ORCID Identifier(s)

0000-0003-0200-2942

Graduation Semester and Year

2019

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering

Department

Civil Engineering

First Advisor

Stefan Romanoschi

Abstract

The measurement of the fundamental shear properties of asphalt mixes is imperative to the improvement of modelling of rutting development in asphalt concrete. The Duplicate Shear Tester (DST) is a recent device developed at the University of Texas at Arlington as a replacement to the Superpave Shear Tester (SST). It measures the average shear properties of two asphalt concrete specimens at the same time. It has ability to perform the two common SST tests: the FSCH and RSCH in according to the standard test method AASHTO T-320. Although the DST has successfully satisfied the objectives of being a reliable, inexpensive and simple test device, further modifications were required to simplify and improve the testing procedure. Therefore, this study aimed mainly to enhance the shear testing for asphalt mixes through modifying the DST device and developing a new shear tester device that is able to measure the shear properties of asphalt mixes under controlled normal stress. The new device is called the “Shear Tester with Normal Stress (STNS)”. The DST device was modified to be lighter in weight and to accommodate other shapes of asphalt mix specimens of circular diameter with two sizes, and rectangular specimens cut from horizontal and vertical slices. The STNS device was developed successfully with only simple and inexpensive testing attachments for the purpose to simulate the state of stresses within the rutting zone of asphalt pavements. Two shear tests were performed by this new device: the Frequency Shear Test at Normal Stress (FSNS), and the Repeated Shear Test at Normal Stress (RSNS). To study the accuracy of the shear test devices, three asphalt mixes of Superpave (types D and C) and dense graded type B were tested. Three shear parameters were obtained from each device: the shear dynamic modulus |G*| and shear phase angle (δ) from the FSCH & FSNS tests, and the total permanent deformation (PD) from the RSCH & RSNS tests. Both STNS tests were performed by applying a normal stress of 113 kPa (16.35 Psi). The test results proved the ability of the DST device to provide repeatable measurements with relatively low coefficient of variations (COV). At high load frequencies of 10 Hz and 5.0 Hz, the |G*| of all DST groups yielded COV values of less than 8% for mixes D and B, and less than 11% for mix C. The phase angle of all DST groups had COV values of less than 8.0% for mixes D and B, and less than 10% for mix C at all loading frequencies. The (PD) measurements of all DST groups had COV values of less than 13% for asphalt mixes D and C, and less than 8% for mix B except that for some groups of mix B as they had a COV values of about 17%. The test results of STNS testing groups showed generally high variabilities for the measured |G*| and phase angle, whereas they had low variabilities for the (PD) measurements. At high load frequencies, the COV values of the |G*| were less than 24%, 35%, and 38% for mixes D, C, and B, respectively. The COV values of the phase angles showed comparable values to that of the |G*| at high load frequencies. They had COV values of less than 30%, 35%, and 26% for mixes D, C, and B, respectively. The maximum COV value of the (PD) at 5,000 load cycles were about 14%, 12%, and 17% for mixes D, C and B, respectively. For each asphalt mix, however, there is at least one STNS group had COV value of less than 8.0% for the measured PD. An analysis of variance (ANOVA) technique was conducted to compare the tests results from both devices. The comparison includes testing the influence of four different test factors on the mean values of the G*@10Hz frequency and the accumulated (PD) at 5,000 load cycles by using the calculated “P-value” at 95% level of confidence. It was found that the daily times production affects the values of both parameters for mix D only and affects the G*@10Hz value for mix B tested with the DST device. Also, it affects both parameters for mixes D and C and the accumulated PD for mix B tested with the STNS device. Using the DST device, different diameter for circular specimens affects the G*@10Hz and accumulated PD values for mix D only. Also, different cut directions for the rectangular specimens affect the G*@10Hz for mix C, and the accumulated PD for mix B. It was shown that varying the testing device would sometimes affect the value of both G*@10Hz and accumulated PD. The DST device usually provided higher values for the G*@10Hz than the STNS device for samples collected at all daily time of production. Testing asphalt mixes with the two devices, however, provided unclear trends for the accumulated PD values.

Keywords

Asphalt concrete, Rutting, Shear tester, Duplicate shear tester, Shear tester

Disciplines

Civil and Environmental Engineering | Civil Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

Download

Share

COinS