BiocementationInfluenceonFlexuralStrengthandChloride...

Research ArticleBiocementation Influence on Flexural Strength and ChlorideIngress by Lysinibacillus sphaericus and Bacillus megaterium inMortar Structures

Daniel Karanja Mutitu 1 Jackson Muthengia Wachira 1 Romano Mwirichia2

Joseph Karanja Thiongrsquoo3 Onesmus Mulwa Munyao 3 and Muriithi Genson2

1Department of Physical Sciences University of Embu Embu Kenya2Department of Biological Sciences University of Embu Embu Kenya3Department of Chemistry Kenyatta University Nairobi Kenya

Correspondence should be addressed to Daniel Karanja Mutitu mutsonjnrgmailcom

Received 27 January 2020 Revised 2 April 2020 Accepted 27 April 2020 Published 28 May 2020

Guest Editor Jorge Sanjurjo-Sanchez

Copyright copy 2020 Daniel KaranjaMutitu et alis is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

e concretemortar durability performance depends mainly on the environmental conditions the microstructures and itschemistry Cement structures are subject to deterioration by the ingress of aggressive mediais study focused on the effects ofBacillus megaterium and Lysinibacillus sphaericus on flexural strength and chloride ingress in mortar prisms Microbialsolutions with a concentration of 10times107 cellsml were mixed with ordinary Portland cement (OPC 425 N) to make mortarprisms at a watercement ratio of 05 Four mortar categories were obtained from each bacterium based on mix and curingsolution Mortar prisms of 160mm times 40mmtimes 40mmwere used in this study Flexural strength across all mortar categories wasdetermined at the 14th 28th and 56th day of curing Mortars prepared and cured using bacterial solution across all curing agesexhibited the highest flexural strength as well as the highest percent flexural strength gain Lysinibacillus sphaericus mortarsacross all mortar categories showed higher flexural strength and percent flexural strength gain than Bacillus megateriummortars e highest percent flexural strength gain of 333 and 370 was exhibited by the 28th and 56th day of curingrespectively e mortars were subjected to laboratory prepared 35 by mass of sodium chloride solution under theaccelerated ion migration test method for thirty-six hours using a 12V Direct Current power source after their 28th day ofcuring After subjecting the mortar cubes to Cl media their core powder was analyzed for Cl content From these results theapparent diffusion coefficient Dapp was approximated from solutions to Fickrsquos 2nd Law using the error function Bacillusmegaterium mortars across all mortar categories showed lower apparent diffusion coefficient values with the lowest being26456 times10ndash10 while the highest value for Lysinibacillus sphaericusmortars was 28005times10ndash10 Both of the test bacteria loweredthe ordinary Portland cement Cl-ingress but Bacillus megateriumwas significantly more effective than Lysinibacillus sphaericusin inhibition

1 Introduction

e durability of concretemortar is related to the charac-teristics of its pore structure [1] Furthermore permeabilityof concretemortar is dependent on the porosity and theconnectivity of the pores [2 3] e degradation mecha-nisms often depend on the way potentially aggressivesubstances can penetrate the cement-based material

possibly causing damage [4] e more open the porestructure and connectivity of the pores the more vulnerableit is to degradation caused by penetrating substances [5 6]

One of the predominant causes of the corrosion of steelin cement-based structures is chloride attack [7ndash9] Chlorideions may be present in a cementitious material either as aresult of aggressive ions ingress or incorporation of theaggressive ions during concretemortar preparation

HindawiJournal of ChemistryVolume 2020 Article ID 1472923 13 pageshttpsdoiorg10115520201472923

Chloride ions may also penetrate from external sources suchas seawater or deicing salts In the marine environment theingress of chloride is the most important problem [10 11]

Chloride is bound if it has reacted with cement and isfree if it is available in pore solution [10] Several chemicalinteractions between chloride and the cement constituentsdo affect the chloride penetration into the concretemortarbulk [5 12]e chemical reactions of chlorides with cementpaste start with calcium hydroxide and calcium aluminatehydrate depending on the cations in solution [13]

Chloride ingress in cement-based materials is mainlythrough capillary absorption permeation and diffusion[14] However it may also occur through a multiple of theaforementioned mechanisms Diffusion is the most preva-lent process [15] e ingress of chloridessulphates due tothe various transport mechanisms obeys different laws [16]Fickrsquos second law of diffusion is commonly applied toquantify the aggressive ion ingress due to the multipletransport phenomena

Chlorides react with C3A and the C4AF present in Portlandcement to produce Friedelrsquos salt Ca6Al2O6middotCaCl2middot10H2O orcalcium chloroferrite Ca6Fe2O6middotCaCl2middot10H2O respectively[5 14] No deleterious effect is associated with theseproducts e reaction between the C3A phase and freechlorides in hydrated cement leads to a reduction of Clminusfrom the pore solution [17] is lowers the risk of rebarcorrosion [18] Solutions with high concentrations ofCaCl2 or MgCl2 may cause chemical attack which maylead to a drop in pore water pH and disruption of thecement matrix [19] is is due to the consumption of thesparingly soluble Ca(OH)2 MgCl2 reacts with portlanditeas shown in

MgCl2(aq) + Ca(OH)2(s) + 2H2O(l)⟶ CaCl2 middot 2H2O(aq)

+ Mg(OH)2(s)(1)

