altering of the selected area. Upon completion of the work, the site shall be cleared of equipment and rubbish and restored to an acceptable condition.

553.13 Enclosures. Enclosures for prestressed reinforcement shall be accurately placed at locations shown on the plans or approved by the Engineer.

Duct enclosures for prestressing steel shall be galvanized ferrous metal or of a type approved by the Engineer, mortartight, and accurately placed at the locations shown on the plans or approved by the Engineer. Transition couplings connecting said ducts to anchoring devices need not be galvanized.

553.14 Placing Steel. All steel units shall be accurately placed in the position shown on the plans, and firmly held during the placing and setting of the concrete.

Ducts may be fabricated with either welded or interlocked seams. Galvanizing of the welded seam will not be required. Ducts shall have sufficient strength to maintain their correct alinement and shape during placing of concrete. Joints between sections of duct shall be positive metallic connections which do not result in angle changes at the joints. Waterproof tape shall be used at the connections.

All ducts or anchorage assemblies shall be provided with pipes or other suitable connections for the injection of grout after prestressing.

Ducts for prestressing steel shall be securely fastened in place to prevent movement. After installation in the forms, the ends of ducts shall at all times be covered as necessary to prevent the entry of water or debris.

All ducts for continuous structures shall be vented over each intermediate support, and at additional locations as shown on the plans. Vents shall be 1⁄2-inch minimum diameter standard pipe. Connections to ducts shall be made with metallic structural fasteners. The vents shall be mortar tight, taped as necessary, and shall provide means for injection of grout through the vents and for sealing the vents. Ends of vents shall be removed 1-inch below the roadway surface after grouting has been completed.

Distances from the forms shall be maintained by stays, blocks, ties, hangers, or other approved supports. Blocks for holding units from contact with the forms shall be precast mortar blocks of approved shape and dimensions. Layers of units shall be separated by mortar blocks or other equally suitable devices. Wooden blocks shall not be left in the concrete.

When acceptable prestressing steel for post-tensioning is installed in ducts after completion of concrete curing, and if stressing and grouting are completed within 10 calendar days after the installation of the prestressing steel, rust which may form during said 10 days will not be cause for rejection of the steel. Prestressing steel installed, tensioned and grouted in this manner, all within 10 calendar days, will not require the use of a corrosion inhibitor in the duct following installation of the prestressing steel. Prestressing steel installed as above, but not grouted within 10 calendar days, shall be subject to all the requirements in this section pertaining to corrosion protection and rejection because of rust.

No welds or grounds for welding equipment shall be made on the forms or on the steel in the member after the prestressing steel has been installed.

Wires, wire groups, parallel-lay cables, and any other prestressing elements shall be straightened to insure proper positioning in the enclosures.

Suitable horizontal and vertical spacers shall be provided, if required, to hold the wires in place in true position in the enclosures.

553.15 Pretensioning. The prestressing elements shall be accurately held in position and stressed by jacks. A record shall be kept of the jacking force and the elongations produced thereby. Several units may be cast in one continuous line and stressed at one time. Sufficient space shall be left between ends of units to permit access for cutting after the concrete has attained the required strength. No bond stress shall be transferred to the concrete, nor end anchorages released, until the concrete has attained a compressive strength, as shown by cylinder tests, of at least 4000 psi unless otherwise specified. The elements shall be cut or released in such an order that lateral eccentricity of prestress will be a minimum.

553.16 Placing Concrete. Concrete shall not be deposited in the forms until the Engineer has inspected the placing of the reinforcement, enclosures, anchorages, and prestressing steel and given his approval thereof. The concrete shall be vibrated with care and in such a manner as to avoid displacement of reinforcement, conduits, or wires.

Prior to placing concrete, the Contractor shall demonstrate to the satisfaction of the Engineer that all ducts are unobstructed.

553.17 Curing. Steam curing process may be used as an alternative to water curing. The casting bed for any unit cured with steam shall be completely enclosed by a suitable type of housing, tightly constructed so as to prevent the escape of steam and simultaneously, exclude outside atmosphere. Two to 4 hours after placing concrete and after the concrete has undergone initial set, the first application of steam or radiant heat shall be made, unless retarders are used, in which case the waiting period before application of the steam or radiant heat shall be increased to from 4 to 6 hours.

During the waiting period, the temperature within the curing chamber shall not be less than 50°F and live steam or radiant heat may be used to maintain the curing chamber at the proper minimum temperature. The steam shall be at 100 percent relative humidity to prevent loss of moisture and to provide moisture for proper hydration of the cement. Application of the steam shall not be directly on the concrete. During application of the steam, or of radiant heat the ambient air temperature shall increase at a rate not to exceed 40°F per hour until the curing temperature is reached. The maximum curing temperature within the enclosure shall not exceed 160°F. The maximum temperature shall be held until the concrete has reached the desired strength. Detensioning shall be accomplished immediately after the steam curing or the heat curing has been discontinued and additional curing is not required after detensioning.

(a) Curing with Low Pressure Steam

Application of live steam shall not be directed on the concrete forms as to cause localized high temperatures.

