| 1. |
- Wang, Shuping, 1987, et al.
(författare)
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High-strength lightweight blocks prepared from the by-product of aluminium removed from fly ash
- 2014
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Ingår i: Proceedings of International Symposium on Eco-Crete – Environmentally Friendly Concrete, 13 - 15 August 2014, Reykjavik Iceland. ; , s. 29-36
-
Konferensbidrag (refereegranskat)abstract
- A large amount of powder by-product is generated when Al2O3 is extracted from fly ash. The purpose of this study is to investigate the properties of the powder and find an effective method to reuse it. XRF, XRD, and SEM were used to analysis its compositions and microstructures. The powder was then compressed at the pressure of from 20 to 100 MPa. Results show that the powder was disordered calcium silicate hydrate with an average Ca/Si molar ratio of 1.08. It becomes hardened blocks by compressing. The bulk density of the hardened blocks is between 500 and 800 kg m-3 corresponding to the pressure of 20 to 60 MPa. Their flexible strength is from 1.60 to 5.35 MPa, and compressive strength from 8.50 to 30.50 MPa. The blocks can be recycled by repeating the procedure of crushing blocks, grinding them into powder, and compressing the powder into hardened blocks. This powder can be sustainably reused to prepare lightweight blocks with high strength.
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| 2. |
- Wang, Shuping, 1987, et al.
(författare)
-
Pb2+ adsorption by calcium silicate hydrate synthesized from steel slag
- 2015
-
Ingår i: Nordic Concrete Research. - 0800-6377. ; 52, s. 77-92
-
Tidskriftsartikel (refereegranskat)abstract
- This study aims to investigate the adsorption properties of Pb2+ by calcium silicate hydrate synthesized from steel slag. The influence of various factors on the adsorption properties was investigated. The static desorption test was conducted to investigate the leaching of Pb2+. The kinetic model and isotherm model of adsorption are then discussed. Results show that Pb2+ adsorption capacity of C-S-H depends on Ca/Si ratios. Kinetic adsorption data is in consistence with Lagegren pseudo-second-order model, and steady-state data fits to Langmuir isothermal model. Leaching result demonstrates that Pb2+ ions are stably adsorbed by C-S-H structures.
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| 3. |
- Yang, Haibin, et al.
(författare)
-
Mechanical properties and mechanisms of alkali-activated slag paste reinforced by graphene oxide-SiO 2 composite
- 2022
-
Ingår i: Journal of Cleaner Production. - : Elsevier BV. - 0959-6526. ; 378
-
Tidskriftsartikel (refereegranskat)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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| 4. |
- Ahlström, Johan, et al.
(författare)
-
Electrochemical properties of oxide scale on steel exposed in saturated calcium hydroxide solutions with or without chlorides
- 2018
-
Ingår i: International Journal of Corrosion. - : Hindawi Limited. - 1687-9325 .- 1687-9333. ; 2018
-
Tidskriftsartikel (refereegranskat)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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| 5. |
- Babaahmadi, Arezou, 1985, et al.
(författare)
-
A study of the accelerated ageing process of cementitious materials
- 2011
-
Ingår i: Advances in Construction Materials through Science and Engineering. ; RILEM PRO 79
-
Konferensbidrag (refereegranskat)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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| 6. |
- Babaahmadi, Arezou, 1985, et al.
(författare)
-
Ageing of cementitious materials for storage of nuclear waste
- 2011
-
Ingår i: Nordic Concrete Research. ; Publication No. 43, s. 429-432
-
Konferensbidrag (refereegranskat)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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| 7. |
- Babaahmadi, Arezou, 1985, et al.
(författare)
-
Ageing process of cementitious materials: Ion transport and diffusion coefficient
- 2012
-
Ingår i: Concrete Repair, Rehabilitation and Retrofitting III - Proceedings of the 3rd International Conference on Concrete Repair, Rehabilitation and Retrofitting, ICCRRR 2012. - 9780415899529 ; , s. 369-374
-
Konferensbidrag (refereegranskat)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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| 8. |
- Babaahmadi, Arezou, 1985, et al.
(författare)
-
Chloride Penetration Resistance of Calcium Depleted Concrete Specimens
- 2014
-
Ingår i: Proceedings of XXII Nordic Concrete Research Symposium, 13 - 15 August 2014, Reykjavik Iceland. ; , s. 487-490
-
Konferensbidrag (refereegranskat)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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| 9. |
- Babaahmadi, Arezou, 1985, et al.
(författare)
-
Development of an electro-chemical accelerated ageing method for leaching of calcium from cementitious materials
- 2016
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 49:1-2, s. 705-718
-
Tidskriftsartikel (refereegranskat)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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| 10. |
- Babaahmadi, Arezou, 1985, et al.
(författare)
-
Electrochemical migration technique to accelerate ageing of cementitious materials
- 2013
-
Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. - 9782759810468 ; 56
-
Konferensbidrag (refereegranskat)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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| 11. |
- Babaahmadi, Arezou, 1985, et al.
(författare)
-
Mineralogical, Physical and Chemical Characterization of Cementitious Materials Subjected to Accelerated Decalcification by an Electro-Chemical Method
- 2014
-
Ingår i: Nordic Concrete Research. - 0800-6377. ; 1/2014:49, s. 181-198
-
Tidskriftsartikel (refereegranskat)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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| 12. |
- Babaahmadi, Arezou, 1985, et al.
(författare)
-
Physical and Mechanical Properties of Cementitious Specimens Exposed to an Electrochemically Derived Accelerated Leaching of Calcium
- 2015
-
Ingår i: International Journal of Concrete Structures and Materials. - : Springer Science and Business Media LLC. - 1976-0485 .- 2234-1315. ; 9:3, s. 295-306
-
Tidskriftsartikel (refereegranskat)abstract
- Simulating natural leaching process for cementitious materials is essential to perform long-term safety assessments of repositories for nuclear waste. However, the current test methods in literature are time consuming, limited to crushed material and often produce small size samples which are not suitable for further testing. This paper presents the results from the study of the physical (gas permeability as well as chloride diffusion coefficient) and mechanical properties (tensile and compressive strength and elastic modulus) of solid cementitious specimens which have been depleted in calcium by the use of a newly developed method for accelerated calcium leaching of solid specimens of flexible size. The results show that up to 4 times increase in capillary water absorption, 10 times higher gas permeability and at least 3 times higher chloride diffusion rate, is expected due to complete leaching of the Portlandite. This coincides with a 70 % decrease in mechanical strength and more than 40 % decrease in elastic modulus.
