Comparison of Nondestructive Evaluation Findings, Constrained and Unconstrained Wave Speeds, Dynamic Moduli, and Poisson’s Ratio of Core Specimens from a Concrete Structure Damaged by Fire

Abstract

This article discusses the use of nondestructive and subsequent laboratory materials testing techniques in evaluation of extent of fire damage to a precast prestressed parking structure. The nondestructive and laboratory testing findings were used in determination of extent of fire damage to concrete and potential effects on the prestressing tendons. The in-situ nondestructive testing phase consisted of scanning affected areas using ultrasonic pulse velocity through concrete members and use of impact echo on a confirmatory limited basis. Subsequently, cores were removed and tested for resonant frequency-based dynamic modulus in accordance with ASTM C 215. Upon determination of dynamic elastic modulus of the entire core per ASTM C 215, the cores were sawn into 25-mm (1-in.) disks. Young’s modulus of individual disks was determined by utilizing nondestructive measurement of resonant frequency. Determination of Young’s modulus at small depth increments permitted assessment of the heat-induced damage gradient into the concrete and more importantly at the level of the prestressing tendons. The data from multiple techniques provided a means of comparison between constrained in-situ ASTM C 597 pulse velocity to unconstrained compression wave velocity obtained from ASTM C 1383, and an estimated unconstrained compression wave velocity based on dynamic modulus based on disks. The results of these comparisons should be of value to practicing engineers utilizing these techniques in forensic evaluations.