369 The vibrators shall be of a type and design approved by the Engineer, and the size of the vibrating head will be governed by the spacing of the prestr essing cables and reinforcement. Vibrators may be used only to consolidate the concrete after it has been properly placed. Internal vibrators shall be operated vertically and shall be slowly pushed into and pulled out of the concrete and shall not be hel d in one spot long enough to cause segregation. Concrete segregated by the vibrator shall be removed and discarded. Partially hardened layers of concrete shall not be penetrated or disturbed by the vibrator. Transmission of vibration into prestressing cabl e or reinforcement embedded in partially hardened concrete by the vibrating equipment will not be permitted. The plans for delivery and placement of Class S -P concrete to the casting beds should ensure that construction of the entire member is completed during the workable period of the concrete established in MP 711.03.23, such that no vibration of the concrete is necessary at any point during construction. If vibration is to be used at any time during fabrication, the Class S -P concrete mix a nd the method of construction must be pre -qualified as outlined in Section 603.6.1.1.1. Batching, transportation and delivery of the Class S -P shall be planned by the manufacturer such that there is a reasonably continuous feed into the formwork and, therefore, at no time shall there be a large pause or delay in the casting process which causes the fresh concrete properties to exceed the limits set forth in Table 603.6.4.1. 603.6.8 -Cold Weather Production: In addition to the requirements of Subsectio n 601.9.1, the following requirements shall apply to outdoor casting operations. When ambient temperatures below 40° F are anticipated, the following shall be used as necessary to keep the temperature of concrete within the prescribed limits:
1.Minimum concr ete temperature shall be 50º F after placement.
2.Concrete shall not be placed on cold forms, steel, or appurtenances. When the temperature of these facilities are below 40º F, steam heat or other means shall be provided to maintain the temperature to at lea st 50° F unless concrete is delivered above 60º F and no frost, snow or ice is present in the form.
3.Placing concrete under covers or in suitable enclosures.
4.Use of heated mixing water.
5.Avoidance of the use of frozen aggregate or aggregate containing frost, snow or ice.
6.Use of insulated forms. 603.6.9 -Hot Weather Production: In addition to the requirements of Subsection 601.9.2, the following requirements shall apply to outdoor casting operations: When the ambient temperature is above 100 F, or other adverse weather conditions are present, it is recognized that plastic shrinkage of concrete, or loss of strength below specification requirements, or both may occur. If such conditions do occur, the following procedures or combination of procedures s hall be used as necessary to correct these deficiencies:
1.Water fog spraying of forms, prior to placement of concrete. Forms exposed to direct sunlight can be misted for cooling prior to placement of concrete.
2.Shaded storage for aggregates.
3.Burying, insulat ing or shading water supply facilities.
4.Sprinkling or fog spraying of aggregates. 370 5. Use of shaved or crushed ice for a portion of the mixing water. Only so much ice shall be used as will be entirely melted at the completion of the mixing period.
6.Use of cold water in batching. Water can be chilled and stored in an insulated tank or pulled from a source if temperatures are low enough to aid mix temperature reduction.
7.Application of wet burlap or mats or fog spraying as soon as the water sheen disappears fr om the concrete. This is especially important for hot, windy, exposed locations.
8.Use of white pigmented curing compound for its heat -reflective properties except on composite surfaces.
9.Use of self -retarding admixtures.
10.Avoidance of the use of cement with t emperatures over 170 F.
