Aggregates constitute a major part of pavement construction. The strength, durability, and quality of the aggregate affects the overall performance of the pavement structure. Materials sourced near a construction site do not always meet the strength required for pavement construction, however, and haulage of aggregates of the required quality is often costly. For better use of locally available materials, stabilizing agents such as lime, cement, asphalt cement, and fly ash are often used to enhance the strength of the local aggregates. Pavement performance is influenced by both the structure itself and the layer materials present in it. The stiffness of the base layer, for instance, influences the tensile strain in the asphalt layer and compressive strains in the subgrade soil. The tensile strains at the bottom of the asphalt layer and compressive strains in the top zone of the subgrade soils are the main response components affecting fatigue cracking and rutting, respectively. In this study, field performance [rutting, cracking, and roughness measured in relation to the International Roughness Index (IRI)] of pavement sections with treated and untreated base layers were compared to determine the effects of stabilizing agents. In relation to fatigue cracking and pavement surface roughness, the treated sections outperformed the untreated sections. The average values of all three distresses showed better performance for the treated base layer sections with fatigue cracking averaging 2.2 times lower than the untreated sections. The combined rutting and IRI of the treated base layer sections averaged about 0.10 in. and 1.4 times lower than those of the untreated base layer sections, respectively.

Over the past decades, traffic volume has increased rapidly throughout the State of Texas and the U.S.A. in general. This continuous increase in traffic loading has resulted in increased roadway construction with the need for stronger structural base layers to support the heavy truck loads. Consequently, the demand for high-quality aggregates has also increased as a result of the increase in highway construction. Haulage of high-quality aggregates from different, distant sources can directly increase the cost of construction. The annual total consumption of aggregates in the U.S.A. has now reached 1.5 billion tons and is expected to increase as much as 50% in the next 10 years (1). This increasing rate of consumption and the continuous demand for higher quality materials are exhausting many suitable aggregate sources. Several areas throughout the country are already experiencing a shortage of certain types or a total lack of suitable local aggregates (1). Quite often, the base materials available near construction sites do not have the required strength to withstand the heavy traffic loading. A base course must be sufficiently strong and rigid to sustain the high unit pressure without excessive consolidation, distortion, or lateral flow. As the surface course becomes thinner, the base course must be stronger and more durable (2). For better utilization of the aggregates present near the construction areas, different treatment methods are used to treat these materials to obtain the optimum strength required to support the heavy traffic loading. Stabilization of materials can be mechanical or chemical and is usually done by asphalt cement, lime, cement, and fly ash for flexible pavements.

Pavement performance is influenced by both the pavement structure and the properties of its respective layers, as well as the traffic loading and environmental conditions, among other things. Structural failure in a pavement occurs when the mechanical responses, such as the horizontal tensile strains at the bottom of the surface layer, the vertical deformation in each of the layers, or both, exceed the threshold design criteria. The stiffness of the base layer can significantly influence the tensile strains in the hot-mix asphalt (HMA) layers and the compressive strains at the top of the subgrade layer of flexible pavements.

Since the stiffness of the base layer depends on the material properties of that layer, the type of base layer used in a flexible pavement can influence the overall performance of a flexible pavement. Generally, two types of base layers are utilized in flexible pavements; unbound bases and stabilized bases. The functions of all base layers are to provide support for the HMA layers and to distribute the traffic loading efficiently onto the subgrade or the subbase layers (3).