The long service life expectations of pavements, bridges, and other components cannot be reliably met by using traditional tests for specification and acceptance, which center around three criteria: slump, air content, and compressive strength. These three criteria are only loosely related to deterioration phenomena and do not always ensure satisfactory field performance. Consistent with the focus of MAP-21 legislation on performance, the FHWA, public agencies, and industry are moving towards performance engineered construction materials for more durable and sustainable concrete infrastructure. Performance engineered mixtures (PEM) include optimized mixture designs (materials selection, gradation, cement content etc.) that provide improved durability and sustainability. FHWA has established the PEM Initiative, which focuses on state agency implementation of PEM guidance provided in AASHTO PP 84, “Standard Practice for Developing Performance Engineered Concrete Pavement Mixtures."
This proposed project includes the second phase of work to support NCDOT's movement towards implementation of performance-based provisions. In 2017, NCDOT initiated efforts focused on PEM, including support of FHWA's PEM Pooled Fund Study and funding a separate PEM research project. RP 2018-14, “Durable and Sustainable Concrete through Performance Engineered Concrete Mixtures" is a first step towards implementation of PEM. However, additional work is needed to provide:
- data to support mixture characteristics that reduce paste content through optimized aggregate gradation
- appropriate performance measures and target values for certain types of mixtures not included in RP 2018-14
- refined QA/QC protocol for new PEM tests, including resistivity, super air meter, and the box test
- expanded specification guidance to include additional PEM performance criteria (such as cracking resistance) as appropriate
- technology transfer strategies and implementation tools for NCDOT and other stakeholder personnel.
As evidenced by several states' successful experiences, the benefits of moving towards performance specifications for concrete are tangible. However, each agency must do the groundwork necessary to identify the components of PEM concrete specifications appropriate for their agency and local stakeholders. Objectives of this research are to 1) perform supplemental laboratory evaluation to expand the catalog of data to support development and refinement of PEM specifications for a broader range of concrete mixtures (class A, class B, overlays, very high early strength mixtures, binary/ternary blends), 2) implement PEM tests and shadow specifications at additional projects (specifically bridge projects and very high strength overlay projects), and 3) develop guidance to support contractor QC plans for PEM.
Capitalizing on findings of ongoing research and implementation efforts, this project will provide:
- Test data on a broadened range of highway concrete mixtures (such as Class A, Class B, overlay, high-early strength, and additional binary/ternary blends) to support movement towards performance engineered specifications.
- Suggested performance criteria for the targeted technologies (surface resistivity, SAM, and Box Test) and some prescriptive specification measures (such as w/cm ratio or paste content). Guidance to achieving these targets through optimized aggregate gradations or other means will be provided.
- Recommendations regarding appropriate performance measures, performance goals, test methods, and QA/QC protocol to support NCDOT's continued movement towards PEM.
- Implementation support and observation of PEM shadow specifications on pilot projects focused on bridge applications, findings of QA/QC data analysis, and NCDOT/contractor insight on PEM specification provisions and tests.
- Resources for training and technology transfer aimed at training for NCDOT Division Construction Engineers and Resident Engineers, as well as contractors and other stakeholders potentially involved in PEM, with guidance specifically focused on contractor QC.
- An updated “roadmap" outlining suggested future work for NCDOT to move towards specification(s) for performance-engineered concrete mixtures.
Ultimately, this project will result in cost savings for construction and QA/QC, and extended life of concrete pavements and bridges.