Biocementation in OPC lowers chloride ingress andpermeability into the cement matrix [20] is is due to therefinement of the pore structure [5] Chloride ions penetratea pore system and form chloride salts which may crystallizewithin the pores inducing internal cracks [21] e cracksaffect the mechanical and durability properties of concretemortar [20 22 23]

e high alkalinity of the concretemortar introducedduring the bacteria MICP prevents the breakup of thepassive film [25 24] Its carbonation accompanied by thepresence of chloride ions lowers the alkalinity of pore waterRasheeduzafar et al [18] Dousti et al [21] and Rao andMeena [26] observed the amount of free chloride decreasewith increasing C3A and the amount of bound chloridedecreased with increasing OH-concentration from the ce-ment Given this the high corrosion of rebars exposed tochloride media can be assumed to be due to the low alka-linity of pore solution [21 22 27]

OPC based structures are well known for achieving highearly compressive and flexural strength due to large contentand early hydration of C3S [15 28 29] Despite the variousOPC concretemortar advantages it has a more open pore

structure than blended cement structures [3 15 30] OPC-made structures also have a high tendency to form cracksduring and after curing allowing aggressive substances topenetrate the structure Permeability or cracks are one of themain causes of deterioration of these structures and decreasein durability Treatment of cracks and pores are generallydivided into passive and active treatments Passive treat-ments can only heal the surface cracks while active treat-ments can heal both interior and exterior cracks [22 25]

Microbial concretemortar biologically produce calciumcarbonate (limestone) to seal pores that appear within itsmatrix or sealrepair cracks that appear on the structurersquossurface [25 31]esemicrobial deposits could also establishnucleation sites that enhance the early cement hydrationprocess leading to improved compressive and flexuralstrengths Microbial precipitation of calcium carbonatemainly occurs by hydrolyzing urea Urea hydrolysis is achemical reaction in which urea reacts with water andproduces ionic products as shown in the following equation

CO NH2( 11138572 + 2H2O Urease⟶

CO32minus

+ NH41+

(2)

When this reaction occurs in the presence of Ca2+CaCO3 (solid) is formed as shown in the following equation

Ca2++ CO3

2minus ⟶ CaCO3 (3)

When this reaction occurs inside a cementitious porousmaterial after settling it produces sediment a coating and abridge is formed sequentially around and between theparticles and increases interparticle linkage [31]

Specific types of the bacteria genus such as Bacillus alongwith a calcium-based nutrient such as calcium lactate orcalcium nitrate could be added to the ingredients of theconcretemortar when it is being mixed [21] e solublecalcium-containing nutrient is converted to insoluble cal-cium carbonate [22 32] e calcium carbonate solidifies onthe cracked surface thereby sealing it up

e densification of cementitious material due to mi-crobial reaction is important in reducing the permeability ofaggressive ionsis paper reports on findings of the flexuralstrength gain of MICP-containing Kenyan-made OPC andlowered diffusivity of chloride in such laboratory-mademortars

2 Materials and Methods

21 Cement Chemical Analysis In this study the ordinaryPortland cement (OPC 425N) KS EAS 18-12017 [33] andstandard sand ISO 6791989 [34] were used Flexuralstrength tests were carried out in accordance to ASTMC2931990 [35] 100 g sample of the test cement sample wasprepared and analyzed in the usual manner following KSEAS 18-12017 [33] Loss on ignition was done followingASTM D7348 2013 [37] e results are given in Table 1

Using Bogues formula [36] the average phase compo-sition for the test OPC is 65115plusmn 0854 14485plusmn 09133899plusmn 0013 and 10355plusmn 0018 for C3S C2S C3A andC4AF respectively

2 Journal of Chemistry

Tabl

e1

OPC

chem

ical

analysisresults

Sample

Cem

entcompo

sition

wwplusmnSD

Al 2O

3SiO2

SO3

Na 2O

K2O

CaO

MgO

Fe2O

3MnO

LOI

Avg

3643plusmn0010

22182plusmn0010

2695plusmn0021

0410plusmn0001

0975plusmn0006

64627plusmn0042

2084plusmn0025

3403plusmn0012

0173plusmn0001

1519plusmn0001

Journal of Chemistry 3

22 Microbial Culturing Nutrients Analytical grade chem-icals were used in the preparation of the culture mediaCalcium lactate C6H10O6Ca peptone from casein and otheranimal proteins meat extract agar sodium hydrogen car-bonate (NaHCO3) anhydrous sodium carbonate (Na2CO3)and distilled water among other nutrients were purchasedfrom Chem-Labs Limited Nairobi Kenya Lysinibacillussphaericus bacteria (DSM 28) and Bacillus megaterium(DSM 32) were purchased from Leibniz-Institut DSMZ-Deutsche Sammlung von Germany

221 Lysinibacillus sphaericus Microbial Culturing eLysinibacillus sphaericus microbial solution was culturedusing nutrients as per the supplier manual e liquidmedium chosen for culturing the bacteria consisted of 500 gof peptone added to 300 g of meat extract and 395 g ofcalcium acetate per liter of distilled water was mixed toobtain liquid medium per stock culture Initially thismixture was sterilized for 20 minutes at a temperature of121degC by autoclaving is mixture was then cooled to roomtemperature After cooling a 1M Na-sesquicarbonate so-lution (10ml in 100ml) prepared by mixing 42 g NaHCO3with 53 g anhydrous Na2CO3 and made up to 1 liter usingdistilled water was added to the stock culture to achieve a pHof 97 e Lysinibacillus sphaericus spore powder samplewas added to this mixture in a laminar flow chamber esecultures were then incubated on a shaker incubator at 130shakes per minute maintained at 30degC for 72 hours Anoptical density test was conducted using a spectropho-tometer for determining the quantity of culture solutionrequired to mixis test was conducted in bacteria growingmedium which was considered as blank is solution wasalso taken to be the reference for experimentation of opticaldensity of the microbial solution Separately 05mL of blankand bacteria solution of 05mL were placed in the spec-trophotometer at a wavelength of 600 nm and the machinewas set to reademicrobial concentration was observed tobe 10times107 cellsmL using the spectrophotometer ismicrobial culture concentration was maintained throughoutthe mortar samples preparation as well as in prism curingsolution

