520 PLAIN AND REINFORCED PORTLAND CEMENT CONCRETE PAVEMENTS
From MDOT Policy Manual
- Construct plain and reinforced portland cement concrete pavements.
Portland Cement Concrete and Related Products 902 Reinforcement Steel 908 Joint Materials 911 Portland Cement Concrete Plant 915.03 Epoxy Coating for Reinforcement 917.02
- Reinforcement, including load transfer assemblies, tie bars, deformed steel bars, and longitudinal tie devices shall meet Section 908 and be epoxy coated.
- Within 30 days prior to the start of paving operations, submit a proposed paving plan for approval. Include the production plants, location of the plants with respect to project site, equipment, proposed material sources, and indicate whether the fixed form method or slip form method is proposed.
- Protect the pavement against damage from all causes. Repair or replace damaged pavement.
- Mix, place, and finish concrete when natural light is sufficient, or with an approved artificial lighting system.
- 520.03.01 EquipmentAll machinery, tools, and apparatus necessary for the proper construction and acceptable completion of the work, together with the necessary supplies for upkeep and maintenance.. All equipment, including the production plant and paving equipment, is subject to approval. The plant, including central mixers, batching plant, truck mixers, and hauling equipment shall meet Section 915. Have the plant ready for inspection at least 48 hours prior to the start of construction operations. Have the paving equipment on the job site and ready for inspection at least 24 hours prior to the start of construction operations.
- Slip form pavers shall be self-propelled on crawler tracks. No other tractive force shall be applied. The paver shall be capable of being automatically controlled for both alignment and grade.
- The equipment and methods used shall provide a means to obtain the prescribed weights within the allowable tolerances, to obtain the consistency specified with a minimum amount of water, to achieve proper placement of the mixture in a condition of maximum density with no segregation, and to finish and cure the pavement as specified herein.
- 520.03.02 Weather Restrictions.
- (a) Temperature and Surface Conditions. Begin concrete placement when the ambient air and surface temperatures are at least 40 F and rising. Discontinue placement whenever the temperature falls below 40 F. These requirements may be waived for incidental concrete construction. Do not place concrete on a frozen base.
- (b) Precipitation. Have sufficient approved material on hand to cover freshly placed concrete as protection against precipitation.
- (c) Wind. Cease placement when the EngineerAny person designated by the Administrator or the procurement officer, acting directly or through his duly authorized representative, such representative acting within the scope of the particular duties assigned to him or of the authority given him. determines that wind conditions may have a detrimental effect on the work.
- When weather conditions differ from these limits, placement of material en route is at the ContractorAny person having a Contract with a procurement agency. Contractor does not include an employee with an employment Contract, or an employee organization with a collective bargaining agreement.’s risk.
- If the EngineerAny person designated by the Administrator or the procurement officer, acting directly or through his duly authorized representative, such representative acting within the scope of the particular duties assigned to him or of the authority given him. for any other reason stops placement, dispose of enroute material at no additional cost to the AdministrationShall mean any one of the Administrations within the Maryland Department of Transportation, as listed in GP 1.02..
- 520.03.03 Foundation. Construct the foundation as specified. Construct the total width of the foundation to the width of the pavement plus at least 4 in. outside the base of the fixed form or the outermost edge of the slip form paver track or wheel. No additional payment will be made for the extended width. Ensure that the foundation is approved prior to the installing fixed forms or the use of slip forms.
- 520.03.04 Forms. Use steel side forms having a thickness of at least 7/32 in. and a depth equal to the edge thickness of the pavement. Forms shall have a base equal to the height, a flat-flanged tread or top surface not less than 2 in. wide, and be of sufficient strength to resist all loads applied during the paving process. Do not use built up forms or warped forms. Use form sections that are at least 10 ft long except for installation along curves with a radius of less than 200 ft. For a curve radius less than 200 ft, use form sections that are no more than 6 ft long or use curved forms. All form sections shall have stake sockets that will accommodate a 1 in. diameter steel stake. Sections 10 ft or greater in length shall have at least three sockets. Sections less than 10 ft long shall have at least two sockets.
