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Nondestructive Condition Assessment and Rating of Concrete Rail Road Cross Ties By: Paul Fisk, President NDT Corporation ABSTRACT: Nondestructive impact velocity measurements are used to document the current condition and integrity of concrete cross ties and provide intrinsic information that can be used to classify concrete cross ties into three categories: 1) functional 2) marginally functional 3) non- functional. These Results can be used to document the condition of each tie and identify ties for immediate replacement, future monitoring (retesting at a later date) or no immediate action. Ties that are “good” (no immediate action required) have compressional wave velocity values greater than 14,000 ft/sec and shear wave velocity values greater than 7,00 0 + ft/sec. Ties classified as Marginally Functional, some cracking and delamination but not deteriorated to the point that they should be immediately replaced, have compressional wave velocity values of 13,000 to 14,000 ft/sec and shear wave velocity values in a range of 6,000 to 7,000 ft/sec. Ties that are classified as non-functional (deteriorated, cracked, delaminated and should be replaced) have compressional wave velocity values less than 13,000 ft/sec and shear wave velocity values either absent or less than 6,000 ft/sec. Based on these results, NDT Corporation developed an automated data acquisition system that rolls along the track testing a tie every second or approximately 1 mile of ties per hour. The system has been fitted to a light weight Nolan Cart so that it can be easily moved along the rails and moved off of the rails to allow traffic to pass. INTRODUCTION: NDT Corporation conducted sonic/ultrasonic impact velocity nondestructive testing of pre-stressed concrete rail road cross ties of varying conditions. Most of the ties tested during these investigations were manufactured by ROCLA and included tie sets that are: • new (never put in services); • out of service severely delaminated and fractured; • spider cracking and indications of alkali silica reaction with cracking; • In-service ties in a siding with minor cracking. • In-services and have little to no evidence of cracking. Sonic/ultrasonic Nondestructive Testing Measurements: The mechanical strength characteristics of concrete are determined by measurement of compressional and shear/Rayleigh wave transmission velocities values. The transmission velocity values determine the elastic deformational characteristics of the concrete, including Young's, Bulk, and shear modulus values as well as Poisson's ratio and calculated strength TRB 2012 Annual Meeting Original paper submittal - not revised by author.
