Scholarly article on topic 'Biological Corrosion of Polymer-modified Cement Bound Materials Exposed to Activated Sludge in Sewage Treatment Plants'

Biological Corrosion of Polymer-modified Cement Bound Materials Exposed to Activated Sludge in Sewage Treatment Plants Academic research paper on "Materials engineering"

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Abstract of research paper on Materials engineering, author of scientific article — Maria Fiertak, Elżbieta Stanaszek-Tomal

Abstract This paper presents a study of 7 and 18 months exposure to activated sludge in a sewage treatment plant on its durability of Portland cement materials (CEM I) containing polymer modifications. The samples were tested for tightness and flexural strength after exposure to a sludge environment containing 108-109 microorganisms per ml, including filamentous heterotrophic bacteria, protozoa, rhizopoda, ciliates and fungi. The corrosion processes were identified by COD analysis, by aid of a scanning microscope with an X-ray microanalyzer and by mercury porosimetry. Studies have shown, that selecting the polymer admixture to of cement materials should be considered: the parameters rallying improvement (tightness, adhesion, chemical resistance), but also the conditions of use mainly susceptibility to biological corrosion of polymers.

Academic research paper on topic "Biological Corrosion of Polymer-modified Cement Bound Materials Exposed to Activated Sludge in Sewage Treatment Plants"

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Procedía Engineering 65 (2013) 335 - 340

Procedía Engineering

www.elsevier.com/locate/procedia

Concrete and Concrete Structures 2013 Conference

Biological Corrosion ofPolymer-Modified Cement Bound Materials Exposed to Activated Sludge in Sewage Treatment Plants

Maria Fiertaka, Elzbieta Stanaszek-Tomala'*

a Chair of Building Materials Technology and Structure Protection, Faculty of Civil Engineering, Cracow University of Technology, 24

Warszawska St., 31-155 Cracow, Poland

Abstract

This paper presents a study of 7 and 18 months exposure to activated sludge in a sewage treatment plant on its durability of Portland cement materials (CEM I) containing polymer modifications. The samples were tested for tightness and flexural strength after exposure to a sludge environment containing 108-109 microorganisms per ml, including filamentous heterotrophic bacteria, protozoa, rhizopoda, ciliates and fungi. The corrosion processes were identified by COD analysis, by aid of a scanning microscope with an X-ray microanalyzer and by mercury porosimetry.

Studies have shown, that selecting the polymer admixture to of cement materials should be considered: the parameters rallying improvement (tightness, adhesion, chemical resistance), but also the conditions of use mainly susceptibility to biological corrosion of polymers.

© 2013TheAuthors. PublishedbyElsevier Ltd.

Selectionand peer-reviewunderresponsibilityof University of Zilina, FacultyofCivil Engineering,Department ofStructures andBridges

Keywords: Microorganisms; cement materials; biodeterioration; activated sludge; sewage treatment plants;

1. Introduction

Microbiological risk of building materials is defined as biodeterioration, the distribution and biological corrosion. It defines the processes that alteration of the material, caused by the activity of living organisms. These processes are classified into several groups: chemical assimilation and chemical dissimilation biodeterioration and biofouling.

* Tel.:+48- 12-628- 23-45. E-mail address: estanaszek-tomal@pk.edu.pl

1877-7058 © 2013 The Authors. Published by Elsevier Ltd.

Selection and peer-review under responsibility of University of Zilina, Faculty of Civil Engineering, Department of Structures and Bridges doi: 10.1016/j.proeng.2013.09.051

Processes described in the literature biodeterioration of building materials are generally processes of chemical assimilation biodeterioration that occurs when the material is degraded because of its nutritional value. Much rarer are reports of research of chemical dissimilation biodeterioration. It occurs when the microbial metabolites damage the material, causing its corrosion, pigmentation or the separation of toxic metabolites into the material. Surveys conducted on cement materials are related to the bacterial action of corrosive acids, carbonate or sulfate concrete [13]. Described are the different methods for the determination of both type of microorganisms that inhabit the building materials and mycotoxins that are produced by them. Relatively, few is known about changes in the properties of minerals as a result of the simultaneous action of fungi and bacteria. Practically, there are no reports concerns the influence of microorganisms on the properties of cement mortar with an admixture polymers. The research carried out and literature sources on corrosion of the materials of the polymer modifiers stimulated by microorganisms are ambiguous and even contradictory [4,5]. On one hand, they demonstrated in positive role of polymers, which involves sealing up structure of materials [6]. On the other hand increased development of biocorrosion associated with organic material as a source of food especially for fungi that inhabit the material under favorable conditions (high humidity, temperature) [7].

