Common use of Measurement and mixing Clause in Contracts

Measurement and mixing. All cement is to be measured by weight, the 50 kg bag of cement being used as aunit. Specification Concrete Work (2/F/10) F.29 Measurement and mixing (Cont‟d.) The amount of water shall be the minimum required to produce a dense cohesive concrete of adequate workability, to be determined by trial mixes. This amount shall be accurately gauged and adjusted from time to time to compensate for variations in moisture content of the aggregate by an approved method. All concrete shall be mixed in a batch type mechanical mixer of approved type having a drum rotating about a horizontal or inclined axis. The speed of the drum is to be not more than twenty and not less than fourteen revolutions per minute. Each mixer is to be fitted with a water measuring device capable of accurate measurement to five litres for one cubic meter mixers and prorata for smaller sizes and so arranged that the accuracy is not affected by variations in the pressure of the water supply line. The fine and coarse aggregate and the cement shall be mixed for at least four turns, after which the required amount of water shall be added gradually while the mixer is in motion and the concrete mixed for not less than one and a half minutes to uniform colour and consistency. The volume of concrete mixed in any one batch is not to exceed the rated capacity of the mixer. The whole of the mixed batch is to be removed before materials for a fresh batch enter the drum. Concrete as mixed in accordance with the foregoing shall not be modified by the addition of further water or in any other manner. On the cessation of work, including all stoppages exceeding twenty minutes, or any change of type of cement used in the mix, the mixer and all handling plant shall be washed out with clean water. At least one slump test shall be made each day concreting is in progress, under the supervision of the Engineer.