# Automated Nonlinear Acoustics System for Real-Time Monitoring of Cement-Based Composites

## TL;DR

A new automated system uses nonlinear acoustics to monitor cement composites in real time, offering high sensitivity and non-contact evaluation for infrastructure health.

## Contribution

A fully automated nonlinear acoustics system using bulk-wave excitation and LDV for real-time monitoring of cement composites is introduced.

## Key findings

- The system demonstrated stability, linearity, and repeatability in long-duration experiments on metallic samples.
- It successfully monitored hydration in cement specimens with varying water-to-cement and CNT ratios.
- The system showed enhanced sensitivity and scalability for structural health monitoring applications.

## Abstract

What are the main findings?

Developed a fully automated nonlinear acoustics monitoring system combining bulk-wave excitation with non-contact Laser Doppler Vibrometry (LDV) detection.

Validated the system’s stability, linearity, and repeatability, and demonstrated its capability for real-time monitoring of cement-based composites during hydration.

What is the implication of the main finding?

Enables autonomous, high-sensitivity, and non-contact evaluation of material microstructure for smart infrastructure and predictive maintenance.

Establishes a scalable framework for integrating nonlinear acoustic monitoring into digital twin and real-time structural health monitoring environments.

The development of automated systems for real-time material evaluation is becoming increasingly critical for structural engineering applications, infrastructure diagnostics and advanced material research. This work introduces a novel, fully automated nonlinear acoustics monitoring platform that employs Bulk Wave excitation in combination with non-contact Laser Doppler Vibrometry (LDV) detection to continuously assess the microstructural evolution of cement-based composites. Unlike conventional approaches—such as ultrasonic velocity measurements or compressive strength tests—which lack sensitivity to early-stage changes and also require manual operation, the proposed system enables unsupervised, high-precision monitoring of the material by leveraging the second and third harmonic generation (β2, β3) as nonlinear indicators of internal material changes. A specialized LabVIEW-based software manages excitation control, signal acquisition, frequency-domain analysis, and real-time feedback. As an initial step, the system’s stability, linearity, and measurement reliability were validated on metallic samples, and verified through long-duration experiments. Subsequently, the system was used to monitor hydration in cement-based specimens with varying water-to-cement and carbon nanotube (CNT) reinforcement ratios, thereby demonstrating its capability to resolve subtle nonlinear responses. The results highlight the system’s enhanced sensitivity, repeatability, and scalability, demonstrating that it as a powerful tool for structural health monitoring, smart infrastructure, and predictive maintenance applications.