Pervious Concrete: The Road Less Raveled

New "Raveling Potential" Test for Pervious Concrete

It's official!  The new ASTM test for determining the raveling potential of a pervious concrete mixure has been published as C 1747-11.  You can download a copy here.

If you're not familiar with the test, it has been discussed in previous blog posts here and here, and this article here.

 

 

 

 

 

My Negative on ASTM Density/Voids Test for Pervious Concrete

What is this ... action to find ME not persuasive!?!

There's all kinds of excitement in the ASTM subcommittee on Pervious Concrete!  Here it is: ASTM C 09 ballot 12-01 item 18 is "Action on Negative To Find Matthew Offenberg's Negative Not Persuasive on the C09 (05-11), Item 46, New Standard (WK29212) WK29212".  

Please understand, I'm a huge supporter of this test method -- it's something the industry needs -- and Walt Flood IV has done a great job leading this task group up to this point.  Specifications today reference ASTM C 140 which gives "density" but not voids.  And I say "density" instead of calling it just density because it gives us a number that looks kind of like a density, but, we all agree, isn't the true mathematical density of the material.  We need a test that measures the true density of pervious concrete, and this standard that was drafted is close to where we need to be.

For those of you following along in the text, it reads:

New Standard Test Method For Density and Void Content of Hardened Pervious Concrete (WK29212) on Ballot Ballot C09 (05-11) Item 046 {1}

blah blah blah{2}

Negative Voter: (Matthew Offenberg, W R Grace)

Negative Comment:The precision and bias statement was drafted based on insufficient data. The task group did a good job in testing different aggregates and placement techniques, but the P&B is only based on three tests. For this standard to be used for acceptance testing, there should be at least 3-5 more tests.

Non Persuasive Rationale:A motion was made and seconded to find it non-persuasive because the data generated by the task group exceeds the minimum ASTM requirement for precision statements which is one lab. The task group intends to run a full ILS within 5 years. During discussions it was mentioned that 2 round robins were conducted by the task group in the development of this test method. The first was based on cylinders made in the lab and included 6 labs. The second was based on cores cut from 3 different field placements. In addition the reference mentioned in the balloted draft standard includes cores cut from 2 placements and 1 set of cylinders placed in the laboratory.

---

However, to clarify what this ballot means, the subcommittee needs to find me not persuasive so that the new test for hardened density and voids of pervious concrete field cores can be published.  This is a BAD idea.  On the previous ballot, I voted negative because with only 3 tests, we don't have a good feel for how accurate the test is and thus what kind of specification limits we can tie to it (for something like ACI 522.1).  My goal was to have the task group provide us with a better feel for how tightly a designer can specify limits for density and voids and not cause either a dispute (because the limits are too tight and thus not achievable) or a project failure (because the specification limits are too loose and thus allow substandard material to remain in place).  Even if this test isn't included in 522.1, or the UFGS for another 4 years, it will find its way into other project specifications and will cause problems if architects and engineers aren't provided with good guidance on setting acceptable ranges (like +/- 5 pcf or +/- 5% voids).  Until we know what those ranges should be, and provide such guidance, it is irresponsible to publish this standard which is clearly written as an acceptance test.

This whole situation is a little weird.  I've been in the position to have people voting for me, but never against me.  So in this situation, a negative vote is a good thing, that's what I'm asking for.  It's like a biopsy, a negative result is good.  If you are an ASTM voter, please vote negative on C09(12-01) Item 18.

Flood IV, I encourage your response below.

{1} Editor's Note: The "Ballot Ballot" is the official wording, not mine.
{2} Editor's Note: The "blah blah blah" is my wording, not the official text.  I've removed some web instructions. 

ASTM C 1747-11 for Pervious Concrete

Saw in an email that the new Standard Test Method for Determining Potential Resistance to Degradation of Pervious Concrete by Impact and Abrasion will be numbered C 1747-11.  It hasn't been published yet, but will be soon!