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| 13. |
- Berrocal, Carlos Gil, 1986, et al.
(författare)
-
Corrosion initiation in cracked fibre reinforced concrete: Influence of crack width, fibre type and loading conditions
- 2015
-
Ingår i: Corrosion Science. - : Elsevier BV. - 0010-938X. ; 98, s. 128-139
-
Tidskriftsartikel (refereegranskat)abstract
- This paper reports results from an ongoing project aimed at investigating the influence of fibre reinforcement on corrosion of rebar in chloride environments. Material tests showed that the resistivity of concrete decreased with the addition of fibres, whereas the chloride migration coefficient remained unaffected. Fibres at low dosages (
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| 14. |
- Boubitsas, Dimitrios, et al.
(författare)
-
An approach for measurement of chloride threshold
- 2013
-
Ingår i: International Journal of Structural Engineering. - 1758-7328 .- 1758-7336. ; 4:1/2, s. 24-34
-
Tidskriftsartikel (refereegranskat)abstract
- Chloride induced corrosion is one of the major causes for degradation of reinforced concrete structures. One of the most important factors in this process is the critical chloride content (chloride threshold value) in the vicinity of the reinforcement that causes initiation of corrosion. In this work the development of a practice-related approach that includes specimen shape, preconditioning, corrosion measurement techniques, and calculation concepts, for determining the critical chloride content are presented. The results in this study showed that the presented approach for determining chloride threshold values functioned fairly well, and suggestions for further improvement are proposed.
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| 15. |
- Boubitsas, Dimitrios, et al.
(författare)
-
An approach for measurement of chloride threshold values
- 2010
-
Ingår i: Advances in Concrete Structural Durability, ed by H. Yokota, T. Sugiyama and T Ueda, Hokkaido University Press, Sapporo, Japan. - 9784832903609 ; , s. 233-242
-
Konferensbidrag (refereegranskat)abstract
- Chloride induced corrosion is one of the major causes for degradation of reinforced concrete structures. One of the most important factors in this process is the critical chloride content (chloride threshold value) in the vicinity of the reinforcement that causes initiation of corrosion. In this work the development of a practice-related approach that includes specimen shape, preconditioning, corrosion measurement techniques, and calculation concepts, for determining the critical chloride content are presented. The results in this study showed that the presented approach for determining chloride threshold values functioned fairly well, and suggestions for further improvement are proposed.
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| 16. |
- Boubitsas, Dimitrios, 1970, et al.
(författare)
-
Estimation of chloride threshold values after 20 years’ field exposure in Swedish marine environment
- 2014
-
Ingår i: Proceedings of XXII Nordic Concrete Research Symposium, 13 - 15 August 2014, Reykjavik Iceland. ; , s. 361-364
-
Konferensbidrag (refereegranskat)abstract
- This paper presents the results from two research projects dealing with reinforcement corrosion measurements in concrete exposed to Swedish marine environment after exposure up to over 20 years. In the beginning of the 1990s, some 40 types of concrete slabs were exposed to seawater at the Träslövsläge field site on the west coast of Sweden. In this study the corrosion conditions of the rebars embedded in the concrete slabs were measured after 13 and 20 years’ field exposure using a non-destructive method. A destructive visual examination was also carried out to confirm the results from the non-destructive method. The results make it reasonable to assume a chloride threshold value of at least 1% by weight of binder for initiation of corrosion of reinforcement steel embedded in the marine concrete structures.
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| 17. |
- Boubitsas, Dimitrios, et al.
(författare)
-
The influence of reinforcement steel surface condition on initiation of chloride induced corrosion
- 2015
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 48:8, s. 2641-2658
-
Tidskriftsartikel (refereegranskat)abstract
- This paper describes a part of the work in the development of a "standard" test method for determining chloride threshold values required to initiate corrosion on reinforcement in concrete. The prerequisites of the test set-up are that the test conditions should be reasonably comparable to those in service and the test method should be fairly reproducible and as rapid as possible concerning the slow diffusion nature of the investigated phenomenon. This paper presents the results from a study on the influence of steel bar surface condition on chloride induced corrosion. Various electrochemical techniques were employed in the study to monitor the corrosion behaviour of the embedded bars with three different surface conditions. It is shown that the steel surface condition has a strong effect on the corrosion initiation of reinforcement in concrete, and can likely be the most decisive parameter attributing to the variability in the reported chloride threshold values.
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| 18. |
- Chen, Y. J., et al.
(författare)
-
Performance of Concrete Subjected to Severe Multiple Actions of Composite Salts Solution under Wet-Dry Cycles and Flexural Loading in Lab
- 2017
-
Ingår i: Journal Wuhan University of Technology, Materials Science Edition. - : Springer Science and Business Media LLC. - 1993-0437 .- 1000-2413. ; 32:4, s. 830-837
-
Tidskriftsartikel (refereegranskat)abstract
- Several action regimes were employed, namely, those exposed to solutions containing single and/or composite chloride and sulfate salts, and under wet-dry cycles and/or flexural loading. The variations in dynamic modulus of elasticity (E-rd values) were monitored, as well as the key factor impacting on the chloride ingress when concrete subjected to multiple action regimes was identified by the method of Grey Relation Analysis (GRA). The changes in micro-structures and mineral products of interior concrete after different action regimes were investigated by means of X-ray diffraction (XRD), mercury intrusion technique (MIP), and scanning electron microscopy (SEM). The test results showed that the cyclic wet-dry accelerated the deterioration of OPC concrete more than the action of 35% flexural loading based on the results of E-rd values and the GEA. The analyses from micro-structures could give certain explanations to the change in E-rd values under different action regimes.
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| 19. |
- Chen, Y. J., et al.
(författare)
-
Resistance of concrete against combined attack of chloride and sulfate under drying-wetting cycles
- 2016
-
Ingår i: Construction and Building Materials. - : Elsevier BV. - 0950-0618. ; 106, s. 650-658
-
Tidskriftsartikel (refereegranskat)abstract
- In this research, combined solution of chloride and sulfate was investigated for three different mixtures, including fly ash and slag. Mass change, dynamic modulus of elasticity, chloride penetration depths were tested in the different solution. Results indicated that OPC specimens showed bigger deterioration compared specimens with fly ash and slag exposed to combined solution attack under drying-wetting cycles. Additional, higher sulfate contend in combined solution retarded damage for OPC under drying-wetting cycle. Concerning the microstructure and deformation of samples, XRD-analyses is in accordance with TG/DSC-analyses, moreover, DSC/TG could quantified the results from XRD-analyses. (C) 2015 Published by Elsevier Ltd.
