Research & Development
It's April, so it's the perfect time for some spring cleaning! Time to clean out those dusty pervious concrete specifications and design details you have laying around, and replace them with something new and fresh. We have released new updates on all the favorites!
Visit our Resources Section and you can download the latest the industry has to offer
Specifications
Typical Design details
Performance Data Sheet
There has been some confusion as to what is the best base material to use for pervious concrete. Watch this video to see why you should specify open-graded crushed rock instead of "Class II Permeable Aggregate" as the base for pervious concrete sections.
Read MoreYes, you read that right, pervious concrete in SPACE! David Liguori, of BAPC, recently worked with the Microbial Ecology / Biogeochemistry Research Laboratory of the NASA Ames Research Center, to design a new form of pervious concrete that is being tested for use in future space flight missions.
Read MoreBay Area Pervious Concrete created a multi-generational and multi-functional driveway for the Tah Mah Lah Residence, the "greenest house in America". Held to a high environmental impact standard, the driveway performs beyond typical requirements, providing regeneration of groundwater resources and representing a 64% savings in embodied carbon. It also features BAPC's latest finish option, Portola!
Read MoreAre you looking for a natural-looking, low-impact hardscape material? BAPC would like to introduce our latest new finish option - Portola™!
Our Portola Pervious Concrete™ provides a similar aesthetic to Decomposed Granite (DG), while providing the same durability, permeability and low-maintenance as the rest of our pervious concrete. All without the mess and maintenance challenges of DG.
Over the past few weeks we have seen the internet explode with interest over the recently announced Topmix Permeable concrete from Tarmac Lafarge in the UK. People are marveling over concrete that allows water to not only go through it, and back into the ground, but at an incredible rate. The video we featured on our last blog post is impressive and demonstrated just how fast. We were excited to see so much interest in pervious concrete by so many different people. However, we did notice some discrepancies in the way that pervious concrete was discussed in some of the media outlets, and we wanted to take some time to clarify a couple things.
Some of the media outlets portrayed pervious concrete as a new product that was not available in the United States - which is false. Pervious concrete has been used for stormwater management throughout the US for over 40 years. What's different, or innovative, about Tarmac's Topmix Permeable concrete is it boasts a whopping 35% air void space, which is why it infiltrates at such a high rate. Tarmac representatives have stated in interviews that the product has some limitations on where, and when, it should be used. They are not recommending Topmix Permeable for high-traffic areas, in places where vehicles make lots of tight turns, or in places with freeze-thaw cycles, as it will eventually start breaking up the surface layer. Some media corespondents have portrayed that all pervious concrete had these limitations - which is also false. While Topmix Permeable may have these limitations, more traditional pervious concrete does not share the same limitations. In the US, mix designs have evolved and have already solved the issues of heavy traffic, weight loads, turning vehicle traffic, and freeze/thaw cycles.
Through trial and error the pervious concrete industry has discovered that 20% air void space provides the proper balance between strength, durability, and high infiltration rates. The additional bonds provided by only having 20% air voids, allows for a stronger, longer-lasting material, with just as much infiltration capacity to mitigate all of a site's stormwater.
In keeping with the Pervious In Paradise look back, we have Dr. Narayanan Neithalath Ph.D. P.E.’s presentation of pervious concrete modeling featuring one of my favorite parts- a clip of a pervious cylinder in a CAT scan!
Dr. Neithalath’s presentation was on his research on the effect of mix design on pore structure and infiltration performance. Currently, the state of the art is rife with trial and error which ends up, at worse, with pavement failures, and best, an inconsistent mix. He wants to really understand how different aspects of the pervious concrete mix affect the different performance attributes. In this way, he wants to be able to dial in a pervious mix, with the exact attributes required for the ideal functioning of the installation.
The key feature of pervious concrete is the porosity, which we are all familiar with. Permeability is linearly related to porosity, and while that is obvious, it forms a helpful and fundamental baseline for one aspect of pervious concrete as a hardscape. Other aspects of pervious concrete are less well understood and they include types and seriousness of particle retention or clogging; oil retention, as some are considering pervious concrete as a bio-filter; strength and fracture, for structural considerations; as well as how mix design informs the size, type and structure of the voids. Dr. Neithalath is working to understand how all of these factors come together to form computational performance models for consistent designable pavements. In turn that would create a matrix of variable that could be controlled to create very precise mix designs for producers and installers.