Polymer additives for of cement materials have gained a strong position [8] of modern building materials. Choosing a polymeric modifier take into account three parameters that may be improving, namely, sealing, adhesion and chemical resistance. This latter quality is usually associated with resistance against aqueous solutions of aggressive substances. Therefore, it becomes important to answer the question, whether and to what extent cement mortar with an admixture the polymer are susceptible to microbial growth and the mechanism of their destructive actions.

Table 1. The nomenclature used in the article.

Nomenclature

CNP Portland cement unmodified

CMPA Portland cement modified acrylic resin

CMPSi Portland cement modified polisiloxane resin

CMPK Portland cement modified polycarboxylate resin

The research carried out by the authors on the impact of acrylic, polysiloxan and polycarboxylate (see table 1) resin modifiers (3% by weight of cement) in CEM I Portland cement (42,5R) on the development of biological corrosion as a result of exposure to an environment containing 10s-109 microorganisms per ml, including filamentous heterotrophic bacteria (Sphaerotilus miteus, Leptotharix and Pseudomonas, Eutrobacter, Vibris-aeromonas, Flauobacterium, Zooglea venigera), protozoa, rhizopoda, ciliates and fungi (Geotriches, Oospora, Penicillum). Besides mortar is carried out without the addition of a polymeric modifier (CNP). The study, which was published in the journal Ochrona przed Korozjq No. 5/2012 [9], involved testing of two groups of samples sized 20x20x160 mm, one was kept for seven months in activated sludge in a sewage treatment plant, while the control group was kept wet in a laboratory for the same period of time. The tests revealed that:

• Even short exposure to microorganisms affected the tightness of cement materials, including those containing organic modifiers;

• The microorganisms initiated two processes acting in opposite directions: on the one hand, unsealing of structure, but on the other hand ettringite (a product of sulphate corrosion) and calcium carbonate were deposited in the microcracks. Therefore, no changes in the strength were found after the seven months exposure to microorganisms;

• Changes in the properties of mortars depends on the type the polymer used. Substantial changes occur short exposure and include resins: acrylic and siloxane;

• Materials modified with polycarboxylate resins (used as superplasticizers) demonstrated levels of resistance comparable to non-modified cement materials;

• The CaC03 deposition was caused by mineralisation (the decomposition of organic matter by microorganisms to simple mineral compounds such as CO2) of organic substances, including the polymer modifiers contained in cement material;

• Further research would be necessary to determine changes of the properties of cement matrixes after a longer period exposure.

The research continued for another 11 months. Its results and these interpretation are presented below.

2. Testing methods

To evaluate of the processes were applied changes:

• mass humidity (|1m), water absorption (n0) and capillary rise (pk) - determined in accordance with PN-85/B-04500;

• flexural strength (fc), test was performed on strength testing machine ZWICK and assessed in accordance with PN-EN 1015-11:2001/A1:2007;

• the chemical oxygen demand (COD), which was studied by the heat chromate using a photometer Slandi LF 205;

• the structure, which was studied in a scanning microscope with field emission FEI Nova NanoSEM 200 and mercury porosimeter Quantachrome Poremaster NovalOOOe.

The research was carried as part of the research project N N506 218738.

3. Results

The tightness of cement materials was investigated by looking at mass humidity, water absorption and capillary action. The highlights of that research are shown on Table 2 which present the average values of six tests after exposure to microorganisms for 7 and 18 months. Scatter of results did not exceed 0,1%.

Table 2. Mass moisture, water absorption, capillary rise, water extract and chemical oxygen demand of cement mortars.

