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More on Spun Concrete

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     I spent a week at a precast shop in Bangkok where we were having 16 
     inch square prestressed piles and some prestressed AASHTO bridge beams 
     manufactured and this shop also fabricated spun concrete piles.  The 
     process was similar to what was described previously for the spun 
     light poles.  Spun hollow piles seem to be very popular in Asia.
     
     The rebar cages are placed in the split metal forms and a 
     predetermined amount of concrete is poured in.  "Poured in" is 
     actually not a good description since this concrete has such a low 
     water/cement ratio it looks like someone forgot the water.  This is 
     true no slump concrete.  The forms are closed up and the entire tube 
     is slowly spun to distribute the concrete.  After several minutes they 
     crank it up to a very high speed for a short duration. Even with such 
     a low water/cement ratio, water actually trickles out the ends during 
     the high speed spinning.  After spinning and opening the metal form 
     the concrete pile is so stiff and dry that it can be immediately 
     handled as if it had already completed it's set.  I would expect that 
     this process produces a very dense concrete and an efficient cross 
     section.  The only problem I saw was that the piles can only be made 
     in the length of the metal form.  If you need longer piles you would 
     have to splice them together somehow.  This was one reason we went 
     with the solid square prestressed piles since they can be made to 
     almost any practical length.
     
     Thomas Hunt
     Fluor Daniel