Browsing by Author "Williamson, Gregory Scott"

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    Investigation of Testing Methods to Determine Long-Term Durability of Wisconsin Aggregate Resources Including Natural Materials, Industrial By-Products, and Recycled/Reclaimed Materials
    Williamson, Gregory Scott (Virginia Tech, 2005-04-14)
    The Wisconsin Department of Transportation (WisDOT) uses approximately 11,000,000 tons of aggregate per year for transportation projects. Being able to select durable aggregates for use in transportation projects is of considerable importance, if the aggregate deteriorates then the constructed facility requires premature repair, rehabilitation or replacement. Realizing the importance and also that deficiencies in the current WisDOT testing protocol may exist, it has been concluded that the durability-testing program for Wisconsin aggregates needs to be updated. For example, WisDOT is currently using the Sodium Sulfate Soundness Test (ASTM C 88) to measure durability, a test that was put in place in 1960. The ability of this test to predict durability performance and simulate field conditions is questionable and it has also been criticized for its lack of precision. It should also be noted that the use of recycled and reclaimed aggregates has increased in recent years and not all typical durability tests can be used for testing these aggregates. The Sulfate Test in particular cannot be used for testing Recycled Concrete Aggregates (RCA) because the chemical reaction produces erroneous and misleading results. This project has identified recent advances in the understanding and testing of aggregate durability. An in depth literature review has been conducted and from the compiled information a laboratory testing program was developed. Selection of the tests was based upon the tests' precision, efficiency, and predictive capabilities. In the laboratory-testing phase of this project the proposed durability tests along with current WisDOT durability tests were used to evaluate the full range of Wisconsin aggregates. From the test results it was found that the WisDOT aggregate testing protocol could be reduced substantially by eliminating many of the testing requirements for aggregates that have a vacuum saturated absorption of less than 2%. Also, the addition of several tests was ruled out due to their lack of correlation with field performance records. The Micro-Deval abrasion test is recommended for inclusion in WisDOT testing protocol as a test to measure the abrasion resistance of aggregate while the L.A. Abrasion test is better suited as a measure of aggregate strength. Additional conclusions were made based on the durability testing conducted and an overall testing protocol has been developed and is recommended for implementation by WisDOT.
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    Service Life Modeling of Virginia Bridge Decks
    Williamson, Gregory Scott (Virginia Tech, 2007-03-20)
    A model to determine the time to the End of Functional Service Life (EFSL) for concrete bridge decks in Virginia was developed. The service life of Virginia bridge decks is controlled by chloride-induced corrosion of the reinforcing steel. Monte Carlo resampling techniques were used to integrate the statistical nature of the input variables into the model. This is an improvement on previous deterministic models in that the effect of highly variable input parameters is reflected in the service life estimations. The model predicts the time required for corrosion to initiate on 2% of the reinforcing steel in a bridge deck and then a corrosion propagation time period, determined from empirical data, is added to estimate the EFSL for a given bridge deck or set of bridge decks. Data from 36 Virginia bridge decks was collected in order to validate the service life model as well as to investigate the effect of bridge deck construction specification changes. The bridge decks were separated into three distinct groups: 10 bare steel reinforcement decks â 0.47 water/cement (w/c), 16 Epoxy-Coated Reinforcement (ECR) decks â 0.45 w/c, and 10 ECR decks â 0.45 w/(c+pozzolan). Using chloride titration data and cover depth measurements from the sampled bridge decks and chloride corrosion initiation values determined from the literature for bare steel, service life estimates were made for the three sets of bridge decks. The influence of the epoxy coating on corrosion initiation was disregarded in order to allow direct comparisons between the three sets as well as to provide conservative service life estimates. The model was validated by comparing measured deterioration values for the bare steel decks to the estimated values from the model. A comparison was then made between the three bridge deck sets and it was determined that bridge decks constructed with a 0.45 w/(c+p) will provide the longest service life followed by the 0.47 w/c decks and the 0.45 w/c decks, respectively. From this it can be inferred that the addition of pozzolan to the concrete mix will improve the long-term durability of a bridge deck while a reduction in w/c appears to be of no benefit.