Assessing the preservation state of a Romanian historic ...Assessing the preservation state of a...
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ECOTERRA - Journal of Environmental Research and Protection www.ecoterra-online.ro 2017, Volume 14, Issue 3 Assessing the preservation state of a Romanian historic concrete icon – the Constanta Casino 1 Florina-Diana Dumitru, 1 Ana-Maria Panait, 1 Marius-Viorel Olteanu, 1 Elena Holban, 1 György Deák, 2 Robert Szép, 3 Ágnes Keresztesi 1 National Institute for Research and Development in Environmenal Protection, Bucharest, Romania; 2 University Sapientia, Miercurea-Ciuc, Romania; 3 Babeș-Bolyai University, Cluj- Napoca, Romania. Corresponding author: Á. Keresztesi, keresztesiagi@gmail Abstract. Assessing the corrosion condition and structural modifications which occur in old concrete structures could provide valuable information regarding the preservation state of the historical construction as well as the needed support for future maintenance works in order to minimize as much as possible the loss of these structures with important historical value. This paper discusses the compositional modifications which occur in an old concrete in correlation with the particularities of the exploitation environment. This investigation could provide the support for the initiation of a monitoring program related to the assessment of concrete structures damage and implementation of minimum maintenance measures. The investigation methods were scanning electron microscopy (SEM), energy- dispersive X-ray spectroscopy (EDS) and X-ray fluorescence (XRF) analyses. Key Words: concrete corrosion, SEM analyses, X-ray fluorescence analyses, chemistry. Introduction. The marine environment, especially the sea water, represents a real challenge for reinforced concrete durability due to its charge with aggressive chemical species (Mg 2+ , Cl - , alkalis etc.) that have the capacity to start the deterioration mechanisms of concrete (mainly of reinforcements by their depassivation) (Biczok 1965; Dupray et al 2010). On the contrary, the river or lake waters, which are generally poorly charged with saline ions (Kucche et al 2015; Anghel et al 2016; Anghel et al 2017a; Anghel et al 2017b) subject the concrete structures to dealkalinization or carbonation corrosion processes (Teoreanu et al 1982; Neville 2003; Wang 2014). From the reaction of alkalis (Na 2 O and K 2 O) with reactive aggregates from concrete composition, an expansive silica gel is formed, which causes irregular cracking and the early degradation of the concrete (Winter 2012). The acid ions, present in the concrete exposure environment, as well as magnesium ions, which have greater destructive power of the hydrated products of cement paste, lead to the loosing of binder properties of cement matrix (Song & Saraswathy 2007; Moncea et al 2012a). Concrete structures located in marine environment are particularly in danger due to the reinforcement corrosion in presence of Cl - , from sea water and coastal air (Poteras et al 2014) conducing to the reduction of the reinforcement bars cross-section area (Duffó et al 2004; Duffó et al 2012). For the Romanian coastal structures, constructed over more than 70 years ago, were not adopted any monitoring plan or any preventive action for their deterioration. In order to maintain the initial characteristics of concrete, making it able to satisfy the functions for which was designed, and also in order to avoid expensive repair costs, it is extremely important the control of structure behavior over time. The current work presents relevant results related to preservation state of some old concrete constructions located in the Romanian coastline, enhancing the available information in the field. For this purpose the old concrete structures depicted by coastal defense structures embedded into Constanta casino sidewalls were localized. In order to establish the level of degradation, in situ visual assessment was performed. Subsequently, concrete specimens were sampled and laboratory tested. The chemical species implied in corrosion processes (Fe 2 O 3 , MgO, Na 2 O, K 2 O and Cl - ) were determined by using X-ray fluorescence (XRF) difractometer. In order to identify the corrosion products, formed especially at the concrete/metal reinforcement interface, microstructure analyses using scanning electron microscopy (SEM) coupled with dispersive energy spectroscopy (EDS) were performed.
Transcript of Assessing the preservation state of a Romanian historic ...Assessing the preservation state of a...
