Built to custom specs, the prominently branded trailers are becoming a common sight on the country’s roads. Inside is specialist equipment that measures the density, moisture, and strength of road building materials.
The trailers run compaction tests that check samples of aggregates, foamed bitumen, and cement binders. It's important work. Compaction testing helps make sure that ground beneath roads is dense enough to support traffic loads.
Rotorua-based laboratory manager Portly Griffiths says the fifth, just-built trailer will be based in Christchurch, and travel where it’s needed. It’s the only one in the South Island. Like the others, it’s set to prove its worth on remote projects where conventional lab access is more than an hour’s drive away.
Portly says compaction tests are required under NZ Transport Agency Waka Kotahi road construction specifications. They must be done close to the work site, and within tight timeframes.
“Tests used to be done on-site using a vibrating hammer. Technicians would manually attempt apply thirty to forty kilonewtons of downward force with their ‘calibrated arm’. It was a very hands‑on process. Now, we're using calibrated frames, moulds, and vibrating hammers that sit in the trailers. These let us apply the correct force on-site, faster, more accurately and consistently.”
Since being developed and hitting the road early last year, WSP has built a sizeable fleet of the trailers - based in Whangarei, Hamilton, Taupō, Rotorua, and Christchurch, along with a compaction van in Auckland.
On any given project, the trailers and their operators are hard at work. Maximum Dry Density (MDD) tests are done for every 5,000 cubic metres of roading material laid down. Sets of Indirect Tensile Strength (ITS) and Unconfined Compressive Strength (UCS) tests are also often done to find out how strong the materials are before they're used.
Testament to its positive impact, Portly’s trailer innovation has been making waves in the industry – last year being awarded a technical innovation award by the Civil Engineering Testing Association of New Zealand.