My favorite part of Dr. Neithalath’s presentation was the video he presented of a pervious concrete cylinder in a CATscan, going all the way throughout, such that the void patterns were completely observable. Below you can see the video. I found the whole thing hypnotizing. What do you think?
To see more about Dr. Neithalath’s work, you can go to his faculty page here.
(‘View from the Hotel’ photo credit: Bob Banka)
Pervious in Paradise was a great conference. There were great presentations, solid attendance and wonderful networking! And every night, FIREWORKS!! Well, those might have been for the SeaWorld guests, who were adjacent to the conference site, but we enjoyed it nonetheless!
As we get materials and permission, we will be posting briefs on a few of the presentations. There were some fantastic new ideas, ongoing development of existing ideas and industry knowledge getting more refined. Highlights included
pervious concrete site and pavement design with Michael Hein P.E. and Chris Estes, ASLA,
notes from the Puget Sound with Andrew Marks P.E.,
some truly innovative applications of pervious concrete with Muhannad Suleiman, Ph.D.,
great modeling of voids and their implication with Narayanan Neithalath, Ph.D. P.E.
discussions of fibers and silica fume with John Kevern Ph.D. P.E. LEED AP
There were many good speakers, and solid content throughout. More soon, and we are already looking forward to the next conference! Did you go? What did you think? Your comments are always appreciated!
We have been working with architects, engineers, homeowners and municipalities to really explain how pervious concrete is a comprehensive storm water mitigation device. It has proven difficult to help people to wrap their heads around how allowing water to soak in to where it falls, using pervious concrete, is a viable storm water management strategy - so we have started to use Dynamic System Modeling as a tool to help explain what is happening in a pervious concrete slab, and how much water it can infiltrate over time.
When we use the concept of infiltration over time, pervious concrete systems provide huge capacity, far exceeding most climate’s most intense storm events. That is most easily demonstrated using a software modeling system. This allows insight as to a system’s capacity, and informs design, to ensure that the pavement and drain rock base will meet or exceed the required storm water infiltration amounts.
Contact us for a consultation on your project or to schedule an office presentation to learn more!
David had taken some samples at a recent pour and wanted to get them tested. Fortunately, Cristian Gaedicke, Concrete Materials Professor at CSU East Bay, had a new lab with new equipment to break in. We headed over for a tour and a testing field trip. Below are some photos of our compression testing.
Read More
It is time again for the most glorious of the pervious concrete conferences - The NPCPA Pervious in Paradise! It is where many of the pervious concrete thinkers and doers get together to exchange ideas and enjoy a new beautiful location - this time in San Diego.
We are looking forward to it particularly as BAPC’s David Liguori will be discussing reinforced pervious concrete and how rebar is not ever an appropriate reinforcement technique for pervious concrete. You can see more of the speakers here. We invite you to join us!
To get you all more excited about the conference we have some of the photos from the last Pervious In Paradise here!
Recently, maintaining pervious concrete has come up several times in a week, prompting this blog post. The good news is that this conversation is happening. The bad news is that some people who are not on board with pervious are using an ill-informed maintenance opinion to shape their judgement. We here at Bay Area Pervious Concrete would like to clear up a few of the misconceptions around maintenance.
Firstly, we have found the relevance of maintenance is tied directly to the porosity of the slab itself. A healthy infiltration rate for a slab of pervious concrete is 250-1000 inches per square foot per hour. That ensures that even if the slab was 99% clogged, and the 5 year storm event was 3 inches in 24 hours (as we have here in the Bay Area), that slab would easily be able to absorb that entire storm. So at 99% clogged, the slab would take in 2.5 inches - 10 inches of stormwater per hour per square foot!
Secondly, here are three helpful resources to help with installing a good slab, maintaining it and the fixing a worst case scenario:
1) In order to make sure you get your healthy infiltration rates, an experienced and qualified contractor is required. We have performance based specs that you may review, so that you can be sure to get a good contractor and get a great pervious concrete installation! We also have a BAPC PolishedTM Pervious Spec that we will send at your request.