ECOTERRA - Journal of Environmental Research and Protection
www.ecoterra-online.ro 2017, Volume 14, Issue 3
Assessing the preservation state of a Romanian historic concrete icon – the Constanta Casino 1Florina-Diana Dumitru, 1Ana-Maria Panait, 1Marius-Viorel Olteanu, 1Elena Holban, 1György Deák, 2Robert Szép, 3Ágnes Keresztesi 1 National Institute for Research and Development in Environmenal Protection, Bucharest, Romania; 2 University Sapientia, Miercurea-Ciuc, Romania; 3 Babeș-Bolyai University, Cluj-
Napoca, Romania. Corresponding author: Á. Keresztesi, keresztesiagi@gmail
Abstract. Assessing the corrosion condition and structural modifications which occur in old concrete structures could provide valuable information regarding the preservation state of the historical construction as well as the needed support for future maintenance works in order to minimize as much as possible the loss of these structures with important historical value. This paper discusses the compositional modifications which occur in an old concrete in correlation with the particularities of the exploitation environment. This investigation could provide the support for the initiation of a monitoring program related to the assessment of concrete structures damage and implementation of minimum maintenance measures. The investigation methods were scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray fluorescence (XRF) analyses. Key Words: concrete corrosion, SEM analyses, X-ray fluorescence analyses, chemistry.
Introduction. The marine environment, especially the sea water, represents a real challenge for reinforced concrete durability due to its charge with aggressive chemical species (Mg2+, Cl-, alkalis etc.) that have the capacity to start the deterioration mechanisms of concrete (mainly of reinforcements by their depassivation) (Biczok 1965; Dupray et al 2010). On the contrary, the river or lake waters, which are generally poorly charged with saline ions (Kucche et al 2015; Anghel et al 2016; Anghel et al 2017a; Anghel et al 2017b) subject the concrete structures to dealkalinization or carbonation corrosion processes (Teoreanu et al 1982; Neville 2003; Wang 2014). From the reaction of alkalis (Na2O and K2O) with reactive aggregates from concrete composition, an expansive silica gel is formed, which causes irregular cracking and the early degradation of the concrete (Winter 2012). The acid ions, present in the concrete exposure environment, as well as magnesium ions, which have greater destructive power of the hydrated products of cement paste, lead to the loosing of binder properties of cement matrix (Song & Saraswathy 2007; Moncea et al 2012a). Concrete structures located in marine environment are particularly in danger due to the reinforcement corrosion in presence of Cl-, from sea water and coastal air (Poteras et al 2014) conducing to the reduction of the reinforcement bars cross-section area (Duffó et al 2004; Duffó et al 2012). For the Romanian coastal structures, constructed over more than 70 years ago, were not adopted any monitoring plan or any preventive action for their deterioration. In order to maintain the initial characteristics of concrete, making it able to satisfy the functions for which was designed, and also in order to avoid expensive repair costs, it is extremely important the control of structure behavior over time. The current work presents relevant results related to preservation state of some old concrete constructions located in the Romanian coastline, enhancing the available information in the field. For this purpose the old concrete structures depicted by coastal defense structures embedded into Constanta casino sidewalls were localized. In order to establish the level of degradation, in situ visual assessment was performed. Subsequently, concrete specimens were sampled and laboratory tested. The chemical species implied in corrosion processes (Fe2O3, MgO, Na2O, K2O and Cl-) were determined by using X-ray fluorescence (XRF) difractometer. In order to identify the corrosion products, formed especially at the concrete/metal reinforcement interface, microstructure analyses using scanning electron microscopy (SEM) coupled with dispersive energy spectroscopy (EDS) were performed.
ECOTERRA - Journal of Environmental Research and Protection
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Material and Method. In order to investigate the compositional changes and the chemical species involved in corrosion processes the three concrete structures situated in the proximity of the Constanta Casino were located using a GPS station (Leica Viva GS 08 Plus) in the summer of 2015. To underline the effects produced by the exploitation environment (coastal marine environment) on the concrete after long periods of time (over 100 years), the ancient concrete was visually assessed in situ. The chemical and microstructure analyses were performed on concrete specimens sampled from the three coastal defense structures. The chemical species involved in corrosion process were identified by x-ray fluorescence (XRF) analyses performed with a Rigaku Supermini fluorescence spectrometer equipped with Pd target. Thus, the concrete specimens (sampled from each structure) were dried at T = 100°C for 2 hours, ground and sieved on a 90 μm mesh to remove the rough sand granules and to obtain a good homogeneity of the material. On the bulk specimens scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) analyses were performed, using the Hitachi SU-70 FE-SEM microscope equipped with EDS detector, X-Max N. For this reason the bulk specimens were preliminary dried at T = 55ºC for 3 hours (to prevent the ettringite decomposition) and subsequently coated with an AuPd conductive layer. Results and Discussion. The location of the investigated concrete structures is showed in Figure 1. It can be observed that these concrete structures are embedded into the coastal defense structures, found in the proximity of the Constanta Casino, being permanently exposed to the salt water.
