Detection of the corrosion damage of rebar in concrete using impact-echo method

Abstract

The main purpose of this study is focused on the feasibility, reliability, and applicability of detecting the rebar (reinforcing steel bar) corrosion in concrete blocks by using impact-echo method associated with three electrochemical methods; that is open-circuit potential (OCP), direct current (DC) polarization, and alternating current (AC) impedance. The result of present study indicates that the impact-echo method can certainly detect the development of microcrack in the concrete blocks. With respect to predicting corrosion damage, the displacement spectrum obtained from the impact-echo method should be transferred as acceleration spectrum. Thus, the degree of corrosion damage can be predicted from relative amplitude obtained from acceleration spectrum. The OCP method can evaluate the corrosion state of steel in concrete. However, it is not useful in predicting the corrosion damage of the interior of the specimen. Both the DC polarization and AC impedance methods can predict the corrosion rate. The corrosion thickness of specimen obtained from integrating the corrosion rate can directly evaluate corrosion damage. It is very obvious that the proposed method can be applied to the nondestructive testing for reinforced concrete (RC) structures.

Introduction

The corrosion damage of reinforced concrete (RC) structures is often a severe and invisible injury. At the present, evaluating the corrosion state is done by measuring both the corrosion potential and corrosion rate of steel in concrete using electrochemical method. However, the electrochemical method cannot indicate the failure state of RC structures. As to nondestructive testing widely used in civil engineering, both the physical properties and internal and external crack state of RC structures are the major tests done. The results obtained from the method of nondestructive testing can only provide qualitative description for RC structures. Thus, the results of nondestructive testing cannot predict the bearing capacity and service life of RC structures. Thus, if one uses the measurement results of impact-echo method associated with electrochemical method, then one takes into account every aspect of corrosion damage evaluation.

Carino et al. [1] established the impact-echo method wherein the transient time domain waveforms obtained from the impact of a steel sphere on a concrete slab containing artificial flaws are recorded and analyzed in the frequency domain. Carino and Sansalone [2] provided a brief explanation of the impact-echo method and presented results that illustrate the capabilities of the method to locate a variety of flaws in plain and reinforced concrete. Sansalone and Carino [3] carried out experiments on laboratory specimens that contained artificial flaws at known locations. Frequency analysis of recorded surface displacement waveforms was used to determine the location of honeycombing, the depth of surface-opening cracks, and ungrouted ducts. Sansalone and Carino [4] used the impact-echo method to detect determination in RC slabs with and without asphalt concrete overlays. Lin et al. [5] studied experimentally the integrity of concrete shafts and piles containing flaws and embedded in soil using the impact techniques. Sansalone et al. [6] summarized the developments in the impact-echo technique for locating defects in concrete structures. Pratt and Sansalone [7] used artificial intelligence called neural network to automate impact-echo signal interpretation from concrete slabs contained voids and cracks. Lin and Sansalone [8] demonstrated the feasibility of using the impact-echo method for detecting flaws in RC beams and columns. Lin and Sansalone [9], [10] studied the transient response of thick circular, square, and rectangular bars subjected to transverse elastic point impact. Cheng and Sansalone [11] used finite element method and impact-echo method to demonstrate the effects of different variables with rebar diameter, rebar depth, impact duration, and impact-echo test configuration. Cheng and Sansalone [12] used the impact-echo method for detecting delaminations in concrete plate-like structures such as bridge decks, slabs, and walls. Lin and Sansalone [13] determined the transient elastic impact response of thick-walled hollow cylindrical structures and determined how this response was effected by the presence of flaws in the cylinder. Lin and Sansalone [14], [15] demonstrated that the impact-echo method can be used for integrity testing for concrete pipes, mine shaft liners, and tunnel liners in contact with soil and rock. Sakata and Ohtsu [16] used ultrasonic spectroscopy to measure the depth of surface cracks in concrete members. Lin and Sansalone [17] demonstrated how the unbounded fraction at an interface affects impact-echo response. Lin et al. [18] explained how bond tensile strength affects impact-echo response. Jaeger et al. [19] used the impact-echo method to detect both complete and partial voids in grouted tendon ducts of post-tensioned concrete structures. Lin and Su [20] determined the depth of surface-opening cracks in concrete structures with the use of stress waves so that a safety evaluation of such cracked structures can be subsequently performed. Sansalone [21] provided, for the first time, a unified explanation of the impact-echo method as it applies to the testing of structural concrete elements. Sansalone et al. [22] described the time-of-flight technique that can be used in conjunction with techniques for measuring P wave speed to determine the depth of surface-opening cracks in concrete structures. Lin et al. [23] provided a clear explanation for the effects caused by rebars on transient stress wave propagation and crack depth measurement. Lin et al. [24] demonstrated the capability of the time-of-flight diffraction technique for measuring the depth of surface-opening cracks in RC structures and determining errors in measurement. Hill et al. [25] described an investigation of the use of the impact-echo method and the excitation of cross-sectional modes to distinguish between a grouted and an ungrouted duct in a rectangular beam. Yeih and Huang [26] used the amplitude attenuation method in ultrasonic testing to evaluate the corrosion damage of RC members. To date, however, no studies have attempted to study the corrosion damage of rebar in concrete using the impact-echo method associated with the electrochemical method. This is a notable shortcoming, because the use of the impact-echo method in previous studies may have resulted in detection of flaws in concrete structures.

The main purpose of this paper is to study the feasibility, reliability, and applicability of the rebar corrosion in concrete blocks using impact-echo method associated with electrochemical methods. The result of this study may give aid for applying the impact-echo technique in predicting the rebar corrosion in concrete.