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Talk:EB 237 Concrete Pavement Field Reference: Pre-Paving
Proper Procedures Checklists
NOTE: All proper procedure checklists contained herein can be downloaded for free at: www.pavement.com/fieldreference .
Joint Types (Section 1.1)
- Ensure that all parties involved in joint design and construction understand each joint type.
- Check that the location of special joint types (i.e., isolation, tied contraction, etc.) are clearly indicated on project plans.
Special Considerations for Intersections (Section 1.2)
- Check plans and attempt to eliminate all joints that intersect another joint or the pavement edge at an acute angle. Where it is not possible for joints to intersect at 90 degrees, ensure that the angle at the intersection is at least 60 degrees.
Rules for Joint Layout (Section 1.3)
- If paving immediately adjacent to existing pavement, as an overlay, or on a jointed lean concrete subbase ensure that the locations of existing joints or cracks are matched with new joints.
- Make certain that joints intersect any in-pavement structures, or else isolate those structures properly.
- Ensure that isolation joints are placed only where needed.
- Check that no slab is less than 2 ft (0.6 m) wide or greater than the maximum allowable width (approximately 15 ft [4.5 m]).
- Check that the aspect ratio (length-to-width) of mainline slabs is kept between 1.0 and 1.5 whenever possible.
- Check that there are no acute angles less than 60 degrees (90 degrees is best).
- Ensure that all joints meet at 90 degrees by performing doglegs at curve radius points and tapers.
- Check that there are no interior corners (L-shaped slabs) and that, where possible, any odd-shaped slabs are avoided.
- Remind the appropriate paving crew members that field adjustments can and should be made to joint locations where necessary.
The 10-Step Method for Intersections (Section 1.4)
The following is the 10-step method for intersection joint design for concrete pavements:
- Draw all pavement edge and back-of-curb lines in the plan view. If integral curbs and gutters are to be used, draw only the back-of-curb lines.
- Lightly draw the circumference-return, the taper-return, and the crossroad return lines as offsets of 1.5 to 3.0 ft (0.5 to 1.0 m).
- Draw all lines that define lanes on the mainline and crossroad. Do not extend these lines past the circumference-return, taper-return, or crossroad-return lines.
- Define the mainline lanes for paving. Find all locations where the crossroad intersects the mainline paving edges and, at these locations only, extend the mainline paving edge lines past the circumference-return or taper-return line(s). Block-outs & doglegs will occur in the gutter at these locations.
- Add transverse joints at all locations where a width change occurs in the pavement (begin and end of tapers, tangents, curves, curb returns, etc.) and extend these joints through the curb and gutter and/or concrete barrier walls that are not isolated from the adjacent pavement. On the cross road(s), the joint at the tangent point farthest from the mainline becomes an isolation joint.
- Add transverse joint(s) between and beyond the joints defined in the last step, but do not add joints to the center of the inter- section. Attempt to keep the distance between joints the same, and less than the maximum desirable length (approximately 15 ft [4.5 m]).
- Extend the edge of pavement lines for the mainline and cross-road to define the intersection box. (Note: For skewed inter- sections, do not extend the lines for the turning lanes. Instead, place a transverse joint normal to the crossroad centerline starting from the corner of the intersection box that is nearest to the acute angle of the intersection.)
- Check the distances between the intersection box and the surrounding joints. If the distance is more than the maximum desirable joint spacing, add transverse joint(s) at an equal spacing. Do not extend these joints past the circumference- return or cross-road return lines.
- Lightly extend lines from the center of the curb return radii to the points defined by the intersection box, any intermediate joints surrounding the intersection box, and point(s) along any islands. Add joints along these radius lines. Also, make slight adjustments to eliminate doglegs in mainline edges.
- Make any additional adjustments for in-pavement objects.
Alternate Skewed Intersection Layout (Section 1.5)
- Add additional longitudinal joints in any slabs that would otherwise be more than 15 ft (4.5 m) wide, beginning and ending this new joint at transverse joints.
- To avoid sympathy cracking when ending a longitudinal joint at a transverse joint, either core or form holes through the entire depth of the pavement to arrest the cracking or, alternatively, include reinforcing bars transverse to the joint in the uncut slab to prevent cracks from propagating.
Handling Wide Medians and Dual-Left Turn Lanes (Section 1.6)
- Before planning the joint layout for dual-left turn lanes, consider all construction staging possibilities.
- If possible, use a skew joint through the intersection box instead of moving the isolation joints closer to the intersection; isolation joints usually require more maintenance than typical joints.
Roundabouts (Section 1.7)
The following is a 6-step guide to successful joint layout of concrete roundabouts:
- Draw all pavement edge and back-of-curb lines in the plan view. Draw locations of all manholes, drainage inlets, and valve covers so that joints can intersect these.