2) Regular maintenance that can be done, if there is a budget and a desire for a plan. We have put together a maintenance manual that we give to clients at their request when we finish work for them. This gives an idea what you can anticipate, allows one to set up a maintenance schedule, and has resources to call if clogging does occur.
3) Pervious concrete can recover porosity after clogging over years as shown from a research paper from Florida that came out a few years ago. The paper shows several slabs of unmaintained pervious ranging in age from 6 to 20 years old that were able to recover significant infiltration after a pressure washing, vacuuming or a combination of both - after YEARS of neglect. So, no maintenance, no problem!
Do you have any unanswered questions about maintenance and pervious concrete? Submit them here, and we may add them to this post!
This was originally posted June 19, 2013.
Lauren Wray, our Director of Marketing, attended the USGBC’s Greener Builder Conference last week. Apparently the Greener Builder Conference is even GREENER then the Green Builder Conference that occurred in November! This conference did not disappoint. From the opening panel, pictured below, featuring Jeffrey A. Birdwell, Michael Deane, Kevin Hydes, Kirsten Ritchie and moderated by Cliff Brewis, the focus was on leading edge sustainability, and strategies to get regenerative planning and innovation into the building industry.
There were good options for every panel, but as pervious concrete sub-contractors, we went to the subcontractor panel, hosted by John Home and Jeff Swinyer of Rudolph and Sletten, pictured below.
Lauren, pictured below, was interested in the drive toward clear performance specs to allow for differentiation at the sub-contractor level. As a pervious concrete subcontractor, we differentiate ourselves with our embrace of leading edge technologies for mix design and installation. Unfortunately, many current specs don’t reflect the progress in the installation, mix designs, equipment and curing materials that has developed in the last few years.
The next panel we attended discussed Environmental Product Disclosures (EPDs), a labeling system that discloses the resource footprint of the many materials that go into the built environment. The panel also included the next iteration, the Health Product Disclosures, which discloses the materials and chemicals that have been proven or correlated in causing health problems for humans.
Central Concrete, a sponsor of the event, has been heavily involved in the EPD project for disclosing the materials for the concrete industry. Below is a photo of the panelists from this panel.
The last panel of the day went over Net Zero Energy buildings with John Andary and Scott Shell, pictured below. It was a fascinating look at what is currently possible with technologies now: buildings that use as much energy as they make. The building case studies discussed also illustrated how livable and workable these spaces were, with thought for passive heating and cooling. Many of the designs features windows that bounced daylight far into the building envelope, as well as fresh air ventilation. It was a wonderful talk, even though their topics stayed primarily inside the building envelope.
The final speaker, Jason McLennan, pictured below, gave a wonderful talk on self limits. His talk really stood out for his candor and optimism. For a young guy, has accomplished quite a bit in the green building spaces. Currently he is pioneering the Living Building movement.
After his talk, Jason McLennan was joined by George Salah, of Google, and David Gottfried of the USGBC. They discussed everything from George’s living-building home construction project to Jason’s motivation to do the work that he does: “I give a shit.” That was wonderful.
FInally, after it was all over, we found that there was a fantastic array of beers, wine and snacks to round out the day’s networking. It was a great event, and one we will look forward to attending next year!
A BIG thank you to Charlie Nucci, who took these photos at the event. You can find more about Charlie and his work at his website here.
David teaches the NRMCA Pervious Concrete Technician class by the NRMCA local sponsoring group ACI Northern California chapter. The class location was in Truckee, CA and after the class and test, the class went out the TNT Materials Yard for a demonstration pour. We had good pervious pouring weather and great participation! If you would like more information for upcoming NRMCA pervious concrete training classes, go to the ACI website here: www.ACI-NCAWNV.org.
Check out the photos below:
The Bay Area Pervious Concrete team went to visit Graniterock at their Aromas location. Lauren arranged for a tour with Graniterock with their testing group. We piled into a car wit Katha and Greg, both in the Graniterock materials testing group. First we went to visit Big Bill, the massive material spreader.
