Shrinkage Limits and Testing Protocols for High Performance
||Oregon State University|
|Start Date for ODOT:
|Completion Date for ODOT:
The research goals are to 1) provide shrinkage threshold limits for ODOT Materials Specifications and 2) provide a robust test procedure (or set of procedures) so that materials suppliers can easily determine compliance with specified threshold limits. OVERVIEW:
ODOT has observed varying degrees of cracking in concrete structures. Cracking of high performance reinforced concrete structures, in particular bridge decks, is of paramount concern to ODOT. Cracking at early ages (especially within the first year after placement) results in additional costs and a significant maintenance burden to ODOT. These added costs could be avoided through improved testing techniques, improved material specifications, and improved construction requirements related to reducing cracking risks in such structures. The most significant challenge to overcoming cracking risk is to reduce the shrinkage, and ultimately the stresses generated as a result of such shrinkage, in concrete mixtures. Without a commonly agreed upon testing method and subsequent shrinkage threshold limits, it is essentially impossible for ODOT, under current guidelines, to specify and receive crack-free concrete with a high degree of confidence.
The literature along with several state DOTs and materials suppliers purport shrinkage limits, but these values vary widely. From the testing perspective, several well-established relatively simple tests exist for assessing shrinkage and/or cracking risk of concrete mixtures (e.g. ASTM C 157 and ASTM C 1581); however, each of these tests has deficiencies that do not allow complete characterization of concrete shrinkage. Research in the past 10 years has developed laboratory-based analytical tools such as rigid cracking frames that enable researchers to more accurately quantify concrete behavior. Additionally, powerful computer models such as ConcreteWorks (a free program) provide further guidance for minimizing cracking risk in HPC. A development effort that draws on the existing understanding of concrete shrinkage and the tools available for measuring cracking potential would be able to define appropriate shrinkage threshold limits and a test procedure for Oregon’s concrete bridge decks. PROPOSED ACTIVITIES: Task 1: Literature Review.
Perform literature review with a particular focus on other DOTs and industry that have shown advanced procedures for dealing with concrete bridge deck cracking (Kansas DOT, Texas DOT, Illinois DOT). This review will also focus on identifying the best testing method(s) for shrinkage evaluation in concrete materials. Task 2: Evaluation Plan.
Develop the experimental plan based on statistical methods for conducting shrinkage tests and analyzing the results. The evaluation will consider shrinkage test correlation with a baseline measure of cracking potential (rigid cracking frame), sensitivity, and repeatability over a range of Oregon bridge deck concrete mixes. . Task 3: Laboratory Evaluation. Task 3a
: Determine shrinkage values of a range of concrete used in Oregon bridge decks based on standard testing methods (e.g. ASTM C 157, 1581 and 1698). It is anticipated that these test methods will require at least some modification to more accurately predict cracking potential of field concrete. Other test methods also may be investigated as deemed necessary by the research team and the TAC. Task 3b
: Once shrinkage values are established, a subset of concrete mixtures from Task 3a will
be tested using rigid cracking frames. The rigid cracking frame provides the best laboratory predictor of how concrete will behave in the field. Task 3c
: The results of Tasks 3a and 3b will be evaluated using the statistical analysis plan from Task 2. Shrinkage threshold criteria will be established based on the outcome of the analysis and information from the Task 1 literature review. Task 4: Testing Method Determination
. Based on the results from Task 3, a testing procedure for evaluating shrinkage across a wide range of concrete mixture designs for Oregon bridge decks will be defined. Ease of use and cost will be important considerations in addition to test capabilities and limitations. A round-robin evaluation of the test procedure will be conducted among Oregon concrete materials suppliers and contractors as a final check on the efficacy and practicality of the test method. Task 5: Reporting and Implementation.
A final report documenting all findings from the research project as well as methodologies for technology transfer will be prepared. Presentations will be made to ODOT, suppliers, and contractors to explain the research outcomes and to provide training. SHRINKAGE LIMITS AND TESTING PROTOCOLS FOR ODOT HIGH PERFORMANCE CONCRETE WORK PLAN Quarterly Reports: