Durability is one of the most important requirements for sustainable infrastructure. Federal, state, and local agencies expend significant effort to maintain the quality and condition of aging civil structures, especially those in aggressive service environments. Among many factors, durability influences the service life and integrity of concrete materials and structures. Extensive research has been conducted to understand the deterioration mechanisms of concrete in an effort to extend the longevity of concrete members. In this session, presentations of both experimental and analytical investigations are of interest, which may include the durability of concrete structures reinforced with steel or fiber-reinforced polymer bars, modeling of service life for concrete under aggressive environments, and the structural integrity and resilience of rehabilitated members. The session emphasizes recent research findings and provides an opportunity to discuss present challenges and technical issues. Critical information is given to those who lead tomorrow’s structural design and construction with an emphasis on durability, service life, and integrity, including practicing engineers, government officials, and academics.
(1) Describe the influence of aggressive environments in the performance of concrete structures;
(2) Review the recent advances in research concerning infrastructure durability;
(3) Recognize a new direction for the design of concrete structures subjected to environmental loading;
(4) Explain how research outcomes are translated into practice.
This session has been approved by AIA and ICC for 2 PDHs (0.2 CEUs). Please note: You must attend the live session for the entire duration to receive credit. On-demand sessions do not qualify for PDH/CEU credit.
Structure and Properties of Alkali-silica Reaction Gels Treated with Lithium Nitrate
Presented By: Jianqiang Wei
Affiliation: University of Massachusetts Lowell
Description: Alkali-silica reaction (ASR) is a deleterious reaction between reactive silica in aggregates and the alkalis in concrete. The reaction forms hygroscopic ASR gels, which can absorb water, swell, and exert pressure on surrounding concrete, causing internal stresses, volume expansion, and cracking. Mixing lithium admixtures in fresh concrete has been proven to be effective in ASR mitigation at the concrete level. However, the exact mechanism has not been fully understood. The chemical composition and properties of ASR gels might vary with their age and forming location in concrete. To uncover the role of lithium in mitigating ASR, synthetic ASR gels containing various dosages of lithium nitrate admixture were prepared. Structure, composition and crystallization of ASR gels in the presence of lithium were investigated through spectrographic and X-ray diffraction techniques. Physical and mechanical properties, such as water absorption, swelling and strength development, were also studied through dynamic vapor sorption, static volume change and compressive strength tests, respectively. The results indicate that the gelation time of ASR gels was extended, and the swelling, stiffness, and strength of ASR gels were decreased in the presence of lithium.
Recent Developments and Case Studies on Concrete Bridges in Florida Using Ultra-High Performance or Fiber-Reinforced Polymer Reinforcing
Presented By: Steven Nolan
Affiliation: Florida Department of Transportation
Description: Although advances in concrete structures with conventional materials and prestressing technology have definitely improved the durability of bridges in the last century, engineers’ initial expectations have not been fully realized, especially considering the increasing environmental and societal demands on these structures. The continued pursuit of barrier technologies for protecting carbon-steel reinforcing and strand using combinations of concrete enhancement, coatings, and metallurgical manipulation, cannot fulfill the true potential of concrete structures in more aggressively corrosive environments. A new class of reinforcing materials has emerged that can provide enduring and sustainable solutions both structurally and environmentally. Eliminating corrosion through the use of FRP reinforcing materials, or highly corrosion-resistant grades of stainless steel and even titanium for retrofitting, are practical and cost-effective solutions when the whole life costs are evaluated. Ultra-High-Performance Fiber-Reinforced Concrete is another emerging technology with great potential. Tools for service life design and life-cycle cost analysis are maturing and life cycle assessment for environmental sustainability is becoming increasingly important to asset owner. This presentation highlights these recent developments and showcases completed bridges where these methods have been successfully deployed.
Integrity of Reinforced Concrete Beams Strengthened with CFRP Sheets under Torsional Distress
Presented By: Abdulaziz Alqurashi
Description: This research presents the torsional behavior of inverted tee-beams strengthened with carbon fiber reinforced polymer (CFRP) sheets when simultaneously subjected to shear-and flexure-combined loading. Two types of CFRP-bonding are tested: complete wrapping and side-bonding with single and double layers at variable coverage areas. The capacity of the beams with completely wrapped sheets is higher than that of the beams with side-bonded sheets, whereas such a tendency diminishes as the intensity of the combined loading increases. Moreover, the torsional stress of the test beams is in part relieved by the interaction with the flexural component. For the side-bonded beams, the cross-sectional area of CFRP controls the load-carrying capacity.