222 Bacillus megateriumMicrobial Culturing e Bacillusmegateriummicrobial solution was cultured using nutrientsas per the supplier manual e same procedure and nu-trients as used in preparing the Lysinibacillus sphaericusmicrobial solution were used in preparing the Bacillusmegaterium microbial solution e Bacillus megateriumspore powder sample was added instead of Lysinibacillussphaericus

Figure 1 shows (a) OPC mortar prepared and beingcured in distilled water (b) OPC mortar prepared usingBacillus megaterium solution but being cured in distilledwater (c) OPC mortar prepared using distilled water butbeing cured in Bacillus megaterium solution and (d) OPCmortar prepared and being cured in Bacillus megateriumsolution

23 Mortar Prism Molding and Flexural Strength TestingMortar mix prisms were fabricated according to KS EAS18-12017 [33] 450 g of OPC was placed in the mixing basinof an automatic programmable mixer model number JJ-52250ml of distilled water was then added e mix basinand its contents were clamped onto the automatic pro-grammable mixer and allowed to run for three minutes1350 plusmn 5 g of the standard sand was placed in an automaticpour-trough and allowed to add automatically until all1350 plusmn 5 g sample was added while the mixer was stillrunning at a speed of 30 vibrations per minute e ma-chine was let to run for ten minutes e mortar preparedhad wc ratio of 05 and was sufficient to prepare threemortar prisms Once the mortar was mixed it was pouredinto steel molds of 40mm times 40mmtimes 160mm Using atrowel the mortar paste was scooped from the automaticprogrammable mixing basin and placed in a compactionmold of a jolting compaction machine with 60 rpm vi-brations Leveling of the paste was done with a mold trowelin each of the three chambers of the mold after every joltingcycle until a good finish was achieved at the surface emold with the mortar paste was then placed in a humidchamber maintained at 95 humidity and 270degC for 24hours e mortar was then removed from the molds after24 hours to obtain the usual OPC mortar e distilled-water prepared mortars were categorized into two cate-gories depending on their curing regime e first categorywas cured in distilled water (labeled as OPC-H2O [H2O])e second category was cured in microbial solution (la-beled as OPC-H2O [LB] for Lysinibacillus sphaericus andOPC-H2O [BM] for Bacillus megaterium) e aboveprocedure was repeated but this time using 225ml of themicrobial solution as mix media instead of distilled waterwhich resulted in two more mortar categories (referred toas the third and fourth category) the third category was theOPC mortar prepared using the microbial solution andcured in distilled water (labeled as OPC-LB [H2O] Lysi-nibacillus sphaericus and OPC-BM [H2O] for Bacillusmegaterium) while the fourth category was the OPCmortar prepared using the microbial solution and cured inmicrobial solution (labeled as OPC-LB [LB] for Lysini-bacillus sphaericus and OPC-BM [BM] for Bacillus meg-aterium) e mortars were placed in requisite water ormicrobial solution for curing in a chamber maintained at27 plusmn 1degC for curing e flexural strength tests were con-ducted at the 2nd 7th 14th 28th and 56th day of curingFlexural strength tests in this study were performed onthree samples per category for obtaining average results

24 Scanning ElectronMicroscopy (SEM) Sample Preparationand Analysis SEM analysis was determined for each set oftest mortars after the 28th day of curing e SEM modelused was Zeiss Ultra Plug FEG-SEM e test mortar wasprepared for SEM analysis as described in Scrivener et alrsquos[38] guide for microstructural analysis of cementitiousmaterials as summarized in Figure 2 Isopropanol alcoholwas used to stop the hydration process while resin ERL-4206was used to impregnate the hardened cement mortar


25 X-Ray Diffraction (XRD) Analysis XRD analysis wasdetermined for each set of test mortars after the 28th day ofcuring e mineralogy of the newly formed cement hy-drationbacterial material was determined using an X-RayDiffraction (XRD) Instrument PW1710 Phillips Beforerunning the XRD analysis samples were oven-dried at 100degCand powdered with an electronic grinder ey were thenplaced in a zero-background silicon sample holder egoniometer was calibrated using a silicon standard Sampleswere analyzed using PANalytical software with goniometerstart and end angles at 500 and 80002degeta step size of00202degeta and scan step time of 05 seconds at an ad-justed current and voltage of 40mA and 35 kV respectively

26 Chloride Ingress For each category of mortar threeprisms cured for 28 days were subjected to chloride pro-filing using the method prescribed in ASTM C 1552 [39]After the NaCl solution exposure a mortar prism waspolished on the 40mmtimes 40mm face using sandpaper eprism was drilled through the core center up to 10mm

interval along the length using a 15mm radius drill bit up to80mm per mortar category e powder was dried to aconstant mass in an oven at 105degC e dried powder waspulverized Between each pulverization the pulverizer wasthoroughly cleaned to avoid cross-sample contaminatione ground samples were kept in individual-sample sealedreagent bottles awaiting chloride analysis

261 Chloride Profiling e chlorides at each depth ofpenetration were analyzed using Mohr titration procedurein all the mortar categories e estimation of apparentchloride diffusion coefficients was achieved under non-steady state conditions assuming boundary conditionsC(xt) 0 at t 0 0lt xltinfin C(xt) Cs at x 0 0 lt t ltinfinconstant effects of coexisting ions linear chloride bindingand one-dimensional diffusion into semi-infinite solid [16]Crankrsquos solution to Fickrsquos second law of diffusion is givenby

