Unformatted text preview: ine and coarse aggregates )
shall he simultaneously
ribboned into the mixer in such a manner
that the pcrioci of flow for each ingredient is about the same.
12 IS : 457 - 1957 4
4 Eighty to ninety percent of the total quantity of water required for
mixing shall be added uniformly along with the dry ingrcdicnts.
The remaining quantity of water shall be added after all the other
ingredients are in the mixer.
Cobbles or a portion of the coarwst aggregate, howcvcr, may be
added last; tllis facilitates the clcarancc of the chutes and removes
any fine aggrcgrzte or cement adhering to the sides. Time af mixircg 22.214.171.124 a) Unless othcr\vise permitted,
machine mixing of each batch shall
continue for not less than the period indicated in Tnljle I.
this period the drum shall be rotated at a speed recommended
by the manufacturer.
The mixing period shall be timed after all
materials, including water, art in the drum.
The efficiency of the
of the mixer shall be periodically checked.
one mix, the variation in the air-frw wit weights of three samples
taken from the front, centrc and back of a batch of concrete in
the mixer, shall not exceed the following: For :one
of 9 batches
of 2h, batches
of 90 batches TABLE
14.6 I kg
kg TIME per
cu OF m
m ( or 2.3
( or I.6
( or 1.2
( or 0.9 lb
per cu ft
cu ft ! )
) MIXING OF MIXER M~~IMIJM 'l‘inm 01' MIXING .____*_...- . . r--- ..~_..._ Natural Aggregates Manufactured
f\g:gregatcs 2 minutes
1 f minutes 3 cu m ( or 3 cu yd ) or larger
2 cu m ( or 2 cu yd )
1 cu m (or 1 cu yd ) 0~ smaller ) 2! minutes
1 .j miuutes b) Each mixer shall have a mechanically
oIwratc~t1 timmg device for
of the rccIuired mixing
actual time of mix+
shall bc checked at least twice during. each
shift and the timing tlcvicc shall be adjusted if in error. 4 The timing device shall be so interlocked
wit11 the discharge gate
of the batch hopper that timing does not start until the discharge
gate is fully closed.and all ingredients are in the drum.
record shall be kept of the average time consumed in charging,
mixing aud discharging a batch during each run.
13 IS : 457 - 1957
d) Excessive mixing, necessitating
workability shall be avoided. the addition 126.96.36.199 Dischargiltg - The full contents
charged quickly so as to avoid segregation of water of the drum ko provide
shall be dis- 188.8.131.52 When the mixer is stopped, before placing again any inedients in the mixer all hardened concrete or mortar shall be removed
rom the inner surface of the mixer.
4.7.2 Central Plant Mixing -- Concrete mixing at the central plant
shall be done in accordance with the requirements
for machine mixing
at sate ( see 4.7.1 ) before being loaded into the transporting
4.7.3 Truck Mixing - Truck mixers, unless otherwise approved, shall
be of the revolving drum ty...
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- Fall '13
- Bombay, Concrete Association, Concrete Section31 Committee, Concrete Subcommittee