Tests on the size effect of UHPFRC prisms with a compressive strength of 169 MPa subjected to bending and uniaxial tension

Tests on prism out of ultra-high-performance fibre reinforced concrete (UHPFRC) were performed in order to further clear up the size effect, i.e. the strength decrease with increasing depth for axial tension and bending. An additional aim was to investigate the influence of the prism shape. i.e. the width to height ratio b/h. The test specimens were cast by the firm Sebastian Wochner GmbH & Co.KG, Dormettingen with the material Duracrete Plus from Schwenk Zement AG, Ulm. The average compressive strength was 169 MPa. These tests supplemented the tests with a UHPFRC with 211 MPa reported in [6]. The bending tests on prisms with depths from h = 25 to 150 mm showed that the elastic limits as well as the maximum bending stress, the flexural tensile strength, decreased with increasing depths. The elastic limit for the series with b/h = 3 dropped from f(ctfl,el) = 13,2 MPa for h = 50 mm by about 20 % to f(ctfl,el) = 10,6 MPa for h = 150 mm; the flexural tensile strength exhibited a decrease by about 44 % from f(ct,fl) = 36,4 MPa for h = 50 mm to f(ct,fl) = 20,4 MPa for h = 150 mm. The elastic limits of the flexural tensile stress as well as the flexural tensile strengths decreased with increasing ratio b/h from 1 to 5. The theory of Weibull could not explain the decrease of the elastic limits of the flexural tensile stress f(ctfl,el) with increasing depth. For axial tension the tensile strength exhibited a decrease with increasing depth from f(ct) = 11,8 MPa for h = b = 50 mm to f(ct) = 9,4 MPa for h = b = 75 mm. The elastic limit of the axial tensile stress was f(ct,el) = 8,8 MPa for h = 25 mm and b = 3 . h = 75 mm, and it dropped to f(ct,el) = 6,3 MPa for prisms with h = 50 und 75 mm and b = h. However, further tests should be performed with Duracrete Plus to investigate the size effect as well as the influence of the width to height ratio b/h.