C(xt) C(s) 1 minus erfx

4Dappt1113872 1113873(12)

⎛⎜⎝ ⎞⎟⎠⎧⎪⎨

⎪⎩

⎫⎪⎬

⎪⎭ (4)

where C(xt) is the concentration of Clminus at any depth x in themortar bulk at time t Cs is the surface concentration andDapp is the apparent diffusion coefficient e error cor-rection function erf is the Gaussian error function obtainedfrom computer spreadsheets e chloride profiles wereobtained by fitting equation (4) to experimentally

(a) (b)

(c) (d)

Figure 1 Cement mortar curing in varied regimes (a) OPC-H2O [H2O] (b) OPC-BM [H2O] (c) OPC-H2O [BM] (d) OPC-BM [BM]

Sample cleaning

Sample stabilizing

Sample rinsing

Sample dehydration

Sample drying (CPD)

Sample mounting

Sample coating

SEM sample analysis

Figure 2 SEM sample preparation


determined chloride profile concentrations thus deter-mining the values of Dapp and Cs mathematically

By using the accelerated migration diffusion coefficientDmig determined graphically Dapp can be determined byusing the following equation [40]

Dapp RT

ziFDmig

Int2

Δempty (5)

where R is the Gas constant F is the Faraday constant T isthe temperature of the electrolyte in K zi is the valency of theion i ∆Oslash is the Effective Applied Voltage in V and t is theduration of the testexposure in seconds

3 Results and Discussion

31 Scanning Electron Microscope (SEM) AnalysisFigures 3(a)ndash4(c) show SEM analysis for both control andmicrobial mortar prisms after the 28th day of curing eSEM images display the formation of calcium-silicate-hy-drate C-S-H calcium carbonate precipitation CaCO3needle type ettringite and presence of portlanditecalciumhydroxide CH

As SEM images in Figure 3(a) illustrate the OPC-H2O(H2O) mortar had no visible calcium carbonate depositsHowever the SEM images in Figures 3(b)ndash3(d) as well inFigures 4(a)ndash4(c) the microbial mortars OPC-H2O (LB)OPC-H2O (BM) OPC-LB (H2O) OPC-BM (H2O) OPC-LB(LB) and OPC-BM (BM) showed significant calcium car-bonate precipitates is is attributed to the MICP depositsfrom both Lysinibacillus sphaericus and Bacillus megateriumeither present in mix media or present in the cultured curingsolution [1 41] e morphology of C-S-H densifies fromFigure 3(b) through Figures 3(c)ndash3(d) as well as fromFigure 4(a) through Figures 4(b)ndash4(c) is is attributed tothe calcium carbonate precipitation by the two bacteriaunder study Image (c) from Figure 3 clearly shows bio-deposition over ettringite needles resulting in the formationof biofilms on their surface and plugging of the pores on themortar structure

32 X-Ray Diffraction Analysis (XRD) Table 2 shows XRDanalysis results for both control andmicrobial mortar prismsafter the 28th day of curing e results show formation of anew hydration compound Bavenite in both bacterialmortars

e XRD analysis of the OPC mortars confirms thatmicrobial biocementation introduces a new cementitiousproduct Bavenite Al2Be2Ca4H2O28Si9 which is absent inthe control mortar OPC-H2O (H2O) but present in themicrobial mortars OPC-LB (LB) and OPC-BM (BM) at253 and 133 respectively Calcite CaCO3 is signifi-cantly more in OPC-BM (BM) and OPC-LB (LB) at 1027and 1023 respectively as compared with 064 in OPC-H2O (H2O) is relates with improved calcite (CaCO3)deposits and depleted Portlandite Ca(OH)2 in microbialmortars as seen in SEM morphological images in Figures 3and 4 XRD diffractograms also confirmed the same asdepicted in Figures 5(a)ndash5(c) e depleted Ca(OH)2 in

microbial mortars compared to that in control mortarscould be attributed to the binding of Ca2+ with the microbialprecipitated CO3

2minus More densification of C-S-H in microbial mortars than

in control mortar is observed in SEM micrographs due tothe high percentage of both Bavenite Al2Be2Ca4H2O28Si9and Dellaite Ca6H2O13Si3 either individually or ascombined in OPC-BM (BM) and OPC-LB (LB) comparedto in OPC-H2O (H2O) as depicted in Figures 5(a)ndash5(c)and summarized in Table 2 e XRD quantificationsconfirm the presence of calcite as well as more C-S-H inmicrobial mortars ese depositions in the pores maxi-mized the packing density of cement mortar consequentlyimproving the mortarrsquos physicochemical and mechanicalproperties

33 Flexural Strength Gain e percent gain flexuralstrength results obtained at 14th 28th and 56th day of curingare given in Figure 6

Table 3 summarizes the significant difference in flexuralstrength gain between the control andmicrobial mortars across2nd 7th 14th 28th and 56th day of curing

