602 - Concrete Pavement Construction
- 1 GENERAL
- 2 MATERIALS
- 3 EQUIPMENT
- 4 PRECONSTRUCTION
- 5 CONSTRUCTION
- 5.1 Placing and Finishing Concrete
- 5.2 Production Paving Projects
- 5.3 Opening to Traffic
- 5.4 Pavement Coring
- 6 INSPECTION & TESTING
- 6.1 Inspection During and Following Concrete Placement
- 6.2 Inspection Focus
- 7 MEASUREMENT, DOCUMENTATION, & PAYMENT
Before paving operations start, the paving Inspector should verify that all materials that need to be incorporated in the pavement have been tested and accepted. Most materials will be stockpiled in the Contractor’s yard on the project site. Often this is also the location of the batching plant.
When the load transfer assemblies arrive on the project site, call Region materials personnel so they can verify that the assemblies were built according to the standard plans. Acceptance by Region materials personnel is the required documentation.
Check to see if the dowel bars and the fiber joint filler material are certified. Sampling and testing may be required.
After the Contractor starts to set the load transfer assemblies on the grade, they must be visually inspected for:
The entire bar is to be coated with an approved epoxy coating to prevent corrosion, and the entire bar’s length is to be coated with an approved material to prevent concrete from adhering to the bar (typically beeswax).
Any material of uncertain origin should be stored separately and not used until it is determined that it meets specification requirements.
Visually inspect the handling and storage of all materials used in the concrete paving operation.
Contractor must cover load transfer assemblies, if stored on site for more than six (6) months.
These items should be checked for certification or sampled and tested when they arrive on a project.
- Check certification or sample and test each batch or lot.
- Material may be in drums or in a large tank. Inspection consists of seeing that the material is not contaminated or diluted and that it is mixed according to the manufacturer’s recommendations.
- A curing compound should not be used when stored from one construction season to the next without resampling and testing.
- Check yield of material to confirm correct coverage.
Subsection 602.03 of the Standard Specifications for Construction set forth the equipment requirements used in the concrete paving operations. The specific equipment requirements have been greatly reduced during recent years. The Department is less concerned about the specific type or piece of equipment the Contractor uses and more concerned with the result.
Equipment capacity and capability will not be the same on a small urban widening project as on a high production rural project. If there are questions about the condition and/or equipment capability, contact the Engineer or the State-Wide Concrete Paving Specialist.
The Contractor must have determined, using equipment or hand work, how they will do the following:
- Trim the base;
- Deliver and place the concrete on the grade in a timely manner and without segregation;
- Install lane ties and / or reinforcement, if required;
- Consolidate and finish the concrete including straight edging and floating;
- Edge and texture the surface;
- Cure the pavement; and,
- Saw and seal the joints.
Concrete forms serve the dual purpose of containing the plastic concrete and providing a track on which most of the concrete placing and finishing equipment rides.
After the aggregate base or open-graded drainage course (OGDC) is placed, shaped and compacted, it is brought to final grade, usually by an automatic trimmer. This machine operates off a string line for line and grade. The string line should be checked for sags before the final cut on the aggregate base, as most slipform paving equipment runs on the aggregate base for final grade.
After the base is properly compacted and fine trimmed, transfer assemblies are placed at joint locations. The Inspector should work closely with the Contractor’s crew while they are setting these assemblies. It is preferred that joints connect to one corner of drainage structure castings. This will help prevent random cracking.
The assembly itself holds the dowel bars in position so they will not move during concrete placement and consolidation.
- The distance between joints must match the Standard Plans.
- The assemblies must be positioned at right angles to the centerline as shown in Figure 602-5.
- After they are properly positioned, they must be staked to the base using six pins per basket assembly.
The basket pin must be in contact with the lower horizontal wire as shown in Figure 602-6.
The DBI is an approved mechanical device that automatically installs load transfer bars into the full-depth plastic concrete at, at the required depth and location, and properly consolidates the surrounding concrete. It shall be capable of consolidating the concrete around the dowel bars such that no voids exist, without the supplemental use of hand-held vibrators. The device may be used in lieu of load transfer assemblies.
When a dowel bar inserter (DBI) is used to install load transfer bars, the bars shall be placed at the same spacing as detailed for dowel bar assemblies in the Standard Plan R-40 series. The pavement shall be placed and consolidated full depth prior to insertion of the dowel bars.
The alignment of the dowel bars is crucial to the life of the pavement. If a dowel or group of dowels is not perfectly aligned longitudinally with the pavement, the life of the pavement and the joints can be significantly reduced. Therefore, wet depth and position alignment checks need to be performed to confirm proper depth, vertical and horizontal alignment of the dowels are being provided by the paving equipment and DBI. The Contractor will take the measurements of the inserted dowels to verify the dowels meet the specification tolerances. These measurements will be made every 500 feet and as required by their Quality Control Plan. The Engineer will witness these measurements and may request documentation of these measurements.
