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Measurement and batching of cement, fine and coarse aggregates shall be by weight. Scales in use shall be accurate when static load tested to + 0.4 percent of the total capacity of the scale. One sack of cement shall be considered to weigh 94 pounds net. Bulk and cement from fractional sacks shall be weighed.
3.1 STRENGTH OF CONCRETE: The concrete shall attain a minimum expected strength of concrete at 28 days of 3,500 pounds per square inch compressive strength and/or 550 pounds per square inch flexural strength "modulus of rupture".
Concrete specimens to check the adequacy of the delivered concrete for strength shall be made and cured in accordance with ASTM C-31, making and curing concrete compressive and flexural test specimens in the field. Compressive strength specimens shall be tested in accordance with ASTM C-39, and flexural strength determination shall be in accordance with ASTM C-78. If concrete test(s) is ordered by the Planning Commission, or its duly authorized representative, testing shall be performed by a commercial laboratory.
3.2 PROPORTIONING CONCRETE: It shall contain not less than six sacks of cement (94 lbs. per sack) per cubic yard of concrete and a maximum of 5-1/2 gallons of water per sack of cement, including surface water contained in the aggregates. The proper proportions of cement, water and aggregates shall be determined in accordance with ACI Standard 613, "Recommended Practice for Selecting Proportions for Concrete", or the Portland Cement Association booklet "Design and Control of Concrete Mixers".
The entrained air shall be obtained by using air-entraining agent. All concrete shall be air- entrained in accordance with the following:
Maximum size of Aggregate (inches) | Air Content Percent by Volume |
1-1/2, 2, 2-1/2 | 5 " 1% |
3/4, 1 | 6 " 1% |
3/8, 1/2 | 7-1/2 " 1% |
The air content of freshly mixed air-entrained concrete shall be checked by the Planning Commission, or its duly authorized representative. Concrete with air contents above or below the amount specified shall be corrected by adjustments in the mix design or quantities of air-entraining admixture being used.
3.3 CONSISTENCY: The slump of the concrete shall be from 1 to 4 inches when hand finishing techniques are employed and 1 to 3 inches when a mechanical finishing machine is used. The consistency shall be measured as described in the current ASTM Standard Method of Slump Test for Consistency of Portland Cement Concrete (Designation C-143) or the Method of Test for Ball Penetration for Portland Cement Concrete, ASTM (Designation C-360).
3.4 READY-MIXED CONCRETE: All ready-mixed concrete shall be furnished in accordance with the current ASTM specifications for ready-mixed concrete (Designation C-94).
When construction conditions are such that it is absolutely necessary for trucks hauling concrete to operate on the grade between forms, they shall not back over previously deposited fresh concrete.
3.4.1 TIME OF DELIVERY: Concrete shall be delivered and discharged from a truck mixer or agitator truck within a period of 1-1/2 hours at air temperatures up to 85°F. and one hour at air temperatures higher than 85°F. after introduction of the water to the cement and aggregates or of the cement to the aggregates. Delivery tickets shall have this time clearly shown thereon, and the contractor shall check the same to be certain that delivery is made within the period specified.
3.4.2 TYPE OF DELIVERY EQUIPMENT: Concrete shall be delivered in truck mixers or agitator truck (trucks providing mechanical agitation by revolving drums or revolving blades in a stationary drum) operated after time required for thorough mixing of the concrete at the speed designated by the manufacturer as agitating speed.
3.5 JOB-MIXED CONCRETE: Job-mixed concrete shall be mixed in a drum mixer which shall conform to the concrete paving mixer standards of the Mixer Manufacturers Bureau of the Association General Contractors of America. The mixer shall be capable of combining the aggregates, cement, and water into a thoroughly mixed and uniform mass within the specified time and of discharging the material without segregation. The entire contents of the drum shall be discharged before recharging. The volume of the mixed materials per batch shall not exceed the manufacturer's guaranteed capacity of the mixer.
3.5.1 TIME OF MIXING: The mixing of each batch shall continue for not less than one minute after all materials, except water are in the mixer. The mixer shall rotate at the rate recommended by its manufacturer. The mixer shall be provided with a batch timing device which shall be subject to inspection and adjustment by the Planning Commission, or its duly authorized representative, at any time.
3.6 RETEMPERING OF CONCRETE: Retempering of concrete which has partially hardened, by remixing, with or without water, shall not be permitted.