ASTM Pervious Concrete Winter Meeting 2011 Update

To say the body of knowledge in pervious concrete is growing is an understatement -- it is exploding!  This week the ASTM meeting added to that explosion with the first ASTM Symposium on Pervious Concrete.

The symposium featured eight speakers covering some of the latest research and updates on test methods for pervious concrete.  Some of the more interesting presentations included:

 

• "Validation of the Performance of Pervious Concrete in a Field Application with Finite Element Analysis (FEA)" Md. Ashraful Alam, Liv Haselbach, William F. Cofer, Washington State University, Pullman, WA USA 
• "Pervious Concretes Pore Structure Characterisation by 3D image analysis - Impact on their Permeability" Samuel Meulenyzer, Eric Stora, Fabien Perez Lafarge Centre de Recherche, Saint-Quentin Fallavier, Franc
• "More Information on ASTM C 1688 Variability" L. K. Crouch, Ph.D., P.E. Tennessee Technological University,  Cookeville, Tennessee, USA; John Hendrix, P.E. Tennessee Technological University,  Cookeville, Tennessee, USA; Alan Sparkman, CAE, CCPf, LEED AP Tennessee Concrete Association, Nashville, Tennessee, USA; Daniel Badoe, Ph.D. Tennessee Technological University,  Cookeville, Tennessee, USA 
• "The Development, Implementation and Use of ASTM C1701 Field Infiltration of In Place Pervious Concrete" Heather J. Brown, MTSU, Murfreesboro, TN, USA; Alan Sparkman, Tennessee Concrete Association, Nashville, TN, USA 
• ...and, of course:"Development of a Test Method to Determine the Raveling Potential of Pervious Concrete" Matthew Offenberg, W.R. Grace, Canton, GA, USA 

The papers and presentations are not available, yet.  But I'll post an update as soon as they are, or you can sign up to get an alert from ASTM here. 

ASTM's subcommittee on pervious concrete also met on Monday.  The raveling test has moved a step closer as it passed the main committee ballot, so is headed off for staff review.  The hardened density and voids test likewise is advancing, but had a few negative votes to resolve by the close of the meeting.  The compressive strength task group has a draft standard, but will also be testing out a new compaction technique using a hammer drill.  They expect to open their first ballot this coming spring.

ASTM C09/C01 Symposium on Pervious Concrete

There is no better way to spend a Sunday afternoon in Tampa, FL than listening to speakers from all over the world talk about how to test pervious concrete.  Sure, the Buccaneers kick-off at home against the Panthers at the same time, but this will be the place to be!  

Here is the Official information from ASTM:

REGISTRATION INFORMATION AND HOTEL INFORMATION
Symposium on Pervious Concrete

December 4, 2011,  1:00-6:00 pm, Tampa Marriott Waterside,   Tampa, FL

Online registration is open and hotel reservation information is posted on the symposium webpage at http://www.astm.org/C09C01Concrete.htm

• Registration will close November 30, 2011

• Hotel cutoff date is November 9, 2011

The Future of Raveling Testing for Pervious Concrete

It's nice to come up with a new, repeatable test method, but before unleashing it on the world, a few questions must be asked:

1) Does the world need it?

2) Is the test meaningful?

3) Will it do more good than harm?  

At both the ASTM winter and summer meetings there was lively debate about the new test method, under development, for raveling resistance.  Trying to answer these questions was not an easy task for the subcommittee, and at more than one point I almost talked myself out of continuing on the path towards publication.  So, here's an attempt to summarize the discussion and answer these three critical questions as gathered from my thoughts, and those in the meeting room.

To provide some background, the test is being developed under ASTM Work Item #23367 (if you need a copy of the lastest draft email me).  In the current version, it is intended only to help a concrete producer or researcher select the best possible mixture proportions based on potential raveling resistance, or to compare the potential raveling resistance of different pervious concrete mixture proportions.  Samples may be cast from either laboratory or truck mixed concrete.  The round robin testing showed a very low coefficient of variation, but was based on controlled conditions – not cores or field cast specimens.  