Any out of tolerance joints shall be marked and replaced at the Contractor’s expense. If the dowels are consistently out of tolerance with respect to alignment and/or depth, the Contractor must stop production paving and take steps to correct the alignment problems. Dowel alignment problems can be created when too much concrete, commonly referred to as head, develops in front of the paver that has the DBI mounted to it. The amount of head carried must be in accordance with the DBI and paver manufacturer’s recommendations to provide consistent proper dowel alignment.
Many other factors can contribute to dowel alignment and depth problems when using a DBI. The important thing to remember is to be sure the DBI is consistent when placing dowels throughout each day’s production. Periodic wet and dry alignment/depth checks are necessary to confirm consistency.
The Contractor must construct test headers throughout the project to verify proper consolidation of concrete around the dowel bars and alignment of dowel bars in hardened concrete. Three are required in each direction of travel, but the Engineer may request more depending on Contractor quality control measurements. See picture and spreadsheet for checking alignment of test header.
Expansion caps must be securely placed on opposite unwelded ends of the bars, with 1 inch space left between the end of the bar and the inside of the cap. Most expansion caps have inverted dimples 1 inch from end of cap as an indicator. When using the slipform paving method, the outside 4 inches of the expansion felt will be removed and replaced after the paver goes by. Felt paper tabs will be placed across the finished concrete for proper alignment of the sawing operation.
The Contractor must mark the center of the load transfer assemblies so that a saw cut can be made over these joints after the concrete has hardened. Usually, this is accomplished by setting a basket pin opposite the center of the joint outside the pavement limits and a ribbon is attached to the stake to identify its location.
When setting load transfer assemblies for a widening, do not use the previous saw cut as a method of aligning the basket unless checked for angles. Align this joint with a right angler, or the 3-4-5 triangle method described in Figure 602-5.
Concrete will be produced in a central mix plant. Concrete will be transported to the job site in dump trucks or agitator trucks. The allowable haul time will depend on the type of hauling unit and the concrete temperature, as stated in subsection 1001.03.E.3 .
The Contractor will provide a ticket system to record the batch numbers with information required by subsection 1001.03.A.3. See Delivery Tickets section below.
The concrete spreading operation should be kept reasonably close to the pavers so no more than 30 minutes elapse between layers of concrete, or between placing and finishing the concrete (see subsection 602.03.D ).
Tie bars are placed at the center longitudinal joint. A lane tie bar installer is often mounted on the rear and in the center of the paver. It will place reinforcement bars of proper length and diameter according to Standard Plan R-41 Series.
An Inspector should check the spacing of bars as soon as possible after paving starts. Check the bar depth after finishing operations are complete, as they have a tendency to settle due to the vibration of paving equipment. This is done by using the work bridge to access the longitudinal joint between lanes.
The slipform paver uses a lower slump concrete to minimize edge slump. Therefore, full width vibrators are necessary to eliminate all internal honeycombs. Contractors should have a vibrator monitor as required by subsection 602.03.A.7.
It is important that the slipform paver, or finishing machine, has the correct concrete amount in the screed, or strike-off plates, to prevent overloading that will cause slipping of the track or drive wheels. This will result in chatter bumps on the surface. Inadequate concrete in the screed fronts will leave low spots on the surface.
Form riding finishing machines, and some slipform pavers, have two oscillating screeds that shape the surface of the concrete. For the best results, the front screeds should have about an 8 inch roll of concrete in front of it. The second should have a smaller roll, about 4 inches. A slow, steady forward movement with a uniform supply of concrete in front of the finisher will produce the best surface finish. Slipform pavers are equipped with extrusion plates to form and finish the concrete. Slipform pavers are equipped with spray bars to add water as an aid to finishing but the addition of water should be kept to a minimum. It should not be added continually, but only occasionally when a minor delay has occurred, or for other similar reasons. It is better to use a slightly higher slump initially than to continually add water to the pavement surface. The Contractor should attach burlap to the slipform paver and spray water on burlap.
If a pan float, or other mechanical float, is used behind the slipform paver or the finishing machine, it should leave the concrete surface in a substantially finished condition.
Some slipform paving machines are equipped with transverse screeds for additional floating. Tears or open areas indicate improper screed adjustments, inadequate vibration or perhaps a harsh mix. Attempts to correct the equipment should be made before changing the mix.
The edge condition should be noted immediately behind the slipform paver. The edgers on the paver should be adjusted to minimize edge slump. When the concrete leaves the trailing edge of the edgers, it should slump down and out to the proper width and elevation. For this reason, it is essential to maintain a uniform slump from load to load.
After machine finishing, the slab surface should be checked by the Contractor’s finisher using a 10 foot straightedge and the 5 foot lap method of straight edging. Any high or low areas indicated by the straightedges are to be corrected. The areas needing correction may be hand floated, if necessary, to seal the surface. On slipform paving, the finisher should stop the straightedge about 4 to 6 inches from the edge to keep the edge from slumping due to the added weight of the straightedge.
