Scale effects on the fracture of high-strength concrete

Thirty-one (31) single-edge notched beam specimens with a beam depth ratio range of 1:2:4 are tested under three-point bending. The span/depth ratio is kept constant at 4 and the width is held constant at 12.7 cm. The largest beams are 50.8-cm deep and 203.2-cm long. The crack length/depth ratio is 0.3 for all specimens. A total of six (6) concrete mixes are tested corresponding to three (3) target cylinder concrete compressive strengths of 28, 55 and 83 MPa and two (2) maximum aggregate sizes of 10 and 25 mm. The effects of macro-scale and micro-scale for the high strength concrete specimens are examined and the test results are analyzed based on standard fracture test methods. Fracture toughness values are calculated and compared between the high- and low-strength beams for different scales (macro- and micro-structure). The experimental data of the pre- and post-peak load-LPD and load-CMOD response especially for the experiments of the large-size beams and high-strength concrete is also presented and indication of possible snap-back instability is discussed.