The Missouri Department of Transportation (MoDOT) is considering the replacement of its deleterious materials test method (TM-71) with test methods that are more objective. MoDOT contracted with the Missouri University of Science and Technology (Missouri S&T) to develop a system of test methods. Nine quarry/ledge samples representing seven geologic formations (four limestones and three dolomites) were supplied by MoDOT. The ledge samples represented three aggregates each for use in concrete, asphalt, and granular base. Samples with controlled contamination were also tested, bringing the total to 18. The aggregates were subjected to fifteen test methods. This data, coupled with MoDOT historical specific gravity, absorption, and TM-71 deleterious materials data of the samples formed the basis of the test study dataset. Multiple linear regression was used to produce 15 models of varying accuracy and complexity for TM-71 predictions. The TM-71 deleterious data were used as the response (dependent) variables. The best models entailed test methods not normally performed by MoDOT, such as sieved slake durability, point load strength, vacuum saturated bulk specific gravity/absorption, and aggregate crushing value, along with the more. familiar micro-Deval and plasticity index. Model adjusted-R2 values ranged from 0.603 to 0.895. Thus, three to four options (models) were open to MoDOT for consideration for each type of deleterious material (Total Deleterious Material, Total Deleterious Material Plus Hard Chert, Deleterious Rock Plus Soft Chert, and Shale). As an alternate to the regression models, a threshold-limits method was presented. The models themselves were not exact enough to predict the various deleterious contents with the level of accuracy required for routine decisions concerning aggregate product acceptance or rejection. As a result, a method of baseline ledge-specific initial calibration of the models was developed to enable MoDOT inspectors to make acceptability decisions on a routine basis without the necessity of performing TM-71.
- Deleterious material,
Available at: http://works.bepress.com/david_richardson/84/