A concrete overlay is used when existing concrete pavement is to be overlaid with a new concrete surface. The existing concrete typically undergoes hot mix asphalt (HMA) or concrete joint repairs and is then overlaid with an HMA bond breaker layer before the new concrete surface is paved. This is often referred to as an unbounded overlay due to the bond breaker between the old and new concrete.
Random unscheduled daily yield checks, using the random number sheet, on the volume produced by the batch plant should be performed to verify the amount of concrete produced per batch. This volumetric yield check can then be applied to all batches leaving the plant and compared to the computed total volume placed during the day’s production. The yield check should provide a simple verification of the batch ticket volume printed by the batch plant. This procedure should be part of the Contractor’s quality control plan and periodically verified through MDOT quality assurance testing where appropriate. This method of checking the volume of concrete can be used wherever concrete is being paid for by volume.
Grade control is critical when paving a concrete overlay. Overruns can be controlled by monitoring the grade of the surface the overlay is to be placed on prior to paving the bond breaker layer and the overlay. Recorded string line depth checks on the grade control prior to paving the overlay are important to monitor the volume of concrete to be placed and keep it close to the actual plan quantity.
Grade control is again the critical item for controlling Contractor material quantities, and final profiles when paving miscellaneous concrete. Smaller miscellaneous areas are typically formed prior to paving miscellaneous concrete. The forms can benefit the grade control process. However, matching the grades in approaches, and ramp gore areas can lead to pavements that do not drain properly or have a safe profile for the public. If not included in the plans, a set of detail grades should be computed and plotted prior to the beginning of the project to attempt to alleviate grade problems. The detail grades should be computed from the plan profiles for the adjacent pavement. After the detail grades are computed, they should be plotted to determine the proposed gore/approach cross sections prior to beginning the project. If the detail grades are determined prior to any paving, with the approval of the Engineer, the Inspector can typically adjust the mainline and/or ramp grades to provide acceptable transitions for gores and approach pavement.
Conventional edgers should be used to round the top corner. It should be left with a radius not exceeding 1/4 inch . Edge slump should be rechecked with the 5 foot straightedge behind all finishing operations. Any edge slump exceeding 3/8 inch should be corrected before the concrete sets. If continuing slumps of up to 1/4 inch occur, the Contractor should adjust the edgers on the trailing end of the side forms to eliminate the slump.
During final finishing operations. The previously removed 4 inch end section of the expansion filler material should be replaced and the concrete consolidated around the joint filler. The expansion joint filler location should also be marked for sawing at a later date. The best method of doing this is by working from a bridge spanning the pavement. The expansion filler top is exposed in about five locations across a 24 foot pavement by using a small trowel to remove the concrete. A small block is then placed on top of the expansion filler. The block should extend to the surface and be held in place by nails extending into the filler. Later the joint is sawed out from block to block (Figure 602-7).
Following floating, the surface is to be textured longitudinally with a burlap drag (see subsection 602.03.K ). Even though the final grooving (tining) will be by metal tines, it is important that the slab be properly textured initially with burlap to give the surface a slightly roughened, gritty texture.
Usually 36 to 60 inches of burlap should be in contact with the pavement surface. Two layers of burlap may be required to impart a gritty surface. The burlap should be cleaned of built-up mortar daily and replaced when it is no longer effective. It should be kept moist to avoid removing water from the concrete surface.
When slipform paving, it is better not to have the burlap drag extend over the edges, as it may cause the concrete to slump or tear the edges. The last 4 inches should be hand dragged by the finishers doing the edging.
A strip of artificial grass mat may be used in place of burlap. After burlapping, the surface is to be grooved transversely or longitudinally with a steering controlled machine. A manual texturing device may be used for miscellaneous pavement. The Contractor must place grooves with a width and depth of ⅛ inch, with a tolerance of 1⁄32 inch, spaced ¾ inch on center with a tolerance of 1⁄16 inch. Do not groove the pavement surface within 1½ inches of longitudinal joints. Grooves should not be overlapped. Overlapping decreases the spacing, which results in breakage. The grooves should be installed in one continuous pass across the entire pavement surface.
Texturing operations shall not delay curing. Timely application of curing compound is critical to the final strength and durability of the concrete pavement. Application of the curing compound must take precedence over texturing the surface with the metal tines. If texturing has to be delayed, it will follow at a later date when the concrete has attained the minimum required class design strength. When texturing is delayed, the Contractor shall submit a plan for the Engineer’s approval for texturing the pavement after the concrete has reached the strength required to support the equipment. This work shall be at the Contractor’s expense.
