Asphalt mixes made easy
February 1, 2015 by Patrick Callan
The Ontario Hot Mix Producers Association (OHMPA) liaison committee has created a spreadsheet to simplify measuring asphalt mixes to ensure they meet Ontario Provincial Standard Specification (OPSS) 310.
The OHMPA says current testing processes can be cumbersome and result in the removal of acceptable mix. In addition, not all municipalities have qualified staff that understand how to interpret quality-assurance test results.
Enter the spreadsheet. It is designed to allow municipalities to easily test asphalt to find out which mixes are acceptable, borderline and rejectable. It also calculates a payment for that asphalt based on the quality that was actually produced.
To determine the quality of the asphalt, samples are taken from different lots and sub-lots of the paving project. For example, if you were paving 2,000 tons in one day, you should have four sub-lots of up to 500 tons. Once you have the samples, you test them and then run the numbers into the spreadsheet to see how well the asphalt sample compares to the original job mix formula submitted by the contractor.
The tolerances for the job mix formulas are based on OPSS310 and variation between the job mix formula and the actual samples will determine if the asphalt is acceptable, borderline or rejectable.
To make sure the testing is done fairly, three samples are taken from each lot. The municipality tests the quality-assurance sample, the quality-control sample goes to the contractor to do their own in-house sampling, and a reference sample is kept in case there are any disputes between the first two.
Sub-par mixes will result in deductions from the “payment factor,” meaning the contractor will not receive full payment for asphalt that is not up to standard.
“If you’re supposed to pay them $100 for all their work, but they only have a payment factor of 98.3, you’d only pay them $98.30,” explains Mark Eby, construction manager for the County of Wellington and member of the OHMPA’s liaison committee.
“We’re still working on actually making sure the reduction is appropriate for what is going wrong. We need more sampling out in the field to get the results to adjust it,” he says. “We really do want to ensure that the payment adjustment factor is appropriate for how much they’re going to lose.”
Since the spreadsheet was introduced in November, 2013, a total of 32 lots results have been reviewed (mainly from the County of Wellington). Fifteen received 100 percent payment, 12 between 90 and 100 percent, one between 60 and 90 percent and four were considered rejectable (less than 60 percent payment factor).
“Thirty-two lots is a very small sample size, considering how much paving occurred within the province last year…But it’s a starting point,” says Eby.
One of the problems that arises with testing asphalt is that the results often take a couple of weeks to come back and the testing only takes place once the paving has already been completed.
“The entire job could be done and all of a sudden you find out that you’ve got bad asphalt,” says Eby. “Municipalities don’t want to pay full price for something that’s not full-price material.”
But it’s not only municipalities who are concerned about asphalt quality.
“Contractors want to ensure that the payment reduction meets what the outcome of the asphalt is. Typically, a contractor only has between three to 10 percent profit on a job. If they just lose profit that’s one thing—but if you start digging into their overhead, they’re starting to lose money.
“What we’re trying to do is have the contractor be more diligent in his testing and in his mix,” he says. Ultimately, the goal is to produce higher quality pavement across Ontario and to get more municipalitities and contractors on board with using this spreadsheet.
“Paving costs a lot of money, and if you’re hoping your pavement will last 20 years but you’re getting pavements that are routinely only performing to 14 or 15 years, you’re losing time and it’s costing you more money,” explains Eby.
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