skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Modeling of the link between microstructure and effective diffusivity of cement pastes using a simplified composite model

Abstract

The knowledge of the relationship between porosity and transport properties of concrete is a point of major importance to run properly the models coupling chemistry, transport and mechanics in order to simulate the engineered barrier degradations in the context of the nuclear waste deep repository. The present work proposes a simplified composite model aiming at linking microstructure and effective diffusivity of cement pastes. The proposed analytical method allows the estimation of the evolution of effective diffusivity of such materials submitted to porosity opening or plugging, at the scale of the Representative Elementary Volume (REV). The method is then applied to Ordinary Portland Cement (OPC) pastes. The porosity-diffusion evolutions determined from the composite model for various OPC pastes are implemented into simplified chemo-transport simulations aiming at describing the leaching of cementitious materials. Using these evolutions, OPC paste leaching simulations are in good agreement with the available experimental data, indicating a good reliability of the simplified composite model.

Authors:
 [1];  [2]
  1. CEA Saclay, DEN/DPC/SCCME/LECBA, 91191 Gif-sur-Yvette (France). E-mail: syriac.bejaoui@cea.fr
  2. CEA Saclay, DEN/DPC/SCCME/LECBA, 91191 Gif-sur-Yvette (France)
Publication Date:
OSTI Identifier:
20995374
Resource Type:
Journal Article
Resource Relation:
Journal Name: Cement and Concrete Research; Journal Volume: 37; Journal Issue: 3; Conference: International Conference on cementitious materials as model porous media: Nanostructure and transport processes, Centro Monte Verita (Switzerland), 17-22 Jul 2005; Other Information: DOI: 10.1016/j.cemconres.2006.06.004; PII: S0008-8846(06)00170-0; Copyright (c) 2006 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; COMPOSITE MODELS; CONCRETES; DIFFUSION; ENVIRONMENTAL TRANSPORT; LEACHING; MICROSTRUCTURE; POROSITY; PORTLAND CEMENT; RADIOACTIVE WASTE FACILITIES; RADIOACTIVE WASTES; SIMULATION

