Bituminous patching mixtures

Bituminous patching mixtures are combinations of bituminous binders and aggregates that have special characteristics needed for filling holes in pavements. The different types of patching mixtures can be placed in one of three groups: hot-mixed, hot-laid; hot-mixed, cold-laid; and cold-mixed, cold-laid. Among the properties that a bituminous patching mixture should have are: stability, to allow the patch to resist displacement by traffic; stickiness, so the patch will stick to the sides of the hole; resistance to water action, to keep the binder from stripping of the aggregate; durability, so the patch does not ravel or crack; skid resistance as good as the pavement in which it is placed; workability, to enable the material to be easily shoveled, raked, and shaped; and storageability, so the mixture can be stockpiled without hardening excessively or having the binder drain off the aggregate. Various tests are used for specifying, designing, and approving patching mixtures. Stability tests are rarely used and then only to control hot-laid mixtures. Adhesion tests are used more often. These include coating tests, stripping tests, or an immersion-compression tests (only for hot-laid mixtures). Design of hot-laid patching mixtures is essentially the same as for dense-graded, hot-mixed asphalt concrete. For cold-laid mixtures, there is no widely adopted formal design process; however, successful procedures, usually involving trial- and-error, have evolved over time. Production methods for patching mixtures are essentially the same as for other bitumionus mixtures. The hot-laid materials are used immediately, and cold-laid mixtures are stored for use as needed. In recent years, composite bituminous mixtures have been developed. These include sulfur-asphalt mixtures, addition of portland cement, and reinforcement with polyester fibers, rubber, or inorganic fibers. However, there is only limited field experience with these composites.