W0061

Spatially Resolved Energy Dispersive Diffraction and Sulfate Attack on Cement. Angus P. Wilkinson, Andrew C. Jupe, Kimberly E. Kurtis and Nikhila N. Naik, Georgia Institute of Technology, Atlanta, GA; Sarvjit D. Shastri and Peter L. Lee, XOR, Advanced Photon Source, Argonne National Laboratory, IL; Stuart. R. Stock, Northwestern Univ., Chicago, IL.

The presence of sulfates in water or soils surrounding portland cement concrete structures leads to progressive degradation. Spatially resolved energy dispersive diffraction (EDXRD) in combination with computed microtomography (μCT) and mechanical measurements provide the information needed to understand, in detail, the degradation mechanisms that are associated with sulfate attack and to validate accelerated test methods used to evaluate the sulfate resistance of cements. Highly penetrating, high energy, X-rays allow the use of EDXRD to determine depth profiles for the crystalline phases in cement paste specimens several millimeters below the sample surface (see Figure 1). These depth profiles, and how they vary with sulfate exposure conditions and duration, can be directly correlated with mechanical changes and the crack patterns seen in the microtomographs.

a)b

Figure 1. a) EDXRD data for a Type V specimen exposed to 33,800 ppm sulfate for 52 weeks and b) depth profiles for its major crystalline phases.

An overview of spatially resolved EDXRD will be provided along with some results from EDXRD and μCT for both magnesium and sodium sulfate attack on general use Type I and sulfate-resisting Type V cements.