Big Bill (pictured above) was at the end of a 3mile conveyor belt bringing material from the waste end of the crushing processing to the spreader. The wheels were at least 10 feet in diameter! It was a massive machine! The material being spread looked like moon dust!
After leaving Big Bill we went into the quarry. You could see the step-like traces of material that had been removed. The terraces started at the top of the hill and went rather deep, below sea level! There was this massive truck (pictured above)that was moving the 'raw' rock and rubble close to the initial crushing machine (picture below). The crushing machine was in the quarry and it was even more massive then Big Bill the spreader! Here are a few photos of the team with the crusher. It was not running at the time, I would imagine it would be deafening! From the large initial crusher, another conveyor, shorter then the 3 miler, takes the material to the processing yard.
The material on the initial conveyor is then sorted into two sizes (big, for dry processing, and smaller, for wet processing) before being further sifted, crushed and rinsed to final product sizes and blends. The processing yard was a maize of conveyors, buildings on stilts (the crushing/processing/screening) and piles of material. Going into their control tower, we could see the levels of complexity and organization to keep all of that machinery moving that went unseen in the maize outside the windows. Even further beneath the surface of the processing yard was another conveyor in a tunnel beneath the main stockpiles, to allow for high control of the custom blends and product development.
Graniterock's newest addition to the quantitative analysis even had this fabulous quality assessment program that noted the size of final aggregate moment to moment to ensure consistency of the final product. They could, in real time, plumb their data and understand how consistent their product was, and make appropriate adjustments to bring it back into line. That type of feedback allows the quality team to be responsive to current inventory as well as give the operations team insights as to how well their processes are processing. It was a fantastic set-up, although I may be a data geek.
It was a fantastic tour of a great facility. We learned a lot about the aggregates that we use frequently in the Peninsula as well as how it gets to us. Really good quality rock makes even better pervious concrete! Please send us comments or questions! :)
Our own Lauren Wray attended the USGBC and P&E’s Water Conservation Showcase this year. The Bay Area Pervious Concrete Booth was in this video, above, and photos of Wray and pervious concrete made it into PG&E’s “Currents”, a P&E news site. Check out the video and let us know your thoughts! Did you attend the Water Conservation Showcase this year?
The Rational Method is used by many storm water civil engineers to understand storm water runoff. Frequently it is being invoked to understand the impacts of pervious concrete. Frankly, the Rational Method has no place designing with pervious, and this is what we are going to discuss.
The simplest reason being, the Rational Method is there the allow engineers to size the necessary sewer line appropriate to the runoff on the site. However, when pervious concrete is well designed and installed for most or all of the parking or access areas, there will be no runoff from that area. It is even possible, pending some limitations**, to capture most if not all of the adjacent runoff from impervious roofs or other impervious. That would make the runoff coefficient 0 or even negative. Given that, Q becomes zero, or less then zero. At that point, no drain pipe is needed to carry away the storm water, and the Rational Method is not the appropriate method for quantifying storm water.
This hints at the total shift that is before us - the way we previously understood hardscape and the associated negative externalities (runoff, storm water pollution, heat island effect, aquifer depletion) is turned on its head. Now these previous negative externalities are accounted for and reversed, and we are able to maintain the preferred hard & durable surface with pervious concrete. Pervious concrete allows storm water and pollution to filter in and infiltrate, allowing microbes and soil to be the filter that they are for the rest of nature. Pervious concrete mitigates the heat island effect in 2 ways, having a high solar reflectivity index as well as allowing a water and air exchange between the soil below and air above the pavement.
But given that codes are still being written, and some building and design professionals do not know about pervious concrete and its benefits we must still use the Rational Method. So I propose a stand-in coefficient.
To review the Rational Method for those of you who don't use this equation frequently,
Q = the necessary size of the pipe to capture the runoff being generated by C, I and A.
A = The area whose runoff is being measured.
I = The rate of rainfall in a given time horizon.
C = The coefficient that is determined by the type of ground covering being measured, below you can see one version of the chart referenced.
