Bulk density determination of concrete by gamma-ray transmission using a 137Cs source and NaI(Tl) spectrometry: MCNP-based calibration and experimental validation across varying aggregate compositions
Huynh Dinh Chuong, Van Thi Thu Trang, Vo Hoang Nguyen, Le Thi Ngoc Trang, Nguyen Thi Truc Linh, Tran Thien Thanh
Radiation Physics and Chemistry, Vol 248(2026),114145
Abstract:
This paper presents a gamma-ray transmission method for the non-destructive determination of concrete bulk density. The experimental setup comprises a137Cs source, a NaI(Tl) detector, and lead collimators arranged in a narrow-beam transmission geometry. An MCNP model was developed to closely replicate the measurement configuration and was subsequently used to generate pulse-height spectra for elemental and concrete specimens covering densities of 2.10 – 8.96 g cm−3 and thicknesses of 1 – 15 cm. From each spectrum, the net area of the 661.7 keV peak was extracted, and the attenuation indicator R was defined as the ratio of the peak areas recorded with and without the specimen. The simulations were benchmarked against measurements for aluminum and copper reference specimens at different thicknesses, showing good agreement in spectral response and relative deviations between simulated and experimental R values below 0.8%. Using the simulated R dataset, a linear calibration curve was established, enabling concrete bulk density to be determined without prior knowledge of the elemental composition. The method was applied to 22 concrete specimens fabricated with different aggregate systems, including ordinary concretes and concretes incorporating heavyweight additives (e.g., barite, Bi2O3, Fe2O3, and steel chips). These specimens covered densities of 2.2 – 2.6 g cm−3 and thicknesses of 3 – 15 cm. Each specimen was measured at nine locations to assess spatial variability, and the weighted mean was taken as the representative bulk density. The resulting densities agree well with reference values obtained from mass-to-volume measurements, with relative deviations not exceeding 3.74% for all specimens. A coverage-probability–based statistical framework, augmented by additional sampling, was introduced to assess and improve measurement reliability when structural heterogeneity produces spatial variations in the inferred density. These preliminary results demonstrate that the proposed method is reliable and well suited for rapid concrete quality control.
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