determination of road surface hardness prior to surface dressing is an important step in arriving at the correct chipping size to use with any particular traffic intensity, an essential prerequisite if adequate surface texture is to be maintained. this report describes the development of a simple probe test for this purpose and puts forward a graphical method for temperature correction to a standard test temperature of 30 deg c. proposed values of penetration corresponding to the five hardness categories defined in road note no 39 are:- very hard: 0-2 mm penetration at 30 deg c, hard: 2-5 mm penetration at 30 deg c, normal: 5-8 mm penetration at 30 deg c, soft: 8-12 mm penetration at 30 deg c, very soft: more than 12 mm penetration at 30 deg c. measurements of road surface hardness are made in the left-hand wheel track where embedment of chippings under traffic is likely to be at a maximum. good correlation between probe test results and rate of embedment of surface dressing chippings into a range of different bituminous surfacings was found using a multi-wheel-tracking test technique.(a)

Want to know more about this project?