QUANTITATIVE DAMAGE EVALUATION METHOD FOR CONCRETE BY DIGITAL-IMAGE-PROCESSING TECHNIQUE

摘要

Most of the concrete dams built between 1950 and 1970 in China are inevitably aging and it is of great significance to identify and quantitatively evaluate the damage degree and aging status for the concrete in those dams.However, all of the current damage evaluation parameters such as resonant frequency, ultrasonic wave velocity and CT numbers are phenomenological descriptions and cannot reveal the essence of damage in concrete, which is the initiation and propagation of microcracks.This paper proposes a method of evaluating damage in concrete by quantitative microcrack analysis based on vacuum-epoxy-impregnation method and digital-image-processing (DIP) techniques.Mechanical tests and quantitative microcrack analyses were performed on impregnated and grinded series of concrete specimens which suffered different expansions caused by alkali-aggregate reaction (AAR) and different freezing-thawing (FT) degrees respectively.Results show that the microcrack density in length and area increases with the increase of damage degree caused by either FT or AAR.Very good correlations are established between the macro properties such as the flexural strength, the tensile strength, the damage degree and the microcrack length density in the damaged concrete, respectively.Quantitative microcrack analysis by DIP technique could be developed as a new powerful and promising tool to quantify and evaluate damage degree and aging status in concrete.