| 1. |
- Yang, Haibin, et al.
(author)
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Mechanical properties and mechanisms of alkali-activated slag paste reinforced by graphene oxide-SiO 2 composite
- 2022
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In: Journal of Cleaner Production. - : Elsevier BV. - 0959-6526. ; 378
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Journal article (peer-reviewed)abstract
- Alkali-activated slag (AAS) binders-based composites are considered potential alternatives to conventional cement-based composites. However, the quasi-brittle mechanical behavior of AAS binders-based composites limits their widespread application. In this study, a graphene oxide-SiO2 (GO-SiO2) composite was produced to address this issue. The experimental results showed that the flexural strength of an AAS paste increased by 133.2% with 1.5 wt% GO-SiO2 composite, and its corresponding flexural-to-compressive strength ratio increased 95% i.e. from 0.063 to 0.123. To explore the strengthening mechanism, the stability of the GO-SiO2 composite in alkaline solutions and the dispersion effect of GO-SiO2 composite on the mechanical properties of AAS paste were investigated. The experimental results showed that the prepared GO-SiO2 composite had stable C–O–Si chemical bonds connected GO with hydration products, thereby improving the strength of the AAS paste. The molecular dynamics study revealed the mechanism that the high-dispersed GO-SiO2 composite could improve the mechanical properties of the AAS paste dramatically.
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| 2. |
- Ahlström, Johan, et al.
(author)
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Electrochemical properties of oxide scale on steel exposed in saturated calcium hydroxide solutions with or without chlorides
- 2018
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In: International Journal of Corrosion. - : Hindawi Limited. - 1687-9325 .- 1687-9333. ; 2018
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Journal article (peer-reviewed)abstract
- The electrochemical properties of various iron oxide scales on steel exposed in saturated calcium hydroxide solutions were investigated. The iron oxide scales were manufactured by different heat treatments and grinding processes and characterized using X-ray diffraction and scanning electron microscope. The electrochemical properties of the scales were assessed by measuring the corrosion potential and using electrochemical impedance spectroscopy and potentiodynamic polarization curves. It was found that wustite and magnetite are less noble compared to hematite but are more effective as cathodic surfaces. The results show that the electrochemical properties of the mill scale can be an important contributing factor in the corrosion of steel in concrete.
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| 3. |
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| 4. |
- Babaahmadi, Arezou, 1985, et al.
(author)
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A study of the accelerated ageing process of cementitious materials
- 2011
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In: Advances in Construction Materials through Science and Engineering. ; RILEM PRO 79
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Conference paper (peer-reviewed)abstract
- This paper presents part of a study in a research project called “Ageing of the cementitious materials for storage of nuclear waste”. The goal is to establish a mechanistic model for predicting longevity of concrete in storage facilities for nuclear waste. As deposition of low and intermediate level radioactive waste (LILW) needs up to 100 000 years, it is necessary to analyze the service life of cementitious materials in this time perspective. Laboratory methods are, therefore, needed for accelerating the ageing process without making any influencing distortion in the properties of the materials. Chemical and electrochemical acceleration approaches were tried in this study. Chemical acceleration involves leaching of samples under conditions of actual groundwater. Electrochemical migration is also applied to accelerate leaching process. Chemical and XRD analysis is carried out to identify the compositions before and after the acceleration tests. The results indicate a possibility to produce aged specimens for further mechanical tests and other physical tests, such as porosity and diffusivity.
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| 5. |
- Babaahmadi, Arezou, 1985, et al.
(author)
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Ageing of cementitious materials for storage of nuclear waste
- 2011
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In: Nordic Concrete Research. ; Publication No. 43, s. 429-432
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Conference paper (peer-reviewed)abstract
- This paper presents an on-going research project dealing with ageing process of cementitious materials in a perspective of hundreds and thousands years. As it is risky to use empirical models for extrapolation of performance data from relatively short term experiments, a mechanism-based (chemo-mechanical coupled) model for safer prediction of longevity of concrete in storage facilities for nuclear waste is needed. The project work involves thermodynamic modeling, development of accelerated aging tests, physical, chemical and mineralogical characterization of young and aged cementitious materials, including mechanical, transport (diffusivity) properties, binding (adsorption) capacities and surface complexation (charging) behavior.
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| 6. |
- Babaahmadi, Arezou, 1985, et al.
(author)
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Ageing process of cementitious materials: Ion transport and diffusion coefficient
- 2012
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In: Concrete Repair, Rehabilitation and Retrofitting III - Proceedings of the 3rd International Conference on Concrete Repair, Rehabilitation and Retrofitting, ICCRRR 2012. - 9780415899529 ; , s. 369-374
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Conference paper (peer-reviewed)abstract
- Risk assessment analysis concerning service life predictions of concrete structures in nuclear waste repositories requires broad knowledge about long-term concrete deterioration processes. It is well known that the degradation process of cementitious materials involves diffusion of internal and external ions, interaction between these ions and re-deposition of the interacted products. However, although diffusion properties play an important role in the deterioration process, there is a lack of reliable data on ion diffusivity in concrete, especially co-existing ions rather than chloride. The aim of this study is to further analyze multi-component ionic diffusion accompanied with surface complexation and selective adsorption. Natural diffusion cell and field immersion tests are used to analyze transport properties of ions present in groundwater surrounding nuclear waste repositories such as chloride, sodium, lithium and calcium ions, through cement paste. Analytical techniques such as Ion chromatography, potentiometric titration, inductively coupled plasma mass spectrometry and X-ray fluorescence methods are used. Results indicate that the ionic diffusion coefficients differ between different ions and the higher the concentration of the ions, the lower the diffusion coefficient will be.
