How to Perform Winter Maintenance on a Porous Pavement
BY Sandy Lender
Contractors performing winter pavement maintenance should be clamoring for the jobs that service porous asphalt pavements. It would be irresponsible to say merely “you get to leave it alone,” but the fact is porous asphalt pavements require fewer deicing chemicals and less work than do impervious pavements. Here’s why.
First, the Federal Highway Administration (FHWA) technical brief Porous Asphalt Pavements with Stone Reservoirs points out “Porous asphalt pavements have been successfully used for more than 35 years in a variety of climates around the United States. They provide a pavement surface that is also part of the stormwater management system, reducing stormwater runoff and pollutants and replenishing groundwater. A number of porous asphalt parking lots have lasted more than 20 years with no maintenance other than cleaning.”
Regular cleaning is something FHWA recommends, suggesting pavement owners include vacuuming two to four times a year to keep dirt and debris from clogging the voids that are meant to allow stormwater to pass through the pavement and stone layers.
In the technical brief, FHWA warns that pavement owners should never sealcoat or crack seal the porous asphalt pavement—for the obvious reason that these strategies close the system. The FHWA technical brief states: “If patching is necessary, conventional mixes may be used if less than 10 percent of the pavement area is affected.” Companies that have been contracted to maintain commercial or residential properties should verify the pavement structure before performing maintenance treatments to ensure they aren’t negating the owner’s stormwater management, etc.
One concern agencies in northern climates have mentioned when it comes to the use of porous asphalt pavements is that of winter maintenance, specifically icing conditions and how to handle them.
In her December 2016 Master of Science thesis “Winter Deicing Methods for Porous Asphalt,” Heidi Whitney Lemay of the University of New Hampshire, addressed the concern, stating, “porous asphalt has created challenges in colder climates with respect to deicing operations. It has been found that the traditional deicing method of applying rock salt is not as compelling on porous surfaces because much of the salt remains days after a storm event. This study presents the findings of deicing an active porous asphalt parking lot using liquid reduced chloride or non-chloride deicers under winter storm conditions.”
The National Asphalt Pavement Association (NAPA) Information Series 131 (IS-131) document titled Porous Asphalt Pavements for Stormwater Management includes specific information about snow removal on an asphalt parking lot at the University of New Hampshire. One hour after plowing, the porous asphalt area of the parking lot showed significantly more snow melt and cleanliness of the pavement. But that’s just the visual cue that the porous pavement is doing its job. NAPA authors point out that the two areas were evaluated for the degree of snow and ice cover and for the friction factor of the surface using ASTM E303-93. The measurements showed a 75 percent reduction in salt application was possible for the porous pavement area in relation to the conventional dense-mix area. IS-131 states: “For the friction factor, a 100 percent reduction was determined (porous asphalt, even with no salt, has higher frictional resistance than dense-mix asphalt with 100 percent of the normal salt application). Therefore, a sizable reduction in salt application rate is possible for porous asphalt without compromising braking distance or increasing the chance of slipping and falling.”
Deicer types include, but are not limited to, in alphabetical order: acetates, chlorides, formates, glycols, succinates. Be aware that a host of researchers have found some acetate-based deicers can emulsify the asphalt binder in an asphalt pavement and can cause an alkali-silica reaction on some aggregates in concrete pavements. In other words, you might not be asked to use an excessive amount of Potassium acetate (KAc) deicer. The parameters of this article don’t include a deep discussion of chemical reactions; we’re not diving into the pros and cons of various deicers. Instead, we want to emphasize the reduction in use of chemicals to maintain the porous asphalt pavement through winter weather. Lemay’s study tested three liquid deicers specifically: Potassium acetate (a non-chloride), beet and brine (a reduced-chloride), and beet and water (a non-chloride). “The three liquid deicers were found to be effective during this study, producing results similar to that of rock salt used on impermeable asphalt,” Lemay stated in her paper.
Don Watson, P.E., of the National Center for Asphalt Technology (NCAT), shared that “A mineralized de-icer that has an operating range lower than normal sodium chloride may be used, and is applied with the truck sanders just like the sand-salt mixtures. Anti-icing chemical application is probably the most preferred and uses a 20 to 30 percent solution of magnesium chloride mixed with water to form a brine.”
Watson offered real-world use of the mix. “The product is applied at 20 to 40 gallons per lane mile in advance of a predicted winter storm. The actual rate may be varied due to existing pavement condition, severity of predicted storm, and whether any residual remains from previous applications…Anti-icing chemicals are effective to about -30 degrees F.”
Lemay’s study concluded, in addition to the positive results of liquid deicing agents on porous asphalt pavements, “based on the results of this study, reduced chloride or non-chloride deicers applied on porous asphalt may be used to effectively control snow and ice from porous asphalt surfaces in the manner expected of rock salt on traditional impervious surfaces.”
With minimal use of chemicals, the contractor performs plowing as he would for any other storm event.
