Sustainable Engineered Materials

Summary

To develop and deploy measurement science tools that enable the manufacturing, construction, and transportation industries to reliably assess the performance of sustainable materials for current manufacturing processes and develop service life prediction methodologies for cement and polymer materials that are faster and more accurate for long-term performance.

Description

NIST will advance measurement science tools to reliably assess the performance of sustainable materials for the manufacturing, construction, and transportation industries. These industrial sectors must meet demands for higher performance, multi-functionality, and for longer life to ensure a sustainable economy. New sustainable products, based on nanotechnology, recycled or by-product materials, hierarchical composite materials, and manufacturing processes, are continually introduced to consumers. The challenge for producers and users of these products is a lack of measurement science tools to support the evaluation of sustainable technologies. This program will develop measurement science tools that help industry make informed decisions regarding sustainability of materials: utilizing new technologies or materials to increase performance and high-throughput methodologies for accurate service life prediction.

What is the problem?

Measurement science tools are lacking for U.S. manufacturing, construction, and transportation industries to reliably engineer sustainable materials into product lines and manufacturing processes, predict the service life of current and new materials, and reliably repair existing infrastructure. The most common material classes used across the sectors mentioned above are steel, concrete, polymers, and polymer composites. This program will focus on concrete and polymers/composites, while steel will not be directly addressed.

The pressure is growing on U.S. Industry to develop innovative solutions to meet increasing customer and regulatory demands for sustainable manufacturing, construction, and transportation materials. This is particularly true for infrastructure where structures have not been properly maintained and are in use beyond their design lifetimes. There are examples of failures and potential failures that arrive in headlines everyday for roads, water, and energy materials. There are no quick fixes because the cost of replacement is astronomical. The U.S. must look to innovative methods to accelerate the introduction of new materials that reduce the cost of construction, increase the design life of current structures, or provide efficient structural repair strategies. Polymeric materials play a critical role and have been identified as a major national need to meet these demands. Coatings prevent corrosion and structural adhesives are critical in the repair of existing infrastructure. Polymer materials provide fuel savings, reduce environmental impact, and can save labor installation costs. A challenge for polymeric materials is the measurement science for long term performance. Often materials perform well in the laboratory, but underperform in the real world due to a lack of understanding of the exposure environment or degradation kinetics. U.S. Industry spends significant investment and time to insure materials will not fail early because the liability costs are prohibitive. Accelerating this process, while providing more accurate predictions of service life, is a competitive advantage on the global scale.

The concrete and cement industry contributes up to 8 % of CO2 emissions, but can reduce fly ash and slag waste by 24 % by investing in innovative alternative cementitious materials. 3.5 billion metric tons of Portland cement is used by this industry and reducing this amount by one ton would produce a comparable reduction in CO2 emissions. Rehabilitation and repair of existing infrastructure is critical to reducing emissions and economically extending the life of current infrastructure. Several examples show the urgency of this problem. The total costs of repairing/replacing the US infrastructure is estimated to exceed $3.6 trillion and the American Society of Civil Engineers (ASCE) has recommended that "as infrastructure is built or rehabilitated, life cycle cost analysis should be performed", which will not be performed in sustainable manner without SLP. The Administration has stated that building a world-class physical infrastructure is one of its top priorities for innovation. A technology gap in the long-term strategic plan for highways is an inability to ensure reliable and sustainable performance of "green" concrete in the short and long term.

The capability to predict service life of materials is becoming paramount to developing successful metrics and standards. The International Code Council is updating its International Green Construction Code to include Environmental Product Declarations (EPD) that communicate the environmental impact of a product throughout its lifecycle, but appropriate standards are required for life cycle assessment of building materials. Software tools, such as Building Environmental and Economic Sustainability (BEES), can guide industry decisions, but they require quantitative service life prediction data and models in order to predict the environmental impact of a building material. These changes will have important impacts on critical polymers used in the construction and infrastructure industries. Polyethylene, one of the most ubiquitous polymers globally, is a replacement material for piping, cables, wrap in construction for sealing, geomembranes for environmental protection, and environmentally stable films. Polymeric coatings are critical for protecting surfaces from corrosion, wear, and maintaining the appearance of consumer products. The yearly global market in sealants and adhesives is approximately $40B, and standards that accurately measure their durability are an outstanding problem in their sustainable use.

