Concrete Pavement Design FAQ
Why use concrete shoulders with concrete pavement lanes when asphalt concrete shoulders are less expensive?
Answer: Truck axle loading is the main distress that pavements endure. The largest amount of stress from truck tires is along the outside edge of pavement. Tied concrete shoulders (with tie bars) provide stress reduction along the longitudinal joint between the outside lane and the shoulder, in addition to avoid lane separation. Note that this stress reduction is very limited under construction joints. Ideally, that joint would be a contraction joint but that depends on the construction schedule. In order to be safer, it is recommended to use widened lane with tie bars except if the shoulder is anticipated to become a future lane. The use of asphalt shoulder requires more maintenance throughout the concrete pavement life. One of the major issues is the construction joint between the asphalt concrete shoulder and concrete pavement lanes, which fails early due to temperature and settlement.
Why does the department place dowel bars in shoulders?
Answer: Experience has shown, particularly in urban areas, that shoulders do get converted to traffic lanes to improve mobility. In some instances, shoulders which were intended to be converted to future traffic lanes, were not designed with dowel bars which lead to expensive change orders. It is also difficult to predict when a shoulder will be converted to a lane in the future. Because the cost to incorporate dowel bars by change order or to retrofit them into existing shoulders is expensive when compared to placing them when the concrete pavement is first built, it was determined that it is in the best interest of the State to include dowel bars in new concrete shoulders and except them on a case-by-case basis. Considerations for exceptions will be based on the likelihood of the shoulder being converted into a traffic lane in the future and the geometric configuration of the shoulder. The HDM includes a blanket exception for shoulders next to existing undoweled concrete lanes. Also, the shoulder portion of widened slabs will always be doweled. The Pavement Program is always looking for ways to improve this guidance and would welcome input. Please forward your comments to the Office of Concrete Pavement.
How joints are saw cut? (new 11/2019)
Answer: The current specification allows the contractor to choose the depth and the time for the initial saw cut. The Contractor will make a single 1/8 inch saw cut to control cracking at the joint. If the joint will be sealed, a second cut is required to form the reservoir. Refer to Standard Plan P15 and Revised Standard Plans - P18, and P20.
Why are some joints sealed and not others? (new 11/2019)
Answer: Joint sealing keeps debris and surface moisture from entering the joint. Over the course of a day, temperature changes cause slabs to contract and expand. This movement is more pronounced in desert and mountain climate regions, allowing joints to open more, increasing susceptibility to debris in unsealed joints. If enough hard particles build up in the joint, joint movement is restricted and deterioration can occur. Seals also reduce moisture infiltration, which will help prevent pumping of fines, premature base erosion, and slab cracking.
The current HDM (11-20-2017) stated that no joint seal on new construction, widening, or reconstruction except for the following conditions:
- Isolation joints
- Expansion joints
- Transverse joints in JPCP in all desert and mountain climate regions
Why is no saw cut needed on a cold longitudinal construction joint?
Answer: When a lane is slip formed and allowed to cure for a day, a cold longitudinal construction joint is formed when an adjacent lane is poured up against the new lane. The longitudinal joint will remain tight due to the tie bars, so it is anticipated very little water will penetrate this joint early on. Therefore, to saw cut or seal a tight longitudinal construction joint would not be beneficial.
How do I know if the alignment of the dowel bars is correct?
Answer: The dowels require coring. The contractor provides coring at each end of one dowel. By comparing the two cores, the dowel tips indicate the alignment of the dowel relative to the surface. There are measures in the special provisions to handle misaligned dowel bars. Tolerances are covered in the specifications and schematics are shown on Standard Plan P10.
There are no approved non-destructive techniques for determining dowel locations. The Department is looking into promising potential research that may change the way that dowels are checked for alignment in the future.
Is there a rapid setting lean concrete base specification? (new 11/2019)
Answer: Yes, Section 28-4 of the Standard Specifications was developed for lean concrete base rapid setting.
Can we use dowels in transverse joints when replacing panels? (new 11/2019)
Answer: Standard Plan P8 shows the detail for placing dowels for random slab replacement. When the existing slab is longer than 15 feet or there are multiple and continuous slabs need to be replaced, adding dowels at the transverse contraction joints has been eliminated.
Why don't we have a standard plan for intersection joint layouts?
Answer: It is not practical to develop a standard plan for intersections because each intersection is different. Intersections have various widths and lengths with possible turn pockets, cross walks, etc. Also, various manholes and drainage inlets may be located in the intersection that impact joint locations. With all these various elements, it requires good judgment to determine the best design for each particular intersection to layout the jointing pattern for saw cutting.