Here’s How it Was Built
The porous asphalt pavement follows a simple structure, which maintenance contractors will want to understand. Even if you aren’t called upon to pave any of the layers of the system in the future, you’ll want to be aware of what you’re working with.
For example, Rons Construction Corporation, Honolulu, built a porous asphalt pavement for Vineyard Investment Realty LLC in Wahiawa, Hawaii, in 2017. The private driveway is 300 feet long, 20 feet wide and the first use of a porous asphalt pavement for a road or parking lot in the state.
According to Engineering Dynamics Corp. (EDC), the engineer for the project, the new development would create an increase in stormwater runoff from the site. The city required any increase in stormwater runoff from development be retained onsite instead of flowing into the city’s drainage system. EDC determined that the most cost-effective solution was to retain additional runoff onsite with the use of porous asphalt. The Hawaii Asphalt
Paving Industry (HAPI) developed a specification for the porous asphalt mix. HAPI member Grace Pacific LLC produced it, and HAPI member Rons Construction Corp. placed it.
The system is built like this: Above the uncompacted subgrade is a geotextile fabric, which prevents the migration of fines from the subgrade into the stone recharge bed while still allowing for water to pass through. The next layer is a stone reservoir consisting of uniformly graded, clean crushed stone with 40 percent voids serving as a structural layer and to temporarily store water as it infiltrates into the soil below. Then, to stabilize the surface for paving, a thin (about 1-inch) layer of clean, smaller, single-size crushed stones is often placed on top; this is called the stabilizing course or choker course.
The last layer consists of one or more layers of open-graded asphalt mixes with interconnected voids, allowing water to flow through the pavement into the stone reservoir. These open-graded asphalt layers consist of asphalt binder, stone aggregates and other additives.
By excluding fines, the open-graded mix allows for more air voids (typically between 16 and 22 percent voids.
Notice: there is no tack coat or bond layer. You don’t want the tack material filling the voids, which are supposed to allow water through.
Source: Hawaii Asphalt Paving Industry
Skid Steers Vs. Compact Track Loaders for Snow Removal
By Brad Stemper and George Mac Intyre
The equipment industry is still moving from traditional, rubber-tired skid steers to rubber-tracked compact track loaders (CTLs). CTLs offer lower ground pressure, greater lifting capacities in a comparable footprint, smoother operation over varied terrain, but there are still some applications where skid steers hold an advantage. Dedicated snow removal is one of them.
It’s important to note: if snow removal is a secondary/seasonal job for you, and you’re using CTLs that you deploy for dirt work in the summer for snow work, they’re going to work just fine. But it’s the one thing that makes these machines different that gives skid steers the advantage: where the rubber meets the road. Literally.
Wear: Skid steers with traditional rubber tires provide a lower initial investment than CTLs—the rubber tracks and undercarriage of the CTL add cost, and ultimately cost more to replace/maintain over the service life. While snow and ice does provide a slight buffer between the rubber tracks and the asphalt, rubber tracks are still subject to abrasion and wear from operation on improved surfaces such as asphalt. Rubber tires on a skid steer are subject to the same abrasion, but those tires can last longer and cost less to replace than the rubber tracks of the CTL.
Speed: Speed isn’t everything, especially in parking lots of retail centers, etc. where safety is paramount, but skid steers provide faster ground speed than CTLs. As an example: The 90-horsepower SV340 skid steer offers a top ground speed four miles per hour (MPH) faster than a comparable CTL. Skid steers offer a significant advantage in speed when working in wide-open spaces and commercial parking lots, allowing operators to work and reposition more quickly.
Downward Pressure: The hallmark advantage of a CTL is its low ground pressure. This actually provides a disadvantage when working in snow removal applications. A skid steer, with its four tires and less per-square-inch contact with the surface below, can exert more downward pressure on the bucket, plow or pusher than a CTL. This provides better scraping action along the surface and helps remove more snow and ice on the first pass.
Where do CTLs provide an advantage? Landscapers and other contractors who work in the dirt during the other three seasons of the year will be able to leverage the low ground pressure advantages of CTLs in their other work. And snow contractors who buy/lease machines and flip those units at the end of a season or two will find a stronger aftermarket demand for CTLs, making it easier to unload those units.
Truth is: Both machines will get you there. The nuance of which machine will offer a lower total cost of ownership/operation will come down to how you use that machine when it’s not snowing. Skid steers offer distinct advantages if the machine is only used in snow work and for operation on improved surfaces. CTLs provide greater operator comfort and a smoother ride, especially when working in off-road applications, and contractors have proven willing to pay extra in terms of the initial price and long-term undercarriage costs.
Brad Stemper is the product manager, and George Mac Intyre is the global product portfolio manager, light equipment, CASE Construction Equipment. CASE wishes to thank Robert Velazquez of Semper Fi Land Services and Nate Kohn of Nate’s Landscape for their input.