Cement pastes and mortars are complex multiple phase composites which are passing through a complex structural and chemical metamorphosis during their hardening process. Of particular interest is the capillary pore network which is highly associated with many important intrinsic material properties like strength, permeability and durability. Quantitative morphological and topological characterization of pore structures is an important key for the physical modeling of such properties.

Data Acquisition

The inter-connectivity of the capillary pores is controlled by pore necks with dimensions between 1nm and 1000nm, while the size of air voids ranges from micrometers to millimeters. Hence, their examination requires microscopic imaging at different scales. Since, moreover, the three dimensional context for the percolation of the pores is decisive, 3D microscopy is required.

3D microscopy of cement pastes, cements and mortars is achieved by means of focused ion beam nanotomography (FIB-nt, [Holzer et.al., 2004]) in the 10 - 1000nm range, by synchrotron radiation micro computer tomography (SRmCT) in the 100nm - 10mm range, .and by conventional micro computer tomography (mCT) in the 10mm – 1mm range. Internal water transport process (such as internal curing) within cementitious materials can be observed with relatively coarse time- and lengthscale resolutions using neutron microtomgoraphy.

Data Analysis

After segmentation, the 3D locations of the phases are located with the help of object recognition and segmentation techniques adapted to the respective imaging approach. In addition to 3D visualization, the segmented 3D masks are useful for quantitative measures such as size distributions and morphological or topological parameters. The figure to the left shows some of the segmented phases at different size scales, from the grey level image volumes displayed above.

Process Modeling

The left image shows details from the morphology of cement paste (OCP CEM I) at the 10 nanometer scale. The void area represents pore space. Two ettringite needles are visible in the focus.

Such 3D phase information allows the virtual simulation of many relevant processes inherent to cement, like the growth of hydration processes, drying shrinkage, the mechanism of mercury intrusion porosimetry (MIP), flow and permeability. Elastic properties can be derived form 3D images as well. Likewise, the virtual vapor condesation can be modeled on such microstructures.

Our Research field

The strength in our research is the multidisciplinary team, which, in addition to material scientists in the field of cement and concrete includes specialists in microscopy, tomography, image processing and computational modeling. This collaboration enables combined top quality data acquisition and 3D physical modeling of complex processes as those mentioned in the latter section, where experts in different scientific fields are asked. This diversity also leads to new ways of perception and scientific questioning.

Your contact

• Dr. Beat Münch