Bacteria-based Self-healing Concrete in Cold Climates

Concept

Lorena Skevi[1]*, Kevin Paine[1][2], Susanne Gebhard[3], Neil Abbott[4]

*L.Skevi@bath.ac.uk

Initial Findings

[1] Architecture and Civil Engineering Department, University of Bath[2] BRE Centre for Innovative Construction Materials, University of Bath[3] Biology & Biochemistry Department, University of Bath[4] BRE Group

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HEA

T P

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DU

CTI

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RA

TE, W

/KG

TIME, HOURS

NUTRIENTS

Control

Sodium AcetateSodium LactateStarch

Malate

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BACTERIA

Control

BC10^5

BC10^7

BC10^9

DBC10^5

DBC10^7

DBC10^9

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14

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29 29

2523

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2725

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Control BC10^5 BC10^7 BC10^9 DBC10^5 DBC10^7 DBC10^9

Co

mp

ress

ive

str

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gth

, M

Pa

3 days 7 days 28 daysBacteria have the ability to precipitate calcium carbonate in the form of calcite,CaCO3, through their metabolic activities, which act as a sealant for cracks as shownin Fig. 1a and 1b.

Fig. 3: Heat of hydration for cement pastes containing nutrients (left) and bacteria (right).

Mortar samples with bacteriaat the previously mentionedconcentrations were made andtested under compression.Compressive strength wasnotably improved for most ofthe samples containingbacteria, especially for theones with dead cells (Fig. 4).The sample with dead cells at aconcentration of 105 cells/ml,DBC105, had the higheststrength, even at 28 days.

Influence of bacteria cells and nutrients on the properties of concrete.

Maintenance and repair of concretestructures account for approximately 34% ofthe total budget in the UK constructionindustry. Dealing with the problem ofcracking in concrete is, therefore, crucial.

Scanning Electron Microscopy (SEM) images of the control and DBC105 sample (Fig.5 and 6, respectively) show a denser and more cohesive surface of the latter, whichexplains its higher strength. The high magnification images show ettringite (AFt)needles in the control sample (Fig. 5b) and monosulfate (AFm) in the bacterialsample (Fig. 6b).

Isothermal calorimetry was used for studying the hydration rate of cement pastescontaining 1% (per cement dry mass) of various organic nutrients (Fig. 3a). Thehydration of cement pastes with live and dead bacteria cells (named as BC and DBC,respectively in Fig. 3b) of the B. Cohnii type in different concentrations (105, 107, 109)was also examined. In both cases, control samples, without nutrients or bacteria, wereused as points of reference.

Certain bacteria promote the oxidation oforganic compounds, provided to them as anutrient source (Fig. 2a). The oxidation leadsto the production of CaCO3 and CO2 (Fig. 2b).The negatively charged bacterial cell wallattracts calcium cations, Ca+2, which reactwith the CO2, resulting in more calciteprecipitated around the bacteria (Fig. 2c).

1a

1b

2

High pH

Limited O2

High stresses

Challenges• Protection of the bacteria inside the concrete

matrix• Access of bacteria to nutrients and oxygen• Preservation/improvement of the concrete’s

strength properties.

3a 3b

As shown in Fig. 3a, sodium acetate, starch and malate are promising candidates asnutrients since they do not affect the hydration of cement significantly. The sameapplies to the bacteria cells, live and dead (Fig. 3b).

Future steps

Fig. 4: Compressive strength of control (no bacteria) andbacterial mortar (BC for live and DBC for dead cells) indifferent concentrations (105, 107, 109 cells/ml) at 3, 7 and 28days.

4

5a

5b

6a

Fig. 5, 6. SEM images of the control (5a,b) and the bacterial DBC105 (6a,b) sample at 7 days in two magnifications: x103 (5a, 6a) and x104 (5b,6b) .

6b

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dTG

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TG (

%)

Temperature (oC)

Control

DBC10^5

Control

DBC10^5

TG

Thermogravimetric analysis(TGA), shown in Fig. 7,showed that the control andthe bacterial sample havesimilar calcite content. Thismeans that the strengths arenot improved due to calciteformation by the bacteria. Adifferent mechanism relatedto their surface propertiesand composition seems to bea possible explanation.

CaCO3

dTG

Fig. 7. TG and dTG curves of the control and the bacterial DBC105 sample at 7 days.

7

Protocol

• Establish a protocol on the self-healingprocedure (curing conditions, cracking,healing evaluation) using B. Cohnii in room(20 oC) and low (10 oC) temperature.

Self-healing

• Examine the self-healing ability of differentbacteria types (cryophilics) in the above-mentioned temperatures. Test alternativenutrients and importation methods for thebacteria.

Combination

• Combine different types of bacteriafor achieving self-healing in a widerange of temperatures. Attemptrepetitive healing.

AFt AFm

Aim of the projectExtend the use of the bacteria-based self-healing concrete (BBSHC) in cold and temperate climates.

Bacteria

Nutrients