I suspect Superpave will lead to some improvements in paving technology. It will not prevent paving failures in most Highway’s Agency paving programs without major changes in there systems of Project Management. Quality must be built in.
The Province of Manitoba Highways Department has not experienced a mix-related paving failure in 22 years. This involves approximately 500 asphalt paving projects, and in excess of 1,000 bituminous mixes.
This has been accomplished through our Quality Control and Quality Assurance System initiated in 1975. The system is based on pro active concepts. We control the mix to a greater degree than most other agencies. Nothing goes to the road until the mix properties are acceptable and the mix is under control.
The mixing operation is controlled more through the asphalt plant than the mix. We have developed extensive monitoring systems for drum mix plants. We monitor the asphalt metering system, feed belts, moisture and plant temperature.
If the plant goes out of control, our system will pick it up quickly. In the 22 years we have followed this system, the longest a drum mix plant has operated out of control is about one hour. Usually the problem is identified, the plant is shut down and the mix is rejected before it is placed on the road.
In the instances where it is placed, we know exactly where it is and how deficient it is. We can then decide whether it should be removed and replaced, or if it can be accepted as is.
This system has been developed over a period of 22 years. In that time past projects have been continuously monitored. We monitor mixes to find out where and why particular mixes last longer or shorter than expected. Changes are based on past experience and hard data. Our control of the mix is an ongoing and ever changing process based on ensuring what goes on the road is the best mix possible.
The key to Manitoba's success is our system and key to our system are the Quality Assurance Field Inspectors. The system is set up with quality control provided by Regional Highways staff and Quality Assurance provided by the Engineering Audit & Quality Assurance Section. The Quality Assurance portion consists of 6-8 individuals who possess expertise in asphalt technology, testing procedures, drum mix plants, asphalt paving, construction equipment and construction practices.
We have in-house training programs to ensure all testing personnel possess the required skills to do their jobs.
At the start of aggregate production the Quality Assurance Field Inspector makes up a preliminary mix design based on what the Contractor is producing and what is specified. He sets tight ranges that the Contractor must stay between. He informs the Contractor on whether they require supplementary material. The Regional testing staff run continual testing of the raw aggregates rejecting material that runs outside the set crushing ranges. There is some flexibility in the system with ranges adjusted as pits change. New ranges constitute new piles.
During the aggregate processing, split samples are sent to the Materials Central Laboratory for correlation testing. Where there is a variance outside normal tolerances the Quality Assurance Field Inspector reviews field-testing operations and ensures it is under control.
Once the aggregates are substantially complete, the Quality Assurance Field Inspector forwards a mix design request to Highways Material Lab for processing. With drum mix plants, what goes in must be uniform or what comes out will not be. Control of the processing of the raw aggregates is crucial to producing quality mix.
When the Contractor moves his asphalt plant to the project, a field lab is set up to monitor the plant, run extractions and sieve analysis. Two Regional Field Technicians work out of this lab. One Technician tests the mix on a continual basis (4-6 samples/day). The other Technician continually monitors and records the plant operations. If the plant goes out of control, the plant is shut down.
A Quality Assurance Field Inspector assisted by Regional Staff calibrates the asphalt plant. A Mobile Testing Lab is on site for start up to check the properties before mix goes to the road and to assist the Quality Assurance Field Inspector in setting the mix.
The Mobile Testing Lab is correlated with the Field Lab and with the Material Central Lab on each mix. A trial mix is run and tested. If the mix meets acceptable design criteria, road operations start. If it does not, the Quality Assurance Field Inspector adjusts plant settings and another trial batch is mixed. When the mix meets acceptable design criteria, operations start.
The Mobile Testing Lab stays on-site until the Quality Assurance Field Inspector releases it. This is usually 2 - 4 days while the mix is adjusted to get the best possible mix. All labs are continually correlated during this period. Once the mix is set, the Field Lab controls it. If the gradation and A.C. content remain constant so do the properties. A sample per day is forwarded to the Material Central Lab and if required, Field Technicians store extra samples for job summary samples. (We require a minimum of 20 top lift samples for statistical analysis of the final mix.)
The road operation is monitored for density and smoothness. Density’s are taken with a nuclear machine correlated with cores. The correlation process involves testing ten sites with the nuclear densometer. Cores are taken at the exact same location. A correction factor is established for the machine.
The machine is used for further testing corrected by the established factor. (The Mobile Testing Laboratories are equipped with a coring unit).
If density’s are a concern, they are rechecked with cores. The Quality Assurance Field Inspector and Regional Road Inspector coordinate test strips working with the Contractor to achieve the best density possible. A high-low beam is used closely behind paving operations to ensure the paver is operating properly. If the paver goes out of control paving is stopped. The Region contacts Materials Central Lab to arrange coring and profilograph readings at project completion. This data is used in Quality Assurance job summary files (history files).
At the conclusion of the project the Quality Assurance Manager reviews the project with the Project Supervisor. This Contract Review includes a check that the project met design criteria, specifications were met and all areas of dispute are settled.
The Quality Assurance Field Inspector, in the off season, completes his or her job summary for historical purposes. This summary includes statistical analysis of aggregate, mix, a.c.’s and other pertinent data.
This system has aided in producing quality asphalt paving projects. Since Manitoba Highways incorporated Quality Assurance 22 years ago, we have constructed approximately 500 asphalt paving projects without a mix related failure. We have designed our mixes above the maximum density line and they are performing extremely well. These mixes typically last 20+ years.
Quality mixes are easy to make in a controlled labratory environment. Unless there is an equally controlled field environment these lab mixes will not be consistently reproduced in the field.
Douglas L. Fisher, Manager
Engineering Audit & Quality Assurance
The Province of Manitoba
Highways & Transportation
16-215 Garry Street
Winnipeg MB. R3C 3Z1
Phone: 204-945-5307
Fax: 204-945-3841
E-mail: dfisher@hwy.gov.mb.ca