CATEGORY 400 STRUCTURES SECTION 440 — PRESTRESSED CONCRETE BEAMS AND SLAB PANELS
440.01 Description
Furnish and place prestressed concrete beams and slab panels, elastomeric bearing pads, bearing plates and other embedded items, all steel strands, jacks, and other required devices. The concrete overlay riding surface for slab panel bridges is included in this work.
440.02 Materials
Fine Aggregate 901.01 Coarse Aggregate 901.01 Fine Aggregate for Overlay Bonding Grout 901.01, Fine Aggregate/Sand Mortar and Epoxies Cement 902.03 and 902.04 Admixtures: Air Entraining 902.06.01 Retarding 902.06.02 Water Reducing 902.06.02 , 902.06.03 Pozzolans 902.06.04 , 902.06.05 Concrete Overlay 902.10, Mix No. 8 Nonshrink Grout 902.11(c) Self-Consolidating Concrete 902.17 Reinforcing Steel 908.01 Welded Steel Wire Fabric 908.05 Prestressing Strand 908.11 Elastometric Bearing Pads 910.02 Closed Cell Neoprene Sponge Elastomer 911.10 Production Plants Section 915 Fusion Bonded Epoxy Powder Coating for Steel 917.02 Water 921.01 Epoxy Adhesive 921.04 2025 STANDARD SPECIFICATIONS FOR CONSTRUCTION AND MATERIALS Threaded Tie Rods A722 Tie Rod Heavy Hex Nuts Supplied by tie rod manufacturer; shall provide full tensile strength of tie rod Concrete Protective Coatings Contract Documents Concrete Chloride Content Contract Documents Chloride Ion Content Contract Documents Epoxy Protective Coatings 917.01 Epoxy Grout 902.11(d)
440.02.01 Self Consolidating Concrete, (SCC). The Contract Documents shall specify cylinder
strength of the concrete at 28 days, required cylinder strength of the concrete at transfer of the tensioning load and the time when forms may be removed. Ensure that the composition, proportioning, and mixing of concrete produces a homogeneous concrete mixture of a quality that meets the specified material and design requirements. Prior to start of fabrication submit all SCC mix design sources for approval. The manufacturer shall furnish certifications as specified in TC-1.03.
a.Trial Batch. As specified in 902.10.04. Proportion the concrete, by weight, with the exception of water and chemical admixtures. Water and chemical admixtures may be proportioned by volume or by weight. The mixture must meet the minimum requirements as specified in 902.17.
b.Sampling and testing. As specified in 902.17. All acceptance testing will have modifications to Specifications to include filling of the testing apparatus in one lift without consolidation or vibration, unless outlined in the Contract Documents. Perform all sampling and testing of SCC by Concrete Field Testing Technician, Grade 1, certified by American Concrete Institute or personnel holding an equivalent or higher level certification as specified in Section 915 and supervised by a Quality Control Manager certified as a Precast/Prestressed Concrete Institute Quality Control Personnel Level 2, or a Precast/Prestressed Concrete Institute Quality Control Personnel Level 3 in the case of plants producing beams with deflected strands. All fabrication facilities producing SCC shall have adequate equipment and staff to perform the specified tests. An independent laboratory or inspection agency may perform the testing for the producer only in the event the independent laboratory or inspection agency is named in the Quality Control Manual and approved by the Administration. The Engineer will take six test cylinders from each member or members cast and to be cured with the member as a unit for the purpose of checking the quality of the concrete being produced; for determining the time when the forms may be removed, and for determining the time when prestressing forces may be applied to a member. 2025 STANDARD SPECIFICATIONS FOR CONSTRUCTION AND MATERIALS The manufacturer shall provide metal or plastic molds for all test cylinders. The manufacturer’s quality control technician shall make at least three cylinder specimens to be cured under laboratory conditions as specified in R 39 to determine the 28-day compressive strengths. The technician shall make and test the cylinders at the manufacturing site according to T 22 and in the presence of the Engineer. A test is defined as the average strength of three companion cylinders.
c.Fabrication. During fabrication the manufacturing facility shall maintain a continuous placement of SCC to eliminate possibility of formation of a cold joint. This process shall be outlined in the Quality Control Manual.
d.Mechanical Consolidation. Do not internally or externally vibrate, rod or otherwise mechanically consolidate SCC without prior written approval.
