Graduate Thesis Or Dissertation
 

Development of a standard accelerated weathering test for aggregates using dimethyl sulfoxide (DMSO)

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/cn69m846x

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  • Some basaltic rocks common in Oregon when incorporated into a pavement structure as the base course aggregate or in the surfacing layer degrade and disintegrate owing to the minerals contained within the rock and the environment in which it is placed. To simulate the chemical degradation of basaltic rocks an accelerated weathering test using Dimethyl Sulfoxide (DMSO) was developed. The objective of the research reported herein was to: 1) study the interaction of DMSO with clay standards, 2) develop a reliable method of determining clay type and content In basalt rocks, 3) study the parameters influencing the current test and develop a standard procedure, and 4) determine acceptable weight loss limits for untreated basalt aggregates after immersion in DMSO. By investigating the electro-static interaction between clay standards and DMSO it was found that the DMSO molecule has a preference for cations and it is able to donate hydrogen ions. Both factors allow DMSO to penetrate into a rock matrix seeking out the cations held either to clay minerals or zeolites. After a thorough study of the parameters influencing the current procedure, such as container geometry, aggregate particle size, sample weight, and immersion time, a standard test was developed. The recommended procedure consisted of immersing a l000g sample of aggregate in the size range between 2.38 mm (#8) and 4.76 mm (#4) for a period of five (5) days. At the end of the immersion time the aggregate is re-screened over the 2.38 (#8) sieve and the percent weight loss is calculated. The acceptable weight loss limit for the DMSO Accelerated Weathering Test was established by correlating the test results to those obtained through petrographic analysis. The petrographic analysis consisted of determining the percentages of deleterious secondary minerals and their textural distribution within the rock matrix. With these two parameters a Secondary Mineral Rating for each quarry was calculated and compared to the DMSO test results. In addition, it was found that DMSO may overreact if the minerals analcime and calcite are present in the quarry rock. A second indirect test, the Clay Index, was presented as a simple method to determine the likelihood of DMSO to overreact, since it was found to be insensitive to the type of minerals present in the rock.
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