Biomedical subjects

J-P Korb

Publications and source records attributed to J-P Korb.

7 recordsLinked to original sources

PubMed2005

Microstructure evolution of hydrated cement pastes.

We propose an original method based on both proton nuclear magnetic relaxation dispersion and high-resolution NMR spectra to investigate the microstructure of synthesized Ca3SiO5-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 Df = 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.

Journal Article↗

PubMed2005

Surface relaxation and chemical exchange in hydrating cement pastes: a two-dimensional NMR relaxation study.

We report the first nuclear magnetic resonance (NMR) two-dimensional correlation T(1) - T(2) and T(2) - T(2) measurements of hydrating cement pastes. A small but distinct cross peak in the two-dimensional relaxation spectrum provides the first direct evidence of chemical exchange of water between gel and capillary pores occurring over the first 14 days of hydration. A correlation of features along the line T(1) = 4T(2) provides strong supportive evidence for the surface diffusion model of (1)H nuclear spin relaxation in cements and for a multimodal discrete pore size distribution. Differences in detail of the results are reported for white cement paste and white cement paste with added silica fume. Both the method and the theory presented can be applied more widely to other high surface area materials with other reactive surface areas.

Journal Article↗

PubMed2004

Universal nuclear spin relaxation and long-range order in nematics strongly confined in mass fractal silica gels.

We show how the low-frequency dependence of the proton spin-lattice relaxation time T1(nu) of octylcyanobiphenyl liquid crystals confined in high-density silica gels evidences a long-range order nematic phase in spite of the strong confinement and random disorder of the gels. The universal value and frequency dependence observed, T1(nu) proportional, variant nu(2/3), is interpreted within a relaxation model due to director fluctuations in nematic liquid crystals confined to mass fractal porous media. The model provides a relation T1(nu) proportional, variant nu(2-d/2), giving a reliable value of the structural fractal dimension d(f)=2.67 for all the host silica gels.

Journal Article↗

PubMed2003

Probing the surface area of a cement-based material by nuclear magnetic relaxation dispersion.

We show how nuclear magnetic spin-lattice relaxation dispersion of 1H water can provide a direct reliable value of the specific surface area of a cement-based material. The remarkable features of the relaxation dispersion support an interpretation in terms of coupled solid-liquid relaxation at pore interfaces, surface diffusion, and nuclear paramagnetic relaxation. The measurement is sufficiently fast to be applied continuously during the progressive hydration and setting of the material. This method is relevant to other chemically reactive porous media in chemical engineering and oil recovery.

Journal Article↗

PubMedDate not supplied

Surface nuclear magnetic relaxation and dynamics of water and oil in granular packings and rocks.

Low field proton nuclear spin-relaxation at variable magnetic field strength and temperature provides surface dynamical parameters such as surface diffusion coefficients, activation energies, time of residence and coefficient of surface affinity. These parameters were extracted from measurements on grain packs and natural oil-bearing rocks. On grain packs, we show first that changing the amount of surface paramagnetic impurities leads to striking different relationships between the pore-size and the relaxation times T1 and T2. These relationships are well supported by fast-diffusion (surface-limited) or slow-diffusion relaxation models. Surface relaxivity parameters rho1 and rho2 are deduced from the pore size dependence in the fast-diffusion regime. Then, we evidence the frequency and temperature dependence of the surface relaxivity rho1 by field cycling NMR relaxation and relevant theoretical models. The typical frequency dependence found allows an experimental separation of the surface and bulk microdynamics in granular packings and petroleum rocks and the determination of the above mentioned surface dynamical parameters. Finally, we present the first field cycling nuclear spin relaxation experiments performed in water/oil saturated petroleum rocks. We believe that these experiments give new information about the surface localization of these two saturating liquids in pores.

Diffusion↗

PubMedDate not supplied

What is the surface specific area of porous cement-based material? A nuclear magnetic relaxation dispersion approach.

We propose a new NMR method to measure and follow the evolution of the surface specific area, Sp, of a porous cement-based material. This method, that does not require any preliminary drying process, uses nuclear magnetic relaxation dispersion (NMRD), the measurement of spin-lattice relaxation rate as a function of magnetic field strength or nuclear Larmor frequency. The method is applied for three different mortars samples prepared by mixing cement, sand, silica fume, water and superplasticizer with a water to cement ratio w/c=0.25, 0.38 and 0.65, respectively. The evolution of Sp grows linearly with the degree of advancement of chemical reactions measured by thermal heating and we evidence two relaxation processes independent of the w/c ratio.

Construction Materials↗

PubMedDate not supplied

Micropore size analysis by NMR in hydrated cement.

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 (1H-NMR) and field-cycling relaxation in C3S hydrated paste. The non-exponential decay was interpreted as a distribution of discrete relaxation rates. The attribution of T1 is supported by both a spectral and a dispersion curve analyses. These experiments allow us to follow the structuration of the material during setting.

Calcium Compounds↗