Determination of the coefficient of thermal contraction of asphalt concrete using the resistance strain gage technique

The suitability of using the resistance strain gage technique to measure the coefficient of thermal contraction (α) of asphalt concrete has been investigated in the temperature range from 0 to -25 C. The technique consisted of using TYPE EA-06-20 CBW-120 gages bonded to the reference and test specimens, and connected to a Wheatstone quarter bridge. Forty-four asphalt concrete specimens selected from 22 pavement sections used in the Strategic Highway Research Program A-005 project were tested. The measured values of coefficients of thermal contraction of different asphalt concrete specimens varied from 1.33 to 2.97 × 10^-5/°C, and the corresponding standard deviations between gages on a specimen varied from 0.05 to 0.39 × 10^-5/°C. The values measured using the same system on aluminum alloy beams verified the accuracy of the measurements. The observations made showed that measured strain was linearly related to the temperature. This relationship was not affected by the thermal schedule method used to cool the specimens (a series of constant temperatures or a cooling rate of 0.1°C/min). It was also observed that the differences of strain measured on the top and bottom sides of test specimens are statistically insignificant. The comparison of the measured values to those predicted using the volumetric relationship in SUPERPAVE, revealed that at least 70 percent of predicted values were higher than the experimental values.