Rail exposed to solar radiation increases in temperature from radiant solar heating. This results from absorption at near infrared (NIR) wavelengths of ～1-3 micrometers (μ). Welded rails are typically installed with a target neutral rail temperature (NRT) of 85-95℉. As rail temperature increases, stresses build from thermal expansion producing track distortion (sun kink). As a precaution, railroads commonly issue slow orders when the measured or estimated rail temperature could reach 120-130℉. FRA data analyses have shown that many track buckles occur near a fixed structure. In general, if rail solar gain can be reduced, it may be possible to decrease the number of track buckle incidents. NIR reflective coatings to reduce solar absorption in the 1-3μ range are in use on civil structures. Most are based on paints with filler additives. Certain ceramic like coatings are also capable of reflecting NIR light, and coatings for spacecraft are effective on satellites or re-entry vehicles. Products representing all three approaches have been investigated in this program for the potential: (1) to keep rail temperature at least 10℉ cooler or (2) control overall temperature gain to ＜30℉ compared with untreated rail. The products were measured for natural NIR reflectance on instruments, then by measuring temperature gain of coated steel plates irradiated with a natural NIR spectrum lamp, and finally by monitoring temperatures on exposed short rail sections. Predicted thermal performance and actual performance based on exposed, treated rails were compared. Some coatings were effective in reducing thermal gain to desirable ranges.
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