THE FRACTURE TOUGHNESS OF INTERFACES BETWEEN ROCKS AND CONCRETE. THE RESULTS OF EXPERIMENTAL INVESTIGATIONS

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The current test investigated the fracture toughness KIC of the interfaces between rocks comprising gypsum stone and concrete. The experiments used the methodology of the International Society for Rock Mechanics and Rock Engineering (ISRM). The cylinder samples had a diameter of 40 mm and a length of 150 mm with a V-shaped cutout in the middle part. 19 samples consisted of two halves. Gypsum stone minerals made up one part 75 mm long of the samples. Pouring sand-cement mortar into the matrix together with the first half made it possible to obtain samples with a rock-concrete interface. 4 samples consisted entirely of concrete. Deformation of samples during bending according to a three-point scheme made it possible to determine the fracture toughness factors KIC based on the maximum force at 5–6 cycles with an increase in maximum bending in each subsequent cycle. The fracture toughness of interfaces containing rock with concrete was extremely lower in quality than that of only rocks and even for only concrete separately. The average KIC value for samples with concrete was 0.323 MPa×√m. For samples without concrete, it was 1.327 MPa×√m, i.e. 4 times more. Moreover, the average value only for concrete specimens was 0.858 MPa×√m. It was higher than that for rock with concrete samples.

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