- Fasten keyways rigidly to the form. Provide holes through both the form and the keyway to accommodate tie bars or dowels.
- Place the forms to a tolerance of 1/8 in. in 10 ft for the top, and 1/4 in. in 10 ft for the face. Provide a means for locking the ends of abutting sections. Forms shall be clean and coated with an approved form release compound. Remove or repair forms that are bent, deformed, or broken.
- Set grade controls at intervals of no more than 25 ft. Set the forms at least 400 ft ahead of concrete placement. When the foundation has been disturbed subsequent to the forms being set to the correct grade, make corrections as approved. Check the alignment and grade for conformance with the Contract DocumentsThe written agreement executed between an Administration and the successful bidder, covering the performance of the work and furnishing of labor, equipment and materials, by which the Contractor is bound to perform the work and furnish the labor, equipment and materials, and by which the Administration is obligated to compensate him therefore at the mutually established and accepted rate or price. The Contract Documents shall include the Invitation for Bids, Notice to Contractors, Instructions to Bidders, Proposal, Contract Forms and Bonds, General Provisions, Specifications, Supplemental Specifications, all Special Provisions, all Technical Provisions, all Plans and Notices to Proceed, also any written Change Orders and Supplemental Agreements that are required to complete the construction of the work in an acceptable manner, including authorized extension thereof. Use an approved device such as a scratchboard and make any necessary corrections prior to concrete placement.
- Wooden forms may be approved for use in exceptional cases, such as for curves of very short radius or when a nonstandard length of straight form is required.
- 520.03.05 Slip Form Paving. Unless otherwise approved, the minimum width of slip form paving shall be 24 ft. The total foundation width shall be graded using machine methods.
- Set grade controls using string lines at intervals of no more than 25 ft. Construct the foundation as specified in 520.03.03; completed and approved at least 1000 ft ahead of the paver before paving begins. Stop paving whenever the paving machine comes to within 200 ft from the end of the approved foundation, and install a bulkhead construction joint. When paving adjacent to an existing pavement, the portion of the equipment supported by the existing pavement shall have wheels with rubber tires or crawler treads on protective pads. Maintain a clearance of at least 1 ft from the inner edge of the paver track or wheel to the edge of the existing pavement.
- Slip forms shall be spaced and braced in a vertical position at a uniform and constant width, and of a length sufficient to prevent slumping or sagging of the sides and top edges of the pavement slab. Slip form equipment shall be capable of placing and securing embedded tie bars and keyways in proper position in the plastic concrete before the edge of the pavement slab is free of the slip form.
- 520.03.06 Reinforcement. Reinforcement shall be as specified. Maintain the reinforcement in a clean condition, free from foreign material that may prevent proper bonding of the concrete. Secure all reinforcement to prevent displacement or movement.
- (a) Install dowel bars at joints on the approved foundation parallel to the foundation grade, sufficiently ahead of the placement of slab reinforcement and concrete. Coat each dowel bar with an approved water insoluble lubricant. Dowel bars may be machine placed or set on approved chairs or prefabricated assemblies. Maintain proper alignment, depth, and spacing.
- (b) Tie bars for longitudinal construction joints may be placed on chairs or machine placed so that upon the initial set of the concrete they are at the proper alignment, depth, and spacing, and at right angles to the center line of the pavement. Prior to use, submit chairs and machine placement devices for approval.
- (c) Furnish fabric and mat reinforcement in flat sheets. Keep the material flat during placement. Maintain the specified reinforcement clearance.
- (d) When using slip forms, the tied reinforcement bars or prefabricated mats may be installed ahead of the placement of concrete by being supported on chairs. Reinforcement installed in this manner shall be in place at least 500 ft ahead of the paver or a two-hour run of the paver before any paving may begin. Stop paving whenever it comes to within 100 ft of the end of the steel placement, and install a bulkhead construction joint.
