Modeling Moisture Transport In Asphalt Concrete Of Open-Graded Friction Course (OGFC) Using Lattice Boltzmannn Method And X-Ray Computed Tomography Technique

With the construction of high speed highways at massive scale, asphalt pavement becomes widely adopted and rapidly developed. However, many of the asphalt pavement distresses such as surface cracks and pot holes are caused by moisture damage, which is mainly due to the destruction of adhesive bond between aggregate and the asphalt binder in the presence of moisture. As a result of these distresses can cause excessive asphalt pavement roughness and excessive deflections that might necessitate replacement of the entire asphalt pavement layer. There are numerous studies that indicated the susceptibility of asphalt pavements to moisture damage. So understanding the fluid transport in porous asphalt at pore scale is critical in determination of moisture damage in asphalt pavements.To investigate the fluid flow due to the constant pressures gradient in asphalt pavements, a three-dimensional fluid flow model was developed using the Lattice Boltzmann Method (LBM). The model was validated using the well-known closed form solution of some classic examples. An excellent agreement was observed between the Lattice Boltzmann Method and the closed form analytical solution or the experimentally and numerically established results. A number of simulations were carried out to calculate the permeabilities of different asphalt pavements exposed to the constant pressures gradient. As an input to the Lattice Boltzmann model, three-dimensional pore geometries of porous asphalt specimens were reconstructed employing the X-Ray computed tomography imaging technique. Major research work conducted includes:(1) Explaining in detail the theory of Lattice Boltzmann Method and validation of the Lattice Boltzmann Models.Derived from the Lattice Gas Automata (LGA), the basic theory of the Lattice Boltzmann Method (LBM) is introduced here including the BoltzmannTransport Equation, the basic steps (streaming and collision), the key concept (distribution function), the macroscopic variables and the common terminology (one-dimension:D1Q2, D1Q3 and D1Q5; two-dimension:D2Q5 and D2Q9; three-dimension:D3Q15 and D3Q19). Boundary conditions such as bounce back boundary, periodic boundary, Von Neumann (velocity) boundary and dirichlet (pressure) boundary are described in detail.The Lattice Boltzmann Method was validated using the well-known closedform solution of some classic examples including the plane Couette flows, the plane Poiseuille flows, the two-dimension flow around a circular cylinder and the flow in idealized porous media or in random porous media. An excellent agreement was observed between the Lattice Boltzmann Method and the closed form analytical solution or the experimentally and numerically established results.(2) Describing the theory of operation of X-Ray Computed Tomography imaging technique and developing the image anslysis algorithms.X-ray computed tomography (CT) is a completely nondestructive technique for visualizing features in the interior of opaque solid objects to obtain digital information on their three-dimensional geometry and properties. A three dimensional microstructures of the specimen can be reconstructed by stacking the image slices. Based on the interior successive two-dimensional slice images of asphalt specimen, X-ray Computed Tomography reflects the three-dimensional real pore structures of the specimen. Three-dimensional real pore structures of the Open-graded friction course asphalt mixtures specimens were generated using X-ray CT technique and used as input in the Lattice Boltzmann Models.The theory of operation of X-ray CT technique was described in Chaper 4. The geometrical properties of the specimens such as porosity were determined using different image analysis algorithms developed as a part of this study. The three-dimensional binary (black and white) images of the specimens that are necessary for those algorithms were processed using morphological thresholding technique. The developed algorithm is given in Chapter 5.(3) Discussing the results of three-dimensional flow simulations at pore scale in different asphalt specimens.The results of three-dimensional fluid flow simulations at pore scale in different asphalt specimens under different pressure gradients are presented in Chapter 6. By developing a three-dimensional image-based Lattice Boltzmann Model that is capable of simulating single-phase, Newtonian and incompressible fluid flow within any pore geometry. The "lattices" in the model are divided into three categories:Where "lattices" evaluates to 0, use LBGK; where "lattices" evaluates to 1, use bounce-back; where "lattices" evaluates to 2, use no-dynamics (which does nothing). It greatly improved the efficiency.The permeability variation in different depths of asphalt pavement was investigated in this paper, which is expected to characterize the vulnerability of different zones within asphalt pavements to moisture damage.