440.02.02 Reinforcing Steel and Tie Rod Tubes. Except for prestressing strands, epoxy coat all
reinforcing steel in and extending from beams and slab panels, and in the concrete overlay. Tie rod tubes shall consist of corrugated, rigid or semi-rigid type, galvanized steel sheathing, or rigid plastic sheathing.
440.02.03 Debonding Material. Use solid or split plastic sheathing having a thickness of at least
0.025 in. for debonding of pretensioning steel strands. 440.02.04 Joint Sealers. According to the manufacturer’s specifications.
440.03 Construction
440.03.01 Working Drawings. Refer to Section 499. Address reinforcing, anchorages, steel
strand profiles, lifting inserts, and all other pertinent information. If methods other than specified are proposed, submit changes as specified in Section 499. When proposed changes are accepted or rejected, construct members accordingly at no additional cost to the Administration.
440.03.02 Prestressed Concrete Plants. The prestressed concrete manufacturing plant shall be
registered and certified under the Precast/ Prestressed Concrete Institute Program. Submit a valid certificate to the Engineer prior to the start of production.
440.03.03 Beds and Forms. Support casting beds on unyielding foundations. Clean the beds and
forms after each use. Prevent accumulation of bond breakers. Prior to stringing steel strands, inspect the bottom of forms for cleanliness and alignment. Coat the contact surfaces of forms with bond breaker that dries to a surface hardness. Ensure that the coating is dry to prevent contamination of the steel strand. 2025 STANDARD SPECIFICATIONS FOR CONSTRUCTION AND MATERIALS
440.03.04 Meetings. Conduct a pre-pour meeting prior to beginning any prestress concrete work.
Ensure a representative of the prestress concrete plant is present.
440.03.05 Protection of Prestressing Steel Strand. Store under shelter and keep it free of
deleterious material such as grease, oil, wax, dirt, paint, loose rust, or other similar contaminants. Do not use steel showing corrosion, etching, pitting, or scaling. A light coating of surface rust is acceptable if it can be removed completely from the steel by wiping with a cloth. Do not store on a surface that contributes to galvanic or battery action. Do not use steel strand as a ground for electric welding. Protect it from electric welding sparks. 440.03.06 Reinforcing Steel, Inserts, and Chairs. Place reinforcing steel within the specified tolerances, and secure it to beds and forms using chairs, blocking, or ties. Fabricate cages of bars by tying only. Do not support cages by tensioned strands. Bend tie wire ends into the slab panel. Show the type and placement of inserts on the working drawings. Except for stainless steel accessories, recess form ties, chairs, and inserts in the concrete by at least 1 in.
440.03.07 Methods of Force Measurement. Use one of the following methods as the primary
measuring system. Check it by using one of the other methods as a secondary measuring system:
a.Curves. Use current stress-strain or elongation curves furnished by the strand manufacturer. An average modulus may be used if acceptable to the Engineer. Provide means for measuring the elongations of the strands to at least 1/8 in.
b.Pressure Gauges. Use gauges to measure force by the pressure applied to hydraulic jacks. Furnish gauges with dials calibrated with the jacking system.
