such a manner that each transverse pass overlaps the previous pass by a distance equal to or at least one-half the length of the float.

When hand-operated float boards are used they shall be from 12 feet (3.66 m) to 16 feet (4.88 m) long, ribbed and trussed as necessary to provide a rigid float and shall be equipped with adjustable handles at each end. The float shall be wood, not less than one inch (25.4 mm) thick and a minimum of 8 inches (203 mm) wide. Adjusting screws spaced at not to exceed 24 inches (610 mm) on centers shall be provided between the float and the rib. The float board shall be maintained free of twist and true at all times.

Hand-operated float boards shall be operated from transverse finishing bridges. The finishing bridges shall span completely the roadway area being floated and a sufficient number of finishing bridges shall be provided to permit operation of the floats without undue delay. Not less than 2 transverse finishing bridges shall be provided when handoperated float boards are used. When a finishing machine is used for longitudinal floating, one finishing bridge equivalent to the transverse finishing bridge specified herein shall be furnished for use by the Engineer.

All finishing bridges shall be of rigid construction and shall be free of wobble and springing when used by the operators of longitudinal floats and shall be easily moved.

In advance of curing operations, the surface of the concrete shall be textured by brooming with a stiff bristled broom or by other suitable devices which will result in uniform scoring. Brooming shall be performed transversely from the finishing bridge. The operation shall be performed at a time and in a manner to produce a hardened surface having a uniform texture.

Fogging equipment to be furnished shall be capable of applying water to the concrete in the form of a fine fog mist in sufficient quantity to curb the effects of rapid evaporation of mixing water from the concrete on the deck resulting from wind, high temperature or low humidity, or a combination of these factors. The fog mist shall be applied at the times and in the manner directed by the Engineer.

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

552.13 Curing of Concrete. All newly-placed concrete shall be cured, and curing shall be begun immediately after finishing and continued for at least 7 days. Curing shall be done so that moisture is always present, and shall be an integral part of the concreting operations. Improperly cured concrete will be considered defective, and the Engineer will stop all of the Contractor's placing operations until proper procedures are put into effect.

When the air temperature is expected to fall below 35° F (2 t° c) the Contractor shall provide suitable measures to maintain the concrete surface temperature between 50° F (10 t° c) and 90° F (32 t° c).

One of the following methods of curing, or a combination thereof, shall be used.

(a) Supplying Additional Moisture.-This method shall include supplying additional moisture by ponding, sprinkling, or fogging. Coverings such as burlap shall be used to retain water so supplied. The use of sawdust will not be allowed and coverings which cause unsightly discoloration of concrete shall not be used. Any method which results in the concrete being alternately wet and dry will be considered an improper curing procedure. Coverings shall be placed as soon as possible after finishing operations have been completed and there is no danger of surface damage. They shall be kept continuously moist.

(b) Preventing Moisture Loss.-This method shall consist of preventing moisture loss from the concrete. It may be done with the use of approval waterproof paper, plastic sheets, or liquid membrane curing compound except where other requirements prohibit the use of these compounds. If a formed surface is to be rubbed, the concrete shall be kept moist before and during the rubbing, and the curing shall be initiated immediately following the first rub while the concrete surface is still moist. Bridge decks, approach slabs, sidewalks and curbs shall be covered with burlap, or sand blankets as soon as the concrete is sufficiently set to support this material without damage to the finish. This moisture-retaining material shall then be saturated with water and the entire area covered with waterproof paper or plastic sheeting.

(1.) Waterproof Paper. The paper shall be the widest practicable width and adjacent sheets shall overlap a minimum of 6 inches (152 mm) and shall be tightly sealed with pressure sensitive tape, mastic, glue, or other approved methods to form a complete waterproof cover of the entire concrete surface. The paper shall be secured so that wind will not displace it. Should any portion of the sheets be broken or damaged before expiration of the curing period the broken or damaged portions shall be immediately repaired. Sections which have lost their waterproof qualities shall not be used.

(2.) Plastic Sheets. The sheets shall be used in the same manner as required above for waterproof paper.

(3.) Curing Compounds. Type 1 or Type 2 liquid membrane curing compounds as specified in AASHTO M 148, may be used as the initial and final curing agents on structural concrete subject to the following limitations:

a. If the membrane film is broken or damaged at any time during the curing period, the area or areas shall be re-coated to the original requirements.

b. Curing compounds shall be applied to unformed areas as soon as the water sheen has practically disappeared from the concrete, or as soon as the forms have been removed from surfaces not to be rubbed.

c. Areas receiving a rubbed finish shall be cured with Type 1 curing compound only, as specified in AASHTO M 148.

d. If there is to be any delay in applying curing compound, the surface shall receive moist curing until the compound can be applied.

e. Curing compound shall be applied with equipment which will produce a fine spray, and all compounds shall be thoroughly agitated just prior to use. The surface shall be sprayed again immediately at

right angles to the first application. The rate of each application shall be not less than 1 gallon for each 150 square feet (3.79 dm3 for each 13.94 m2) of surface. Care shall be taken to prevent application to joints where concrete bond is required to reinforcement steel, and to joints where joint sealer is to be placed.

