Streetworks

To ensure that skid resistant is achieved it is important to check, not only the quality of the materials used, but also that the texture depth has been achieved by measuring the roughness of the surface.

The sand patch test is a quick on-site method to measure the texture depth of any surface to ensure skid resistance is achieved. On coated macadam the choice of material in relation to aggregate size and grading helps to achieve the texture depth required. On asphalt surfaces using finer graded materials the texture depth is achieved by application of pre-coated chippings.

Contents of the Kit

Dividers
Ruler
80mm high cylinder with a diameter of 20mm
65mm diameter wooden disc backed with rubber and about 1.5mm thick
Container for sand
Soft brush
Fine dry sand that would pass through a No 52 BS sieve, being retained on a No 100 BS sieve

The kit comes pre-packed in a wooden case with a full list of instructions and conversion tables.

Testing
The test is carried out on a dry surface by pouring a known quantity of sand onto the surface and spreading it with the wooden disc in a circular area. When the sand spreads no further all the voids are filled and the dividers used to measure the diameter of the circle to the nearest millimeter. This figure is then recorded and further tests are carried out in different places. The mean average is then calculated and the tables provided used to determine texture depth. A texture depth of about 1.5mm is normally required for heavily trafficked areas.

Mini Texture Meter

The Mini Texture Meter (MTM) is used to measure the surface texture of roads, airfields and footways. The equipment is hand propelled and operated at walking speed. Output from the machine comprises a printout showing 5 consecutive 10m texture calculations followed by a 50m average.

Texture depth is measured with the meter as soon as possible after the surfacing has been laid and before being opened to traffic. The surface should be clean, free from loose material and dry or barely damp. The meteris operated at a speed between 3 and 6 km/h. The performance of the meter is checked daily on a mat provided with the equipment.

A rapidly pulsing laser, producing an infra-red light, is projected onto the road surface. Light is diffusely scattered from the projected image and is focused by a receiving lens onto a linear array of photodiodes. The position of the diode receiving most light gives a measure of the distance to the road surface at that instant. The root mean square texture depth (RMSTD) is computed from a series of such measurements over a fixed length of 300mm. The 10 and 50 meter results are averages of the 300mm RMSTD calculations. The meter provides a 100% sample along the measurement line taken.