An Approach to Quantitative Image Analysis for Cement Pastes

Porosity Measurement of Low Permeable Materials Using Gas Expansion Induced Water Intrusion Porosimetry (GEIWIP)

Porosity measurement is a key factor to identify the hydraulic performance of low permeable porous materials (e.g. rock or concrete). Porosimetry tests such as Mercury Intrusion Porosimetry (MIP), Nuclear Magnetic Resonance (NMR), or Gas Expansion (GE) are cost-prohibitive, use hazardous materials, or are incapable of accessing all inter-connected pores. An alternative Gas Expansion Induced Water Intrusion Porosimetry (GEIWIP) method was developed to measure the porosity of a low permeable porous medium using a gas/water intrusion apparatus. This method overcomes the previously mentioned porosimetry drawbacks by using distilled de-aired water (DDW) as a hazard-free liquid which is a wetting fluid to intrude the porous structure and fill the pores. As the DDW has the tendency to fill all inter-connected pores, no back-up pressure is required. This method has lower cost and needs less preparation time comparing to MIP test. Additionally, the GEIWIP set-up, the gas/water intrusion apparatus, can be moved to the field site and provide mobile measurement feasibility. The reliability of the test results was obtained by a repetitive testing process. The porosity of concrete samples with different mixtures was obtained and compared to those of MIP and NMR tests.

X-ray diffraction microtomography (XRD-CT), a novel tool for non-invasive mapping of phase development in cement materials

A recently developed synchrotron-based imaging technique, X-ray diffraction microtomography (XRD-CT), has been applied here for the first time to a complex system, the hydrating Portland cement paste, in order to monitor the evolution of microstructure and phase formation with a 3D non-invasive imaging approach. The ettringite-XRD-peak-based image reconstructions, combined with transmission microtomography (X-microCT) images, allowed to assess the ubiquitous distribution of this phase, which appears early in the hydration process and showed its preferential concentration in the relatively less compact regions of the paste. The comparison of greyscale histograms for cement pastes after 9 and 58 h from hydration showed an increase of ettringite content with age, in agreement with the quantitative Rietveld analysis of the sum patterns. By renormalizing the greyscale histograms to the relative weight fraction, as obtained from Rietveld refinements, a new technique which allows estimation of phase contents with spatial resolution has been developed. The results achievable by combining XRD-CT, X-microCT and Rietveld appear very promising to provide experimental snapshots of the cement hydration process to be compared with results obtained from computer simulations.