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Concrete in a pipe pressure

  1. Jul 21, 2015 #1
    If you had a pipe with a ID of 125 mil and was over 500 meters long filled with 5m3 of concrete what would the pressure be at the bottom
     
  2. jcsd
  3. Jul 21, 2015 #2
    or 5 inch pipe
     
  4. Jul 21, 2015 #3
    Is the pipe vertical?
    Anyway, you will need the density of that concrete mixture.
     
  5. Jul 21, 2015 #4

    SteamKing

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    The pressure at the bottom of any vertical pipe is independent ( = not influenced by) of the diameter of the pipe.

    P = ρ g h,

    where,

    P = pressure, pascals
    ρ = mass density of the fluid, kg / m3
    g = acceleration due to gravity, e.g. 9.81 m/s2
    h = depth of the fluid, m

    The density of Portland cement ranges from 2240 kg/m3 to 2400 kg/m3

    http://www.engineeringtoolbox.com/concrete-properties-d_1223.html

    h = 500 m

    P = 2400 * 9.81 * 500 = 11,772,000 Pa or 11.772 MPa, or about 1700 psi.
     
  6. Jul 21, 2015 #5
    I wonder if the density might be different for the wet concrete (assuming the OP is interested in wet concrete being pumped through the pipe). There isn't much water in the wet mix so maybe it isn't significant.
     
  7. Jul 21, 2015 #6

    SteamKing

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    It's basically an order of magnitude calculation, to show how it's done. Concrete, wet or dry, has a range of densities.
     
  8. Jul 21, 2015 #7

    sophiecentaur

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    I don't think that a practical situation could exist in which a vertical pipe of 500m could have concrete pumped through it. I guess a 500m pipe with a mainly horizontal run would be quite possible (I 've seen a 100m run with a rise of a few metres outside my house.) The pipe was only mild steel, afaics so I reckon it couldn't stand 500m head of concrete, - not to mention the problems of building a pump for the task. Also, is it not the case that builders of high rise buildings use cranes to lift the concrete? If it were feasible, piping would be far more convenient.
     
  9. Jul 21, 2015 #8

    SteamKing

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    Yes, you are correct. Since the internal pressure of the pipe is more than 1700 psi, it would take a very strong pipe to withstand that pressure.

    Small batches of concrete can be mixed on the ground and lifted with concrete buckets. These buckets typically hold about 2 cubic yards of concrete.
     
  10. Jul 21, 2015 #9
    Not a problem. The yield strength of mild (low grade) steel is 63,000 psi. Ignoring the seam, 0.340" thick walls in a 5 inch pipe would burst at 1700 psi.
     
  11. Jul 22, 2015 #10
    It's been done - vertical pumping.
    The record stands at 601 m. or just below 2000 feet.
    ( I just had to look it up )

    http://www.constructionweekonline.com/article-7400-how-the-burj-was-built/1/print/
     
  12. Jul 22, 2015 #11
  13. Jul 22, 2015 #12

    SteamKing

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    It's not clear what specific grade of steel you are talking about here.

    The lowest grade structural steel you will ordinarily find on the market (at least in the US) is ASTM A-36 steel, which has a minimum yield of 36,000 psi.

    Grade A pipe steel, on the other hand, must have a minimum yield of only 30,000 psi, and Grade B goes all the way to 35,000 psi. There are grades of steel which are stronger, of course, but more expensive.

    In any event, whether for pipes or structures, one never designs to yield strength anyway. A variety of design and safety factors are always included to bring the max. allowable working stress below yield.
     
  14. Jul 22, 2015 #13
    Right. I transposed 3,600 to 6,3000.
     
  15. Jul 22, 2015 #14

    sophiecentaur

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  16. Jul 22, 2015 #15
    Thoughtful question.

    I would imagine financial considerations vs engineering considerations.
    And return on investment. Quick and expensive, and sooner for recuperation, Or slower and less expensive but a longer wait time to begin payback.

    That particular pumping machine doesn't seem to be all that grandiose, with a running HP in the ballpark of 600 hp, so it in itself can't be all that expensive.
    Although, I would expect the teams laying the pipes to command a hefty fee, along with the crew running the logistics when it is up and running. Organizing a continuous supply of concrete with cement mixers, cement plant, aggregate, water, etc is, sometimes 24 hrs or more in a go, I would expect also to be demanding. Everything would have to be pre-arranged to be nearby and ready to go without interruption, as once the pumper is operational one does not want any wait time to fill the hopper. One plans for no air entering the flow, nor a stoppage in flow. The first can be an explosive and deadly situation; the second a possible catastrophic complete work stoppage ( hardening concrete in the pipes if let to set ), or lose the whole pipes worth of concrete.

    It could be the type of construction determines the concrete pouring schedule. Local contractors can fulfill most schedules.
    Some construction must have a "mini" pumper that moves up along with the floors of the building, set up to be filled with the buckets from crane supply down below.
     
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