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| 20. |
- Correia, Vera, et al.
(författare)
-
Effect of the addition of GGBS on the frost scaling and chloride migration resistance of concrete
- 2020
-
Ingår i: Applied Sciences (Switzerland). - : MDPI AG. - 2076-3417. ; 10:11
-
Tidskriftsartikel (refereegranskat)abstract
- Ground Granulated Blast-furnace Slag (GGBS) can partially replace cement in concrete to improve certain properties. However, some concerns regarding its performance have been raised. This research aimed at investigating the properties of concrete with GGBS, with special focus on its frost scaling and chloride ingress resistance. Concretes with different amounts of GGBS, different efficiency factors, and different air contents have been tested. The effects of other factors, namely the curing temperature, the use of superplasticizer and carbonation, have also been investigated. The results showed that the frost resistance generally decreases with the increase of the amount of GGBS. However, this research showed that it is possible to produce frost resistant concrete with up to 50% of GGBS by changing some properties of the mix (such as increasing the air content). The results also showed a significant improvement of the chloride ingress resistance for concrete with high additions of GGBS.
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| 21. |
- Cronstrand, Peter, 1965, et al.
(författare)
-
Electrochemical leaching of cementitious materials: an experimental and theoretical study
- 2011
-
Ingår i: Procedings of the 1st International Symposium on Cement-Based Materials for Nuclear Wastes, NUMCEM 2011. ; Session 3:Paper O344
-
Konferensbidrag (refereegranskat)abstract
- The acceleration of aging processes using forced ionic migration has been studied from a combined theoretical and experimental point of view. The preliminary results indicate that only a fraction of the reactive-transport through the sample is associated with dissolution of portlandite and the subsequent release of calcium. Further experimental work is needed in order to characterize the sample in terms of mineral composition and microstructure and to verify the modeling approach.
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| 22. |
- Cui, Hongzhi, et al.
(författare)
-
Possible pitfall in sample preparation for SEM analysis - A discussion of the paper “Fabrication of polycarboxylate/graphene oxide nanosheet composites by copolymerization for reinforcing and toughening cement composites” by Lv et al.
- 2017
-
Ingår i: Cement and Concrete Composites. - : Elsevier BV. - 0958-9465. ; 77, s. 81-85
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a discussion of the paper published by Lv et al. in Cement and Concrete Composites, 2016, 66: 1–9. The discussion is mainly focused on whether or not graphene oxide (GO) nanosheets can regulate formation of flower-like cement hydration crystals. Lv et al. in their paper proposed a regulation mechanism stating that GO nanosheets can control ettringite (AFt), monosulfate (AFm) and calcium hydroxide (CH) to form the flower-like and polyhedron crystals, whilst our experimental results show that there might be a possible pitfall in sample preparation for SEM analysis. It is here suggested that the main chemical components of flower-like and polyhedron crystals are calcium carbonates, which are not the products from cement hydration but from carbonation of cementitious hydrates. It is therefore suggested that further study is needed to verify the regulation mechanism of GO on cement hydration crystals proposed by Lv et al. in the discussed paper.
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| 23. |
- Dias Ferreira Da Silva, Nelson, 1978, et al.
(författare)
-
Application of LA-ICP-MS for meso-scale chloride profiling in concrete
- 2013
-
Ingår i: Materials and Structures/Materiaux et Constructions. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 46:8, s. 1369-1381
-
Tidskriftsartikel (refereegranskat)abstract
- Chloride represents a major risk for reinforced concrete structures because at a certain concentration, it can promote depassivation of the steel bars and initiate corrosion. Therefore it is important to be able to measure the chloride content in concrete. In this paper the application of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for the study of chlorides in concrete is proposed. This scanning technique enables quick multi-element profiling, directly at the sample without the need for further preparation, within a range of sub-millimetre (meso-scale) resolution and with low limits of detection. Optimization of the operating conditions was performed in pressed concrete powder pellets. Linearity of the calibration was verified and limits of detection below 0.05 wt% of cement were determined. Chlorine, calcium and iron distributions were studied in cement based materials of increasing heterogeneity (paste, mortar and concrete). This technique is furthermore proposed for the study of the chloride induced corrosion process, by following element distributions along the concrete-steel interface at the time of depassivation.
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| 24. |
- Dias Ferreira Da Silva, Nelson, 1978, et al.
(författare)
-
Chloride analysis in concrete by LA-ICP-MS
- 2011
-
Ingår i: Advances in Construction Materials through Science and Engineering. ; RILEM PRO 79, s. 137-
-
Konferensbidrag (refereegranskat)abstract
- Chloride induced corrosion is the main problem affecting the durability of reinforced concrete structures. Therefore, the ability to measure chlorides in cementitious materials is of great importance. In this paper, we propose the application of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for the determination of the total chloride content in concrete, highlighting the potential of the technique for overcoming two main difficulties: the time consuming depth profiling and the representativeness of the sampling procedures in concrete at the interface with steel. Portland cement concrete powder pellets were used for calibration purposes and the accuracy of the chloride determination is verified by the analysis of certified reference materials. Experimental conditions were adjusted in order to optimize the detection limit which was found to be of 0.011 wt%. Using fly ash and slag cement concretes, the influence of the matrix was assessed by comparing the results from LA-ICP-MS measurements to those obtained by potentiometric titration. The method was applied for chloride profiling along the concrete-steel interface of a specimen subjected to chloride exposure, showing good reproducibility within the calibration range.
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| 25. |
- Dias Ferreira Da Silva, Nelson, 1978, et al.
