The mayors of Oakland & San Francisco have challenged each other to a Battle for the Bay on Creek to Bay Day, Sept. 21.
Types of pavement treatments used by the Department of Transportation
Crack Sealing is a preventive measure that can be performed prior to any of the preventive maintenance treatments. Cracks can be sealed from 0.1 inches to 1 inch wide, provided the base is sound. The sealant will prevent infiltration of water into the pavement.
Slurry Seal is the least costly and preferred treatment for streets that are in both good and fair condition, but needs protection against traffic loading and water intrusion. Slurry is a mixture of slow-setting emulsified asphalt, well-graded fine aggregate, mineral filler and water.
Microsurfacing is a thin maintenance treatment consisting of a mixture of crushed aggregate, mineral filler and latex-modified, emulsified asphalt. It is applied by a truck equipped with a squeegee or spreader box. Instead of curing via evaporation, like slurry, a chemical reaction causes the material to set and harden. This treatment is effective at sealing low-severity cracks, including fatigue cracks, longitudinal cracking and transverse cracking. It also helps control raveling, friction loss, moisture infiltration and roughness.
Rubber Chip Seal applies a very thin layer of fine aggregate (either rock or, in some cases, rubber particles) with a binder. This method falls within the category of “pavement preservation” and is not intended to produce a new pavement section. Rather, it is intended to prevent further deterioration of the existing pavement. The final pavement is granular and coarse. A green element to this treatment is that 100% recycled tires are used in this treatment. Chip seal is often used in conjunction with microsurfacing for what is described as a “cape seal.” The surface will be smoother with the "cape seal". It is expected that rocks come loose in the construction site. Frequent street sweeping is required as it takes at least one month for the rocks to settle. However, chip seal is a very cost-effective pavement treatment as more streets can be paved as compared to conventional methods.
Cape Seal is a multi-step process combining chip seal and microsurfacing. This process of adding the layer of microsurfacing on top of the chip seal provides a uniform color and smoother surface than chip sealing alone.
Rehabilitation and Reconstruction Treatments
Asphalt Base Repairs are done at selected locations where the pavement section has failed and needs to be repaired. Typical signs that base repair is needed include “alligator cracking” where the surface takes on the look of alligator skin for an area. Asphalt base repairs consist of removing a deep section of asphalt. If necessary, base rock underneath the asphalt may need to be replaced.
Mill and overlay using conventional Hot Mix Asphalt (HMA) is widely used in the Oakland. This overlay process involves milling the existing pavement and then applying a new asphalt overlay in the range of 2 to 6 inches. The result is a “like new” street.
Full-depth reclamation (FDR) is a full-pavement rehabilitation process in which the pavement and a portion of the sub-base below pavement are uniformly crushed, pulverized and mixed with cement, and then reapplied to form a new pavement. Ideally, the roadway needs to be completely closed for this work.
Cold-in-place Replacement (CIR) is a full-pavement rehabilitation process in which the pavement is recycled and mixed with new binder. The paving process is performed under one operation. Asphalt overlay is needed after the placement of CIR in high traffic areas. Microsurfacing is applied after the placement of CIR in low traffic areas such as in residential streets.
Bonded wearing course consists of a thin hot mix asphalt overlay placed over a polymer modified emulsion membrane. The benefit of this over a cape seal, is that traffic can be placed back quickly for arterial and collector streets.