7.1.2 Machine Mixing—Prior to starting rotation of the
mixer add the coarse aggregate, some of the mixing water, and
the solution of admixture, when required, in accordance with
6.5. When feasible, disperse the admixture in the mixing water
before addition. Start the mixer, then add the fine aggregate,
cement, and water with the mixer running. If it is impractical
for a particular mixer or for a particular test to add the fine
aggregate, cement, and water while the mixer is running, these
components may be added to the stopped mixer after permitting
it to turn a few revolutions following charging with coarse
aggregate and some of the water (Note 11). Mix the concrete,
after all ingredients are in the mixer, for 3 min followed by a
3-min rest, followed by a 2-min final mixing. Cover the open
end or top of the mixer to prevent evaporation during the rest
period. Take precautions to compensate for mortar retained by
the mixer so that the discharged batch, as used, will be
correctly proportioned (Note 12). To eliminate segregation,
deposit machine-mixed concrete in the clean, damp mixing pan
and remix by shovel or trowel until it appears to be uniform