Consolidation. All concrete shall be consolidated by vibration,
spading, rodding or forking so that the concrete is thoroughly worked
around the reinforcement, around embedded items, and into corners
of forms, eliminating all air or stone pockets which may cause honeycombing,
pitting, or planes of weakness. Internal vibrators used shall be the
largest size and the most powerful that can be properly used in the
work. They shall be operated by competent workmen. Use of vibrators
to transport concrete within forms shall not be allowed. Vibrators
shall be inserted and withdrawn at points approximately 18 inches
apart. At each insertion, the duration shall be sufficient to consolidate
the concrete but not sufficient to cause segregation, generally from
five to 15 seconds. A spare vibrator shall be kept on the job site
during all concrete placing operations. Where the concrete is to have
an as-cast finish, a full surface of mortar shall be brought against
the form by the vibration process, supplemented if necessary by spading
to work the coarse aggregate back from the formed surface.