c.Dynamometers. Dynamometers connected in tension to the stressing system for the initial force may be used. Gauging System. Use tensioning systems equipped with accurately calibrated hydraulic gauges, dynamometers, load cells, or other devices for measuring the stressing load to an accuracy of reading within 2 percent. Have a qualified testing laboratory calibrate and issue a certified calibration curve with each gauge. Recalibrate a gauging system whenever it shows erratic results; at intervals not exceeding six months, and when directed. Gauges for single strand jacks may be calibrated by an acceptable and calibrated load cell. Calibrate gauges for large multiple strand jacks, acting singly or in parallel, by proving rings or by load cells placed on either side of the movable end carriage. Calibrate all jacks and gauges by an independent laboratory at no additional cost to the Administration and documentation forwarded to the Engineer. Provide pressure gauges and dynamometers preferably with full pressure and load capacities of approximately twice their normal working range. Limit loads to within 25 to 75 percent of the total graduated capacity, unless calibration data establishes consistent accuracy over a wider range. 2025 STANDARD SPECIFICATIONS FOR CONSTRUCTION AND MATERIALS Each gauge shall indicate loads directly in pounds or be accompanied by a chart with which the dial reading can be converted into pounds. Equip tensioning systems employing hydraulic gauges with appropriate bypass pipes, valves, and fittings so the gauge reading remains steady until the jacking load is released. Gauge readings, elongation measurements, and calculations for elongation shall include appropriate allowances for operational losses in the tensioning system due to strand slippage, movement of anchorages and abutments, elongation of abutment anchorage rods, strand rotation, temperature variation, friction, bed shorting, and other forces and influences acting on the strand. In multiple strand tensioning systems, clean and lubricate the sliding surfaces to minimize friction. Establish a force override (compensatory operational loss correction) for standard strand pattern series. Thermal Effects. Increase the design prestress force by 0.5 percent for each 5 F ambient temperature below 80 F. No adjustment is required when the ambient temperature is above 80 F. Do not stress steel strands when the ambient temperature is below 40 F. After the steel strands are tensioned, maintain the temperature of the air surrounding the steel strands at 40 F or more until the prestress force is transferred to the concrete. Control of Jacking Force. Use either manual or automatic pressure cutoff valves for stopping the jacks at the required load. Use automatic cutoffs capable of adjustment to ensure that the jacking load corresponds to the required load. Verify the setting accuracy for the automatic cutoff valves whenever there is reason to suspect improper results and at the beginning of each day’s operation.
440.03.08 Stringing Steel Strands. Do not reuse strands containing former vise grip points unless
the points are outside the new vise locations. Do not reuse strands that have been draped. All steel strands shall have the same lay or direction of twist. Use shears or abrasive cutting wheels to cut the ends. Position over chairs to eliminate sagging of strands in the bottom rows.
440.03.09 Steel Strand Splices. Only one splice is permitted per strand. For single strand
tensioning, the number of strands that may be spliced in each bed is not restricted. For multiple strand tensioning, either splice all strands and adjust the elongation for average slippage, or no splices are permitted.
440.03.10 Steel Strand Vises. Use vises capable of anchoring stressing loads positively with
minimum slippage and which are cleaned, lubricated, and inspected between each use. Do not use grips that show wear or distortion, or that allow slippage in excess of 1/4 in. Clean and inspect the full set of vises before starting each prestressing operation. The maximum permissible time for holding tensioned strands in the bed before placing concrete is 72 hours. 2025 STANDARD SPECIFICATIONS FOR CONSTRUCTION AND MATERIALS
440.03.11 Wire Failure in Steel Strands. Remove and replace any seven wire steel strand that
contains a broken wire. Check all strands for wire breakage before placing concrete.
440.03.12 Pretensioning. Apply the specified total load to each strand. Apply the load as a total
of two loading stages. The initial load shall straighten the strand, eliminate slack, and provide a starting or reference point for measuring elongation. Limit the initial load to 10 percent of the specified tensioning force. Receive approval from the Engineer for any initial loading exceeding 10 percent (i.e. multiple bed casting). Measure the initial load within a tolerance of ± 100 lb. Do not use the initial elongation measurement to determine the initial force. In all stressing operations, keep the stressing force symmetrical about the vertical axis; however, in tensioning single strands, the initial and final loads may be applied in immediate succession to each strand. Use jack mounted pressure gauges as the primary system of force measurement for the final tensioning of straight single strands. Check elongation against pressure gauge readings on all strands. Check vise slippage. The computed elongation, including operational losses and equivalent elongation for the initial tensioning force, shall agree with the pressure gauge reading within 3 percent. Use jack mounted pressure gauges as the primary system of force measurement for the final tensioning of multiple strands. For uniform application of load to the strands, place the position of the face of the anchorage at final load parallel to its position under initial load. Verify parallel movement by measurement of equal movement on opposite anchorage sides and by checking the plumb position of the anchorage before and after final load application. Check vise slippage. After stressing the steel strands as specified and placing all other reinforcement, cast the concrete member to the specified length. Maintain strand stress between anchorages until the concrete has reached the specified compressive strength.