The problems can be broken into manageable pieces that address critical areas and move industries closer to the overall US sustainability goals. Deterioration due to aging and mechanical fatigue place these structures at risk for failures, which could cost the U.S. hundreds of billions of dollars and directly impact our personal and economic health. Faced with constrained budgets, decision makers seek cost-effective alternatives to revitalize the Nation's infrastructure. Unfortunately, a significant barrier to the consideration of these alternatives is the lack of validated cost-benefit tools that include a reliable estimate of the total cost over the entire duration of service. Without these tools, decision makers will be strongly inclined to make direct replacements, using the same materials and methods, rather than new approaches that could save the Nation time and money. In cementations materials, the industry is not able to predict performance based on any feedstock source, predict the reliable pumping of a concrete, or accurately specify the long-term performance of repairs, or support efficient incorporation of waste materials into cement. In polymeric materials, accelerated aging methodologies and equipment are prescriptive and without a clear methodology to generate predictive models for any material or any arbitrary exposure conditions.

What is the new technical idea?

This research has two thrusts:

1) service life prediction (SLP) of polymer materials and 2) the prediction of performance, concrete placement, repair for traditional portland cements, and the performance of alternative cement materials.

The service life prediction of polymeric materials state-of-the-art continues to focus on simulating the outdoor environment. The outdoor environment is never repeatable and in a world of shifting climates, the past is not indicative of the future patterns. Therefore, new reliability-based damage-dose models are required to predict damage based on input from any local environment and change the paradigm for service life prediction. In order for these techniques to work, modelers need material data and better accelerated weathering devices to reduce uncertainty.

Transforming the concrete construction industry from prescriptive and empirical design to performance based requires the development of new measurement tools. These tools are need both for new constructions and existing constructions. Both scenarios require development of new techniques for material characterization, placement metrology, prediction of performance of concrete repair. New additive manufacturing technologies, i.e., 3D printing, are being explored for increasing productivity and reducing cost of concrete construction.

What is the research plan?

The majority of projects within this program are focused to deliver a strategic plan on critical problems in sustainable engineered materials. The accelerated aging of polymeric materials projects will fully develop the foundations of the service life prediction methodology. Input from concrete stakeholders has shown that a focus on hydration models, concrete placement, and repair technologies are needed to continue to make concrete a sustainable infrastructure material.

The Sustainable Engineered Materials program remains distributed into two thrusts: 1) service life prediction (SLP) of polymer materials 2) prediction of the performance, concrete placement, repair for traditional portland cement, and the performance of alternative cement materials.

The goal of thrust 1 is to deliver the next-generation weathering standards, materials degradation databases (data management systems), and models for SLP in a form that accelerates the timeline for materials development for our stakeholders. The SPHERE exposure device, developed at NIST, has been the cornerstone that has world-class performance for ultraviolet light uniformity and temperature/humidity control. The current program builds on the past lessons learned using the SPHERE technology that include; proof-of-concept for the SLP methodology and weathering of specialized materials (nanocomposites, elastomers, and fibers). The SLP methodology at its heart does not seek to mimic outdoor exposure cycles indoors, but build a database of performance over time in specific aggressive exposure conditions. This database is used to model performance degradation for any outdoor exposure profile using a damage-dosage model that accounts for the damage caused by each stressor (UV, T, humidity). Stakeholders have recognized the potential of the SLP methodology to deliver results, but have cited the lack of technology transfer, traceable materials degradation databases, and validated, predictive models are hindering adoption. In addition, questions remain on the ability of this high intensity UV source to not change photodegradation kinetics for all polymeric material chemistries. This SLP of polymer materials thrust is broken down into two projects: A) The NIST Accelerated Weathering Laboratory: Metrology and Operations and B) the Measurement Science Tools for Accelerated Weathering of Polymers. Project A will deliver world-class weathering exposure, based on the 2m SPHERE, to support SLP for materials. Within this project the process for transferring the 2m SPHERE technologies to a stakeholder accessible 0.5m SPHERE design (MUUSIC and strain SPHERE) is supported. The deliverables are the development of control chambers, safety interlocks, and validation of the smaller devices, including a strain SPHERE against the 2m SPHERE. Standards will be developed for weathering equipment, exposure controls, and reciprocity protocols. Project B will deliver the foundation for SLP methodology for critical polymer chemistries in infrastructure and transportation. The deliverables will directly address the demands of stakeholders for the expansion of the materials database and predictive models based on the SLP methodology. Standard protocols and guidelines will be delivered that accelerates the development of predictive models for critical performance parameters and maintain data integrity. The project teams will engage stakeholders through publications, workshops, and participation in standards committees. This project will support the investigation of a second material system and increase the technical support for completing materials characterization. Both projects will solidified and delivered the foundations for the SLP methodology to stakeholders the most relevant polymer chemistries.