1) Does the world need a test method to determine the raveling resistance potential of a pervious concrete mixture?  

When pervious concrete fails, it usually fails in raveling.  The goal of any producer, therefore, is to make a mix that is resistant to such distress.  Likewise, researchers need a tool to assess the impact of varying mixture proportions on the raveling resistance of pervious concrete.  Therefore, it is easy to say, there is a need for this test method.

2) Is the test meaningful?

Unfortunately, I can’t say it is with 100% confidence.  

Some of the properties of pervious concrete that we would expect to impact raveling resistance (void content, ash content), impact the performance of pervious concrete in this test.  For example high void content and high fly ash content reduce raveling resistance.  Until we have enough data to develop correlations (if those correlations truly exist) between test results and field performance, we can’t definitively state that the test is meaningful.  But, if we don’t publish the standard and incorporate it in specifications, producers won’t readily use the test to select mixture proportions.

3) Will a test method to determine the surface durability potential of a pervious concrete mixture do more good than harm?  

This is where I get nervous.  

Anybody in the concrete industry has experience with specifiers either misinterpreting or using test methods where they are explicitly stated not to be used.  So, as the subcommittee debated the fate of this test method, we discussed which applications specifiers could misuse the test, and the implications of such misapplication.  The list of improper applications of this test includes:

• Construction acceptance of delivered concrete.  At some point in the future, it would be nice to use this test as a means of quality control and acceptance. Comparing the mass loss of specimens cast every 100 yards might prove to be a good QC/QA test.  However, there has been no research to verify that it works as a QC/QA test – the test isn’t ready for this application, yet.  Of critical concern is the variability of the test as conducted in a field application.  As the standard is written today, it is intended for use in a controlled environment.  If a specifier or purchaser were to require such testing for a field application, the results would likely not agree with the laboratory results used for mixture selection.  The end result of such an inequitable comparison could unreasonably penalize the concrete producer.

• Construction Acceptance of in-place concrete.  The test method, as written and evaluated in the round robin testing, is for cylindrically cast specimens.  The applicability with respect to cores has not been broadly evaluated.  Some testing has shown that the test can differentiate between different levels of raveling resistance based on compaction.  However, neither the applicability nor the repeatability has been established. Again, if a specifier or purchaser were to require such testing for a field application, the results would likely not agree with the laboratory results used for mixture selection.  The end result of such an inequitable comparison could unreasonably penalize the concrete producer and contractor.

• Specification limits for mixture submittal and prequalification.  Plain concrete mixtures today are prequalified based on compressive strength of laboratory specimens or field history.  This is based on a history of what works.  With pervious concrete, we don’t know what specification limits for mass loss from this test might work, and for which applications.  Or, they might need to be correlated with some other test that we haven’t developed, yet. As suggested earlier, until we have enough data to develop correlations between test results and field performance, we can’t set specification limits for mixture prequalification.

The consensus is that this test is not a perfect test (as few are), but is the easiest, cheapest way to determine the potential raveling resistance of a pervious concrete mixture.  Hopefully, somebody smarter than me will develop a better test in the near future.

ASTM Pervious Concrete Summer Meeting Update 2011

The ASTM C09.49 pervious concrete subcommittee had a healthy meeting this morning. The activity focused on the work of four of the task groups:

Compressive Strength: The task group has round robin data ready to be analyzed, and hopes to have a draft to ballot by September 2011.

Fresh Concrete Density and Voids: Mike Kohout's task group continues to refine ASTM C 1688. Changes to be balloted include editorial and formatting corrections, and adding a section on reporting.

Hardened Concrete Density and Porosity: After being beaten up a bit in a concurrent ballot, Walt Flood's task group has made many changes to the draft and will focus on reballoting this summer. My biggest concern is the data set behind the precision and bias statement. I'd prefer to see it be a little bigger with work done by more labs.

Surface Durability: The draft standard was also cleaned up after many comments were submitted in the last concurrent ballot. The biggest hurdle this document passed (barely) was the question of whether this even needed to be standardized. In the current form, it is only to be used for a concrete producer or researcher to compare mixture proportions. It is not for acceptance, yet. The next draft will be balloted this summer.