(författare)
-
CHLORIDE CONTENTS AT THE CONCRETE-STEEL INTERFACE
- 2010
-
Ingår i: Advances in Concrete Strutural Durability - Proceedings of the 2nd International Conference on Durability of Concrete Structures ICDCS2010, 24-26 November 2010, Hokkaido University, Sapporo, Japan, edited by Hiroshi Yokota, Takafumi Sugiyama and Tamon Ueda, Hokkaido University Press. - 9784832903609 ; , s. 275-284
-
Konferensbidrag (refereegranskat)abstract
- The composition and microstructure of the concrete-steel interface influences the criticalchloride content (Ccr) for initiation of pitting corrosion and can differ from the conditions inthe bulk concrete. This paper describes the development of a methodology for chlorideprofiling along the interface by means of LA-ICP-MS. SEM-EDS and XRD techniques wereused for semi-quantitative analysis of Ccr, microstructure characterization of the pittingpositions and distribution and composition of the corrosion products. A range of chloridelevels along the interface was measured by means of LA-ICP-MS showing good agreementwith the results from EDS analysis. A number of interface defects were found to influencepitting corrosion. Several Fe(III) oxy-hydroxides, including akaganeite, were identified. XRDanalysis suggested the existence of FeCl2. These corrosion products tended to accumulate atthe aggregate-paste interface and in air voids at the cement paste.
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| 26. |
- Dias Ferreira Da Silva, Nelson, 1978, et al.
(författare)
-
Chloride profiles along the concrete-steel interface
- 2013
-
Ingår i: International Journal of Structural Engineering. - 1758-7328 .- 1758-7336. ; 4:1/2, s. 100-112
-
Tidskriftsartikel (refereegranskat)abstract
- The composition and microstructure of the concrete-steelinterface influences the critical chloride content for initiation of pitting corrosion and these characteristics may differ from those of the bulk concrete. This paper describes the development of a methodology for chloride profiling along the interface by means of LA-ICP-MS. For semi-quantitative analysis, microstructure characterisation of the pitting positions and distribution and composition of the corrosion products, SEM-EDS and XRD techniques wereemployed. The results indicate that along the interface a range of chloride levels can be expected. These varied between 0.15–1.5 wt% of concrete with higher levels around the active corrosion sites. Good agreement has been foundbetween the results from LA-ICP-MS and EDS techniques. Interface defects strongly influenced the pitting corrosion. Several Fe(III) oxy-hydroxides accumulated at the aggregate-paste interface and in air voids at the cementpaste. XRD analysis suggested the presence of akaganeite and FeCl2 (rokuhnite).
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| 27. |
- Dias Ferreira Da Silva, Nelson, 1978, et al.
(författare)
-
Critical Conditions for Depassivation of Steel in Concrete: Interface Chloride Profiles
- 2011
-
Ingår i: Nordic Concrete Research. ; Publication No. 43, s. 115-118
-
Konferensbidrag (refereegranskat)abstract
- This paper describes an ongoing research project that aims to improve the knowledge and understanding of the critical conditions for depassivation of steel by studying the micro/meso-scale chloride profiles along the steel-concrete interface and correlating these with aspects of its microstructure and composition.
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| 28. |
- Dias Ferreira Da Silva, Nelson, 1978, et al.
(författare)
-
Critical Conditions for Depassivation of Steel in Concrete: Interface Chloride Profiles and Steel Surface Condition
- 2012
-
Ingår i: Nordic Concrete Research. - 0800-6377. ; 45, s. 111-123
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The composition and macrostructure of the concrete-steel interface and the surface finish of the steel are fundamental for the chloride induced corrosion initiation in reinforced concrete, with direct influence in the chloride threshold values (Cth). In this paper these characteristics were examined for vertically cast samples immersed in salt solution. After depassivation, the specimens were open for visual examination. Corrosion always initiated at the front side and surface defects were found to influence the corrosion onset. Chloride, calcium and iron profiles along the interface were drawn by means of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and higher chloride contents were measured around active corroding areas.
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| 29. |
- Fan, Xu, et al.
(författare)
-
Effects of different supplementary cementitious materials on the performance and environment of eco-friendly mortar prepared from waste incineration bottom ash
- 2022
-
Ingår i: Construction and Building Materials. - : Elsevier BV. - 0950-0618. ; 356
-
Tidskriftsartikel (refereegranskat)abstract
- Municipal solid waste incineration bottom ash (MSWIBA) is a by-product produced by municipal waste incineration treatment. In this study, MSWIBA particle size distribution, chemical composition and particle shape were investigated and confirmed its value for reuse in the construction field and its good research potential. MSWIBA was used as fine aggregates, while coal fly ash (FA) and ground granulated blast furnace slag (GGBFS) were used as auxiliary cementitious materials to replace part of cement to manufacture the eco-friendly mortar (EFM). The effect of FA/GGBFS on the mechanical and microscopic properties of EFM with different material ratios was mainly investigated. And the analysis of the environmental friendliness and economy of this EFM was made. The results show that the combination of FA and GGBFS at the same time reduces the early mechanical properties of the mortar. However, the strength developed rapidly after 7 days, with an increase of more than 6 times the rate before 7 days. Compared with GGBFS, FA is more helpful in improving the mechanical properties of the EFM. After 28 days of full hydration, the hydration products within the EFM are numerous and well bonded to each other. Not only do these hydration products increase the mechanical strength of EFM, but they also successfully solidify the hazardous components in MSWIBA and reduce their negative environmental effects. In addition, the use of MSWIBA instead of sand for mortar preparation reduces energy consumption and CO2 emissions, and it reduces the cost by more than 50 %. This indicates that MSWIBA may perform well in the future development of the civil infrastructures. As well as recycling waste resources, it makes a valuable contribution to the development of green and sustainable building materials.
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| 30. |
- Fan, Xu, et al.
(författare)
-
New applications of municipal solid waste incineration bottom ash (MSWIBA) and calcined clay in construction: Preparation and use of an eco-friendly artificial aggregate
- 2023
-
Ingår i: Construction and Building Materials. - 0950-0618. ; 387
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this study is to prepare MSWIBA as eco-friendly artificial aggregates (EFAAs) by cold bond granulation technique using a low carbon limestone calcined clay cement (LC3). The water absorption rate of EFAAs is between 14.42 and 21.82%, and the maximum compressive strength can reach 2.5 MPa. Calcined clay particles can effectively adsorb heavy metal ions after absorbing water, and EFAAs can reduce the leaching value of toxic elements in MSWIBA by more than half on average. Compared to standard OPC cementitious materials, LC3 composites only need 50% of the energy and discharge 43% of the CO2, producing a more environmentally friendly artificial aggregate. In addition, the 28-day compressive strength of concrete was higher than 30 MPa on average after applying EFAAs to concrete. The good application capability shown by EFAAs, as well as their low energy consumption and low carbon environmental characteristics, promote the better application of MSWIBA in buildings.
