How do you keep roads and parking lots in good condition cost-effectively?  We’ve already talked about many of our routine maintenance suggestions, such as filling in cracks and sealcoating, but sometimes a surface is too damaged for these small actions – in these cases, it would take more money and time to repair than it would to perform a full rehabilitation.  But asphalt pulverizing offers a very economical way to fully rehabilitate a road or lot with minimal traffic disruption. It’s also a great way to save on paving materials. 

What is pulverization?

Pulverizing is a process that grinds up existing surface layers right in place, blending the asphalt layers with any sub-layers, essentially creating a new paving mix using all the old materials. No pavement is hauled away, saving costs on excavating and trucking, and rarely does new material have to be brought in (though sometimes additives or a new overlay are suggested).  Asphalt pulverizing solves most common problems, such as severe cracking and sharp edges created by continuous traffic (called “polishing”). 

Perpetual pavement is a flexible but strong asphalt pavement that doesn't exhibit structural damage even when very high traffic flows over long periods of time. They’re made up of multiple layers of durable asphalt. The bottom layer is designed to be strong but flexible to resist strains that could cause cracks to form from the bottom up. A similar intermediate layer adds additional structural protection, and the final layer, made of rut-resistant hot-mix asphalt (HMA), requires only minimal maintenance. 

These surfaces have been around a long time. Some of the oldest perpetual pavements have been around since before the 1960s. The surfaces created then that were well designed and executed have provided very long usefulness without much maintenance even with heavy traffic. These days, advancements in milling, recycling, and asphalt production technologies make it even more likely that perpetual pavements will perform better and longer.

Have you ever felt like the terminology of a subject strands you in an unknown land?  Take asphalt -- if you’re just learning about it, terminology can be a barrier.  Those in the industry don’t think twice about terms like “hot-mix” or “sealcoating,” but for the layman, these can be confusing.

Pervious and Permeable and Porous, Oh My! 

Some terms that often get mixed up are pervious, permeable, and porous.  These sound similar, like they all mean the same thing.  In fact, if you look up “pervious,” “permeable” is part of the definition!  Both mean a substance that allows liquids or gases to pass through (as opposed to being a solid barrier).  These terms are also used synonymously in asphalt. Pervious or permeable pavements have connected spaces that allow water to percolate through the surface. 

“Porous” has a similar, but slightly different, meaning.  Holes or spaces in the surface allow water in, but these are not necessarily connected.  While fluids could get in, they have nowhere to go from there and can't easily percolate down to the water table.  This distinction, however, is not generally recognized in the industry. 

You may already be aware that the asphalt being laid down for new roads and patching older roads is largely made up of recycled material.  In fact, asphalt is one of America’s most recycled materials.  You may also be aware that, in some cases, the recycled material comes from roofing shingles as well as roads. 

Using RAS in Asphalt Mixtures

The use of recycled asphalt shingles, or RAS, has been fairly limited in the past, though, mostly because roofing materials contain a lot of extra material besides the asphalt itself.  For example, roofing shingles may have nails, plastic, fiberboard, paper, cellophane, and wood.  This makes the recycling process much more challenging. 

Additionally, local and state governments have been waiting on additional studies to be done regarding whether asphalt-using RAS is as reliable as asphalt that does not use it. These studies are increasingly showing that asphalt that uses RAS is as reliable and durable as more standard asphalt mixes, provided they are properly mixed.  Therefore, the use of RAS mixtures is on the rise.

The Milwaukee Metropolitan Sewerage District (MMSD) is continuing its work on keeping Milwaukee “green.” In July 2012, an article in the Milwaukee Journal Sentinel revealed that MMSD began required rooftop plants and the installation of other “green infrastructures” to help collect and absorb storm water. MMSD announced in a recent article that permeable pavement will be used along portions of three Milwaukee county roads.

One goal of this work is to improve the water quality in nearby wetlands and along rivers. “Reducing the volume of soil and sand eroding from the shoulder and capturing storm water laden with pollutants washed off the pavement will improve water quality.”