Time Properties

[month] Mortar CNP CMPA CMPSi CMPK

mass humidity control samples [% of mass] 2.523 3.029 2.735 2.036

■ft capillary rise control samples [% of mass] 2.932 2.602 2.5 1.543

1 = ■3 ^ water absorption control samples [% of mass] 6.745 6.305 6.266 4.928

2 1 pH control samples 12.67 12.78 12.67 12.75

COD [mg02/dm3] control samples 6.3 46 40 14.1

mass humidity mortar contaminated [% of mass] 7.423 8.205 7.721 4.648

capillary rise mortar contaminated [% of mass] 2.001 2.389 2.075 1.821

= water absorption mortar contaminated [% of mass] 8.066 8.644 7.962 4.762

pH mortar contaminated 12.23 12.58 12.34 12.48

COD [mg02/dm3] mortar contaminated 43.10 134 92 36

mass humidity mortar contaminated [% of mass] 9.142 9.267 8.761 5.489

capillary rise mortar contaminated [% of mass] 3.149 2.766 2.780 2.234

= X water absorption mortar contaminated [% of mass] 8.485 8.482 7.921 4.744

pH mortar contaminated 11.67 11.78 12.27 12.12

COD [mg02/dm3] mortar contaminated 86.16 249.24 170.20 67.32

The acrylic and polysiloxan resins used as modifiers of cement materials had only a minor negative effect on the initial water absorption, at 6.5% and 7.2%, respectively, but the polycarboxilate resin reduced water absorption of cement by ca. 30%. The 7-month exposure to a microorganism environment increased the water absorption in the two types of materials from about 20% (CNP) to 37% (CMPA) and reduced it in the case of one material (CMPK), when compared to the initial water absorption test materials. The further 11 months, practically no effect on the characteristics of differentiation.

Much greater change occurred in the mass humidity of the samples, which increased between 2 and 3 times compared to the control samples. After 18 months, the wetness increased by a factor of 3-4, which was more than the increase in water absorption of the samples (see: Table 2) as a result of the samples being covered by highly

absorbent biofilm. Also capillary rise increased after 18 months from ca. 20% to 50% compared to the results obtained after 7-month exposure to activated sludge.

The changes described above, which represented a reduction in tightness of the cement materials, had a minor effect on the flexural strength of most of the samples, including practical intents no change to the CNP, CMPA and CMPSi samples. CMPK was the only exception with its flexural strength increased by 45% after the first seven months and then decreased by ca. 20%, as shown on Fig. lb.

The pH of the extracted water (Table 2) did not change in the polymer-modified CEM I Portland cement materials, but after 18-months exposure was reduced, the strongest in the mortar non-modified cement and in polyacrylic resin modified cement. This suggests a loss of capability to passivate reinforcement steel. The pH of 11.8 achieved when the mortar was collected from across volume of the sample, and while the surface layer had a pH<9.

Fig. 1. Changes of (a) porosity and; (b) flexural strength of control mortars and contaminated biologically.

The chemical oxygen demand (COD) testing (Table 2) revealed the demand for oxygen used up for the oxidation of organic and inorganic compounds in the samples tested. In non-modified samples only inorganic compounds were oxidised. Therefore it is plausible to assume that the nearly 7x and 14x increase in the COD of CNP cements was linked to the oxidation of organic compounds exposed to biological contamination for 7 and 18 months, respectively. In the control samples with modifiers, oxygen was also used to oxidise organic modifiers and for this reason their COD rose by more than 7, 6 and 2 times respectively, in non-contaminated CMPA, CMPSi and CMPKA cement. The contamination of modified cement materials caused a very strong increase in their oxygen demand after 7 and 18 months. The increase in cements with acrylic resin was 134 and 249.24 mg02/dm3; with polysiloxan resin was 92 and 170 mg02/dm3; and with polycarboxylate resin it was 36 and 67 mg02/dm3. These values illustrate the susceptibility of polymer-modified cement mortar to biodeterioration.

The investigation of the porosity of materials after 18 months exposure to activated sludge (see in Figure la) showed:

• a significant increase in pore volume in the range of 3 ^ 10000 nm pore diameter for CNP;

• a significant reduction of the pore volume for CMPA and CMPSi throughout the range of the pore diameter;

• pore volume increase to 20 nm and a reduction in the range of 20 + 1000 nm pore diameter for CMPK compared to the respective control samples.

point 1

0.90 1.S0 2.70 3.60 4.50

Fig. 2. The observed: (a) unsealing (cracks) the CNP structure; (b) the presence of ettringite in the pores of the CMP A; (c) EDS analysis at the

point.

C I.-.. CaKa

point 1

¡2 =5 0

il .""kid I«™» K Ka 1

......

Fig. 3. The observed: (a) the pores of CMPSi filled with gypsum; (b) EDS analysis at the point, a b

r<!llfo

point 1

AlKai u CIKb , ClKa

0.90 1 80 2.70 3.60 4.50

Fig. 4. The observed (a) mineralization of calcium carbonate CMPK; (b) EDS analysis at the point.

