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XRD and TGA Investigation of Hardened Cement Paste Degradation

It is generally recognized that the environmental degradation of the concrete infrastructure is a serious, large scale and costly problem in many parts of the world. In this paper a deterioration of concrete by leaching of hardened cement paste due to aggressive water action is considered. Concrete from a hydro-electric power plant’ s pipeline 30 years old was characterized with X-ray diffraction (XRD), and thermogravimetric analysis (TGA/DTA). The study highlights the capabilities of the methods for the analysis of concrete towards the determination of hardened cement paste degradation. On the basis of a visual survey of drilled cores, a number of representative spots were selected for detailed testing and verification of visual estimates. The methods ascertain a leach of hardened cement paste on samples taken from a surface concrete cover layer of few millimetres, and from flaws like cracks, segregations or cold joints. On these samples XRD results showed small quantity of ettringite, calcium carboaluminate hydrate and Friedel’ s salt, and a complete leach of portlandite, while TGA results indicated small quantities of hydrates. Samples taken from flawless inside of concrete layer showed expected quantities of hydrates for the concrete.

X-ray diffraction; thermogravimetric analysis; concrete; degradation

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