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| 31. |
- Grammatikos, Sotirios, 1985, et al.
(författare)
-
Concrete setting and hardening monitoring using a novel graphene-based sensor
- 2017
-
Ingår i: ICF 2017 - 14th International Conference on Fracture. ; 2, s. 1204-1205
-
Konferensbidrag (refereegranskat)abstract
- This paper presents the procedure towards the development of a durable structural sensor based on graphene and other carbon fillers, for the monitoring of structural performance of concrete. The sensor captures electrical resistivity as a strength development and durability index during the whole service life of concrete. To date, performance monitoring systems usually fail in the long-run before the failure of the actual structure. The proposed sensor is embedded in the interrogated structure and ensures sustainable consolidation via appropriate physico-chemical adherence and mechanical interlocking. This allows for an efficient performance monitoring 'build-up' expected to surpass the service life of the parent concrete structure. The effects of different concentrations of graphene and other fillers on the electrical properties of concrete were studied. After an initial investigation to select the appropriate synthesis, the ability of the sensor to monitor the development of resistivity during setting and hardening was tested and the results are presented herein.
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| 32. |
- Grammatikos, Sotirios, 1985, et al.
(författare)
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On the Mechanical Recycling of Decommisioned Insulation Polymer Composite Components
- 2020
-
Ingår i: IOP Conference Series: Materials Science and Engineering. - : Institute of Physics Publishing. - 1757-8981 .- 1757-899X. ; 842:1
-
Konferensbidrag (refereegranskat)abstract
- Fibre reinforced polymer composites (FRPs) are being increasingly used in aerospace and automotive applications due to their high specific mechanical properties. The construction industry has also started taking advantage of the potential of FRPs for both structural and non-structural purposes. The result of this remarkable absorption of FRPs within the worldwide production market, has led to an immense increase of decommissioned thermoset-matrix components. Nowadays, the majority of the decommissioned FRP components are recovered energy-wise through incineration or simply discarded in landfills around the globe. Within the framework of this paper, we present a solution for the extension of the service life of decommissioned FRP components. Decommissioned electrical insulation FRP pipes were granulated and incorporated as fillers within both cementitious and polymer matrix composites. The effect of FRP granulates on the mechanical performance of cementitious and polymer matrix composites is examined to determine the maximum granulate-filler fraction that can be recycled without compromising the mechanical performance and manufacturing process.
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| 33. |
- Grammatikos, Sotirios, 1985, et al.
(författare)
-
Recycling and re-purposing decommisioned construction polymer composites for construction applications
- 2018
-
Ingår i: ECCM 2018 - 18th European Conference on Composite Materials. - : Applied Mechanics Laboratory. - 9781510896932
-
Konferensbidrag (refereegranskat)abstract
- Fibre reinforced polymer composites (FRPs) are being increasingly used in aerospace and automotive applications due to their high specific mechanical properties. The construction industry has also started taking advantage of the potential of FRPs for both structural and non-structural purposes. The result of this remarkable absorption of FRPs within the worldwide production market, has led to an immense increase of decommissioned thermoset-matrix components. Nowadays, the majority of the decommissioned FRP components are recovered energy-wise through incineration or simply discarded in landfills around the globe. Within the framework of this paper, we present a solution for the extension of the service life of decommissioned FRP components. Decommissioned electrical insulation FRP pipes were granulated and incorporated as fillers within both cementitious and polymer matrix composites. The effect of FRP granulates on the mechanical performance of cementitious and polymer matrix composites is examined to determine the maximum granulate-filler fraction that can be recycled without compromising the mechanical performance and manufacturing process.
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| 34. |
- Green, Colleen, 1960, et al.
(författare)
-
The introduction of Key Performance Indicators (KPI) for predicting the state of health
- 2012
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Ingår i: International Congress on Durability of Concrete, 18-21 June 2012, Trondheim, Norway.
-
Konferensbidrag (refereegranskat)abstract
- As durability of concrete infrastructure is a major concern worldwide, numerous approaches have been developed. It is a common practice nowadays to ensure durability of reinforced concrete structures by specifying a concrete mix and a nominal cover at the design stage to cater for the exposure environment. This in theory should produce the performance required to achieve a specified service life. Although the European Standard EN 206-1 specifies variations in the exposure environment, it does not take into account the macro and micro climates surrounding structures, which have a significant influence on their performance and service life. Therefore, in order to construct structures which will perform satisfactorily in different exposure environments, the following two aspects need to be developed: a performance basedspecification to supplement EN 206-1 which will outline the expected performance of the structure in a given environment; and a simple yet transferrable procedure for assessing the performance of structures in service. This will allow the asset managers not only to designstructures for the intended service life, but also to take informed maintenance decisions should the performance in service fall short of what was specified.The approach adopted in the paper is to select a reliable service life model and outline all the quantifiable (measurable) variables that contribute to the performance of structures in chloride environments. These variables are termed as Performance Indicators (PI). A case study of three concrete piers exposed to the North Sea is used to evaluate the relative influence of the PI on service life. A sensitivity analysis is carried out to determine the most significant of the PI termed as key performance indicators (KPI) which will have the greatest impact on theperformance and service life of the structure. It is expected that KPI’s would allow asset owners to easily assess the state-of-health of their structures and devise appropriate maintenance strategies.
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| 35. |
- Hong, Shuxian, et al.
(författare)
-
Determination of impressed current efficiency during accelerated corrosion of reinforcement
- 2020
-
Ingår i: Cement and Concrete Composites. - : Elsevier BV. - 0958-9465. ; 108
-
Tidskriftsartikel (refereegranskat)abstract
- Impressed current technique is a widely adopted method for accelerating corrosion of steel reinforcement. The mass loss of steel can be theoretically estimated by Faraday's law with the assumption that all of the impressed current participated in the corrosion reaction. In the present study, accelerated corrosion process of reinforcing steel with impressed current was non-destructively traced by X-ray micro-computed tomography (μCT) with high accuracy. The mass loss of steel at different accelerated corrosion periods was analyzed and the efficiency of impressed current was calculated. It was found that the mass loss of steel did not always follow Faraday's law, and impressed current efficiencies varied with different corrosion periods. In the early corrosion periods, the water electrolysis occurred and lowered the current efficiency due to the high anode potential. While in the late corrosion periods, the natural corrosion caused the current efficiency to exceed 100%.