440.03.13 Steel Strand Tensioning. In all methods of tensioning, measure the stress induced in
the strands both by jacking gauges and by elongation. Recalibrate any jack or gauge that appears to be giving erratic results or gauge pressures and elongations indicate materially different stresses during manufacturing. Provide means for measuring elongation to the nearest 1/8 in. For differences in indicated stress between jack pressure and elongation of up to 5 percent, place the difference so that the discrepancy will be on the side of a slight overstress rather than understress. For discrepancies in excess of 5 percent, carefully check the entire operation and determine the source of the discrepancy before proceeding. Thoroughly seal split plastic sheathing for debonded steel strands with tape prior to placing concrete. 2025 STANDARD SPECIFICATIONS FOR CONSTRUCTION AND MATERIALS
440.03.14 Surface Finish and Curing.
440.03.14 01 Surface Finish.
a.Slab Panels. Rough finish the top surface of all members with a rake, wire brush, or other approved means to a full amplitude of 1/4 in. Prior to shipping the slab panels, abrasive blast the shear key surface to provide an exposed aggregate finish.
b.Beams. Rough finish the top surface of all members with a rake, wire brush, or other approved means to a full amplitude of 1/4 in.
440.03.14 02 Curing.
a.Initial Curing. Begin initial curing of all members by fogging, wet burlap, or other approved methods as soon as the concrete is hardened sufficiently to withstand surface damage. Continue the initial curing until the concrete has attained its initial set, but at least three hours; however, when a retarding agent is used, continue the initial curing for at least five hours. Following the initial curing, resume curing using an accelerated curing method.
b.Accelerated Curing. Use one of the following methods to accelerate curing of the concrete:
1.Low Pressure Steam Curing. Use a suitable enclosure to contain the live steam and minimize moisture and heat loss. Ensure that the concrete has attained initial set before application of the live steam. Do not permit live steam to be directed on the concrete or the forms so as to cause localized high temperatures. Maintain the temperature of the interior of the enclosure at 80 F to 160 F. During initial application of the steam, increase the ambient air temperature within the enclosure at a rate not to exceed 40 F per hour. Hold the maximum temperature until the concrete has reached the required release strength. Maintain the steam temperature and the curing temperature uniformly throughout the extremities of the prestressed member. At the end of curing, reduce the concrete temperature at an average of 40 F per hour. Ensure that the producer furnishes at least one recording thermometer for each enclosure. If the enclosure is longer than 300 ft, furnish an additional recording thermometer for each additional 300 ft of length or fraction thereof. The temperature at any point within the enclosure shall not vary more than 10 F from that of the recording thermometer or the average of the recording thermometers if more than one is used.
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. Provide 2025 STANDARD SPECIFICATIONS FOR CONSTRUCTION AND MATERIALS a suitable enclosure to contain the heat. Minimize moisture loss by covering all exposed concrete surfaces with plastic sheeting or by applying an approved liquid membrane curing compound to all exposed surfaces. Uniformly maintain the heat application throughout the extremities of the member. Apply the same temperature constraints as outlined for low pressure steam curing.
440.03.15 Detensioning.
a.Slab Panels. Do not transfer the tension force to the prestressed slab panel until the concrete strength as indicated by cylinder strengths meets the specified transfer strength. Do not ship slab panels before the 28 day design strength is met. Prior to detensioning, remove or loosen forms, ties, inserts, hold downs, and other devices that restrict longitudinal movement along the bed, or use a method and sequence to minimize longitudinal movement. Detension strands in the presence of the Engineer using a method that minimizes sudden or shock loading. Single strand detensioning may be accomplished by heat cutting the strands. The sequence shall maintain prestressing forces nearly symmetrical around the slab panel’s vertical axis. Eccentricity around the vertical axis shall be limited to one strand. Obtain approval of the cutting pattern prior to use. Multiple strand detensioning may be accomplished by gradually reducing the force applied to each strand equally and simultaneously.
b.Beams. The schedule for detensioning of beams having deflected steel strands shall incorporate the following:
1.Follow approved manufacturer’s sequence of releasing deflected steel strands and uplift points.
2.Disengage all hold down devices for deflected steel strands, and remove all hold down bolts from the beams.
