BACTERAL CONCRETE- A BACTERAL CONCRETE- A CONCRETE FOR THE FUTURECONCRETE FOR THE FUTURE

BACTERAL CONCRETE- A BACTERAL CONCRETE- A CONCRETE FOR THE FUTURECONCRETE FOR THE FUTURE

-BY NILESH R. KAUTHE-BY NILESH R. KAUTHE

S.E.CIVILS.E.CIVIL

ROLL NO.33ROLL NO.33

CONTENTSCONTENTS• ABSTRACT

• INTRODUCTION

• PRINCIPLE

• APPLICATIONS

• EXPERIMENTAL INVESTIGATIONS

• SEM EXAMINATIONS

• CONCLUSIONS

• LIMITATIONS

• FUTURE SCOPE

• REFERENCES

ABSTRACTABSTRACT The paper presents the latest research of The paper presents the latest research of

producing concrete with the help of bacteria.producing concrete with the help of bacteria.

As a part of metabolism,these bacteria promotes As a part of metabolism,these bacteria promotes calcite precipitation forming CaCOcalcite precipitation forming CaCO3 ---3 ---which acts which acts as binding material. as binding material.

So it can be used as sealent in crack So it can be used as sealent in crack remediation,for sand & dyke consolidation etc.remediation,for sand & dyke consolidation etc.

This research has been introduced by This research has been introduced by “Dr.Ramakrishnan, Sookie Bang & Ramesh “Dr.Ramakrishnan, Sookie Bang & Ramesh Panchalan.”Panchalan.”

•The paper presents the research done by American scientists that tells us how bacteria can produce a bacteria can produce a cement !cement !

• When these bacteria are injected in sand, they form a natural layer of cement around each individual grain.

•The fact is that microbial metabolic activities promote calcite precipitationcalcite precipitation which acts as binding material.

•Bacillus pasteruiiBacillus pasteruii, a common soil bacterium can be used to induce calcite precipitation.

INTRODUTIONINTRODUTION

Sand grains

Calcite bridging

PRINCIPLEPRINCIPLE

As a part of metabolism, B.Pasteruii produces urease which catalyzes urea to produce CO2 & ammonia,

resulting in an increase of pH in the surroundings ,

leading to the precipitation of (Ca32+) & (CO32-) as CaCO3.

Ca2+ + Cell Cell-Ca2+ . . . . (1)

Cl- + HCO3- + NH3 NH4Cl + CO3

2- . . (2)

Cell-Ca2+ + CO32- Cell-CaCO3

APPLICATIONS APPLICATIONS • It is mostly used as microbial sealantmicrobial sealant for cracks &

fissures under the technique called MECR(i.e.microbiologically enhanced crack remediation. )

• for temporary cementationtemporary cementation of mine tailing heaps to prevent removal by wind/water & in bore wells to prevent collapse.

• This MECR allows to “set”“set” sand into a solid rock-type material without removal of sand from its location.

• Main advantage is that it pollution free & naturalpollution free & natural

• In- situ Cementation of retaining walls(domestic & commercial).

• A way to fight erosionto fight erosion in sand-stone monuments & historic buildings.

• Also has aesthetic equivalenceaesthetic equivalence in monuments & historic buildings.

• It can also be used to bioremediate polluted soilsto bioremediate polluted soils containing Strontium(Sr) & Barium(Ba).

• It offers chemically identical material that can be can be colour matchedcolour matched to the original material & made to retain the desired porosity.

• It is used for sand & dyke consolidationsand & dyke consolidation.

EXPERMENTAL INVESTIGATIONS

TO CHECK RESULTS OF

“MECR”

STRENGTH CHARACTERITSICS

EFFFECT ON STIFFNESS OF CEMENT MORTER BEAMS:

Increasing stiffness of beams by 23.9% for 3.2mm & 14% for 9.5mm

more effective remediation in shallower cracks more effective remediation in shallower cracks than in deeper ones. than in deeper ones.

EFFFECT ON COMPRESSIVE STRENGTH OF CEMENT MORTAR CUBES:- tested by “ Olsen compression testing machine”.Increased the compressive strengthcompressive strength by approx..80% when compared to that of controlled specimens.

EFFECT OF DIFF.. CONCENTRATIONS OF BACTERIAL CELLS:-

4.3 × 108, 8.6 × 108, 4.3 × 109 cells per ml. 8.6 × 108.6 × 108 8 cells per mlcells per ml conc... has found to induce

maximum compressive strength & was taken as optimum concentration.optimum concentration.

