What makes up chipseal?
Chipseal is made of sprayed hot bitumen, or cold bitumen emulsion (bitumen that's sprayed on cold). Crushed stone, known as 'chips', is rolled into the surface. It's usually applied to state highways that carry lower traffic volumes (those outside the main urban areas), with the more expensive 'asphaltic concrete' typically reserved for high-traffic state highways. Asphaltic concrete (hot mix) is a mixture of bitumen and stones and is less noisy and harder wearing than chipseal.
The 'chips' in chipseal are small, sharp-edged rocks. In the South Island they come from rivers, while in the North Island they're sourced mostly from quarries. In both cases the rock must be dense, strong and not slippery when it gets wet.
Chipseal has different colours in the North and South Islands. In the South Island it's more grey than black because the greywacke that washes off the surfaces of the Southern Alps into the rivers contains quartz, which makes the rock grey. North Island chipseal used more pure volcanic materials, such as andesite and basalt, which means North Island roads are darker.
