Characterization of alkali-silica reaction (ASR) products and C-S-H using SWIR spectroscopy for nondestructive detection of ASR

Abstract

This study explores the feasibility of characterizing alkali-silica reaction (ASR) products and calcium silicate hydrates (C-S-H) from short-wave infrared (SWIR) spectroscopy. ASR products and C-S-H samples with different Ca/Si ratios were synthesized and analyzed through XRD, 29Si nuclei magnetic resonance (NMR) and SWIR spectroscopy. Fourier-transform infrared spectroscopy (FTIR) was collected to help interpret the results from the SWIR spectroscopy. The obtained spectroscopic features were applied to quantify the ASR product abundance denoted by the length expansion of mortar bars after an accelerated ASR test. The results show that the SWIR spectra of the synthetic ASR gels are similar regardless of the crystallization status but differ from C-S-H samples. ASR products show only one major absorption at 5210 cm-1 in SWIR while C-S-H samples yield two significant bands at 5820 cm-1 and 4370 cm-1. Shoulders around 6865 cm-1 and 5102 cm-1 are two unique features for ASR products. The length change of mortar bars after the accelerated ASR test logarithmically increases the shoulder absorptance around 6865 cm-1 irrespective of the alkali environment. The disappearance of the shoulder 5102 cm-1 is exclusively observed in the K dominated ASR environment. However, this shoulder absorptance is approximately linear to the ASR expansion of the mortar bars cultivated in Na thriving environment.