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Materials Research

Print version ISSN 1516-1439

Mat. Res. vol.12 no.4 São Carlos  2009

http://dx.doi.org/10.1590/S1516-14392009000400015 

REGULAR ARTICLES

 

Biodeterioration of coastal concrete structures by Macro algae - Chaetomorpha antennina

 

 

Sriharibabu JayakumarI; Raman SaravananeII,*

IAssistant Professor, Sri Manakula Vinayagar Engineering College, Madagadipet,Pondicherry, 605 107, India
IIAssistant Professor, Environmental Engineering Laboratory, Department of Civil Engineering, Pondicherry Engineering College, Pondicherry - 605 014, India

 

 


ABSTRACT

Puducherry is a coastal region in India where the growth of Chaetomorpha antennina is very abundant on all marine concrete structures. Though the detrimental effect of this Macro algaeChaetomorpha antennina is secondary, its effect has to be ascertained. To know its effect, M20 grade concrete cubes were cast and kept in the coastal area where there is abundant growth of Chaetomorpha antennina and also laboratory simulation has been carried out. The basic mechanism by which Chaetomorpha antennina deteriorates concrete structures has been highlighted and also the detrimental effect on the algal grown concrete surface were ascertained using SEM, EDX and XRD. The result showed that there is sustainable effect by the marine algae on the concrete surface.

Keywords: Marine algae, marine concrete structures, Chaetomorpha antennina, deterioration


 

 

1. Introduction

About 71% of the world is surrounded by ocean. The most important herbivores in ocean are phytoplankton and benthic algae. The marine algae familiarly known as seaweeds are a diverse group of photoautotrophic organisms of various shapes (filamentous, ribbonlike, or platelike) that contain pigments such as chlorophyll, carotenoids, and xanthophylls. The growth of marine algae is abundant in coastal area since sandy beaches provide excellent attachment points in a constantly moving and dynamic environment of the sandy shore. The first type of plant life to attach itself to the coastal concrete structure is filamentous macroalage. The colonisation is likely to be, due to the constant abrasion of the lower regions by the action of the tide lifting the sand and small stones from around the base of the structure. A number of seaweeds can be found in this type of environment although there are usually a few dominant species like Chaetomorpha antennina. These green algae are classified in the Phylum Chlorophyta. Many species of green algae grow attached to rocky and concrete substrates on or near the ocean's surface. In general, because they are attached to a substrate, they are not tossed up on the beach by the waves. These macroalgae are able to obtain different elements for their metabolism e.g. calcium, aluminum, silicon, iron etc by biosolubilization of materials. Such biosolubilization involves the production of organic acids by the metabolic activity of macroalgae. This acid deterioration is one of the best known biogeochemical mechanism of concrete decay16,17,18.

Puducherry is an Indian coastal region on the Bay of Bengal. There are many marine structures located in the coastal area. These structures deteriorate due to the macro flora Figure 1, 2 and 3 present in the sea water3,4,5,6,7. Though a secondary deterioration process, there is significant detrimental effect due to this macro flora9,14,15. The ambient condition prevailing in the coastal area helps the growth of Chaetomorpha antennina round the year. The growth of Chaetomorpha antennina on concrete structure in Puducherry region is found almost on all the structures. This study aims to ascertain the effect of marine chlorophyceae Chaetomorpha antennina on concrete structure. For this, concrete cubes were immersed in the coastal area where there is abundant growth of Chaetomorpha antennina and also simulated in the laboratory. Apart from this phycochemical analysis of Chaetomorpha antennina was carried on to find the chemical constituents occurring in the algae due to secondary metabolites. The surface of the concrete cube was chipped where there is a growth of Chaetomorpha antennina. Their morphological characteristics were observed using Scanning Electron Microscope (SEM) and surface analysis was done using Energy Dispersive X-ray analysis (EDAX). Mineralogical analysis is done using X-ray Diffraction (XRD).

 

2. Materials and Methods

2.1. Concrete cubes

To ascertain the effect of Chaetomorpha antennina on concrete, concrete cubes of M20 grade (Recommended in Indian Standard (IS 456-2000), M20 grade concrete mix was used for normal conditionwithw/c ratio 0.5) were prepared using OPC 53 Grade cement. OPC- 53 Grade was used since it is a high quality cement prepared from the finest raw material owing to optimum water demand, it contributes to a very low co-efficient of permeability of the concrete prepared. This improves the density of the concrete matrix and increases the durability of the concrete.

2.2. Methods

The procedures followed to determine the effects of Chaetomorpha antennina on concrete cubes were:

a) To culture Chaetomorpha antennina naturally, several concrete cubes were kept in the coastal area where there was abundant growth of Chaetomorpha antennina (Figure 4);

 

 

b) Concrete cubes were allowed to cure in ordinary water; and

c) Laboratory simulation was carried out to culture the Macro algae on the concrete cube. For the simulation, Humidity oven was used (Figures 5 and 6). The details of the oven are as follows:

 

 

2.2.1. Construction

Double walled, inner Stainless Steel.304 / 316 grade and outer Stainless Steel or GI dully Epoxy Powder coat / finish, gap filled with Glass wool with outer metallic door provided. Chamber is illuminated with bulb.

