Study Reveals Laser Technique’s Role in Monitoring Concrete Corrosion

A recent study published in Spectrochimica Acta Part A: Atomic Spectroscopy, led by Yuhua Hang from the Suzhou Nuclear Power Research Institute, sheds light on a novel approach using laser-induced breakdown spectroscopy (LIBS) to detect and monitor chloride ingress in concrete structures, which is a leading cause of rebar corrosion (1). The findings revealed in this study provide valuable insight to the infrastructure industry.

Hang and his team, all of which were from Xi'an Jiaotong University, explored questions of structural integrity and how to make structures or buildings safer. One factor that threatens the structural integrity of a building is concrete corrosion because of chloride ingress. By using LIBS as an in situ technique, the team showed that LIBS can be a reliable method for assessing cement distribution in concrete profiles, crucial in restricting chloride concentration, especially in compliance with government standards both in China and around the globe (1).

The study examined the utilization of dual-pulse LIBS, a technique previously known to enhance plasma emission (1). By employing an advanced optical diagnostic system coupled with fast photography, shadowgraph, and optical emission spectroscopy, the research team captured critical insights into plasma evolution within cement pastes (1).

The team’s research sheds more insight into plasma behavior, including morphology, shockwave propagation, and spatially resolved emission spectra in both single-pulse and dual-pulse configurations (1). Notably, the research highlighted the shift in the action mechanism of the second laser pulse, transitioning from initial plasma reheating to ablation enhancement (1). This transition influenced plasma morphology, changing it from hemispherical to umbrella-shaped (1).

The team identified a new shockwave generated within the initial shockwave because of secondary ablation, propagating faster and leading to shockwave fusion upon approach. The spatially resolved chlorine emission closely correlated with plasma temperature, particularly with a signal-to-background ratio peaking when the plasma temperature reached over 9200 K (1).

The dual-pulse technique was able to identify chlorine emission in samples. The study demonstrated that chlorine emission could be improved by optimizing the inter-pulse delay (1). As a result, it reveals that a pathway exists for monitoring concrete corrosion with enhanced detection capabilities (1).

Using LIBS can help us to understand plasma behavior better, which in turn aids our understanding of accurately assessing chloride ingress, potentially mitigating the damaging effects of rebar corrosion in concrete structures (1).

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Reference

(1) Qiu, Y.; Guo, X.; Shi, M.; et al. Plasma Dynamics and Chlorine Emission Characteristics on Cement Pastes Using Collinear Dual-pulse Laser-induced Breakdown Spectroscopy. Spectrochimica Acta Part A: At. Spectrosc. 2023, 209, 106799. DOI: 10.1016/j.sab.2023.106799