- 520.03.07 Concrete Placement. Prior to placement of the concrete, ensure that the foundation is in a moist condition. In addition, if the concrete is exposed to the direct rays of the sun and the ambient temperature is 70 F and rising, sprinkle the forms and reinforcement with cool water just before placement of the concrete. Once deposited within the forms, keep any rehandling to a minimum.
- Where concrete is to be placed adjoining a previously constructed lane of pavement, mechanical spreading and finishing equipment may be operated upon the existing lane of pavement only after the existing concrete has reached a compressive strength of 3000 psi in conformance with 902.10.03. Wheels that rest on the previously completed concrete shall be flat without flanges, at least 3 in. wide, and located far enough from the edge of the slab to preclude spalling or damage. Perform sampling for control testing at the time of concrete placement and as specified in 902.10.08.
- Deposit the total depth of the slab in a single layer except as otherwise specified herein or approved. For pavement constructed using bar mat or wire fabric reinforcement, place the concrete in two layers, unless it is demonstrated that the bar mat or wire fabric can be properly supported on approved devices.
- Single Layer Placement. Set the reinforcement on chairs capable of maintaining the stability and proper elevation of the reinforcement. Welding of reinforcement to the chairs in lieu of wire ties will be permitted, except welding for epoxy-coated reinforcement will be permitted only if the epoxy coating is applied after the welding. Repair damage to epoxy coating using materials specified in 917.02.
- Two Layer Placement. Place the concrete and bar mats or wire fabric reinforcement in a continuous operation. First, place the concrete to the specified depth of reinforcement. Then place the reinforcement on the freshly deposited concrete; follow immediately with the second layer of concrete.
- 520.03.08 Consolidation of Concrete.
- Fixed Form Paving. Consolidate the concrete by using immersion type vibrators. Vibrators shall advance with the paving equipment and be set at the spacing and depth necessary to clear reinforcement by 1/2 in. Maintain the amplitude required to obtain thorough consolidation within the slab, along the faces of the forms, and at the joint assemblies. Avoid excessive vibration that results in segregation, and any vibrator contact with the side forms, joint assemblies, or underlying material. The consolidation system and settings are subject to approval.
- Slip Form Paving. Concrete consolidation systems shall be incorporated in the paving equipment. Submit the systems for approval.
- 520.03.09 Finishing.
- Machine Finishing. The machine shall be equipped with two transverse screeds with provision for adjustment to ensure that the concrete is at the specified crown and grade. Following the transverse screeds, the concrete shall be screeded longitudinally. The width of the working face of the screeds shall be at least 6 in. Use a chevron ("V" type) nonreciprocating finishing float or other approved type. The float shall be suspended from a frame that does not ride directly on the forms. Following the finishing float, use a long handled scraping straightedge 10 ft long to bring the pavement to the correct grade. When the finishing machine is operated over concrete that has partially set, make provisions to prevent damage to the concrete by the machine wheels.
- Hand Finishing. With approval, hand finishing may be substituted for machine finishing. Do not use rakes for handling concrete.
- 520.03.10 Slab Surface and Thickness Checks.
- Surface Check. After finishing, and before texturing of the concrete, check the entire surface by using an approved 10 ft long metal straightedge. Limit the surface deviation from a straight line or vertical curve transversely or longitudinally to 1/8 in. in 10 ft.
- Thickness Check. After the pavement is placed and before final acceptance, cut cores by which the EngineerAny person designated by the Administrator or the procurement officer, acting directly or through his duly authorized representative, such representative acting within the scope of the particular duties assigned to him or of the authority given him. will check the thickness. Perform coring per MSMT 552. Locate cores every 1000 ft for each lane unless otherwise specified or directed. Fill core holes at no additional cost to the AdministrationShall mean any one of the Administrations within the Maryland Department of Transportation, as listed in GP 1.02.. Pavement deficient in thickness by more than 1 in. will be unacceptable. Remove and replace the full pavement section. Deficiencies up to 1 in. will be subject to reduced payment as specified in 520.04.
