The reference method for determining pavement macrotexture has historically been the volumetric sand patch method (ASTM E965), which is a simple test but its results are operator dependent (Henry 2000). The Circular Texture Meter (CT Meter), also known as the Circular Track Meter, is a road surface macrotexture profiler that uses a charge coupled device (CCD) laser-displacement sensor to measure the vertical profile of a pavement surface. The CT Meter software calculates and reports the Mean Profile Depth (MPD) and Root Mean Square (RMS) statistics that characterize profile macrotexture. Comparison of a surface's MPD and RMS statistics provide an indication of whether the texture is positive (surface projections) or negative (depressions). The International Friction Index (IFI) can also be computed when using the CT Meter along with the Dynamic Friction Tester (DF Tester), which measures the coefficient of friction (Henry 2000).
The CT Meter is designed to measure the same circular track that the DF Tester measures. The device measures the profile of a circle 284 mm (11.18 in) in diameter, and the circumference (892 mm [35.12 in]) of that circle is divided into eight segments of 111.5 mm (4.39 in) in length. The average MPD and/or RMS are determined for each of segment, and these values are used to calculate the overall average. As illustrated in the figure at the left, two segments (A and E) measure profile in the direction of travel, while two others (C and G) measure it perpendicular to the direction of travel.
CT Meter: 400 x 400 x 270 mm (15-3/4 x 15-3/4 x 10-5/8 in)
13 kg (28.7 lbs)
Carrying Case: 470 x 590 x 330 mm (18-1/2 x 23-1/4 x 13 in)
11 kg (24.3 lbs)
Henry, J. J., H. Abe, S. Kameyama, A. Tamai, A. Kasahara, K. Saito. 2000. "Determination of the International Friction Index (IFI) Using the Circular Texture Meter (CTM) and the Dynamic Friction Tester (DFT)." Publication No. 109.01.06.B-2000. Permanent International Association of Road Congresses (PIARC). Nantes, France.
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