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OHMPA fall seminar updates attendees on various surface matters

Dan O'Reilly
OHMPA fall seminar updates attendees on various surface matters

Ranging from a brief acknowledgement of the auditor general’s report, to industry issues, to product developments, the 25th fall seminar of the Ontario Hot Mix Producers Association (OHMPA) was a comprehensive event and its last as an independent organization.

A major highlight was a short history of the long and rather complicated process which led to the resumption of the use of stone mastic asphalt (SMA) in road projects after a seven-year halt, a period which the Ministry of Transportation (MTO) describes as a "pause."

First developed in Germany, SMA is a highly textured and durable surface mix with a much higher percentage of stone and more asphalt cement than conventional hot mix asphalt.

In 2007, however, the MTO halted its use over concerns with initial friction.

With the endorsement of a special MTO/OHMPA task force, that halt was finally lifted in late 2014 after a series of successful coated gritting trials and contracts.

SMA was first adopted for use as a premium surface course mix on Ontario highways for its durability and resistance to rutting and cracking in 2002, said Pamela Marks, head of the ministry’s bituminous section.

But in 2005 the ministry began noticing that SMA was providing low initial friction, although further testing and analysis showed surface friction improved with traffic wear over time, she said.

Those concerns led to the creation of a MTO/OHMPA task force that same year to investigate different alternatives to improving the friction problem. A number of causes were examined and remedies proposed including water blasting the surface.

What followed was a series of mix attribute evaluation trials in 2009/2010 and then a number of embedded grit trial test sections along and adjacent to the Queen Elizabeth Way in 2011. Conducted by a number of different contractors, the sections included the use of both coated and uncoated grit.

The coated grit definitely performed better, said Marks, citing less dust and no pick-up issues and no need to remove excess grit material.

A major finding was the placement of a certain percentage (0.8 to one per cent) of asphalt cement coated sand, "immediately after initial compaction and then embedding it into the mat using normal compactions rollers was found to be effective in improving the low initial friction."

Within six to eight weeks friction values for both the gritted and ungritted sections were about the same, the audience was told.

Then, in 2012/2013, sections of Highway 6 and Highway 401 were constructed using SMA with coated grit.

"Tests indicated acceptable friction for both contracts," said Marks.

There are number of next steps in the incorporation of SMA in road projects, including updating specifications. The ministry will specify the use of the material when warranted, but will also continue to monitor the friction and performance of all SMA projects as well as reviewing the experiences of other transportation agencies, said Marks.

Other seminar topics included a short review of the research conducted by the recently-wrapped-up Quality of Asphalt Task Force. It was created by the association a few years ago in response to concerns by the MTO, municipal road departments and even OHMPA’s own members about premature cracking. Those concerns led to a series of bulletins by the task force on details such as asphalt cement content.

In reviewing the task force’s work, OHMPA executive director Vince Aurilio expressed the hope some of the material might eventually be incorporated into specifications.

There was only a brief reference to the auditor general’s report which was unveiled the day before.

OHMPA came under fire in the report with the auditor general stating the association provided substandard asphalt that has been shown to crack years before it is supposed to, with taxpayers picking up tabs amounting to millions of dollars for premature fixes.

"The asphalt industry, specifically the asphalt cement suppliers, were adding cheaper materials, notably excessive amounts of recycled engine oil, into the cement they supplied for use on ministry projects," she wrote.

In showing a slide of a short news release, Aurilio said the association wouldn’t be making any further comments until it had time to read and evaluate the report.

Held at a Vaughan, Ont. banquet hall, the fall seminar was the last hosted by the association as an independent organization. It will be reconstituted as a council of the Ontario Road Builders’ Association after members of both organizations voted to merge earlier this fall. The merger comes into effect this January. OHMPA president Donn Bernal said he was confident the new council will be able to maintain its identify and predicted the fall seminars would continue.

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