The goal of thrust 2 , related to concrete, will continue to leverage NIST world-recognized expertise in measurement science for concrete to address new challenges for stakeholders in concrete placement, chemical kinetics, repair, and innovative materials. This thrust is broken down into four projects, where the measurement science deliverables continue to increase the capability to accurately predict the properties of traditional and innovative concrete, increase reliability of concrete placement, and assessment of repair integrity of concrete structures. Significant risks remain for concrete producers because an unforeseen change in cement composition leads to poor concrete performance and decreased service life. This lack of materials science has limited the ability of producers to engineer concrete performance. It has created a need for raw material characterization protocols that are relevant for predicting hydration. These protocols, databases, and models will be delivered in the Project A, Chemical, Structural, and Kinetic Measurement Technologies for Cementitious Materials. Project B, the Properties of Sustainable Fresh Concrete will deliver measurement science tools for evaluating whether a concrete can be pumped. Pumping has become a critical process for the placement of concrete into modern construction, but improper placement will significantly reduce the performance and service life of the concrete. There are no predictive models or standards that tell a user whether a concrete can be pumped and placed. Modeling is used, from the computational materials science-type models using high-powered computers to simple parameterized equations, to understand measurements, suggest new measurements, and transform performance measurements into performance predictions. Project C, Assuring Performance of Infrastructure Repair Materials, addresses repair and rehabilitation of concrete structures. Stakeholders responsible for the maintenance and repair of the public infrastructure have little measurement science tools available for assessing repair technologies or the proper surface preparation to maximize the repair strength. Without these tools, owners do not know whether the repair returned the structure to original performance metrics, stops the corrosion process around the repair, or the service life of the repair. This project will deliver the measurement science tools for optimum surface preparation and measurement of bond strength once the repair is applied. Project D, Measurement Science to Assure the Performance of Innovative Concretes, reflects the core strengths in chemical and processing characterization of innovative concrete materials. The performance of innovative concrete effort will build on the group core expertise in characterization, curing kinetics, and ASTM standards to provide measurement science that improves reliability of fly ash and limestone feedstock, ASTM standards for these materials, and new construction technologies for innovative concrete to reduce energy. The project will also explore novel additive manufacturing methods for increasing energy efficiency and performance of concrete materials.

Major Accomplishments

Some recent accomplishments for the Sustainable Engineered Materials Program include:

• Published archival journal article indicating that ternary blend HVFA blends are less sensitive to low temperatures than binary blends of only cement and fly ash.
• In collaboration with CNST utilized new metrologies for quantitative assessment of CNT microstructure.
• All the weathering standards for sealants and building joints in ASTM C24 Building Joints and Sealants have been changed to include mechanical movement. "Weathering" in this committee now is defined as having a mechanical movement component, a key variable in service life prediction, solely due to the measurement science research of this program.
• ASTM C1760-12 Standard Test Method for Bulk Electrical Conductivity of Hardened Concrete and ASTM C1585 Sorptivity Test Method, approved in FY12. These two documents standardize two key transport property measurements that are used in service life prediction.
• ASTM C1749-2012: Standard Guide for Measurement of the Rheological Properties of Hydraulic Cementitious Paste Using a Rotational Rheometer. First of a suite of standards that will allow the quantitative use of calibrated concrete rheometers.

• ASTM C1761-2012  Standard Specification for Lightweight Aggregates for Internal Curing of Concrete. Standardizes how to cure concrete to achieve low-cracking potential, giving more durable concrete.