Philip Park

Behavior of Bridge Asphalt Plug Joints under Thermal and Traffic Loads

An asphalt plug joint APJ is a type of expansion joint providing quick, easy, and cheap installation along with good surface flatness. However, APJs are known to suffer from premature failure, and their behavior, especially under thermal movement, has not yet been fully established. In this paper, the behavior of a typical APJ subjected to thermal and traffic loads is examined through a series of finite element analyzes employing a temperature-dependent viscoplastic material model. The material parameters are calibrated by using previously published test data, and the model is validated by comparing simulated responses to APJ test data. The developed models are then used to investigate stress and strain distributions, vulnerable locations to cracking failure, and local demands at those locations when a prototype APJ is subjected to various loading and temperature conditions. Sensitivity studies are also conducted to quantify the effect of debonding the bottom of the APJ and loading rate. The model results shed light about APJ response under traffic and thermal loading and provide new, fundamental information that can be used to improve the durability of APJs. For example, the simulation results suggest that intentionally debonding the interface between the gap plate and the APJ is a practical and low cost solution to mitigate the risk of premature APJ failure.

Improved Geometric Design of Bridge Asphalt Plug Joints

Asphalt plug joints (APJs) have several advantages over traditional bridge joints. They are easy and cheap to install and have good surface flatness. However, widespread application of APJs in bridges has been hindered by frequently observed premature failures. Detailed finite-element simulations are conducted to develop a better understanding of the parameters that influence APJ response under traffic and thermal loading conditions. The computational model employs a time and temperature dependent viscoplastic material model and is validated by comparing model results to previously published experimental data. The key parameters investigated are gap plate width, gap plate thickness, gap plate edge geometry, and geometry of the interface between pavement and APJ. The resulting information is synthesized into a proposed alternative APJ design that minimizes local demands deemed to be responsible for the observed early failures.

Effects of thermally modified asphalt concrete on pavement temperature

ABSTRACT This study investigates the feasibility of mitigating temperature-related issues, such as heat island effect, ice layer formation and thermal distresses of asphalt pavement, by controlling thermal properties of hot mix asphalt (HMA). Expanded polypropylene (EPP) beads and graphite powder are selected as the additives to change the thermal properties of HMA, and their effects on thermal and mechanical properties are evaluated experimentally. The test results show that the EPP modified HMA yields a reduction in thermal conductivity, heat capacity and indirect tensile strength up to 17, 32, and 27%, respectively. Conversely, replacing a part of traditional fillers with graphite powder increases indirect tensile strength and thermal conductivity up to 40 and 43%, respectively. A series of heat transfer analysis was conducted using a finite difference heat transfer model to investigate the effects of the thermally modified HMA on the pavement temperature gradient and surface temperature. The simulation results show that the amplitude of daily surface temperature variation reduces as the HMA thermal conductivity increases. The HMA containing 4.8% graphite by volume of the mixture reduces the daily surface temperature amplitude by 8.1% in the summer simulation and 9.6% in the winter simulation. The graphite modified HMA also has 1.5 °C lower maximum pavement surface temperature than the non-modified HMA in the simulation for a summer day at Texas. This implies that the modified HMA with improved thermal conductivity, such as the graphite modified one, is effective in mitigating thermal cracking, rutting and urban heat island effect. In addition, the improved indirect tensile strength of graphite modified HMA will bring extra extension of pavement service life. The parametric study for wide ranges of thermal conductivity and heat capacity shows that the daily temperature amplitude on a pavement surface can be reduced up to 28.9% by selecting highly conductive aggregates and graphite powder.