Across all mortar categories for both Lysinibacillussphaericus and Bacillus megaterium there was no signif-icant difference (Tcalc 05 p 005) in their flexuralstrengths at 2nd and 7th day of curing e flexural strengthacross all mortar categories for both bacteria under studyincreased with an increase in curing age as depicted inFigure 6 Considering the control and the microbialmortars across all the test bacteria mortars the flexuralstrength increase was higher and more statistically sig-nificant between the 14th and 28th day than between the28th and 56th day of curing as demonstrated by the resultsin Table 3 However among the microbial mortarsflexural strength appears to be influenced more by the typeof the bacteria as well as the preparation or curing regimethan the curing age

ere was a statistically significant difference in flexuralstrength across all microbial mortar categories betweendifferent days of curing as well as between the Lysiniba-cillus sphaericus mortars and Bacillus megaterium mortarsas depicted in Table 3 is could imply the fact that theformation of C-S-H increases with curing age and thatintroduction of the microbial solution either duringpreparation of mortars or as the curing regime enhancesthe formation of C-S-H results in improved flexuralstrength

e flexural strength improvement for mortars of bothbacteria under study was more pronounced when themicrobial solution was used as the mix water than as thecuring regime Across all curing ages OPC-LB (LB)exhibited the highest percentage gain in flexural strengththan the other mortar categories e highest percentflexural strength gain was observed at the 56th day ofcuring at 370 ere was observed a statistically sig-nificant difference in percent flexural strength gain bothfrom one curing age to another as well from one microbialmortar category to another for all microbial mortar


(a) (b)

(c) (d)

Figure 3 SEM analysis for (a) OPC-H2O (H2O) (b) OPC-H2O (LB) (c) OPC-LB (H2O) and (d) OPC-LB (LB)

(a) (b)

(c)

Figure 4 SEM analysis for (a) OPC-H2O (BM) (b) OPC-BM (H2O) and (c) OPC-BM (BM)


Table 2 XRD ( wwplusmn SD values) summary for hydrated OPCmicrobial mortars prepared and cured in respective bacteria against controlOPC mortar after 28th day of curing

Hydration compoundMortar category ( wwplusmn SD)

OPC-H2O (H2O) OPC-LB (LB) OPC-BM (BM)Bavenite Al2Be2Ca4H2O28Si9Sample 1 mdash 255 136Sample 2 mdash 252 133Sample 3 mdash 251 129

Average mdash 253 133Std dev mdash plusmn002 plusmn003 Averageplusmn SD mdash 253plusmn 002 133plusmn 003Dellaite Ca6H2O13Si3Sample 1 8389 8349 8421Sample 2 8395 8347 8418Sample 3 8394 8345 8416

Average 8393 8347 8418Std dev plusmn003 plusmn002 plusmn002 Averageplusmn SD 8393plusmn 003 8347plusmn 002 8418plusmn 002Calcite CaCO3

Sample 1 067 1026 1024Sample 2 063 1022 1029Sample 3 061 1021 1027

Average 064 1023 1027Std dev plusmn002 plusmn002 plusmn002 Averageplusmn SD 064plusmn 002 1023plusmn 002 1027plusmn 002Portlandite CaH2O2Sample 1 1543 386 421Sample 2 1548 382 417Sample 3 1549 384 419

Average 1547 384 419Std dev plusmn003 plusmn002 plusmn002 Averageplusmn SD 1547plusmn 003 384plusmn 002 419plusmn 002

1200

OPC H2O(coupled twothetatheta)

1100

1000

900

800

700

600

500

400

300

200

100

0

Dellaite Ca6H2O13Si3 839Portlandite CaH2O2 155

Calcite CCaO3 06

2theta (coupled twothetatheta) WL = 15406020

178

06lowast

206

76lowast

292

52lowast

264

338

55lowast

363

55lowast

392

88lowast

401

04lowast

422

54lowast

456

17lowast 49

938

lowast

547

00lowast

30 40 50

Cou

nts

(a)

Figure 5 Continued


categories as shown in Table 3 and Figure 7 respectivelye increase in flexural strength is attributed to thematerials precipitated by the Lysinibacillus sphaericusbeing involved in the hydration process forming C-S-H

responsible for strength development e added Ca2+together with calcium acetate in presence of the microbialcell-wall as the nucleation site readily combine with theprecipitated CO3

2minus and crystallizes out as CaCO3 which

1600

1500

1400

1300

1200

1100

1000

900

800

700

600

500

400

300

200100

0

OPC LB(coupled twothetatheta)

Dellaite Ca6H2O13Si3 887Calcite CCaO3 77

Portlandite CaH2O2 27Bavenite Al2Be2Ca4H2 O28Si9 09

266

180

26lowast

208

25lowast

300

49lowast

341

36lowast

364

86lowast

394

36lowast

402

97lowast

423

93lowast

457

94lowast 50

111

lowast

548

25lowast

20 30 40 502theta (coupled twothetatheta) WL = 154060

Cou

nts

(b)

OPC BM(coupled twothetatheta)

1500

1400

1300

1200

1100

1000

900

800

700

600

500

400

300

200

1000


Portlandite 42Bavenite AlBe3Ca4H3O28Si9 13

265

179

57lowast

207

75lowast

229

28lowast

293

47lowast

340

28lowast

364

56lowast

393

83lowast

402

22lowast

4237

4lowast

457

37lowast

470

39lowast 50

031

lowast

547

78lowast


Cou

nts

(c)

Figure 5 (a) Diffractograms for OPC-H2O (H2O) (b) Diffractograms for OPC-LB (LB) (c) Diffractograms for OPC-BM (BM)


stimulate and accelerate the hydration of C-S-H[31 32 42]

