Bacteria-based Self-healing Concrete in Cold Climates · The negatively charged bacterial cell wall...
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Bacteria-based Self-healing Concrete in Cold Climates Concept Lorena Skevi [1]* , Kevin Paine [1][2] , Susanne Gebhard [3] , Neil Abbott [4] *[email protected] 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 0 0.5 1 1.5 2 2.5 3 3.5 4 0 10 20 30 40 50 60 70 HEAT PRODUCTION RATE, W/KG TIME, HOURS NUTRIENTS Control Sodium Acetate Sodium Lactate Starch Malate 0 0.5 1 1.5 2 2.5 3 0 10 20 30 40 50 60 70 HEAT PRODUCTION RATE , W/KG TIME , HOURS BACTERIA Control BC10^5 BC10^7 BC10^9 DBC10^5 DBC10^7 DBC10^9 19 14 18 22 29 29 25 23 19 27 25 33 34 28 33 32 40 35 47 42 38 0 5 10 15 20 25 30 35 40 45 50 Control BC10^5 BC10^7 BC10^9 DBC10^5 DBC10^7 DBC10^9 Compressive strength , MPa 3 days 7 days 28 days Bacteria have the ability to precipitate calcium carbonate in the form of calcite, CaCO 3 , through their metabolic activities, which act as a sealant for cracks as shown in Fig. 1a and 1b. Fig. 3: Heat of hydration for cement pastes containing nutrients (left) and bacteria (right). Mortar samples with bacteria at the previously mentioned concentrations were made and tested under compression. Compressive strength was notably improved for most of the samples containing bacteria, especially for the ones with dead cells (Fig. 4). The sample with dead cells at a concentration of 10 5 cells/ml, DBC10 5 , had the highest strength, even at 28 days. Influence of bacteria cells and nutrients on the properties of concrete. Maintenance and repair of concrete structures account for approximately 34% of the total budget in the UK construction industry. Dealing with the problem of cracking in concrete is, therefore, crucial. Scanning Electron Microscopy (SEM) images of the control and DBC10 5 sample (Fig. 5 and 6, respectively) show a denser and more cohesive surface of the latter, which explains its higher strength. The high magnification images show ettringite (AFt) needles in the control sample (Fig. 5b) and monosulfate (AFm) in the bacterial sample (Fig. 6b). Isothermal calorimetry was used for studying the hydration rate of cement pastes containing 1% (per cement dry mass) of various organic nutrients (Fig. 3a). The hydration 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 (10 5 , 10 7 , 10 9 ) was also examined. In both cases, control samples, without nutrients or bacteria, were used as points of reference. Certain bacteria promote the oxidation of organic compounds, provided to them as a nutrient source (Fig. 2a). The oxidation leads to the production of CaCO 3 and CO 2 (Fig. 2b). The negatively charged bacterial cell wall attracts calcium cations, Ca +2 , which react with the CO 2 , resulting in more calcite precipitated around the bacteria (Fig. 2c). 1a 1b 2 High pH Limited O 2 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 as nutrients since they do not affect the hydration of cement significantly. The same applies to the bacteria cells, live and dead (Fig. 3b). Future steps Fig. 4: Compressive strength of control (no bacteria) and bacterial mortar (BC for live and DBC for dead cells) in different concentrations (10 5 , 10 7 , 10 9 cells/ml) at 3, 7 and 28 days. 4 5a 5b 6a Fig. 5, 6. SEM images of the control (5a,b) and the bacterial DBC10 5 (6a,b) sample at 7 days in two magnifications: x10 3 (5a, 6a) and x10 4 (5b,6b) . 6b -1.6 -1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 70 75 80 85 90 95 100 105 0 200 400 600 800 1000 1200 dTG (%/min) TG (%) Temperature ( o C) Control DBC10^5 Control DBC10^5 TG Thermogravimetric analysis (TGA), shown in Fig. 7, showed that the control and the bacterial sample have similar calcite content. This means that the strengths are not improved due to calcite formation by the bacteria. A different mechanism related to their surface properties and composition seems to be a possible explanation. CaCO 3 dTG Fig. 7. TG and dTG curves of the control and the bacterial DBC10 5 sample at 7 days. 7 Protocol • Establish a protocol on the self-healing procedure (curing conditions, cracking, healing evaluation) using B. Cohnii in room (20 o C) and low (10 o C) temperature. Self-healing • Examine the self-healing ability of different bacteria types (cryophilics) in the above- mentioned temperatures. Test alternative nutrients and importation methods for the bacteria. Combination • Combine different types of bacteria for achieving self-healing in a wide range of temperatures. Attempt repetitive healing. AFt AFm Aim of the project Extend the use of the bacteria-based self-healing concrete (BBSHC) in cold and temperate climates. Bacteria Nutrients
Transcript of Bacteria-based Self-healing Concrete in Cold Climates · The negatively charged bacterial cell wall...
Bacteria-based Self-healing Concrete in Cold Climates
Concept
Lorena Skevi[1]*, Kevin Paine[1][2], Susanne Gebhard[3], Neil Abbott[4]
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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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).
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1b
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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.
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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) .
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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.
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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
