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cement to two parts of sand, which shall be thoroughly tamped into place. The mortar shall be preshrunk by mixing it approximately 30 minutes before using. The length of time may be varied in accordance with brand of cement used, temperature, humidity, and other local conditions. The surface of this mortar shall be floated with a wooden float before initial set takes place and shall be neat and workmanlike in appearance. The patch shall be kept wet for a period of 5 days.

For patching large or deep areas, coarse aggregate shall be added to the patching material and special precautions shall be taken to insure a dense, well-bonded, and properly cured patch.

Areas of excessive honeycombs, as determined by the Engineer, may be considered sufficient cause for rejection of a structure. Upon written notice from the Engineer that a given structure has been rejected, the Contractor shall remove and rebuild the sti re, in part or wholly as specified, at his own expense.

The mortar patches shall be cured as specified in subsection 601.13. All construction and expansion joints in the completed work shall be left carefully tooled and free of all mortar and concrete. The joint filler shall be left exposed for its full length with clean and true edges.

All surfaces which cannot be repaired to the satsifaction of the Engineer shall be “rubbed" as specified for a class 2 finish.

(b) Class 2, rubbed finish.After removal of forms the rubbing of concrete shall be started as soon as its condition will permit. Immediately before starting this work the concrete shall be kept thoroughly saturated with water. Sufficient time shall have elapsed before the wetting down to allow the mortar used in the pointing to thoroughly set. Surfaces to be finished shall be rubbed with a medium coarse carborundum stone, using a small amount of mortar on its face. The mortar shall be composed of cement and fine sand mixed in proportions used in the concrete being finished. Rubbing shall be continued until all form marks, projections and irregularities have been removed, all voids filled and a uniform surface has been obtained. The paste produced by this rubbing shall be left in place.

After all concrete above the surface being treated has been cast, the final finish shall be obtained by rubbing with a fine carborundum stone and water. This rubbing shall be continued until the entire surface is of a smooth texture and uniform color.

After the final rubbing is completed and the surface has dried, it shall be rubbed with burlap to remove loose powder and shall be left free from all unsound patches, paste, powder and objectionable marks.

(c) Float finish.Immediately after the concrete has been placed, horizontal surfaces shall be struck off with templates to provide proper crowns and shall be hand finished to smooth, even surfaces by both longitudinal and transverse movement of wooden floats, or by other suitable means.

After floating has been completed and the excess water removed, but while the concrete is still plastic, the surface of the concrete shall be tested for trueness with a 10-foot straightedge. The straightedge shall be held in contact with the surface in successive positions parallel to the slab centerline and the whole area gone over from one side of the slab to the other. Advance along the slab shall be in successive stages of not more than one-half the length of the straightedge. Any depressions found shall be filled immediately with freshly mixed concrete, and any high areas shall be cut down. The surface shall be struck consolidated and re finished. Special attention shall be given to insure that the surface across joints fully meets the requirements for smoothness. The straightedge testing and refloating shall continue until the entire surface is found to be free from observable departures from the straightedge and the slab has the required grade and crown.

Final finish shall be slightly but uniformly roughened by brooming or other methods as directed by the Engineer.

As soon as the concrete has hardened sufficiently, the surface shall be given a further test for trueness using a 10-foot straightedge or other specified device. Areas showing high spots of more than 48-inch shall be marked and immediately ground down with an approved grinding tool to an elevation where the area or spot will not show surface deviations in excess of 18-inch when tested with a 10-foot straightedge.

(d) Special finishes.Details for special finishes shown on the plans will be given in the special provisions.

601.13 Curing Concrete. Immediately after forms have been removed and finishing completed all concrete shall be cured by one of the following methods. The Engineer will specify the concrete surfaces which may be cured by either method.

(a) Water method.--All surfaces other than slabs shall be protected from the sun and the whole structure shall be kept wet for a period of at least 7 days. Curbs, walls, handrails and other surfaces requiring a rubbed finish may have the covering temporarily removed for finishing, but the covering must be restored as soon as possible. All concrete slabs shall be covered as soon as possible with sand, earth or other suitable material and kept thoroughly wet for at least 7 days. This covering material shall not be cleared from the surface of the concrete slab for a period of 21 days.

(b) Membrane forming curing compound.-All surfaces shall be given the required surface finish prior to application of the curing compound. During the finishing period, the concrete shall be protected by the water method of curing.

The rate of application of curing compound shall be as prescribed by the Engineer with a minimum spreading rate per application of one gallon of liquid coating for 300 square feet of concrete surface. All concrete cured by this method shall receive two applications of the curing compound. The first coat shall be applied immediately after stripping of forms and acceptance of the concrete finish. If the surface is dry, the concrete shall be thoroughly wet with water and the curing compound applied just as the surface film of water disappears. The second application shall be applied after the first application has set. During curing operations, any unsprayed surfaces shall be kept wet with water.