Figure 1. Localization of the analyzed concrete constructions.
In situ preliminary assessment was performed in order to evaluate the concrete structure preservation state and the results are presented in Figure 2. The visual inspections showed the consequences of destructive effects of marine environment on concrete structures, especially manifested by exfoliation of concrete surface layer and visible macro cracks which affected the integrity of the construction. It can be noticed that some parts of the coastal defense concrete structures benefited from some refurbishment works (Figure 2a and b) but there are still large areas (especially around the firing holes of these ancient casemates) in which the metallic elements and the concrete structure affected by the aggressiveness of the marine environment can be observed (Figure 2c and d).
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a b c d
Figure 2. Visual aspects of the analyzed concrete structures. In Table 1 are presented the results of the XRF analyses performed on the three fine fractions (P1, P2 and P3) from the sampled concrete specimens. The interest oxides are those whose ions have corrosive action on concrete (MgO, alkali), the ones that could result by the corrosion process (Fe2O3) and the Cl- ion. The maximum allowed limits of oxides and chlorides in cements were considered as reference, these limits being imposed by ASTM C150-07 and SR EN 197-1 / 2011 standards. The alkalis values represent the equivalent alkalis (Na2O + 0.658K2O).
Table 1 Oxides proportion involved in concrete corrosion process determined by XRF
Oxides P1 (%) P2 (%) P3 (%) Allowed limits (%) CaO 41.8 32.6 20.1 - SiO2 26.4 28.1 59.3 -
MgO* 16.9 7.65 1.90 6 Al2O3 5.29 4.85 10.8 -
Fe2O3** 5.25** 21.2 2.19 6 SO3 0.895 1.32 0.512
Alkalis* 2.126254 1.911624 3.91544 0.6 TiO2 0.183 0.150 0.310 P2O5 0.117 0.104 0.226 MnO 0.0902 0.164 0.106 Cl- 0.67 1.56 0.1 0.1
* the oxides of whose ions have corrosive action on concrete; ** the oxides resulted by the corrosion process. The results showed that the concentration values of MgO determined for the three specimens are generally within limits, exceeding the maximum allowed limit only in the case of the P1 sample, which highlights that the magnesium aggressiveness is generally missing. However, for P1 sample the 16.9% value represent a concentration almost three times bigger than admissible limits (6%) which indicates that the magnesium corrosive ions, from the marine environment, exert their effect on concrete structure, taking into account that the P1 specimens originated from an area in permanently contact with the seawater.
The Fe2O3 content has values over the limits imposed by the standards for the P2 sample. Although this value, probably, is not characteristic for the depth layer of the concrete structure (the specimen was sampled from a surface layer) this result can be explained by diffusion in the concrete matrix of supplementary Fe quantities from metallic reinforcements, due to their excessive corrosion. Due to the high content of saline ions in the atmosphere, the concentrations of alkalis and chlorine exceeded the allowed limit values for all the analyzed samples.
SEM analyses coupled with EDS were selectively performed which allowed the identification of different crystalline formations developed as result of the cement hydration process or due to chemical interactions between the concrete matrix and marine environment. Thus in Figure 3 are presented SEM images of P1 sample which highlights the presence of calcium silicates hydrates (C-S-H), crystallized as needle shape, well
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defined on the concrete surface (Figure 3a) or into the pores (Figure 3b) underlining also the concrete’s age. These type of compounds also have an important role in the concrete strength, as observed in other investigations (Moncea et al 2012b; Munteanu et al 2012; Moncea & Georgescu 2013; Moncea et al 2016).
a b
Figure 3. SEM images of P1 sample representing C-S-H crystallized at the concrete surface (a) and into a pore (b).
In Figure 4 are presented the results of SEM analyses coupled with EDS performed on P2 sample. The image shows the presence of compact crystals disposed in circular arcs, attributed to the magnetite compound (Fe2O3), such formations being identified also in other works (Moncea et al 2017). The elongated prismatic formations, located near the magnetite cord, are assigned to the Ca(OH)2 compound.
The EDX spectra were performed punctually on the various crystalline formations and confirm the presence of the aforementioned products. For areas A (Figure 4b) and B (Figure 4c), the main element identified was Fe - element of magnetite composition and Mg as the second element after Fe. These results are in good correlation with XRF analyses in which Fe2O3 and MgO oxides exceed the allowed limit. Magnetite appears as an elliptic cordon that divides two areas of different chemistry and structure: a Ca rich area represented by prismatic formations assigned to Ca(OH)2 - C area, and an area where Mg is the predominant element.
a b
cd
Figure 4. SEM image coupled with EDS of P2 specimen.
