Quick Test for Durability Factor Estimation
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The Missouri Department of Transportation (MoDOT) is considering the use of the AASHTO T 161 Durability Factor (DF) as an end-result performance specification criterion for evaluation of paving concrete. However, the test method duration can exceed 75 days before results are known. MoDOT contracted with the Missouri University of Science and Technology (Missouri S&T) to develop a method of approximation of DF based primarily on aggregate testing that would be of a shorter duration. Nineteen different ledge samples representing 18 ledges, 10 geologic formations (nine limestone and one dolomite) were sampled by MoDOT and delivered to Missouri S&T. The ledge samples represented DFs of 28 to 95 and nominal maximum aggregate sizes of ⅜ to 1 in. The aggregates were subjected to twelve different test methods. This information, coupled with MoDOT historical gradation, specific gravity, absorption, and deleterious materials data, formed the basis of the test study dataset. Multiple linear regression was used to produce seven models of varying accuracy and complexity for DF prediction. Historical T 161 DF data for the same aggregate materials (different samples) was used as the dependent variable. Model R2 values ranged from 0.804 to 0.974. Thus, seven options were open to MoDOT for consideration. As an alternate to the regression models, a threshold-limits method was presented.