4. Pavement Maintenance/ Preservation Methods
The specific activity to perform on each road depends upon the pavement distresses observed. The following pavement maintenance and preservation methods are currently being utilized or under evaluation for future use by the city.
Crack Seal (Concrete and Asphalt)
A localized treatment method used to prevent water and debris from entering a crack, which might include routing to clean the entire crack and to create a reservoir to hold the sealant. It is only effective for a few years and must be repeated. However, this treatment is very effective at prolonging the pavement life. Cracks that are sealed are typically less than 3/4-inch wide.
Joint Repair (Concrete)
Portland cement concrete joints are provided to accommodate concrete volume changes due to temperature and moisture variations. Additionally, transverse construction joints are installed as a terminus following the end of production or abutment to existing pavement. Joint sealants are provided to seal and protect the joints from the infiltration of water and incompressible foreign materials. Any cracking, breaking, or spalling of slab edges on either side of transverse joints need to be repaired. Typically, partial depth repairs are used where the joint or crack deterioration is in the top one-third of the slab and the existing load transfer devices, if any, are still functional. Material is removed by sawing or chipping, although milling is becoming more prevalent in some locations. The repair area is cleaned to removed dust and fine debris with a compressed air. Compressible material is placed in the joint to act as a bond breaker. A cement grout is applied to the repair surface, and the patch material is placed. The joint is then sealed with silicon or hot-poured materials.
Mill & Overlay (Asphalt)
Mill & Overlay is similar to Overlay, but milling of the road’s surface is required to remove distresses that extend into the pavement. This type of rehabilitation will address alligator cracking, longitudinal/transverse cracking, raveling/weathering, friction loss, roughness, bleeding, block cracking, and rutting. This method performs well in all climatic conditions and will add an expected life of 7 to 10 years to the pavement.
Diamond Grinding (Concrete)
Diamond grinding is a pavement preservation technique that corrects a variety of surface imperfections on both concrete and asphalt pavements. Most often utilized on concrete pavement, diamond grinding is typically performed in conjunction with other concrete pavement preservation (CPP) techniques such as full -depth repair, and joint and crack resealing. Diamond grinding restores rideability by removing surface irregularities caused during construction or through repeated traffic loading over time. The immediate effect of diamond grinding is a significant improvement in the smoothness of a pavement. Another important effect of diamond grinding is the considerable increase in surface macrotexture and consequent improvement in skid resistance, noise reduction and safety.
Patching (Concrete and Asphalt)
All pavements require patching as some time during their service life. Surface patching can be one of the most cost effective means of pavement maintenance. Patching consists of removal and replacement of the defective pavement material. Pavement patching is best utilized to repair pavement surfaces prior to pavement deformation occurring. Typically, material is removed to a point where the existing pavement is stable. The perimeter of the patch area should be cut to create a vertical face. Replacement asphalt or concrete is used to fill the void.
Full Depth Replacement (Concrete and Asphalt)
Full depth pavement replacement is similar to patching, but includes excavation of the base material (compacted stone) and subgrade. Full depth replacement is required when the pavement condition includes pavement deformation which is a sign that the pavement foundation (subgrade) has failed. Typically, unstable materials (stone base and soil subgrade) are removed to a point below the original soil subgrade elevation. The perimeter of the pavement patch area is cut to create a vertical face. The open area is filled to a point with 2-3 inch diameter clean stone (no fines) and then covered with compacted crushed stone. The patch is then filled with replacement asphalt or concrete to the original pavement surface.
In addition, these other pavement maintenance activities might be considered in the future:
A fog seal is a light application of a diluted slow-setting asphalt emulsion to the surface of an aged (oxidized) pavement surface. Fog seals are low-cost and are used to restore flexibility to an existing hot mix asphalt pavement surface. They may be able to temporarily postpone the need for a surface treatment or non-structural overlay. Fog seals are suitable for low-volume roads which can be closed to traffic for the 4 to 6 hours it takes for the slow-setting asphalt emulsion to break and set. An excessive application rate may result in a thin asphalt layer on top of the original HMA pavement. This layer can be very smooth and cause a loss of skid resistance.
Slurry seal is a mixture of aggregate (small rock), asphalt emulsion, cement, and water. The asphalt emulsion serves as a binder, holding the crushed aggregate together and adhering the new slurry surface to the old surface which it is being applied over. Mixing and spreading are accomplished in one continuous operation, with the applied surface being ready for traffic within a few hours. This is similar to a chip seal but, mainly used on low volume traffic roads.
It consists of the application of a mixture of water, asphalt emulsion, aggregate, and chemical additives to an existing asphalt concrete pavement surface. A polymer is commonly added to the asphalt emulsion to provide better mixture properties. The asphalt emulsion used in micro surfacing contains chemical additives which allow it to break without relying on the sun or heat for evaporation to occur. Roadways chosen for cyclical micro surfacing applications would typically be treated every five to seven years.