11.Shading of product surface during and after casting to avoid heat buildup in direct sunlight. Concreting operations shall be discontinued when concrete temperatures exceed 100 F at the time of placing. 603.7 -PRESTRESSING : 603.7.1 -Protection of Prestressing Steel: All prestressing steel shall be protected against physical damage and rust at all times during storage and manufacturing. Prestressing steel shall also be fre e of deleterious material such as grease, oil, wax, or paint, except where called for on the plans. Prestressing steel that has sustained physical damage at any time shall be rejected. The use of prestressing reinforcement having kinks, bends, nicks, or ot her defects will not be permitted. The development of pitting, other than slight rusting shall be cause for rejection. Prestressing steel shall be packaged in containers or shipping forms for the protection of the strand against physical damage and corro sion during shipping and storage. A corrosion inhibitor which prevents rust or other results of corrosion shall be incorporated in a corrosion inhibitor carrier type packaging material, or when permitted by the Engineer, may be applied directly to the stee l. The corrosion inhibitor shall have no deleterious effect on the steel or concrete or bond strength of steel to concrete. The shipping package or form shall be clearly marked with a statement that the package contains high strength prestressing steel, and the type of corrosion inhibitor used, including the date packaged. All anchorages, end fittings, couplers, and exposed strands, which will not be encased in concrete or grout in the completed work, shall be permanently protected against corrosion. If an anti -bonding agent is used on the forms to facilitate member removal, every precaution shall be taken to protect the prestressing strands against any ° of coating by the anti - bonding agent. 603.7.2 -Storing of Prestressing Steel: Prestressing steel shall be stored in a protected area which includes a roof (and sides if necessary) to keep moisture off the strand. In addition the cover must have a floor or at least the strand must be placed on supports to keep it out of mud and water until it is to be used. It shall not be removed from its protective packaging until immediately prior to installation in the forms and placement of concrete. Openings in the packaging shall be resealed as necessary to protect the unused steel. While expos ed, the steel shall be protected to prevent corrosion. 603.7.3 -Placement of Prestressing Steel: Prestressing shall be accurately installed in the forms and held in place by the stressing jack or temporary anchors and, when tendons are to be draped, by hold -down devices. The hold down devices used at all points of change in slope of tendon trajectory shall be of a low -friction type. 603.7.4 -Safety Measures: Effective safety measures shall be taken to prevent injuries to personnel due to the breakage of strands or failure of anchorage devices during the tensioning operations. The protection provide d shall be adequate and shall permit the inspector to perform his normal duties. When the safety precautions, in the opinion of the Engineer, are inadequate the contractor will revise the procedures or equipment to the satisfaction of the Engineer. The inspector will abide by the safety rules established by the producer. 603.7.5 -Stressing Requirements: 603.7.5.1 -General: The provisions set forth in this section refer to the application and measurement of stresses to prestressed concrete members manuf actured by the process of pretensioning. Prestressing forces shall not be transferred to any member nor shall end anchors be released before the concrete has attained a minimum compressive strength as specified on the plans or in the special provisions as determined by tests of standard cylinders cured identically as the member. An initial force shall be applied to each strand such as to develop a load of approximately 10% of the final prestressing load as shown on the plans. A record shall be maintained o f the jacking force and elongations thereby. Several prestressed members may be cast in one continuous line and stressed at one time. Forms shall be removed and members detensioned immediately after steam curing or heat curing is discontinued while the co ncrete is still warm and moist. The elements shall be cut or released in an order such that lateral eccentricity of prestress forces will be a minimum. 603.7.5.2 -Tensioning of Strands: In all methods of tensioning, stress induced in the strands shall b e determined by monitoring applied force and independently by measurement of elongation. Applied force may be monitored by direct measurement using a pressure gauge piped into the hydraulic pump and jack system. The elongation measurements shall agree with their computed theoretical values within a tolerance of ±5%. If discrepancies are in excess of 5% between the calculated forces, determined by elongation measurement and gauge reading, the tensioning operation shall be suspended and the source of error d etermined, evaluated, and corrected by qualified personnel before proceeding. Calculations for elongation and gauge readings must include appropriate allowances for friction in the jacking system, strand seating, movement of bulkheads, bed shortening if under load, thermal corrections, and any other compensation for the setup. 603.7.5.3 -Methods of Stress Measurement: Methods of measurement of the stressing force consist of pressure gauges to measure force from the pressure applied to hydraulic jacks or any other method approved by the Engineer. 372 603.7.5.4 -Gauging Systems: Hydraulic gauges shall conform to the provisions set forth in Section 603.3.3. All gauges measuring the stressing load shall be graduated so they can be read within a tolerance of ±2%. Tensioning methods employing hydraulic gauges shall have appropriate bypass valve snubbers and fittings so that the gauge pointer will not fluctuate but will remain steady until the jacking load is released. 603.7.5.5 -Control of Jacking Force: Pressure bypass valves may be used for stopping the jack at the required load or for manually stopping the load with the valve. The accuracy of setting of automatic cutoff valves shall be verified by running to the desired cutoff load whenever there is re ason to suspect improper results, and at a minimum, at the beginning of the operation each day. 603.7.5.6 -Wire Failure in Strands: Failure of wires in a pretensioning strand is acceptable provided the total area of wire failure is not more than 2% of t he total area of strands in a member, and providing the breakage is not symptomatic of a more extensive distress condition. Failure of any individual wire prior to placing concrete will require replacement of the strand. 603.7.5.7 -Calibration Records for Jacking Equipment: All jacking and load measuring equipment shall be calibrated as specified in Section 603.3.3. Calibration records should show the following data.
1.Date of calibration.
2.Agency, laboratory or registered WV Professional Engineer (PE) super vising the calibration.
3.Method of calibration; i.e. proving ring, load cell, testing machine, etc., and its calibration reference.