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| 36. |
- Huang, Liming, 1993, et al.
(författare)
-
Distribution and dynamics of water in the blended pastes unraveled by thermoporometry and dielectric properties
- 2023
-
Ingår i: Cement and Concrete Research. - 0008-8846. ; 174
-
Tidskriftsartikel (refereegranskat)abstract
- Water distribution in hardened paste and its dynamics determine many properties related to durability. Moisture distribution was determined by thermoporometry combined with vacuum drying. Dynamics of confined water were measured by broadband dielectric spectroscopy. Water in pores <2.4 nm cannot form tetrahedral ice structure due to geometrical constraints. The volume of unfrozen water (in interlayer and gel pores) decreases after the drying at all relative humidity levels. An evident coarsening of gel pores occurs with drying between 75 % and 55 % RH. 35 % fly ash and slag have limited effects on relaxation processes of silanol hydroxyl groups and interlayer water. However, they slow down the dynamics of water in small gel pores, thereby enhancing interactions between water and the solid interface. This study clarifies the microstructural changes during the drying and reveals the sensitivity of water dynamics to the chemical environment in C-S-H of blended pastes.
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| 37. |
- Huang, Liming, 1993, et al.
(författare)
-
Moisture and ion transport properties in blended pastes and their relation to the refined pore structure
- 2022
-
Ingår i: Cement and Concrete Research. - : Elsevier BV. - 0008-8846. ; 161:106949
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a study of the moisture transport properties in blended pastes measured by a new procedure and setup. The dependence of moisture transport coefficient on relative humidity (RH) is confirmed. The differences in the moisture dependency may be due to discrepancies in the critical RH for the percolation of liquid. Fly ash and slag increase the percentage of mesopores or “ink-bottle” pores with a mesoscale neck and they strongly reduce the pore connectivity in pastes. These effects cause the evident reduction in the moisture and chloride diffusivity. The additional replacement with limestone filler has little effect on the pore connectivity. The formation factor controls the moisture transport at the high RH interval, but the volume of small pores (middle capillary and mesopores) is the major determinant at a low RH interval. The relationship between water-binder ratio, pore structure and moisture transport or chloride migration coefficient is discussed.
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| 38. |
- Huang, Liming, 1993, et al.
(författare)
-
New insights into the reaction of tricalcium silicate (C 3 S) with solutions to the end of the induction period
- 2022
-
Ingår i: Cement and Concrete Research. - : Elsevier BV. - 0008-8846. ; 152
-
Tidskriftsartikel (refereegranskat)abstract
- Although dissolution theory is widely used, in certain circumstance, it seems to be unable to explain the hydration of C3S. In this article, more attention is paid to the nucleation of hydration products. We find that the precipitation of C-S-H is a nonclassical nucleation process. It starts with nucleation of primary particles and then grows by particle attachment. A sharp increase in the reaction rate after induction period may come from the accelerating growth rate of C-S-H instead of dissolution of etch pits. The duration of induction period relates to the size of primary floc. Potassium salts influence the primary globule floc size and mitigate the effect from Al. The pH impacts ion species in solution to affect the dissolution and precipitation. A hypothesis regarding the dissolution of C3S and nucleation of C-S-H within the near-surface region may narrow the gap between dissolution theory and protective layer theory.
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| 39. |
- Huang, Liming, 1993, et al.
(författare)
-
Non-destructive test system to monitor hydration and strength development of low CO2 concrete
- 2023
-
Ingår i: Construction and Building Materials. - 0950-0618. ; 408
-
Tidskriftsartikel (refereegranskat)abstract
- Application of supplementary cementitious materials for production of low CO2 concrete affects the reaction kinetics, which alters the setting time and strength development. The different early-age behavior is of concern for quality control of concrete. Non-destructive test is very useful for monitoring the quality of low CO2 binder systems. This paper presents a new technique to monitor the electrical conductivity and temperature at different depths of hydrating concrete. Indices from monitoring system (conductivity, maturity and formation factor) are compared with data from widely-used methods (ultrasonic pulse velocity, penetration resistance and isothermal calorimetry). Results show that indices from the system can replicate the hydration evolution, setting time and compressive strength of low CO2 concrete. Electrical conductivity of concrete is very sensitive to mineral reactions and it reflects the hydration kinetic consistent with evolution of heat release. Linear correlations are found for penetration resistance in relation to ultrasonic pulse velocity, formation factor and maturity, respectively. The effects of binder type and water-to-binder ratio on hardening are strongly dependent on temperature. The proposed approach enables to include all these factors in characterizing the hardening process of concrete onsite. It is shown that formation factor performs better than ultrasonic pulse velocity on indicating the setting process. Formation factor is also a good parameter for quantitative description of compressive strength development, which is independent of the binder types, mixture proportions and curing ages.
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| 40. |
- Huang, Liming, 1993, et al.
(författare)
-
Real-time monitoring the electrical properties of pastes to map the hydration induced microstructure change in cement-based materials
- 2022
-
Ingår i: Cement and Concrete Composites. - : Elsevier BV. - 0958-9465. ; 132
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of the supplementary materials (SCMs) on the moisture content and ion diffusivity at different hydration time is important for the service life modelling of modern concrete. This study designed a simple but valid method to monitor the microstructure change in pastes during hydration. A procedure easy to implement was proposed to detect the water content in pastes. The electrical conductivity of pore solution was evaluated by the evaporable water content in pastes and chemical composition in the binders. Results show that the electrical properties of pastes (conductivity, formation factor and its growth rate) can effectively indicate the hydration reactivity of binder, pore connectivity and volume of pore solution in the hardened pastes. The effect of waterbinder ratio and SCMs on the structure of pastes are effectively indexed by the formation factor which is the conductivity of pore solution divided by that of paste. The inflection point of average growth rate of formation factor is a good index for the final setting of pastes. The relation between volume of evaporable water and formation factor is well demonstrated by the extended percolation theory. The real-time monitored electrical conductivity and formation factor of pastes can be used to calculate the chloride migration coefficient in hardened cement pastes.
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| 41. |
- Huang, Liming, 1993, et al.
