1925 (#1403-1607) - Laserfiche WebLink

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canebe precisely and regularly proportioned and thoroughly mixed. The Contractor shall mix, without slopping or spilling, such quantity of aggregates, as will be within the capacity of the mixer and in no case shall ihe quaotity be such as to require the splitting of a sack of cement. The mixing shall continue for a minimum time of one (1) minute within the drum after all of the ingredients, including the water, are assembled therein, during which time the drum shall revolve at the speed for which it was designed, but shall not make less than fourteen (14) nor more than eighteen (18) revolutions per minute. The entire contents of the drum shall be discharged before any materials are placed therein for the succeeding batch. Leaking water valves, pipe, or hose connections either within the mixer drum or else- where, will not be permitted, and will be considered sufficient grounds for suspending the work until the same is repaired. No concrete shall be used that shows evidence of having become set or that has become unfit for use from any cause, and no remixing of concrete will be permitted. SECTION 4. CONSISTENCY. The concrete shall be mixed with only sufficient water to produce a mass which will hold its shape when struck off with a templet, and in no case shall it be such as to permit a separation of the coarse aggregate from the fine aggregate in handling. The consistency of the concrete shall be determined by the following test: A truncated cone, eight (8) inches at the base, four (4) inches at the top and twelve (12) inches high, shall be filled with the freshly mixed concrete and worked with a pointed three-eighths (-If) inch round rod, as the concrete is placed in the mold. It shall then be struck off level with the top, and the mold gently removed by a continuous upward pull. The difference between the height of the concrete after the mold is removed and the height of the mold will be considered the slump. Thc slump shall not exceed two (2) inches. SECTION 5. PLACING CONCRETE, Immediately before placing the concrete, the subgrade shall be brought to an even surface and all loose earth removed or thoroughly compacted. The surface shall then be thoroughly sprinkled, but no pools of water shall exist when the concrete is placed. After mixing, the concrete shall be deposited rapidly upon thc subgrade to a depth of three-eights (~v~) of an inch greater than thc required thickness of the base, to allow for tamping, and to thc full width of thc base. Thc concrete next to curbs, gutters, headers, and side forms shall be spaded with a flat · tool, so that sufficient mortar will exude from the mass to form a dense and smooth vertical surface. Should it become necessary, from any cause, to suspend the work for a period of one (1) hour or more, an emergency header shall be placed at right angles to the center llne of the base and the concrete l~nished to such a header. SECTION 6. FINISHING. Immediately after pouring, the concrete shall be tamped by means of a templet of approved design, built rigid and conforming to the true cross.section of the finished base, and used at right angles to the center line of the street. It shall then be struck off with the same templet and re-tamped until the concrete has become a solid compact mass with an even surface. All excess material shall be moved ahead and any low point appearing during tamping shall be filled and retamped.