3.Follow approved manufacturer’s sequence of releasing the remaining straight steel strands. All hold down devices may be released prior to release of tension in deflected steel strands if:
i.The weight of the prestressed beam is more than twice the total of the forces required to hold the steel strands in the low position. 2025 STANDARD SPECIFICATIONS FOR CONSTRUCTION AND MATERIALS (ii) The weight or other approved vertical restraints are applied directly over the hold down points to counteract the uplifting forces, at least until the release of deflected steel strands has proceeded to a point that the residual uplifting forces are less than half the weight of the beam. Follow all procedures for releasing prestressing forces of deflected steel strands. Failure to follow these procedures may result in the rejection of the beams. Adequately separate all beams in storage immediately following removal from the bed to facilitate the repair of surface blemishes and to allow inspection of the finished surfaces.
c.Cutting and Protecting Strand Ends. After the beams or slab panels have been detensioned, clean the ends of the strands to remove all foreign material such as rust, slag, grease, etc until the surface is visibly clean and water break free. Use wire brushing or abrasive blast cleaning to remove all dirt and residue that is not firmly bonded to the metal and concrete surfaces. Work a protective coating into all voids of the strands using the following methods:
1.Where strands in beam or slab ends are to ultimately be encased in a concrete deck or end section, cut the strands flush with the concrete end. Prepare the surface and apply an epoxy protective coating to the strands and adjacent concrete as specified in Section 464. Extend the limits of the coating a minimum of 1 inch beyond the strand perimeter at each strand location.
2.Where strands in beam or slab ends are to be exposed to the air, recess the cuts a minimum of 1/2 inch into the end of the beam. Fill the recessed area with an approved epoxy grout conforming to 902.11(d) in accordance with the manufacture’s recommendations. Match the surface finish of the epoxy gout to that of the beam end. Prepare the surface and coat the entire end of the beam with an epoxy protective coating as specified in Section 464.
3.If the end of the beam or slab will bear on a substructure unit directly under a bridge deck joint, protect the ends as specified in 440.03.15(c)(2). Prepare the surfaces and coat the bottom of the top flanges, the web, and bottom flanges for an additional five feet beyond the end of the concrete member with the same epoxy protective coating as specified in Section 464.
440.03.16 Camber. Clearly and permanently identify all beams so that the camber readings taken
as indicated below can be associated with the proper beam. Take camber readings as follows, in the presence of the Engineer.
a.Just prior to detensioning. (b) Immediately after detensioning. 2025 STANDARD SPECIFICATIONS FOR CONSTRUCTION AND MATERIALS 2025 STANDARD SPECIFICATIONS FOR CONSTRUCTION AND MATERIALS
c.At two weeks after detensioning.
d.At one month after detensioning. (e) In the event any camber measurements, at two weeks or one month, exceed plan camber tolerances, continue to take camber readings at two week intervals until the Engineer determines otherwise, or just prior to shipment from the casting yard to the job site.
f.Continue camber determinations at two week intervals if the beams are stored or stockpiled at the job site. Furnish two copies of the camber reports to the Engineer prior to erecting the beam.
440.03.17 Tolerances. The tolerances for each beam or slab panel shall be as shown in Tables
440.03.17 A or B, respectively unless otherwise specified:
TABLE 440.03.17A PRESTRESSED CONCRETE BEAM TOLERANCE Depth (overall) ± 1/4 in. Width (flanges & fillets) ± 1/4 in. Width (web) ± 1/4 in. Length of Beam ± 1/8 in. per 10 ft or 1/2 in. whichever is greater Exposed Beam Ends (deviation from square or designated skew) Horizontal ± 1/4 in. Vertical ± 1/8 in. per ft of beam height Side Inserts (spacing between center of inserts and from the centers of inserts to the ends of the beams) ± 1/2 in. Bearing Plate (spacing from the centers of bearing plates to the ends of the beams) ± 1/2 in. Stirrup Bars: Average of all bars Individual bar longitudinal spacing ± 1/2 in. ±1 in. Horizontal Alignment (deviation from a straight line parallel to the center line of beam) 1/8 in. per 10 ft max Camber Differential between adjacent beams of same type and steel strand pattern 1/8 in. per 10 ft at time of erection or 1/2 in. max Center of Gravity of steel strand group ± 1/4 in. Center of Gravity of depressed group steel strand