Three-point-bending (3pb) test results of small concrete specimens are used to predict unstable fracture of large concrete beams with shallow or no visible cracks. Small specimens and large beams with any notch depth (0, shallow or deep) are linked together…
Three-point-bending (3pb) test results of small concrete specimens are used to predict unstable fracture of large concrete beams with shallow or no visible cracks. Small specimens and large beams with any notch depth (0, shallow or deep) are linked together by one simple formula. It models quasi-brittle fracture of concrete and the associated size effect by modelling the notch-tip fracture process zone (FPZ), which is intrinsically linked to the aggregate size. A comprehensive set of concrete fracture data published in the literature was analyzed by the model, which was further substantiated by three new sets of 3pb concrete tests: 48 un-notched, 46 shallow-notched (1 mm) and 44 deep-notched (6 mm) specimens, with span of 160 mm, thickness around 40 mm and width/height around 38 mm. The average aggregate size is 4 and 5 mm for the two concrete mixes. Both FPZ length and width at the peak fracture load were estimated and linked to the average aggregate size, and then FPZ interactions with the specimen/structure boundary were modelled for quasi-brittle fracture and size effect. Statistical functions were added to this “boundary effect model” so that large experimental scatters were defined by the statistical reliability.