| 1. |
- Dias Ferreira Da Silva, Nelson, 1978, et al.
(författare)
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Application of LA-ICP-MS for meso-scale chloride profiling in concrete
- 2013
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Ingår i: Materials and Structures/Materiaux et Constructions. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 46:8, s. 1369-1381
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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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| 2. |
- Dias Ferreira Da Silva, Nelson, 1978, et al.
(författare)
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Chloride analysis in concrete by LA-ICP-MS
- 2011
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Ingår i: Advances in Construction Materials through Science and Engineering. ; RILEM PRO 79, s. 137-
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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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| 3. |
- Dias Ferreira Da Silva, Nelson, 1978, et al.
(författare)
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CHLORIDE CONTENTS AT THE CONCRETE-STEEL INTERFACE
- 2010
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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
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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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| 4. |
- Dias Ferreira Da Silva, Nelson, 1978
(författare)
-
Chloride Induced Corrosion of Reinforcement Steel in Concrete - Threshold Values and Ion Distributions at the Concrete-Steel Interface
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The chloride threshold value (Cth), or critical chloride content, is defined as the chloride concentration at the depth of the reinforcement, which initiates the depassivation of steel in concrete. However, very limited information is available regarding the chloride distributions at the interface with the steel. The main objective of this work is to improve the knowledge and understanding about the mechanisms leading to depassivation of steel in concrete, by studying the influence of the steel surface condition and the concrete-steel interface on the corrosion initiation and the chloride distributions along the concrete-steel interface at the time of depassivation. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used for spatial resolved chloride profiling in cementitious materials. A range of materials with increasing degree of heterogeneity (i.e. cement paste, mortar and concrete) and exposed to chlorides under different conditions (i.e. mixed-in, diffused and migrated) was studied. The system was optimized for maximum chloride sensitivity, while allowing for the detection of other elements such as calcium and iron. At a scan speed of 100 µm/s, a spatial resolution of 300-400 µm and limits of detection of 0.05 wt% of cement were determined. The chloride distributions along the concrete-steel interface and possible differences between passive and active regions were studied, for different steel surface conditions under free corrosion conditions as well as under potentiostatic control. The results have shown that along the interface, a range of chloride concentrations can be expected, with higher values around the corroding active sites. It was suggested that chlorides preferentially accumulate at the anodic regions even prior to depassivation, leading to pitting corrosion. A local migration mechanism was proposed to account for the chloride build-up around the anode regions, due to the formation of local potential gradients on the passive layer of the steel as a result of differences in the moisture content and oxygen availability, concentration of aggressive species and metallurgical properties, such as inclusions or mill-scale along the steel. In particular the steel surface condition and the presence of air voids at the concrete-steel interface were recognized as major factors influencing the development of potential gradients along the steel surface.
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| 5. |
- Dias Ferreira Da Silva, Nelson, 1978, et al.
(författare)
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Chloride profiles along the concrete-steel interface
- 2013
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Ingår i: International Journal of Structural Engineering. - 1758-7328 .- 1758-7336. ; 4:1/2, s. 100-112
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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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| 6. |
- Dias Ferreira Da Silva, Nelson, 1978, et al.
(författare)
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Critical Conditions for Depassivation of Steel in Concrete: Interface Chloride Profiles
- 2011
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Ingår i: Nordic Concrete Research. ; Publication No. 43, s. 115-118
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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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| 7. |
- Dias Ferreira Da Silva, Nelson, 1978, et al.
(författare)
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Critical Conditions for Depassivation of Steel in Concrete: Interface Chloride Profiles and Steel Surface Condition
- 2012
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Ingår i: Nordic Concrete Research. - 0800-6377. ; 45, s. 111-123
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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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