at end of beam ± 1/2 in. Position of hold down points for depressed strand ± 6 in. Camber deviation from plan camber, as measured at release or at beginning of beam storage at the fabricating plant ±50% of plan camber or ±1/2 in. whichever is greater TABLE 440.03.17B PRESTRESSED CONCRETE SLAB PANEL TOLERANCE Depth (overall) ±1/2 in., -1/4 in. Width (overall) ±0 in., -1/2 in. Slab Panel Length @ center line (based on design length specified) ±1/2 in. Horizontal Alignment (deviation from a straight line parallel to the slab panel center line) ¼ in. max Horizontal Misalignment of adjacent panel sections ½ in. max Camber Deviation from specified camber, as measured at prestress transfer or at the beginning of slab panel storage at the fabrication plant ±1/2 in. Location of each strand ±1/8 in. Center of Gravity of strand group ±1/4 in. Stirrup Bars (longitudinal spacing) ±1 in. Longitudinal Position of handling devices ±3 in. Concrete Bearing Area (variation from plane surface when tested with a straightedge through middle half of slab panel ±1/8 in. Tie Rod Tubes (spacing between the tube centers and from tube centers to slab panel ends) ±1/2 in. Tie Rod Tubes (spacing from tube center to slab panel bottom) ±3/8 in. Threaded Inserts (spacing between the center of inserts and from center of inserts to ends of slab panels) ±1/2 in. Skew Ends (deviation from designated skew) ±1/2 in. Vertical ends (deviation from specified dimension) ±3/8 in. Camber deviation from plan camber, as measured at release or at beginning of beam storage at the fabricating plant ±50% of plan camber or ±1/2 in. whichever is greater
440.03.18 Slab Panel Plant Assembly. Before shipping the slab panel units to the job site,
assemble all slab panels in the presence of the Engineer for the entire bridge width. This requirement is essential to ensure that the overall bridge width is within the specified tolerances and that there is no misalignment. Any misalignment of the holes will be cause for rejection of the affected slab panels. Do not drill or core holes into the slab panels.
440.03.19 Marking, Handling, Shipping, and Storage. Mark each member with an erection
mark for identification, weight marks for beams 6000 lb or more, and inspection stamps. For beams, paint the erection marks on the top surface of the top flange. Do not place markings of any kind on any surface of a beam that will be visible in the completed structure. Mark slab panels with an individual, consecutive identification mark at a permanently exposed location. The identification mark shall match that shown on the approved working drawings. Furnish an erection diagram clearly indicating erection marks that show the position of the member in the structure. 2025 STANDARD SPECIFICATIONS FOR CONSTRUCTION AND MATERIALS Utilize the cast-in-place lifting devices and a sufficient number of cranes and spreader beams whenever the prestress concrete members are lifted. Furnish copies of material orders and shipping statements. Show the weight of each individual prestress concrete member. During shipment, ensure that blocking is placed at intervals that will prevent sag and distortion. Ship all members in the upright position, adequately braced and supported to dampen vibrations during transport as shown on the working drawings. Members too long to fit inside of a truck or trailer shall not cantilever beyond the bed more than one quarter of their length. Support members too long to comply with this requirement on dollies, additional vehicles, or other vehicles that will support the long pieces as approved. Load restrictions are as specified in GP 5.10. Do not ship prestress members until approved, at least five days have elapsed since the prestress transfer, and the minimum 28 day compressive strength has been attained. Store beams off the ground in an upright position. Protect them as far as practical from surface deterioration, and keep them free of accumulations of dirt, oil, and other deleterious material.
440.03.20 Erection. Refer to 430.03.27, 430.03.28, 430.03.29, 430.03.31, 430.03.32, and
430.03.33 Slab Panels. Follow the following sequence of operations for the erection of slab panel units.
a.Immediately prior to erecting slab panels, clean the abrasive blasted shear key surfaces with compressed air, stiff bristle fiber brushes, or vacuuming.
b.Pull the slab panels together and field tighten in the transverse direction using tie-rods to the initial tensioning force as specified in the contract plans. For beams with more than two lateral tie-rods, tension lateral tie-rods near mid-span first and then progress towards the ends of the beam. Alternate left and right of mid-span for beams with five lateral tie-rods.
