Proposal for experimental standardization of impact resonance tests for different materials

Abstract

The characterization of stiffness parameters in construction materials, such as cement concrete and asphalt mixtures, is critical for quality control and the development of mechanistic design methods. Vibrational techniques offer a cost-effective alternative for material testing. While standardized procedures exist internationally for perfectly elastic materials, like Portland cement concrete, this is not the case for viscoelastic materials such as asphalt concrete. Recently (August 2024), a technical committee from the International Union of Laboratories and Experts in Construction Materials (RILEM) was formed to address the topic “Mechanical Wave Propagation to characterize bituminous mixtures” (TC MWP). This MSc study proposes experimental standardization for performing impact resonance test (IRT) to determine stiffness parameters in different materials using non-destructive (ND) techniques. The research methodology was divided into four main stages: (i) a literature review on traditional and ND techniques for the characterization of cementitious and asphalt materials; (ii) material selection and execution of experimental tests, focusing on vibration modes (longitudinal and flexural); (iii) analysis of test results through 3D solid vibration modeling and creation of a database; and (iv) development of a standard protocol for IRT, which are not yet standardized in Brazil. After a general introduction and literature review (Chapters 1 and 2), the thesis is structured with Chapters 3 to 5 as papers on specific aspects of the research, with Chapter 6 presenting general conclusions. Chapter 3 discusses IRT conducted on cylindrical specimens of aluminum, conventional concrete, and asphalt concrete. The influence of various test configurations was examined, including impact force, accelerometer attachment techniques, and the use of foam under the specimen. Significant variations in frequency response functions (FRF) and resonant frequencies were observed depending on the test configuration, highlighting the importance of standardizing experimental conditions. Chapter 4 investigates the effect of temperature on the test system, particularly the attachment of the accelerometer to cement and asphalt concrete specimens during IR tests. Stiffness properties were analyzed at temperatures from -30°C to 50°C, using glue or elastic bands with wax for attachment. Results showed that both temperature and attachment method significantly affect stiffness measurements, especially in viscoelastic materials. Chapter 5 examines the effect of different flexural vibration modes (symmetric and antisymmetric) on material properties determined through IRT. Cement concrete and asphalt mixture specimens were tested under varying conditions, including different impact forces, sensor positions, and temperatures (room temperature of ~22°C and - 20°C). The results emphasized the need for standardized methods to ensure reproducibility of modulus values derived from different vibration modes. In conclusion, non-destructive techniques like impact resonance offer significant potential for characterizing elastic and viscoelastic materials, providing greater accuracy and lower costs than traditional methods. The standardization proposed in this study aims to address gaps in Brazilian standards for ultrasonic tests and, more generally, IRT for asphalt mixtures. This research contributes to advancing testing methods in civil engineering, improving the efficiency and reliability of quality control processes and material design.