(Ord. 1971-2, passed 4-6-71)
The air content of freshly mixed air-entrained concrete may be checked by the Planning Commission, or its duly authorized representative. Concrete with air contents above or below the amount specified shall be corrected by adjustments in the mix design or quantities of air-entraining admixture being used.
The air content shall be measured in accordance with ASTM Method of Test for Air Content of Freshly Mixed Concrete by the Pressure Method (Designation C-231) or ASTM Method of Test for Air Content of Freshly Mixed Concrete by the Volumetric Method (Designation C-173).
(Ord. 1971-2, passed 4-6-71)
Forms may be made of wood or metal and shall have a depth equal to or greater than the prescribed edge thickness of the pavement. Each section of form shall be straight, free from bends or warps.
The method of connections between the form sections shall be such that the joint thus formed is tight and free from movement in any direction.
Forms shall be of such cross sections and strength and so secured as to resist the pressure of the concrete when placed and the impact and vibration of any equipment which they support without springing or settlement.
Approved forms shall be used for curved construction where the radius is 100 feet or less.
5.1 SETTING FORMS: The subgrade under the forms shall be compacted and shaped so that the form when set will be uniformly supported for its entire length at the specified elevation. The supply of forms shall be sufficient to permit their remaining in place for at least 12 hours after the concrete has been placed. All forms shall be cleaned and oiled each time they are used.
5.2 GRADE AND ALIGNMENT: The alignment and grade elevation of the forms shall be checked by the contractor immediately ahead of concrete placement and necessary corrections will be made. Any forms that have been disturbed or subgrade that has become unstable shall be corrected and forms reset and rechecked. Any variations in grade and alignment shall be subject to approval by the Planning Commission, or its duly authorized representative, prior to placing the concrete.
(Ord. 1971-2, passed 4-6-71)
The concrete shall be mixed in quantities required for immediate use and shall be deposited on the subgrade to the required depth and width of the construction land in successive batches and in a continuous operation without the use of intermediate forms or bulkheads. The concrete shall be placed as uniformly as possible in order to minimize the amount of additional spreading necessary. While being placed, the concrete shall be vibrated and compacted with suitable tools so that the formation of voids or honeycomb pockets is prevented. The concrete shall be especially well vibrated and tamped against the forms and along all joints.
No concrete shall be placed around manholes or other structures until they have been brought to the required grade and alignment. Additional tamping and compaction will be required after raising manholes.
6.1 COLD WEATHER CONCRETING: Concrete may be placed when the air temperature in the shade and away from artificial heat is more than 35°F. and rising. Concrete shall not be placed when the air temperature in the shade and away from artificial heat is less than 40°F. and falling.
6.2 HOT WEATHER CONCRETING: Except by written authorization, concrete placing shall cease if the temperature of the plastic concrete cannot be maintained at 90°F. or lower.
To facilitate the placement of concrete in hot weather, a retarding chemical admixture Type B or D in conformance with ASTM C-494 may be used.
(Ord. 1971-2, passed 4-6-71)
The pavement shall be struck off and consolidated with a mechanical finishing machine or by hand-finishing methods. When a mechanical finishing machine is used, the concrete shall be struck off at such a height that after consolidation and final finishing, it shall be at the elevation as shown on the plans.
The finishing machine shall be provided with a screed which will consolidate the concrete by pressure, vibration or both. The concrete shall be brought to a true and even surface, free from rock pockets. The edge of the screeds along the curb line may be notched out to allow for sufficient concrete to form the integral curb. Hand-finishing tools shall be kept available for use in case the finishing machine breaks down.
When hand-finishing is used, the pavement shall be struck off and consolidated by a vibrating screed to the elevation as shown on the plans. When the forward motion of the vibrating screed is stopped, the vibrator shall be shut off; it shall not be allowed to idle on the concrete.
7.1 SCRAPING AND STRAIGHTEDGING: The pavement shall be scraped with a straightedge equipped with handles to permit it to be operated from the edge of the pavement.
When irregularities are discovered, they shall be corrected by adding or removing concrete. All disturbed places shall be floated with a wooden or metal float not less than three feet long and not less than six inches wide and again straightedged.
7.2 EDGING: Before final finishing is completed and before the concrete has taken its initial set, the edges of the slab and curb shall be carefully finished with an edger, having a radius of 1/8 inch.