(författare)
-
Using water vapour and N2 isotherms to unveil effects of SCMs on nanopores and evaluate hydration degree
- 2023
-
Ingår i: Cement and Concrete Research. - : Elsevier BV. - 0008-8846. ; 164:February 2023
-
Tidskriftsartikel (refereegranskat)abstract
- Nanopores are critical for the durability of cement-based materials, but the refinement of these pores by SCMs is yet to have a clear understanding. This paper studied effects of the water–binder ratio, SCMs and the drying on the distribution of nanopores using water vapour and N2 sorption isotherms. Results show that data of water vapour sorption can be used for a practical evaluation of the hydration degree of SCMs with thermodynamic simulation. Fly ash increases the volume of large gel and capillary pores. It lowers the difference between the sorption of water vapour and N2. Slag evidently refines the nanopores by increasing the volume of ink-bottle gel pores with an interlayer-size neck. A higher w/b produces more large pores to reduce the effect of drying. Removal of water induces contraction of interlayer and reduces gel pores volume, which causes large difference between sorption of water vapour and N2.
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| 42. |
- Induchoodan, Govindan, 1990, et al.
(författare)
-
GRAPHENE EMBEDDED BITUMINOUS ROADS: A NEW LOOK INTO THE DESIGN OF COMPLEX NANOCOMPOSITES
- 2019
-
Ingår i: NANOCON 2018 - Conference Proceedings, 10th Anniversary International Conference on Nanomaterials - Research and Application. - 9788087294895 ; , s. 107-112
-
Konferensbidrag (refereegranskat)abstract
- The chemistry of bitumen and the percentage of asphaltene can vary significantly depending on external and internal factors such as the source and method of bitumen extraction. This makes graphene embedded bitumen a complex ternary phase system. Within the framework of this paper, we focus on the phase stability and particle interaction between graphene and asphaltene in order to optimize the process of tailoring the microstructure of graphene embedded bitumen to improve the gas barrier and mechanical properties. We use characterization techniques such as rotational-rheometer, DSC, chemical titration and road engineering standards such as RTFOT and penetration-grade to study the critical-clustering-concentration, phase behavior and the impact of embedding graphene to manufacturing process of asphalt. Phase separation and agglomeration of dissimilar nanoparticles was observed when graphene embedded bitumen (1 % vol) was subjected to RTFOT, increasing the change in viscosity by around 13 % when compared to 10 % in std. bitumen. Hence this paper aspires to provide a brief look into tailoring of nanocomposites with dissimilar nanoparticles and embedding nanoparticles such as graphene into complex matrices.
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| 43. |
- Jansson, Helen, 1964, et al.
(författare)
-
Carbon enhanced cementitious coatings: Alternative anode materials for impressed current cathodic protection systems intended for reinforced concrete
- 2024
-
Ingår i: Materials and Corrosion - Werkstoffe und Korrosion. - 1521-4176 .- 0947-5117. ; 75:6, s. 705-718
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, the functionality of self-formulated carbon-based conductive coatings (CBCCs) with incorporation of graphite as the anode in an impressed current cathodic protection system is studied. The anode materials are tested and evaluated for long-term durability and performance by an accelerated durability test method. The results show that the functional time is highly dependent on the acceleration factor, and thus the charge passed through the material during testing, as well as the material composition. From the results, there are also indications that the addition of graphene into the CBCC matrix has a positive effect on the homogeneity of the material, but without any major influence on the conductivity and performance.
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| 44. |
- Jansson, Helen, 1964, et al.
(författare)
-
Parameters influencing the initial setting time of alkali-activated ground granulated blastfurnace slag materials
- 2015
-
Ingår i: Nordic Concrete Research. - 0800-6377. ; 52, s. 63-76
-
Tidskriftsartikel (refereegranskat)abstract
- Various parameters influencing the initial setting time of alkali-activated slag materials have been investigated using the Vicat method. The alkali solutions used for the activation were liquid sodium silicate (water glass) of different moduli n (SiO2/Na2O ratio) and pH. The results indicate that the initial setting time is mainly influenced by two parameters; 1) the specific surface area of the slag and 2) the modulus of the solution. The results also suggest that the problem with controlling the initial setting time of alkali-activated slag can be solved by controlling the characteristics of the solvent used for the activation.
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| 45. |
- Jansson, Helen, 1964, et al.
(författare)
-
The Influence of Silica Species Configuration on the Hydration of Alkali-Activated Ground Granulated Blast-Furnace Slag
- 2014
-
Ingår i: RILEM Proceedings: 2nd International Conference on Advances in Chemically-Activated Materials (CAM-China). - Bagneux : Rilem publications. - 1461-1147. - 9782351581421 ; 92, s. 309-318
-
Konferensbidrag (refereegranskat)abstract
- There are indications on that the initial setting time is dependent on the relative ratio of Na2O to SiO2 when sodium silicate solutions (Na2SiO3) are used for the alkali-activation of ground granulated blast-furnace slag (GGBS). One possible reason for this is that the ratio (called modulus) not only influences the pH but also the viscosity of the solution. The viscosity is, in turn dependent on the structures in the liquid. Therefore, we have investigated the structure of sodium silicate solutions of different moduli by infrared spectroscopy (IR) and silicon nuclear magnetic resonance (Si-29-NMR). The results, which show that the silica configuration is highly dependent on the modulus, will be discussed in relation to the initial setting time of corresponding measurements on GGBS hydration
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| 46. |
- Jansson, Helen, 1964, et al.
(författare)
-
The Initial Setting Time of Ground Granulated Blastfurnace Slag GGBS and Its Relation to the Modulus of the Alkali-Activating Solution
- 2014
-
Ingår i: 2nd International conference on Advances in chemically-activated materials (CAM'2014), RILEM Proceedings. - 1461-1147. - 9782351581421 ; 92, s. 309-318
-
Konferensbidrag (refereegranskat)abstract
- There are indications on that the initial setting time is dependent on the relative ratio of Na2O to SiO2 when sodium silicate solutions (Na2SiO3) are used for the alkali-activation of ground granulated blast-furnace slag (GGBS). One possible reason for this is that the ratio (called modulus) not only influences the pH but also the viscosity of the solution. The viscosity is, in turn dependent on the structures in the liquid. Therefore, we have investigated the structure of sodium silicate solutions of different moduli by infrared spectroscopy (IR) and silicon nuclear magnetic resonance (Si-29-NMR). The results, which show that the silica configuration is highly dependent on the modulus, will be discussed in relation to the initial setting time of corresponding measurements on GGBS hydration
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| 47. |
- Jansson, Helen, 1964, et al.
