Terahertz spectroscopy of concrete for evaluating the critical hydration level

Abstract

Concrete, a mixture of cement, coarse aggregate, sand and filler material (if any), is widely used in the construction industry. Cement, mainly composed of Tricalcium Silicate (C3S) and Dicalcium Silicate (C2S) reacts readily with water, a process known as hydration. The hydration process forms a solid material known as hardened cement paste which is mainly composed of Calcium Silicate Hydrate (C-S-H), Calcium Hydroxide and Calcium Carbonate. To quantify the critical hydration level, an accurate and fast technique is highly desired. However, in conventional XRD technique, the peaks of the constituents of anhydrated and hydrated cement cannot be resolved properly, where as Mid-infrared (MIR) spectroscopy has low penetration depth and hence cannot be used to determine the hydration level of thicker concrete samples easily. Further, MIR spectroscopy cannot be used to effectively track the formation of Calcium Hydroxide, a key by-product during the hydration process. This paper describes a promising approach to quantify the hydration dynamics of cement using Terahertz (THz) spectroscopy. This technique has been employed to track the time dependent reaction mechanism of the key constituents of cement that react with water and form the products in the hydrated cement, viz., C-S-H, Calcium Hydroxide and Calcium Carbonate. This study helps in providing an improved understanding on the hydration kinetics of cement and also to optimise the physio-mechanical characteristics of concrete.

Hydration kinetics of cement composites with varying water-cement ratio using terahertz spectroscopy

“…Once the C-S-H hardens at around 7 days, the Si-O bending modes become stiffer which varies the resonance peak resulting in decreased area. Similar trend has already been reported in the earlier work by the above authors 16 . For the above water-cement ratios, there is again a gradual dip around 20-21 days, which is because of the onset of reactions of C2S.…”

Applications of Terahertz Spectroscopy in the Field of Construction and Building Materials

“…Based on THz spectra, Maruyama et al (71) determined that the lower frequencies of 0.1 and 0.05 THz are more appropriate for evaluating the moisture content of hardened cement paste due to the nonsensitivity to chemically bounded water that occurs at higher frequencies. Moreover, Dash et al (72) reported that THz spectroscopy is a promising tool to quantify the hydration process; that is, the time-dependent reaction of cement with water, which can significantly contribute to the improved understanding of the hydration kinetics of cement necessary to optimize the mechanical characteristics of concrete. Concerning the fact that THz sensing is able to detect the hazardous gases (24), another issue related to the contamination of concrete can be studied.…”

The perspectives and trends of THz technology in material research for future communication - a comprehensive review

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