MATERIALS TESTING EQUIPMENT LTD
Gilwilly Industrial Estate Penrith Cumbria. UK CA11 9BQ
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40-34106 Road Hardness Probe with carry case

As described in UK road note 39 regarding surface dressing, the hardness of the road surface directly affects the way dressing chippings embed into the surface over the life of the surface dressing.

The use of chippings that are too small will result in early embedding of the chippings into the surface and result in a loss of texture depth. In severe cases the binder may well up and cover the entire surface of the carriageway.

Using chippings that are too large may lead to an immediate failure of the dressing caused by stripping of the binder from the aggregate under the load of traffic. Excessive surface texture will also increase noise generated by traffic.

The road hardness probe aids in the calculation of the rate of binder application for a given size of surface dressing chipping. The rate of spread must be adjusted to compensate for the embedment of chippings under the action of traffic.

In the UK the categories of road hardness for existing surfaces for the purposes of surface dressing are noted in Road Note 39. Four graphs take account the geographical location and altitude of the site within the UK and gives five hardness ranges from very soft through to very hard.

On site, the road hardness probe is used in conjunction with the four graphs to give a strength in one of the five categories. The road hardness probe measures the depth that a 4mm semi spherical head penetrates the surface after a load of 340N is applied for 10 seconds.

The average of ten or more readings from the inside wheel track of the carriageway under treatment is calculated. Consideration must also be given to the surface temperature and recorded as experience has shown that only temperatures in the range 15°C to 35°C give significant results.

A series of ten measurements were taken from a carriageway under treatment and the results were averaged. This was repeated 10 times to give 10 averages. These averages were plotted on the graph depicted in Road Note 39 as graph D North Category more than 200m altitude.

These results will form the basis of how the surface will be dressed. Materials Testing Equipment can provide all the equipment, documentation and relevant Standards for this and all other tests commonly carried out in civil engineering projects.

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