Technical Specifications
The process is carried out in the following stages:
1. The existing road surface is broken up to a depth of 75/80 mm. This material is then harrowed and rolled until it is reduced to a suitable grading containing no material over 75 mm in size. If required 40 mm to 14 mm graded aggregate is added to correct any deficiencies there may be in the grading of the existing surfacing. The surface is then reshaped to the required profile using an approved grader.
2. Depending on the grading and type of surface to be treated, bitumen emulsion to BS 434 class K2, A2-50 or A3 is applied by a bulk distributor complying with BS 3136 at a total rate of 5.5to 8.0 I/ in two or three applications. After each application, except the last, harrows are traversed to turn the stone and to distribute the emulsion evenly.
3. If necessary the road is reshaped with a grader, and then rolled preferably with an 8 to 10 tonne deadweight roller. The surface voids are filled with 14 mm chippings, applied at an appropriate rate and rolled.
4. The surface should then be sealed by applying bitumen emulsion to BS 434 class K1-60. A1-70, A1-60 or A1-55 at a rate of 0.9 to 1.2 I/ and according to the texture blinded with 6 mm or 10 mm chippings. The surface is then rolled.
5. After a period which may vary from a few days to three months depending on weather conditions, traffic etc.. the retreaded surface should be surface dressed with bitumen emulsion to BS 434 class K1-60, K1-70. A1-60 or A1-55 using 6 mm or 10 mm chippings. Depending on the road category the rate of application of the emulsion should be increased by approximately 0.2 I/ over the appropriate recommendation for hard surfaces in BS 434.
Alternatively a slurry surfacing or bituminous wearing course may be applied. For further information see Summary and Reference Sheet.