Identifying the effects of different construction practices on the spectral characteristics of concrete

The objective of this study was to investigate the effects of different construction practices on the spectral characteristics of the concrete. Concrete blocks of identical shape and size (20 × 20 × 6 cm3) were prepared using different treatment processes to establish eight different concrete characteristics. The different concrete treatments were: TC (control), TNC (no cure), TCL (cool cure), TH (heat cure), THW (high water content), THC (half cement), TG (gravel), and TL (limestone). Spectral reflectance of all the concrete blocks was obtained in the laboratory from 350–2500 nm spectral range using a portable, hand-held spectroradiometer. The spectral reflectance of the different concrete treatments varied systematically with changes in the concrete characteristics that resulted from different construction practices. Detailed spectral analysis shows that the spectral absorption features around 450, 1380 and 1850 nm are highly correlated with changes in the characteristics of the concrete. The spectral ratios R600/R450, R1380/R1440, R1850/R1950 and R2150/R880 can clearly differentiate the TNC- and TCL-treated concrete blocks from the other blocks with different concrete treatments. The spectral ratio R600/R450 can differentiate the TC-, TG- and TL-treatments, which were considered to have better concrete quality from the rest of the concrete treatments. The spectral results clearly indicate the potential application of spectral reflectance in assessing concrete characteristics after the concrete has hardened.