2.2.2. Cooling facility

By Hermetically sealed branded compressor coupled with air cooled condensing unit fitted with Motor, fan blade, Electrical Accessories etc. Mounted on bottom of unit on heavy base frame.

2.2.3. Humidity creation

Humidity Created with Steam and injected into working chamber.

2.2.4 Heating facility

Provided by long lasting Stainless Steel Tubular Heater with fins

2.2.5. Temperature control

Electronic Digital Temperature Controller-Cum Indicator with Dry Bulb and Wet Bulb principle.

The ambient condition maintained in the chamber is as follows. Samples were incubated under lighting conditions of 2000 lx, 12 h/day with a ''daylight'' with white fluorescent lamp. The temperature was maintained at 30 ºC. The relative humidity was maintained as 90%3.

To ascertain the detrimental effect of marine algae on concrete, 50 cubes were kept in coastal area where there is abundant growth of algae. Every three months, four cubes were tested to ascertain the effect of marine algae on the cubes. Totally 20 cubes has been tested for the past one and half years. The cubes tested after nine months only showed predominant changes in the surface analysis done using SEM and EDAX and mineralogical analysis using XRD. Moreover the concrete cubes showed a weight loss of around 0.4 kg after 9 months.

The laboratory simulated concrete cubes were started testing after six months and here also there is sustainable effect after eight months only and weight loss in this case is ± 0.6 kg.

2.3. Samples and microbiological procedures

Concrete sample for analysis were taken from the concrete cube where Chaetomorpha antennina had attached itself from natural and artificial conditions. Before chipping the concrete surface for analysis, the biomass namely the marine chlorophyceae grown on the surface was scarped and placed in sterile plastic vessel and taken to the laboratory for identification. Apart from this concrete sample was chipped from the concrete cubes immersed in ordinary water in the laboratory.

2.4. Morphological observations and surface analysis

SEM was employed in studying the morphological characteristics of the structure. For this, samples were dehydrated by using an acetone series; critical point dried; and gold coated at 10-3mm Hg in sputter coat apparatus prior to SEM observations and EDAX analysis using a Hitachi S-3400N microscope.

2.5. Mineralogical characterization

The concrete samples were analyzed by powder X-ray Diffraction using Philips® PW1710 diffractometer with an automatic slit under the following conditions: emission radiation = CuKα, voltage = 40kV, intensity = 30 nA, gonimeter speed = 0,1 20/s. Gonimeter calibration was performed using silica standard. Data was interpreted using X'Pert High Score. Samples were ground in agar mortar and sieved to obtain a fraction of particle size less than 53 µm.

2.6. Phycochemical investigation of marine

Algae Chaetomorpha antennina

Marine algae Chaetomorpha antennina was collected from the coastal area of Puducherry. It was washed thoroughly to remove epiphytes, animal casting, attached detritus and sand particles. Then it was rinsed with distilled water and shadow dried with aeration to avoid the breakdown of secondary metabolites under sunlight and high temperature. The dried algal materials were chopped and milled. The following procedures were followed to isolate fatty acid from the dried algae;

• Extraction

The dried, chopped and milled algal material was then soaked in methanol (MeOH) in a large glass jar and was kept in the solvent for one month at room temperature. The extract of the material thus obtained was then filtered to remove all solid algal particles. Next it was evaporated on a rotary evaporator under reduced pressure. This yielded a dark green, thick residue;

• Saponification

An aliquot of the extract obtained was saponified with 10% KOH in 50% methanol and refluxed at 100 ºC for 6 hours. The mixture was then concentrated under reduced pressure and later H2O and diethyl ester (Et2O) were added. It was then shaken vigorously and the Et2O layer was separated. The Et2O layer was evaporated and used for fatty acid analysis;

• Esterification

All the fatty acid fractions obtained were subjected to methylation and 1.5 -2.0 mL ethereal diazomethane was added to the fatty acid mixture. The reaction mixture was left in the fuming chamber at room temperature, over night until dissolved. The aliquots were then directly injected to a Hewlett Packard® gas chromatograph - mass spectrophotometer (GC-MS) with 11/73 DEC computer system (Figure 7); and

• The methanolic extract of Chaetomorpha antennina revealed the presence of three saturated and six unsaturated fatty acids. The details are as show in Table 1.

2.7. Experimental Method - Flow Chart

Scheme 1 shows the schematic way of experimental method carried on to determine the effect of marine algae on concrete.

 

3. Result and Discussion

3.1. Macro-algae results

The species collected by scarping from the surface of concrete was identified as Chaetomorpha antennina (Figure 8).

