The session addresses how pavement materials interact with the urban climate as well as technologies and practices to mitigate Urban Heat Island (UHI) impacts.
Assessment of Heat Island Impact from Asphalt Concrete Field Cores
Sushobhan Sen, University of Illinois, Urbana ChampaignShow Abstract
Jeffery Roesler, University of Illinois, Urbana Champaign
Pavements contribute significantly to the development of Urban Heat Islands (UHIs). This is impacted by the local climate and urban form, as well as the thermal and optical properties of the pavement, which are usually not measured. Field cores of asphalt concrete (AC) pavements from five locations in Illinois were used to evaluate the optical and thermal properties of existing pavements. Thermal conductivity ranged from 1.0 to 3.0 W/mK, diffusivity 0.6 to 2.0 mm2/s, and heat capacity 0.7 to 3.0 MJ/m3K, which differ significantly from values typically used in pavement design. The same cores were used to extend a simplified bilinear aging albedo model, with the asymptotic albedo and at-construction albedo being largely within the expected range of 0.10 to 0.20 and 0.05 to 0.10, respectively. These properties as well as historical weather data from each of the locations were used to evaluate the local pavement Radiative Forcing (RFp) and Global Warming Potential (GWP). The highest RFp of about 65 W/m2 was observed in a location in Southern Illinois, which receives more sunlight annually than the other locations. GWP was found to increase with service life. An Average Day (AD) metric was also applied on net surface heat flux and surface temperature to highlight differences because of thermal properties, which GWP does not properly capture. Surface temperatures were found to vary by 1 to , with lower values of conductivity and heat capacity leading to higher surface temperatures and hence an increased UHI.
Assessing the Use of Phase-Change Materials to Control Temperature in Asphalt Pavements
Tharanga Dissanayaka, Texas Tech UniversityShow Abstract
Sanjaya Senadheera, Texas Tech University
Asphalt Concrete containing Phase Change Materials (Micro PCM) can reduce the distresses like rutting in flexible pavements. Therefore the pavement service life can be extended, and the maintenance cost can be minimized. So the significant amount of natural sources such as water, crude oil and aggregates can be saved for other purposes. Urban Heat island (UHI) significantly affect to residents living in that environment. Being a black-color material asphalt cement has a high heat absorptivity (0.85 to 0.93). Asphalt concrete pavements are much economical than other pavements. So this leads to build more pavement with black color asphalt concrete surface layer and cause to increase the UHI. However, PCM has a capability to control the maximum pavement temperature, and it can adjust the mixture operating temperature. Asphalt binders containing Micro PCM shows that PCM can be used to control the temperature in the asphalt-Micro PCM mastics.
The Impact of Pavement Albedo on Radiative Forcing and Building Energy Demand: Comparative Analysis of Urban Neighborhoods
Xin Xu, Massachusetts Institute of Technology (MIT)Show Abstract
Jeremy Gregory, Massachusetts Institute of Technology (MIT)
Randolph Kirchain, Massachusetts Institute of Technology (MIT)
Albedo is the measure of the ratio of solar radiation reflected by the Earth’s surface. High-albedo reflective surfaces absorb less energy and reflect more shortwave radiation. The change in radiative energy balance at the top of atmosphere (TOA), which is called radiative forcing (RF), reduces nearby air temperatures and impacts the surrounding building energy demand (BED). The impact of reflective surfaces on RF and BED has been investigated separately by researchers through modeling and observational studies, however, no one has compared RF and BED impacts under the same context and the net effect of these two impacts remains unclear.
This manuscript presents a comprehensive approach to assess the net impacts of pavement albedo modification strategies in selected urban neighborhoods. We apply an adapted analytical model for RF and a hybrid model framework combining two different models for BED to estimate the impacts of increasing pavement albedo from 0.1 to 0.3 for different urban neighborhoods in Boston and Phoenix. The impact of several context-specific factors, including location, urban morphology, shadings etc., are taken into account in the models. Comparative analysis reveals that the net impact of changing pavement albedo can vary from one neighborhood to another. In Phoenix downtown, reflective pavements create net GWP burdens, while increasing pavement albedo results in potential savings in Boston downtown area. This work will provide insights into pavement albedo impacts at urban scale and support more informed decisions on pavement designs that will save energy and counteract some of the global warming effects.
From Trade-Offs to Equivalent Solutions: A Life-Cycle Thinking Informed Approach to Design Decision Making
Chaitanya Ganesh Bhat, Michigan Technological UniversityShow Abstract
Amlan Mukherjee, Michigan Technological University
As the infrastructure industry moves towards adopting Environmental Product Declarations (EPD) as instruments for communicating environmental impacts of products and processes, there is a growing need to develop methods that support the informed use of mid-point impact indicators such as Global Warming Potential (GWP) in the design decision-making process. This research presents a framework that will aid decision-makers to inform the design of pavement systems by explicitly accounting for performance requirements, and environmental impact indicators associated with a product or process at different life cycle stages. It develops a method that departs from a trade-off based approach towards embracing a life cycle thinking approach, through inclusion of relevant life cycle flows that can offset trade-off margins. An illustration of the framework is provided for the design of a benchmark asphalt mixture, considering its GWP, Reclaimed Asphalt Pavement (RAP) content and its Thermal Cracking (TC) performance. The outcomes of the analysis provide decision-makers with guidelines on margins of tolerance, and indicates the possibility of identifying equivalent functionalities (for GWP and TC) across designs with varying RAP content. The framework is expected to be extensible and capable of building on existing LCA frameworks and mechanistic-empirical models. As EPDs become part of the decision-making process, this method can provide decision-makers guidelines to avoid trade-offs between performance and environmental impacts, instead emphasizing control over associated life cycle flows.