- Draw all lane lines on the legs and in the circular portion. If isolating the roundabout circle from the legs, do not extend these through the circle. If using the “pave-through” method, determine which roadway will be paved through. Make sure no distance is greater than the maximum recommended width.
- In the circle, add “transverse” joints radiating out from the center of the circle. Make sure that the largest dimension of a pie-shaped slab is smaller than the maximum recommended slab width. Extend these joints through the back of the curb & gutter.
- On the legs, add transverse joints at all locations where a width change occurs (at bullnose of median islands, beginning and end of curves, tapers, tangents, curb returns, etc.). Extend these joints through the back of the curb and gutter.
- Add transverse joints beyond and between those added in Step 4. Space joints out evenly between other joints, making sure not to violate the maximum joint spacing.
- Make adjustments for in-pavement objects, fixtures, and to eliminate L shapes, small triangular slabs, etc.
Cul-de-sacs (Section 1.8)
- Construct joint layout plans for cul-de-sacs by following the Rules for Joint Layout (Section 1.3) and the 10-Step Method for Intersections (Section 1.4).
Adjusting Joints for Utilities and Boxing out Fixtures (Section 1.9)
- After all other steps of a joint layout process are completed, adjust joints that fall within 5 ft (1.5 m) of a fixture to intersect the fixture.
- If a joint must be moved to intersect a fixture, and the resultant slab exceeds the maximum slab width, adjust several joints immediately adjacent to the moved joint so that no joint spacing is greater than the maximum.
Problematic Soils (Section 2.1)
- With adequate time before paving begins, examine existing soils and identify potential problems, such as swelling and heaving.
- If expansive soils are found, address the problem by providing proper grading and/or relocation and mixing, moisture-density control during compaction, a non-expansive cover of compacted aggregate subbase, or chemical modification, such as cement treatment or lime stabilization.
- If frost susceptible soils are found, address the problem by providing proper grading and/or relocation and mixing, high grade lines and low ditches, moisture-density control during compaction, drain tiles to lower the water table, or a non-frost susceptible aggregate subbase layer to protect the subgrade.
Uniformity and Stability (Section 2.2)
- Proof roll the area with a loaded 10-wheel dump truck to check the uniformity of support and to detect soft spots that require correction. Ensure that the entire field crew understands that the degree of rutting is indicative of both uniformity and stability.
- If subgrade remediation techniques are not necessary (i.e., no actions were taken to correct problematic soils), address any uniformity and stability issues by cross hauling and mixing of soils.
- Stabilize any nonuniform or instable areas of the soil, or the entire area if necessary, with portland cement, blended cement, fly ash, or lime.
Construction (Section 2.3)
- If necessary, bring the subgrade material to the optimum moisture content before compaction by adding water.
- Adequately compact the subgrade by achieving a minimum of 95 percent of the standard proctor density (AASHTO T99/ ASTM D698); check local specifications as density requirements may vary.
- Repeat proof rolling after compaction to detect areas that may require additional corrective action.
- Within a week of completing the compaction, trim the grade to the correct elevation and cross-slope. When using a slip- form paver, reference the same stringline to be used for subbase construction operations and pavement placement if site conditions allow.
Subbase Design (Section 3.1)
- If possible, extend the subbase far enough beyond the pavement edges to provide a stable track line for the formwork or slipform paver (approximately 3 ft [1 m] on each side of the pavement).
- Ensure that unstabilized subbases, if used, have a maximum aggregate size of no more than one third the subbase thickness, a plasticity index (PI) of less than 6.0 and contain a maximum of 15 percent fines.
- If used, ensure that unstabilized (granular) subbases are compacted to no less than 95 percent of the standard proctor ASTM T99/ASTM D698 density.
- Ensure that stabilized subbases, if used, have a plasticity index (PI) of less than 10.0; contain a maximum of 35 percent fines; and the maximum aggregate size is limited to 1 in. (25 mm), or more preferably 3⁄4 in. (19 mm).
- Ensure that subbase thicknesses are at least 4 in. (100 mm) for unstabilized subbases, 4 in. (100 mm) for cement-stabilized subbases (i.e., cement-treated subbases and lean concrete subbases), and 2 in. (50 mm) for asphalt-stabilized subbases.
Subbase Construction (Section 3.2)
- Ensure that the proportions of the subbase mixture conform to the approved job mix formula (JMF) or mixture design and that there is consistency within and between batches.
- Check that the permeability of the free-draining subbase materials, if used, comply to project specifications.
- Check for damage caused by trucks and/or laydown equipment to the subgrade/subbase surface. Ensure that subbase material is placed without segregating or mixing into the subgrade.
