Concrete decontamination by electro-hydraulic scabbling (EHS). Final report Page: 99 of 177
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6.2.2 Deep scabbling
Deep scabbling removed a thick -3/4" to 1 1/4" - layer of concrete using
an electric pulser equipped with PFN-L. The main features of these trials are
summarized below:
" The electrodes (32" long, as used for shallow scabbling) of angled
configuration should have re-enforcement to avoid bending/gap
changes due to strong shocks.
" Ranges and selected values of operating conditions for 32 kW DC
supply which was used with PFN-L and delivers up to 75% of the
installed power, are given in Table 6.1. There is no marked difference
in scabbling performance whether the PFN-L used 2 or 3-capacitors.
A 2-capacitor unit was used in most tests.
* Processing of the 7 sq. ft. concrete area took 20 to 30 min.
" In spite of the larger amount of debris generated by deep scabbling,
the operation is less sensitive to the water quality. Still, scabbling is
more efficient and uniform when water is clean.
. The deterioration of performance manifests itself mainly by worsening
scabbling uniformity in a lateral (Y) direction: scabbling depth
recedes in the direction of one (or both) swath edges.
" Injection of fresh water in the electrode gap improves scabbling
quality; but a more efficient measure is insulation of the
electrode/water interface area. Unfortunately, protective coatings
are damaged by strong shocks, cavitation and turbulence even
faster than with the less intense pulses delivered by the PFN-H.
Only 3-4 segments could be processed without deterioration of
performance before electrodes or coating are replaced.
" With PFN-L in operation, other components of the scabbling chamber,
especially foam gaskets at the chamber bottom, are affected by the
strong shock waves. The gaskets are vulnerable also because their
working conditions are more severe when deeper swath is formed.
To prevent water leakage from the chamber, we had to install denser
foam gaskets, provide higher negative pressure in the chamber, and
to block lateral propagation of shocks by side baffles. Operation with
three storage capacitors delivering (at lower frequency) 7 kJ pulses is
even more difficult.
* Concrete debris was removed by the same pressure washer as for
shallow scabbling. Because the debris bed is thicker, washing time
had to be longer (4-5 minutes). A more powerful (4 HP) washer
should shorten the cleaning time.-87-
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Concrete decontamination by electro-hydraulic scabbling (EHS). Final report, report, October 1, 1997; United States. (https://digital.library.unt.edu/ark:/67531/metadc704121/m1/99/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.