TxDOT Research Library - TxDOT Research Project

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Improved Overlay Tester for Fatigue Cracking Resistance of Asphalt Mixtures

What Was the Need?

Premature fatigue cracking is a major distress that deteriorates the pavement structure under the combined action of traffic loads and environmental impacts at a rapid rate. The present overlay tester (OT) characterizes the cracking resistance of asphalt mixes by evaluating the number of cycles to failure of a specimen. The number of cycles to failure is not sufficient to capture and predict the fatigue properties of asphalt mixtures. Through appropriate instrumentation, interpretation and analyses, the fatigue properties of the specimen can be obtained from the OT results. This goal cannot be achieved until the high degree of uncertainty in OT results especially in dense-graded mixtures is addressed.

Fatigue cracking of hot mix asphalt continues to be a recurring problem in Texas. Pavements with fatigue cracking deteriorate rapidly under the combination of traffic, moisture, and aging of the asphalt layer. Similar to Hamburg Wheel Tracking device (HWTD) for rutting potential, TxDOT has implemented the Overlay Tester (OT) to evaluate the cracking susceptibility and resistance to reflective cracking of hot mix asphalt (HMA). The OT is a relatively simple empirical laboratory method. Despite several previous attempts to improve OT so that parameters related to quantify resistance to fatigue cracking can be measured, additional work in that area is required. Recent studies have brought about some concerns about the utility of the OT in dense graded HMA mixes such as Types C and D, which make up about 75% of all HMA used in Texas. The use of OT to measure resistance to fatigue cracking of HMA reliably in a robust manner is greatly needed for all mixture types and HMA specifications.

What's the Solution?

Through a systematic approach, full consideration of the previous work on the subject, and in consultation with the manufacturers, the Research Team will evaluate and improve the hardware and software, laboratory test procedures and specifications of the OT to allow direct measurement of fatigue properties of asphalt mixtures with much less variation.

Project Number

0-6815

Status

Completed

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