Honeycomb
Honeycomb
Rectification
Honeycombs
are hollow spaces and cavities left in concrete mass on the surface or inside
the mass where concrete could not reach. These look like honey bees nest
(Figure 8.4). Improper vibration and workability of concrete are main causes of
honeycombs in concrete.
After
removal of formwork, loose particles were removed from honeycomb to achieve
sound substratum. If necessary cutting around affected area, care to be taken
to not disturb the hardened concrete. While cutting, only around the boundary
of the affected area should cut down. Then, the concrete surface which were
affected by honeycomb was cleaned by using compressed air to be free from dust,
cement laitance and grout deposits. After that, bonding agent (Barra emulsion)
was applied to concrete surface.
Then, non-shrinkage grout (MasterFlow 810) in
trowellable stage was applied to surface defects from 5 mm to 40 mm in a small
area. If honeycomb identified as a severe damage up to rebar exposure, grouting
should be done with outer formwork.
Outer Formwork for
Honeycomb
Affected area was selected by
outer line and 4 mm thick 50mm – 100mm wide sponge sheet layer was laid along
that outer line using adhesive. After that, bonding agent was applied to
affected area and plywood board piece was nailed to concrete member to have
sufficient top opening to pour the grout from top side (Figure 8.5).
Immediately after fixing the formwork, non-shrinkage grout in self flowable
stage was poured.
Flowable stage: 4.5 liters of
water for 25 kg bag
While continuing the pouring,
hammering was done by rubber hammer to have proper filling.
Any
foreign aggregate should not be mixed with the grout for lager honeycomb
rectification. For lager honeycomb deeper than 50 mm at vertical surface and
top horizontal surfaces Mapefill 06 – shrinkage compensated, super flow micro
concrete was used (Figure 8.6) Outer formwork was removed after 24 hours from
the casting time and cured using MASTERKURE 128 (Figure 8.7)
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