Upload
others
View
2
Download
0
Embed Size (px)
Citation preview
High albedo surfaces for thermal stabilisation of road embankment built on permafrost Simon Dumais1, Guy Doré, Department of Civil Engineering and Centre for Northern Studies, Université Laval, 1 [email protected]
• Micro texture • British pendulum (BPN) • Low speed skid resistance
• Macro texture • Sand patch test (MTD) • High speed skid resistance and
water management • Provides durability and thermal
benefits
Skid resistance
Methodology Test section in Beaver Creek, Yukon along the Alaska Highway • Four surfaces with different albedos
• Bituminous surface treatment with light coloured aggregates • Asphalt cold mix • Lafrentz (white coating) • Nippo (grey coating with high infrared reflection)
• Surface temperatures recorded from august 2012
Model for surface temperature calculation Introduction Heat absorbed by dark pavement can increase thaw penetration within a road embankment and can induce instability caused by thaw settlement of the underlying permafrost. High albedo road surfaces (HAS) can reduce the heat absorbed by the pavement thus increasing stability of the embankment. Past experiments with HAS have shown that they can efficiently reduce thaw penetration but that they present some technical flaws mainly regarding skid resistance.
Conclusion Solar reflectivity and skid resistance properties of high albedo surfaces have been evaluated on the Beaver Creek test section.
Beaver Creek test section August 2012
Albedo measurement May 2013
Incident solar
radia.on
Reflected solar
radia.on
Wind
Convec.on Emi6ed FIR
radia.on
Absorbed FIR
radia.on
Conduc.on
Pavement Embankment
Energy balance at the surface
Albedo Cold mix L-‐BST Nippo Lafrentz
August 2012 0,04 0,23 0,40 0,60
Mai 2013 0,14 0,23 0,29 0,55
0=𝑞↓𝑟 + 𝑞↓𝑐 + 𝑞↓𝑒 + 𝑞↓𝑔
Solar radiation 𝑞↓𝑟 =(1−𝑎)𝑞↓𝑖
Convection 𝑞↓𝑐 = ℎ↓𝑐 ( 𝑇↓𝑠 − 𝑇↓𝑎 )
FIR radiation 𝑞↓𝑒 =𝜎(𝜀↓𝑠 𝑇↓𝑠↑4 −
𝜀↓𝑠𝑘𝑦 𝑇↓𝑎↑4 )
Conduction 𝑞↓𝑔 =−0,11 𝑞↓𝑟_𝑚𝑎𝑥
𝑠𝑖𝑛((𝑛−2)𝜋/6 )
Objectives • Evaluate skid resistance and solar reflectivity of HAS • Quantify the effect of albedo on pavement’s temperature
0
5
10
15
20
25
30
0 50 100 150 200 250
Surface tempe
rature [°C]
Absorbed solar radiaIon qr [W/m2]
Monthly average surface temperature
Model Ta=5°C Model Ta=10°C Model Ta=15°C BC May Ta=6°C BC September Ta=7°C BC August Ta=11°C BC July Ta=14°C BC June Ta=15°C
For Ta>0°C with U=1,5 m/s, ε=0,85 and εsky=0,70
Skid resistance testing
A model has been developed to predict surface temperature of pavements in function of their albedo based on energy balance at the surface of the pavement. The model has been validated using data from the test section in Beaver Creek, Yukon.
Skid resistance Cold mix L-‐BST Nippo Lafrentz
BPN 94 97 74 59
MTD (mm) 0,746 1,910 0,702 0,589
Solar reflectivity • Albedo • Measured with pyranometer