Testing and analysis of LWT and SCB properties of asphalt concrete mixtures.

Testing and analysis of LWT and SCB properties of asphalt concrete mixtures.

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    Currently, Louisiana’s Quality Control and Quality Assurance (QC/QA) practice for asphalt mixtures in pavement construction is mainly based on controlling properties of plant produced mixtures that include gradation and asphalt content, voids filled with asphalt, air voids, moisture susceptibility tests (Modified Lottman), and roadway parameters such as pavement density [1]. These controlling properties have served Louisiana well, yet with growing interest in considering alternative paving materials such as rubber modified asphalts, reclaimed asphalt pavement (RAP), recycled shingles, and warm-mix asphalt (WMA) technologies, there is a pressing need to implement laboratory mechanical testing capable of ascertaining an asphalt mixture’s ability to resist common distresses. This research presents an evaluation of LWT and SCB tests for rutting and cracking evaluation of commonly produced mixtures from around the state. This research also presents the results of a balanced mixture design methodology being developed by DOTD. A total of 51 mixtures were evaluated with both the SCB and LWT tests. With respect to LWT Testing, 46 of the 51 mixtures evaluated (90%) passed the criteria specified for acceptable rutting resistance. The criteria (10 mm at 20,000 passes for unmodified binder; 6 mm at 20,000 passes for polymer-modified binder) currently being utilized by DOTD appears to be appropriate for mixtures being produced. With respect to Semi-Circular Bend Testing, the percent of mixtures passing this criterion for mixtures containing PG 64-22, PG 70-22M, PG 76-22M and PG 82- 22CRM is 38, 68, 91, and 20 respectively. For the mixtures designed according to the DOTD proposed balanced mixture design specifications, 7 out of 11 met or exceeded the cracking criteria and rutting criteria. The comparison of field and laboratory compacted specimens shows there may be an effect of specimen type on the computed Jc. This relationship would need to be further investigated before using field cores for quality assurance practices.
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