In this study it has been found that Bacillus megateriumand the Lysinibacillus sphaericus biomineralization processenhance the flexural strength e enhanced MICP processcould also be ascribed to the metabolic conversion of theorganic acetate added as a microbial feed in form of calciumacetate which was aerobically oxidized under improvedalkaline conditions by these ureolytic alkaliphilic Bacillusspp Lysinibacillus sphaericus MICP precipitate is morecrystalline while that from Bacillus megaterium is moreamorphous as shown in Figures 3 and 4rsquos SEM imagesrespectively Perhaps the more the crystalline MICP de-posits the more and the better the C-S-H bonding resultingin enhanced flexural strength gain by Lysinibacillus

sphaericus which deposits relatively more crystalline pre-cipitate than Bacillus megaterium which deposits moreamorphous precipitates [3 4 31 42] e amorphous MICPdeposition serves as a barrier as it fills any porepathwayreducing porosity and thus improves impermeability andingress resistance Perhaps this difference in MICP crys-tallinity and the quantity between the two test bacteriaexplain why Lysinibacillus sphaericus is a better flexuralstrength enhancer while Bacillus megaterium improvesimpermeability thus a better chloride ingress inhibitorSimilar observations have been made by other researchersAzadi et al [6] Chahal et al [31] Abo-El-Enein et al [43]and Kim et al [44] though using other bacteria species eMICP precipitation occurs according to the followingequation [1 32]

169 138 123 185 215 246

278236 208

264306

333

288260

233

315342

370

OPC-BM (BM)

OPC-BM (H2O)

OPC-H2O (BM)

OPC-H2O (LB)

OPC-LB (H2O)

OPC-LB (LB)

g

ain

flexu

ral s

tren

gth

Mortar preparation and curing regime

Per cent gain flexural strength for varied microbial mortars

Flexural strength (MPa) 14 daysFlexural strength (MPa) 28 daysFlexural strength (MPa) 56 days

00

200

400

600

800

1000

1200

Figure 6 Percent gain flexural strength of test mortars at 14th 28th and 56th day of curing

Table 3 Tcalc values summary for microbial mortars against control mortar and among varied microbial mortar categories flexural strengthacross 2nd 7th 14th 28th and 56th day of curing (Tcrit 05 p 005)

Mortar categoriesTcalc values

2nd dayTcalc times 10minus1

7th dayTcalc times 10minus1




OPC-H2O (H2O) vs OPC-H2O (LB) 50 50 137908 68664 04725OPC-H2O (H2O) vs OPC-LB (H2O) 50 50 464869 49426 12694OPC-H2O (H2O) vs OPC-LB (LB) 50 50 266329 61408 24344OPC-H2O (H2O) vs OPC-H2O (BM) 50 50 49845 37064 39136OPC-H2O (H2O) vsOPC-BM (H2O) 50 50 671730 94017 10106OPC-H2O (H2O) vs OPC-BM (BM) 50 50 12815 12371 06787OPC-H2O (BM) vs OPC-H2O (LB) 50 50 3025298 3025298 1332461OPC-BM (H2O) vs OPC-LB (H2O) 50 50 5350033 388954 1332461OPC-BM (BM) vs OPC-LB (LB) 50 50 223619 4024947 4365515


CH3COO1minus

+ 2O2⟶ 2CO2 + OH1minus+ H2O

CO2 + OH1minus ⟶ HCO31minus

HCO31minus

+ OH1minus ⟶ CO32minus

+ H2O

Bacterial Cell minus Ca2++ CO3

2minus ⟶ Cell minus CaCO3

(6)

Bacillus megaterium and Lysinibacillus sphaericus bac-teria cause densification of the mortar due to increasedcement products CaCO3 CSH and ettringite

34 Chloride Ingress

341 Chloride Profiling Results for chloride ingress into thetest microbial OPC mortars determined at the varied depthof cover within the mortar are presented in Figures 7 and 8for Lysinibacillus sphaericus and Bacillus megateriumrespectively

In all cases the bacterial presence affected thepresence of the Clminus As observed the Clminus ingress wassharper across all penetration depths in OPC-H2O (H2O)than in all microbial mortars up to the 60 mm and 40mmalong the penetration depths respectively Perhaps this isdue to the lower chloride binding capacity in OPC-H2O(H2O) than in microbial mortars [1] is could be at-tributed to the increased content of C-S-H and CAH gelsthat seal the microbial mortar pore connectivity as ob-served from SEM results above e reduction in chlorideion in microbial mortars prepared and cured usingmicrobial solution was higher than in the ones eitherprepared or cured in microbial solutions is could alsobe attributed to more MICP precipitates in mortar hy-drates further decreasing the permeability e trendcorrelates with that observed by Mutitu et al [1] Chahalet al [31] and Nosouhian et al [45] although involvingother types of Bacillus spp bacteria e authors at-tributed higher chloride ingress in OPC-H2O (H2O) thanin microbial mortars to continuous and interlinked voidsthrough which the ions ingress

342 Chloride Apparent Diffusivity Coefficients e resultsobtained from the chloride error function fitting curve forselected mortars OPC-H2O (H2O) OPC-BM (BM) andOPC-LB (LB) are summarized in Table 4 showing Dapp andDmig with corresponding chloride surface concentration (Cs)and r2 values of the test mortars from the two bacteria understudy using 35 by mass sodium chloride solution

OPC-BM (BM) and OPC-LB (LB) mortars exhibited thelowest apparent diffusion coefficient (Dapp) compared to theother microbial mortars in both BM and LB mortar cate-gories With low chloride ingress low Dapp values wereobserved OPC-H2O (H2O) mortar had the highest Dappvalue Lower chloride Dapp values were demonstrated byBacillus megaterium across all mortar categories thanLysinibacillus sphaericus mortars Perhaps Bacillus mega-terium could be a suitable internal and external crack healingbacterium than Lysinibacillus sphaericus bacteria is could

be attributed to the MICP deposits present in the microbialmortars which upon reacting with hydration cementproducts results in additional cementitious material thatmakes the mortar denser with increased resistivity to Clminusingress and lower chloride diffusivity