4.The full range of calibration with gauge readings indicated against actual load. Calibration records for all tensioning sys tems being used shall be available for preparing theoretical tensioning values. Personnel involved in preparing tensioning calculations shall have a copy of these records for reference. 603.7.6 -Pretensioning and Strand Debonding: Pretensioning shall co nform to the provisions set forth in Article 2.2, “Pretensioning” of the latest edition of the PCI Quality Control Manual MNL -116. Plastic sheathing shall be used for strand debonding and shall be approved by the Engineer prior to use. Items such as ani mal fat, reactive greases, or PVC pipes shall not be used. Any other material shall be approved by the Engineer prior to use. 603.7.7 -Detensioning: Detensioning shall conform to the provisions set forth in Article 2.3, “Detensioning” of the latest ed ition of the PCI Quality Control Manual MNL -116. 603.7.8 -Concrete Cover : Minimum concrete cover for prestressing steel shall be 1 ½ inches unless otherwise shown on the plans. 373 603.8 -CURING : 603.8.1 General: Careful attention shall be given to the proper curing of concrete. Prior to placing of concrete, the contractor shall submit the proposed curing methods and procedures to the Engineer for approval. Elevated temperature curing facilities shall be tested pr ior to approval. Approved equipment and materials for curing shall be available for use prior to casting. Inadequate curing facilities or lack of attention to the proper curing of concrete shall be sufficient cause for the Engineer to stop all concrete p lacement until approved curing is provided. Inadequate curing may be cause for rejection of the member. All test cylinders shall be cured in the same environment as the precast/prestressed concrete members. Curing shall be commenced prior to the formatio n of surface shrinkage cracks. The curing mats, sheets, or blankets shall be carefully placed in contact with the concrete member to avoid damage to the freshly finished concrete. The following curing requirements shall apply for precast/prestressed mem bers. Any other special method of curing shall meet with the approval of the Engineer. Concrete shall not be exposed to temperatures below freezing until the specified minimum strength as shown in plan notes has been attained. All concrete shall be cured by water curing, accelerated temperature curing, or any other method approved by the Engineer. 603.8.2 -Water Curing: All exposed surfaces of the concrete shall be kept wet continuously for the required curing time. The water used for curing shall meet the requirements of subsection 603.2. Water curing shall be permitted as follows: 603.8.2.1 -Wet Mat Method: For water curing by the mat method, cotton mats, polyethylene sheeting, or polyethylene burlap blankets may be used. The mats, sheets or blanket s shall be adequately anchored and weighted to provide continuous contact with all concrete surfaces. Any concrete surfaces which cannot be cured by contact shall be enclosed by mats, adequately anchored, so that outside air cannot enter the enclosure. Sufficient moisture shall be provided inside the enclosure to keep all of the surfaces of the concrete wet for the required curing time, but in no case less than 36 hours. 603.8.2.2 -Saturated Cover Curing: The member, covered as specified for the initial phase of curing, shall be maintained on the casting bed in an approved enclosure designed and equipped to insure complete saturation of the covering. The temperature within the enclosure and that of the covering material shall be maintained to provide a un iform curing temperature at the surface of the member, within the limits of 80 F to 130 F, until the specified strength is attained, but in no case less than 36 hours. The covering shall be kept thoroughly saturated throughout the entire curing period an d the temperature of the water used shall be controlled uniformly to maintain the selected curing temperature of the surface of the member. 603.8.2.3 -Water Spray Curing: The member, covered as specified for the initial phase of curing, shall be maintain ed in the casting bed in an approved enclosure. When the concrete is sufficiently hardened to resist damage, the covering shall be removed and the exposed surfaces of the unit shall be subjected to a continuous fine spray of water. The temperature within t he enclosure and that of the water used shall be controlled to provide 374 a uniform curing temperature at the surface of the member, within the limits of 80 F and 130F until the specified member strength is attained, but in no case less than 36 hours. 603.8.3 -Accelerated Curing: Accelerated curing of the concrete shall be done by low pressure steam curing, or radiant heat curing. Transfer of stress shall be accomplished immediately after the heat curing has been discontinued. Accelerated curing shall b e applied at a controlled rate following initial set of the concrete as per ASTM C403. Accelerated curing shall be done under suitable enclosures which minimize all heat losses and maintain uniform cure conditions within the enclosed area. Members must be maintained wet during accelerated curing time. If accelerated curing is used, the contractor/fabricator shall furnish recording thermometers showing the time -temperature relationship of the concrete throughout the entire curing period. Recording thermome ters shall be kept in proper calibration and recalibrated at least annually. 