Chemical stabilization with cementitious and chemical additives such as portland cement, lime, fly ash, and calcium chloride (CaCl2) is now being extensively used in road base or subgrade primarily to enhance mechanical strength and improve resistance to chemical attack, resulting in a more durable roadway. In recent years, there has been renewed interest in the combined use of these additives to induce a synergistic effect on the strength, as well as to improve deficiencies of a single-chemical treatment process (e.g., slow early strength development of fly ash and susceptibility to leaching of CaCl2 in wet environments). The effect of adding CaCl2 to the fly ash-treated roadbed during construction was investigated. The role of CaCl2 in the system was studied, where determination was made as to how the soluble calcium species plays a role in bringing particles closer in the aggregate system and how it has an effect on the setting time, compaction efficiency, and ultimate strength. Laboratory test data revealed that the addition of CaCl2 not only accelerated the setting rate but also increased the initial and long-term strength of the constructed roadbed. On the basis of these laboratory tests, a mathematical model was developed that predicts the strength of the composites. Finally, field performance data showed that fly ashes can be effectively used in road construction if CaCl2 is added to the system.