An Assessment of the National Institute of Standards and Technology Engineering Laboratory: Fiscal Year 2014 (2015)

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Materials and Structural Systems Division

The Materials and Structural Systems Division (MSSD) serves as a global resource for developing and promoting the use of science-based tools—measurements, data, models, protocols, and reference standards—to support innovations in building materials and construction technology and to ensure the safety, security, and sustainability of the nation’s buildings and physical infrastructure.¹

Areas of focus include sustainability, service life prediction and life-cycle assessment of materials performance and safety, and resilient performance of structures. The MSSD is organized into five formal groups: Structures, Inorganic Materials, Polymeric Materials, National Earthquake Hazards Reduction Program, and National Windstorm Impact Reduction Program. During the course of this review, five areas of work were examined: sustainable engineered materials—inorganic materials, sustainable engineered materials—polymeric materials, structures, wind research, and community disaster resilience. The first four of these areas are relatively mature within the Engineering Laboratory (EL); the community disaster resilience work is in the early stages of development.

TECHNICAL PROGRAMS

Sustainable Engineered Materials—Inorganic Materials

Within the MSSD, materials research is performed separately by inorganic and polymeric materials groups. Although the groups have similar objectives, they operate independently with separate staff and resources.

The Inorganic Materials Group’s focus is on characterizing the properties of concrete from early age to hardened materials state. This includes the rheology² of cement pastes and concrete slurries and the character of cured concrete. Increasing the understanding of these short-term and long-term properties will help to achieve one of the MSSD’s goals: to double the current service life of concrete, which will greatly enhance the sustainability of the material.

The group is also working on reducing the cement content of concrete by developing measurement protocols and standards related to the substitution of fly ash and limestone powder to decrease the carbon footprint of concrete. This work on fly ash characterization, limestone powder replacement, and internal curing is excellent and well connected with the goal of sustainability. The group’s work on hydration modeling is pioneering and highly regarded nationally and internationally, and its model of hydration has been widely adopted by others. Building on the hydration modeling work, the group has established the Virtual Cement and Concrete Testing Laboratory, an industrial consortium, to carry out work in computational modeling and experimental validation.

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¹ National Institute of Standards and Technology, “The Engineering Laboratory—Summaries of Our Activities, Accomplishments and Recognitions,” Gaithersburg, Md., July 2014.

² Rheology is the study of the flow of matter, primarily in the liquid state, but also as “soft solids” or solids under conditions in which they respond with plastic flow rather than deforming elastically in response to an applied force.

As concrete is increasingly pumped during construction, the number of failures due to flow problems has also increased. The group’s work on cement and concrete rheology combines rheometric measurements with simulations of particles being sheared within non-Newtonian dense suspensions. This work is very challenging. On the measurement side, these materials are highly prone to wall slip, and care needs to be given to texturing the shearing fixtures of rheometers to avoid this phenomenon. The simulations are difficult due to the high volume fractions of the solid fractions and the irregular shapes of the solid particles. Furthermore, in the case of concrete slurries, the interstitial fluid is a non-Newtonian cement paste, and proper characterization of the rheology of the cement is an important ingredient for a successful simulation. The group is seeking to develop standard reference materials (SRMs) based on simulation modeling that mimic the actual rheological properties of paste, mortar, and concrete.

Sustainable Engineered Materials—Polymeric Materials

Photodegradation impacts a very large number of materials used in buildings and infrastructure applications. These range from coatings for metals, window glazing, and solar panels to a wide variety of building and joint sealants. The group’s work on polymer sustainability has focused on photodegradation of this class of materials and has taken advantage of the work on the ultraviolet (UV) photophysics of polymeric materials that began 12 years ago with the development of the 2-m integrating sphere. The existence of this unique test apparatus to accelerate the degradation process has allowed the group to produce important results on a number of polymeric materials. The group has developed a smaller, commercial version of the large integrating sphere that looks very promising. It is limited, however, in the size and quantity of samples that can be accommodated within the measurement chamber. A goal of this work is to develop a predictive model for the lifetime performance of polymeric materials. This would be best achieved by combining their existing capabilities in experimental measurements with computational molecular modeling.

The group’s photophysical work is very well developed, and once the commercial unit is launched, thought could be given to redirecting the work on polymers to consider other products used in buildings and infrastructure. Many polymers are used in applications that are not exposed to light but still age and degrade by different mechanisms. Common examples are PVC and CPVC pipe and DuPont’s Tyvek building wrap. Another important class of products hidden from light are elastomers used in plumbing applications. Many cities have switched to chloramines to purify water; this can cause degradation in O-rings that were previously unaffected by the chlorination process.

