Nondestructive testing of pavements and backcalculation of moduli / by Bush, Albert J., Baladi, Gilbert Y., ASTM. Committee D-4 on Road and Paving Materials, ASTM. Committee D-18 on Soil and Rock, International Symposium on Nondestructive Testing of Pavements and Backcalculation of Moduli (1st : 1988 : Baltimore, Maryland)