Evaluation of the Effectiveness of ASR Mitigation with Lithium Nitrate

Since 1980 alkali-silica reactivity (ASR) has become an increasingly critical concern with regards to the durability of concrete pavements and structures nationally. There has been a concerted effort to inform State Highway Agencies (SHA's) of the problems arising from ASR, beginning with work done as part of SHRP C-343 Eliminating or Minimizing Alkali-Silica Reactivity and continuing with Showcase presentations and workshops. The level of knowledge concerning ASR and its mitigation in new concrete has risen to a point where the use of pozzolans and other admixtures for this purpose is routine. Unfortunately, there are a tremendous number of pavements and structures around the country, which have or will be developing serious problems due to ASR. Because the use of lithium salts is a recognized method of mitigating potential ASR in new concrete, the South Dakota Department of Transportation participated in SHRP Concrete and Structures ASR Showcase Test and Evaluation Project 34 Mitigation of Potential Alkali-Silica Reactivity Using Lithium. This work involved the construction of new concrete test sections incorporating various lithium admixtures as well as treatment of a series of 500-foot test sections on an ASR affected severely deteriorated pavement with several dosage levels of lithium nitrate and acetate solutions in 1995. Monitoring of these test sections over the last five years has provided strong evidence of the beneficial effects of lithium treatments on ASR in existing pavements. It has also led to the development of strategies designed to monitor in situ changes in pavement properties that reflect a reduction in the magnitude of expansive stresses. A paper detailing these results, which was presented at the 11th International Conference on Alkali-Aggregate Reaction in June 2000, is attached. The work did not directly address determining the optimum point for applying the treatment or evaluating its cost benefit ratio. This research should address these issues. south Dakota Department of Transportation (SDDOT) continues to search for methods to mitigate ASR in existing concrete that are cost effective, environmentally sensitive, user-friendly, and effective. With research in this area that examined methacrylate, silane, sealers, and polymers, the SDDOT has identified lithium salts as a product that may meet all of these criteria. Laboratory research has shown that lithium salts are effective in treating ASR affected samples. Unfortunately, there are still unknowns that exist when this technology is applied to existing pavements or structural concrete. These unknowns include when to treat an ASR affected pavement, how deep does the lithium penetrate, how effective is the application, what should the application rate be, how many applications are needed, and how is the effectiveness measured. The objectives of this research project are to:  (1) Verify the effectiveness of using lithium nitrate on pavements and structures that contain reactive aggregate at various levels of ASR severity; (2) Determine the cost benefit of using a topical lithium nitrate treatment for mitigating ASR based on life cycle cost analysis; and (3) Develop detailed guidelines for field application of lithium nitrate for mitigation of ASR on existing concrete pavements and structures. Research tasks of this project are as follows: (1) Review literature pertinent to ASR and its mitigation with lithium. (2 )Conduct laboratory tests on concrete slabs using typical coarse and fine aggregate representing a range of ASR reactivity and treat with lithium nitrate. (a) Fabricate slab specimens for treatment with lithium nitrate.(minimum size 1' x 1' x 6") (b) Develop a system to accelerate ASR in the specimens. (c) Apply lithium nitrate at different rates at different ASR levels. d)Test samples by measuring pulse velocity, impact echo, static modulus, lithium nitrate penetration, void/volume determination, and other tests as applicable. e)Evaluate the effectiveness and life cycle equivalency, application rates, and best time of application. (3 )Identify existing ASR-deteriorated pavements based on valid selecting criteria such as age, traffic, ASR severity levels, aggregate type and treat the selected pavements with lithium nitrate. (4) Conduct baseline testing of the selected pavements before treatment. (5) Extract sufficient' x 1' x d" concrete slabs from selected pavements from the proposed treatment areas prior to treatment for laboratory testing. Evaluate the in situ properties using impact-echo and other appropriate means and conduct the same testing sequence on the slabs after extraction. (6) Apply various rates of lithium nitrate solution to the slabs in a laboratory environment simulating field conditions as closely as possible with controls and monitor strain, slab expansion, impact-echo velocities and other appropriate parameters over the course of the testing. (7) Obtain cores from each test slab at the completion of the testing sequence for stereographic analysis, scanning electron microscopy, and static modulus testing and other testing as necessary. (8) Estimate life cycle cost savings and equivalent cost savings based on research results. (9) Prepare design/application criteria covering range of application rates based on the severity of ASR and covering the time of placement to provide the maximum benefit. (10) Prepare construction specifications that address the material requirements, equipment requirements, construction requirements, method of measurement, and basis of payment. (11) Provide project summary, construction, quarterly and annual evaluation reports. (12) Prepare a final report and executive summary of the literature review, research methodology, findings, conclusions, and recommendations. (13) Make an executive presentation to the SDDOT Research Review Board at conclusion of the project.