Have a question or need some advice related to any aspect of concrete pavements?

Welcome to “QandO” (Questions and opinions), a new benefit for members of ISCP and collaborating partners ASCP and EUPAVE.

This benefit consists of an on-line forum for colleagues to pose concrete pavement related questions and receive opinions and advice from other colleagues. The rules of engagement are simple and are designed to create an archive of information that will benefit all members of the societies.

To access send an email to iscp@iastate.edu with your question.

Rules:

• This service is designed for general questions and advice related to concrete pavements. Posted opinions and advice shall not be constituted as legal engineering design advice or opinion, and do not reflect the opinions of the forum host organizations.
• To post a question, you must be an active or honorary member of ISCP, or on the approved QandO members list provided to ISCP by ASCP or EUPAVE.
• Access to the service will be monitored by the forum host (CPTech Center @ ISU) and designated ISCP Board member(s). Designated monitors will screen for active membership status and review questions for relevance to concrete pavements. Persons posting questions unrelated to concrete pavements will be notified of the reasons for denial of a posting.
• Once verified that you are a qualified member and have posed a relevant question, your question will be forward to everyone on the list, i.e. society members that have agreed to receive questions from this service.
• Responses to questions should be sent only to the person asking the question.
• Please never hit reply all – this is the death knell of any listserve.
• The requestor is expected to summarize (within 2 weeks) the question(s) and opinions received and send them to Thomas Burnham at tom.burnham@state.mn.us.

ISCP Q&O Summaries

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COLD WEATHER PAVING

Question: Is there any industry document that reflects current best practice for cold weather paving (as defined in ACI 306)?

Opinions:

• NRMCA has a good cold weather publication CIP 27 available here
• Minnesota DOT also has a one pager here
• Document produced for the UK Highways Agency: Concreting Pavements in Winter (Published by Britpave)
• Our French colleagues have this (in French)
• One up-to-date source of info on cold weather paving can be found on Page 232 of this publication

JOINT STABILIZATION

Question: What filler product can be liquid-applied (poured or injected) into contraction joints, sets to a toughness similar to epoxy, but does not adhere to concrete for the purposes of a ‘lite’ rehabilitation by means of joint stabilisation? Any ideas, tangential or otherwise, related to materials, methods or treatments?

Details: We’re developing a rehabilitation scheme for an old (200% life consumed) concrete pavement (PCP, over lean mix concrete) with partial minor stepping of joints. The slabs are being overlaid with an asphalt geogrid composite to subdue the damage caused by thermal effects and loading. The intent of the rehabilitation is to nurse the existing pavement to a 10 year life (with 90% reduced traffic loading due to a deviation). Whilst the slabs are too thin to dowel-bar-retrofit, it occurs to me that it might be possible to ‘mould‘ a transverse joint filler [much like the process of moulding a mouthguard], to restore some of the interlock that’s been lost to erosion. For this to work, there’d be several operation considerations (such as timing to coincide with expanded slabs, ie, closed joint), however the properties of the filler would be critical. Whilst a conventional epoxy has the downside of adhering the joint faces and silicone not insufficient toughness, it led me think about specification for the ‘ideal’ material (which even though sounds like a riddle, is not).

• What filler product can be liquid-applied (poured or injected), sets to a toughness similar to epoxy, but does not adhere to concrete? Not to suggest that such a treatment would provide significantly long life, such an approach, if feasible, could extend the functional life of the currently degraded joints (by limiting movement and grinding the interlocked shape down further) – the idea is essentially to identify a treatment that would measurably prolong likely imminent breakdown.
• Any ideas, tangential or otherwise, related to materials, methods or treatments? Context: 4.2 x 4.2 m PCP (undowelled) concrete slabs 35 years since construction, approximately 15% failure.

