Hyperspectral vision-based detection and random field modeling of age-dependent compressive strength of concrete segments

The spatial distribution of compressive strength in shield tunnel concrete segments and its age-dependent dynamic evolution are vital to the safety and longevity of tunnel structures. However, traditional compressive strength assessment relies heavily on destructive testing, which is labor-intensive, time-consuming, costly, provides only localized information, and cannot capture the inherent spatial variability across the segment. To overcome these limitations and enable efficient, non-destructive, and spatially comprehensive evaluation, this study proposes a novel non-contact method integrating hyperspectral imaging (HSI) analysis with random field modeling (RFM). A hyperspectral camera (900–1700 nm) captured spectral data of concrete segments at various ages. Coupled with a proposed Spectral 3D ResNet deep learning model, this enabled high-precision compressive strength prediction, achieving an average cross-validation coefficient of determination ( R cv 2 ) of 0.918 and an average ratio of performance to deviation (RPD cv ) of 3.78, markedly superior to traditional models (partial least squares regression (PLSR), random forest regression (RFR), and convolutional neural network (CNN)). Further analysis revealed that segment strength development progresses through three distinct stages: the plastic stage (0–7 days) characterized by rapid growth but high variability and uneven distribution; the setting stage (7–15 days) with slowing growth and more concentrated distribution; and the hardening stage (15–33 days) where strength stabilizes with significantly enhanced uniformity and stability. Based on these findings, random field models of compressive strength at various ages were established, revealing the dynamic evolution of strength distribution from heterogeneity to homogeneity. At plastic ages, the random field exhibits pronounced spatial variability and longer correlation lengths; with increasing age, spatial correlation diminishes, resulting in a more uniform distribution with shorter correlation lengths at hardening ages. This study provides crucial theoretical backing and a data basis for non-destructive testing and comprehensive performance assessment of concrete shield segments, offering valuable guidance for quality control and structural design optimization in tunnel engineering.