The grooving device must be a tracked machine accurately adjusted to the crown and the pavement slope to provide uniform contact between the metal tines and the pavement. It must also be adjusted to lift off the pavement just as the tine head reaches the edge to avoid breaking down the edges when slipform paving. Check the grooving periodically to see that the operator is obtaining a uniform surface, with groove depths from 1/8 to 1/4 inch. Following grooving, the Contractor is to stencil station numbers in the pavement 16 inches from the edge of the pavement so the numbers can be read in the direction of traffic (see subsection 602.03.L.)
Membrane curing compound is to be applied as soon as the free water has left the surface. Often the same machine is used for texturing and applying the curing compound. Usually this is as soon as texturing is complete but, texturing shall not delay the curing compound application.
The Contractor must mix the curing compound according to the manufacturer’s recommendation before the compound is transferred from the drums to the tank on the curing machine. It should be constantly re-circulated or stirred during application.
One coat is required for non-textured surfaces and two coats on grooved surfaces. Coverage is 1 gallon per 25 square yards for each coat. The slab edges should be spray cured promptly if the forms are removed before the required strength is met. Depending on the wind, sometimes the curing compound may have to be applied in two different directions to get proper coverage.
Paving is normally suspended on a transverse contraction or expansion joint and a night header is installed. An adjustable header board is staked at the center of the load transfer device assembly. The header top should be left at least ½ inch below the pavement surface and the finishing equipment passed over the header.
The area adjacent to the header must be filled with fresh concrete. However, partially hardened concrete, or laitance, carried in the vibratory box shall not be used in this area. Just before the finishing equipment passes over the header, the concrete adjacent to the header should be vibrated with a handheld vibrator. It is a good idea to spread burlap or plastic over the projecting ends of the dowels to facilitate cleanup of excess concrete.
Since the header board may not match the crown of the pavement, Contractor’s often insert pieces of ¼ inch Masonite board behind the header board and adjust it to the exact elevation of the finished pavement after the finishing equipment has passed over the header joint (Figure 602-8). The finishers will now be able to straightedge the pavement up to and across the header.
When slipform paving, the last 10 feet or so of the longitudinal bulkhead joint adjacent to the header should be formed to prevent the slab from becoming over width. An over width section will cause spalling of the edge when the paver is backed to the header.
A transverse end of pour joint is also acceptable and is commonly referred to as a runoff header or plastic tube header. See the Standard Plan R-39 series for details. A transverse end of pour joint runoff header includes a plastic tube basket that is pinned to the grade. Concrete is placed and vibrated through the runoff header and beyond it by at least 5 feet. Once the concrete has hardened, a joint, centered over the plastic tube basket, is sawn full depth and the concrete is removed on the waste side to provide a clean smooth face against which the next day’s paving operation can start. Smooth dowel bars are installed in the plastic tubes and paving resumes.
When paving resumes, the Contractor needs to use care as they pull away from the header to avoid damaging the green concrete. As the slipform paver or finishing machine starts forward, there is a tendency for the concrete to cling to the screeds and the float pans, leaving the surface low in these areas. After the concrete is placed, the header should be thoroughly vibrated to eliminate voids. It is important that the Contractor straightedge this area carefully.
Date and stationing should be stenciled in the concrete by the Contractor, on the night and morning sides of the header.
Often the Contractor will want to use the new pavement as a haul road for his batch trucks at the earliest possible time or he may want to place a wheel or track on new pavement edge to pave the adjacent lane. Other times it will be important to open an intersection or drive to traffic as soon as possible.
The Inspector and Contractor should try to anticipate the need for early openings and arrange to make an extra set of beams when the concrete in question is being cast. These beams should be cured under environmental conditions similar to the pavement being cast.
Follow Table 104-2 in subsection 104.11.B.4 of the Standard Specifications for Construction, to determine when equipment may be allowed on the pavement. No load is to be permitted on the pavement until the centerline joint is sawed, the contraction joints relief cut, the expansion joints sawed out to full width and temporary or permanent seals installed. Curing is to be continued until a flexural strength of 550 psi has been obtained.
When job control beams are not available, the curing surface treatment film will not be broken by Contractor’s equipment or other traffic until the concrete has attained 70 percent of the anticipated minimum strength as determined from the following table.
MDOT will take cores, before final acceptance, from pavement, shoulder, and base course to determine the thickness of the pavement according to MTM 201. Refer to subsection 602.04 and the following flow chart (see Figure 602-9) for this determination.
The State-Wide Concrete Paving Specialist will visit the project when paving starts to assist in determining equipment suitability, to discuss other concrete related items and to assist with getting the project properly started.
The Inspector should review the trimming, placing, spreading, consolidation, finishing, texturing and curing equipment the Contractor plans to use to see if it is appropriate for the quantity and type of paving included on the project. Screeds and pan floats must be checked for proper slope adjustment.
The Inspector should verify that the curing compound sprayer is in working condition before paving starts. If in doubt, the Contractor should demonstrate its capability. Check to see that the Contractor has all the necessary hand tools, such as 5 foot and 10 foot straightedges, floats, edgers, and stencils. If forms are used, they should be checked for straightness, general condition, condition of locks, etc. before form setting operations begin.
