the provisions of COE CRD-C 143 shall be provided for measuring of moisture
in the fine aggregate. The sensing element shall be arranged so that
measurement is made near the batcher charging gate of the fine aggregate
bin or in the fine aggregate batcher.]
1.12.2
Concrete Mixers
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NOTE: Edit bracketed items according to whether use
of truck mixers is to be permitted. Truck mixers
should not be permitted for mixing or transporting
concrete if slipform paving is permitted.
**************************************************************************
Mixers shall be [stationary] [truck] mixers. [Truck mixers shall not be
used for mixing or transporting slipformed paving concrete.] Mixers shall
be capable of combining the materials into a uniform mixture and of
discharging this mixture without segregation. The mixers shall not be
charged in excess of the capacity recommended by the manufacturer. The
mixers shall be operated at the drum or mixing blade speed designated by
the manufacturer. The mixers shall be maintained in satisfactory operating
condition, and the mixer drums shall be kept free of hardened concrete.
Mixer blades or paddles shall be replaced when worn down more than 10
percent of their depth when compared with the manufacturer's dimension for
new blades or paddles.
1.12.2.1
Stationary, Central Plant, Mixers
Stationary mixers shall be [drum mixers of [tilting] [nontilting]
[horizontal-shaft] [vertical-shaft] type]. Mixers shall be provided with
an acceptable device to lock the discharge mechanism until the required
mixing time has elapsed.
1.12.2.2
Truck Mixers
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NOTE: Retain this subparagraph only if truck mixers
have been permitted above.
**************************************************************************
[The only truck mixers used for mixing or transporting paving concrete
shall be those designed with extra large blading and rear opening
specifically for low-slump paving concrete. Truck mixers, the mixing of
concrete therein, and concrete uniformity and testing thereof shall conform
to the requirements of ASTM C 94/C 94M. The number of revolutions between
70 to 100 for truck-mixed concrete and the number of revolutions for
shrink-mixed concrete shall be determined by uniformity tests as specified
in ASTM C 94/C 94M and in requirements for mixer performance stated in
paragraph TESTING AND INSPECTION FOR CONTRACTOR QUALITY CONTROL. If
requirements for the uniformity of concrete are not met with 100
revolutions of mixing after all ingredients including water are in the
truck mixer drum, the mixer shall not be used until the condition is
corrected. Water shall not be added after the initial introduction of
mixing water except, when on arrival at the job site, the slump is less
than specified and the water-cement ratio is less than that given as a
maximum in the approved mixture. Additional water may be added to bring
the slump within the specified range provided the approved water-cement
ratio is not exceeded. Water shall be injected into the head of the mixer
(end opposite the discharge opening) drum under pressure, and the drum or
SECTION 02753
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