Bao-Liang Chen

Harvesting energy from asphalt pavements and reducing the heat island effect

A rise in temperature of asphalt pavements contributes towards the urban heat island effect, causes problems with air quality and increases the power requirement for cooling buildings. A high temperature would also lead to the potential of rutting failure in asphalt pavements. The concept of mining heat from asphalt pavements, utilising an appropriate fluid flowing in pipes installed within the pavement, has been proposed. Theoretical considerations and results of laboratory testing and modelling simulation have been presented. The results indicate that the concept is feasible, and that the efficiency of heat mining can be improved by selecting appropriate surface layer and aggregates for pavement materials. The use of this proposed method would lead to a significant reduction in pavement and near-surface air temperature, and extension of asphalt pavement life.

Nonlinear system identification of large-scale smart pavement systems

This paper proposes a novel model for predicting complex behavior of smart pavements under a variety of environmental conditions. The mathematical model is developed through an adaptive neuro fuzzy inference system (ANFIS). To evaluate the effectiveness of the ANFIS model, the temperature fluctuations at different locations in smart pavement systems equipped with pipe network systems under solar radiations is investigated. To develop the smart pavement ANFIS model, various sets of input and output field experimental data are collected from large-scale experimental test beds. The solar radiation and the inlet water flow are used as input signals for training complex behavior of the smart pavement ANFIS model, while the temperature fluctuation of the smart pavement system is used for the output signal. The trained model is validated using 20 different data sets that are not used for the training process. It is demonstrated from the simulation that the ANFIS identification approach is effective in modeling complex behavior of the pavement-fluid system under a variety of environmental conditions. Comparison with high fidelity data proves the viability of the proposed approach in pavement health monitoring setting, as well as automatic control systems.

Harvesting heat energy from asphalt pavements: development of and comparison between numerical models and experiment

The use of flowing water in embedded pipes to harvest heat energy from asphalt pavements and thereby reducing its temperature and the urban heat island effect has been proposed. A successful use of such an approach would require a complete understanding of the effect and the interaction of various mechanisms such as conduction, convection and radiation and factors such as solar radiation, diameter of pipe and rate of flow. A large-scale experiment was conducted to understand such effects, and numerical modelling was conducted for prediction of temperature. The experiment was modelled using finite element method, and a good match was obtained between predicted and experimentally obtained results. Effects of pipe diameter and flow rate were also analysed. This model could be used in future for selection of appropriate levels of critical variables and hence successful implementation of this concept to sustainable pavements.

Practical Method to Understand the Effect of Aggregate Drying on the Moisture Content of Hot-Mix Asphalt

The drying of aggregates is a critical step in obtaining moisture-free hotmix asphalt (HMA). The drying depends on many factors, which include the absorption and the moisture content of the aggregates as well as the drying temperature and time. The effect of drying of the aggregates on the moisture content of the resultant HMA needs to be understood so that adequate drying can be carried out for mixes, such as warm-mix asphalt (WMA), which are produced at lower than conventional temperatures. The objectives of this study were (a) to develop a laboratory method to produce HMA samples with various moisture contents that mimic insufficient drying of aggregates in a drum mixer and (b) to develop a nondestructive laboratory testing procedure to determine moisture content of compacted HMA samples. Aggregates with relatively high and low absorption rates were selected. A practical method was developed to mimic the retention of aggregate moisture in HMA in the laboratory. Good correlation was obtained between drying time and moisture-content loss for the aggregates of high and low water absorption. An experiment with heat transfer and a simulation with a finite element method confirmed the presence of moisture and its significant effect on the thermal conductivity of the mixes, which provided a nondestructive approach to determine moisture content of compacted HMA samples.

Cool and Long-Lasting Pavements with Geosynthetic Reinforced Chip Seals

Pavements absorb a large amount of solar radiation. High pavement temperatures in warm climates cause problems such as rutting and accelerated aging of the mix, the urban heat island effect, and deterioration of air quality. This paper discusses, with models and experimental results, the concept of using an insulation layer, such as a geotextile, and aggregates with higher reflectivity in chip seals to reduce the conduction of heat through an asphalt pavement and increase the reflectivity of the surface. Reductions of temperature in the range of 8-10 °C were noted at the surface and 75 mm below the surface with the use of a 2.4 mm thick Petromat geotextile with chip seal. The study showed that a significant improvement in temperature reduction can be achieved with the use of a thicker insulation layer and/or an insulation of lower conductivity.

Insulating Pavements to Extend Service Life

Temperature fluctuations in asphalt pavements can increase the potential for rutting and cracking distresses. One way of countering this problem is to insulate a pavement from the extremes of air temperature and to also use a high reflectivity surface in warmer climates to reduce the absorption of solar radiation. This paper presents modeling and simulation results of the application of these concepts. Pavements with and without insulation layers were modeled in low temperature (Juneau, AK) and high temperature (Houston, TX) cities. A high reflectivity surface was also modeled in Houston. Temperature and solar radiation data for an entire year were analyzed for each city and the data corresponding to lowest and highest temperature (respectively) were utilized in the low and high temperature city pavement models. Results indicate that high temperatures were significantly reduced and that low temperatures were increased, depending on the thermal conductivity and thickness of the insulation layer. The presence of a highly reflective layer was also found to be very effective in reducing high temperatures in pavements. The positive effects of high temperature reduction on the service life of pavements was found to be significant, and the use of conventional materials of sufficient thickness was found to be feasible. Based on these findings, an ideal pavement section is suggested as one with an insulation layer near the surface, which could also serve as a moisture prevention layer; with a high reflectivity surface; and which is economical, durable, and capable of retaining its properties.