At completion of a pour, count the tickets to determine the total concrete received. Compare this to the theoretical amount required to compute the overrun or underrun. The cause of any underrun should be determined and corrections should be made immediately. Possible causes include thin pavement, narrow width of slab, incorrect measurements or improper scale readings at the concrete plant.
Night header joints should receive the Inspector’s attention, as they are often the location of bumps in the finished pavement. Stretch a string line parallel to the centerline from 10 feet behind the header to 30 feet in front to check the header for the need of corrective work while the concrete is plastic.
Inspect the previous day’s pavement for uniformity of texturing and curing. Have areas been missed, or textured too shallow or too deep? Are there thin spots or streaks in the curing membrane? Has the edge of the slab been completely coated with curing compound? Check for any honeycomb in the edge and have it patched. It is recommended to monitor the texturing operation when started. This will aid the Contractor in providing a quality product everyone will be satisfied with.
At this time, the relief sawing of the transverse joints should be complete or in progress. Look for any random cracks that would indicate sawing was not completed in a timely manner. Also, look at the relief saw cuts for excessive raveling, indicating they were sawed too soon. Check for correct depth of the saw cuts.
When sawing of the joints to final width begins, the Inspector should check on the width and the depth (Standard Plan R-39 series). The location of saw cuts for contraction joints should be over the center of the assembly. It is important that the expansion joint saw cuts be made exactly over the expansion felt. This is accomplished by sawing from block to block as explained under Placing and Finishing the Concrete.
The centerline longitudinal joint will be sawed within 24 hours, but not until the concrete has hardened sufficiently so that no raveling or spalling occurs. All traffic must be kept off the pavement until the longitudinal joint has been sawed. Since the upper 1 inch of the longitudinal joint must be sawed a minimum of 1/4 inch wide, and the lower one-third need only be 1/8 inch wide, the Contractor will often use two saws operating in tandem. (Standard Plan R-41 series ).
Transverse joints will be sealed with hot poured rubber.
During hot weather, additional precautions must be taken to obtain high quality pavement. Concrete placement is prohibited when the concrete temperature exceeds 90°F. Even with concrete temperature at 80°F, it may be difficult for the final finishing and texturing to be completed before the concrete hardens. Under these conditions, there is a strong desire by the Contractor’s finishers to add water to the pavement surface to lubricate their floats and straightedges. Any water added is to be in the form of mist from a fog sprayer. This limits the amount of water added and minimizes dilution of the cement paste on the concrete surface.
For hot weather conditions, the Inspector should refer to Table 706-1 of the Standard Specifications for Construction. This table gives evaporation rates for conditions for paving concrete based on air temperature, concrete temperature, relative humidity, and wind velocity. If the evaporation rate exceeds 0.15 lbs/ft2/hr from the table, then the Contractor should not pave. In any combination of weather conditions, the Contractor must be able to ensure to the Department that they can prevent premature drying of the pavement surface during the paving process.
In extreme weather conditions, timely application of the curing compound is not always the complete solution to preventing premature drying of the pavement surface. Extreme weather conditions can require additional steps to aid in the prevention of premature surface drying and other adverse effects caused by hot weather. Continuous, constant temperature moist curing, covering the entire surface of the pavement with continuously wet burlap, and reducing the concrete mix temperature (cement, aggregate, and/or water temperature) are examples of other options for helping reduce the impact of hot weather on concrete pavement. Except for when continuous moist curing is used, the curing compound should still be applied when using these options for paving in hot weather. The Contractor’s Quality Control Plan must be reviewed before paving begins. The Quality Control Plan must contain adequate detail regarding the plan for properly curing the concrete in accordance with MDOT standards.
Protection from cold weather is the Contractor’s responsibility. Although concrete will withstand below freezing temperature due to heat of hydration, it is considered good practice to provide a protective covering of insulated blankets or straw when freezing temperatures are anticipated. When cold weather is anticipated, the pavement should be covered as soon as possible. However, the pavement must be able to support the weight of the insulating blankets or straw without damaging the surface.
If the Contractor neglects to cover the pavement in a timely manner and the temperatures drop below freezing during the curing period, the Inspector should note the areas involved and notify the Engineer. Arrangements can be made to take special cores from the area in question to determine whether the concrete has been damaged.
Protection from damage by rain is the Contractor’s responsibility and the Inspector should avoid giving the Contractor any instructions as to covering the concrete, or other protective measures. If the Contractor is unable to texture the pavement, or the texture is washed away, they will be required to groove the hardened concrete.
If serious rain damage occurs, such as breaking down of slipformed edges or erosion of the surface by water running off the pavement, repairs should be made as soon as the rain stops. Water on the surface should be carefully removed with straightedges to avoid working the water into the concrete. Fresh concrete should then be added and the surface refinished.
