Gore sizzles and the tar is melting

Wednesday, 14 December 2022

Gore District Council roading asset manager Murray Hasler says the melting happens on newly sealed stretches of road when the kerosene and diesel that was mixed with the bitumen evaporates.

As the mercury hit 26.1C in Gore on Tuesday, it caused some issues for the council as its roading team fixed melting tar on some streets.

On Wednesday morning, sealing chip was added to Traford St, Charlton Rd, Waimumu Rd and Kana St in Mataura to strengthen the surfaces.

Gore District Council roading asset manager Murray Hasler said the melting, which technically was called bleeding, happened on newly sealed stretches of road when the kerosene and diesel that was mixed with the bitumen evaporated.

“It happens in the first couple of years when it gets reasonably hot and it semi-liquifies, so that is when bleeding occurs,’’ he said.

* Carnage on the corner: farmer calls for agency to permanently fix road

* Motorist found himself 'swimming in tar' on section of Waikato Expressway

The hot weather is causing the tar on some streets around Gore and Mataura to melt.

Kerosene and diesel were mixed with the bitumen to allow it to be flexible in extremes of hot and cold weather, he said.

“It doesn’t just happen here, we hear about it happening around the country. The bitumen used in the North Island is different to the South Island. Down here it is softer because it has to deal with more of a range between the extremely cold and the extremely hot – Central Otago’s weather is a good example of that.’’

Harder bitumen would crack in the winter and allow water under the road surface, he said.

Areas like eastern Southland seemed to be getting more frequent hot weather, and it was possible that the quantities of diesel and kerosene mixed with the diesel could change to cope with that.

“We are stuck between a rock and a hard place because we like the hot weather but it causes roads to bleed. It is a dynamic process we will try to factor in, in the next couple of years depending on the temperatures we are likely to get.’’

MetService meteorologist Dan Corrigan said while the air temperature at the Gore weather station reached 26.1C, the maximum ground temperature at the Gore weather station at 3pm on Tuesday reached 44.9C.

“… that was only on the grass, so you can imagine the tarmac, which is black and black absorbs the solar radiation, why it got so hot,” he said.