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Title:Displacement rate and temperature effect on asphalt concrete cracking potential
Author(s):Khan, ASM Tamim Uddin
Department / Program:Civil & Environmental Eng
Discipline:Civil Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Asphalt Concrete (AC)
Time-Temperature Superposition Principle (TTSP)
Displacement Rate
Variable Displacement Rate
Loading Rate
Reduced Displacement Rate
Reduced Loading Rate
Shift Factor
Binder Grade
Fracture Energy
Abstract:One of the major distresses of asphalt concrete (AC) in flexible pavements is thermal cracking alongside fatigue, weathering related cracking and rutting. Pavements in Illinois road network are highly prone to different sources of cracking because of the climatic conditions and heavy traffic loads. Daily temperature fluctuations and traffic loading are among the external causes of crack initiation and development in pavements whereas structural design of pavements, base and subgrade support and conditions, material properties, and drainage conditions are the pavement related factors influence cracking development. Since cracking related damage occurs over a wide range of temperature and loading conditions, a good understanding of fracture behavior of AC over a spectrum of conditions including temperature and rate of displacement is needed. This thesis has two major objectives. First is to gain an overall understanding of fracture behavior of AC under a wide spectrum of temperature and rates of displacement. Second is to identify the combination of temperature and rate of displacement that would allow cost effective and reasonably accurate screening of AC mixes against cracking related damage. To address the issues above, fracture experiments using the semi-circular bending (SCB) geometry were carried out for different AC mixtures using multiple displacement rates at various temperatures ranging from –38°C to 38°C. Fracture tests were conducted using crack mouth opening displacement (CMOD) and load-line displacement control modes. The results presented in this thesis showed that the fracture energy distribution showed a phase angle relationship with a plateau region at low temperatures and reaching a peak at or around intermediate temperatures. . Mixes with higher degrees of viscoelasticity (due to binder content and type) are more susceptible to changes in displacement rates and temperatures. Plateau value of fracture energy can be governed by mixture volumetric, aggregate skeleton and binder grade. Mixes with similar volumetric, generally defined by aggregate gradation and binder grade, could have similar low temperature fracture energy in this region. However, it was shown that when these mixes were tested at elevated temperatures, differences in the mixes became more apparent. Therefore, it was concluded that AC mixtures are better screened at intermediate temperatures tested at relatively high displacement rates This thesis also evaluated the application and validity of time-temperature superposition principle (TTSP) for SCB fracture experiments. In order to accomplish this objective, displacement rates were shifted for each temperature using the shift factors obtained from the complex modulus test conducted for the same AC mixture. According to the superposition theory, same viscoelastic material characteristics could be obtained when time (represented by rate of displacement in fracture experiments) and temperature were adjusted according to a superposition rule. A generalized viscoelastic mechanical analog model was shown to successfully represent strength of the two mixes over a wide range of temperatures. However, the application of TTSP for fracture energy is limited and varying with the change in temperatures and material properties. Mixes with higher degrees of viscoelasticity and resulting in smaller stiffness showed greater deviation from TTSP; however, TTSP was applicable for stiffer mixes for a greater span of temperature range. At 12°C and above, TTSP was found to be inapplicable to representing fracture energy for the AC mixes.
Issue Date:2016-03-21
Rights Information:Copyright 2016 ASM Tamim Khan
Date Available in IDEALS:2016-07-07
Date Deposited:2016-05

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