New Nondestructive Technique to Investigate Concrete Surface Topography

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Title: New Nondestructive Technique to Investigate Concrete Surface Topography

Author(s): A. M. Hammad and M. A. Issa

Publication: Special Publication

Volume: 143

Issue:

Appears on pages(s): 191-206

Keywords: concretes; fracture surface; nondestructive tests; surface defects; Structural Research

Date: 5/1/1994

Abstract:
Fracture surfaces of concrete and mortar are irregular, tortuous, and stochastic in nature. To describe irregular and rough surfaces, quantitative fractographic parameters such as profile and surface roughness, fractal dimension, Fourier spectral analysis, etc., are often used. A fractal description of fracture surfaces of concrete and mortar by utilizing a new nondestructive technique, introduced by the authors, will be presented in this paper. Compact tension-fractured concrete specimens with a compressive strength of 46.8 MPa and a maximum aggregate size of 37.5 mm and a projected fracture area (ligament area) of 46,000 mm 2 (367.5 mm long by 125 mm wide), are analyzed. Through this technique, a microphotograph is taken and stored as a binary image using an image analyzer equipped with a stereo-microscope. The result is a topographical map of the fracture surface. Since the elevation of each point on the fracture surface is defined by its intensity value, the need for actual sectioning through the fracture surface, often employed, is eliminated. One-dimensional Fourier spectral analysis (1D FFT) to estimate the fractal dimension is carried out. To check the method of analysis, synthetic profiles with a known fractal dimension are generated. The results of the analysis suggest that concrete fracture surfaces are fractal for the range of scales considered, the digitized fracture surface images are found to mimic the actual fracture surfaces, their spectra follow a power lower behavior, and the technique is very promising and suitable for such materials.