While many construction projects around the state are just getting underway, crews are close to wrapping up work on I-90 between SR 21 and Ritzville. And on this project, we tried something a little different.
Stone Matrix Asphalt. No, it doesn't involve Keanu Reeves – though that would be amazing – but it's still pretty cool. But more on that in just a bit.
|Trucks line up on I-90 near Ritzville as part of a paving project nearing completion. This stretch of I-90|
near Ritzville hasn't had a significant paving job in more than 15 years.
The last time this stretch of I-90 – covering about 10½ miles – had a full pavement grind and inlay of asphalt was 2002. There was some minor reconstruction work in 2008 but overall the highway has remained relatively unchanged for more than 15 years. You may have noticed more wear on the road in the past couple years, with some significant rutting and cracks causing the roadway to look aged.
Typically the pavement cycle for resurfacing is about every 10 to 15 years, so 17 years is longer than normal. To extend the life of this next pavement cycle, we're using Stone Matrix Asphalt, or SMA, for the driving lane.
|A look at the difference between Hot Mix Asphalt and Stone Matrix Asphalt|
Generally a standard asphalt mix is called Hot Mix Asphalt (HMA) or dense graded asphalt. The roadway is ground down and paved over. The HMA, made up of a mix of sand, oil and aggregate stone between 3/8- to ½-inch in size, is poured on the road. It gets heated, pressed down and rolled into that smooth surface we all know and love.
SMA is similar with its use of ½-inch rock. The different and more challenging part is packing the rock down with the use of less oil or sand. If you can pack the rock down, over time you'll be driving on rock rather than a higher concentration of sand and oil. That means with SMA, it's the rock – rather than the sand and oil – which will take the brunt of the wear, allowing for a much slower breakdown of the roadway over time. This means less rutting and cracking of the pavement and a longer life of the roadway.
|This 10½-mile stretch of I-90 will soon have a new layer of asphalt.|
We've used SMA a few other times on projects around the state with some success and given the level of traffic on this stretch of highway, this seemed like a good opportunity. The goal with an SMA roadway is to get 15 to 20 years of life out of it and have it last longer than with HMA pavement.
There's still a couple of weeks left on the project but once it's done, fresh asphalt that should last longer will be in place to give drivers a smoother trip on I-90.