Evaluation of Fire-Damaged Concrete: An Experimental Analysis based on Destructive and Nondestructive Methods

Abstract

Fire damage to concrete causes contact-type defects that degrade its durability through impaired mechanical properties. Various nondestructive tests are used to evaluate defects induced by fire damage. Recently, nonlinear ultrasonic methods such as the nonlinear resonance vibration method and nonlinear modulation method have been introduced. These nonlinear methods are more sensitive to fire-induced contact-type defects than the linear ultrasonic method. This study involved an experimental analysis of the residual material properties of fire-damaged concrete, specifically, compressive strength, splitting tensile strength, and static elastic modulus. The residual material properties of 116 cylindrical concrete samples with various mix proportions and subjected to various heating temperatures were measured by a destructive method, and their nonlinearity parameters were measured by two nonlinear ultrasonic methods. Through regression analysis, correlated relationships that can facilitate the prediction of residual material properties of fire-damaged concrete using measured nonlinearity parameters were identified. In addition, the effect of fire damage on the mechanical strength of concrete was investigated by comparison with the relationships for undamaged concrete, and relationships for the evaluation of fire-damaged concrete were identified through regression analysis.

The Use of Destructive and Non-Destructive Testing in Concrete Strength Assessment for a School Building

“…The compressive cubic equivalent strength of concrete, Rc, was derived from empirical correlations proposed in the literature as a function of the surface rebound index, Ir, and of the ultrasonic speed, V evaluated in the 40 measurement points. Figure 4 shows the Rc values for the pillars at the basement using the expressions (2)(3)(4)(5). It is possible to note that the Sonreb relations used give almost equal Rc values for all the pillars with low standard deviation values as shown in the graph.…”

“…The coefficients on the equation (1) have to be determined by the correlation with some destructive tests. As an example, some proposed exponents and coefficients are reported in the literature and summarized in equations (2)(3)(4)(5). The obtained expression of Rc can be used, in the subsequent indirect testing to obtain the desired concrete resistance whether one does not have sufficient core test results [32].…”

“…It has to be stressed that in equations (2-5) dimensional units affect the results and the coefficients order of magnitude; in particular, Rc is the compressive cubic strength of equivalent cube in N/mm 2 , Ir is the rebound index and V is the ultrasonic speed expressed in m/s in expression (2,3,5) while in km/s in expression (4).…”

“…The values are a little above the line at 45 ° for the C1-C2-C3 cores while for the C4 core are coincident. In Figure 9, the relation (9) has been also compared with the relationships (2)(3)(4)(5). Figure 10 shows, for the pillars of both floors, the Rc values estimated with the Sonreb relationship and with the equation (9).…”

“…The most advanced seismic legislations [1,2] have showed interest to the existing buildings indicating that the type, technique and urgency of a possible intervention must be based on a careful evaluation of the structure in question. Therefore, it is needful to define the mechanical characteristics of concrete in situ [3,4,5], and its compressive strength, using not much onerous and invasive tests and methods. Among the methods some indirect testing can be used that are based on overall displacement and strain measures after load bearing tests nowadays such testing can be done with very effective and accurate measure of strain and displacement [6].…”