Opinions:

• I give you one word of advice: “bituminous”.
• We have a county in Minnesota that had a 165 mm thick whitetopping (bonded concrete overlay on asphalt) with 3.6m x 3.6 m panels. It was installed undoweled, and due to unexpectedly high truck volumes, developed severe transverse joint faulting (4+ mm) within 5 years after construction. To rectify the situation, the county was able to successfully retrofit 25 mm diameter dowel bars, 4 bars in each wheel path. This was followed by diamond grinding. I would expect this to perform well for a 10 year life span like you are seeking, and avoids the need for an asphalt overlay. A write-up case study was featured by IGGA. I fear that installing any type of material able to restore load transfer through aggregate interlock may lead to panel buckling due to lack of room for expansion during hot temperatures (which I know you guys have!). Pumping any type of material into joints and under pavement slabs can work, however this process often leads to large cost overruns due to the lack of knowledge of how much material it will take to fill voids.
• My limited knowledge of asphalt overlays suggested that a 70 mm thick overlay will simply be along for the ride, and reflective cracking will happen soon after paving. Unfortunately, I don’t have enough knowledge or experience with geogrids in asphalt overlays. In Minnesota we tend to install thicker (100+ mm) asphalt overlays on concrete pavement for such cases, and of course due to our extreme climate, still get reflective cracking that slowly deteriorates over 8 to 15 years.
• Insertion of dowels would anyhow be a very expensive intervention for a life-time extension of only 10 years. I don’t think that the joint filling, as you suggest, would contribute much and/or would last long. And I’m afraid you won’t find the ‘miracle’ product to use. In fact, the steps at the joints are not the problem, they will be covered with the geogrid and asphalt and will be gone. So the problem is the vertical movement of these joints, because of the continued discomfort and because this will induce cracks in the asphalt. The procedure we’d follow in Belgium is to fragmentize the concrete (pieces smaller than 1 m²) and stabilize them with a roller, followed by the overlay. If you keep the slabs complete, it can also be an option to maintain the joints also in the asphalt pavement (bituminous joints in a bituminous layer). I’ve seen a few successful projects like that (with moderate traffic).
• My comment on potential bituminous treatments was genuine though I can’t offer specific advice. The background is as follows. As you know I spent 3 months in 1989 touring highway authorities in America & Europe. As the saying goes, to a worm in horseradish the whole World is horseradish, and so it was with me living in concrete pavements for 3 months. One of the issues I pursued was an improved technique to replace ‘groutjacking’ on our aging JRCP network with sand or clay ‘subbases’. I have to admit that I’ve never been out in the field to watch a jacking operation but I’ve discussed it with various DMR/RMS practitioners over the years. My understanding is that it works very well for a period but due to its brittle nature it eventually cracks below the joint thereby allowing water back into the support layer and so pumping starts all over again.
• During my travels, I began thinking along the lines that what we really needed was a flexible material that was resistant to cracking. This suggested a product such as a stiff silicone but that would obviously be very expensive so I then pursued the idea of cementitious grouts with additives (polymers ??) that would render it relatively flexible. With those thoughts in mind I was visiting the Indiana DOT discussing maintenance practices and one of my hosts (with a title something like Chief Engineer Maintenance) mentioned (almost in passing) that for many years they had been jacking with hot bitumen in lieu of grout and that it was very successful. He was under the impression that they were the only state using bitumen and he couldn’t understand why it hadn’t been adopted more widely. Sure it was potentially risky if you had a burst and hot bitumen started spraying the workers, but so is concrete pumping risky (ask anyone who has witnessed a concrete pipe burst when they’re pumping up 20-30 storeys) and we didn’t abandon concrete pumping after 1 or 2 accidents; we tackled it with improved equipment and added safety measures. The Engineer who had refined the technique was Joe Sudol, and I met him a day or so later for further discussions. Unfortunately there was very little documentation of the process [snip] .. I raised the topic a few times with various people (managers, R&D funders etc) but invariably got a response along the lines “you’ve got another thing coming if you think I’m going to advocate high pressure pumping of hot bitumen !”.
• So, there you have it. Now to recap:  I know you’re talking about a PCP on LCS whereas Indiana DOT was treating JRCP over granular. They involve very different issues but I think the principles still apply. We have PCP slabs that are curled and rocking so we want to reduce this movement (possibly before placing an overlay), and I still think that a semi-flexible material would be ideal. In some cases I expect we also have voids (due to pumping of the subgrade below the LCS) that we’d like to fill.
• I don’t think we’d necessarily use hot bitumen these days but I’d be very surprised if we couldn’t find or develop a bitumen emulsion type product with fancy additives to provide the required properties, perhaps with delayed set.

PRECAST CONCRETE PAVEMENTS

Question: Please advise where I can find information or case studies on the use of prefabricated concrete for airports in either the runway or apron?

Opinions:

• The most up-to-date information on precast concrete pavement resources can be found here.