The coating shall be protected against marring for a period of at least 10 days after application. Any coating marred, or otherwise disturbed shall be given an additional coating. Should the surface coating be subjected continuously to injury, the Engineer may require that water curing be applied at once.

When using a curing compound, the compound shall be thoroughly mixed within the hour before use.

If the use of a curing compound results in a streaked or blotchy appearance, the method shall be stopped and water curing, as set out in subsection 601.13(a), applied until the cause of the defective appearance is corrected.

When the temperature is expected to fall below 35° F., the Contractor shall provide suitable measures to maintain the concrete surface temperature between 50° F. and 90° F. in accordance with subsection 601.08.

During hot weather all surfaces from which the forms have been removed and all unformed surfaces shall be kept moist by wet curing for at least 24 hours. Curing shall be started as soon as the concrete is hardened sufficiently to avoid surface damage. All concrete surfaces shall be kept completely and continuously moist. At the end of the 24-hour curing period, the surfaces may be treated with a curing compound, except that all construction joints shall be cured exclusively by the water method, unless sandblasting or other effective means are used to clean the concrete surface and exposed reinforcing steel before placing fresh concrete.

Method of Measurement

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601.14 Concrete will be measured by the cubic yard in accordance with the dimensions shown on the plans or ordered and accepted. No deduction will be made for the volume occupied by pipes less than 8 inches in diameter nor for reinforcing steel, anchors, conduits, weep holes or piling.

The measurement will not include forms or falsework and no pay allowances will be made for any increased cement content, for any admixtures, nor for any finishing of any description of concrete or concrete floor. Any class A concrete permitted to be constructed where class B, C, or X concrete was specified will be measured for payment as class B, C, or X concrete, respectively. Any class B concrete permitted to be constructed where class C concrete was specified will be measured for payment as class C concrete.

The quantities of reinforcing steel and other contract items which are included in the completed and accepted structure will be measured for payment in the manner prescribed for the several items involved.

When estimated quantities, required for structure work, ere shown on the plans as "final quantities,” these quantities will be the final quantities for which payment will be made unless the dimensions of structure work shown on the plans are revised by the Engineer. If the dimensions of structure work are revised and such revisions result in an increase or decrease in quantities, the final quantities for payment will be revised in the amount represented by the change in dimensions subject to the provisions of the “Changes” and “Differing Site Conditions” clauses of SF-23A.

If a lump sum payment is specified, no measurement for payment will be made.

Basis of Payment

601.15 The accepted quantities of structural concrete, determined as provided above, will be paid for at the contract unit price per cubic yard, or lump sum, as indicated in the bid schedule, complete in place. Payment will be made under: Pay item

Pay unit 601(1) Structural concrete, class A

Cubic yard. 601 (2) Structural concrete, class AA Cubic yard. 601(3) Structural concrete, class B

Cubic yard. 601(4) Structural concrete, class C

Cubic yard. 601(5) Structural concrete, class X

Cubic yard.

Pay item
601(6) Structural concrete, class Y
601(7) Structural concrete, class S
601(8) Structural concrete, class
601(9) Class concrete for class A pipe

bedding.

Pay unit Cubic yard. Cubic yard. Lump sum. Cubic yard.

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Section 601A-PRESTRESSED CONCRETE

STRUCTURES

Description

601A.01 General. This work shall consist of prestressed concrete structures, and the prestressed concrete portions of composite structures, constructed in reasonably close conformity with the lines, grades, design, and dimensions shown on the plans, or established by the Engineer and in accordance with this and other specification items involved.

It shall include the manufacture, transportation, and storage of beams, slabs, piling, and other structural members of precast concrete, prestressed by either pretensioning or posttensioning methods. It shall also include the installation of all precast prestressed members except piling, which shall be placed as provided for concrete piling in section 600A.

601A.02 Prestressing Methods. The method of prestressing to be used will be optional with the Contractor, subject to all requirements hereinafter specified.

Prior to casting any members to be prestressed, the Contractor shall submit to the Engineer for approval complete details of the method, materials, and equipment he proposes to use in the prestressing operations. Such details shall outline the method and sequence of stressing, complete specifications and details of the prestressing steel and anchoring devices proposed for use, anchoring stresses, type of enclosures, and all other data pertaining to the prestressing operations, including the proposed arrangement of the prestressing units in the members.

601A.03 Consulting Service. Unless otherwise ordered by the Engineer, the Contractor shall certify to the Engineer that a technician skilled in the approved prestressing method will be available to the Contractor to give such aid and

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