Confocal Raman Microscopy: new perspective on the weathering of anhydrous cement

Abstract

Abstract. Raman spectroscopy when is combined with Confocal microscopy is a nondestructive technique that allow us to obtain information in cementitious materials. In this study, we present non-destructive image and structural analysis of anhydrous cement with carbonation evidences by Confocal Raman Microscopy (CRM). The results obtained by CRM show a direct relationship between the presence of the weathering processes of an anhydrous cement with the presence of sulphates and surprisingly, with the existence of amorphous carbon in the medium. IntroductionRaman spectroscopy is a vibrational spectroscopic technique complementary to the more widely used infrared spectroscopy. The use of Raman spectroscopy in the characterization of the various cements and supplementary cementitious materials (SCMs) has been investigated over the last four decades [1][2][3][4]. However, in 2013, Schmid et al. [5] published the first successful and to date only Raman imaging study on cementitious materials. In this study was possible to reveal the chemical heterogeneity of distinct clinker phases with different crystal orientations. Recent studies have evaluated the use of Confocal Raman Microscopy (CRM) as a non-destructive technique in the determination of the hydration process of the C3S phase present in the clinker [6].Raman spectroscopy when is combined with Confocal microscopy is a non-destructive technique that allows identifying the phase composition in inorganic [7] and carbon based materials [8] with high spatial resolution. Supporting us in Raman investigations of anhydrous and hydrated cementitious pastes, the use of CRM can give us excellent information about the properties of this material.The aim of the present work is to study cement weathering features by CRM. Conventional techniques, such as FTIR and DTA/TG, are also applied on different cement samples in order to determine the degree of weathering. In addition of the good agreement between conventional techniques and CRM, a correlation between presences of amorphous carbon species is established with the extent of cement weathering. The present findings confirm CRM as a fast and reliable technique for the determination of weathering in cement and a key tool to understand the weathering mechanism.

Mechanical and microstructural changes in reactive magnesium oxide cement-based concrete mixes subjected to high temperatures

“…Structural characterization of the exterior surfaces of the respective paste samples was performed with Raman spectroscopy. The technique has been successfully used to identify chemical composition and atomic configuration of both anhydrous and hydrated phases of cement [48,49,61] and was shown to be sensitive to the carbon-oxygen (C-O) vibration bond at local atomic environments [62]. The features made it a good candidate to evaluate the prevalence of the carbonation phase in the RMC composites.…”

“…The morphology evolution of the samples was analyzed by both scanning electron microscopy (SEM) and environmental scanning electron microscopy (ESEM). Meanwhile, the phase transformation was investigated with Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and confocal Raman spectroscopy [47][48][49]. Finally, nanoindentation, a technique generally used for characterizing the micro-mechanical properties of cement-based materials and their binding phases [50][51][52][53][54][55], was used to estimate the elastic modulus of the carbonated samples.…”

Chemo-mechanical characterization of hydrated calcium-hydrosilicates with coupled Raman- and nanoindentation measurements

“…Raman spectra of synthetic C-S-H phases with different C/S ratios have been extensively studied in [ 10,11 ]. While C-S-H was readily detected in the Raman spectra of C3S pastes [ 24 ], it remains a challenging task in OPC pastes [ 25 ] for which only a few studies have detected C-S-H unambiguously [ 26 ]. The primary difficulty is due to the very complex nature of OPC and its hydration products.…”

Time-Space-Resolved Chemical Deconvolution of Cementitious Colloidal Systems Using Raman Spectroscopy

“…These advances have opened more possibilities for Raman techniques to tackle open questions associated with cement chemistry. First, the hydration products of C 3 S were studied, and a high signal-to-noise (S/N) ratio spectrum of nonsynthetic C–S–H was obtained and mapped. , More recently, the state-of-the-art CRM system with a spatial resolution of 300 nm and a temporal resolution of 0.1 s per spectra enabled the in situ monitoring and imaging of the hydration process, , cement deterioration such as alkali-silica reaction, , and cement carbonation . Even though the Raman tools effectively visualize each phase distribution, previous research overlooked the diverse chemical and crystallographic environments of the phases. ,, Another critical issue from previous studies is the dry imaging condition.…”

“…41,42 More recently, the state-of-the-art CRM system with a spatial resolution of 300 nm and a temporal resolution of 0.1 s per spectra 27 enabled the in situ monitoring and imaging of the hydration process, 43,44 cement deterioration such as alkalisilica reaction, 45,46 and cement carbonation. 47 Even though the Raman tools effectively visualize each phase distribution, previous research overlooked the diverse chemical and crystallographic environments of the phases. 41,43,44 Another critical issue from previous studies is the dry imaging condition.…”