- 520.03.11 Texturing and Edging.
- Texturing. Texture the surface of the pavement with longitudinally tined grooves using a mechanical device (such as a wire comb), following concrete finishing and surface check. The device shall have a single row of tines with nominal widths of 5/64 inch to 1/8 in. each. The nominal spacing of the tines shall be 3/4 ± 1/8 in. center-to-center. The nominal depth of the tined grooves shall be 1/8 ± 1/32 in. The device shall have horizontal and vertical controls to ensure straight, tined grooves of uniform depth.
- Begin texturing when the concrete is plastic enough to allow texturing to the depth specified, but dry enough to prevent the concrete from flowing back into the grooves. Avoid overlaps and tearing of the concrete. Protect a 2 to 3-in. wide strip of pavement surface from tining for the length of the pavement; centered along longitudinal joints. Extend the tining as close as possible to the edge of any adjacent pavement to be placed without damaging the edge. Do not tine areas 6 in. from the edge of pavements where adjacent pavement is not placed. Do not tine areas 1 ft from the curb in closed sections. Hand operated tining equipment that produces an equivalent texture with the specified spacing may be used on small or irregularly shaped areas. The completed textured finish shall exhibit a uniform appearance.
- Edging. Edge textured transverse and longitudinal slabs using a 1/4 in. radius edging tool when the concrete has reached its initial set.
- 520.03.12 Curing. Following texturing and edging, cure the concrete for at least 72 hours. Whenever the ambient air temperature falls below 40 F during the curing period, use insulated blankets to maintain the concrete temperature above 40 F. Use insulated blankets in addition to any curing material that is used. Provide a sufficient number of high/low thermometers to monitor the temperature of the concrete. Cure the concrete using one of the following methods:
- (a) Liquid Membrane Forming Compound. Use a liquid membrane forming compound that is in conformance with 902.07.03. Apply the material to the surface as soon as the free water has disappeared. Use an approved spraying machine having drive wheels that straddle the freshly placed concrete. Have standby equipment on site in the event of failure of the spraying machine. The spraying machine shall be equipped with an adequate wind guard and be capable of producing a fine spray of material that covers the surface with a uniform continuous film. Apply the compound in two applications, each at a rate of 1/2 gal/200 ft2. Maintain the film free of pin holes, checks, cracks, peelings, and other imperfections. Correct discontinuities in the film by the application of an additional coat to the affected area within 30 minutes of the original coat. If sprayed surfaces are subjected to damaging rainfall within three hours after the second application, respray the surface at no additional cost to the AdministrationShall mean any one of the Administrations within the Maryland Department of Transportation, as listed in GP 1.02..
- Use rope or other approved masking methods to keep the vertical surfaces of longitudinal and transverse joints free of curing compound. Protect the sprayed surfaces to maintain the continuity of the membrane. Application of compound by hand operated spraying equipment in irregular areas shall be as directed.
- (b) Burlap Curing. Place burlap conforming to 902.07.01 on the freshly placed concrete as soon as practical, without damaging the concrete. Overlap the burlap to provide a double thickness on the entire surface. Saturate the burlap with water before placement and keep it continuously wet during the curing period.
- (c) Cotton Mat Curing. Place cotton mats conforming to 902.07.04 on the freshly placed concrete as soon as practical, without damaging the concrete. Saturate the mats with water before placement and keep them continuously wet during the curing period.
- (d) Sheet Materials. Place sheet materials conforming to 902.07.02 on the freshly placed concrete as soon as practical without damaging the concrete. Overlap the material at least 1 ft and extend it outside the slab. Secure all laps and edges in place to provide continuous contact of the sheet with the pavement surface.
