GUIDELINES FOR MIXTURE DESIGN AND THICKNESS DESIGN FOR STABILIZED BASES AND SUBGRADES

Abstract

The Texas Department of Transportation (TxDOT) uses stabilized subgrades and bases extensively. In fact subgrade stabilization is almost routine in many districts and especially in those with clay subgrades. A pressing need exists to determine the effectiveness of stabilization of subgrades and base courses, to evaluate the current mixtures and thickness design approaches and to suggest realistic structural properties associated with these stabilized pavement layers. This report considers both base course and subgrade stabilization. Stabilized bases are divided into three categories: heavily stabilized, moderately stabilized and lightly stabilized depending on the amount of stabilizer used. Heavily stabilized bases perform as rigid structural layers. This report suggests modifications to currently used TxDOT mixture design and thickness design approaches to minimize structural damage within the stabilized base layer due to both non-load associated cracking and load associated fatigue cracking. Moderate and light levels of base stabilization significantly improve the structural contribution of the layer without, in most cases, producing a rigid structural layer. This type of stabilization is advantageous in many applications. The report suggests appropriate mixture design approaches and thickness design approaches employing current TxDOT testing and analytical tools for moderately and lightly stabilized bases.