A Strong but Flexible Base
Cost-Effective Engineered System for Upgrading Roads
There are many miles of secondary roads that are in need of upgrading. If unpaved, they require constant maintenance attention to potholes, ruts and dust control. Speed limits must also be low to prevent accidents. If paved, very often the loadings exceed the structural capacity. Many suffer from base problems. If they are to qualify to carry standard 80,000 pound trucks, the pavement structure needs to be improved. Full depth reclamation (FDR) and base stabilization have been used for many years on such roads with various additives, including asphalt emulsions, lime, cement and foamed asphalt. The results have been mixed. To date there has been no standard method for designing emulsion stabilized mixes. SemMaterials' Fortress® technology addresses the problems with an engineered design, a set of performance-related specifications and a new chemistry emulsion formulated specifically for the stabilization process. One of the biggest problems facing most road owners is the lack of sufficient funding to maintain all the roads in their system. The Fortress system is a cost-effective first step to upgrading the roads, eliminating dust problems, protecting the existing pavement structure, and increasing property values, thus providing economic benefits for both the agency and the road users.
The SemMaterials Fortress® system is a cost-effective technology for correcting deficiencies, reclaiming distressed pavements and providing structurally sound bases for existing roads. Following an engineered design, the existing pavement and / or granular base is uniformly pulverized to a depth of 6 to 8”, treated with a solventless asphalt emulsion, and compacted in preparation for the recommended new surface. The Fortress stabilized base could be a first step in staged construction. Staged construction avoids excessive initial investment, but enables the pavement to be easily upgraded by adding structure as traffic volumes and loads increase.
The Fortress® pavement has the strength of an asphalt-bound base to withstand traffic, and the flexibility of the bituminous material to withstand repeated traffic loadings as well as temperature fluctuations. The engineered design is responsible for the strength. When needed, the design may call for rock to be added to correct the gradation. The design is based on performance tests, such as the resilient modulus (MR), indirect tensile strength and a short-term strength test, all run on samples prepared in the Superpave Gyratory Compactor (SGC).
The Fortress® stabilized material is flexible because of the new technology asphalt emulsion. The new chemistry allows a better dispersion and coating of asphalt on the materials, and the base asphalt is selected on climatic needs. The indirect tensile test is used as a design tool to specify a thermal cracking temperature for the specific pavement. The emulsion is also designed to cure quickly, allowing faster construction, cure, surfacing and traffic return than emulsions conventionally used for reclamation and stabilization.
The Fortress® system is cost-effective because it uses the existing materials in the roadway, building structure down into the pavement. If the traffic is light, a chip seal or other surface treatment is all that is needed. More structure can be built as funds and traffic dictate. The profile of the pavement can be maintained, meaning minimal realignment adjustments. The process also facilitates road widening.
The Texas Department of Transportation, counties in Minnesota, Illinois, Nebraska, Georgia, and an industrial park in Colorado have all been pleased with the results of their Fortress® projects.