c.Isolate lateral tie-rods from shear key grout by installing expandable spray foam sealant at all tie-rods locations, following the manufactures guidelines and as detailed in the Contract Documents.
d.Seal the joint below the shear keys using an approved method.
e.Once the expandable spray foam sealant has met the manufacture's curing requirements, procedures for placement of the shear key grout may begin.
f.Clean the shear key surface with compressed air and keep it moist until the grout is placed. 2025 STANDARD SPECIFICATIONS FOR CONSTRUCTION AND MATERIALS
g.Grout the shear keys by overfilling the joints. Drive the grout or compactly tamp it into the keyways; do not vibrate. After 5 minutes, strike off the excess grout flush with the top of the panels. Follow the manufacturer’s recommendations for grouting in cold or hot weather.
h.Start curing of the shear key grout immediately after the grout has been finished, but do not leave any portion of the grout uncovered for more than 45 minutes after placement.
i.Keep the surfaces wet, even in areas where there is no ready water supply.
j.Cure the shear key grout for three days with burlap or cotton mats as specified in
420.03 09(b) or 420.03.09(d), respectively.
k.Allow a minimum of 24 hours between grouting of shear keys and final tensioning of lateral tie rods provided temperature is 70 F and above when shear key grout is placed. If temperature is below 70 F during the initial 24 hours, cure for a total of 72 hours or according to the approved manufacturers specifications. Contractor has the option to provide cold weather protection to ensure temperature does not fall below 70 F during the initial 24 hours.
l.Tension lateral tie-rods to final tensioning force according to the Contract Documents following procedure details above for beams with more than two lateral tie-rods.
m.Perform field tightening by placing the washer and nut on the tensioning end of the tie-rod and running them down to the recessed concrete face. Attach a jacking assembly or other type of loading apparatus to the threads extending beyond the nut. Provide the Engineer with certification that the gauge or other load measuring device has been calibrated within one year; however, the Engineer may require the load measuring device to be recalibrated if it appears to have been damaged or mishandled. Use a loading apparatus capable of applying a load to the tie-rod nut equal to 120 000 lb. Maintain the load until the tie rod nut is snug tight as specified in 430.03.17(d). Do not use a torque wrench to apply the tensioning load. Equipment may be placed on the slab unit prior to placing the concrete overlay if all slab units are in place, the tie-rods have been tensioned to the final tensioning force according to the Contract Documents, and the shear key grout has met the curing requirements.
440.03.21 Bearing Pads. Store them at the site on suitable blocking or platforms at least 4 in.
above all surfaces and vegetation. Keep free from vegetation growth and accumulations of dirt, oil, and other foreign material. Coat the surfaces of the concrete bearing areas that will be in contact with the bottom of the bearing pads and the full contact area of the bottom of the bearing pads with epoxy adhesive. Adhere to the manufacturer’s recommendations for mixing and applying the epoxy adhesive material. Applying epoxy adhesive when surface temperatures are at least 50 F with a predicted ambient 2025 STANDARD SPECIFICATIONS FOR CONSTRUCTION AND MATERIALS 2025 STANDARD SPECIFICATIONS FOR CONSTRUCTION AND MATERIALS temperature for the next four hours of 50 F or above. Ensure that the surfaces are clean, dry, and sound. Be prepared to use water jets, abrasive blasting, and air blasting, for satisfactorily cleaning the surfaces. Accurately set the bearing pads in the epoxy adhesive and secure them in place by blocking or other mechanical means until the adhesive sets.
440.03.22 Placing and Finishing Concrete Overlay. Place and finish the overlay as specified in
420.03 including superstructure placement restrictions. Unless otherwise noted on the contract plans, place the entire bridge slab overlay in one continuous
pour. No transverse or longitudinal joints will be permitted. Place the finishing machine’s supporting rails outside the overlay limits. Do not use hold down devices that are shot or drilled into the concrete. Submit plans for anchoring support rails and the concrete placing procedure for approval. Take precautions to secure a smooth riding surface as specified in 420.03.07(d). Prior to placement operations, review the equipment, procedures, and personnel with the Engineer. Place the concrete overlay using the following sequence of operations.
a.Placement of the overlay may occur once the parapet and curbs have cured for 24 hours. Concrete curbs and parapets may be placed once the lateral tie rods have been tensioned to the final tensioning force and the shear key grout has met the curing requirements.