- 520.03.13 Form Removal of Fixed Form Paving. Unless otherwise directed, leave forms in place until the concrete has set at least 12 hours. If the sides of the slab show no damage, continue curing for the remaining 60 hours of the 72 hour curing period. Repair damaged or honeycombed areas and then cure for an additional 72 hours.
- 520.03.14 Joints. Construct joints in conformance with the details specified, perpendicular to the finished grade of the pavement, and sealed as specified in Section 523. Transverse expansion and contraction joints shall be straight and continuous from edge to edge of the pavement.
- (a) Transverse Construction Joints. Place a transverse construction joint at the end of each day’s placing operations and at any other points within a paving lane where concrete placement is interrupted for 30 minutes or longer. Locate these joints at a planned joint except in the case of an equipment breakdown. When concrete placement cannot be continued, the transverse construction joint may be located within the slab unit but not less than 10 ft from a planned transverse joint. Dowel transverse construction joints as specified, and saw the joints in conformance with (c)(1).
- (b) Expansion Joints. Form expansion joints by placing a preformed filler material conforming to 911.02. Use approved metal supports to hold the filler securely in position. Leave the metal supports in the pavement. Install a removable metal channel cap bar to hold the parts of the joint in proper position and to protect the filler from damage during concreting operations. Remove the cap bar without damaging the pavement to provide a space for sealing the joint. Fit adjacent sections of filler tightly together, and extend them across the full width of the paving lane to prevent concrete from entering the expansion space. Use a joint filler of the specified type, thickness, and width to form expansion joints around structures and features that project through, into, or against the pavement.
- (c) Contraction Joints. Construct longitudinal and transverse contraction joints by sawing. If gravel aggregate is used, tool the joint, or form it by using an approved insert.
- (1) Sawed Joints. Sawcut to the specified depth using a 1/8 in. blade. Base the time of sawing on current and anticipated weather conditions and to prevent uncontrolled cracking of the pavement. Start the sawing operation as soon as the concrete has hardened sufficiently to permit cutting the concrete without chipping, spalling, or tearing. Respray damaged membrane cured surfaces as soon as the surface is dry. After completion of the curing period, widen the upper portion of the groove by sawing to the specified width and depth. The saw blades may be single or gang type, with one or more blades mounted in tandem. Do not sawcut into load transfer devices. Immediately after sawing the joint, thoroughly flush the saw cut and adjacent concrete surface with water to remove all waste.
- (2) Insert Type Contraction Joints. Construct insert type contraction joints by installing a preformed insert in the plastic concrete to form a weakened plane to induce cracking. Use a machine equipped with a vibratory bar for cutting a groove in the plastic concrete for placement of the insert and for vibrating the insert into place. Arrange vibration units to distribute vibration uniformly throughout the bar. The intensity of vibration shall be adjustable as necessary to form a groove of proper size for the filler, to force the insert into the plastic concrete, and to consolidate the concrete around the insert. Immediately following final machine finishing, install the insert at the specified location and required depth for the full width of the paving lane. Ensure that there are no more than two joint spacings between the finishing machine and the inserter. For concrete placed by slip form pavers, support the edges of the plastic concrete to prevent slumping during the vibration and placement of the inserts. Join adjacent sections of the joint inserts within each slab securely together, and thoroughly consolidate the concrete against the full depth of the insert. Maintain the insert perpendicular to the finished grade of the pavement and straight in alignment. Keep the top of the insert flush or not more than 1/8 in. below the pavement surface. Following placement of the insert, use the vibratory float in lieu of hand floating and troweling. Perform any additional straightedge and texturing operations without disturbing the insert.
- After the completion of the curing period, remove the top portion of fiberboard fillers or sawable preformed inserts by sawing with a power saw as approved.
- 520.03.15 Pavement Profile. Refer to pavement surface profile requirements specified.
- 520.03.16 Opening to Traffic. The pavement may be opened to vehicular traffic after having attained a compressive strength of 3000 psi. Field samples will be tested per T 23.
