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, which are only loosely related to deterioration phenomena and do not always ensure satisfactory field performance. FHWA, public agencies, and industry are moving towards performance engineered construction materials for more durable and sustainable concrete infrastructure. Performance engineered concrete mixtures (PEM) include optimized mixture designs (materials selection, aggregate 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 R 101, “Standard Practice for Developing Performance Engineered Concrete Pavement Mixtures." To support movement towards performance specification provisions, NCDOT has invested in two research studies and two pilot projects. These projects have provided an advanced understanding of testing and specification approaches that could be used to support PEM, shadow specification development and deployment on two pilot projects. Although proposed testing targets and initial pilot projects have been largely successful, additional laboratory testing, field trials and technology transfer are needed to support implementation of these approaches in upcoming NCDOT specification revisions.
Recently, FHWA, agencies, and external stakeholders have increasingly called for improvements in the sustainability of highway infrastructure. Initiatives to lower embodied carbon, reduce greenhouse gas emissions, and mitigate other environmental impacts are underway at both federal and state levels. PEM approaches directly support improvements to the sustainability of concrete infrastructure through use of concrete efficiently, use of cement efficiently, reducing construction impacts, and reducing user costs (Taylor 2023). The mixture proportioning approaches advanced by this and previous projects support a reduction in cement content, increased use of sustainable materials such as Type IL cement and supplementary cementitious materials (SCMs), and reducing waste and rework through improved constructability. PEMs also support longer-lasting concrete for North Carolina infrastructure, reducing maintenance and rehabilitation costs as well as potentially increasing service life. Rapid testing technologies included in the PEM initiative provide an improved understanding of concrete performance, promoting longer-life infrastructure while also reducing the burden on NCDOT and partner entities.
Although a number of the PEM approaches support more sustainable concrete, the environmental impacts of conventional and PEM concrete mixtures used by NCDOT for structures and pavements have not been quantified and compared to each other and to other types of construction. Quantification of the sustainability benefits of PEM concrete through life cycle analysis (LCA) is now possible using LCA frameworks supported by FHWA and other tools used in sustainability assessments. Quantification of the sustainability benefits (via LCA) and economic benefits (via life cycle cost analysis, LCCA) of conventional and PEM mixtures would allow NCDOT to understand cost savings associated with longer service life and reduced maintenance costs, improved performance due to an enhanced focus on quality during construction, and understand the link between laboratory test results and performance. This assessment will assist NCDOT in meeting its goals and requirements to improve the sustainability of its concrete infrastructure directly supporting NCDOT's Climate Strategy Report, Activity 1.0 - Reduce Greenhouse Gas Emissions, since the PEM mixture design and proportioning approaches and testing technologies support Activity 1.5 - Initiate other initiatives to decarbonize the transportation sector and Activity 1.6 – Initiate other projects aimed at reducing statewide greenhouse gas emissions.
This proposed project includes the third phase of work to support NCDOT's movement towards implementation of performance-based provisions, with an added focus of quantifying the economic and sustainability benefits of PEMs. Objectives of this research are to 1) perform additional laboratory testing and evaluation to support development and deployment of PEM tests and mixture design approaches, 2) implement PEM tests and shadow specifications at additional projects (specifically bridge projects and pavement projects using optimized aggregate gradation mixtures and other PEM approaches), and 3) perform assessments of sustainability benefits (economic, environmental, and social) of PEMs using LCA and LCCA. This project will provide:
- Recommendations regarding appropriate performance measures, performance goals, test methods, and QA and QC protocol to support NCDOT's continued movement towards PEM.
- Data to support implementation of surface resistivity in future specification revisions.
- Recommendations regarding use of this information in design, specifications, construction, and QA and QC testing.
- Additional field experience using PEM approaches and technologies in pavement and bridge pilot projects.
- An increased number of agency, contractor, and industry personnel familiar with PEM approaches and technologies.
- Quantification of the benefits (economic, environmental, and social) that would be achieved by using PEM technologies and approaches in structural and pavement concrete.
- Data that benchmarks where NCDOT infrastructure as currently designed, constructed, and maintained currently stands in terms of sustainability, and an improved understanding of what sustainability strategies can be readily integrated into practice.
- Opportunities for sustainability improvements for different types of infrastructure components, along with cost analysis to support application for funding for proactive improvements and recovery.
- A roadmap of objectives and activities to support mid-range and longer-range advancements to support future research and implementation activities.
Ultimately, this project will provide evidence indicating that PEMs can assist NCDOT in meeting its sustainability goals, provide cost savings for construction and QA and QC, and extend the life of concrete pavements and structures.