Structures

The MSSD is performing work on structural robustness and the mitigation of disproportionate collapse. The staff are well-qualified and possess excellent capabilities in structural analysis, computational modeling, and physical validation testing. The tests and modeling of collapse conducted by the team (off-site for the tests) are very good and have provided potentially useful data on detailing of structural steel. However, this expertise could be applied to a broader range of scenarios for disproportionate collapse. In addition, the planned path toward recommendations for achieving robustness and resistance to disproportionate collapse (without having to test each proposed structure or element) was not made clear.

Wind Research

The staff performing wind research are well qualified and are focused on achievable goals. The project to develop improved wind-speed maps for incorporation in the ASCE 7 standard and subsequently

in statutory building codes promises to be a significant service to the nation. The team spoke of examining the database on wind tunnel tests from various sources in an attempt to develop pressure coefficients for building design that are more realistic than those now in the ASCE 7 standard; this would also be a valuable service to the nation, although the team did not present a clear roadmap for the way forward. The development of a virtual wind tunnel is a worthwhile long-term goal, and the EL is arguably the best body to pursue it; more resources in this area would be a good investment. The study and report on the Joplin, Missouri, tornado in 2011 are outstanding and could serve as a model for future disaster studies.

Community Disaster Resilience

The Community Disaster Resilience Program in the MSSD is in its infancy. However, the division is well positioned to apply its expertise in construction materials and structural performance to address the challenge of improving the nation’s disaster resilience by reducing the vulnerability of buildings and infrastructure to a broad array of physical hazards and to prolong the service life of the built environment in general. The group’s effort to develop metrics to rank resilience will help to identify the most vulnerable communities so that priorities for adaptation and mitigation efforts can be undertaken. This is a critical and appropriate first step in the process. The community disaster resilience research and development contracts and the center of excellence are excellent ways to quickly access the global state of the art for methods and approaches in this area. In particular, the request for proposal for a Community Resilience Center of Excellence contains an appropriate set of objectives for study and action in this area.

PORTFOLIO OF SCIENTIFIC EXPERTISE

The MSSD is staffed by high-quality personnel at various levels of professional development. Internationally recognized researchers work alongside postdoctoral fellows in a collaborative and synergistic research environment. With certain exceptions, skill sets are appropriate to the mission objectives, and within the programs reviewed there appears to be good diversity of age, gender, and ethnicity. Professional development is encouraged through publication and participation on code and standards writing groups, but government-wide travel restrictions are limiting opportunities for broader collaboration within the research community and for attendance at conferences and workshops.

Two areas requiring staffing attention are molecular modeling and community disaster resilience. Within the Polymeric Materials Group, hiring someone to help link the existing capabilities in experimental measurements with computational molecular modeling has been under consideration, but this has not yet occurred. Although well qualified, the staff assigned to the Community Disaster Resilience Program do not possess expertise sufficiently broad to address the range of issues contained within the resilience mission. This is being addressed in the short-term through temporary fellows, contract support, and the proposed center of excellence. Staffing needs of the Community Disaster Resilience Program will need to be closely monitored to assure that human resources are adequate and in the appropriate disciplines for the magnitude and scope of the tasks assigned.

FACILITIES, EQUIPMENT, AND HUMAN RESOURCES

Available research infrastructure is adequate for ongoing and anticipated efforts, and in some cases, such as for polymer and materials characterization, MSSD facilities are among the best in the world. The MSSD is also able to access on an as-needed basis advanced research capabilities within NIST such as those possessed by the Materials Measurement Laboratory and the Information Technology Laboratory. Onsite structural test facilities are adequate for smaller-scale testing congruent with the

Structures Group’s mission. For large-scale structural testing, where the onsite facilities are sometimes insufficient, division staff have made use of facilities at universities and other government laboratories such as the Engineering Research and Development Center (ERDC) operated by the U.S. Army Corps of Engineers in Vicksburg, Mississippi. This is a cost-effective solution that has resulted in savings in both cost and time. Overall, research infrastructure is not an impediment to accomplishment of the MSSD mission.

DISSEMINATION OF OUTPUTS

Dissemination of research results follows fairly traditional lines of peer-reviewed journals, conference proceedings, internal NIST reports, and input to technical codes and standards. Division staff are prolific in this regard and have produced many award-winning papers. However, government-wide travel restrictions are seen as an impediment to fuller dissemination of the division’s work. To a greater or lesser degree, all groups within the MSSD make use of workshops, symposia, and site visits to scope projects and identify issues. This, along with well-planned collaborations, is an effective means of securing stakeholder input, provided that attendance from all affected user groups is assured. Outreach to the practitioner community could be improved through more articles in professional and trade journals and more aggressive use of the Internet to quickly disseminate important findings.