4 Conclusions

(1) Both Bacillus megaterium and Lysinibacillussphaericus have the ability to precipitate calciumcarbonate that improves both flexural strength aswell as the pore structure and thus lowering chlorideingress

(2) Flexural strength of the mortar has a positive cor-relation with CaCO3 precipitation for both Bacillus

OPC H2O (H2O)OPC LB (LB)

OPC LB (H2O)OPC H2O (LB)

000002004006008010012014016018020

[Clndash ]

x 1

0ndash3 g

g ce

men

t mor

tar

20 30 40 50 60 70 80 9010Penetration depth (mm)

Figure 7 Chloride ion concentration at different depth of pene-tration for control OPC and varied Lysinibacillus sphaericus mi-crobial mortars

OPC H2O (H2O)OPC BM (BM)

OPC BM (H2O)OPC H2O (BM)

000002004006008010012014016018020

[Clndash ]

x 1

0ndash3 g

g ce

men

t mor

tar


Figure 8 Chloride ion concentration at different depth of pene-tration for control OPC and varied Bacillus megaterium microbialmortars


megaterium and Lysinibacillus sphaericus bacteriais was exhibited by the higher strengths in mi-crobial mortars cured in cultured solutions thanthose cured in distilled water

(3) Lower chloride ingress was observed in both Bacillusmegaterium and Lysinibacillus sphaericus bacteriamicrobial mortars prepared and cured using cul-tured solutions than those cured in distilled wateris was exhibited by the lower Dapp values in mi-crobial mortars cured in cultured solutions thanthose cured in distilled water Bacillus megateriumbacteria improved the chloride ingress resistivitymore than the Lysinibacillus sphaericus bacteria

(4) Lysinibacillus sphaericus bacteria improved flexuralstrength more than the Bacillus megaterium bacteriais was demonstrated by the higher flexuralstrength as well as higher percent flexural strengthgain across all mortar curing ages across all mortarcategories than Bacillus megaterium mortars Per-haps Lysinibacillus sphaericus could be a betterflexural strength enhancer than Bacillus megateriumbacteria

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that they have no conflicts of interest

Acknowledgments

e authors wish to acknowledge the support granted byvarious institutions during the experimentation and writingof this paper e institutions gave access to scholarly re-pository and library materials laboratory facilities anddisposablese institutions include the University of EmbuKenyatta University and Savannah Cement Limited allfrom Kenya and the University of Pretoria South Africa

References

[1] D K Mutitu O M Mulwa J M Wachira R MwirichiaJ K iongrsquoo and J M Marangu ldquoEffects of biocementationon some properties of cement-based materials incorporatingBacillus species bacteriandasha reviewrdquo Journal of SustainableCement-Based Materials vol 8 no 5 pp 309ndash325 2019

[2] R K Verma L Chaurasia and V Bisht ldquoBio-mineralizationand bacterial carbonate precipitation in mortar and concreterdquoJournal of Bioscience and Bioengineering vol 1 pp 5ndash11 2015

[3] C X Qian X N Yu and X Wang ldquoA study on the ce-mentation interface of bio-cementrdquo Materials Characteriza-tion vol 59 pp 1186ndash1193 2018

[4] M Luo and C Qjan ldquoInfluences of bacteria-based self-healingagents on cementitious materials hydration kinetics andcompressive strengthrdquo Construction and Building Materialsvol 4 pp 1132ndash1141 2016

[5] D K Mutitu Diffusivity of Chloride and Sulphate Ions intoMortar Cubes Made Using Ordinary Portland and PortlandPozzolana Cement Chemistry Department Kenyatta Uni-versity Nairobi Kenya 2013

[6] M Azadi M Ghayoomi N Shamskia and H KalantarildquoPhysical and mechanical properties of reconstructed bio-cemented sandrdquo Soils and Foundations vol 57 no 5pp 698ndash706 2017

[7] Z H Dong W Shi and X P Guo ldquoInitiation and repas-sivation of pitting corrosion of carbon steel in carbonatedconcrete pore solutionrdquo Corrosion Science vol 53 no 4pp 1322ndash1330 2011

[8] T W Zewdu and S Esko ldquoService life prediction of repairedstructures using concrete recasting method state-of-the-artrdquoin Proceedings of the 11th International Scientific Conferenceon Modern Building Materials Structures and TechniquesMBMST pp 1138ndash1144 Vilnius Lithuania May 2013

[9] M U Khan S Ahmad and H J Al-Gahtani ldquoChlorideinduced corrosion of steel in concrete an overview of chloridediffusion and prediction of corrosion initiation timerdquo In-ternational Journal of Corrosion vol 2017 Article ID 58192029 pages 2017

[10] M V A Florea and H J H Brouwers ldquoChloride bindingrelated to hydration productsrdquo Cement and Concrete Re-search vol 42 no 2 pp 282ndash290 2012

[11] P K Mehta e Durability of Concrete in Marine Environ-ment-A Review the Performance of Concrete in a MarineEnvironment Vol 68 ACI Publications Farmington HillsMI USA 2011

[12] M Uysal K Yilmaz and M Ipek ldquoe effect of mineraladmixtures on mechanical properties chloride ion perme-ability and impermeability of self-compacting concreterdquoConstruction and Building Materials vol 27 no 1 pp 263ndash270 2012

[13] T Luping and J Gulikers ldquoOn the mathematics of time-dependent apparent chloride diffusion coefficient in con-creterdquo Cement and Concrete Research vol 37 no 4pp 589ndash595 2007

[14] J M Marangu J K iongrsquoo and J M Wachira ldquoChlorideingress in chemically activated calcined clay-based cementrdquoJournal of Chemistry vol 2018 Article ID 1595230 8 pages2018