(b) Curing with Radiant Heat

Radiant heat may be applied by means of pipes circulating steam, hot oil or hot water, or by electric heating elements. Radiant heat curing shall be done under a suitable enclosure to contain the heat and moisture loss shall be minimized by covering all exposed concrete surfaces with plastic sheeting or by applying an approved liquid membrane curing compound to all exposed concrete surfaces. Top surface of concrete members to be used in composite construction shall be clear of residue of the membrane curing compound so as not to reduce bond below design limits. Surfaces of concrete members to which other materials will be bonded in the finished structure shall be clear of residue of the membrane curing compound so not to reduce bond below design limits.

If the Contractor proposes to cure by any other special method, the method and its details shall be subject to the approval of the Engineer.

553.18 Post-Tensioning. Tensioning of the prestressing reinforcement shall not be commenced until tests on concrete cylinders, manufactured of the same concrete and cured under the same conditions, indicate that the concrete of the particular member to be prestressed has attained compressive strength of at least 4000 psi unless otherwise specified.

After all concrete has attained the required strength, the prestressing reinforcement shall be stressed by means of jacks to the desired tension and the stress transferred to the end anchorage.

Cast-in place concrete shall not be post-tensioned until at least 10 days after the last concrete has been placed in the member to be post-tensioned and until the compressive strength of said placed concrete has reached the strength specified for the concrete at the time of stressing.

All side forms for girders shall be removed before post-tensioning. The falsework under the bottom slab supporting the superstructure shall not be released until a minimum of 48 hours have elapsed after grouting of the post-tension tendons nor until all other conditions of

the specifications have been met. The supporting falsework shall be constructed in such a manner that the superstructure will be free to lift off the falsework and shorten during posttensioning. Formwork left inside box girders to support the roadway slab shall be detailed in such a manner so as to offer minimum resistance to girder shortening due to shrinkage and post-tensioning.

The tensioning process shall be so conducted that the tension being applied and the elongation of the prestressing elements may be measured at all times. The friction loss in the element, i.e., the difference between the tension at the jack and the minimum tension, shall be determined in accordance with article 1.6.7 of AASHTO "Standard Specifications for Highway Bridges."

Suitable shims or other approved devices shall be used to insure that the specified anchor set loss is attained.

Prestressing tendons in continuous post-tensioned members shall be tensioned by jacking at each end of the tendon. Such jacking of both ends need not be done simultaneously. A record shall be kept of gage pressures and elongation at all times and submitted to the Engineer for his approval.

553.19 Bonding Steel. Prestressing steel shall be bonded to the concrete by filling the void space between the duct and the tendon with grout.

Grout shall consist of portland cement, water, and an expansive admixture approved by the Engineer.

Water shall be potable.

No admixtures containing chlorides or nitrates shall be used.

Water shall be first added to the mixer followed by cement and admixture.

The grout shall be mixed in mechanical mixing equipment of a type that will produce uniform and thoroughly mixed grout. The water content shall be not more than 5 gallons per sack of cement. Retempering of grout will not be permitted. Grout shall be continuously agitated until it is pumped.

The pump-ability of the grout shall be determined by the Engineer in accordance with the U.S. Corps of Engineers Test Method CRD-C 79. The efflux time of a grout sample immediately after mixing shall not be less than 11 seconds.

Grouting equipment shall be capable of grouting at a pressure of at least 100 pounds per square inch.

Grouting equipment shall be furnished with a pressure gage having a full-scale reading of not more than 300 pounds per square inch.

Standby flushing equipment capable of developing a pumping pressure of 250 pounds per square inch and of sufficient capacity to flush out any partially grouted ducts shall be provided.

All ducts shall be clean and free of deleterious materials that would impair bonding of the grout or interfere with grouting procedures.

All grout shall pass through a screen with 0.0787 inch maximum clear openings prior to being introducted into the grout pump.

Grout injection pipes shall be fitted with positive mechanical shutoff valves. Vents and ejection pipes shall be fitted with valves, caps, or other devices capable of withstanding the pumping pressures. Valves and caps shall not be removed or opened until the grout has set. Post-tensioned steel shall be bonded to the concrete. All prestressing steel to be bonded to the concrete shall be free of dirt, loose rust, grease or other deleterious substances.

Immediately after completion of the concrete pour, the metal conduit shall be blown out with compressed oil free air to the extent necessary to break up and remove any mortar in the conduit before it hardens. Approximately 24 hours after the concrete pour, the metal conduits shall be flushed out with water and then blown out with compressed oil free air. Prior to placing forms for roadway slabs of box girder structures, the Contractor shall demonstrate to the satisfaction of the Engineer that all ducts are unobstructed and if the prestressing reinforcement has been placed, that the steel is free and unbonded in the duct.

After the tendons have been stressed to the required tension, each conduit encasing the prestressing steel shall be blown out with compressed oil free air. The conduit shall then be completely filled from the low end with grout under pressure. Grout shall be pumped through the duct and continuously wasted at the outlet until no visible slugs of water or air are ejected and the efflux time of ejected grout is not less than 11 seconds. All vents and openings shall then be closed and the grouting pressure at the injection end shall be raised to a minimum of 100 psi and held for a minimum of 10 seconds.

