THREE DIMENSIONAL CRACK DETECTION IN HARDENED CEMENT PASTES USING SYNCHROTRON-BASED COMPUTER

Fracture patterns induced in the hardened cement pastes by instrumented indentation technique were investigated. The fracture patterns were monitored by synchrotron-based computer microtomography (SRµCT) and scanning electron microscopy. The indentation tests were carried out on specially produced microspecimens using Berkovich diamond probe. The size of the samples has been dictated by the requirements of synchrotron-based microtomography observation. The samples were of cylindrical shape and the diameter of the samples varied between 500 and 550 µm. Samples were tomographed both before and after indentation testing. Such approach enables to reveal and possibly quantify indentation induced fracture damage reliably. The crack/damage patterns induced by indentation were also observed using environmental scanning electron microscope (ESEM). The comparison of the electron microscopy signal with 3D synchrotron-based images provides very useful information about the true size of the microcracks induced. As the microcracks induced in the heterogeneous structure of Portland cement smear themselves into the intrinsic cement paste porosity, it is not easy to set a clear boundary between them, which makes a quantitative assessment of the indentation-induced fracture a difficult task. In spite of that a quantitative assessment of indentation induced fracture has been attempted. The outcomes of this research provides (i) very useful input for further development of micromechanical models of cement-based materials and (ii) better understanding of microfracture of cement-based materials