OVERALL ASSESSMENT

The MSSD is carrying out important work within its mission responsibilities in a highly competent and professional manner. The staff are well-qualified and motivated to perform the theoretical and experimental investigations within their areas of responsibility and fully engaged with research at the national and international levels.

The current staff mix does not appear unduly skewed by age, gender, or ethnicity. Available research infrastructure is adequate for ongoing and anticipated efforts, and in some cases, such as for polymer and materials characterization, MSSD facilities are among the best in the world. For large-scale structural testing, where onsite facilities are sometimes insufficient, division staff have made use of facilities at universities and other government laboratories. This solution results in savings both in cost and time. Overall, research infrastructure is not an impediment to accomplishment of the division’s mission. Dissemination of research results follows fairly traditional lines of peer-reviewed journals, conference proceedings, internal NIST reports, and input to technical standards. Division staff are prolific in this regard, although government-wide travel restrictions are seen as an impediment to fuller dissemination of the division’s work. Outreach to the practitioner community could be improved through more articles in professional and trade journals and more aggressive use of the Internet to quickly disseminate important findings.

FINDINGS AND RECOMMENDATIONS

Contained within the mission of the MSSD are two of the foremost issues confronting the nation’s built environment: how to cost-effectively address the large stock of physical infrastructure that is nearing or has exceeded its normal service life, and how to make communities more resilient in the face of multiple natural and anthropogenic hazards that are uncertain in both likelihood and severity.

Both the challenges and the stakes are huge. Delaying necessary remediation of infrastructure systems increases the probability of failure and attendant higher life-cycle costs, community disruption, and the very real possibility of injury and death of those impacted. However, replacing or refurbishing

systems prematurely spends money unnecessarily and reduces the limited funds available to address other system needs.

As for resilience, depending on physical location, the vulnerabilities of communities to various hazards differ widely as do the consequences of a specific event. Even though the principles of resilience apply equally across the nation, those communities least resilient and the relevant threats or hazards need to be identified so that appropriate investments in adaptation, mitigation, and emergency response and recovery can be made in a timely and cost-effective manner.

In this regard, the technical work of the division needs to be supported by sound economic and financial analysis. The Office of Applied Economics within the EL is a world-recognized leader in economics of building and has performed state-of-the-art analyses on such topics as the benefit-cost calculation of building protection strategies to address terrorist attacks. Such innovative analytical techniques are called for in evaluating options for infrastructure renewal and community disaster resilience owing to the long time horizons and the great degree of uncertainty involved.

Although the MSSD programs reviewed are producing high-quality work, the projects and their results tend to be isolated from one another. That is, they are focused on answering a specific question or solving a specific problem, and opportunities for cross-cutting findings are missed. For example, there appears to be untapped potential to integrate the capabilities of the materials work in physical and chemical degradation with the capabilities of the Structures Group in mechanical performance. The Inorganic Materials Group possesses appropriate expertise in the chemical degradation of concrete, while the Structures Group has a vital interest in how such degradation affects strength and performance in applications. A quantitative method to determine the strength of partially degraded materials would be of enormous value in practice and could inform the decision of whether the time for necessary replacement had been reached. At present, inspection processes for infrastructure emphasize visual appearance as an important aspect of condition assessment. The MSSD could provide the means to greatly improve the precision and value of such assessments.

Findings from individual projects can also apply to multiple situations. For example, the Nuclear Regulatory Commission is facing the arduous task of recertifying many of the nation’s aging nuclear power stations and has commissioned the Inorganic Materials Group in collaboration with the Structures Group to assess the effects of the alkali-silica reaction, which occurs in all concrete, on the residual strength of the material. Their findings will apply far beyond the immediate question, because there is an enormous amount of aged concrete in the nation’s bridges, dams, and other structures that will ultimately need to be replaced, but the quantitative science to underpin such decisions has yet to be developed. This project will provide a unique opportunity to incorporate the microscale research of the Inorganic Materials Group with the macroscale work on physical performance being carried out by the Structures Group.

Despite the importance of inorganic and polymeric materials in buildings and infrastructure and the need to improve our understanding of their degradation and performance, steel remains an important material for infrastructure applications whose characterization is also incomplete. At the same time, masonry and timber structures are still in use and, like steel, could also benefit from additional study and possible code updates. None of these materials are currently under study by the MSSD, although the Structures Group has tested some steel assemblies as part of its work on disproportionate collapse.

The recommendations that follow should not be viewed as a list of shortcomings; rather, they are intended to help the MSSD in its efforts to make an excellent program even better.

It is important that the MSSD continue to recruit for diversity in gender, age, and ethnicity to enhance long-term capabilities across the materials, structures, and resilience groups, with attention to strategic opportunities for collaboration among the groups.