Pervious Concrete Paper from World of Coal Ash 2011

If you're looking for a copy of my team's paper from World of Coal Ash 2011, you can find it here.

This is a study where we looked at the impact fly ash and bottom ash have on the raveling potential of pervious concrete.

 

 

Image Analysis of Surface Voids in Pervious Concrete

For Dave Mitchell...

Recently I had the opportunity to observe the placement of three sections of pervious concrete, each placed using one of three different screeds, all out of the same load of fresh concrete.  Of interest to me was the difference in surface voids observed on the finished pavement.  

Being the peabody that I am, I wanted to know the difference in voids in each section.  To put numbers to it, then, I photographed each section, under identical lighting conditions, at the same angle, using the same equipment (See example below).  In retrospect, I should have taken three shots of each, but only took one.  The images were then imported into an image analysis software (ImageJ), converted to binary images, then analyzed for black/white area.  Converting the color images to binary allows you to separate the voids from the solid parts of the concrete surface (See example below).  Manually adjusting the binary threshold allows you better distinguish void from solid.  The software will report the number of total pixels in the image and the number of black pixels (voids).  Void content may then be calculated as the number of black pixels divided by the number of total pixels in the binary image.

 
So for the three sections, here are my (randomized, anonymized, disguised so you can't tell which section relates to which piece of equipment) results:

Section A: 12.6% Voids

Section B: 13.6% Voids

Section C: 14.1% Voids

We can probably argue that these values are a rough first pass, and may not be truly representative of the void content at the surface of the pavement.  However, the do give us a tool to relatively compare performance of different mixtures, equipment, or compaction techniques.  While clearly not ready for ASTM or specifiers, this technique might help a contractor select an appropriate piece of equipment, or act as a quick QC check. 

Raw Surface Image

 

 

ASTM Pervious Concrete Winter Meeting Update

Here is a quick update on the pervious concrete subcommittee meeting at the ASTM Winter Committee Week.  There are six task groups active within this subcommittee, each working on their own testing standard:

a. Fresh Concrete Density and Voids Content – Minor changes to ASTM C 1688 were balloted to the subcommittee and C09 main committee, including a formal definition of Pervious Concrete.  All proposed items passed, and the five changes will be incorporated in the revised C 1688 next month.  

b. Surface Durability – The first version of this new testing standard was balloted to the subcommittee.  Due to a persuasive negative vote, the ballot will be withdrawn; the document will be revised, and submitted for concurrent ballot with C09. 

The subcommittee discussed in detail whether or not we should proceed with publishing this standard.  The debate centered around whether or not there was practical use for such a test, and if it was the best method available.  The subcommittee agreed that this is the best available test method currently to give producers and researchers a tool for assessing possible mixture proportions.  However, it is not intended for use as an acceptance test, nor is it intended for use on drilled cores.

c. Hardened Concrete Density and Porosity – As with surface durability, the first version of this new testing standard was balloted to the subcommittee.  Due to a persuasive negative vote, the ballot will be withdrawn; the document will be revised, and submitted for concurrent ballot with C09. 

The subcommittee discussed the negative vote, and discussed whether or not the test method should proceed without round robin core data.  The task group will discuss how to proceed.  

d. Compressive Strength – The subcommittee reviewed the latest round robin data from the task group.  They evaluated three different casting methods for cylinders: Proctor Hammer with 2 lifts 10 drops/lift; and Marshall hammer with 5 drops per lift in both single and double lift.  The task group will submit the latest data to ILS for analysis, while concurrently drafting a standard.

e. Field Permeability (Infiltration Rate) – Dr. Brown presented a case study of practical applications of the standard.  It addresses maintenance well, but still may not be applicable for acceptance.

f. Flexural Strength (Yes, its back!) – With Bruce Glaspey of Magruder construction volunteering to head this task group, it is back in business.  The new task group will provide a progress report at the next meeting.