PSI - Issue 35

Kai Friebertshauser et al. / Procedia Structural Integrity 35 (2022) 159–167 K. Friebertsha¨user and M. Werner and K. Weinberg / Structural Integrity Procedia 00 (2021) 000–000

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Fig. 2. (a) Penny-shaped crack in an infinite domain under pressure; (b) Comparison of the analytical and the numerical pressure-displacement relation for the pressure driven penny-shaped crack growth

4. Pressure induced cracks in a concrete block

This section investigates the pneumatic fracture of a cylindrical concrete block and compares the experimentally and numerically obtained crack patterns with each other.

4.1. Experiment

For the experimental investigation, a common low-chromate fast-curing concrete is filled in a plastic vessel with a diameter of D cyl = 108 mm and a height of H cyl = 90 mm. Soft flat polyethylene pads are mounted to a pressure hose and embedded inside the specimens. Such a setup models an initial crack and enables us to load the crack pneumatically by an increasing air pressure. We investigated three di ff erent polyethylene pad arrangements: (i) horizontal, (ii) inclined, and (iii) curved, see Fig. 3. (i) In the horizontal setup, the pad is rectangular with an edge length of 50 mm and a thickness of 0.8 mm. The pad is embedded in the center of the concrete specimen. (ii) In the inclined setup, the same pad as in (i) is used but with an inclination angle of 30 ◦ . (iii) For the curved setup, a 15 mm wide cross allows for a bent arrangement of the pad (see also Fig. 4 c). The polyethylene pressure pads are not hermetically sealed and serve to create an initial cavity inside the concrete cylinder. When air pressure is applied, the air can escape from the pad and penetrates the growing crack. In that way we expected di ff erent crack patterns; the intuitive assumptions are indicated with yellow dots in Fig. 3. Because the concrete is a very brittle material the crack grows to the specimens boundary within few microseconds. We remark that a direct measurement of the pressure within the crack was not possible. We determined it indirectly from the pressure in the hose but the results were rather fuzzy and so we focus in this section solely on the shape of cracks and fragments. In Fig. 4, cracked specimens of all three pad configurations are shown. It is clear that the boundary conditions have a significant influence on the results. Because the concrete specimen had been left in the plastic vessel, the crack growth is in part contrary to our a-priori expectations. In configuration (i), the cracks did not evolve along a plane parallel to the pad but moved slightly upwards. In configuration (ii), the cracks evolve as expected for the inclined