Portland Cement Concrete (PCC) Design FAQ
Note: Both the Long Life Pavement FAQ and the AC Design FAQ are being developed.
1. WHY USE CONCRETE SHOULDERS WITH PCC 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. Tied shoulder spreads the load more uniformly across the longitudinal joint. The joint between asphalt concrete shoulders adjacent to PCC lanes usually fail earlier because of temperature and settlement.
2. 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 PCC is first built, it was determined that it is in the best interest of the State to include dowel bars in new PCC 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 PCC lanes. Also, the shoulder portion of widened slabs (see PCC FAQ #1) will always be doweled. The Pavement Standards Team is always looking for ways to improve this guidance and would welcome input. Please forward your comments to the Office of Pavement Design.
3. HOW JOINTS ARE SAW CUT? (NEW 9/2013)
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” 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 Revised Standard Plans RSP P15, P18, and P20.
4. WHY ARE SOME JOINTS SEALED AND NOT OTHERS? (NEW 9/2013)
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 (11-02-2012) stated that no joint seal on new construction except for:
- Isolation joints
- Expansion joints
- Longitudinal construction joints in all desert and mountain climate regions
- Transverse joints in JPCP or JPCPRSC in all desert and mountain climate region
5. 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.
6. 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.
7. ARE THERE DOWEL BASKETS FOR REPLACING EXISTING SKEWED JOINTS IF DOWELS ARE TO BE USED?
Answer:There are a few dowel manufacturers who can make skewed dowel baskets. Skewed baskets are used infrequently. If a significant quantity is not being ordered, it would be assumed that this would be an expensive option. However, this should not prevent the Design Engineer from specifying dowels at skewed transverse joints if they are warranted. If the Engineer includes a schematic of the skewed dowel basket in his Construction Detail plan sheets, then this would be covered. The Designer needs to put information into the Resident Engineer's file to ensure that the location of these dowels is documented for future use. Future retrofitting will be a problem if there is no information on locating dowels during slab replacement or lane replacement.
8. IS THERE A RAPID SETTING LEAN CONCRETE BASE SPECIFICATION? (NEW 9/2013)
Answer:yes, there is a specification 28-4 available located in the office engineer website, or download the word document with this link 28-4.
9. CAN WE USE DOWELS IN TRANSVERSE JOINTS WHEN REPLACING PANELS? (NEW 9/2013)
Answer:Revised Standard Plan P8 shows the detail for placing dowels for slab replacement. When the existing slab is longer than 15 feet or there is multiple and continuous slabs need to be replaced, adding dowels at the contraction joint and transverse joint has been eliminated.
10. 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. The Office of Pavement Design is currently developing training for placing joints in an intersection.
Please forward any questions/comments/suggestions to Amy Fong (firstname.lastname@example.org). Last updated 09/19/2013.