Quantitative damage evaluation of AAR-affected concrete by DIP technique

This paper presents a method to evaluate alkali-aggregate reaction (AAR) damage in concrete by digital-image-processing (DIP) technique. A vacuum fluorescent-epoxy impregnation technique is used to highlight microcracks in the AAR-damaged concrete and a Matlab-based software package is developed to quantitatively analyse the microcrack characteristics (area, length, width etc.) in the fluorescent microscopic images of concrete. Six microcrack pattern parameters - the total length, the length density, the total area, the area density, the maximum width and the average width of microcracks - in slices from the concrete specimens that suffered different degrees of AAR damage were obtained. Results show that the length density, the area density and the average/maximum width of microcracks all increase as the degree of AAR damage increases. Relationships between the mechanical properties and the microcrack characteristics are established and results show that both the relative flexural strength and relative axial tensile strength have quadratic correlations with the microcrack density. The degree of AAR damage has a good logarithmic correlation with the microcrack density and the expansion ratio has a linear correlation with the microcrack density. Quantitative microcrack analysis based on DIP techniques could be developed as a new powerful tool of quantifying AAR damage in concrete.