Experimental Investigations of Fracture Process Using DIC in Plain and Reinforced Concrete Beams under Bending

Abstract

The fracture behaviour of concrete and reinforced concrete beams under quasi-static three-point bending was comprehensively investigated with experiments at laboratory scale. The eight various concrete mixes were tested. The influence of the shape, volume and size of aggregate particles and reinforcement on concrete fracture under bending was studied. Displacements on the surface of concrete beams were measured by means of the digital image correlation (DIC) technique. Attention was paid to the formation of a localized zone and its characteristics. In order to avoid the effect of the search patch size and the cut-off value at displacement and strain profiles, a consistent method was proposed to determine uniformly and accurately the width of a localized zone. Measured surface displacements from DIC were fitted by the error function ERF, whereas surface strains calculated from displacements were fitted by the usual normal distribution (Gauss) function. The width of a localized zone preceding a macro-crack grew strongly with increasing maximum aggregate size and slightly with diminishing aggregate volume. It did not depend on the aggregate roughness and reinforcement presence.

Fracture process zone and tensile behavior of blended binders containing limestone powder

“…The ratio of the pre-defined width of the arbitrary FPZ and the obtained width of the localized zone defined by σ were close to 4.0. Similar observations have been noted elsewhere [25,28]. It, however, needs to be noted that the FPZ width is highly influenced by the image resolution; a higher image resolution resulting in a smaller FPZ width [25].…”

“…It is plausible that microcracks coalesce into larger cracks beyond this level, thus expectedly reducing the FPZ widths. Some studies have also attributed this to inaccuracies in the image correlation procedure and algorithms [28,53].…”

“…While several experimental techniques such as high speed photography [12], acoustic emission [13][14][15], scanning electron microscopy (SEM) [16][17][18][19], and laser-speckle interferometry [20,21] have been used to investigate FPZ in concretes, this study employs a non-contact digital image correlation (DIC)-based speckle-tracking method [10,[22][23][24][25][26][27][28] to assess the surface displacements and strains, and thus the width of the FPZ. The presence of soft(er) limestone particles and ductile clay phase (from metakaolin), which improves the fracture performance of multiple-material binders through improved inelastic energy dissipation [10], influences the FPZ, which is explored in detail.…”

Modelling of concrete fracture at aggregate level using FEM and DEM based on X-ray μCT images of internal structure

“…The crack height in the specimen '2' changed along the specimen depth, from h c = 45 mm up to h c = 56 mm on the front specimen side. The width of the localized zone above the notch on the beam surface, measured by DIC, was w lz = 3.11-3.40 mm [38]. In order to measure the width of ITZs, the scanning electron microscope (SEM) Hitachi TM3030 with the maximum magnification factor 30,000 was used.…”

“…2. The mesoscopic characteristic length was always assumed l m c = 1.5 mm, based on own experiments on concrete-beams using the digital image correlation technique DIC and FE analyses [38], [47]. With the assumed valued of l m c = 1.5 mm, the experimental width of a localized zone was realistically reproduced in FE-analyses at the aggregate level.…”