 

 

3.2. Biodeterioration mechanisms

All surfaces in natural environments either aerial or sub-aerial are colonized by microorganisms and sub-aerial structures are colonized severely. Concrete is one material that can be readily colonized by Macro algae10 as it is revealed in this work. Macro algae are able to obtain several elements they need for their metabolism (e.g. calcium, aluminium, silicon, iron and potassium) from the concrete1,2,8,12,13 by biosolubilization in the presence of sea water. This biosolubilization process generally involves the production of various organic acids (Table 1) by the marine algae. The release of aggressive acids is one of the best known biogeochemical destructive mechanisms16,17,18 on concrete surfaces. It occurs through the leaching of binding materials with the consequent weakening of the crystal structure11. The final result of this type of biodeterioration is the physical and mechanical breakdown of the concrete matrix16.

3.3. Surface analysis by EDAX

SEM Figures 9, 10, 11, and EDAX results depicted in the Table 2, 3 and 4 and EDAX Figures 12, 13, and 14 elucidate that the base material has been modified. In the case of concrete cubes cured in ordinary water (control concrete) the silica level is 10.37% atom while calcium level is 9.18% atom. The EDAX results of the algal affected concrete shows that the calcium level has tremendously increased to 46.06% atom while silica level had decreased to 1.29% atom7,15. While in the case of simulated condition, calcium level had tremendously increased to 44.01% atom while silica level had increased to 4.23% atom. This proves that the calcium level in the algal affected concrete surface in natural and laboratory condition has increased tremendously. This high level of calcium is due to dissolution of calcium in concrete by organic acid produced by marine chlorophyceaeChaetomorpha antennina and precipitation of the organic salt upon dehydration. This is an indication of the alteration of the base material.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3.4. Mineralogical analysis by X-ray diffraction

Figure 15 shows the mineralogical analysis of concrete by XRD. The following are the crystals present in concrete specimen immersed in ordinary water Portlandite (Ca(OH)2), Silica, Yeelimite (Ca3Al6O12 · CaSO4), Gismondine (CaAl2Si2O8 · 4H2O), Dolomite (CaMg ( CO3)2), Maragarite-2 (CaAl2 ( Si2Al2 ) O10 ( OH )2), Calcium Silicate Hydroxide(Ca4H2O15.5Si5). The intensity of Portlandite is 34 at 18º, 34º, 50º while silica has a maximum intensity of 846 at 26º and Calcium Silicate Hydroxide has a intensity of 294 at 28º.

Figure 16 shows XRD pattern for algal attached concrete in natural condition. Compounds like Foshagite (Ca4H2O11Si3), Calcium Silicate Hydrate (Ca1.5SiO3.5 ·xH2O), Calcite(CaCO3), and Cristobalite(SiO2), Calcium Aluminum Chromium Oxide Hydrate are present here which are absent in the concrete specimen immersed in ordinary water (Control Concrete). Apart from this, it is noticed that the Silica intensity (1452) is very high at 21º compared to 26º which is 1119 only. Similarly the intensity of Calcium Silicate Hydroxide at 60ºis 64º in control concrete while it is 187 here. Compounds like Yeelimite, Gismondine and Portlandite are completely absent here. The absence of Portlandite (i.e. Calcium Hydroxide) shows that the alga has utilized it for its metabolic actiity1,2.

Figure 17 shows the XRD pattern for algae attached concrete in simulated condition. It is notified that the intensity of Yeelimite is very high (218) while there are two Silica peaks at 20º and 26º with more or less equal intensity of 126. The intensity of Calcium Silicate Hydroxide at 60ºis 64º in control concrete while it is 87 here. Apart from this new compounds like Cristobalite and Calcite are present here which is not notified in control concrete. Three peaks are noticeable for portlandite in control concrete which is totally absent in this case. Similarly Margarite-2 is not noticeable here. This shows that algae have utilized the calcium hydroxide for its metabolic activity1,2.

 

4. Conclusion

Samples obtained from the concrete cubes immersed in ordinary potable water and the Macro algae, Chaetomorpha antennina attached concrete surfaces from natural as well as laboratory simulated conditions were studied and the detrimental effect of metabolic activity of Chaetomorpha antennina on concrete was identified. Surface analysis obtained from EDAX suggests that biodeterioration may be affected through biosolubilization mechanism involving the production of metabolic acids by algae. EDAX results elucidate that the calcium level is tremendously increased to 46.06% in natural condition and 44.01% in laboratory simulation, while the silica level is decreased remarkably. XRD reveals that crystals like Yeelimite, Gismondine and Portlandite which are present in control concrete are found to be completely absent in algal attached concrete. This showed that the marine algae have utilized them for their metabolic activity. Hence, it is concluded that the base material has been altered severely. Thus the presence of chlorophyceae would serve as a primary support for heterotrophic biofilm, supporting organic matter for growth through photosynthesis.

 

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Received: June 26, 2009; Revised: October 8, 2009

 

 

* e-mail: saravananae@gmail.com

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