Influence of overlay thickness on interface bonding
Overlaying is an efficient and proven pavement preservation approach for flexible pavements. The overlay thickness varies from 1 in. to 4 in. depending on the conditions of the existing pavement, financial resources, etc. In the recent decade, financial constraints in conjunction with the push for pavement preservation, the overlay thickness is being reduced to less than an in. The ultra-thin overlay is a new cost-effective method that can be used to preserve functional pavement problems and provide satisfactory ride quality. Although studies have been conducted to evaluate pavement systems using numerical simulation, the research in the area of evaluating existing layer and overlay layer as a composite layer is limited. With the advent of Ultra-thin layers, the durability of pavement system will be significantly influenced if both layers separate from each other. The several experimental studies have focused on the interface bonding between the overlay and existing asphalt layer. They evaluated how different criteria like tack coat type, dust, or moisture can affect the interface bonding strength between layers. But the impact of different interface bonding strength on pavement structure and durability of overlay itself has not been extensively evaluated. Overlay thickness impact on pavement structural characteristics is another aspect of the subject that still needs a lot of research. The main purpose of this study was to perform numerical simulation of several pavements systems with different overlay thicknesses and to evaluate the effect of overlay thickness and overlay-existing asphalt layer interface bonding on pavement performance. Three-dimensional finite element models have been used to simulate different pavement systems using ABAQUS software. Different interface bonding strength has also been implemented for each of the pavement systems to evaluate the effect of interface bonding strength. Models with linear elastic-perfectly plastic behavior for the base and subgrade was selected for the base and subgrade layer. Viscoelastic behavior of the asphalt material has been modeled using dynamic modulus test results and Prony series. Finite and semi-infinite elements have been developed to model the pavement systems. Passing (moving) vehicle’s load used to see the impact of overlaying in highways or other places that vehicles drive at nearly constant speed. The pavements performance under braking conditions was also necessary to see how overlay works under stop and go traffic conditions or near intersections. Rather than uniform distributed load, the load was non-uniformly distributed in the tire footprint are to simulate actual field conditions. Frictional and cohesive contact approach was followed to define interface layer and bonding between the two layers. Frictional contact has been used to simulate the interface characteristics between existing asphalt and base layer. The cohesive contact was used to define the tack coat layer properties. Maximum deflection at the top surface of the pavement and the maximum tensile strength at the bottom of the existing asphalt layer has been observed as the two most important criteria determining pavement performance. To evaluate the durability of the overlay itself, contact opening between the overlay and existing asphalt layer has been observed. The evaluation results identified that overlay thickness of less than 2 in. doesn’t add structural strength to the pavement system. The overlays with the thickness of less than 1 in. significantly influences stress levels at the interface; therefore, bonding between the two layers is important. The moving load versus braking loads should be considered for evaluating the composite pavement design system.
Dormohammadi, Aliasghar, "Influence of overlay thickness on interface bonding" (2017). ETD Collection for University of Texas, El Paso. AAI10619592.