Method of Measurement

552.14 The quantity of concrete to be paid for on this contract shall be the quantity shown in the bid schedule, unless changes in design are made which affect this quantity, in which case the quantity shown in the bid schedule will be adjusted by the amount of the change for the purposes of payment. No deduction will be made for the volume occupied by pipes less than 8 inches (203 mm) in diameter nor for reinforcing steel, anchors, conduits, weep holes or piling.

Basis of Payment

552.15 The accepted quantities of structural concrete complete in place will be paid for at the contract unit price per cubic yard, or lump sum as indicated in the bid schedule.

553.01 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.

The work shall include the furnishing and installing of any appurtenant items necessary for the particular prestressing system to be used, including but not limited to ducts, anchorage assemblies and grout used for pressure grouting ducts.

For cast-in-place prestressed concrete, the term "member" as used in this section shall be considered to mean the concrete which is to be prestressed.

It shall include the manufacture, transportation, and storage of beams, slabs, piling, and other structural members of precast concrete, prestressed by either pretensioning or post-tensioning 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 551.

553.02 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, pressure grouting materials and equipment.

553.03 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 instruction in the use of the prestressing equipment and installation of materials as may be necessary to obtain required results.

Materials

553.04 Concrete and Grout. The materials for concrete and grout shall conform to Section 552. The concrete shall be class P as shown in table 552-1 unless otherwise shown on the plans or specified in the special provisions. The proportions of the grout will be as set out in subsection 553.19, Bonding Steel.

553.05 Reinforcing Steel. Reinforcing steel shall conform to subsection 709.01.

553.06 Prestressing Steel. Prestressing steel wire shall conform to the requirements of subsection 709.03.

All prestressing steel shall be protected against physical damage and rust or other results of corrosion at all times from manufacture to

grouting. Prestressing steel that has sustained physical damage at any time shall be rejected.

Prestressing steel shall be packaged in containers or other shipping forms for the protection of the steel against physical damage and corrosion during shipping and storage. A corrosion inhibitor which prevents rust or other results of corrosion shall be placed in the package or form, or when permitted by the Engineer, may be applied directly to the steel. The corrosion inhibitor shall have no deleterious effect on the steel or concrete or bond strength of steel to concrete. Packaging or forms damaged from any cause shall be immediately replaced or restored to original condition.

This shipping package or form shall be clearly marked with a statement that the package contains high-strength prestressing steel, and the care to be used in handling; and the type, kind and amount of corrosion inhibitor used, including the date when placed, safety orders and instructions for use.

All post-tensioned prestressing steel shall be secured at the ends by means of approved permanent type anchoring devices.

All anchorage devices for post-tensioning shall be capable of holding the prestressing steel at a load producing a stress of not less than 95 percent of the guaranteed minimum tensile strength of the prestressing steel.

The load from the anchoring device shall be distributed to the concrete by means of approved devices that will effectively distribute the load to the concrete.

Such approved devices shall conform to the following requirements: (1) The final unit compressive stress on the concrete directly beneath the plate or assembly shall not exceed 3,000 pounds per square inch (20.7 MPa).

(2) Bending stresses in the plates or assemblies induced by the pull of the prestressing shall not exceed the yield point of the material or cause visible distortion in the anchorage plate when 100 percent of the ultimate load is applied as determined by the Engineer.

Should the Contractor elect to furnish anchoring devices of a type which are sufficiently large and which are used in conjunction with a steel grillage embedded in the concrete that effectively distributes the compressive stresses to the concrete, the steel distribution plates or assemblies may be omitted.

Where the end of a post-tensioned assembly will not be covered by concrete, the anchoring devices shall be recessed so that the ends of the prestressing steel and all parts of the anchoring devices will be at least 2 inches (51 mm) inside of the end surface of the members, unless a greater embedment is shown on the plans. Following post-tensioning, the recesses shall be filled with grout, and finished flush.

553.07 Miscellaneous

All water used for flushing ducts shall contain either quick lime (calcium oxide) or slaked lime (calcium hydroxide) in the amount of 0.1-pound per gallon (45 grams per 3.785 dm3). All compressed air used to blow out ducts shall be oil free.