The effect of silica nanoparticles on the pore structure of hydrating cement paste: a spatially resolved low-field NMR study (original) (raw)
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The roles of hydration and evaporation during the drying of a cement paste by localized NMR
Cement and Concrete Research, 2013
The moisture distribution during the setting of a thin mortar layer can be particularly complex to manage under dry (20% RH) and hot weather (above 25°C) conditions. To better understand the fundamental phenomena at stake, we used static gradient relaxation NMR tools such as Profile MOUSE and STRAFI. This allowed disentangling the mutual effect of evaporation and self-desiccation by hydration. The interest of combining the two techniques is that the capillary water is observed with the MOUSE while STRAFI reveals quantitatively the build-up of the hydrate gel nanostructure. Spatially resolved and 2D relaxation exchange experiments on a model white cement paste revealed that although evaporation induced a capillary water gradient, the kinetics of the building of the pore structure and its homogeneity remained unaffected.
Microstructure evolution of hydrated cement pastes
Physical Review E, 2005
We propose an original method based on both proton nuclear magnetic relaxation dispersion and highresolution NMR spectra to investigate the microstructure of synthesized Ca 3 SiO 5 -hydrated cement paste. This method allows a clear assessment of the local proton chemical sites as well as the determination of dynamical information of moving proton species in pores. We show also how the microstructure evolves during and after completion of hydration in a range of length scales between 2 and 500 nm. In particular, we show how the pore size distribution of the cement paste reaches progressively a power-law characteristic of a surface-fractal distribution with a dimension D f = 2.6, which takes into account the hierarchical order in the material. Last, we study how this pore size distribution is modified during setting by varying either the water-to-cement ratio or addition of ultrafine particles. This shows that our method could be relevant to relate the mechanical properties to the microstructure of the material. This proposed NMR method is general enough for the characterization of microstructure of any porous media with reactive surface involving water confinement.
Hydration Studies of Cementitious Material using Silica Nanoparticles
Journal of Advanced Concrete Technology, 2015
In the present study, non-evaporable water (NEW) and degree of hydration (DOH) of cement paste in the presence of silica nanoparticles (SNPs) and silica fume (SF) have been investigated. The incorporation of SNPs increased the NEW content due to the formation of more amount of hydration products. On the basis of NEW content, DOH was also calculated at different time intervals and it was found to increase from 28% to 85% in SNPs modified cement, while with the addition of SF increment was 74% at 56 days of hydration. In addition, capillary porosity of SNPs incorporated cement paste was also calculated and observed ~75% reduction as compared to plain cement. These results attributed that the SNPs refines the pore structure as a result of pozzolanic reaction and formation of additional calcium-silicate-hydrate (C-S-H). FTIR results show the appearance of bridging silicate tetrahedral (Q 2), characteristic peak at 970 cm-1 and a hump at ~1108 cm-1 due to the formation of polymerised C-S-H. The microstructure studies through SEM revealed that the SNPs refined the pore structure of the cement paste leading to denser microstructure as a result of more polymerized C-S-H gel formation, desirable for high strength and durability.
Applied Magnetic Resonance, 2007
The aim of the present study was to apply nuclear magnetic resonance (NMR) relaxation measurements for understanding the microstructure evolution of cement paste during hydration. Ordinary Portland cement (OPC), powder was mixed with double-distilled water, and hydration process was analyzed via 1 H proton NMR spinspin relaxation time. In order to induce strong modification of the rate of hydration, water-to-cement ratio, curing temperature and OPC fineness were varied. The evolution of the NMR spinspin relaxation time, T 2 , of hydrating water versus the hydration time was monitored from the very first few minutes after the mixing up to several hours.
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.
Molecules
The hydration process of Portland cement is still not completely understood. For instance, it is not clear what produces the induction period, which follows the initial period of fast reaction, and is characterized by a reduced reactivity. To contribute to such understanding, we compare here the hydration process of two cement samples, the simple cement paste and the cement paste containing calcium nitrate as an accelerator. The hydration of these samples is monitored during the induction period using two different low-field nuclear magnetic resonance (NMR) relaxometry techniques. The transverse relaxation measurements of the 1H nuclei at 20 MHz resonance frequency show that the capillary pore water is not consumed during the induction period and that this stage is shortened in the presence of calcium nitrate. The longitudinal relaxation measurements, performed at variable Larmor frequency of the 1H nuclei, reveal a continuous increase in the surface-to-volume ratio of the capillary...
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.
An Investigation of Nano Silica in the Cement Hydration Process
2009
With the advent of nano technology, materials have been developed that can be applied to high performance concrete mix designs. Nano silica reacts with calcium hydroxide (CH) to develop more of the strength carrying structure of cement: calcium silica hydrate (CSH). In this paper, relationships have been developed to distinguish the benefits when using different sizes of nano silica in cement paste. An extensive regime of experimental analysis was carried out to determine the effect of nano silica. Through these experiments the heat of hydration of multiple cement mix designs was measured. After that, the concentration of CH was recorded through X-ray diffraction. Then, the grain structures were examined through Scanning Electron Microscopy. Finally, the compressive strength was determined for each cement paste mixture. Through these experiments it was found that as the silica particles decreased in size and their size distribution broadened, the CSHs became more rigid; this increas...
Magnetic Resonance Imaging, 2004
Proton nuclear magnetic resonance (NMR) spin-spin relaxation and imaging have been applied to investigate white Portland cement pastes during hydration in the absence and in the presence of organic solvents. The main organic solvent investigated was methanol, alone or together with the organic waste 2-chloroaniline (2-CA), an aromatic amine representative of an important class of highly toxic compounds. For all the analysed samples, prepared with a solvent-to-cement ratio of 0.4, the decay of the echo magnetization has been fitted by adopting a model that combines an exponential component with a gaussian one. The calculated independent relaxation parameters have been discussed in terms of morphological and dynamical changes that occur during the cement hardening process and pore formation. Three kinds of water molecules: “solid-like” (chemically and physically bound), “liquid-like” (porous trapped) and “free” water, endowed with anisotropic, near isotropic and isotropic motion, respectively, were identified. Spin-echo images collected on the same samples during the hydration kinetics, allowed the changes of water and solvents spatial distribution in the porous network to be monitored, showing percolation phenomena and confirming the multimodal open channels structure of the hardened cement system. Both T2 relaxation and imaging data indicated that a pronounced delay occurs in the cement hardening when organics are present. © 2004 Elsevier Inc. All rights reserved.
NMR observation of water transfer between a cement paste and a porous medium
Cement and Concrete Research, 2017
We show that it is possible to follow the liquid transfer between a cement paste and a porous medium in contact with it, by analyzing the evolution of the distribution of 1 H NMR relaxation times. This in particular makes it possible to see that whatever the initial water fraction in the paste, a porous medium with sufficiently small pores can rapidly extract a significant amount of water from this paste. Afterwards, during the hydration process, the cement paste progressively gets water back from this porous medium. The amount of water thus extracted by the paste finally appears to just compensate the volume loss due to water consumption by the hydration process.