7.3 FINAL SURFACE FINISH: A burlap drag shall be used as the final finishing method for concrete pavement. The drag shall be at least three feet in width and long enough to cover the entire pavement width. It shall be laid on the surface of the pavement and dragged forward in the direction in which the pavement is being laid. The curb shall have the same final finish as the pavement.
The final surface of the concrete pavement and curb shall have a uniform gritty texture, free from excessive harshness and true to the grades and cross sections shown on the plans. The Planning Commission, or its duly authorized representative, may require changes in the final finishing procedure as required to produce the desired final surface texture.
(Ord. 1971-2, passed 4-6-71)
When integral vertical curbs are required along the edges of all street pavement, depressed curbs shall be provided at all driveway entrances and at such other locations as designated by the Planning Commission, or its duly authorized representative.
The integral curb shall be constructed with or immediately following the finished operation. Special care shall be taken so that the curb construction does not lag the pavement construction and form a "cold joint".
In placing curb concrete, sufficient spading shall be done to secure adequate bond with paving a slab and eliminate all voids in the curb.
Curbs shall be formed to the cross section as shown on the drawings.
(Ord. 1971-2, passed 4-6-71)
Concrete shall be cured by protecting it against loss of moisture, rapid temperature change, from rain, flowing water and mechanical injury for a period of not less than five days from the beginning of the curing operation. Moist curing, waterproof paper, white pigmented liquid membrane compound or a combination thereof may be used for curing. Immediately after finishing operations have been completed, the entire surface of the newly laid concrete shall be covered by the curing medium which is applicable to local conditions and approved by the Planning Commission, or its duly authorized representative.
The edge of concrete slabs exposed by the removal of forms shall be protected immediately to provide these surfaces with continuous curing treatment equal to the method selected for curing a slab surface and to prevent injury to concrete edges.
The covering material shall be kept free of any substances which may be detrimental to the surface of the concrete. The initial curing medium shall be effective and shall be applied so as to prevent checking, cracking and the appearance of dry spots in the surface of the concrete. The contractor shall have the equipment needed for adequate curing at hand and ready to install before actual concrete placement begins. In all cases in which the curing medium requires the use of water, the curing shall have prior right to all water supply. Failure to provide sufficient cover material of the type selected, failure to maintain saturation for the entire curing period in the moist-curing methods, lack of water to adequately care for both curing and other requirements or other failures to comply with curing requirements shall be cause for immediate suspension of concreting operations.
9.1 MOIST CURING: Moist curing shall be accomplished by covering of burlap, cotton mats, or other approved fabric mat used singly or in combination.
Curing mats shall be thoroughly wet when applied and kept continuously wet and in intimate contact with the pavement surface for the duration of the moist curing period. Other fabric mats shall conform in design and shall provide a curing medium at least equal to cotton mats. Cotton mats, other fabric mats, burlap mats, and burlap strips shall be furnished in the widths or lengths, after shrinkage, required to cover the entire width and edges of the pavement lane. Mats or burlap shall be lapped at joints between adjacent sheets to prevent drying of this location. Moist curing, when used as initial curing, shall be continued for not less than 24 hours. Type and weight of cotton mats for curing concrete shall conform to ASTM C-440 or AASHO M-73. Burlap strips shall conform to AASHO M-182.
9.2 WATERPROOF PAPER AND POLYETHYLENE SHEETING CURING: The surface of the concrete shall be wetted with a fine spray of water and then covered with the waterproof paper or sheeting. The paper or sheeting shall be in pieces large enough to cover the entire width and edges of the slab and shall be lapped not less than 12 inches. Paper or sheeting shall be adequately weighted to prevent displacement or billowing due to wind. Paper or sheeting folded down over the side of the pavement widths shall be secured by a continuous bank of earth. Tears or holes appearing in the paper or sheeting during the curing period shall be immediately repaired.
9.3 LIQUID MEMBRANE CURING COMPOUND: Pigmented liquid membrane during compound shall meet the specifications under ASTM C-309. The curing compound must be applied to cover the surface completely and uniformly at a rate which will achieve the performance requirement specified in AASHO specifications M-148 or ASTM Designation C-309. This method of curing shall be applied immediately behind the final finishing operation or after the initial curing when a combination of methods are used. Failure to provide complete and uniform coverage at the required rate will be cause for discontinuance of this method of curing and the substitution of one of the other approved methods. The compound shall be kept agitated to prevent the pigment from settling. Special care shall be taken to apply the curing compound to the pavement edges immediately after the forms have been removed.
(Ord. 1971-2, passed 4-6-71)
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