Posts Tagged ‘permeable concrete’

Pervious Concrete at Lyngso

Sunday, April 29th, 2012

Don’t tell anyone, but Lyngso Garden Materials in Redwood City, CA can make pervious concrete!  We just helped them to make a yard of pervious concrete out of their little batch plant and it worked great.  We put it in the back of one of their special concrete dump trucks, drove around for awhile and emptied it out over a half hour later and it was still nice and wet and fresh.

After placing Lyngso’s pervious concrete, naturally we placed our PerkTop™ on top.

Lyngso2

PerkTop™ up close:

Lyngso

PerkTop™

Sunday, November 28th, 2010

Porous concrete has been a passion of mine ever since the second job we did with it failed in 2006.  The surface had raveled, it became loose like gravel, starting a couple of months after it was installed.  At the time I was unaware just how sensitive this product can be.  I take some comfort these days now knowing that I wasn’t alone in my underestimation of how tricky pervious concrete is to install.  As it turns out around 50% of pervious / porous / permeable concrete installations are considered failures.  This is true in spite of the fact that it has been used in the U.S. for over 30 years now.

Since that initial failure I have dedicated myself to making our porous concrete installations more reliable.  We certainly can’t afford to go replacing half of our jobs.  In the process too, I decided it should be better looking.  Regular pervious concrete with its chunky, rice crispy treat looking appearance may be acceptable for certain industrial applications, but it isn’t a realistic aesthetic option for most of our residential clients.

The result of this dedication incorporating years of research & product testing, is what I call’PrettyPervious’.  PerkTop™ is more of a process than an actual product.  The process has to do with overlaying a thin layer of a finer, colored pervious concrete over regular pervious concrete, as it is being laid and is still in its plastic state.  The aggregate in PerkTop™ is so fine that from just a short distance the concrete looks like regular concrete and it certainly doesn’t look like it has the permeability that it has.  Our clients are always surprised at how much water just flows right through that tight, smooth surface.  Sometimes they even break out their 9″ stiletto high heels and parade around on it or don their roller skates and glide across it, because they can do these activities on our very ADA compliant version of pervious concrete!

By the way, the job that failed, we were able to make good on.  In the process of creating PerkTop™, we discovered that we could also make a version of it that was capable of overlaying on cured pervious concrete.  Therefore we removed the loose, raveled stone to get to the solid base and applied our modified PerkTop™ on top.  We now have a solid, attractive expanse of pervious concrete, without having had to remove and replace all that material.

Ryan

How to make porous / pervious concrete for homeowners.

Saturday, October 16th, 2010

If you are a homeowner and you’d like to do a little area of pervious concrete, aka porous or permeable concrete, you are going to have to make your own mix, because pervious concrete is not available in bags yet.  Fortunately the basic ingredients for pervious concrete are simple.  They are the same as regular concrete, rock, sand, cement & water, but minus the sand.

The basic pervious concrete mix is:

3 parts rock

1 part loose cement

just enough water

The rock is generally a 3/8″ pea gravel that should be readily available from your local rockery.  But really almost any rock will do as long as it is clean, meaning no or little dirt or fine sand is in it.  Round or angular rocks are both okay.  For aesthetic purposes the smaller the rock  the nicer the final product will look.  Though a word of caution here, because the smaller your rock is, the more angular and/or uniform in size it needs to be or your concrete won’t be pervious.  We have mastered this process with our PerkTop™.

The cement portion refers to any type of Portland cement, type I-II, type III-V, etc.  Get whatever they have at your rockery or local hardware store.  When you are filling your container, do not pack the cement or you will end up with too much in your mix as cement does compact quite a bit.

The water portion is the trickiest part of your pervious concrete mix to get right.  Don’t feel bad if it takes you a couple tries to get the hang of the what the right amount of water is, because even the professionals have a hard time with this one.  Unlike regular concrete, the correct amount of water to add to pervious concrete lies within a very narrow range, if you add a little too much you could end up with impervious concrete and if you add too little you might get raveling (loose rocks on the surface) later.  The general rule of thumb to know if the water amount is correct is to make a ball (wearing gloves of course) and the ball should hold together and have a nice shine to it.   Note: If your rock is pretty wet to begin with, you probably will need to add very little water to the mix.

When we mix our pervious concrete by hand, I like to always be in the shade.  Pervious concrete is very moisture sensitive and once you’ve worked so hard to get that moisture just right, you don’t want it drying out before you have a chance to finish placing it.  Again pervious concrete is not like regular concrete, pervious concrete will dry out very fast and you generally can’t retemper it (add water) to bring it back like you might for regular concrete.

Now that you know how to make your own porous / pervious / permeable concrete, whatever you want to call the stuff, check back in later to find out how to place and cure it.

Ryan

Amount of Cement in Pervious Concrete

Monday, September 20th, 2010

During a conversation with one of my colleagues at the Bay-Friendly Conference, she reminded me of an earlier environmental concern I had when I first started working with pervious concrete several years ago. The concern was regarding the amount of cement in pervious concrete, or for that matter in any concrete. Cement, the main binder used in concrete, is energy intensive to produce, emitting approximately one ton of Carbon Dioxide for every ton of cement that is created. Considering that cement accounts for approximately 14% of the volume of concrete and knowing how much concrete can be used even on a single job, in this light it would appear that concrete has a large environmental footprint.

I am not saying it doesn’t. I’d just like to make a couple key points that I have learned over these past 8 years or so that I have been dedicated to finding and creating more environmental hardscapes. In that oft-sited statistic about one ton cement = one ton CO2, what they don’t tell you, is that half of the carbon dioxide that is emitted is as a result of a chemical reaction in the limestone as it is being turned into Portland Cement. It is well known that once concrete is placed it recaptures some of that carbon where it can, which is typically only on the uppermost exposed surface. So in the case of pervious(porous, permeable) concrete, with voids throughout the entire matrix, there is a tremendous amount of surface area exposed to the air and therefore sequestering more of that carbon dioxide that was lost during the limestone’s transition into cement.

I do not know what percentage of carbon dioxide is recaptured. I believe it is fairly significant as there have been studies showing how when concrete is crushed at the end of its lifecycle to be re-used, it actually carbonates then, and within the first couple of months re-captures up to 40%(exact # needs to be verified) of the carbon emitted during production.

The second point I would like to make is that most cement is produced locally. In our case it is literally produced within walking distance of our office in Cupertino. The old Kaiser plant is one of the largest cement kilns in the country. I believe that most other products aren’t produced this close to home, and I believe that fact is usually minimized in any discussion of how ‘green’ a product may be – that transportation is never given its full environmental weight.

I realize concrete is not environmentally benign, but hopefully I have been able to offer a more objective view of its true environmental footprint.

At the end of the day, generally the best thing for the environment is no hardscape or at least less of it, unfortunately this is not always practical. Gravel and decomposed granite/fines and others can be more environmental hardscape alternatives, unfortunately they generally have lots of maintenance issues. Due primarily to this reason, I think we are going to be stuck with a little concrete for some time to come. And if we have to put in concrete it might as well be pervious, so water can stay onsite and the soil can breathe underneath.

Ryan