Concrete Curling

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Author Message Dewayne Dean Senior Member Username: ddean Post Number: 25 Registered: 02-2016 Posted on Tuesday, March 01, 2016 - 10:59 am:    I have been reading the archives about concrete curling, lots of good info there. Several years ago ( before my time ), my firm had a GC press for a $400,000 change order to cover the costs of grinding concrete due to curling. The GC's claim was that the mix design was at fault. Now my firm wants to put language in the spec to place the responsibility for floor flatness squarely on the GC. Any experience you folks can share would be appreciated. anon (Unregistered Guest) Unregistered guest Posted on Tuesday, March 01, 2016 - 11:25 am:    Not that simple. Curling of concrete slabs on grade (which is what I assume you are referring to) depends mostly on reinforcement and mix design. These are design issues that have nothing to do with specifying Ff and Fl values. If your firm wants to ensure this doesn't happen again, it needs to hire a structural engineer that fully understands how to design SOG so that curling is minimized/eliminated. There are many excellent technical articles on how this is achieved on the Concrete Construction web site. Ronald L. Geren, FCSI, AIA, CCS, CCCA, SCIP Senior Member Username: specman Post Number: 1388 Registered: 03-2003 Posted on Tuesday, March 01, 2016 - 11:48 am:    Regarding your firm's past experience, who prepared the mix design: the contractor and his concrete supplier, or the design team? If the latter, then the contractor could potentially have a case; however, if it was the former--in most cases it is--then the contractor would have little standing in my opinion (even if the mix design was approved through the submittal process). Writing the specification to be more performance-based rather than descriptive would shift most of the risk from the design team to the contractor. Thus, specifying floor flatness and levelness and minimum compressive strength should be sufficient. There are some design solutions that could be implemented to minimize curling, so those should be investigated as well. Ron Geren, FCSI, AIA, CCS, CCCA, SCIP www.specsandcodes.com Michael Chusid, RA FCSI CCS Senior Member Username: michael_chusid Post Number: 125 Registered: 10-2003 Posted on Tuesday, March 01, 2016 - 01:04 pm:    Don't worry about it. If a slab curls upwards at the edges, it will eventually crack across the center of the slab (due to tension) and the upturned edges will settle, creating a flat floor. ;-) Michael Chusid, RA FCSI CCS www.chusid.com www.buildingproduct.guru Mark Gilligan SE, Senior Member Username: mark_gilligan Post Number: 781 Registered: 10-2007 Posted on Tuesday, March 01, 2016 - 01:35 pm:    I agree with Ronald. Curling is related to curing and will be more of a concern in dry windy environments. Consider invoking the special inspection provisions in Chapter 17 of the IBC related to inspection of curing. This should make sure curing is not ignored. A low water cementitious material ratio which will minimize the amount of free water. A low ratio is desired for a number of other reasons. Current good practice is to specify concrete based on performance criteria. I am assuming that the engineer will be authoring the concrete specification section and the architect will be authoring the concrete finishes section if there is one. Make sure your flatness requirements are not overly aggressive and that they are specified consistent with current ACI recommendations. Clearly understand under what conditions floor flatness measurements are valid. If you want to you could indicate that grinding may be necessary when you specify floor flatness. Scott Piper Senior Member Username: spiper Post Number: 30 Registered: 08-2014 Posted on Tuesday, March 01, 2016 - 03:28 pm:    Our office has added some language specific to the concrete curing process to attempt to control warping, curling, etc. We often call for a wet cure with a curing cover to avoid the differential levels between the top and the bottom of the slab during the cure in the hopes that this will minimize slabs issues. Sometimes it works like a charm, sometimes not so much. We also use a low water/cement ratio but this can lead to the use of water reducing agents to increase workability. This is typically not an issue but some agents can actually increase drying shrinkage so that needs to be considered. I utilize a book by Howard Kanare (Concrete Floors and Moisture) for a great deal of my research and I would recommend it to anyone who is interested. full disclosure: not an very exciting read, but informative Dewayne Dean Senior Member Username: ddean Post Number: 26 Registered: 02-2016 Posted on Tuesday, March 01, 2016 - 07:07 pm:    Thanks Guys, informative as always anon (Unregistered Guest) Unregistered guest Posted on Wednesday, March 02, 2016 - 12:15 pm:    here's an internet gift on the subject - grab it while it's available! http://lauwtjunnji.weebly.com/uploads/1/0/1/7/10171621/aci_302-1r-96_(guide_for_concrete_floor_and_slab_construction).pdf Jerome J. Lazar, RA, CCS, CSI, SCIP Senior Member Username: lazarcitec Post Number: 1610 Registered: 05-2003 Posted on Wednesday, March 02, 2016 - 12:48 pm:    Anon, link does not work, try again? Colin Gilboy Senior Member Username: colin Post Number: 424 Registered: 09-2005 Posted on Wednesday, March 02, 2016 - 01:00 pm:    Updated link - forum software cut off long length. I also saved a copy on my computer for future reference. Colin Gilboy Publisher, 4specs.com 435.200.5775 - Utah 800.369.8008 anon (Unregistered Guest) Unregistered guest Posted on Wednesday, March 02, 2016 - 01:13 pm:    Please note that this document is pretty old - a lot of this is still relevant, but some of the recommendations have been changed. The one that jumped out at me was to place a capillary break between the slab and the vapor retarder in 11.11. ACI has since revised that recommendation... The rest of the recommendations regarding curling I think are still good, but best advice is to purchase the current document from ACI. Michael Chusid, RA FCSI CCS Senior Member Username: michael_chusid Post Number: 126 Registered: 10-2003 Posted on Wednesday, March 02, 2016 - 02:42 pm:    It may be a gift, but I suspect it is bootleg. Michael Chusid, RA FCSI CCS www.chusid.com www.buildingproduct.guru ken hercenberg Senior Member Username: khercenberg Post Number: 990 Registered: 12-2006 Posted on Wednesday, March 02, 2016 - 10:58 pm:    6 mil polyethylene and granular fill? I'd say that is not the type of present you should seek. I agree that proper wet curing can go a long way to preventing curling. ACI has a lot of useful information. Your structural engineer should have access to these references. Usually best to utilize them.