If aluminum powder is used to expand the grout, it shall be added as follows:

From 2 to 4 grams of the unpolished variety (about 1 to 2 teaspoons) shall be added for each sack of cement used in the grout. The exact amount of aluminum powder will be designated by the Engineer. The dosage per batch of grout shall be carefully weighed. A number of weighings may be made in the laboratory and doses placed in glass vials for convenient use in the mix. The aluminum powder shall be blended with pumicite or other inert powder in the proportion of 1 part powder to 50 parts pumicite (or other inert powder) by weight. The blend shall be thoroughly mixed with the cement. The amount of the blend used should vary from 41⁄2 ounces per sack of cement for concrete having a temperature of 70°F. to 7 ounces for a temperature of 40°F. After all ingredients are added, the batch shall be mixed for 3 minutes. Batches of grout shall be placed within 45 minutes after mixing.

553.20 Unbonded Steel. Where the steel is not to be bonded to the concrete, it shall be carefully protected against corrosion by a coating of tar or other waterproofing material, in addition to any galvanizing which may be specified in addition to the requirements of ASTM A 416 (AASHTO M 203) and ASTM A 421 (AASHTO M 204).

553.21 Handling. Extreme care shall be exercised in handling and moving precast prestressed concrete members. Precast girders and slabs shall be transported in an upright position and the points of support and directions of the reactions with respect to the member shall be approximately the same during transportation and storage as when the member is in its final position. If the Contractor deems it expedient to transport or store precast units in other than this position, it shall be done at his own risk after notifying the Engineer of his intention to do so.

Prestressed concrete girders shall not be shipped until tests on concrete cylinders, manufactured of the same concrete and cured under the same conditions as the girders, indicate that the concrete of the particular girder has attained a compressive strength equal to the specified design compressive strength of the concrete in the girder and has attained a minimum age of 14 days.

Care shall be taken during storage, hoisting, and handling of the precast units to prevent cracking or damage. Units damaged by improper storage or handling shall be replaced by the Contractor at his expense.

553.22 Placing. Precast prestressed concrete piling shall be placed in accordance with the requirements for precast concrete piling in Section 551. Other precast prestressed structural members shall be placed in the structure in conformity with the plans and special provisions governing the particular type of structure to be built.

Method of Measurement

553.23 Structural Members. The quantity to be measured for payment will be the actual number of precast prestressed concrete structural members, except piling, of the several types and sizes, installed in place, completed and accepted. Each member will include the concrete, reinforcement and prestressing steel, enclosures for prestressing steel, anchorages, plates, nuts, elastomeric bearing pads, and other such material contained within or attached to the unit.

Piling will be measured as provided in Section 551.

Lump-sum measurement will be in accordance with subsection 109.02.

553.24 Other Items. The quantities of other contract items which enter into the completed and accepted structure will be measured for payment in the manner prescribed for the several items involved.

Basis of Payment

553.25 Structural Members. The quantity, determined as provided above, will be paid for at the contract price per unit of measurement or lump sum for the pay items listed below and shown in the bid schedule, which price and payment will be full compensation for the work prescribed in this section except prestressed concrete piling, which will be paid for as provided for in Section 551.

553.26 Other Items. The quantities of other contract items which enter into the completed and accepted structure will be paid for at the contract unit prices for the several pay items as prescribed for the items involved.

Pay item

553(1) Prestressed structural concrete members (identification) 553(2) Prestressed concrete

Section 554.-REINFORCING STEEL

Description

554.01 This work shall consist of furnishing and placing reinforcing steel in accordance with these specifications and in reasonably close conformity with the plans.

Materials

554.02 Materials. Reinforcing steel shall meet the requirements of subsection 709.01.

Construction Requirements

554.03 Order Lists. Before ordering material, all order lists and bending diagrams shall be furnished by the Contractor for the approval of the Engineer, and no materials shall be ordered until such lists and bending diagrams have been approved. Vertical reinforcement in columns, walls, piers, and shafts shall not be fabricated until footing elevations are established in the field. Approval of order lists and bending diagrams will in no way relieve the Contractor of his responsibility for ascertaining accuracy of such lists and diagrams. Revision of materials furnished in accordance with such lists and diagrams to meet compliance with design drawings shall be at the expense of the Contractor.

554.04 Protection of Materials.

Steel reinforcement shall be stored above the surface of the ground upon platforms, skids, or other supports and shall be protected as far as practicable from mechanical injury and surface deterioration caused by exposure to conditions producing rust. When placed in the work, reinforcement shall be free from dirt, detrimental rust, loose scale, paint, grease, oil, or other foreign materials. Reinforcement shall be free from injurious defects such as cracks and laminations. Rust, surface seams, surface irregularities or mill scale will not be cause for rejection, provided the minimum dimensions, cross section area and tensile properties of a