If the rain has damaged the curing membrane, this should be corrected by respraying the area
In addition to the main paving operation, most projects will involve some miscellaneous paving. This might be semi-production work on service roads or ramps. Other times it will involve strictly hand work at street intersections. The quantity of paving involved will dictate the type of equipment to be used. As with production pavement, the Inspector should verify that methods and equipment proposed are in acceptable working condition and appropriate for the type of paving.
Trimming the base will usually be a combination of a road grader and hand methods. Forms are used for hand work. Radii of less than 150 feet will require flexible forms (see subsection 602.03). Concrete may be placed without a spreader providing it can be placed with no segregation.
All areas along forms and joints will be consolidated with a vibrator. The vibrator will be inserted vertically into the concrete to ensure complete consolidation and will not be used to move the concrete. Screeding of the surface will usually be by a form-riding finishing machine or a hand-pulled vibrating strike off. Sometimes roller screeds or lightweight slipform pavers are used. Straightedging gaps and other areas subject to high-speed traffic is important. A string line check of these areas is also helpful.
Burlapping, groove texturing, and curing will normally be done with handheld equipment. Make sure grooving is done in one continuous pass from edge to edge. Do not permit grooving each way from the centerline, as a poor appearance will result.
Applying the curing compound will be done from a bridge or by using a boom so uniform coverage can be obtained.
When concrete shoulders are called for on the plans, they will be constructed according to the current specifications.
Preparation of the grade is similar to that required for pavement; shaped to the required line, grade, and cross section, and compacted to the required specific density. The edge of the pavement should be cleaned of any dirt or other foreign material. Shoulders adjacent to pavement will require lane ties to keep the shoulder from separating from the pavement.
Expansion joint filler is placed in line with opposite expansion joints in the pavement as per the Standard Plan R-42 & R45 series . Load transfer devices are omitted from concrete shoulders.
Just before concrete is placed, the edge of pavement and the entire base should be dampened. Concrete is usually placed on the grade directly from hauling units. Normally a modified slipform paver will be used to strike off, consolidate, and finish the shoulder concrete.
Immediately behind the machine in the finishing operation, check the surface for proper slope or crown, Edges will be inspected for slump and thickness and to ensure they are all free from contamination by base material. Floating will be done only as necessary to close the surface. Texturing is done with a burlap drag or a stiff broom. The surface and outside edge should be coated with white membrane curing compound at a rate of 1 gallon per 25 square yards.
Relief cuts must be sawed to the proper depth to control cracking. After curing, the joints are to be sawed to the final width and depth and sealed with the same seal as used in the pavement.
Corrugations (rumble strips) will be placed according to Standard Plan R-112 series . [top of page]
Another type of miscellaneous paving is concrete base course. This is usually a widening placed adjacent to an existing pavement which is in need of resurfacing. General construction methods are similar to those described above for concrete pavement. A few important differences are mentioned here.
The edge of the existing pavement may be in poor condition. Check the plans to determine if any corrective work is required on this edge before casting concrete against it.
Base course mats are non-reinforced. Plane-of-weakness joints may be either formed or sawed. No joint seals are required. No load transfer assemblies are used in base course. Review the Standard Plan R-42 series for joint layout and header joints in non-reinforced base course.
Straightedge tolerance is more liberal, 3/8 inch in 10 feet. Texturing is done by burlap drag. The surface should not be grooved, as it will be difficult to clean before placing the overlay.
Cure with a transparent compound instead of white. Only one application is required at the rate of 1 gallon per 25 square yards of surface.
- All testing equipment must be on the job before start of concrete operations including air meters, slump cone and related tools and concrete thermometer.
- Perform tests according to Section 1003 of the Standard Specifications for Construction.
- Behind the grading operation, the aggregate base should be checked for thickness, elevation and proper cross section.
- Thickness is checked by digging through the aggregate and recording the depth of the hole.
- Elevation and cross section are determined by stretching a string line across the grade from stakes set by the instrument crew or may be determined by using rod and laser.
- Measurements are made from the string line to the grade and recorded.
- Any significant variations, greater than ½ inch, from the plan should be brought to the Engineer’s and Contractor’s attention.
- Any areas where the grade appears to have been disturbed should be rechecked.
- Verify that there are no puddles of standing water.
- The following PowerPoint presentation has been created to assist the field inspectors when performing these inspections.
- After the Contractor completes staking the assembly, the Inspector should check vertical alignment with the basket level to verify that dowels are parallel with the pavement surface (Figure 602-6).
- The bars should be visually checked for horizontal alignment by sighting over the tops of the bars to the previously set assemblies to see if the bars are parallel to the string line.
- Even though the assemblies have been set at right angles to the string line, the bars may not be parallel to the string line due to improper fabrication of the assemblies. Any apparent misalignment can usually be corrected by tapping the frame to realign the bars.
- The bars should also be inspected for complete coating on at least two-thirds of the length of the bar.