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| 7. |
- Babaahmadi, Arezou, 1985, et al.
(author)
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Chloride Penetration Resistance of Calcium Depleted Concrete Specimens
- 2014
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In: Proceedings of XXII Nordic Concrete Research Symposium, 13 - 15 August 2014, Reykjavik Iceland. ; , s. 487-490
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Conference paper (peer-reviewed)abstract
- To facilitate the service life predictions regarding durability of nuclear waste repositories acceleration methods enhancing the decalcification process are used. However, in order to reach an efficient leaching rate small sample sizes have been used which limits further testing. In this study an electro-chemical migration method to accelerate leaching of calcium from concrete specimens of size 50×100Ø is presented. Rapid chloride migration test is utilized to account for the changes in chloride diffusion coefficient of concrete specimens due to calcium depletion. The results indicate up to at least 70% of increase of chloride diffusion coefficient as a result of decalcification.
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| 8. |
- Babaahmadi, Arezou, 1985, et al.
(author)
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Development of an electro-chemical accelerated ageing method for leaching of calcium from cementitious materials
- 2016
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In: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 49:1-2, s. 705-718
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Journal article (peer-reviewed)abstract
- To facilitate the long term durability predictions of nuclear waste repositories, acceleration methods enhancing calcium leaching process from cementitious materials are needed, even though mechanisms not necessarily comparable to those predominant in a natural leaching process may be developed. In the previously published acceleration methods the samples are very small, which limits further physical or mechanical tests. In this paper, a new acceleration method based on electro-chemical migration is presented. The method although not driven with the same kinetics as in natural leaching, was designed in such a way that unnecessarily destructive by-effects could be minimized while promoting a higher leaching rate for a sample size suitable for further testing the mechanical and physical properties. It is shown that approximately 1x10^6 C of electrical charge per paste specimen of size Ø50 x 75 mm (approximately 230 g) is required to leach out the total amount of Portlandite. The chemical and mineralogical properties of leached samples are characterized by various techniques. It is concluded that aged samples are comparable to those leached in a natural leaching process as both are characterized by a layered system comprising an unaltered core delineated by total dissolution of Portlandite followed by a progressive decalcification of the calcium silicate hydrate gel.
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| 9. |
- Babaahmadi, Arezou, 1985, et al.
(author)
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Electrochemical migration technique to accelerate ageing of cementitious materials
- 2013
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In: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. - 9782759810468 ; 56
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Conference paper (peer-reviewed)abstract
- Durability assessment of concrete structures for constructions in nuclear waste repositories requires long term service life predictions. As deposition of low and intermediate level radioactive waste (LILW) takes up to 100 000 years, it is necessary to analyze the service life of cementitious materials in this time perspective. Using acceleration methods producing aged specimens would decrease the need of extrapolating short term data sets. Laboratory methods are therefore, needed for accelerating the ageing process without making any influencing distortion in the properties of the materials. This paper presents an electro-chemical migration method to increase the rate of calcium leaching from cementitious specimens. This method is developed based on the fact that major long term deterioration process of hardened cement paste in concrete structures for deposition of LILW is due to slow diffusion of calcium ions. In this method the cementitious specimen is placed in an electrochemical cell as a porous path way through which ions can migrate at a rate far higher than diffusion process. The electrical field is applied to the cell in a way to accelerate the ion migration without making destructions in the specimen's micro and macroscopic properties. The anolyte and catholyte solutions are designed favoring dissolution of calcium hydroxide and compensating for the leached calcium ions with another ion like lithium.
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| 10. |
- Babaahmadi, Arezou, 1985, et al.
(author)
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Mineralogical, Physical and Chemical Characterization of Cementitious Materials Subjected to Accelerated Decalcification by an Electro-Chemical Method
- 2014
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In: Nordic Concrete Research. - 0800-6377. ; 1/2014:49, s. 181-198
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Journal article (peer-reviewed)abstract
- To facilitate the service life predictions regarding durability of nuclear waste repositories acceleration methods enhancing the decalcification process are needed. In this study an electro-chemical migration method to accelerate leaching of calcium from cementitious specimens of sizes 50×100Ø and 75×50Ø mm is presented. The mineralogical, physical and chemical properties of degraded samples are characterized. The results demonstrate that up to 70% decrease in strength, 50 % decrease in E-modulus, 90 % increase in gas permeability, at least 70% increase in chloride diffusion coefficient and 70 % increase in pore volume could be expected due to leaching of portlandite from concrete.
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