3.0 Design Considerations
Partial-depth repairs extend the life of PCC pavements by restoring ride quality to pavements that have spalled joints. Partial-depth repair of spalled areas also restores a well defined, uniform joint or crack sealant reservoir prior to joint or crack resealing. When properly placed with durable materials, these repair can perform well for many years. The following factors should be considered during the design of partial-depth repairs.
Partial-depth repairs may have several objectives. In adverse conditions, a temporary partial-depth repairs may be needed. In this case, the design should provide for adequate temporary repair life until a permanent repair can be made.
If a partial-depth repair is being placed prior to an overlay construction, tolerances are not as stringent. For example, repair edges do not have to be completely vertical and straight, the repair material does not need to wear well, and the joint does not have to be sealed. This is because the overly will reduce the load and environmental stresses on the repair. Furthermore, an overlaid repair material will experience smaller temperature changes than a repair that is not overlaid.
If a spall must be repaired because it presents a hazard to the highway user, but the pavement is scheduled for an upcoming rehabilitation that will destroy the partial-depth repair, design considerations should reflect this anticipated short service life.
A partial-depth repair that will not be covered or destroyed in a future rehabilitation will be exposed to traffic and climate for a long time. In this case, it is cost-effective to select high quality materials, repair methods, and workmanship.
An important step in constructing a successful partial-depth repair is the identification and removal of all deteriorated concrete. The actual extent of the deterioration in the concrete may be greater than is visible at the surface. In the early stages of spall formation, weakened planes often exist in the pavement with no sign of deterioration visible at the surface. The extent of deterioration can be determined by "sounding" as explained in Section 4.2.
Partial-depth repairs should be limited to the top one-third of the pavement and should not be so deep that dowel bars will contact the repair material. The repair boundary should be clearly marked with brightly-colored spray paint.
Material selection for partial-depth repairs should consider the following factors: mixing time and required equipment, working time, temperature range for placement, curing time, aggregate requirements, repair area moisture conditions, cost, repair size, and bonding requirements. The following are guidelines for selection of materials:
- Normal set concrete can be used when the repair material can be protected from traffic for more than 24 hours.
- Normal set concrete should not be used when the air temperature is below 40° F (4° C). At temperature below 55° F (13° C), a longer curing period or insulation may be required.
- Type III cement or an accelerated repairs admixture is used for repairs that need to be opened to traffic quickly. An insulating layer can be placed on the hydrating PCC to retain the heat of hydration thereby increasing the rate of strength development.
- Many rapid-setting materials require special safety precautions to protect the maintenance worker and to protect the environment. For the rapid-setting proprietary materials, it is important that the manufacturer's recommendations be followed.
- Gypsum-based (calcium sulfate) repair materials, such as Duracal and Rockite, can be used in any temperature above freezing or for rapid strength gain. However, gypsum concrete does not perform well when exposed to moisture or freezing weather, and the presence of free sulfates in the typical gypsum mixture may be promote steel corrosion in reinforced PCC pavement.
Highway agencies should select the most cost-effective material that meets the requirements of the project. Cost-effectiveness is a function of repair material performance and life, as well as the characteristics of a given project, such as traffic and user delay costs.