NIST Engineering Laboratory Research on the Performance of Externally Bonded Fiber-Reinforced Polymer (FRP) Composite Systems in Resilient Infrastructure
Presented By: David Goodwin
Affiliation: National Institute of Standards and Technology
Description: The use of externally bonded fiber reinforced polymer (FRP) composites to repair, strengthen, and seismically retrofit structural components of existing buildings and infrastructure has been steadily on the rise. However, more research is needed to assess 1) the extent of structural performance improvements after application of FRP composites and 2) how FRP composite performance changes over time. In FY 2018, researchers from the Earthquake Engineering and the (now) Infrastructure Materials Group in the Materials and Structural Systems Division initiated the FRP composite project to improve the state of practice for design and evaluation of FRP-retrofitted structures. The project team hosted a workshop of national experts in May 2018 to identify material and structural level research needs concerning the use of FRP composites in repair and retrofit of structures. In this presentation, the project team will present (1) the project overview, (2) the prioritized research needs (3) the internal NIST research plan and (4) the progress of the research tasks to-date. The presentation will specifically cover the research tasks concerning development of FRP-retrofitted shear wall design guidelines, accelerated weathering and outdoor weathering studies of FRP composites bonded to concrete, field studies, and in-situ tests for performance evaluation of FRP composites.
Modeling the Service Life Performance of Bridge Deck Overlays
Presented By: Neal Berke
Affiliation: Tourney Consulting Group, LLC
Description: Major bridges are requiring extended service lives of 100 years or more. This requires the use of high-performance concretes and often enhanced corrosion protection provided by improved corrosion resistance of the reinforcing bars by using alloying, coatings, and/or corrosion inhibitors. Producing the entire bridge deck out of high-performance concrete can lead to excessive cracking due to autogenous and drying shrinkage. Though this can be reduced by using shrinkage reducing admixtures or lightweight fines, the cost for a full deck is high. However, a high-performance overlay uses considerably less concrete, and as such can reduce the overall cost of the bridge deck and potentially allow for a more user friendly, less costly base concrete. This presentation models the service life of a bridge deck using high performance overlays. A probabilistic approach is used, and the effect of cracking is included.
Troubleshooting Service Life Predictions: Connecting Construction with Modeling
Presented By: Jose Pacheco
Description: Current specifications for bridge construction in the US specify a minimum service life of 75 years for concrete bridges. In some cases, the specified service life is 100 years or greater. A description of currently available service life modeling tools for bridge construction will be presented. Subsequently, the presentation will cover an overview of various constructability issues and their impact on service life predictions for concrete bridge deck construction. The presentation will finally address different cracking mechanisms, and their impact on chloride ingress modeling and service life predictions.
Remaining Service Life Assessment of Bridge Abutments Using Different Models: Comparative Study
Presented By: Abeer Al-Shammari
Affiliation: Advanced Infrastructure Design, Inc
Description: The United States has over than 600,000 bridges, almost 40% which are 50 years or older. Additionally, 9% of the nation’s bridges were evaluated to be structurally deficient in 2016. While the number of bridges that are in such poor condition as to be considered structurally deficient is decreasing, the average age of America’s bridges keeps going up and many of the nation’s bridges are approaching the end of their design life. Therefore, evaluating the exiting condition and predicting the remining service life (RSL) of these bridges is so important to the agencies in order to make any decision of a bridge (or part/parts of a bridge) replacement Several Models are available to predict the service life of new concrete structures. However, very limited models are available to estimate the remaining service life of existing concrete structures. In this paper, a comparative study of two service life prediction models (Life-365 and NCHRP Report 558) is provided on a bridge abutment subjected to corrosion-induced deterioration. The bridge was constructed in 1958. Visual inspection, field tests and lab tests were performed to evaluate the current condition of the structure and to obtain the parameters needed for the analysis. A good agreement between Life-365 and NCHRP Report 558 analysis results has been obtained.