralogy of all the interphases will be characterised and interpreted on the basis of the surface properties of the fibres as well as the microstructural and chemical features of the matrix. Developments in the properties of the bond characteristics will be investigated by using different storage conditions. A rheological-statistical material model will be developed for a better understanding of bond behaviour. Based on all results and insights a concept for the purposeful design of interactions between fibres and the cement-based matrix will be compiled.