Design, construction, and evaluation of energy-harvesting asphalt pavement systems

Figures & data

Table 1. Studies on the various parameters involved in the design of HAPs.

Reference	Property	Study/Outcome
Abdel-Khalik (1976)	Pipe Configuration	Predicted the variation of fluid temperature in segments of serpentine configuration with arbitrary geometry and number of bends.
Chen, Bhowmick, and Mallick (2009)	Pipe Configuration	A serpentine configuration allows higher outlet water temperatures.
Chiou (1982)	Flow	The efficiency of the system can deteriorate anywhere between 2% and 20% due to flow non-uniformity.
Dakessian et al. (2016)	Pipe Configuration	A one reservoir looping configuration achieves lower efficiency due to the constantly decreasing temperature differential between the inflow and outflow water as opposed to the single pass system.
Deeb et al. (2013)	Pipe Diameter and Flow	The larger the diameter, the greater the decrease in surface temperature. For a constant flow, the larger the diameter pipe, the smaller the decrease in surface temperature.
Gui, Phelan, Kaloush, and Golden (2007)	Thermal Conductivity	The average maximum temperature decreases with increasing conductivity. The minimum surface temperature increases with conductivity.
	Volumetric Heat Capacity	The maximum temperature decreases while the minimum temperature increases with increasing volumetric heat capacity.
	Thermal Diffusivity	The average maximum surface temperature reduces while the minimum temperature increases with increasing diffusivity.
	Albedo	The higher the albedo, the lower the pavement maximum and minimum temperatures. The maximum temperature is more sensitive to albedo.
	Emissivity	The maximum and minimum surface temperatures decrease with increasing emissivity.
Mallick et al. (2009)	Thermal Conductivity	Aggregates with higher thermal conductivity such as quartzite increase the difference between incoming and outgoing water by 100% as compared to using limestone aggregates.
	Albedo	The lower the albedo, the higher the difference between incoming and outgoing water.
	Pipe Spacing	The fluid carrying pipes must be placed at a minimum spacing to avoid “cool” spot formation.
Shaopeng et al. (2011)	Flow	The surface temperature shows a limited decrease with increasing flow rate.
Uponor Wirsbo (2003)	Pipe Configuration	Reverse-return layout allows the surface to heat up equally desirable for snow-melting.
	Heat Transfer Fluid	The use of glycols is recommended for snow-melting (anti-freeze agents). The use of automotive antifreeze products is not recommended (coat and foul heat transfer surfaces).
Van Bijsterveld, Houben, Scarpas, and Molenaar (2001)	Pipe Spacing	Smaller spacing significantly lowers the temperature and results in more homogeneous temperature distribution. Larger spacing increases the temperature of the fluid.
	Flow	At low flow rates, the temperature of the fluid is easily influenced. Increasing the flow rate doesn't have a significant effect on the surface temperature.
	Pipe Depth	A greater depth results in a more homogeneous temperature distribution but the amount of heat extracted decreases.
Wang, Wu, Chen, and Zhang (2010)	Thermal Conductivity	The surface temperature of the pavement increases when thermal conductivity increases while the middle pavement's temperature increases.
	Pipe Spacing	The denser the pipes, the higher the percentage temperature change.
	Pipe Diameter	Larger pipes can decrease the peak surface temperature but could compromise the structural integrity of the pavement.
Zwarycz (2002)	Pipe Configuration	Small plastic pipes can be bent to form variety of heating panel designs without elbows or joints.
	Heat Transfer Fluid	Brine is the least costly heat transfer fluid, but it has a low specific heat. Glycols are the most common (moderate price, high specific heat, low viscosity, and ease of corrosion control). Glycols containing silicates are not recommended (cause fouling, seal wear, fluid gelation, and reduced heat transfer).
	Pipe Material	Steel, iron, and copper pipes are beneficial when there is a concern about temperature limitations and thermal conductivity, but they may rapidly corrode. Plastic pipes are popular because of their low material and installation cost and their corrosion resistance.

Figure 1. Thermal energy balance in HAP system.

Figure 2. Domain boundary conditions.

Figure 3. Temperature variation at: (a) specified depths with time; (b) continuous depths.

Figure 4. Comparison between measured results and FDM results at: (a) surface; (b) 1.5 cm depth; (c) 4 cm depth; and 6 cm depth.

Table 2. Reference values of the conducted simulations.

Parameter	Value	Parameter	Value
Weather Conditions
Relative Humidity	65%	Air Temperature	(Dakessian et al., 2016)
Cloud Cover	0.5	Wind Velocity
		Solar Radiation
Reference Model
Pavement Thermal Conductivity	1.3 W/m$\cdot$k	Pipe Diffusivity	24.3 mm^2/s
Pavement Width	4 m	Inlet Temperature	15°C
Pavement Emissivity	0.93	Fluid	Water
Pavement Absorptivity	0.93	Pipe Thickness	2.5 mm
Cross-sectional Depth	16 cm	Pipe Spacing	25 cm
Time of Simulation	12 h	Inner Pipe Diameter	25 mm
Flow Rate	0.2 L/s	Pipe Depth	2.5 cm

Figure 5. Parametric study results.

Figure 6. Variation of surface temperature with pipe conductivity.

Figure 7. Effect of changing asphalt and pipe conductivities on surface temperature.

Figure 8. Effect of spacing on the cross-sectional temperature distribution.

Figure 9. Effect of: (a) depth and (b) diameter on the cross-sectional temperature distribution.

Figure 10. Evolution of surface temperature distribution with time from numerical simulation.

Figure 11. Surface temperature distribution at the middle of the surface section of the pavement.

Figure 12. Effect of flow rate on the temperature difference between inlet and outlet.

Table 3. Pilot study parameters.

Parameter	Value
Piper Diameter (mm)	20
	25
	32
Depth from the Surface (cm)	2
	4
Pipe Placing Technique	Laying on Subgrade
	Laying on Compacted Asphalt Layer
	Spacers
Pipe Material	Steel
	PPR Class 2
	PPR Class 5
	PPR with Aluminium
	Plastic

Figure 13. Reverse-return configuration of pipes embedded in the asphalt layer.

Figure 14. Schematic of three systems to be constructed.

Figure 15. Gradation (NMAS 19.0 mm) of the asphalt mixture used in large-scale construction.

Table 4. Asphalt mix proportioning.

Material	Percentage by Weight of Total Mix
Fine Aggregates (0–6 mm)	39.6%
Intermediate Aggregates (6–12 mm)	30.5%
Coarse Aggregates (12–18 mm)	22.1%
Bag House Fines	3.5%
Binder Content	4.3%

Figure 16. Road selected for construction of HAP, GCHAP and control sections.

Figure 17. Solar path on 1 July 2017 over the chosen site.

Figure 18. Road: (a) before construction; (b) during pipe placement in the asphalt layer; and (c) during pipe placement in the soil (heat sink).

Figure 19. (a) Sensors locations on the as-built drawing; and (b) sensor placement in the asphalt layer.

Figure 20. Temperature distribution for control section.

Figure 21. Temperature distribution inside the pavement for the HAP section.

Figure 22. Heating/cooling cycle on 14 July for the HAP section.

Figure 23. Temperature distribution inside pavement (GCHAP section).

Figure 24. Heating/cooling cycle on 12 July for the GCHAP section.

Figure 25. Comparison of performance of HAP and GCHAP in reducing surface temperature of pavement.

Figure 26. Rutting prediction associated with each of the three systems.

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