Citation Formats

Bejaoui, S., and Bary, B. Modeling of the link between microstructure and effective diffusivity of cement pastes using a simplified composite model. United States: N. p., 2007. Web. doi:10.1016/j.cemconres.2006.06.004.
Bejaoui, S., & Bary, B. Modeling of the link between microstructure and effective diffusivity of cement pastes using a simplified composite model. United States. doi:10.1016/j.cemconres.2006.06.004.
Bejaoui, S., and Bary, B. Thu . "Modeling of the link between microstructure and effective diffusivity of cement pastes using a simplified composite model". United States. doi:10.1016/j.cemconres.2006.06.004.
@article{osti_20995374,
title = {Modeling of the link between microstructure and effective diffusivity of cement pastes using a simplified composite model},
author = {Bejaoui, S. and Bary, B.},
abstractNote = {The knowledge of the relationship between porosity and transport properties of concrete is a point of major importance to run properly the models coupling chemistry, transport and mechanics in order to simulate the engineered barrier degradations in the context of the nuclear waste deep repository. The present work proposes a simplified composite model aiming at linking microstructure and effective diffusivity of cement pastes. The proposed analytical method allows the estimation of the evolution of effective diffusivity of such materials submitted to porosity opening or plugging, at the scale of the Representative Elementary Volume (REV). The method is then applied to Ordinary Portland Cement (OPC) pastes. The porosity-diffusion evolutions determined from the composite model for various OPC pastes are implemented into simplified chemo-transport simulations aiming at describing the leaching of cementitious materials. Using these evolutions, OPC paste leaching simulations are in good agreement with the available experimental data, indicating a good reliability of the simplified composite model.},
doi = {10.1016/j.cemconres.2006.06.004},
journal = {Cement and Concrete Research},
number = 3,
volume = 37,
place = {United States},
year = {Thu Mar 15 00:00:00 EDT 2007},
month = {Thu Mar 15 00:00:00 EDT 2007}
}
  • A method is proposed for quantitatively predicting the volume of the major phases in hydrated cement pastes as a function of (1) the composition of the cement, (2) the degree of reaction, and (3) the initial water: cement ratio. This procedure is then used to develop a quantitative model for the surface area and volume of porosity that is accessible to nitrogen in calcium silicate hydrate (C-S-H). Published values for surface areas and volume of pores are compared with the predictions made by the model. An implication of the model is that there are two types of C-S-H, or perhapsmore » regions within the C-S-H: one that nitrogen can penetrate and one that it cannot.« less
  • Cement pastes aged from 1 to 60 days were studied using synchrotron microtomography on the MS-X04SA beam line at the Swiss Light Source. This allowed three dimensional images to be obtained with a resolution approaching that of backscattered electron images in the SEM. From these images, several features can be extracted and studied, both quantitatively and morphologically. In this study, attention was focused on the reacting anhydrous cement grains and porosity. Three dimensional imaging of capillary porosity allowed the connectivity and tortuosity of the pore network to be studied. It is shown that the degree of connectivity of the poremore » network is very sensitive to both the spatial resolution of the images and the evolution of contrast resolution during ageing of the cement.« less
  • This paper presents information on the effect of fly ashes on the microstructure of high volume fly ash (HVFA) pastes and how this affect the crack pattern and the stress-strain relationship. The HVFA pastes were prepared incorporating 58% of fly ashes. Fly ash particles appear to act as microaggregates in the pastes. Crack propagation generally deviates around the fly ash particles. Compared with that for the Portland cement paste of similar strength, the stress-strain curves for the HVFA pastes are less linear and begin to deviate at about 60--70% of the ultimate strength at 28 days. Based on these information,more » it was proposed that the HVFA paste may be considered as a composite material microscopically with fly ash particles as reactive microaggregates embedded in a matrix of hydration and reaction products. The effect of high volumes of fly ash on various properties of the concrete such as the modulus of elasticity, shrinkage and creep, as well as permeability were also discussed.« less
  • The reaction of pozzolana with the lime liberated during the hydration process of Portland cement modifies some properties of cement and resulting concrete. This study aimed to investigate experimentally the change occurring in the phase composition and microstructure of pozzolanic cement pastes containing activated kaolinite clay. The artificial pozzolana (burnt kaolinite clay) were thermally activated by firing at 850 C for two hours. The ordinary Portland cement (OPC) was partially replaced by different amounts of activated kaolinite clay by weight. The changes in the electrical conductivity were reported during setting and hardening processes after gauging with water. The change occurringmore » in the phase composition and microstructure of cement pastes were investigated by differential thermal analysis and scanning electron microscopy. The results of this investigation show that, the thermal activated kaolinite clay prolonged the initial and final setting times and reduced the porosity, it also improved the microstructure of the formed hydrates by recrystallization of hydrated calcium silicates (mainly as CSH-(I)) together with the formation of hexagonal calcium aluminate hydrate (mainly as C{sub 4}AH{sub 13}).« less
  • Some experimental investigations on the microstructure and compressive strength development of silica fume blended cement pastes are presented in this paper. The silica fume replacement varies from 0% to 20% by weight and the water/binder ratio (w/b) is 0.4. The pore structure by mercury intrusion porosimetry (MIP), the micromorphology by scanning electron microscopy (SEM) and the compressive strength at 3, 7, 14, 28, 56 and 90 days have been studied. The test results indicate that the improvements on both microstructure and mechanical properties of hardened cement pastes by silica fume replacement are not effective due to the agglomeration of silicamore » fume particles. The unreacted silica fume remained in cement pastes, the threshold diameter was not reduced and the increase in compressive strength was insignificant up to 28 days. It is suggested that the proper measures should be taken to disperse silica fume agglomeration to make it more effective on improving the properties of materials.« less