Higher conc.. did not give higher compressive strength values,because the greater population of bacteria did not have enough nutrients to multiply.

DURABILITY CHARACTERITSICS:-DURABILITY CHARACTERITSICS:-

The objective was to determine whether beams with bacteria performed better, when subjected to

ALKALINE, SULPHATE,ALKALINE, SULPHATE,

& FREEZE-THAW ATTACK& FREEZE-THAW ATTACK.

EFFECT ON ALKALY AGGREGATE EFFECT ON ALKALY AGGREGATE REACTIVITY OF CEMENT MORTAR REACTIVITY OF CEMENT MORTAR BEAMSBEAMS:-

with bacterial concentration of 1 x 106 cells/ml had 11% less mean expansion

with bacterial concentration of 1 x 107 cells/ml had 18% less mean expansion

with bacterial concentration of 8.6 x 108 cells/ml had 27% less mean expansion

The reduction in the mean expansion is due to the formation of calcite on the surface and interior of the specimen due to the metabolic activities of the bacteria.

Image of a micro crack propagating from the air void of the specimen taken from the control (without bacteria) beam subjected to alkali attack. Scale

bar is 100 µm.

Magnified image of calcite crystals developed on the surface of the cement mortar beams with bacteria subjected to alkali attack. Scale bar is 10 µm.

Calcium crystals

EFFECT ON SULPHATE ATTACK EFFECT ON SULPHATE ATTACK RESISTANCE:-RESISTANCE:-

with bacterial concentration of 1 x 106 cells/ml had 12% less mean expansion with bacterial concentration of 1 x 107 cells/ml had 38% less mean expansionwith bacterial concentration of 8.6 x 108 cells/ml had 39% less mean expansion The reduction in the mean expansion is due to calcite precipitation which reduces permeabilityreduces permeability of specimen there by providing resistance to sulphate attack.

Rod-shaped impressions (consistent with dimensions of B. pasteurii, spread around the calcite crystals) formed on the surface of specimens subjected to sulfate attack. Scale bar is 20 µm.

Rod-shaped impressions

EFFECT ON THE FREEZE-THAW EFFECT ON THE FREEZE-THAW DURABILITY OF CEMENT MORTAR DURABILITY OF CEMENT MORTAR BEAMS:-BEAMS:-

cement mortar beams with bacteria performed well than the beams without bacteria.

The higher the bacterial dosage, better was the performance.

Magnified image of calcite crystals, found on the surface II of the specimen subjected to freeze-thaw. Scale bar is 5 µm.

This picture shows that a new layer (Surface II) was formed over the surface of the cement mortar beam (Surface I), which had contributed to the impermeability of the specimen and thus increased the freeze thaw durability. Scale bar is 100 µm.

SCANING ELECTRON SCANING ELECTRON MICROSCOPE (SEM) MICROSCOPE (SEM)

EXAMINATIONEXAMINATION

Developing calcite crystals at higher magnification

Magnified image of hexagonal shaped calcite crystals with distinct and sharp edges, which indicated full growth of the crystals.

-a. Calcite crystals have formed over the sand particles. Bar, 200 ｵm.

b. Details of crystal formations shown in

a. Bar, 20 ｵm.

c. Further magnification of crystals (in b) embedded with B. pasteurii. Bar, 10 ｵm.

Developing calcite crystals at higher magnification. It can be see that rod-shaped objects, consistent with the dimensions of B. pasteurii are spread around the crystals. Scale bar is 10 µm.

CONCLUSIONSCONCLUSIONS

• Microbial remediation of cracks in cement mortar beams specifically increases the compressive strength,stiffness & modulus of rupture.

• Durability characteristics are improved with addition of bacteria.

• Improves the impermiability of the specimen thereby increasing the resistance to alkaline,sulphate & freeze-thaw attack.

• MICP is effective in remediaton of cracks.

LIMITATIONSLIMITATIONS

• Not more bacteria are known that can be used for calcite precipitation.

• Difficulties in the injection technology of the bacteria into sand.

• Extremely high pH of the concrete (above 12.5) hampers the use of bacterial cell in MECR technique.

• Controlled environment is necessary.

FUTURE SCOPEFUTURE SCOPE

• To search for more bacterial varieties that can be used for calcite precipitation.

• To overcome the problems in the injection technology of the bacteria.

• To develope recombinent microorganisms which is expected to complement the results of this study.

REFERENCESREFERENCES

• Research papers presented by Dr.Ramkrishnan, Sookie Bang & Ramesh Panchalan

• http://www.geodelft.nl

• http://wwwstaff.murdoch.edu.au/~vwhiffin/biocement.html