UC Pavement Research Center
Available online at: http://onlinepubs.trb.org/onlinepubs/circulars/ec189.pdf
Harvey, John T., Rongzong Wu, James Signore, Imad Basheer, Sri Holikatti, Peter Vacura, T.J. Holland (2014) Performance-Based Specifications: California Experience to Date. Transportation Research Board 93rd Annual Meeting (E-C189), 1 - 12
Performance-based specifications (PBSs) have been defined as
- Quality assurance specifications that describe the desired levels of fundamental engineering properties (e.g. resilient modulus, creep properties, and fatigue) that are predictors of performance and appear in primary prediction relationships (i.e., models that can be used to predict stress, distress, or performance from combinations of predictors that represent traffic, environment, supporting materials, and structural conditions). (1)
The advantages of using PBS based on mechanistic–empirical (ME) design are clear. PBSs permit the designer to assume that materials constructed on the grade will have similar properties to those that are being used in the ME design structural analyses. They also permit the tailoring of specific materials requirements, such as stiffness, rutting and cracking properties, to unique features of a given project. These unique features include the particular traffic, climate, subgrade and existing pavement layers, and to locally available materials including local reclaimed asphalt pavement (RAP). PBS also allow the designer to “raise the bar” with regard to specific expectations for performance related mix properties compared to what is possible with specifications that rely on aggregate and binder specifications, volumetric mix design, and empirical mix tests.
The development of PBS for pavement and asphalt has been a subject of a great deal of research, including the first Strategic Highway Research Program (SHRP) which included the development of two approaches to ME performance models and testing methods for PBSs for asphalt binders and mixtures to control three distress modes: rutting, fatigue cracking, and thermal cracking (2, 3). There was significant early work in this area in the Netherlands (4), particularly with regard to development and use of four-point bending for stiffness and fatigue. There has been ongoing work in Europe, mostly through RILEM, towards development of performance-based testing methods and specifications going back to the 1960s (5–7 provide snapshots as of 1997, 2003, and 2009) towards the development of international standards for characterizing and specifying mix performance properties. Several European countries are 2 TR Circular E-C189: Application of Asphalt Mix Performance-Based Specifications regularly using PBSs for asphalt, primarily for design–build (DB) and design–build–maintain (DBM) projects where the designer has access to precise understanding of the materials to be used and some control over their properties as part of the design process. There has been extensive work in Australia and New Zealand towards developing tests and PBS for granular bases (8–10). In addition to go–no-go specifications, performance-based incentive–disincentive pay factors for asphalt have been developed based on ME performance estimates (11).
While the benefits of implementation of PBSs are clear, there are a number of issues that have been identified throughout the literature, and in discussions with early implementers. One example was identified in Transportation Research Circular Number E-C037: Glossary of Quality Assurance Terms (1): “…because most fundamental engineering properties associated with pavements are currently not amenable to timely acceptance testing, performance-based specifications have not found application in highway construction”.
The purpose of this paper is to provide a summary of California’s experience regarding development and implementation of PBSs, challenges that have been identified, and ideas for overcoming those challenges from an owner’s headquarters perspective.
Key words: Performance-based specifications, asphalt, pavement, mechanistic-empirical design