Subbase and Subgrade Performance Investigation for Concrete Pavement (0-6037-1)

Recently, TxDOT has become increasingly aware of the rising cost associated with the use of asphalt concrete bond breakers to meet the FHWA requirement of using a permanently stabilized, nonerodable subbase layer below the concrete slab. The main issue associated with this research is if cheaper alternatives are available for subbase construction. Subbase layers have certain functions that need to be fulfilled (one of them being constructability) in order to assure adequate pavement performance. One key aspect is resistance to erosion, and assessment of each of these functions relative to different alternatives is key to understanding the capability of different alternative and provide recommendations accordingly to include test methods and material specifications. This report describes some of the work accomplished summarizing data on subbase performance and testing relative to concrete pavement subbase and subgrade erosion. Findings from investigations are discussed to identify factors associated with erosion in the field based on various analysis methods such as load transfer efficiency (LTE), effective thickness, and ground penetrating radar (GPR). An approach to mechanistically consider the erosion process is introduced and review of current design procedures was also conducted as to how they address erosion. This review was extended to address erosion models included in the literature in terms of the relationship between measurable material properties and performance. Moreover, previous and current laboratory test methods for erosion testing are summarized and the test results of selected alternative subbase materials are discussed. Finally, the relation between k-value and slab behavior is discussed.