- During placement of stabilized subbases, check the adequacy of the volume of cement paste or asphalt binder for coating the aggregate particles and ensure that the material is spread evenly across the paving width.
- Check for stability (firm and unyielding), surface texture (uniform, with no crushing of aggregate), and depth (using probes, string lines and tape/ruler) after each roller pass.
- Test surface and grade tolerances (typically ±1⁄2 in. (12 mm)). Regrade and recompact areas that are out of tolerance.
Setting and Maintaining the Stringline (Section 4.1)
- Ensure that paving hubs, or construction stakes, are installed at appropriate intervals (typically 25 ft (7.5 m) or less) outside the pad line, along with grade/pie stakes (flats) showing the difference in elevation between the top of the slab and the hub. Decrease the interval through sharp horizontal or vertical curves.
- Check that a stringline support stake is securely placed just outside each hub, so that the stringline will be directly over the hub.
- Check that the appropriate stringline height is calculated relative to the hub elevations, the offset distance (either level or projected) between the hub and a pavement reference point, and the desired grade.
- Install stringline winches at about 1,000 ft (300 m) intervals.
- Verify that the stringline is installed between stakes, adjusted to the desired height, and then made taut using hand winches. (Apply tension carefully; a line break may cause injuries.)
- Install stringlines on both sides of the proposed pavement for maximum control.
- Warn all workers to be cautious around the set stringline to avoid tripping over, nudging, or otherwise touching it.
Setting Forms (Section 4.2)
- Examine all forms with a straightedge or stringline before use. Discard, repair, or replace forms that are bent by more than 0.125 in. (3 mm) along the top or 0.25 in. (6 mm) along the inside edge.
- Before placement, ensure the quality of support beneath the forms is assessed so no settlement will occur.
- Ensure that fixed-forms have the proper alignment and elevation to provide the best possible smoothness.
- Check that no forms are shimmed up more than 1⁄4 in. (6 mm).
- Make certain that all forms receive a light application of a form-release agent before casting the pavement.
- If wooden forms are used, ensure that they in good condition and have not been used too frequently.
Placing Dowels (Section 4.3)
- Check dowels for an approved, factory-applied debonding coat or plan and prepare to coat each bar with form release oil after baskets are placed. (Dowels for insertion must have factory-applied coating.)
- After inspection of the subbase, and if you are placing dowel bar assemblies (baskets) manually, ensure that all baskets are aligned perpendicular to, and at the correct distance from, the pavement edge.
- Check that all baskets are correctly aligned and adequately secured with stakes, pins, nails, and/or clips. View down the grade to ensure that all dowels are parallel to the centerline and across the basket to ensure all dowels are level and centered.
- In intersection approaches and other areas where adjustments are likely to the joint locations, ensure that the dowel baskets are placed and marked correctly to the plan.
- Mark the location of every dowel basket on both sides of the roadbed by pens, colored nail heads, or paint marks to identify the location of a necessary sawcut at the center of the dowel basket. Be mindful and careful that the location tolerance for the joint cut is just 1.5 in. (38 mm) or less to either side of the actual center of the dowel, depending on its length.
- For dowel bar insertors, check the carriage spacing and depth control settings to ensure proper dowel placement will be achieved.
Placing Reinforcement (Section 4.4)
- If paving two lanes or more, check machine settings or chairs to ensure that all tiebars will be placed at the proper spacing and perpendicular to the longitudinal contraction joint(s).
- When mechanically placing tiebars along a longitudinal construction joint, ensure that tiebars are being placed at the proper spacing by using a timing device. Check specifications of the owner/agency for the maximum allowable grade and bend for bent tiebars.
- Ensure that no tiebar is placed within 15 in. (380 mm) of a transverse joint.
- For odd shaped slabs or areas requiring mesh reinforcement, ensure that welded wire fabric is set into place prior to paving. Once paved, lift this reinforcement to the proper depth. Alternatively, place the reinforcement on chairs before placing the fresh concrete.
- For a continuously reinforced concrete pavement, ensure that the longitudinal reinforcement is placed at the proper depth in the slab per the project plans.
Paving Equipment Setup (Section 4.5)
- Setup the slipform mold according to the manufacturer’s recommendations. In general, this will require an initial leveling of the paving machine’s frame, followed by a leveling of the slipform mold from front to back and side to side. Then, the slipform pan is typically adjusted for cross slope and edge slump.
- Setup the vibrators according to the manufacturer's recommendations. Typically, this requires setting one vibrator between 6 and 8 in. (150 and 200 mm) from each edge of the slipform mold and uniformly spacing additional vibrators at an interval of approximately 12 to 24 in. (305 to 610 mm). Ensure that the vibrators are set up at the proper spacing and frequency so that the zone of influence of neighboring vibrators overlaps.
