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

• Applicants: Professor Dr.-Ing. Viktor Mechtcherine; Privatdozentin Dr. Alla Synytska, since 10/2017
• Subject Area: Construction Material Sciences, Chemistry, Building Physics
• Term: from 2015 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 280796894

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.

• DFG Programme: Research Grants
• Ehemalige Antragstellerin: Dr. Cornelia Bellmann, until 9/2017