(författare)
-
The Initial Setting Time of Ground Granulated Blastfurnace Slag GGBS and Its Relation to the Modulus of the Alkali-Activating Solution
- 2014
-
Ingår i: Proceedings of XXII Nordic Concrete Research Symposium, 13 - 15 August 2014, Reykjavik Iceland. ; , s. 255-258
-
Konferensbidrag (refereegranskat)abstract
- In this study the initial setting time of water glass activated slag was investigated by the traditional Vicat method. It was found that the initial setting time is mainly influenced by two parameters; 1) the specific surface area of the material and 2) the modulus of the water glass used for the activation. The IR and 29Si-NMR spectroscopies were used to identify the structures of the water glass activator. The results show that the silica configuration is highly dependent on the modulus. The relationships between the initial setting time, specific surface area and silica structures are discussed.
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| 48. |
- Jiang, Jinyang, et al.
(författare)
-
The manner and extent to which the hydration shell impacts interactions between hydrated species
- 2021
-
Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 23:36, s. 20496-20508
-
Tidskriftsartikel (refereegranskat)abstract
- The hydration shell (HS) has a critical impact on every contact between hydrated species, which is a prerequisite for a great many physical and chemical processes, such as ion adsorption at the solution-solid interface. This paper reveals the extent and manner to which the HS interferes with ion adsorption utilizing molecular dynamics. The single-layer HS is the smallest unit that maintains the ionic hydration structure and the force on it. The energy penalty incurred by partial dehydration upon adsorption is one of the approaches through which HS influences ion adsorption, yet the collision of water molecules in HS may be the critical one. The repulsive force during dehydration is, to great extent, neutralized by HS collision. The index for estimating the extent of the influence of the HS is not the hydration energy, but the quantification of the contest between HS' collision and the binding of adsorption sites. The hydration energy is larger for charged functional groups, but the HS' impact is much smaller, as compared with electroneutral group cases. As a result, the order of the adsorption capacity for different ionic species may be quite different between charged and electroneutral cases.
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| 49. |
- Jin, Hesong, et al.
(författare)
-
An experimental study on the influence of continuous ambient humidity conditions on relative humidity changes, chloride diffusion and microstructure in concrete
- 2022
-
Ingår i: Journal of Building Engineering. - : Elsevier BV. - 2352-7102. ; 59
-
Tidskriftsartikel (refereegranskat)abstract
- Most engineering structures are exposed to various harsh environments, such as temperature fluctuations and humidity cycles, simultaneously. Additionally, moisture transfer and corrosive ion transport in concrete are driven by humidity gradients. Therefore, studying Chloride transport in concrete under constant humidity conditions is a meaningful research project. In this work, a new experimental setup was designed, and the Chloride diffusion behavior of concrete under a continuous humidity environment and NaCl immersion was investigated. Meanwhile, to accurately evaluate the internal humidity of concrete, humidity sensors were applied to the concrete. Additionally, the impacts of the water-binder ratio (w/b) and ambient humidity on the humidity diffusion coefficient, free Chloride content and bound Chloride content in concrete were evaluated. The microstructure was characterized by scanning electron microscopy, X-ray diffraction and mercury intrusion porosimetry. The results show that the content of free Chloride increases with an increasing w/b ratio. The humidity diffusion coefficient of concrete during water absorption (continuous high humidity environment) is significantly higher than that during water loss (continuous dry environment). Furthermore, under the drying condition, the Chloride content and the humidity diffusion coefficient on the concrete surface gradually increased, while during the wetting procedure, the Chloride content inside the concrete increased, and the humidity diffusion coefficient gradually decreased. However, the bound Chloride content inside the concrete is not affected by the humidity level in the environment. In the wetting environment, the calcium hydroxide in the matrix is gradually consumed, and the Chloride diffuses to the matrix to form more Friedel's salt and calcium carbonate. Moreover, lowering the w/b ratio or increasing the ambient humidity can enhance the formation of more hydrated compounds (C–S–H gel), which can reduce the total porosity and can also improve the ability of concrete to resist Chloride diffusion. Overall, this study provides a better understanding of and insight into the design and maintenance of seaside RC infrastructures.
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| 50. |
- Jin, Hesong, et al.
(författare)
-
Effects of limestone calcined clay, fly ash and seawater on early hydrating behavior, mechanical properties, microscopic performance and sustainability of eco-friendly cement-based pastes
- 2024
-
Ingår i: Journal of Thermal Analysis and Calorimetry. - 1388-6150 .- 1588-2926. ; 149:5, s. 2087-2107
-
Tidskriftsartikel (refereegranskat)abstract
- In some remote areas or islands, the availability of freshwater for infrastructures has encountered a huge shortage, which has prompted more researchers to explore the possibility of applying seawater to design green concrete or composites. This study investigated the mechanical and microstructural properties of cement-based pastes (CBPs) mixed with fly ash (FA) and limestone calcined clay (LC2) and seawater at different curing ages. The early-age hydration, exothermic evolution, hydration phase, unconfined compressive strength (UCS), pore distribution, microstructure and sustainability of CBPs were investigated. It was observed that seawater has an accelerating effect on OPC hydration and can significantly enhance the early UCS. Combining with seawater, the pozzolanic activity of LC2/FA can result in generating more C–S–H gels. Therefore, the combination of LC2 or FA with seawater can obtain better the mechanical properties of CBPs. Besides, the micro characteristics of CBPs are observed by X-ray diffraction, thermogravimetric analysis, mercury-pressure porosimetry and scanning electron microscopy technologies, and it is revealed that seawater and SCMs play significant role in the micro morphology of CBPs due to silicate, semicarbonate, calcium aluminate, C–S–H gels. This also leads to a denser and more complex microstructure, which lowers the total porosity, obviously leads to transferring macropores into gel pores and enhances the UCS. Additionally, CBPs with FA or LC2 or seawater show about 1/6–1/5 lower embodied energy (EE), 1/6–1/5 lower embodied carbon (EC) and 1/6–1/4 lower cost than the typical CBPs with freshwater, CBPs with SCMs and seawater are even more perfect in terms of EE, EC and cost per unit UCS. Overall, this work assesses the feasibility of adding LC2/FA and seawater to CBPs, and also can provide a better insight into the applications of seawater cementitious composites for marine infrastructures.
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