Monitoring the cementitious materials subjected to sulfate attack with optical fiber excitation Raman spectroscopy

Abstract

Abstract. Formation of ettringite and gypsum from sulfate attack together with carbonation and chloride ingress have been considered as the most serious deterioration mechanisms of concrete structures. Although electrical resistance sensors and fiber optic chemical sensors could be used to monitor the latter two mechanisms on site, currently there is no system for monitoring the deterioration mechanisms of sulfate attack. In this paper, a preliminary study was carried out to investigate the feasibility of monitoring sulfate attack with optical fiber excitation Raman spectroscopy through characterizing the ettringite and gypsum formed in deteriorated cementitious materials under an optical fiber excitation + objective collection configuration. Bench-mounted Raman spectroscopy analysis was also conducted to validate the spectrum obtained from the fiber-objective configuration. The results showed that the expected Raman bands of ettringite and gypsum in the sulfate-attacked cement paste can be clearly identified by the optical fiber excitation Raman spectrometer and are in good agreement with those identified from bench-mounted Raman spectrometer. Therefore, based on these preliminary results, it is considered that there is a good potential for developing an optical fiber-based Raman system to monitor the deterioration mechanisms of concrete subjected to sulfate attack in the future.

Characterisation of carbonated Portland cement paste with optical fibre excitation Raman spectroscopy

“…Surprisingly, up to date, the application of optical fibre Raman system in monitoring the durability of concrete structure has not been attempted in the literature. Previous study carried out by the authors showed that there is a good potential to monitor sulphate attack with optical fibre Raman spectroscopy [7]. This paper, therefore, extends the previous work to explore the potential of using optical fibre Raman system to monitor the carbonation mechanism of concrete.…”

“…In the case of optical fibre Raman system, this could also include optics alignment and initial optimisation. In the current study, the bench-mounted Raman and optical fibre Raman systems were calibrated through the same methodology as the previous work [7] by using the well-defined Raman peak of silicon wafer at 520.2 ± 0.5 cm -1 [36]. Figs.…”

“…However, it has been increasingly recognised that, instead of physical properties, monitoring the changes in the chemical composition of hardened cement paste in concrete is more important because this can provide an in-depth understanding on the evolution of concrete deterioration mechanisms such as chloride ingress, carbonation and sulphate attack over time, so that both the prediction of service life and the diagnosis of the causes of deterioration can be established. Although electrical sensor (ES) [3,4] and fibre optic sensor (FOS) [5][6][7] have been attempted to monitor the deterioration mechanisms of concrete structures, the electrical change of ES can also be attributed to some other factors such as the humidity change or the change of the microstructure of cement matrix due to continued hydration [8]. Therefore, ES cannot clearly differentiate each individual deterioration mechanism.…”

Characterization of alkali silica reaction gels using Raman spectroscopy

“…The availability of portable instrumental configurations of Raman spectrometers opens doors to the possibility of developing a diagnostic tool for ASR gels that can be deployed in the field. A similar approach to investigate the feasibility of applying a portable configuration of Raman spectroscopy to monitor sulfate attack has been recently published [14]. The fiber optic probe of a portable Raman spectrometer can focus the laser beam into cracks of ASR-damaged concrete and potentially collect the Raman signal of gel deposits.…”

“…An important point to be noted is that most of the research efforts focus on characterization of white cement, synthetic calcium silicate hydrate (C-S-H), and hydration of pure cement phases due to the fluorescence associated with the analysis of grey cements [5,8,11]. Raman spectroscopy has also been used successfully to investigate other hydration products such as sulfate phases and hydroxides [5,[12][13][14][15] and to study carbonation [8,16] and secondary deposits of sulfate attacked concrete [12,14].…”