Concrete, rock, and core samples all have an important characteristic in common-their surface roughness and topography can play a vital role in applied use and an explanation to fracture and interaction. For example, concrete surface roughness can play a crucial role in the bonding to applied substrates, during geologic studies a rock surface can provide answers to important fault shifts, and the study of core sample surfaces can provide clues to fluid mechanics. Many of these measurements require portable instrumentation.
Because surface roughness and topography of concrete is vital to applied use and research, it is crucial to understand and control this parameter. The Nanovea 3-D Non-Contact Profilometers uses chromatic confocal technology with the capability to measure concrete and rock surfaces.
Measurement objective, setup and tips
For this application, the JR25 portable profilometer is used to measure the surface of a concrete sample. Several surface parameters automatically will be calculated including the most common, Sa (average surface roughness).
With measurement area randomly selected on the concrete surface, the drastic changes in surface topography is not an issue. Small height variation down to nanometers and up to 27 mm of height variation can easily be measured.
The axial chromatism technique uses a white light source, where light passes through an objective lens with a high degree of chromatic aberration. The refractive index of the objective lens will vary in relation to the wavelength of the light. In effect, each separate wavelength of the incident white light will refocus at a different distance and height from the lens. When the measured sample is within the range of possible heights, a single monochromatic point will be focalized to form the image. Due to the confocal configuration of the system, only the focused wavelength will pass through the spatial filter with high efficiency, thus causing all other wavelengths to be out of focus. The spectral analysis is done using a diffraction grating. This technique deviates each wavelength at a different position, intercepting a line of CCD, which in turn indicates the position of the maximum intensity and allows direct correspondence to the Z height position.
Nanovea optical pens have zero influence from sample reflectivity. Variations require no sample preparation and have advanced ability to measure high surface angles, capable of large Z measurement ranges. Measure any material: transparent/opaque, specular/diffusive, polished/rough.
False color representations of flattened Area 1 (above) and Profile Extraction (below).
|Sa||125.9 µm||Arithmetical Mean Height|
|Sq||170.8 µm||Root Mean Square Height|
|Sp||839.0 µm||Maximum Peak Height|
|Sv||1208 µm||Maximum Pit Height|
|Sz||2047 µm||Maximum Height|
|Sa||Arithmetical Mean Height||Mean surface roughness.|
|Sq||Root Mean Square Height||Standard deviation of the height distribution, or RMS surface roughness.
Computes the standard deviation for the amplitudes of the surface (RMS).
|Sp||Maximum Peak Height||Height between the highest peak and the mean plane.|
|Sv||Maximum Pit Height||Depth between the mean plane and the deepest valley.|
|Sz||Maximum Height||Height between the highest peak and the deepest valley.|
|Ssk||Skewness||Skewness of the height distribution.
Skewness qualifies the symmetry of the height distribution. A negative Ssk indicates that the surface is composed of mainly one plateau and deep and fine valleys. In this case, the distribution is sloping to the top. A positive Ssk indicates a surface with a lot of peaks on a plane. Therefore, the distribution is sloping to the bottom. Due to the large exponent used, this parameter is very sensitive to the sampling and noise of the measurement.
|Sku||Kurtosis||Kurtosis of the height distribution.
Kurtosis qualifies the flatness of the height distribution.Due to the large exponent used, this parameter is very sensitive to the sampling and noise of the measurement.
The area measured shows an average roughness of 125.9 µm and a total height variation of 2,047 µm over a 25mm2 area. This suggests that over the area scanned there were some large peaks and valleys relative to the average roughness, but not enough to skew the average roughness values. With no weight restrictions and a maximum measurement area of 25mm2, the profilometer can be used for portable surface measurements of large immovable surfaces. Vital field study surface measurement will now have the option of 3D non-contact technology with a compact potable profilometer for field studies.
Craig Leising is a product manager with Nanovea.