PACKAGE : I Bid Document VOLUME : II - Public Health Engineering

Uniformity of mix: Concrete shall be mixed in batches in plant capable of mixing
the aggregates, cement and water (including admixtures, if any) into a mixture
uniform in colour and consistency and of discharging the mixture without
segregation.
Contractor’s returns: The contractor shall render to the Engineer, daily return for
each class of concrete of the number of batches mixed, and total volume of concrete
placed, the number of batches wasted or rejected and the weight of cement used. In
case of ordinary mixes, where permitted, the cement bags consumed for quantities
of various classes of concrete shall be furnished. In addition daily details of time of
starting concrete, closure, no. of batches through mixer, W.C. ratio, slump, date of
striking form works etc. shall be maintained. This day-to-day record shall be
authenticated by responsible supervisory staff.
Plant and equipment generally: All mixing and batching plants boxes, containers
and other equipment shall be maintained free of defects or of set concrete or cement
and shall be cleaned before commencing mixing. At such intervals as may be
directed by the Engineer, the contractor shall provide weights, containers and
equipment necessary for testing the accuracy of the weighting plant, water
measuring plant and admixture dispenser.
7.8 Concreting.
Preparation: The Contractor shall clear from the surface of the foundations or
previously placed concrete all oil, loose fragments of rock, earth, mud, timber and
any other foreign matter and shall clear standing water and wash the surface of a
previous lift of concrete to the satisfaction of the Engineer.
Laitance: Where laitance on a lift of concrete is evident or if a substantial bond
between this lift or bay or concrete and the next is required, in the opinion of the
Engineer’s representative, the Contractor shall have the surface wire brushed after
initial set of the concrete or have it bush-hammered at no extra cost to the employer.
Any reinforcing bars covered in laitance shall be wire brushed to clean the surface
of the metal.
Blinding: The formation surfaces on which concrete is to be placed shall be
covered with either blinding concrete not less than 75mm thick, or waterproof,
building paper, or polythene sheeting immediately after completion of the final
trimming of the excavation.
GTS : General Technical Specification. Page 61