AGGREGATE TOUGHNESS / ABRASION RESISTANCE AND DURABILITY TESTS RELATED TO ASPHALT CONCRETE PERFORMANCE IN PAVEMENTS By
i DISCLAIMER The contents of this report reflect the views of the authors who are solely responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views and policies of the National Center for Asphalt Technology of Auburn University. This report does not constitute a standard, specification, or regulation. ii ABSTRACT Numerous tests have been developed to empirically characterize aggregate without, necessarily, a strong relationship with the performance of the final products incorporating these aggregates. This seems to be particularly true for aggregate " toughness and abrasion resistance " and " durability and soundness. " The purpose of this research was to identify and evaluate toughness/abrasion resistance and durability/soundness tests for characterizing aggregate used in asphalt concrete and to determine those test methods that best correlate with field performance. Based on a review of literature and specifications, laboratory tests for characterizing aggregate toughness/abrasion resistance and durability/soundness were selected. Sixteen aggregate sources with poor to good performance histories were identified for evaluation with the selected suite of tests. Performance histories of pavements containing these aggregates in asphalt concrete layers were established through personal contacts with state transportation agencies and performance evaluation questionnaires. Aggregate properties from laboratory tests were correlated with field performance. The Micro-Deval and magnesium sulfate soundness tests provide the best correlations with field performance of asphalt concrete, and are recommended for characterizing aggregate toughness/abrasion resistance and durability/soundness.
MICRO-DEVAL TEST FOR EVALUATING THE QUALITY OF FINE AGGREGATE FOR CONCRETE AND ASPHALT
The sulfate soundness test has been used for many years for evaluating the physical suitability of fine aggregate. This test suffers from poor within-laboratory and multilaboratory precision; it is a time-consuming and expensive test. The work described here was an evaluation of alternative tests for measuring soundness of fine aggregate. The tests studied were the attrition test and a modified version of the French micro-Deval test usually used for coarse aggregate. The micro-Deval test was found to have a significant correlation with magnesium sulfate soundness loss and water absorption of fine aggregate. Unlike the attrition test, the micro-Deval test is relatively insensitive to the gradation of the sand being tested and has excellent precision. The test is conducted by placing 500 g of water-saturated sand in a ball mill with 1250 g of 9.5-mm steel balls and 750 ml of water. The mill is rotated at 100 rpm for 15 min. The aggregate is washed over a 75-microm sieve and the loss is calculated as a mass percent of the original oven-dry weight. The test may be completed in less than 48 hr. Aggregates that give more than 25% loss are judged to be marginal for use in portland cement concrete and asphaltic concrete. The Ontario Ministry of Transportation has adopted the micro-Deval test for measuring the quality of fine aggregate for concrete and asphalt.
ADDITIVES HAVE POTENTIAL TO IMPROVE PAVEMENT LIFE
It is described how, while not being cure-alls, asphalt additives, carefully selected and applied, have the capacity to extend pavement service life. A study at the Texas Transportation Institute is described, which evaluated the performance of materials added to asphalt concrete mixtures for reducing the pavement cracking and rutting potential. Tests examined stiffness, brittleness and flexibility at low temperatures and high loading rates, and evaluated the resistance to fatigue-type-tensile loads such as those caused by vehicular loading and thermal variations. The research consisted of a systematic identification of promising types of asphalt additives designed to reduce plastic deformation and cracking in asphalt concrete pavements. The products selected for evaluation included the following: latex; block copolymer rubber (styrene-butadiene-styrene); ethylene-vinyl acetate; finely dispersed polyethylene; and carbon black. The details of the study results are presented.