Civil Engineering ETDs

Publication Date

2-13-2014

Abstract

Moisture damage in Asphalt Concrete (AC) is not new but an unsolved problem. For decades laboratory studies have been conducted on both loose and compacted mix to understand the effects of moisture on the AC damage. Adhesive and cohesive damages are the two major types of damages occur inside the AC. Adhesive damage is a separation between aggregate and coated mastic or matrix materials and cohesive damage is the degradation of strength of matrix materials within the AC samples. In this study, Finite Element Method (FEM) modeling technique is used to identify initiation and progression of adhesive and cohesive damage. In addition, the effects of moisture in the mastic materials (i.e. mixture of fines passing no. 200 sieve and asphalt binder) are determined by laboratory investigations since mastic materials govern the mechanical properties of AC. The asphalt mastic-aggregate interface damage is quantified using FEM and traction separation law. Model parameters are determined from laboratory pull-off and strength testing of mastic materials. The contact stress is significantly higher in dry conditioned mastic-aggregate interface than in the wet conditioned interface for all load magnitudes and patterns. Lower contact stresses are one of the reasons for higher mastic-aggregate interface damage under wet condition. That is, Lower contact stresses are responsible for de-bonding at the interface. It is shown that 6.8% (% perimeter) interface de-bonding occurs in dry sample. On the other hand, about 49.1% interface de-bonding occurs in wet conditioned sample. Adhesive damage is significantly higher under the wet condition, since interface region is the weakest considering the whole domain. Cohesive damage is determined by maximum stress criteria, which indicates that a material is damaged when it reaches the maximum strength. Cohesive damage initiates at the top of matrix and then damage propagates towards the bottom of matrix and matrix-aggregate interface. Moisture causes 62.8% more damage in the matrix materials when considering only the matrix materials under the applied deformation region. In addition, pull-off test and shear tests are conducted on the mastic film under different Relative Humidity (RH%) conditions. Mastic films show flexible behavior due to high RH% conditioning and brittle behavior due to low RH% conditioning in pull-off tests. Increase in elasticity at high RH% conditioning causes a decrease in viscosity in mastic films. Decrease in viscosity of mastic materials causes binding inefficiency between aggregates due to lack of bonding forces. Damage causes due to binding inefficiency, which results in lack of bonding within asphalt binder and between asphalt binder and aggregates. To support this argument, nanoindentation tests are performed on the mastic materials. It is observed that, dry mastic follows linear Burgers and wet mastic follows Maxwell or modified Maxwell viscoelastic mechanical model. Wet mastic shows high viscous depth (i.e. low viscosity) compare to the dry mastic. In addition, Maxwell model does not show any retardation strain. Hence, it is proved that moisture takes away viscous effects from the AC and causes damage.

Keywords

Modeling, Moisture, Damage, Asphalt Concrete

Sponsors

National Science Foundation

Document Type

Dissertation

Language

English

Degree Name

Civil Engineering

Level of Degree

Doctoral

Department Name

Civil Engineering

First Committee Member (Chair)

Maji, Arup

Second Committee Member

Ng, Tang-Tat

Third Committee Member

Shen, Yu-Lin

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