Measurement Science for Predicting Life Cycle Performance of Nanocomposite Infrastructure Materials

The primary core competencies for the Strategic Priority Area of Measurement Science for Predicting Life Cycle Performance of Nanocomposite Infrastructure Materials are performance, durability, and service-life prediction of building materials. Secondary core competencies include fire protection and fire spread within buildings and communities.

Materials-related areas of expertise within this Strategic Priority Area include concrete, nanotechnology, polymers, and materials flammability. Measurement-related expertise includes chemical, physical, mechanical, optical, and electrical properties of materials from nano- to macroscales, in addition to computational materials modeling. The BFRL divisions active in this area are the Materials and Construction Research Division (MCRD) and the Fire Research Division (FRD). The active groups include the Inorganic Materials Group and the Polymeric Materials Group (in the MCRD) and the Materials and Products Group (in the FRD). The primary BFRL goals in this strategic area are High Performance Construction Materials and Systems and Innovative Fire Protection Technologies. The key programs are the High-Performance Construction Materials and Systems Prediction and Optimization of Concrete Performance Program, the Service Life Prediction of Nanostructured Polymeric Materials Program, and the Reduced Risk of Fire Spread Program.

TECHNICAL MERIT RELATIVE TO STATE OF THE ART

The mission of the work in this strategic area involves the testing of nanocomposite materials to allow long-term structural utility. The utility of nanocomposite materials in the large infrastructural applications requires measurement science and models to predict performance to the level required for engineering applications. An additional concern involves the environmental and safety aspects of nanoparticle release into the atmosphere over the life cycle of the nanocomposite. Both of these concerns are critical for the acceptance of nanocomposite technology into commodity applications of the future, including civil engineering infrastructure applications (e.g., buildings, bridges). These goals are well aligned with the mission of NIST.

The projects of the Polymeric Materials Group and the Inorganic Materials Group were reviewed within this context. The integrating sphere-based ultraviolet chamber was discussed in detail. The information disclosed indicates that it is the most realistic experimental method of providing accelerated weathering data offering excellent agreement with natural outdoor weathering. This is quite important, as it allows for significant decreases in testing time while offering a high level of confidence that the accelerated results can be used to quantitatively predict long-term exterior performance—a testing capability desired by a multitude of industries but not currently available. A goal for this project is to achieve the transfer of this elegant testing methodology to industry and the military for the exterior performance assessment of new materials. In essence, the transfer of this testing capability to an independent laboratory with more routine



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Measurement Science for Predicting Life Cycle Performance of Nanocomposite Infrastructure Materials The primary core competencies for the Strategic Priority Area of Measurement Science for Predicting Life Cycle Performance of Nanocomposite Infrastructure Materials are performance, durability, and service-life prediction of building materials. Secondary core competencies include fire protection and fire spread within buildings and communities. Materials-related areas of expertise within this Strategic Priority Area include concrete, nanotechnology, polymers, and materials flammability. Measurement-related expertise includes chemical, physical, mechanical, optical, and electrical properties of materials from nano- to macroscales, in addition to computational materials modeling. The BFRL divisions active in this area are the Materials and Construction Research Division (MCRD) and the Fire Research Division (FRD). The active groups include the Inorganic Materials Group and the Polymeric Materials Group (in the MCRD) and the Materials and Products Group (in the FRD). The primary BFRL goals in this strategic area are High Performance Construction Materials and Systems and Innovative Fire Protection Technologies. The key programs are the High-Performance Construction Materials and Systems Prediction and Optimization of Concrete Performance Program, the Service Life Prediction of Nanostructured Polymeric Materials Program, and the Reduced Risk of Fire Spread Program. TECHNICAL MERIT RELATIVE TO STATE OF THE ART The mission of the work in this strategic area involves the testing of nanocomposite materials to allow long-term structural utility. The utility of nanocomposite materials in the large infrastructural applications requires measurement science and models to predict performance to the level required for engineering applications. An additional concern involves the environmental and safety aspects of nanoparticle release into the atmosphere over the life cycle of the nanocomposite. Both of these concerns are critical for the acceptance of nanocomposite technology into commodity applications of the future, including civil engineering infrastructure applications (e.g., buildings, bridges). These goals are well aligned with the mission of NIST. The projects of the Polymeric Materials Group and the Inorganic Materials Group were reviewed within this context. The integrating sphere-based ultraviolet chamber was discussed in detail. The information disclosed indicates that it is the most realistic experimental method of providing accelerated weathering data offering excellent agreement with natural outdoor weathering. This is quite important, as it allows for significant decreases in testing time while offering a high level of confidence that the accelerated results can be used to quantitatively predict long-term exterior performance— a testing capability desired by a multitude of industries but not currently available. A goal for this project is to achieve the transfer of this elegant testing methodology to industry and the military for the exterior performance assessment of new materials. In essence, the transfer of this testing capability to an independent laboratory with more routine 19

