Experimental Investigations of Fracture Process in Concrete by Means of X‐ray Micro‐computed Tomography

Abstract

The paper describes investigation results on fracture in notched concrete beams under quasi‐static three‐point bending by the X‐ray micro‐computed tomography. The two‐dimensional (2D) and three‐dimensional image procedures were used. Attention was paid to width, length, height and shape of cracks along beam depth. In addition, the displacements on the surface of concrete beams during the deformation process were measured with the 2D digital image correlation technique in order to detect strain localisation before a discrete crack occurred. The 2D fracture patterns in beams were numerically simulated with the finite‐element method using an isotropic damage constitutive model enhanced by a characteristic length of micro‐structure. Concrete was modelled as a random heterogeneous four‐phase material composed of aggregate, cement matrix, interfacial transitional zones and air voids. The advantages of the X‐ray micro‐computed tomography were outlined.

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

“…1 (with the displacement CMOD up to 0.15 mm for the beam '1' and up to 0.10 mm for the beam '2') are shown in Fig. 3 [37]. The maximum vertical force F was equal to 2.15-2.25 kN (the tensile strength was 3.73-3.91 MPa).…”

“…The width was not dependent upon the aggregate diameter. The experimental results were described in more detail in [37]. …”

“…5). They were distinguished by means of an absorption threshold method [37]. The total volume of initial air voids was 5.02% (specimen '1') and 4.67% (specimen '2').…”

“…For the FE analyses, the effect of E ITZ and j 0,ITZ (Eqs. (2) and (3)) was investigated [37], and for the DEM analyses, the effect of Ec, ITZ and T ITZ (Eqs. (11) and (14)) was investigated.…”

“…13 demonstrate the force-CMOD curves obtained for the concrete beams '1' and '2' with the real aggregate and air voids distribution in three different cross-sections of Fig. 6A and B in the notch region using FEM with the material constants from Table 2 [37] and DEM with the material constants from Table 3. The calculation time for 1 beam was about 4 days (FEM) and 1 week (DEM) using PC 3.2 GHz.…”