Specification Part 3 - Road & Bridge Works - Urban Administration ...

Unless specified otherwise, equipment for production, transportation and compaction of concrete
shall be as under:
a) For Production of Concrete:
i) For overall bridge length of less than 200 melees - batch type concrete mixer diesel or electric
operated, with a minimum size of 200 liters, automatic water measuring system and integral
weighed (hydraulic/pneumatic type)
ii) For overall bridge length of 200 meters or more - concrete batching and mixing plant fully
automatic with minimum capacity of 15 c.m. Per hour. All measuring devices of the equipment
shall be maintained in a clean and serviceable condition. Its accuracy shall be checked ove r the
range in use, when set up at each site and thereafter periodically as directed by the Engineer in
charge. The accuracy of the measuring devices shall fall within the following limits:
Measurement of Cement
± 3 per cent of the quantity °f cement in each batch
Measurement of Water
± 3 per cent of the quantity of water in each batch
Measurement of Aggregate
± 3 per cent of the quantity of aggregate in each batch
Measurement of Admixture
± 5 per cent of the quantity of admixture in each batch
b) For Concrete Transportation depending upon actual requirement
1) Concrete dumpers minimum 2 tonnes capacity
2) Powered hoists minimum 0.5 tonnes capacity
3) Chutes
4) Buckets handled by cranes
5) Transit truck mixer
6) Concrete pump
7) Concrete distributor booms
8) Belt conveyor
9) Cranes with skips
10) Tremie
c) For Compaction of Concrete:
i) Internal vibrators size 25 mm lo 70 mm
ii) Form vibrators
minimum 500 walls
iii) Screed vibrators
full width of carriageway
(Up to two lanes)
1708. MIXING CONCRETE
Concrete shall be mixed either in a concrete mixer or in a batching and mixing plant, as per these
specifications. Hand mixing shall not be permitted. The mixer or the plant shall be at an approved
location considering the properties of the mixes and the transportation arrangements available
with the Contractor. The mixer or the plant shall be approved by the Engineer in charge. Mixing
shall be continued till materials arc uniformly distributed and a uniform colour of die entire mass is
obtained, and each individual particle of the coarse aggregate shows complete coating of mortar
containing its proportionate amount of cement. In no case shall mixing be done for less than 2
minutes. Mixers which have been out of use for more than 30 minutes shall be thoroughly
cleaned before putting in a new batch. Unless otherwise agreed to by the Engineer in charge, the
first batch of concrete from the mixer shall contain only two thirds of the normal quantity of coarse
aggregate. Mixing plant shall be thoroughly cleaned before changing from one type of cement to
another.
1709. TRANSPORTING, PLACING AND COMPACTION OF CONCRETE
The method of transporting and placing concrete shall be approved by the Engineer in charge.
Concrete shall be transported and placed as near as practicable to its final position, so that no
contamination, segregation or loss of its constituent materials Lakes place. Concrete shall not be
freely dropped into place from a height exceeding 1.5 meters. When concrete is conveyed by
chute, the plant shall be of such size and design as to ensure practically continuous flow. Slope of
the chute shall be so adjusted that the concrete flows with out the use of excessive quantity of
water and without any segregation of its ingredients. The delivery end of the chute shall be as
close as possible to the point of deposit. The chute shall be thoroughly flushed with water before
and after each working period and the water used for this purpose shall be discharged outside the