Proper Equipment for Pervious
What is proper equipment for placing pervious concrete? I you asked me that question 25 years ago I would have said a hand screed. The first time I worked with pervious, in the spring of ’86, that’s what we used, a 2×4 magnesium screed. In fact, we would routinely hand rod pervious, using a hand float as a spacer to strike high, and then follow with a static roller for compaction. We quickly learned that a truss screed was a much easier method for larger placements. We did our tie-ins by hand with a large flat rake (spreader), but some jobs were so chopped up, especially when working around trees or on varying slopes, that we would only use a spreader followed by a cross-roller for compaction.
There were some other contractors using plate compactors, but as it required placing a really dry mix and I have always felt that more moisture was needed not less, I stayed away from that technique. For me, that’s pretty much how it was done until 2003. That was when I tried a Bunyan roller screed for the first time and this became my new normal. David Mitchell with Bunyan had been trying to get me to try his screed for years, but I had a pretty narrow mind as equipment was concerned. My hesitation to try the roller screed can be blamed on two things; 1) the type of mixes we were working with; dry, pound into place mixes and 2) my idea that there was only one “best way” to do things.
As admixture companies began developing new products for pervious and making the mix more fluid, the options for equipment choices grew and I soon realized that there are many “best ways”. To explain what I mean, consider the debate of “prescriptive vs. performance”.
At its core, the idea behind “prescriptive” is that there is one “best way” to accomplish the goal. However, as my grandmother always said, “there’s more than one way to skin a cat”. In fact, we spend a lot of time trying to get designers to go to performance based specifications because we know we can reach the goal more often than not without prescriptive requirements limiting our options. The same is true with equipment for pervious. When we “prescribe” the equipment, we lose focus on performance and we fall into the same trap that prescriptive designers find themselves. We say “they want to have their cake and eat it too”. Well now we know how they feel. It’s a tough choice, but we have to choose whether we want to control how to do it, or set the standard for performance. And speaking from experience, the installers will figure out how to get it done with the right equipment if we give them clear, defined goals.
Today, there are even more equipment choices out there, and who knows what tomorrow will bring concerning pervious equipment, mixes, admixtures, uses, etc. By limiting equipment options, we can literally hold pervious concrete technology back. But, by focusing on performance, we can allow pervious concrete technology to continue to advance and become an even better product. So what is proper equipment for placing pervious concrete? Today, I say whatever gets the job done.