603.8.3.1 -Low -Pressure Steam Curing: Low-pressure steam curing shall be done under a suitable enclosure to contain the live steam and minimize moisture and heat losses. The c oncrete shall be allowed to attain its initial set before application of the live steam. Application of live steam shall not be directed on the concrete or forms such as to cause localized high temperatures. During the initial application of live steam, the concrete temperature shall be raised at an average rate not exceeding 80°F /per hour, until the curing temperature is reached. The maximum sustained concrete temperature during the curing cycle shall not exceed 160 F. The maximum temperature shall be held until the concrete has reached the required release strength. The maximum peak concrete temperature during the curing cycle shall be 190°F. The concrete temperature shall be maintained uniformly throughout the extremities of the prestressed member. A t the end of curing, the concrete temperature shall be reduced at an average rate not exceeding 50°F /per hour. 603.8.3.2 -Radiant Heat Curing: 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 a plastic sheeting or by applying an approved liquid membrane curing compound to all exposed concrete surfaces. The heat application shall be maintained to create a uniform concrete temperature throughout the extremities of the member. After the waiting period prior to application of the heat, the concrete temperature shall increase at an average rate not exceeding 80 F /per hour until the curing temperature is reached. The maximum sustained concrete temperature within the curing cycle shall not exceed 160 F. The maximum temperature shall be held until the concrete has reached the required release strength as shown in plan notes. The maximum peak concrete temperature during the curing cycle shall be 190°F. The maximum cooling rate from sustained concrete curing temperature shall be 50°F /per hour. 603.9 -FINISHING : To assure the production of well-formed matching members, all surfaces of the concrete shall be finished, shall be true and even, and shall be free from rough, open, or honeycombed areas, depressions or projections. The ed ges shall be finished or chamfered, or both. Care shall be exercised in removing forms to avoid spalling or otherwise damaging the concrete. 375 Top surfaces of prestressed members shall be screeded or rough floated to bring mortar to the surface and cover a ll aggregate. The top surface of members that will receive cast -in-place concrete on the project site shall be finished as noted on the project plans, or if no finish is noted, they shall have either a raked or stiff broom finish. Aggregate shall not be loosened when roughening the surface. The fascia surfaces of bridge members shall be finished with a PCI Grade A Formed Finish. All other members shall be finished with a PCI Standard Grade Formed Finish. Concrete on exposed reinforcing steel and loose laitance on concrete surfaces to be in contact with cast-in-place concrete shall be removed from all members. Fabrication holes, except box beam vent holes, in the bottom of all beams, shall be filled with nonshrink mortar and made flush with the surround ing surface. No patching is required for small holes and irregularities on the sides of adjacent box beams that are to be sandblasted prior to shipment. Care shall be taken in final cutting the ends of strands to avoid damaging the concrete surface.
603.10 Workmanship :
603.10.1 General: Holes and voids in the surface of concrete resulting from bolts, ties, or
large air pockets shall be wetted and filled with mortar having the same proportion of fine aggregate and cement as in the concrete, after which exposed mortar surfaces shall be finished smooth and even with a wood float. Surfaces to be repaired and finished shall be kept wet for at least one hour before hydraulic cement mort ar is applied. Immediately following patching work, repaired areas shall be wet cured for at least 48 hours. The wet cure may be accomplished by the use of steam, wet burlap or continuous spray wetting. A liquid membrane -curing compound may be used on non - composite surfaces. Beams or girders having honeycomb of such extent to affect their strength or resistance to deterioration will not be accepted.
603.10.2 Defects and Breakage: Defective or damaged members which cannot be
satisfactorily repaired, o r which are not acceptable to the Engineer will not be incorporated into the work. All other members that sustain damage during fabrication, handling, storage or transportation shall be evaluated in accordance with Chapter three of PCI Journal Vol. 30, # 3 entitled “Fabrication and Shipment Cracks in Precast or Prestressed Beams and Columns”, hereinafter referred to as “specification”. This specification is to be used to determine the severity of cracks. All cracks with a width of 4 mils or less may be repa ired by silane treatment if the repair section of the specification allows repairs. All cracks over 4 mils to and including 16 mils shall be repaired by epoxy injection if allowed by the specification. Members with cracks over 16 mils shall not be incorpor ated into the work unless approved by the Engineer.
603.10.2 1 -Epoxy Injection of Cracks: The work shall consist of repairing cracks
with a width greater than 4 mils and up to and including 16 mils on prestressed concrete bridge beams.
603.10.2 1.1 -Materials: The epoxy material used for epoxy injection crack repair shall
meet the requirements specified for epoxy resin adhesives in ASTM C881, Type IV, Grade 1, and Classes B or C. For the epoxy paste or material used to bond and cover the injection ports to the substrate, use the epoxy resin manufacturer’s recommendation.
Source: West Virginia Standard Specifications for Road and Bridge Construction, 2023 Edition. Pages 389–395 of 1,006.