The scanning microscopic studies was only performed on the external layers of the samples (Fig. 2, 3, 4), but not on the surface-covering biofilm. Considerable quantities of calcium carbonate were found in the pores and microcracking of the contaminated samples. Secondary ettringite was also found, crystallised in the openings as shown in Figures 2b. The figures show 1600x enlargements of the corrosion products and an EDS analysis at points shown on the photos. Crystals of CaC03 and 3CaO ■ AI2O3 • 3CaS04 • 32H2O were observed in all the samples tested. Their concentrations diminished at rates that depended on the type of cement moratr, i.e. in the following order: CMPA, CMPSi, CNP and CMPK. Additionally, the same fungi that were detected in the biofilm on the non-modified samples were also detected inside the modified samples.

4. Discussion of the results

The study into the impact of microorganisms in activated sludge in sewage treatment plants on polymer-modified cement materials showed that:

• After 18-months exposure, changes that occurred depend on the type of polymer modifier. The greatest change was observed in non-modified cements and cements modified with acrylic and polysiloxan resins;

• Polycarboxylate resins (used in concrete technology as superplasticizers) were also affected by microorganisms, but to a much lesser degree. Indeed, they displayed adverse changes to capillary rise, mass humidity, COD and significant changes to flexural strength;

• Action of microorganisms on cement-polymer composites causes a continuous decrease of pH (water extract) which is especially important in the assessment of their properties in relation to the protection of reinforcing steel;

• The selection of bending strength and water absorbability as the diagnostic indicators does not fully illustrate changes of the structure of the materials caused by biological corrosion. Indeed, there were two contradictory processes: loss of tightness due to microcracking and deposition of sulphuric corrosion products (ettringite and gypsum) and as well as in to the formed microcracks of calcium carbonate produced during the mineralisation of organic substances including the polymer modifiers;

• COD analysis has provided a good indicator of the biological contamination. COD illustrates not only the concentration of microorganisms in the materials tested, but also its influence on their properties.

5. Conclusions

Summarize studies and the results obtained should be noted that selecting organic modifier for cement materials need to consider a few things. On the one hand, consider the basic parameters, that are improving, ie tightness, adhesion and chemical resistance. On the other hand, the conditions of use of the building in terms of susceptibility of polymers to biological corrosion.

References

[1] J. Montena, E. Vincke, A. Beeldens, N. De Belie, L. Taerwe, D. Van Gemert and W. Verstraete, Chemical, microbiological, and in situ test methods forbiogenic sulfuric acid corrosion of concrete, Cement and Concrete Research, Vol.30, No 4, 2000, p. 623-634.

[2] V.G. Rosato, Pathologies and biological growths on concrete dams in tropical and arid environments in Argentina, Materials and Structures, 41, 2008, p. 1327-1331.

[3] W. De Muynck, V. De Belie, Improvement of concrete durability with the aid of bacteria, Proceedings of the First International Conference on Self Healing Materials, April 2007, p. 18-20.

[4] E. Vincke, E. Van Wanseele, J. Monteny, A. Beeldens, Influence of polymer addition on biogenic sulfuric acid attack of concrete, International Biodeterioration & Biodégradation, Issue 4, 2002, p. 283-292.

[5] J.D. Gu, R. Mitchell, Microbiological influenced corrosion, degradation and deterioration of polymeric materials of space application, Chinese Journal of Materials Research, 9, 1995, p. 473-489.

[6] H. Lajili, C.P. Devillers, C.C. Grambin-Lapeyre, C.J.P. Bournaz, Alteration of a cement matrix subjected to biolixiviation test, Materials and Structures 41, 2008, p.1633-1645.

[7] Ji-Dong Gu, T.E. Fordb, N.S. Berkec, R. Mitchell, Biodeterioration of concrete by the fungus Fusarium, International Biodeterioration & Biodégradation, 41, 1998, p.101-109.

[8] L. Czarnecki, P. Lukowski, Betony cementowo-polimerowe, CWB 5, 2010, p.243-257.

[9] M. Fiertak, E. Stanaszek-Tomal, Trwalosc tworzyw cementowych modyfikowanych polimerami poddanych dzialaniu mikroorganizmôw, Ochronaprzed Korozj^, 5, 2012, p. 266-268.

[10]PN-85/B-04500, Zaprawy budowlane - Badania cech fizycznych i wytrzymalosciowych, 1985.

[11]PN-EN 1015-11:2001/A1:2007, Metody badan zapraw do murôw. Czçsc 11: Okreslenie wytrzymalosci na zginanie i sciskanie stwardnialej zaprawy (oryg.), 2007.