1925 (#1403-1607) - Laserfiche WebLink

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............. , l, reviously measured upon a mixing platform . The water necessary for every batch shall be accurately measured with an apparatus which will positively prevent the use of more water than required. No mixer shall be used which is not provided with an accurate water measuring apparatus. (b) MIXING CONCRETE. Machine mixing shall be done wiht batch mixers only. The Contractor shall mix, without spilling, such quantity of aggregates, as will be within the capacity of the mixer, and in no case shall the quantity be such that will require the splitting of sacks of cement. Sui¥icient water, shall be added to produce a plastic or quaking concrete which can b~ handled without causing a separation o/ the coarse aggrgeate from the mortar. The mixer drum shall have a speed of not less than thirteen (13) nor more htan eighteen (18) revolutions per minute and every batch of concrete shall be mixed in the drum of the mixer not less than sixty (60) seconds before any portion of the batch is discharged from the said drum. At least seventy-five (75) seconds must elapse between the placing of success- ive batches in the mixer. (c) HAND MIXING. Where concrete is mixed by hand, one (1) box of gravel or broken stone shall be placed on a tight platform, not less than ten (10) teet wide and twelve (12) feet long. Upon the rgavel or broken stone shall be placed on (1) box of sand and upon this shall be placed the required number of sacks o! cement. The inspector shall be given the opportunity to check the number of sacks of cement on each batch before tile sacks are opened. The mass shall be turned with shovels two (2) times dry and two (2) times wet, not including shoveling into wheelbarrows. The spceified amount of water shall be supplied in a spray during the wet turns. (d) REMIXIIqG CONCRETE. No concrete shall be used which has partially set, and no concrete shall be retempored or remixed, SRCTION 9, FORMS. All forms shall be smooth, tight, true to the required lines and elevations and securely braced and tied to prevent their movement or deflection during the placing and ramming of the concrete. Forms shall be cleaned of all mortar, dirt and shavings and shall be thoroughly wet immediately before the placing of the concrete. The time for removal of forms shall be determined by the Superintendent of Streets. During the setting of the concrete and before the rmoval of the forms, no extraneous loads shall be placed upon the concrete. In removing forms extreme care must be taken neither to deface the structure nor to disturb the remaining supports. ~CTION 10. PLACING CONCRRTZ. After being mixed, concrete shall be handled rapidly, in as small batches as practicable, from the place o[ mixlr~ to the place o{ final deposit and shall be deposited and manipu- lated in a manner that will insure the most thorough compacting and to prevent voids or pockets. Care shall be taken to insure the complete coating of all parts of the reinforce. ment with mortar. The concrete shall be spaded in a manner such that its ~mer parts will be in contact with the faces of the forms thereby leaving the sur/ace of the structure smooth and free [rom pockets. No concrete shall be deposited {rom a height, but must be lowered into position. 1Arhen joining new concrete with concrete already set, the surface of the old concrete shall be cleaned, roughened, thoroughly wet and then coated with thin, neat cement mortar. The surface of concrete which is allowed to set shall be left rough so ~s to insure a good bond. All concrete shall be kept thoroughly wet {or a period of seven (?) days after being placed. In all places where water is encountered in placing concrete foundations or other p~rts o{ any structure, the Contractor must provide suitable means to keep the work free from such water during placing and for a period of twelve (12) hours thereafter.