Satisfactory pavement performance is largely attributed to a good foundation that provides adequate strength and stability. Base and subgrade layers serve as the foundation of pavement structures. Structurally, base and subgrade layers must provide adequate strength and must distribute loads uniformly and effectively. This structural capacity is obtained by optimizing material engineering properties, ensuring adequate confinement and drainage. When widening or rehabilitating an existing pavement structure, it is essential to match the existing typical section when possible. Frequently, in situ soils and local base materials do not meet the material engineering properties required for good pavement foundation performance. Texas has some of the most expansive soils in the country, which cause distresses in many pavements around the state. Also, a large portion of pavement construction performed today consists of rehabilitating existing roads, which frequently contain reclaimed subgrade and/or base material layers that are inadequate for current or future traffic loading demands. In order to achieve needed engineering properties, subgrade soils and engineered materials (select fill and flexible base) frequently require treatment.

Material properties are improved by incorporating chemical additives, such as lime, cement, fly ash, emulsion, or asphalt. These additives, or a combination of these additives, are effective when the material is designed and applied properly. Proper design and application of materials with additives will minimize premature failures of the material and pavement structure.

“ ” is a document outlining the proper methodology of selecting, designing, and evaluating treated soils and base courses for pavement structures. This document also provides some basic knowledge on the various treatment methods, the goals of treatment, and the mechanisms of each treatment method.

When soils and base contain soluble sulfates, use the " ” to identify the feasibility for treatment and construction considerations for incorporating chemical additives.