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Utility reinstatements: big bubbles, big troubles


Walk through any town, and it’s not difficult to spot badly reinstated utility trenches (even easier if you’re on a bike). Defects can include wide cracks or potholes along the edges of the reinstatement, indentations or even wholesale sinking of the reinstated area.

Often the culprit in these failures is air voids. If the proportion of air voids is too high, the reinstatement will fail prematurely. Depending on weather and traffic conditions, it could be a few months, or a few years before problems start to show.

Currently, utility companies must return to fix any failure that occur within two years of a reinstatement. There were calls for this period to be extended to five years when the fourth edition of the Specification for the Reinstatement of Openings in Highways (SROH) – which came into force from April 2021 – was produced. But these were ditched.

As a result, local authorities are often left carrying the can for failed reinstatements. A research programme back in 2011 found that 50% of the core samples taken from roads in Rochdale and Oldham in the Northwest failed, with the majority of those failures due to air voids. More recently, the Scottish Road Works Commissioner said that in 2018/19, there was a failure rate of 23% among utility work reinstatements.

Getting the right air void proportion is all about getting the compaction right. Compacting asphalt, with a roller, forces the particles of bitumen-coated aggregate in the mix closer together. This increases the interlock between aggregate particles and hence the friction, increasing the strength and durability. Too many voids also means that water can get into the asphalt and speed up the degradation process through freeze-thaw.

The temperature of the asphalt when it is rolled also plays an important role in achieving compaction. For standard asphalt mixes, the material needs to be sufficiently warm and mobile when it is rolled – or those air gaps won’t be reduced. Warm mix or cold mix asphalts contain chemical additives which aid the compaction process.

Thermal Road Repairs’ technology has been deployed for many years to fix failed utility reinstatements. You can read a case study about it here LINK. Our computer-controlled heater raises the temperature enough to allow sufficient compaction but doesn’t raise it above certain limits as that would oxidise the bitumen in the mix, making it brittle and more likely to crack. Since it heats the material around the edges of the reinstatement, it effectively removes the joints, as the material either side of the joint heats up, blends and becomes one.

Now some of our customers are starting to deploy the technology in the original reinstatement process. In response to their feedback, TRR developed a new thermal heater designed specifically for the original reinstatement work, to ensure that they are done right first time. By heating up the joint area as the trench is filled, the old and new material blend into one, effectively removing the joint – along with the risk of air voids.

Thermal Road Repairs is a green technology company which supplies systems to improve the quality, cost and time efficiency of road repairs and paving – at a far lower environmental cost than traditional methods. We invest significantly in R&D, to create new technologies and to continuously improve our existing ones.

High output. Low emission. Permanent solution.

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