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For the P3 concrete specimens, SEM analyses (Figure 5a) showed the presence of expansive silica gel, crystallized as large spherical formations (rosettes) and confirmed by EDS spectra (Figure 5b, c and d). This crystalline formation was formed as results of alkali-aggregate reactions (AAR) whose reaction product (expansive silica gel) lead to the concrete expansion and cracking.
a b
c d
Figure 5. SEM images (a) coupled with EDS spectra of P3 sample performed on different
areas of expansive silica gel (b, c and d) formed as result of AAR.
The EDS analyses performed in different points of the rosettes indicates mainly Ca and Si elements, the chemical species from silica gel composition, these kind of formations being identified also in other research papers (Winter 2012). Conclusions. The article presents a series of investigations performed on three samples representing parts of concrete defense coastal structures, situated in the proximity of the Constanta Casino. The visual inspections of the concrete structures showed a high level of degradation, with exfoliation, extensive cracking and some delaminations of the reinforced concrete, highlighting the poor state of their preservation. The lack of adequate restoration and preservation will, over time, causes the loss of structural integrity.
XRF analyses evidenced in the P1 sample high MgO proportions highlighting that the magnesium aggressiveness exert their effect on concrete structure considering that the P1 specimens is originated from an area in permanently contact with the seawater. The Fe2O3 content exceeded the allowed value for the P2 sample do to the diffusion in the concrete matrix of supplementary Fe quantities from metallic reinforcement. Due to the high content of saline ions in the atmosphere, the concentrations of alkali and chlorine exceed the allowed limit values for all the analyzed samples.
SEM analyses coupled with EDS emphasized the specific compounds of the cement stone as well as the corrosion products. Thus in P1 sample well crystallized C-S-H needles were highlighted, underlining the concrete’s age. The SEM image of P2 shows the presence of magnetite crystals disposed in circular arcs being interrelated with XRF analyses. The P3 microstructure revealed the presence of rosettes formations attributed to expansive silica gel formed as results of AAR. Based on these results, it can be assumed that all concrete structures subjected to investigations are under advanced corrosion process degradation.
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Acknowledgements. This work was financially supported by the National Authority for Scientific Research and Innovation, in the frame of Nucleu Program-Project PN 09 06 03 52: Research regarding Corrosion Produced by the Marine Environment on Coastal Constructions, Phase 2 - PN 09 06 03 52.2 / 2015: Modern investigation techniques of the microstructural particularities of materials used for the construction of old coastal structures. References Anghel A. M., Diacu E., Ilie M., Petrescu A., Ghita G., Marinescu F., Deák G., 2016
Statistical analysis of heavy metals concentration in water and sediments in the lower part of the Danube River – Romanian section. Revista de Chimie 67(11): 2151-2155.
Anghel A. M., Diacu E., Ilie M., Cimpoeru C., Marinescu F., Marcu E., Tociu C., 2017a Statistical correlations between physical and chemical indicators in order to assess the water quality of artificial lakes in south Romania, Bucharest-Ilfov area. Bionterface Research in Applied Chemistry 7(3):2048-2052.
Anghel A. M., Ilie M., Ghita G., Marinescu F., Deák G., 2017b Assessing the aquatic environment quality contaminated with heavy metals as a result of polymetallic mining in the North-West region of Romania using pollution indices. International Journal of Environmental Science and Development 8(2):111-115.
Biczok I., 1965 [The concrete corrosion and protection]. Technical Publishing House, Bucharest, 486 pp. [in Romanian]
Duffó G. S., Morris W., Raspini I., Saragovi C., 2004 A study of steel rebars embedded in concrete during 65 years. Corrosion Science 46(9):2143-2157.
Duffó G. S., Reinoso M., Ramos C. P., Farina S. B., 2012 Characterization of steel rebars embedded in a 70-year old concrete structure. Cement and Concrete Research 42:111-117.
Dupray S., Knights J., Robertshaw G., Wimpenny D., Woods Ballard B., 2010 The use of concrete in maritime engineering – a guide to good practice. London: CIRIA, Classic house, pp. 93-99.
Kucche K. J., Jamkar S. S., Sadgir P. A., 2015 Quality of water for making concrete: a review of literature. International Journal of Scientific and Research Publications 5(1):122-131.
