3.4.2 Salt-affected Pavements
Some pavement materials, particularly rubbles, may contain an appreciable quantity of salt. In addition, water used in compaction may also be saline. Where one or both of these conditions is encountered, it is possible that eruptions of small blisters may occur, with the surface of the pavement immediately beneath the primer being in a loose condition with saline fines.
Generally, the most effective treatment is to apply the initial treatment as an emulsion followed by the secondary treatment within a short space of time to provide a thick impermeable system as soon as possible. Light treatments, including primes and initial seals, are particularly vulnerable to salt damage.
If a prime or initial seal is affected by salt, all loose material, including any visible salt from the exposed base, should be swept off. An effective treatment is to re-prime with an emulsion followed immediately by a light seal using Class 170 bitumen. A further double/double seal should then be applied as soon as possible. Care must be taken when sweeping to avoid roughening the surface and rendering it unfit for sealing.
If a seal shows signs of light damage due to salt, blisters may be flattened by rolling and the surface resealed, if necessary. For severe damage to a seal, the surfacing and any visible salt should be removed. Potholes and severely affected pavement areas should be boxed out to the full depth of powdering, and patched before resealing the full road width. In extreme cases, resealing with PMBs may be required to provide an adequate treatment.
Guidelines for preliminary treatment techniques developed by Januszke and Booth (1992) are presented in Table 3.2. These guidelines are based on adjustment of treatment type depending on the salinity of the pavement expressed as salt content of the fines passing the 2 mm sieve.
|Salt content of fines||Initial treatment|
|0−1.5%||Treat as for a normal pavement.|
|1.6−2.5%||Initial seal followed as quickly as possible by the final seal.|
|2.6−3.0%||A sacrificial prime plus initial seal, followed as quickly as possible by the final seal may be satisfactory. If in doubt, treat as for > 3.0% salt content.|
|> 3.0%||Special investigations will be required and suitable procedures developed.|