Evaluation of Glauconite Aggregate for Pavement Construction (7-3901-S)

Glauconite is an abundant aggregate in east central Texas. However, it is rather soft and thus subject to crushing and abrasion under normal construction processes. The purpose of this research study is to evaluate the quality of glauconite and determine its suitability for use on TxDOT pavement construction projects and if it is suitable, how to optimize its utility. Laboratory tests on chemically stabilized glauconite were conducted.This work was conducted in two phases. Phase I evaluated two unstabilized glauconites: soft and hard. Results of Phase I showed that neither glauconite product was suitable for routine use on TxDOT pavements as a flexible base (Specification Item 247) without some type of stabilization or other strength/durability enhancing strategy. Phase II was conducted to determine selected performance-related properties of stabilized glauconite. The stabilizers included cement, hydrated lime, and lime + fly ash. Unstabilized and stabilized glauconite were compared with unstabilized and stabilized iron ore gravel (which has been used as pavement base materials in East Texas for many years).Glauconite will absorb and hold relatively high quantities of water. Glauconite will not likely pass the wet ball mill test. This further has a negative impact on linear shrinkage which will also not consistently meet specifications. However, the plasticity index is acceptable. Glauconite will not consistently pass the triaxial test. Stabilization with Portland cement yielded the best strength enhancements and resistance to moisture suction when compared to stabilization with lime + fly ash and hydrated lime. Hydrated lime provided the least stabilization for glauconite. Wide variability in glauconite properties manifests potential construction and performance problems related to quality control. This study recommends that the routine use of glauconite on TxDOT roadways be avoided.