- The Inspector should also make sure the Contractor is following all the DBI manufacturer’s recommendations when using a DBI.
- Expansion assemblies should be checked to make sure there are no voids under the expansion felt, between the ends and the forms or around the dowel bars.
- Verify that there is a 1 inch stop in the end when plastic caps are used.
- Determine that elapsed time is within specification limits for temperature and type of hauling unit.
- Hauling units should be mortar tight.
- Trucks should be washed out as necessary to prevent buildup of hardened concrete.
- Grade, including track line, will be trimmed and booked. Issue a permit to place concrete indicating to the Contractor that it is acceptable to start paving.
- Any disturbed area is to be recompacted to the specified density.
- Sight along stringline for sags, adequate supports, and general conditions. On tight radius ramps, stringline stakes may be required at 10 to 13 foot spacing.
- Depth checks on base are to be taken after trimming is complete.
- Use a stringline to check for proper crown or cross slope from grade stakes to top of aggregate base and record on Form 1145. Inform Contractor of grade checks. Issue permit to place for placing load transfer devices.
- Load transfer assemblies should be observed for coating and to make sure they are at right angles to the stringline, parallel to grade, and properly spaced and pinned. Check the free end of the expansion dowel for proper space between cap and end of dowel.
- Base shall be moist at time of placing concrete but no puddles are allowed.
- Spreader and paver must have proper crown setting.
- Operator of spreader must use care to avoid moving dowel bar assembly from pinned position. Equal amounts of concrete must be placed on each side of the expansion joints to avoid moving the assemblies.
- Operation of spray cure machine to be verified before paving starts.
- Concrete spread to cover entire base.
- Observe operation of lane tie bar installer. Inserted ties are to be spaced as indicated in the Standard Plan R-41 series . Keep inserted ties out of the load transfer assembly area. Have a field pull out test performed after the first day’s pour.
- Observe vibrators frequently to see that they are all working. Bubbles should be apparent around each operating vibrator. Paving operation should vibrate concrete full width and depth of pour. Contractor should have some means of observing vibration.
- Verify the concrete is placed within the specified time limits (see subsection 1001.03.E.3) and sign all tickets.
- Observe wet crown checks taken by the Contractor throughout the day.
- Measure spacing depth of lane tie bars behind the paver.
- To get a smooth surface, the surcharge of concrete ahead of the paver should not overload the paver and should be uniform across the grade.
- Pavement is to be checked by the Contractor with a 10 foot straightedge behind the paver. Look especially for dips at baskets.
- Check the pavement behind the paver or finisher to verify the proper width, crown and/or slope.
- The edge condition should be noted immediately behind the slipform paver. Edge slump should be checked frequently behind paver and again behind the texturing equipment with a 5 foot straightedge.
- Machine finishing and floating should minimize the need for hand finishing. Floats and straightedge must not be pulled over edge of slab, as edges will slump.
- Pavement is to be edged to remove any overhanging projections of concrete. Edging should be delayed as necessary to minimize edge slumping.
- Pavement surfaces to be dragged longitudinally with burlap and textured according to 602.03.K.
- The sand patch test per ASTM E965 can be used to check the grooving / texturing. Use Form 0564 to record measurements.
- Observe Contractor stenciling the station numbers in the correct location and direction.
- White pigmented compound is required for curing concrete pavement, curb and gutter, and sidewalk. Transparent or clear compound is required for curing concrete base course.
- The important point is to get enough cure on the exposed surface to completely seal the tops, bottoms and sides of the grooves with an unbroken membrane. Timely coverage is critical to the final strength and durability of the concrete.
- Mechanical agitation of curing compound is required.
- For grooved surfaces, curing compounds shall be applied in two applications, each at the specified rate. Check for proper yield and record.
- Curing compound shall be applied as received. No thinning is allowed.
- Enough pavement should be checked the following morning to determine the quality of workmanship. Advise the Contractor of all deficiencies. Record all findings. Mark areas for review by the Engineer.
- Where adjacent pavement lanes are constructed in separate pours, keep equipment from operating on the recently placed pavement until the pavement has attained adequate strength, as determined by test beams and table in specifications.
Review the items for slipform paving. In addition, the following should be checked:
- Forms are to be measured for proper height. Forms to be a minimum of 10 feet long. Base width equal to or greater than the thickness of the pavement.
- Condition of forms must be checked with 10 foot straightedge before project starts and daily as project is paved. Forms that do not meet specifications are to be rejected.
- Stringline to check the form grade. Stringline shall be taut to eliminate sag.
- Forms must be set directly on trimmed base.
- Three pins of adequate length are required for each form. Each form must lock to the adjacent form.
- If forms are set on disturbed base, material under forms shall be tamped on both the inside and outside of the form.
- Top of form shall be free of mortar prior to placing concrete.
- Forms are to be oiled before each use.