- Ensure that the slipform paving machine (i.e., the slipform paving machine’s frame and tracklines) is perfectly parallel to the stringline(s) by measuring the distance between the slip- form paving frame at both the front and back of the machine and confirming that the two distances are equal. Consult your paving machine’s setup manual for more details.
- Check that neither the elevation nor the alignment sensing wand deflects the stringline by more than 1⁄8 in. (3 mm) and, if either wand does, adjust the wand tension appropriately. Consult your paving machine’s setup manual for more details.
- Confirm that the slipform paving machine is, in fact, perfectly parallel to the stringline(s) and that the elevation and alignment sensing wands are properly functioning by moving the slipform paving machine forward 20 to 30 ft (6 to 9 m) and repeating the previous two steps. Consult your paving machine’s setup manual for more details.
- Check the final grade and cross slope of the slipform mold. This may be done by arranging two rows of three stakes so that the top of each stake is exactly 1 in. (25 mm) below the finished grade, one stake is 2 ft (610 mm) from each edge, one stake is at the centerline, and the lines of stakes are offset by approximately 3 ft (915 mm). Once the stakes are setup, the slipform paving machine is driven on top of the stakes, the grade checked, and final grade and cross slope adjustments are made.
Concrete Mixture Analysis and Approval
Cement (Section 5.1)
- Ensure that the portland cement content of the mixture is optimized, such that the concrete can reliably meet strength and workability requirements while minimizing cost and any negative secondary effects associated with excessive cement content (i.e., higher air entrainment dosage requirements, increased water content, higher shrinkage, etc.).
Cementitious Materials Content (Section 5.2)
- Ensure that the cementitious materials content of the mixture is optimized for the same reasons as noted in Number 1 of the Section 5.1 checklist.
- Check that the dosage of supplementary cementitious materials is within the allowable range of the owner/agency (typically, fly ash and slag cement dosages do not exceed 25% to 50%, by weight, respectively, although special circumstances might allow for even higher addition rates).
Water-Cementitious Materials Ratio (Section 5.3)
- Ensure that the water-cementitious materials ratio does not exceed the maximum of 0.50 for hand pours and 0.45 for slip-form paving, except in special circumstances.
Aggregates (Section 5.4)
- Check that the coarse and fine aggregates, combined, make up 60% to 75% of the total concrete volume.
- Check that the proportion (by weight) of coarse-to-fine aggregates is around 60/40 (roughly 55% to 65% coarse and 35% to 45% fine).
- Ensure that aggregates, both coarse and fine, pass any applicable tests for freeze-thaw durability, alkali-silica reactivity, alkali-carbonate reactivity and “D” cracking susceptibility.
- Ensure that the combined aggregate gradation is properly analyzed and passes all specifications. In doing so, the result should be a well-graded mixture that will provide a workable, strong, and durable concrete.
- Ensure that the fineness modulus of the fine aggregate is analyzed. (A FM of 3.0 to 3.5 or higher works best for concrete paving mixtures and a minimum of 2.7 is recommended.)
- Check that aggregates are clean and free of contaminants such clayballs. Dirty (dusty) aggregates cause paving consistency and quality problems. Wash dirty aggregate before stockpiling for use or make arrangements with aggregate suppliers to improve materials. Ensure the cleanliness of the aggregates when batching concrete.
- Maintain aggregate stockpiles at a surface moisture condition of saturated surface dry (SSD) or greater.
Testing (Section 5.5)
- Prior to using a new concrete mixture in the field, ensure that a sufficient number of tests have been conducted in a laboratory to fully characterize its properties and understand possible strengths and weaknesses. Evaluate the mixture at difference temperatures to understand potential constructability affects when paving in the field.
- Ensure uniformity, quality, and conformance to specifications (ASTM C94 or project specific specifications) at the jobsite by testing the concrete for temperature (ASTM C1064), slump (ASTM C143/AASHTO T119), density (ASTM C138 / AASHTO T121), and air content (ASTM C231 / AASHTO T152; ASTM C457). Also conduct compressive (ASTM C39/AASHTO T22) and/or flexural (ASTM C78/AASHTO T97) strength testing and/or maturity method testing (ASTM C1074/AASHTO T325) to ensure conformance with strength requirements.
- Ensure that all testing and field crews understand that concrete should not be qualified on slump; slump is only appropriate for comparing batch-to-batch consistency and for process control.
- Ensure that all testing and field crews are educated not only on the testing procedures, but also on how to interpret results. Early detection of problems, such as sudden drops in unit- weight, will allow real-time process control and reduce mixture-related paving/durability problems.