b.Before placing the reinforcing steel mat, thoroughly clean and water blast the entire surface that will be in contact with the overlay then clean the surface with air blast.
c.Place and tie the support chairs to the underside of the reinforcing mat to locate the reinforcing mat 2 -1/2 in. clear of the top of the deck overlay.
d.Set-up the finishing screed and make a dry run of the finishing operation to verify that the reinforcing is properly located and the finished deck elevation shown on the plans can be achieved.
e.Prior to concrete placement, air blast the surface to receive the overlay to remove any foreign material that may have collected since the water blasting. Following the air blast, moisten the entire surface with a misting operation for at least 1 hour immediately prior to the placement of the concrete overlay. Keep the top surface of the prestressed slabs moist until the placement of the overlay and throughout the placement operation and remove any puddling of water prior to and throughout the concrete placement.
f.Allow no vehicular traffic on the prepared deck surface before overlay placement.
440.04 Measurement and Payment
Prestressed concrete members will not be measured but will be paid for at the Contract lump sum price for the pertinent Prestressed Concrete Beams or Prestressed Concrete Slab Panels item. The payment will be full compensation for all concrete, forms, reinforcing, bearing pads, steel strands, sheathing, steel components, steel rods, inserts, tensioning, grout, bearing assemblies, epoxy adhesive, testing, furnishing, and applying concrete protective coatings when specified, transporting, storage, erection, and for all material, labor, equipment, tools and incidentals necessary to complete the work.
440.04.01 Concrete overlay for the precast concrete slab bridge deck will not be measured but will
be paid for at the Contract lump sum price for the pertinent Superstructure Concrete item. The payment will be full compensation for surface preparation, overlay bonding grout, furnishing, placing, finishing, curing and grooving the concrete overlay; fabricating, coating and placing the epoxy coated welded steel wire fabric or reinforcing steel within the concrete overlay, roadway angle, and for all material, labor, equipment, tools, and incidentals necessary to complete the work. 2025 STANDARD SPECIFICATIONS FOR CONSTRUCTION AND MATERIALS 450 — RETAINING WALLS 2025 STANDARD SPECIFICATIONS FOR CONSTRUCTION AND MATERIALS CATEGORY 400 STRUCTURES SECTION 450 — RETAINING WALLS
450.01 Description
Construct cast-in-place reinforced concrete footings and stems conforming to the AASHTO definitions of rigid retaining walls. When retaining wall mounted noise barriers are specified, the anchorage assemblies are included in the retaining wall. All components shall be as specified unless prior approval for alternatives is obtained from the Administration. When piles or drilled shafts (caissons) are specified, refer to Sections 410 and 412, respectively. 450.01.01 Preapproved Alternate Retaining Walls. Alternate retaining walls may only be used when specified. Only those retaining walls specified will be permitted. All other retaining walls, even though they are preapproved or have been previously used on Administration projects, are prohibited for use. The Administration will not consider any other alternate retaining walls as a value engineering change proposal. Enforcement. These requirements will be enforced on all projects. Preapproved Alternate Retaining Wall List. Alternate retaining walls are selected from the list of Preapproved Alternate Retaining Walls , which is maintained by the Office of Structures. Procedures for adding products to the prequalified list may be obtained from the Office of Structures. Alternate retaining walls that have been previously used on Administration projects without complying with the preapproval requirements shall be formally submitted through these procedures before they will be added to the Preapproved Lists for consideration to be used on future projects. These and other retaining wall systems may be submitted for addition to the Preapproved Lists, but the Administration will not permit these submittals to be used on an advertised or awarded project. Deviations. Submit any proposed deviation in materials, post size or shape; panel size or shape; reinforcing type, size, or placement from what is shown in the Contract Documents or from the preapproved alternate retaining wall details on file in the Administration’s Office of Structures. All costs for reviews, whether the details are accepted or rejected, shall be borne by the Contractor. Any fabrication or creation of any retaining wall element that is a deviation and is made prior to written approval of the Administration shall be at the risk of the Contractor.
Source: Maryland Standard Specifications for Construction and Materials, 2025 Edition. Pages 534–548 of 1,113.