- Sufficient forms shall be in place ahead of the paver so they may be checked for line and grade in advance of placing concrete. The minimum length of forms in place shall be equal to the anticipated length of pavement to be placed in 2 hours.
- Verify the concrete is placed within the specified time limits (see subsection 1001.03.E.3 ) and sign all tickets.
- Surplus base material left inside of forms is to be removed.
- The depth to base from stringline at top of forms shall be measured and recorded.
- Vibratory strike board or roller screed shall be used on hand work.
- Screeds on finishing machine and/or spreader finisher shall be adjusted to proper crown.
- There should be the proper quantity of concrete being carried ahead of each screed.
- A vibrator must be used throughout the entire pour.
- Observe operator of finishing machine. Care should be taken to avoid moving the pre-molded fiber filler in the expansion joints.
- After form removal, inspect edges of pavement for honeycomb.
- The longitudinal joint shall be sawed within 24 hours.
- Saw must be equipped with guide to maintain alignment.
- Check that the size of saw cut is 1/8 inch wide by 1/3 the pavement depth deep, with the top 1 inch of the saw cut ¼ inch wide to accept sealant. Refer to the Standard Plan R-41 series.
- Bulkhead joints must be sawed and sealed with hot pour sealant.
- Joint faces should be cleaned by sandblasting or other approved method and blown clean before sealing with hot poured sealant.
- Joint should be completely filled, but not overfilled. Sealant should be between 1/8 inch below the adjacent pavement surface to flush with the pavement surface.
- A standby concrete saw is required for relief cuts.
- Two-stage sawing is required, except for slag aggregate. First stage is to be completed as soon as possible without raveling. See the Standard Plan R-39 series .
- Second stage sawing is to be done after the concrete has gained at least 30 percent of its strength. It must be centered over the relief cut. See project plans and the Standard Plan R-39 series for sizes of joint groove for type of seal being installed.
- If soft-cut saws are used for relief cuts, make sure they are addressed in the Contractor’s QC Plan.
- Clean joint with oil-free compressed air before sealing. Inspect for stones or other foreign material.
- Temporary or permanent seals must be installed in expansion joints before construction traffic uses pavement. Construction traffic may run over contraction joints after relief sawing and when the concrete has met minimum strength requirements.
Quality Control and Quality Assurance testing for concrete will be in accordance with Section 1002 and 1003.
Reports and documentation requirements should be reviewed with the Engineer before paving starts. Inspector’s Report of Concrete Placed, Form 1174R, is the primary report required of the paving Inspector. It should be prepared for each day that pavement is cast. In addition to the original copy to the Engineer and a copy to the Construction Field Services, the Inspector should retain a copy.
Any unusual happenings should be noted in the remarks section of the report. Often this is most important when a problem develops and the circumstances surrounding the problem are being investigated later. Also noted in the remarks section should be the method of placement, equipment used for consolidation, equipment used for striking and finishing surface of concrete and type of surface texture. It is recommended to note names of QA & QC personnel and any material accepted on the basis of visual inspection. The back of the form should be used for sketches, when necessary, to describe any irregular areas. It is suggested, but not required, to fill QA test results in on Form 1174. It is necessary to fill as many Form 1174 fields in as possible. The concrete used and noted on Form1174 should be the same as noted in material on the IDR. The Inspector must also complete an Inspector’s Daily Report, Form 1122B documenting traffic control, equipment used, or other work activities in progress.
Keep in mind that some quantities must be documented at the time of placement while others can be checked later. An example of the former is areas where high-strength concrete is used and is to be paid for.
Concrete overlays are typically paid for by volume in cubic yards. The Inspector will determine the volume of concrete used each day, based on the number of batches used for pavement and shoulders, and the nominal volume of concrete per batch. This amount will be documented by the batch ticket printouts. This item shall include all materials, labor, and equipment necessary to furnish and place the concrete mixture. Periodic wet depth checks shall be taken throughout the day to verify the pavement thickness and confirm the volume of concrete placed. Using the wet depth checks, the pavement width, and length of the day’s production, a volume of concrete placed can be computed. This volume can then be compared to the volume from the total day’s production on the Contractor’s batch tickets.
All delivery tickets must be signed by the Inspector and attached to the IDR for each day of concrete placement. Each concrete delivery ticket must contain the following information (see subsection 1001.03.A.3 ):
a. Name of concrete producer; b. Plant designation where batched; c. Ticket serial number; d. Truck number or designation; e. Name of Contractor; f. MDOT job number; g. MDOT grade of concrete; h. Cubic yards of concrete; i. Delivery date; j. Batch loading time; k. Maximum allowable on site addition of water; l. Extra water added onsite; and m. Contractor’s signature or initials. n. An automated printout of actual batch weights must accompany each delivery ticket
If producing concrete for more than one contract, the concrete producer must include a signed certification statement on each delivery ticket stating that all concrete materials are tested and approved, or certified as meeting Department specifications.