Microstructure evolution of hydrated cement pastes (original) (raw)
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Molecular Physics, 2018
The hydration process of four different cement-based materials at different depths inside the sample was investigated using localised nuclear magnetic resonance relaxation measurements. All the samples are based on white Portland cement (CEM I 42.5 R), with a water-to-cement ratio of 0.5. One sample is a simple cement paste and the other three additionally contain 5% (by mass of cement) silica nanoparticles (50-200 nm size), silanised silica nanoparticles (with silane A 174) or silica fume (80% silica; 0.15 µm average size). The localised transverse relaxation measurements were performed using a single-sided NMR instrument. The relaxation rates were monitored for 48 h during the hydration process at different depths inside the sample. The results showed that the presence of nanoparticles influences not only the speed of hydration overall, but also the homogeneity of the materials.
Microstructure and texture of cementitious porous materials
Magnetic Resonance Imaging, 2007
We have characterized the microstructure of different cementitious materials (white and Portland cement pastes, mortars, concretes) by different magnetic resonance techniques. In particular, we show how the measurement of proton nuclear magnetic spin-lattice relaxation as a function of magnetic field strength (and hence nuclear Larmor frequency) can provide reliable information on the dynamics of proton species at the surface of CSH, the specific surface area and the pore size distribution throughout the progressive hydration of cement-based materials. The measurement does not require any drying temperature modification and is sufficiently fast to be applied continuously during the progressive hydration of the material. Coupling this method with the standard proton nuclear spin relaxation and high-resolution NMR allows us to follow the development of microscale texture within the material.
Micropore size analysis by NMR in hydrated cement
Magnetic Resonance Imaging, 2003
The understanding of the microstructure of cement remains incomplete. Especially, the progressive setting of the material is still unclear. Micropore size distribution (microstructure) has been investigated by both standard proton nuclear magnetic relaxation ( 1 H-NMR) and field-cycling relaxation in C 3 S hydrated paste.
Cement and Concrete Research, 2007
The changes in the pore structure of hydrating cement are accompanied by changes in the dynamics of liquid phases contained in the pore system of the hydrating matrix. Dynamic NMR methods (relaxometry, diffusometry) allow the non-destructive observation of these changes. Relaxometry can be performed using quite simple equipment and has been widely used in studies of the kinetics of cement hydration. Diffusion studies, by contrast, require much more sophisticated equipment. On the other hand, the diffusion coefficient has a direct relevance for the transport of moisture or contaminants in the cement matrix while relaxation time measurements provide more indirect information. The purpose of the present paper is to review the possibilities of field gradient NMR in diffusion studies on hydrating cement and to provide an outlook on how this information can be used for improving our understanding of the properties and microstructure of hydrating cement. As an example, new results on the relationship between the diffusive exchange length in the sample and non-exponential relaxation in cement are discussed at the end of the contribution.
The Effect of an Accelerator on Cement Paste Capillary Pores: NMR Relaxometry Investigations
Molecules, 2021
Nuclear Magnetic Resonance (NMR) relaxometry is a valuable tool for investigating cement-based materials. It allows monitoring of pore evolution and water consumption even during the hydration process. The approach relies on the proportionality between the relaxation time and the pore size. Note, however, that this approach inherently assumes that the pores are saturated with water during the hydration process. In the present work, this assumption is eliminated, and the pore evolution is discussed on a more general basis. The new approach is implemented here to extract information on surface evolution of capillary pores in a simple cement paste and a cement paste containing calcium nitrate as accelerator. The experiments revealed an increase of the pore surface even during the dormant stage for both samples with a faster evolution in the presence of the accelerator. Moreover, water consumption arises from the beginning of the hydration process for the sample containing the accelerat...
Journal of Applied Physics, 2001
While the nuclear spin relaxation time changes in hydrating cement materials have been widely studied by various groups during the last 20 years, data on the self-diffusion behavior of the pore water during hydration of a cement paste are much scarcer. Taking advantage of improved spectrometer hardware for pulsed field gradient diffusometry and a specialized pulse sequence which is designed to compensate the detrimental effects of inner magnetic field gradients in the sample we have studied the water self-diffusion behavior in pastes prepared from white cement at various water/cement ratios. For the same mixtures, studies of the transverse spin relaxation behavior were also conducted. A comparison of the results from both techniques shows that the diffusion coefficient starts to decrease only much later than the relaxation times for all pastes studied.
A spectroscopic NMR investigation of the calcium silicate hydrates present in cement and concrete
Magnetic Resonance Imaging, 1996
NMR spectroscopy is applied to study microstructure of calcium silicate hydrates present in cement and concrete. It is shown that 29Si NMR gives information on the siliceous skeleton of the hydrates. *H NMR, using CRAMPS techniques, allows to discriminate between protons linked to silicon atoms or to calcium atoms. A first investigation of reference compounds indicates that 43Ca NMR will be powerful to determine calcium atom sites in the structure.
29 Si NMR in Cement: A Theoretical Study on Calcium Silicate Hydrates
The Journal of Physical Chemistry C, 2012
The NMR spectra of 29 Si in cement-based materials are studied through calculations of the isotropic shielding of silicon atoms within the density functional theory. We focus on the main component of cement, the calcium-silicate-hydrate gel, using widely accepted models based on the observed structures of jennite and tobermorite minerals. The results show that the 29 Si chemical shifts are dependent not only on the degree of condensation of the (SiO 4 ) units, as commonly assumed, but also on the local arrangement of the charge compensating H and Ca cations. We find that the NMR spectra for models of the calcium-silicate-hydrate gel based on tobermorite are in better agreement with experiment than those for jennite-based models. Figure 1. Structures of (a) jennite and (b) tobermorite 14 Å minerals. The pairing Si tetrahedra are denoted as Q 2 ; bridging ones, as Q 2 b (jennite), or Q 2 bOH (tobermorite) when having a SiOH group. Note that there are two types of charge compensating Ca cations, given with light blue balls, in the layered (L) and interlayer (I) positions. Article pubs.acs.org/JPCC
Cement and Concrete Research, 2016
Benchtop 1 H NMR relaxometry was used to measure the fine temporal resolution of microstructural development during the early hydration of ordinary Portland cement under different levels of retardation. Isothermal calorimetry was used to correlate the various distinct events in water transformation with the progress of hydration reactions. The low field (2 MHz) NMR technique used in this study detected signals from only the mobile water contained in the capillary and gel pores with water incorporation into hydration products highly correlated with heat production, including the reproduction of subtle features. Following the induction period, an initial T 2 decline period, which encompassed the acceleration period of hydration, was characterized by incorporation of water into hydration products without any associated gel pore formation. Gel pore formation commenced at the peak in hydration rate, indicating a change in the morphology of C-S-H growth. All the observed features of microstructural development were preserved under retardation.
Abstract The results of one- and two-dimensional 1H nuclear magnetic resonance (NMR) pulsed field gradient (PFG) diffusometry studies of water in white cement paste with a water-to-cement ratio 0.4 and aged from 1 day to 1 year are reported. The study shows that the NMR PFG method is primarily sensitive to the capillary porosity. Data is fit on the basis of a lognormal pore size distribution with pore size dependent relaxation times. The volume mean capillary pore size is 4.2 μm in mature paste, similar to 1 week suggesting that hydrates and gel porosity do not form in the capillary porosity once the latter has been substantially created. No evidence is found of capillary pore anisotropy in cement paste.