2-4" Slump Required On Residential Slab And Footing. - Contractor Talk

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StPete727 S We normally use on-call concrete with 4000psi mix. Im reading these plans that specify a 2-4 slump on all concrete. Seems like a very tight mix for a 1st floor residential footing and slab. I work this area all the time and Ive never read that requirement from any of the dozen or so Architects Ive worked with. I think that will require batch trucks or can I get that from a concrete on-call truck? #1 · Nov 6, 2016 We normally use on-call concrete with 4000psi mix. Im reading these plans that specify a 2-4 slump on all concrete. Seems like a very tight mix for a 1st floor residential footing and slab. I work this area all the time and Ive never read that requirement from any of the dozen or so Architects Ive worked with. I think that will require batch trucks or can I get that from a concrete on-call truck? Sort by Oldest first Oldest first Newest first Most reactions #2 · Nov 6, 2016 Thats a pretty standard slump for concrete at 4 to 5k psi. The question is are you required to perform the test and have signed off ?, or was the slump in the general notes on the plans ?. Most times when i use concrete on call i have a pumper so the mix is a little loose at first (a loose mix runs through the pump easier and is not so quick to block the pump) so performing a slump test gets a little harder unless you got some where to pump and dump. You can get the mix you need from the guys at concrete on call :thumbsup:. #3 · Nov 7, 2016 Just tell the driver you need a 4" slump. That's about what it comes out at without adding any water on the jobsite. #4 · Nov 7, 2016 I order 4" all the time, you practically have to pull it down the chute, I can't imagine 2"... have to butter the chute first. #7 · Nov 7, 2016 I saw some guys pouurr a 2 once. Told them to send it out as a 4 but got stuck in traffic in the middle of summer. Oh boy did it ever not look fun. 0 Reply #5 · Nov 7, 2016 Thanks much appreciated. #6 · Nov 7, 2016 Is the slump test actually even used anymore? It seems like ridiculous way to test concrete other than it's workablity maybe. A slump test will not tell you if it is 2500 PSI of 4500 PSI and the slump will change over a little bit of time on the SAME batch of concrete. Andy. #8 · Nov 7, 2016 Since admixtures became common, a slump test is basically obsolete. Even my ACI tester said it was only really useful to compare one truck with another on big jobs. As long as you keep your water/cement ratio in spec and the aggregate isn't separating, slump is not important. But just try telling that to an inspector... #9 · Nov 7, 2016 It really should be about the mix design yielding a certain psi at a certain water cement ratio. I would guess if you paid enough you could get 5000 psi at a 10" slump. #10 · Nov 7, 2016 Slump is measured by the amount of deformation when the slump cone is removed. A 10" slump = soup. It's done by placing a 12" high cone, open at both ends, on a flat surface, with the wide end down, and filling it with concrete from the top, then removing the cone and measuring the height of what's left. A 4" slump means your pile of concrete is 8" high after the cone is removed (it "slumped 4"). I used to do slump tests as well as time & temperature on the loads and make & break cylinders when I was a threshold inspector. Time is taken from the order ticket from the batch plant. It indicates what time the batch was made. On jobs I was on they had 90 minutes to start placing the concrete or we had to reject the load. To take temperature you climb up on the truck and have the driver discharge some until cement comes to the top of the chute, and stick your thermometer in it. Slump test sample material and test cylinder material are taken from the load after 1/3 of the load has been discharged. A 4" slump is what you get coming out of the batch plant and that's the industry standard. Adding water to the mix on site results in a higher slump. The credential to be qualified to do this testing is a ACI 318 certification. Most major cities have a batch plant which teaches the classes. I did mine in Palm Beach County, FL around 1990 at a Rinker plant. With that credential you can become a threshold inspector working for a 3rd party engineering company. It's not bad for something that takes 2 days of classroom and an easy test and it's a door to becoming a city or county building inspector because you're already doing inspections. Show more replies 0 Reply #11 · Nov 7, 2016 With the use of Pumpers, and the additives to plasticise loads, is the slump specification actually useful any more? I would think that the cylinders used to test the mix strength would be a better indication of proper mix, but they do not become useful until after 30 days or so. #12 · Nov 7, 2016 My concern (based on my inexperience of slump tested concrete) is that the on-call trucks can't make a 2-4 slump because there isn't enough time to "bake" the concrete. I always thought that slump requirements basically mean you need batched concrete. But I guess I'm wrong and that's why I asked. But tell me am I justified in asking to have this removed from the plans, and just spec the psi. Because 2-4 slump sounds awfully hard to work with, especially on a slab. The only thing we are pouring is footings, slab+stem wall, and vertical grouting of 8" cmu. Almost all of that seems to work better with a looser mix. Especially the grouting. In the end it may get tossed aside. I spoke with Architect and he was open to suggestions, which is an indication that he make lack experience in Residential construction at the least, due to the fact that the plans are full of things like a crap ton of steel in an interior slab and huge footings etc. I've smelled this crap before, and it's usually an indication of an Architect with limited engineering skills or knowledge, so when the Engineer gets them he will easily stamp them, as they have been grossly overbuilt. #15 · Nov 7, 2016 Interesting thread. A 12" slump in impossible. The slump can't be higher than 12" minus the diameter of the aggregate, and if that happens, you're dealing with trash. If someone is telling you they have a slump cone higher than 12", don't do business with that man. Grout for fill cells is a different product than concrete for a footing or a slab. Make sure you order grout when filling cells. The footing width is a function of the bearing capacity of the soil. Most plans in Florida are going to assume a 2,000 lb/sf soil bearing capacity unless a geotechnical analysis is performed. If the plans show a 24" footing and you reduce it to 16" and there's a failure, you're going to eat that and it's not going to be fun. The most efficient footing is designed after doing geotech and calculating the weights of building materials and considering all loads to be imposed, but it's cheaper to assume the 2k psf and work from that. You can get close to that from beach sand (which we have a whole lot of down here). #18 · Nov 8, 2016

