PSI - Issue 37

Alexey Tatarinov et al. / Procedia Structural Integrity 37 (2022) 453–461

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Alexey Tatarinov et al./ Structural Integrity Procedia 00 (2019) 000 – 000 © 2022 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of Pedro Miguel Guimaraes Pires Moreira Keywords: concrete deterioration, ultrasonic testing, surface waves, pattern recognition 1. Introduction Aging of infrastructure, buildings and industrial objects made of concrete is a global problem [1]. A large number of concrete structures are deteriorating, often prematurely, and need remedial measures to reinstate their safety and serviceability (Fig.1). The effects of environmental factors, such as moisture, freeze-thaw cycles, water ingress, chemical attack and carbonation and internal factors, such as forces, alkali-aggregate reactions and shrinkage are the main sources of the material degradation and cracking [2]. Adequate quality monitoring is necessary for effective preventive and repair measures. The processes of concrete deterioration are often initiated at the surface progressing into the depth. Therefore, the assessment of the properties of the surface layer in terms of depth is important. 2

Fig.1. Example of concrete deterioration in the road infrastructure facility.

A range of non-destructive testing methods is used in the civil and structural engineering industry, infrastructure monitoring services and materials research in relation to concrete [3]. These include surface hardness testers, particularly by the Schmidt rebound hammer, penetration resistance methods, resonant frequency methods and ultrasonic testing. Ultrasonic testing is the most widely exploited non-destructive technology, where the basis is the correlation of ultrasound velocity with strength of concrete [4,5]. An advanced ultrasonic modality called ultrasound tomography is intended for localization of defects and voids in the concrete bulk [6]. The limitation of current methods based on a single measured parameter, like ultrasound pulse velocity, is the impossibility to separate material properties and the depth of degraded layer. Acquisition of multi-frequency ultrasonic signals during the same measurements act and the analysis of propagation parameters of guided and surface waves allowed the differentiation of changes of the material properties and geometric features in hard biological tissues [7]. Ultrasonic surface waves at different frequencies have been proposed to assess the condition of the surface layer of concrete by depth knowing the dependence of the penetration depth of Rayleigh waves on its wavelength [8]. The same idea was applied in the method of surface acoustic waves spectroscopy for the assessment of the layered concrete using the dispersion of the phase velocity of surface waves [9]. The idea and the aim of the current study was to prove the possibility of determining the depth of the deteriorated surface layer of concrete by the combination of the use ultrasonic surface waves at different frequencies and the implementation of a mathematical approach of pattern recognition. 2. Materials and methods 2.1. Specimens design The specimens design was aimed at creating a two-dimensional data grid for building a mathematical model to recognize two factors of interest - the degree of degradation of concrete as a material and the thickness of the deteriorated surface layer. To achieve homogeneity and reproducibility of the degraded surface layer, the degradation degree was simulated by a decrease of the cement-sand ratio. Firstly, a series of specimens with a gradual change of the cement-sand ratio was fabricated and 3 stages of the conditionally “weak” surface layer W1-W3 were selected based on ultrasound pulse velocity measurements and ensuing prediction of the material strength according to the known empirical dependency [4,5] (Table 1). Concrete of the solid layer S matched to good quality concrete.