An automated method for crack identification and quantitative description of crack systems in concrete was developed in order to aid a service life assessment of concrete elements in structures. Flat polished specimens for crack analysis were impregnated with epoxy resin containing fluorescent dye. The examination of the crack system was performed in ultraviolet light using a stereomicroscope and an Image Pro Plus image analysis system on specimens cored out of several concrete structures. The laboratory tests were performed on cast specimens to establish correlations between water penetration and chloride diffusion and crack system parameters. The analysis of cracks in concrete cores taken from structures resulted in interesting conclusions based on the crack width distribution and crack localization with respect to steel reinforcement. The method was found very effective to support standard concrete diagnostics methods.
The phase composition of the cement paste phase of concrete containing fly ash from circulating fluidized bed combustion (CFBC) was studied. The motivation was to broaden the knowledge concerning the microstructure and the durability of concrete containing new by-products from the power industry. Several air-entrained concrete mixes were designed with constant water to binder ratio and with substitution of a part of the cement by CFBC fly ash (20%, 30% or 40% by weight). X-ray diffraction tests and thermal analysis (DTG, DTA and TG) were performed on cement paste specimens taken from concrete either stored in water at 18° C or subjected to aggressive freeze-thaw cyclic action. The evaluation of the phase composition as a function of CFBC fly ash content revealed significant changes in portlandite content and only slight changes in the content of ettringite. The cyclic freeze-thaw exposure did not have any significant influence on the phase composition of concrete with and without the CFBC fly ash.