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shall be capable of so controlling
the rate of dec) The equipment
livery of each kind and size of materials that the combined inaccuracy in feeding and measuring during normal operations does
not exceed 3 percent for all aggregates, and 1 percent for water.
mechanism -for measuring
the amount of water‘
d) The operating
shall be such that no leakage occurs with the valves closed. The
filling and discharge valves shall not be opened before the IiUing
valve is closed.
e) Test scale weights shall be provided and periodic checks made of
the accuracy of ail weighing equipment.
.1 I. 18.104.22.168 In cases inhere weigh batchers are not available the specification expressing the mix m proportions of weight should be transformed
This should be done in the field
into one measuring material by volume.
*Second revision in 1% 11 IS : 457- 1957
laboratories attached to each construction
The co-efficients transforming weight into volume should be determined anew each time the
,aggregate i’s obtained from a different source.
4.6.3 Cement Content-Cement
in standard packages or sacks need
not ordinarily be weighed, but shall be periodically checked in the field.
Bulk cement and fractional packages shall be weighed.
4.6.4 Water Content 22.214.171.124 The water-cement ratio established for each class of concrete shall be hell within the limits specified under 4.2.
of the concrete shall be varied only by increasing or by decreasing the
amount of cement paste in each batch.
126.96.36.199 Water for mixing may be measured either by volume or
by weight, and the measuring device shall be accurate to within one percent. A reliable method of compensating for free water shall be used for
maintaining a constant water-cement ratio.
188.8.131.52 Whenever concrete is being conveyed over a long distance
during hot or dry wcathcr, an ahowance may be made for probable evaporation during the period concrete is being transported.
4.7 Mixing 4.7.1 Machine iMixing at Sire - The mixing of concrete shall be done
in a batch mixer of such approved type as will ensure the homogeneous
The plant shall be so designed and operated
distribution of all ingredients.
that ‘all materials entering the mixer including water, can be accurately
The entire batch within the mixer
proportioned and readily controlled.
The volume of mixed material
shall be discharged before recharging.
per batch shall not exceed the manufacturer’s rated capacity.
184.108.40.206 Method of charging - 171c proper sequence of operations for
the admission of aggregates into any type of mixer shall be ascertained
by trial runs conductecl in order to determine the method giving the best
The following sequcncc of charging the mixer may be adopted:
a) Five to ten percent of the total quantity of water required for
mixing, adequate to wet the drum thoroughly, shall be introduced
before the other ingredients m order to prevent any caking of
cement on the blades or sides of the mixers.
b) All dry ingredients ( cement and both f...
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This document was uploaded on 10/01/2013.
- Fall '13