Moncea A., Georgescu M., 2013 Influence of the calcium sulfate nature on the hydration and hardening processes of some ternary binders silicate-aluminate-sulfate. U.P.B. Scientific Bulletin, Series B 75(3):119-128.
Moncea A., Georgescu M., Voicu G., 2012a Sulfate and acid corrosion of some ternary binders consisting of Portland cement-calcium aluminate cement-calcium sulfate. Proc. 18, IBAUSIL, Weimar, pp. I-0540-I0547.
Moncea A., Georgescu M., Panait A., Munteanu C., 2012b Physical-mechanical properties of some ternary binders silicate-aluminate-sulfate. Romanian Journal of Materials 42(1):37-51.
Moncea M., Panait A., Deák G., Poteras, G., 2016 Binder microstructures developed during the hydration process in the system Portland cement – calcium aluminate cement – calcium sulfate. MRS Proceedings of XXIV International Materials Research Congress, Cancun, Mexic, vol. 1812, pp. 71-76.
Moncea M. A., Dumitru F. D., Panait A. M., 2017 Compositional and microstructural modifcations in concrete elements from Romanian coastline. Romanian Journal of Materials 47(3):345-352.
Munteanu C., Georgescu M., Moncea A., 2012 The influence of fly ash additions associated with polycarboxylate superpasticizer on the main properties of Portland cement pastes and mortars. Romanian Journal of Materials 42(4):350-355.
Neville A. M., 2003 [Concrete properties]. 4th edition. Technical Publishing House, Bucharest, pp. 505-556. [in Romanian]
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www.ecoterra-online.ro 2017, Volume 14, Issue 3
Poteras G., Moncea M. A., Panait A. M., 2014 Researches regarding marine environment corrosion on coastal structures. Turkish Journal of Fisheries and Aquatic Sciences 14:965-971.
Song H. W., Saraswathy V., 2007 Corrosion monitoring of reinforced concrete structures - a review. International Journal of Electrochemical Science 2:1-28.
Teoreanu I., Moldovan V., Nicolescu L., 1982 [Concrete durability]. Technical Publishing House, Bucharest, pp. 387-391. [in Romanian]
Wang H., 2014 The study of concrete durability in the case of Jinan Yellow River highway bridge. MSc Thesis, Chalmers University of Technology, Gothenburg, Sweden, pp. 13-23.
Winter N. B., 2012 Understanding cement: the fast star user-friendly insight into cement production, cement hydration and cement and concrete chemistry. Woodbridge, UK: WHD Microanalysis Consultants Ltd, ISBN-10:0957104529, 206 pp.
*** ASTM 150-07 Standard Specification for Portland Cement. *** SR EN 197-1:2011 Cement first part: Composition, specifications and conformity
criteria for common cements. Received: 31 July 2017. Accepted: 11 September 2017. Published online: 30 September 2017. Authors: Florina-Diana Dumitru, National institute for Research and Development in Environmenal Protection, 294 Splaiul Independenţei, 6th District, 060031, Bucharest, Romania, e-mail: [email protected] Ana-Maria Panit, National institute for Research and Development in Environmenal Protection, 294 Splaiul Independenţei, 6th District, 060031, Bucharest, Romania, e-mail: [email protected] Marius-Viorel Olteanu, National institute for Research and Development in Environmenal Protection, 294 Splaiul Independenţei, 6th District, 060031, Bucharest, Romania, e-mail: [email protected] Elena Holban, National institute for Research and Development in Environmenal Protection, 294 Splaiul Independenţei, 6th District, 060031, Bucharest, Romania, e-mail: [email protected] György Deák, National institute for Research and Development in Environmenal Protection, 294 Splaiul Independenţei, 6th District, 060031, Bucharest, Romania, e-mail: [email protected] Robert Szép, Sapientia Hungarian University of Transylvania, Faculty of Economics, Socio - Human Science and Engineering, Department of Bioengineering, Piaţa Libertăţii no. 1, 530104, Miercurea Ciuc, Romania, e-mail: [email protected] Ágnes Keresztesi, Babeș-Bolyai University, Institute for Doctoral Studies, Environmental Doctoral School, Fântânele 30, 400294, Cluj-Napoca, Romania, e-mail: [email protected] This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution and reproduction in any medium, provided the original author and source are credited. How to cite this article: Dumitru F. D., Panait A. M., Olteanu M. V, Holban E., Deák G., Szép R., Keresztesi Á., 2017 Assessing the preservation state of a Romanian historic concrete icon – the Constanta Casino. Ecoterra 14(3):1-7.
