Civil Engineering Association

Subbase and Subgrade Performance Investigation and Design Guidelines for Concrete Pavement

The main issue associated with this research is if cheaper alternatives can be configured for subbase construction. Subbase layers have certain functions that need to be fulfilled 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 alternatives to perform adequately. In this respect, this project was poised to examine the design assumptions associated with each alternative and provide design recommendations accordingly to include test methods and material specifications. This report describes some of the work accomplished by summarizing data on subbase performance and testing relative to concrete pavement subbase and subgrade erosion but mainly addresses guidelines for concrete pavement subbase design. Findings from field investigations are discussed to identify factors associated with erosion. An approach to mechanistically consider the erosion process was introduced and review of current design procedures was conducted to reveal how they address erosion. This review was extended to include erosion models described in the literature as a means to shed light on the relationship between measurable material properties and performance. Additionally, past and current design procedures relative to erosion were reviewed in terms of test methods, erosion models, and their utility to characterize subbase materials with respect to erosion resistance. With this information, a new test configuration was devised that uses a rapid tri-axial test and a Hamburg wheel-tracking device for evaluating erodibility with respect to the subbase type and degree of stabilization (cement content). Test devices, procedures, and results are explained and summarized for application in mechanistic design processes. A proposed erosion model was validated by comparing erosion predictions to erosion results. Several computer program analyses were conducted to assess the design and performance implications of different subbases alternatives. Guidelines are provided to promote economical and sustainable design of concrete pavement subbases.