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  •  Pre stressed concrete is the shiz nit. (1+ / 0-)
    Recommended by:
    G2geek

    Lasts decades longer.

    FDR 9-23-33, "If we cannot do this one way, we will do it another way. But do it we will.

    by Roger Fox on Sun Aug 28, 2011 at 05:52:40 PM PDT

    [ Parent ]

    •  for buildings, but not for roads. (1+ / 0-)
      Recommended by:
      Roger Fox

      However keep in mind that Roman concrete has lasted for two thousand years: a "lost secret" that was a complete mystery until Ransome figured out how to make the stuff again in the 1850s and Abrahms figured out the water/cement ratio law.

      I tend to believe that reinforced concrete structures built according to best practices, can last centuries.  Time will tell of course, but I don't see anything about prestressed concrete that provides a major advantage for home construction compared to the use of poured concrete in-situ using ICFs.   In either case, much depends on the training, skill, and care exercised by workers on site.

      (That said, get on YouTube and look around, and you will see some truly appallingly bad practices being touted as "oh boy look what we built, aren't we something!"   The most common one is souping up the mix with enough water to float away the building, followed by failure to moist-cure flatwork, followed by unreinforced masonry of various kinds.)

      •  I learned about prestressed (1+ / 0-)
        Recommended by:
        G2geek

        NYT circa 1980, it was an editorial about roads IIRC.

        I have concrete work I did in '71 in  landscape, steps walkways, retaining walls. Have to re-strike joints repeatedly until it starts to set up. Still fabulous. Keep it wet when curing, yup.
        For flat work I like a mag float swirl finish, vs the swept broom finish. To many municipalities drag a broom across early and leave, not refloating as moisture comes to the top. Ends up with a surface that pits and flakes during the first winter. Have to keep working it until it starts to set up, then you get some strong shit that'll last for decades at a minimum.

        FDR 9-23-33, "If we cannot do this one way, we will do it another way. But do it we will.

        by Roger Fox on Sun Aug 28, 2011 at 09:16:01 PM PDT

        [ Parent ]

        •  alternately... (0+ / 0-)

          .... mix the stuff so stiff that little or no moisture will come to the surface.  This requires a) being able to slow down the drum speed on portable mixers to work with stiff mixes, and b) good consolidation of the stiff concrete in the forms: a lot of tamping with a strike-off board on flatwork or the careful use of a vibrator for walls and suchlike.  

          Swirl finish is nice, also more labor-intensive thus higher cost, and a dragged broom finish does provide non-skid benefits at low cost, hence popular in municipal work.  

          I was unaware of prestressed in road work.  Hmm.  

          Good concrete in structures should at least last a century.  BTW, engineers in Japan have developed superplastic (flowable) mixes that attain 10,000 PSI.  These are for use in highrises, but holy cow I'd love to see a dome-home made out of that stuff in a monolithic pour: it would probably be earthquake proof even right next to a faultline having a 7 or higher.  (Writing this from a short distance from the Hayward fault, uh-oh.)

          •  Yeah a stiff dryer mix is best (1+ / 0-)
            Recommended by:
            G2geek

            Dealing with the water is always problematic, IMHO properly working a dryer mix increases the odds of better results.

            Re: 100 yrs, absolutely.

            FDR 9-23-33, "If we cannot do this one way, we will do it another way. But do it we will.

            by Roger Fox on Mon Aug 29, 2011 at 11:50:57 AM PDT

            [ Parent ]

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