Investigation of localized damage indicators of a carbon short-fibre reinforced high performance concrete under dynamic and flexural load

By using a novel fibre-reinforced cement paste recipe in an additive manufacturing (‘3D-printing’) method, a highly anisotropic material with vastly improved flexural and tensile strength can be created. Extruding the paste through a small nozzle results in unidirectional fibre orientation. A fibre content of 3 vol% results in static flexural strengths of above 100 MPa. High-strength fibre reinforced materials have great potential to be used as small, lightweight construction elements. Those structural members often show susceptibility to oscillating dynamic loads. Using a dynamic-mechanical analyser, miniature samples with a cross-section of 3 mm x 3 mm can be tested for their resistance towards cyclic loading in tests of up to 10 million cycles. Using an ex-situ method, micro-CT scans and optical microscopy are used to check for cracking and other damage indicators. To investigate the tensile fatigue behaviour on macro scale, bone-shaped specimens under pulsating tensile stress with a cross section area of 50 mm x 50 mm are examined. In addition to standard methods, i.e. strain gauges, strain sensors and position sensors, modern and wide range methods like fibre optic sensors, photogrammetry (digital image correlation), acoustic emission analysis and ultrasonic based coda wave interferometry are used. The aim is to describe the local macro crack development. The experimental investigations are accompanied by a multiscale modelling approach incorporating three-dimensional representative volume elements based on micro-CT scans of small test specimens. The representative volume elements reflect the mesoscale in the sense that carbon fibres and otherwise homogenized concrete matrix are distinguished.