Microtensile testing and 3D imaging of hydrated Portland cement

Portland cement has an extremely complex microstructure that defies simple characterizations. While electron microscopy has provided valuable insight on microstructure development, the 2D nature of the data and the required specimen preparation steps continues to provide controversy as to what is real and what is artifact (see for example Diamond (2004a , b ) and Scrivener (2004 )). Here we present the results of synchrotron-based microtomographic investigations of 130 μπι diameter cement specimens subject to uniaxial tension. With the quantitative 3D image analysis of the tomographic data we are able to isolate the different phases, and identify the relationship between the phases and the resulting fracture path. In particular, we see that the crack path shows little if any preference for phase, undermining the notion that at small scales, unhydrated cement grains act as hard aggregates in hydrated cement matrix.