As you can see in the above chart, [impervious] paved surfaces gave a runoff coefficient of 0.94 for the 5-year storm event. Toward the bottom of this chart, "Lawn" and "Parks/Golf Courses/Cemeteries, 8% impervious" have a runoff coefficient of 0.21.
As far as I know, there is no such coefficient for pervious concrete to be used in the Rational Method. On the one hand, it isn't really necessary, as infiltration hardscapes may make the Rational Method less necessary. Or, perhaps the Rational Method will be adapted to vet and verify successful implementations of LID measures. In the meantime, it seems that a stand-in number is necessary - what if we were to use the "Parks/Golf Courses/Cemeteries, 8% impervious" 0.21 as a reference, and then include the >0.21, as it is less then 0.21, however it is unknown how much less at this point, for research has not yet been completed.
What do you think? Is this a reasonable way to discuss the Rational Method and pervious concrete?
** The limiting factor when dealing with pervious concrete is the subbase soil’s infiltration rate. Given enough area and enough reservoir base, it is possible to infiltrate a serious storm.
If you have more information please contact us, and we would be happy to discuss this with you.
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Sources: chart http://www.iowadot.gov/design/dmanual/04a-05.pdf
conversation and cocktail napkin - inspiration to post
David Liguori went out into the field, during the last rain, to see what the stormwater runoff situation looked like in Woodside, California. Watch the video below to see what did and didn't run off!
Come with David Liguori of Bay Area Pervious Concrete as he goes into the field, in the rain, to see first hand the issue of stormwater runoff - or lack there of - on pervious concrete versus other impervious hardscapes!
What did you think? Do you have a Stormwater Sleuthing location (in the Bay Area) that you would like David to investigate the next time it rains? Let us know in the comments below or contact us here. Thanks!
How close can you pave to a tree?
Normally, it is inadvisable to pave inside the drip line of a tree. Depending on the size and age of a tree that can be a fairly sizable area. This can be problematic when traffic or use requires paving close to the tree. When traditional impervious pavements are installed near older established trees, it can spell the end of the tree. Is that true of pervious concrete?
It turns out there are two students at Texas A&M are doing this very research! Their recent work reveals pervious concrete does, in fact, enhance the growing conditions of established trees relative to traditional concrete. They poured traditional concrete around a few established trees, pervious concrete around a few established trees and left a few trees with no cover for the control, and measured tree health for a little over a year. The results: the trees surrounded by the pervious concrete had more trunk growth during the year then the trees surrounded by the traditional concrete!
What does this mean for you? The good news is that you can integrate pervious concrete paving into plant friendly parking lots and hardscape design, knowing that you are not compromising tree health. This also may open previously impossible parking or other paving possibilities due to the ability to extend the pervious concrete closer to the tree, well within the drip line. Yes, it can make installation tricky, but it can be done!
The takeaway is that pervious concrete is great for protecting mature trees. As you can see above, our clients think so too!
You can read more about pervious concrete effect on trees and their growth by reading the Texas A&M research paper listed on our Resources page.
2 Symptoms of Failed Pervious Concrete - Raveling and Sealing
Recently it has come to our attention that there appears to be a discrepancy in what a high-quality pervious concrete jobs looks like, and what has been passed off as high quality but in fact is not at all quality.
Failed installations have 2 main features: raveling and sealing.
Raveling is when the aggregate comes off of the slab as cement coated gravel. That can be an indication of poor mix design, poor installation technique or even misunderstand the weather's impact on the day of the pour.
Sealing is when the water pools and does not go through. It is possible to have sealing at the top, where it looks blotchy, or just beneath the surface such that the finish looks appropriate but does not drain. This is an indication of poor mix design. An experienced pervious concrete installer understands how critical the proper mix is and works closely with his ready-mix partners to get it right.
As we at BAPC have said before, pervious concrete is a tricky material and only those who are qualified, experienced and show a commitment to ongoing learning about techniques and mix designs are able to install and place pervious concrete with a consistent high quality.
We have created this video, complete with an amazing sound track, to illustrate what failed pervious concrete looks like, and what successful pervious concrete looks like. If you would like us to come out and evaluate your slab, or better yet, if you would like it done well the first time, please contact us.
