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[hreg] Flame Tests on Papercrete/Fidobe

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  • Kim & Garth Travis
    The following articles are from issue No.5 of Earth Quarterly. The first article is on papercrete alone and the second includes tests on fidobe. COMBUSTION
    Message 1 of 1 , Sep 13, 1999
      The following articles are from issue No.5 of Earth Quarterly. The
      first article is on papercrete alone and the second includes tests on


      by Robert Secrest

      Over the past few months, I have been conducting some tests aimed
      at getting data that can
      be used to assess combustion hazards for various papercrete formulas.
      This is a brief report on
      the results to date.
      I will save the details of my preparation methods for a full
      report. It will suffice here
      to say that care was taken to accurately weigh the components of the
      mixtures and to prepare
      and test the samples in a consistent manner. A propane torch flame held
      at one point on the
      sample for 60 seconds was the ignition standard used. This is much like
      tests used by fire
      safety inspectors.

      Samples made using nothing but newspaper pulp continued to flame
      for 30 sec. to 1 min.
      after removal of the ignition source. The flame spread was fairly slow.
      After the flame
      extinguished, the samples continued to smolder in a way similar to
      charcoal in a barbecue.
      Some samples self extinguished after a time. Others were completely
      camumed, leaving a residue
      of white ash and unburned carbon.

      As a theater person, I have used boric acid as a fire retardant on
      scenery. I felt it was
      worth testing in this context. I added a quantity of boric acid to some
      samples of plain paper
      at 20% boric acid by weight to the dry paper. These samples did not
      support flame at all after
      the ignition source was removed. They continued to smolder and produce
      smoke for about a minute
      after, but soon self extinguished completely. Boric acid is clearly
      effective as a fire
      retardant, but represents an added step and cost factor (even when
      purchased as common roach
      powder). I have not, as yet, established the minimum effective ratio for
      this additive. It is
      possible that a saturated solution applied to the surface like paint
      would also be effective.

      In spite of being the most popular formulae for paper based
      blocks, the cement mixtures
      are the most troubling in terms of combustion. Samples containing
      moderate amounts of cement
      (50% and 100% by weight to dry paper) all exhibited the intense
      flameless combustion, which I
      refer to as "slow burn." Unlike ordinary combustion, which produces
      smoke and a visible flame,
      the "slow bum" produces a great deal of heat, (and I suspect Carbon
      Monoxide) while showing no
      flame and little smoke. The process is tenacious and will continue to
      run through every sample
      until it is completely reduced to a light brown ash. Quenching the
      sample in water is about the
      only way to extinguish this reaction. Samples containing a portion of
      sand equal in weight to
      the cement showed no difference with respect to the bum. I have not yet
      tried samples with high
      ratios of cement (2:1 and 4:1). These levels, while of interest to the
      tests, would probably
      represent impractically high ratios in block production.
      I also made samples containing an equal quantity of Portland cement
      and paper (by weight),
      to which I added 20% boric acid. In this case, the samples did burn,
      despite the addition of
      boric acid.
      One should bare in mind that, in spite of this disturbing evidence
      on cement formulae, the
      ignition method used represents a rather intense starting energy level.
      The risk of ignition in
      our applications may be acceptable.
      This testing is to be ongoing and I hope to have a wider range of
      results to report on
      later this year. I am quite interested in clay/paper mixtures, which
      show much promise.
      I am happy to accept questions, comments, and suggestions by e-mail
      Thanks to the Solbergs for including my report in EQ.

      After we performed the strength tests at NMSU (see page 21) we had
      plenty of broken
      fragments left over, so I performed some flame tests on them. All the
      papercrete formulations
      listed on page 21 burned. These had a nonflammable (cement and sand)
      content ranging from 44%
      (the roof panel mix) to 65% (the formula for large tow mixer). Pure
      paper pulp produced a lot
      of smoke; of the papercrete samples, the higher the cement content, the
      less smoke was produced.
      I also flame tested my paper adobe test bricks. The 1:1
      (dirt:paper; 50% nonflammable)
      and 2:1 (67% nonflammable) bricks burned. The other bricks, starting
      with 3:1 (75% nonflammable)
      and ending with 5:1 (83% nonflammable) did not burn.
      Flammability evidently depends on the ratio of flammable to
      nonflammable material. For a
      nonflammable formula, the critical level of nonflammable material is
      between 67-75%. A little
      bit of further testing should allow us to accurately pin down this
      ---Gordon Solberg, Editor
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