Rebar vs. Wire mesh and fiber in concrete

Discussion in 'Heavy Equipment & Pavement' started by concrete man, Feb 18, 2001.

  1. thelawnguy

    thelawnguy LawnSite Silver Member
    Messages: 2,411

    I will snip a few wires in the mesh and bend them down and the mesh will stand on these "legs" and it seems to keep it up in the middle of the slab. Seems to work okay for sidewalks but I dont know what long term problems this may cause.
  2. concrete man

    concrete man LawnSite Member
    Messages: 7

    Thanks Walt that was nice to know. Let me ask you a question. What have you had luck with in the summer time to cut down on the craze cracks or spider cracks on the top of a slab? The concrete company here gave me some evert surface retarder, not the same as retarder for exposed aggregat. I tried it last summer it helped a little but then I had trouble with the top 1/8" start to blister off when I start to run my trowel machine. The concrete company had to pay to fix a basement floor and garage that the top came off of it. If digman or whatever your name is reads this email or call later. You need a different name like gravedigger.
  3. WALT

    WALT LawnSite Member
    Messages: 27

    When I used to live in Georiga, that was a constant problem, even worse when the humidity was lower. The stuff would dry so quick and the urgency to finish the placement increased. We used a liquid curing compond,that was sprayed on after all the finishing was complete. I can't remember the brand, but make sure it's non-yellowing. This worked well by actually creating a thin membrane, retaining the water from hydrating so quick. It's important that when it's hot out to be sure to apply the compound when the water has dissapeared. The longer it hydrates the better. Water curing is not reccomended on hot days, and plastic too retain the water on cold days is good. Never the less, curing is very important process that shouldn't be shortened or overlooked.

    Some other problems may be the slump. 3" is good for flat work, much more slump then that causes the water to cement ratio to be off. Never trust the company, take a slump test at the site and don't hessitate to send it back if it's not what you want.
    Over-working or Over-finishing causes too much segregation, bullfloating too much is the most common I've seen, or screeding along with the use of a jitter-bug does this, and cause to much paste to rise, giving that weak 1/8 you talked about. And wait until the excess water is off the top before hand floating. This is personnely the problem I look out for on my concrete jobs. If they work for me, they WILL know at least that cause I watch EVERYONE to make sure that does not happen. I've seen scalling and spalling due to that, and is a peeve of mine.
    I hope this helps... :)
  4. concrete man

    concrete man LawnSite Member
    Messages: 7

    I use a curing compound whenever I get done slick finishing a slab or even brooming. We try to keep it a good 4" slump from the plant. I started tring not to close up my concrete to much with the bullfloat. I found it sets up a little faster if it is still alittle rough, and it doesn't trap the water under that top surface. I'm going to try to find the flat mesh you recommended. My dad just died in may and I'm still learning a few things.
  5. WALT

    WALT LawnSite Member
    Messages: 27

    I am always learning too and when I answer questions, or see other techniques, it helps me much also by refreshing my memory. Sorry to here about your Dad, and wish you good luck. Concrete is one of my favorite occupations and always looking for new techniqes. Oh and welcome to Lawn Site... :)
  6. 66Construction

    66Construction LawnSite Member
    Messages: 125

    Concrete Man

    I only use rebar on an Alaskan slab #4 2' oc 6" thick. However I have seen it in parking garages and structural slabs. The mesh should work fine. I was on a job with a huge basement and the owner wanted no cuts in the floor. Around all the coulmns and corners where it would crack we used two layers of mesh. Nothing more then a slight surface crack.

    I give you credit for pouring a slab at a 4. someone said a three not me not on a slab. If you have an inspector on the site watching you i'd pay for the super plasticiser. Don't go nuts with the water but there is a safety factor built into the concrete 3000 psi is realy like 3400 psi you can have a littlt water. It's right in your ACI manual. I was an Inspector for a summer you can do some amazing things to concrete. It depends on the suiplier. If the suplier has good concrete you will get better rersults.

    With the mesh settling to the bottom try puting pieces of broken block under it. Definitly use the sheets, it lies nice and flat and it's eassy to tie together.

    Have any of you tried daratard. I saw it used on the top deck of a parking garage in August. It was about 95 degrees it worked out ok.

    When the top layer comes off when you trowel it's because the top is hard and underneath it's still soft. When it's hot and you're in the sun you have to have the retarder put in right at the plant and dont let it get old 90 min max! Tell them the conditions and what has happened in your experience they know their product and what to do to fix a problem. When you're finishing dont squirt water on the surface....I know everybody and their brother blesses a slab when you're floating troweling etc but it's lowering the cement water ration right at the surface. Don't finish to soon that can ruin your finish.

    This is what I've seen as an inspector as a contractor as a loborer. Comments questions think I'm way off with something I'd love to hear about it I learn something every day and it comes from you guys.
  7. WALT

    WALT LawnSite Member
    Messages: 27

    You are on the money, my friend. Especially the points on finishing, very important. A point I'd clairify, just in case somebody is confused, when you utilize the 2 layers of mesh, they are spaced out about evenly in the pad. The bottem layer increasing the strength and top layer for preventing cracks as well as strength. Always making sure to have enough concrete around the reinforcement, limiting voids.

    I hope to find out tips from you, I am sure as an inspector you seen some wild stuff, both right and wrong.
    Just curious, were you an inspector and was it for the gov't?
    What does it take (education, etc.) to be an inspector?
    Look foward to more insight..Thanks
  8. 66Construction

    66Construction LawnSite Member
    Messages: 125


    I got the inspector job through school it was like an internship I got credits for but I also got paid. All you realy need to be an inspector is ACI certification. I wasn't actualy a building inspector I was a technician for a testing lab. I monitered the slump air content temp revolutions on the barrel time from batch water added strength at 7 and 28 days and aroung 56 days if you have a lot of fly ash in the mix. To work for the gvt it may require some school I'm not sure those guys are strict. I did a couple of bridge jobs and they dont hesitate to throw away a $1500 load of concrete or charge it to an inspector or a pump company for being late to the job.

    Here's a wild story I was on a job at a parking garage. Satae Building inspectors Engineers the works. #5 rebar @1' O.C. 5000psi concrete w/ water reducer and some other hi tech stuff real expensive. It was wierd stuff it almost stuck to the scoop I used to do the test. On the first day the contractor found out that the concrete wasn't user friendly. It was actualy sliping under the power screed and not coming out very flat. It was also seting up before they could realy float the high and low spots out. To remedy this situation they started power troweling it before it set. They were leaving foot prints about 3" into the concrete. The trowel was throwng around concrete like a side discharge lawn mower. They also ended up using a straight edge in stead of the power screed. Surprisingly none of the engineers or state inspectors knew that troweling it like this was bad. Only me and the contractor knew, we were friends so neithre of us said a thing. I haven't been able to go back and see this slab but I'd bet it cant be in very good condition. After the first placement they changed the mix design and the next 1300 yards went pretty smoth. Accept for a barrel that went hard while it was being pumped. 2.5 hrs old they wanted to make cylinders and let it go so i did as they asked. This all happened right infront of the state inspector and the engineer on the project. The driver got fired and if the super hadn't had around 30 years in the company he would have gotten fired too.

    my name's Casey incase you were wondering 66 construction is the name of my company
  9. DIG'EM

    DIG'EM Guest
    Messages: 0

    hey cretewalker you really eating this stuff up. you got a good post .Mine is on fire .

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