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materials evaluation by a myriad of customers would constitute a major NIST achievement. NIST has been at the forefront of nanocomposite research over the past several years. The BFRL staff members are leaders in developing a fundamental understanding of nanocomposites for decreasing the flammability of polymers by lowering the heat release rate (HRR) as measured by a cone calorimeter, and reducing the flammability of polyurethane (PU) foams using nanoadditives; they are also the first to develop flammability testing methods of flexible PU foams using a cone calorimeter. One of the major issues in the real world with respect to polymer flammability is the flammability of furniture and mattresses. The BFRL team has leveraged years of experience in polymer flammability and nanocomposites to tackle the problem of PU flammability by aligning the project to the mission of NIST that involves improving public safety and assisting industry in competitiveness. PU foam is highly flammable due to its low thermal conductivity, low decomposition temperature, and viscosity. The BFRL team developed a modified vertical cone calorimeter method to measure the flammability of flexible (melting) PU foams. The methodology developed will be useful in getting closer to solving the PU foam flammability problem and will develop bench-scale test methods for screening purposes, which will help speed the research and development of new solutions. NIST has years of experience and competence with modeling techniques in various areas to provide high-quality prediction tools for flammability and related material properties. The modeling work on the mixing and dispersion of carbon nanotubes and fibers in polymers shows, for example, the dependence of the energy of mixing on the the radius of carbon nanotubes. As with any modeling work, steps need to be taken to verify the modeling results with real-world experiments to define the region of applicability and the accuracy that can be expected from predictive models and to clarify the goals for subsequent research efforts. NIST also has a long tradition in the original and creative research on cementitious materials. The excellence of this work has been maintained and expanded into new endeavors. The BFRL staff has identified and addressed fundamental needs from the cement, aggregate, and concrete industry. The number of consortia in this area shows the impact of the research on the construction industry. The NIST computer model for cement hydration is the best in the field, and it has been widely used in academia and industry. HydratiCA, the new version of this software program, is a significant improvement over earlier versions. It integrates well with the BFRL’s Virtual Cement and Concrete Testing Laboratory. The Inorganic Materials Group has done an important service by taking the leadership in the new ASTM C1365 test method for the determination of the phases in Portland cement. The development of sustainable materials and construction is of paramount importance for American leadership in civil infrastructure. The BFRL project whose goal is doubling the service life of these materials is potentially of breakthrough significance that could lead to a methodology for casting a new generation of reinforced concrete structures. To be successful, this project will require greater resources so that the researchers can optimize the chemicals to be added to the concrete mixture. 20

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ADEQUACY OF INFRASTRUCTURE While the Polymeric Materials Group and the Inorganic Materials Group would benefit from additional equipment (specifically, transmission electron microscopy), the need to add a technical staff member to support this capability is not considered a high enough priority relative to the other group responsibilities. There appears to be a concern among the BFRL staff that the time spent on administrative activities (such as budget planning, recruitment, and related activities) by the principal investigators may be interfering with their key technical responsibilities. Increased global interaction by the BFRL with the areas of the world experiencing technological growth (including China, India, and South America) is an important future goal. The flow of information thus far has been more unidirectional—specifically, other countries are deriving information from NIST. Competitive technology today requires global interaction; the United States no longer has a monopoly on emerging technology. The updating and the modernizing of NIST-related test equipment and procedures should be considered (the cone calorimeter is a case in point). This effort will enable the easy comparison of historical data and ensure continuity of standardized measurement methods. ACHIEVEMENT OF OBJECTIVES AND IMPACT The accelerated weathering testing and modeling have been highly successful and appear to have met the project’s goals and objectives to date, with the remaining goal being the adoption by end users and the availability of the capability in an independent laboratory. The development of a vertical flammability test for flexible polyurethane foams using the cone calorimeter could lead to bench-scale screening tools that will accelerate discovery and time to commercialization. The development of the internal curing of concrete was an efficient method of reducing or eliminating the internal cracking of concrete leading to more durable structures. The Materials and Products Group within the FRD has attracted a number of guest researchers from renowned institutions that complement the ongoing projects. The international reputation of the division is reflected in the fact that several graduate students have come to do research projects at NIST, in some cases bringing their own funding. The number of publications, presentations, and workshop reports from the Fire Research Division are cited by scientists around the globe for their technical content, the importance of their subject, and the technical novelty of the approaches employed. CONCLUSIONS The projects in the strategic area of Measurement Science for Predicting Life Cycle Performance of Nanocomposite Infrastructure Materials are well aligned with the mission of NIST and should continue to focus on measurement science based on fundamental mechanistic understanding. This Strategic Priority Area is of paramount importance to nanotechnology, because the assessment of the nanoparticle release into the environment is of considerable concern. To best accomplish this activity and disseminate results, the projects in this area should be highly integrated with those of the National Institutes of Health. 21

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The BFRL has shown leadership in the development of the materials science of construction materials. This fundamental science has already found practical application in construction practice. The new activity of doubling the service life of construction materials could be critical to maintaining American competitiveness in the field of civil infrastructure. Increasing the life cycle of concrete is vital for the repair and upgrade of the aging civil infrastructure. The group can create a new paradigm in advanced cementitious material by optimizing the nanostructure of the material with appropriate chemical admixtures. Reducing the flammability of polyurethane foam is extremely critical considering the worldwide use of these polymers in a number of applications. Using nanocomposites to reduce flammability and developing bench-scale flammability testing capabilities will not only develop fire-safe materials but will also accelerate the speed to market for these materials. The budgeting process for the BFRL should include funding for principal investigators to support time for the exploration of other projects that are aligned with the NIST mission. This will encourage discovery and out-of-the-box thinking. NIST should further highlight the accomplishments and the reports of the World Trade Center investigation program. 22