The risk of material cooling is relatively high for narrow reinstatements. Depending on the specifics of the asphalt material, relatively fast cooling can lead to difficulty in achieving the required level of compaction, and this can result in reduced durability of asphalt materials. Therefore, dependent on the site specifics, resourcing to ensure compaction of asphalt materials in narrow trenches may require additional consideration. Examples of this includes material choice and working practice (number of operatives).
An alternative is hand compaction; however, it is not the preferred method and should only be used where conventional compaction equipment cannot be used, and only for the minimum possible proportion of the reinstatement. Where narrow trenches or small openings make compaction impracticable, and where conventional equipment cannot be used owing to existing restrictions, PMMA is preferred.
PMMA are recommended when compaction cannot be readily achieved with conventional materials or equipment owing to existing restrictions (kerbs, ironwork, street furniture, narrow trenches, etc).
In some systems pre-manufactured PMMA blocks can be lightly bedded into the hot PMMA. Sufficient space between the blocks is needed to allow the surrounding hotter material to flow around the blocks and fill any voids. For deeper excavations, extra layers of PMMA and blocks are used as required.
When all the blocks have been placed, the material is allowed to cool for 10 minutes. The excavation is typically filled to within 30 to 50 mm of the finished carriageway surface to allow final installation of the PMMA surfacing. The following information should typically be retained by the undertaker in relation to any potential future defects:
- Confirmation from the certificate holder that the installer is approved to install the proposed system.
- A copy of the Method Statement in line with the certificate for the chosen system.
- A copy of the material data sheets and/or company COSHH sheets.
- Results of all quality control checks carried out on site by the undertaker and quality assurance information compiled in accordance with the requirements of the certificate, including results from surveillance.