After receiving reports regarding Avondale Road and several other areas where recently repaired sections of road appear to soften or “melt” as soon as temperatures rise, even slightly, and raising the issue with the Highways Department, I’m pleased to say the issue is now already added into their work-schedule for the matter to be investigated and granite to be applied to the surface, and assessed if any other repairs are required. Below is the response I have just received from our highways director:
“Unfortunately, prolonged hot weather can raise the road surface temperature to rise to a point where it can cause the bitumen binder to soften and rise to the surface which creates the black shiny film you are seeing in the below photograph. This is usually at 50degree + road surface temperatures. This is more prevalent in surface dressed roads, or repairs where we have used tar and chip.
The heat reduces the viscosity of the binder and causes it to expand into the aggregate voids and then push upward when trafficked. Whilst undesirable, this process is normal when exposure to heat is prolonged as I mentioned earlier and is probably becoming more common across the UK as summer temperature rises, or like recently, we have a snap change in the weather.
To remedy this, we place granite dust on the surface with our gritters. This absorbs the excess binder and makes the surface denser.
I have contacted our out of hours service this morning following your email and have asked them to ensure that Avondale Road is added to the list of roads we are treating over the next few days to ensure this issue is kept to a minimum. I will ask the team to inspect this road early next week to determine if any other treatment is required, or whether applying granite dust is dealing with the problem. “