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View Diary: Tar Sands oil from allies is preferable to oil from people who want us dead. (46 comments)

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  •  bitumen is road-making material. (1+ / 0-)
    Recommended by:
    Roger Fox

    It's the black stuff that binds together the aggregates in asphalt.  

    Portland cement (PC) concrete works by a one-way chemical reaction where the cement turns into a glue that binds the aggregates together and then crystallizes, thereby making rock.  That makes it ideal for buildings where compressive strength is needed, but not the best material for roads.

    Asphalt is a "concrete" but one that works by the reversible effects of heating and cooling on the bituminous binder: when hot it's liquid so it mixes well with aggregate into a uniform material that can be spread and rolled out; and when cool, it solidifies to set hard into a solid road surface.

    Asphalt provides a smoother road surface than PC concrete because it gains a degree of flexibility in hot weather, that helps control cracking of the pavement.  Asphalt repairs can also be knit together with the existing surface in a manner that's not possible with PC concrete.

    Given that roads will exist as long as any type of wheeled vehicles (bicycles) exist, we need to save our supplies of bitumen for road construction and maintenance.  

    •  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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