How a Mt Maunganui company’s world-class laboratory expertise won a major award for enabling efficiency gains and cost savings to be made on a long-term road-maintenance contract. BY GAVIN RILEY.
AN IMPORTANT AND LASTING contribution to getting more value from the roading dollar proved a winning entry in the “maintenance and management of assets” category of Civil Contractors NZ’s 2014 Hirepool construction excellence awards.
Winning company Road Science’s advanced design, testing and investigation methodologies enabled significant savings to be made on the Transport Agency’s East Waikato hybrid-model maintenance contract.
Developed from the doctorate studies of Road Science’s Greg Arnold and Transport Agency research over the past 15 years, the methodologies using repeated load triaxial and flexural beam tests are considered the most advanced in the world in the area of granular and stabilised pavements.
For the 2006-2015 East Waikato contract, the Transport Agency has a requirement to reduce the total budget by about 10 percent each year. In addition, due to the fixed lump sum for pavement renewals, sites that were low risk and low cost were treated. So the problem sites with the greatest pavement distress were avoided due to the extra cost to repair them falling on the contractor (Downer) and the high risk of their early pavement failure.
Another imperative for change was the agency’s need to reduce the number of early failures the contract was experiencing.
As a result, Road Science’s Mt Maunganui-based pavements team was asked to use its advanced testing & design techniques to create the optimal treatments for the renewals. The process that has evolved contains a no. of steps:
- Site identification. Each year the worst sites (about 12) are identified by the contract asset management team for a full design and pavement rehabilitation.
- Site investigation and test pits. Pavement distress type and existing pavement depths are determined along with samples of the existing pavement taken for advanced testing. This work is carried out by Road Science in conjunction with the operations team of Opus and Downer.
- Advanced laboratory investigation. Road Science conducts repeated load triaxial and flexural beam tests on the pavement materials and proposed stabilised mixes to determine performance criteria for the pavement design.
- Pavement design using advanced laboratory test data. The triaxial tests determine the rutting life of the pavement and the flexural tests estimate the fatigue life of any proposed stabilised pavement treatment. The testing and analysis is carried out by Road Science’s specialist team.
- Writing the pavement design report. This contains various options and predicted lives from the advanced lab testing.
- Collaboration with the client, contractor and consultant to obtain agreement on the best pavement treatment solution. Selection is based on available funding, risk of early failure, constructability, and agreed design life.
- Production tests on site to confirm design assumptions. This work is carried out by Road Science in collaboration with the infield construction team.
- Monitoring performance on constructed pavement rehabilitations. This is done by Road Science in consultation with Opus and the Transport Agency.
A prime example of challenges on the East Waikato contract to determine the cause of early failure and the best solution can be found on the Waikato side of the Kaimais.
Here the climbing lane had significant wheel-track rutting. The road site already had 600mm of aggregate over a subgrade CBR (California bearing ratio) of 6 percent, and current Austroads pavement design rules could not determine why the road had failed early.
The pavement depth had been deemed to be sufficient for both past and future traffic. Thus, for a neighbouring road section the design was simply to stabilise in situ with 1.5 percent cement to a depth of 200mm which, using Transport Agency and Austroads design rules, was considered to have a 25-year design life. Yet this newly stabilised road section has 50mm ruts after three years and is also in need of repair.
Road Science undertook repeated load triaxial (RLT) tests on both the basecourse and subbase aggregate, which identified a weakness in the latter. Using the RLT test data in design it was found the subbase aggregate had the shortest life.
These results were discussed with the Transport Agency, along with several other design options. A suitable treatment was designed and constructed to remove the subbase aggregate and replace it with better quality aggregate. The RLT test of the top 150mm of basecourse was found to be of good quality and was stockpiled and then re-used in the pavement.
A number of first-rate results have been delivered from the innovative changes that the East Wakaito maintenance contract adopted. These benefits include a 20 percent saving on reseal costs in the 2012-13 season, a 12 percent saving on rehabilitation costs over the same period, an average saving of 10 percent on the total contract budget, the production of cost-effective and suitable treatments, greater confidence in the design process using Road Science’s advanced methodologies, and an option to reduce costs and accept greater risk.
Savings have been made in reducing the length of reseals to what was actually needed based on network conditions, along with some sites needing only low-cost pavement-renewal treatments as determined by the Road Science team. Some of the savings have been used to undertake more exhaustive treatments as recommended by the team on problematic and weak pavement sites, while other savings have enabled the team to meet the Transport Agency’s reduced budget.
Road Science says the quality-control sampling carried out post-construction in East Waikato not only confirms the effectiveness of its innovative approach to pavement rehabilitation but helps refine future design and construction methods. “The initial investment in this design and testing process is quickly recovered in finding out the optimum treatment for each site with the certainty of performance to ensure the pavement-renewal treatment will meet the agreed design life.”
The Transport Agency is enthusiastic about Road Science’s East Waikato input. “This is the most comprehensive design and testing process I have seen, which is surprising on a contract that has been squeezed the most in terms of reduced budget,” says the agency’s network maintenance and operations adviser, Alan Burkett, quoted in Road Science’s Hirepool-award submission.
The agency has commissioned Greg Arnold, Road Science’s technical manager pavements, to rewrite the agency’s pavement rehabilitation design guide and its training notes to include his team’s advanced testing.
It’s a feather in the cap of a company which was formed in 2005 from Downer’s bitumen supply-and-operations businesses, and in mid-2012 adopted its present name to reflect its expertise and role as an independent, standalone supplier of products and services to the New Zealand roading industry.