MikeFL said: A 12" slump in impossible. The slump can't be higher than 12" minus the diameter of the aggregate, and if that happens, you're dealing with trash. If someone is telling you they have a slump cone higher than 12", don't do business with that man. Click to expand...

You're wrong. You need to research Super-Plasticizers and SCG. Or not. I don't care. Part of it is my fault, I used the wrong terminology. It's called a Slump Flow, and it regularly goes 18" -24". It flows like water, and THERE'S NOTHING WRONG WITH IT. Quite the contrary, that's what it's designed to do. It's called Self-Consolidating Grout. Have you ever had to consolidate grout below a window?? :rolleyes:

MikeFL said: Grout for fill cells is a different product than concrete for a footing or a slab. Make sure you order grout when filling cells. Click to expand...

I don't know how long you've been out of school for, kid, but I've been doing this long enough to know the difference between grout and concrete. I don't think the OP is going to order grout for his slab, the only way grout came up was in the discussion about slumps.

MikeFL said: The footing width is a function of the bearing capacity of the soil. Most plans in Florida are going to assume a 2,000 lb/sf soil bearing capacity unless a geotechnical analysis is performed. If the plans show a 24" footing and you reduce it to 16" and there's a failure, you're going to eat that and it's not going to be fun. The most efficient footing is designed after doing geotech and calculating the weights of building materials and considering all loads to be imposed, but it's cheaper to assume the 2k psf and work from that. You can get close to that from beach sand (which we have a whole lot of down here). Click to expand...

I have no idea what you're talking about. Why are you talking about footing width??? :blink: :confused1: Delta 0 Reply #17 · Nov 7, 2016 (Edited) So we are back to the question is it a copy and paste ?, or do we have to get some guy up at 7 am to perform a slump test and sign off on it ?, We all understand a 4'' slump is about the norm, but i have never had a set of plans for a slab ask for a slump test. Now columns are some what different I have no idea where to buy a cone locally, to perform a slump test for my self. #21 · Nov 8, 2016 Does anything say the test has to be performed on site? I think it's just the spec for the concrete. 0 Reply #20 · Nov 8, 2016 I used to be an ACI certified field technician. The highest strength break I ever got from a test cylinder was some 11-sack grout that looked like slurry water coming out of the truck. It broke at over 11,000 psi. Slump doesn't matter, water/cement ratio does. #22 · Nov 8, 2016 Maybe it's backwards but the test is still used to check the variance between batches. Large pours often have a guy there to check each truck that pulls up. Slump isn't measured past 6", if it's sloppy they do a flow table test. #23 · Nov 9, 2016 We'd do time & temp on every load and slump & cylinders every 50 yards. 1 Reply #25 · Nov 27, 2016 Concrete is an interesting material and can take on many forms and functions. What one calls standard in one art of the country or field is way out to lunch for others. I Used to work in commercial and industrial as a carpenter and also running volumetric mix trucks. Believe me I have seen a lot of concrete good and bad. A 40 mpa mix at 2 inch will be very difficult coming out of a mix truck unless it has super plasitcers and water reducers etc. Then you switch it up and get high strengh early break concrete like Lafarge agilia. Forms need to be designed for it as it has 2x the pressure on the forms and does not need vibrating. Basically The slump cone indicates the workablity of the concrete has no baring on strength out come unless excessive water was added after initial mix has started. As with ever turn of the drum concrete is having the setting reaction stalled and weakening the mix. Thats why timing is important and temperature. Voulmetric mixers make the best concrete as the time from initial reaction to final placement is so short. less than 15 minutes on a bridge. Then there is the rapid strength concrete that hits 40 mpa in 45 minutes and has a 4 inch slump. Water cement and then all the other chemicals they add. My last concrete job did had no cement was polyester resin rock and sand Insert Quotes Post Reply

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