- 520.03.17 Dowel Bar Placement Checks. After each day’s placement of the PCC pavement is complete and cured, the alignment and placement of the dowel bars will be checked by the AdministrationShall mean any one of the Administrations within the Maryland Department of Transportation, as listed in GP 1.02. using a non-destructive test method. All joints will be tested to determine conformance with the following.
- (a) Vertical Skew. The vertical skew shall be no greater than 1/2 in. tolerance over a 12 in. length of dowel bar.
- (b) Horizontal Skew. The horizontal skew shall be no greater than 1/2 in. tolerance over a 12 in. length of dowel bar.
- (c) Depth of Dowel Bar. The dowel bar shall be located within the middle third of the slab thickness. A minimum cover depth of 3 in. is required for the top, and a minimum cover depth of 2.5 in. is required for the bottom.
- (d) Joint. The joint saw cut shall be in the middle third of the dowel bar length. The minimum embedment length on either side of the joint shall be 4 in.
- (e) Missing Dowel Bar. A missing dowel bar shall be considered misaligned.
- A joint is in nonconformance or misaligned if any dowel bar in the wheelpaths are not in conformance.
- (a) For 12 ft wide or narrower lanes, the 3 outermost bars and 3 bars under the inside wheelpath must be in conformance.
- (b) For widened slabs, the 3 bars under the outside wheelpath and the 3 bars under the inside wheelpath must be in conformance.
- (c) In addition, a joint is in nonconformance or misaligned if at least 3 dowel bars in non-wheelpath areas do not conform to the above.
- After testing is complete, the percentage of those joints not meeting the above will be determined. Deficiency will be subject to a reduced payment as specified in 520.04. This is in addition to the reduced pay for slab thickness.
520.04 MEASUREMENT AND PAYMENT.
- Plain and reinforced portland cement concrete pavements will be measured and paid for at the Contract unit price per square yard for the pertinent Portland Cement Concrete Pavement item. The square yard measurement will be computed on the basis of plan width and as-built length measured along the pavement center line. The payment will be full compensation for all concrete, forms, reinforcement steel, chairs, epoxy coating, finishing, curing, joints, joint construction, saw cutting and joint sealing, and for all material, labor, equipment, tools, and incidentals necessary to complete the work.
- 520.04.01 Pavement Thickness Price Adjustment. Payment for areas that are accepted at a reduced price for deficient thickness will be adjusted by the factors shown in the following table. Deficiencies will be determined by procedures specified in 520.03.10. There will be no additional payment for excess thickness.
PAVEMENT THICKNESS PRICE ADJUSTMENT DEFICIENCY IN INCHES PERCENT OF PAYMENT CONTRACT UNIT PRICE 0.00 to 0.20 100 0.21 to 0.30 80 0.31 to 0.40 72 0.41 to 0.50 68 0.51 to 0.75 57 0.76 to 1.00 50 Greater than 1.00 *See 520.03.10 0*
- 520.04.02 Dowel Bar Misalignment Price Adjustment. Payment for the percentage of joints accepted at a reduced price for not conforming to the proper alignment will be adjusted by the factors shown in the following table. Alignment is determined by procedures specified in 520.03.17. This shall be a reduced price for the portland cement concrete pavement item in addition to any reduction due to pavement thickness.
DOWEL BAR PRICE ADJUSTMENT Percent of Misaligned Joints * Percent of Payment, Contract Unit Price ** 0 to 10 100 >10 to 15 95 >15 to 20 90 >20 to 25 85 >25 to 30 75 >30 to 50 70 Greater than 50 Corrective action***
- *This is the percentage of all joints tested.
- **This price adjustment is to the PCC price and not for the dowel bars or joints. This is in addition to any price adjustment for pavement thickness.
- ***Corrective action may include removal and replacement, dowel bar retrofit, or other method approved by the AdministrationShall mean any one of the Administrations within the Maryland Department of Transportation, as listed in GP 1.02..