Concrete form of tunnel lining is generally demolded earlier than other concrete structures. In particular, the demolding of ceiling form of tunnel lining is approximately 12-20 hours of concrete age. Note is that such early strength of concrete is hardly examined at site. Hence, a proper strength-estimation of tunnel lining concrete at early age is needed to demold the concrete form. Strength development of concrete at early age must be strongly related to cement hydration process. To develop a non-destructive testing (NDT) technique evaluating concrete strength, a hyperspectral camera which can quantify cement hydration was used in this study. Hyperspectral images consist of wide-range wavelength, it can obtain invisible variations of hydrated cement compared to general red-green-blue (RGB) images. A fundamental study was conducted to examine cement hydration by using the hyperspectral camera. The study proposed a cumulative reflectance for quantitative evaluation of the hyperspectral image. The study examined the relation between the cumulative reflectance and compressive strength of hydrated cement paste. In addition, chemical reaction of alite and calcium hydroxide in the cement paste were examined to quantify the cement hydration. The fundamental test revealed that the cumulative reflectance is applicable to estimate cement hydration degree. The NDT technique using hyperspectral image has a possibility for estimating the strength of tunnel lining concrete.
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