Mohammad I. Hossain

Characterisation and modelling of vapour-conditioned asphalt binders using nanoindentation

Nanoindentation tests were conducted on unconditioned and vapour-conditioned asphalt binder samples to determine damage processes by characterising contact creep data and using viscoelastic mechanical models. For vapour-conditioned asphalt binders, a thin film of asphalt binder was prepared on a glass slide and subjected to relative humidity (RH) of 25%, 49% and 71% inside enclosed desiccators using three aqueous solutions: potassium acetate, potassium carbonate and sodium chloride, respectively. Based on the nanoindentation contact creep test data, it was observed that vapour-conditioned asphalt binders showed larger indentation viscous depth than the unconditioned binders. Indentation test data were modelled using viscoelastic mechanical models such as Burgers and Maxwell models. The models showed that elasticity increased and viscosity decreased in the vapour-conditioned asphalt binders. In 71% RH-conditioned binders, elastic components of Burgers model, E1 and E2 increased about 10% and 15%, respectively, compared to the unconditioned binder. The relaxation time decreased about 35% and retardation time increased about 69% in 71% RH-conditioned binders compared to unconditioned binders.

Field Validation of the Arching Phenomenon of Earth Pressure Cell to Measure Vertical Stress in Flexible Pavement

Earth pressure cell (EPC) is used to measure vertical stresses at different depths of pavement due to traffic loading. Typically, it is considered that this sensor is not affected by arching phenomenon. As the sensor is made up of steel, its stiffness is greater than the surrounding soil materials. Therefore, the sensor may report greater stress for arching action compared to the actual value. This study investigated the arching effect by finite element model (FEM) and validates the results by field data from installed EPCs due to traffic and falling weight deflectometer (FWD) loads on an instrumented pavement section in New Mexico, USA. Results show that vertical stress response measured on the top of subbase (445 mm depth) and top of subgrade (645 mm depth) increases up to 2.72 and 2.21%, respectively, for arching action. The vertical stress on top of base decreases with increase in EPC stiffness. Field measured vertical stresses under traffic and FWD loads at different depths agree with these FEM outputs.

Finite Element and Mechanical Modeling of Fatigue Behavior of Partial Vapor-Conditioned Viscoelastic Material

Past studies have shown that vapor conditioning to 100% Relative Humidity (RH) reduces the fatigue life of viscoelastic materials such as asphalt binder. However, it is not known how partial vapor conditions such as RH 25%, 49%, and 71% affect asphalt binder’s fatigue behavior. In addition, it is unknown which viscoelastic material parameter (i.e. viscus or elastic parameter) is responsible for damage in asphalt binder or Asphalt Concrete (AC) in general and what steps can be taken to reduce fatigue damage. In this study, films of asphalt binders were prepared and partially vapor-conditioned in enclosed chambers containing potassium acetate (25% RH), potassium carbonate (49% RH), and sodium chloride solutions (71% RH). Creep nanoindentation tests were performed on the vapor-conditioned asphalt film samples. The nano-creep test data are fitted using Burgers models. The Burgers model shows that elasticity increases and viscosity decreases as RH% increases. To this end, a Finite Element Method (FEM) model is developed in ABAQUS to examine the fatigue performance of the asphalt binder at 49% vapor-conditioned only. Using the spring and dashpot elements of Burgers model as FEM inputs, simulations are run. Results indicate that an increase in binder viscosity would reduce permanent deformation in the viscoelastic material.Copyright

Temperature and Moisture Impacts on Asphalt before and after Oxidative Aging Using Molecular Dynamics Simulations

AbstractTemperature and moisture impacts on unoxidized and oxidized asphalts’ thermodynamic and rheological properties were studied using molecular dynamics (MD) simulations. Changes in asphalt pro...

Use of Thermodynamics and Heat Transfer Principles to Predict Virgin Aggregate Temperature in a Hot-Mix Asphalt Drum Plant

AbstractVirgin aggregate is heated and dried in a drum dryer and uses this heated mass to heat and dry reclaimed asphalt pavement (RAP) and/or recycled asphalt shingles (RAS) materials in a drum mi...