What Slump?

cleveman

I'm pouring c-4 concrete in sidewalks in 70 degree temperature with 4 people, about 6-9 yards at a time.

What slump should I shoot for at the pour?

I have a screed vibe on the screed and would like to just place, screed, float on a stick, trowel on a stick, walking edger, then broom finish. Ideally there would be no hand floating and troweling.

I figure all four guys placing in the beginning, then two placing and two screeding, then one placing/two screeding/one finishing. After placement is complete, everyone would edge/broom/clean tools/go home.

So what slump to achieve good results without puking?

Chris Johnson

4" usually works without issue

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Chris

cleveman

Chris,

I can't get it down the chute with a 4" slump. I poured a 5.5 today and that was ok. Will try for a 6 next time because the bull float wouldn't flatten it and had to go with hand floating.

WarnerConstInc.

A 6 is pretty wet, we saved 6's for big slabs on hot days. 4" for walls and most flat work, 5" seems like the norm.

If you cant get a 4" slump to roll down the chute, tell the driver to clean his chutes better.

We always call the Amish creter's Wet and Wild Concrete. I think they make the driver empty his water in the drum before they start pouring.

Cleveman you didnt have any chemicals in that batch did you?

cleveman

Warner,

It's c-4 concrete, so it has more cement than normal. I think about 90 lbs per yard more than normal. I can only say that it doesn't act like 4000 psi concrete. Usually when I float and trowel, I get water right up to the surface. I don't seem to get any water up to the surface with this stuff. My float wants to stick to it.

When you think about it, this is very normal for a mix with a lot of cement. It is sticky and doesn't give up water.

Chris Johnson

I don't pour regular straight concrete, everything I do is loaded with 30-50% fly ash or slag. Check with the project specifier for this addition. It serves several purposes, 1) it's green, recycling, good for leed points 2) Flowability, works much nicer, delayed set time 3) increases break tests after 56 days, 28 is close to spec, 56 increases it another 80-120% more than spec.

4" can be tough, sometimes it is easier to add 10-20 gallons to a truck...just don't get caught

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Chris

TERM101

With that particular mix and the hot weather I wouldnt be a bit scared to go with atleast a 7, honestly!

Hoven

Frits pak makes a small throw in bag of plasticizer and mini delay set. I usually use their mini delay set for my decorative work. It gives me more time to work it and less turn around time than say a plant added retarder. Great stuff it has saved me on plenty of hot or windy days. and its cheap. Regular walks I start at a 5 and add a little water half way through if your in the direct sun. 9 yards and 4 guys that can finish you got that.

KennMacMoragh

Do you have the design for the concrete mix? I don't know the exact specs for a c-4 mix. You really can't say which slump is safe to use unless you have the design. You can have it designed for 4000 psi at a 7" slump if you want. It depends on the ground it's sitting on too, was the dirt compacted good? . Generally if it's flat, guys go for a 6" slump. If it's on a slope then go for a 5" so it stays in place. But you can't say for sure that it's safe unless you have it engineered and then inspected on site by a special inspector.

cleveman

The design is 474 lbs cement, 119 ash, 1506 sand, 1517 rock, 255-290 water. This is per yard. The first amount of water is minimum and I guess the second is maximum.

We're doing alright by requesting a 5 1/2 delivered. We'll add a bit of water after we're half through a pour.

We're having to hand float the entire sidewalk from both sides, then a quick troweling by hand, then broom finish. With a 120 or 140 long sidewalk, we're getting to the broom finish in about 90 minutes. It has set up enough in some areas at that time that I have to lean on the broom a bit. This is at about 70 degree temperatures. Of course in other areas (shaded) it is still plenty wet. We're pouring mostly on compacted rock.

As the temperature climbs we'll have to look at adding more water to the mix, wetting down the base, or putting plastic down.

Everyone I talk to likes to complain about the C4 mix. I can't get it to flatten with a bull float. I don't know how much weight I'd have to put on the float to get it knocked down. And this is after a power screed. It makes it easier. It broke and we had to do one pour without it before it was repaired. The help said, "we've got to get that electric screed back".

Yeah, we had a pour with a good slope to it and we poured it as dry as possible. Maybe I'll try adding some more water to a flat pour and see how it goes. The bull float acts like the concrete is too sticky. Usually with normal concrete, I can get water to the surface quite easily. I have left my bull float and trowel on a stick at home after the first few tries.

KennMacMoragh

Do your tickets tell you the allowable water you can add? I was thinking back to the times I was a special inspector, I don't think I ever did sidewalks though, so I'm not sure of a good mix. Maybe more flyash would help with what you're doing, as that helps with workablity. Have you talked with your concrete company about the mix design? If you tell them the problems you're having, they might be able to design something better. Mix designs are changed sometimes throughout a job.

willworkforbeer

Some years ago a HO I was doing some work for asked me to give her a price on putting in a concrete driveway. I had just a smattering of concrete finish experience but what the heck. She like the price so I dug, filled and formed it up, even a banked 90 degree curve. 40 yards.

I had 2 guys neither one with concrete experience, its morning and the lady concrete truck driver asks me what slump I want. Slump I asked, what the heck is slump? You know that ugly feeling when your in over your head? She recommended a 7 and then was nice enough to boss us through the first pour, crazy... I mean it was an insane crazy day, in the 90's, wildly undermanned but we pulled it off, it turned out good.

We sat in the bar that evening shellshocked by such a brutal day drinking the pain away. Pitcher after pitcher after pitcher. So sore and beat up the next day I couldnt even work.

KennMacMoragh

That's not a good idea putting in a slab with no experienced help. If something goes wrong there's a lot of liability, concrete isn't easy to fix. You could always sub out the finishing part and do everything else yourself.