Table 4 CS Dmig Dapp and r2ndashvalues for different microbial mortars in NaCl

Mortar type Cs Dmig times10minus9 (m2s) Dapp times 10minus10 (m2s) r2

OPC-H2O (H2O) 02255 56052 28430 09730OPC-BM (BM) 01997 52161 26456 09655OPC-BM (H2O) 01965 53982 27380 09523OPC-H2O (BM) 02000 54596 27691 09555OPC-LB (LB) 02016 52764 26762 09510OPC-LB (H2O) 02033 54801 27796 09552OPC-H2O (LB) 02099 55213 28005 09531


[15] J Wang P M Basheer S V Nanukuttan and Y Bai ldquoIn-fluence of compressive loading on chloride ingress throughconcreterdquo in Proceedings of the Civil Engineering ResearchAssociation of Ireland (CERAI) pp 28-29 Belfast UK August2014

[16] J Crank e Mathematics of Diffusion Oxford UniversityPress New York NY USA 2nd edition 1975

[17] L Cheng and R Cord-Ruwisch ldquoSelective enrichment andproduction of highly urease active bacteria by non-sterile(open) chemostat culturerdquo Journal of Industrial Microbiologyamp Biotechnology vol 40 no 10 pp 1095ndash1104 2013

[18] T Rasheeduzzafar E S Hussain and S S Al-Saadoun ldquoPoresolution composition of hydrated cement pastes with refer-ence to corrosion resistance performance of reinforcing steelin concreterdquo in Proceedings of the Vetch Middle East NACECorrosion Conference pp 386ndash389 Manama Bahrain Oc-tober 2004

[19] J M Wachira ldquoChloride ingress in pozzolana based cementrdquoin Proceedings of the 7th Kenya Chemical Society InternationalConference Kisumu Kenya October 2012

[20] R Alizadeh J J Beaudoin and L Raki ldquoMechanical prop-erties of calcium silicate hydratesrdquo Materials and Structuresvol 44 no 1 pp 13ndash28 2011

[21] A Dousti M Shekarchi R Alizadeh and A Taheri-MotlaghldquoBinding of externally supplied chlorides in micro silicaconcrete under field exposure conditionsrdquo Cement andConcrete Composites vol 33 no 10 pp 1071ndash1079 2011

[22] C eodore and S Karen ldquoAlkali fixation of CSH in blendedcement pastes and its relation to alkali-silica reactionrdquoLaboratory of Construction Materials vol 42 no 8pp 1049ndash1054 2012

[23] P Bamforth ldquoConcrete classification for RC structures ex-posed to marine and other salt-laden environmentsrdquo inProceedings of 5th International Symposium on StructuralFaults and Repair pp 31ndash40 Edinburgh UK June 2003

[24] L Bertolini B Elsner P Pedeferri and R Polder Corrosion ofSteel in Concrete Prevention Diagnosis and Repair Wiley-VCHVerlag GMbHampCo KGaAWeinheim Germany 2004

[25] N De Belie and J Wang ldquoBacteria-based repair and self-healing of concreterdquo Journal of Sustainable Cement-BasedMaterials vol 5 no 1-2 pp 35ndash56 2016

[26] V N Rao and T Meena ldquoA review of carbonation study inconcreterdquo IOP Conference Series Materials Science and En-gineering vol 263 no 3 pp 1ndash10 2017

[27] K De Weerdt D Orsakova A C A Muller C K LarsenB Pedersen andM R Geiker ldquoTowards the understanding ofchloride profiles in marine exposed concrete the impact ofleaching and moisture contentrdquo Construction and BuildingMaterials vol 120 pp 418ndash431 2016

[28] O S B Al-Moudi MMasleuddin and Y A B Abdulal ldquoRoleof chloride ions on expansion and strength reduction in plainand blended cement in sulphate environmentsrdquo Constructionand Building Material Journal vol 13 pp 38ndash43 2011

[29] J M Wachira J K iongrsquoo J M Marangu andL G Muriithi ldquoPhysicochemical performance of Por-tlandndashrice husk ash-calcined clay-dried acetylene lime sludgecement in sulphate and chloride mediardquo Advances in Ma-terials Science and Engineering vol 2019 Article ID 561874312 pages 2019

[30] J W Jeffrey P Mondal and C M Mideley ldquoMechanisms ofcement hydrationrdquo Cement and Concrete Research vol 41no 12 pp 1208ndash1223 2012

[31] N Chahal R Siddique and A Rajor ldquoInfluence of bacteria onthe compressive strength water absorption and rapid chloride

permeability of fly ash concreterdquo Construction and BuildingMaterials vol 4 pp 98ndash105 2012

[32] Y C Ersan N Hernandez-Sanabria and N De Belie ldquoEn-hanced crack closure performance of microbial mortarthrough nitrate reductionrdquo Cement and Concrete Researchvol 70 pp 159ndash170 2015

[33] EN 196-1 Cement Part 1 Composition Specifications andConformity Criteria for Common Cement European UnionStandards Beckum Germany 2011

[34] KS EAS 18-1 Kenya Standard Test Method for Oxides Spec-ification of Hydraulic Cement KEBS Nairobi Kenya 2017

[35] ASTM C 293 Standards of Flexural Strength of Concrete Part3 Effects of Variations in Testing Procedures American Societyfor Testing and Materials Elservier London UK 1990

[36] ASTM D7348 Standard Test Methods for Loss on Ignition(LOI) of Solid Combustion Residues ASTM InternationalWest Conshohocken PA USA 2013

[37] R H Bogue ldquoChemistry of Portland cementrdquo British PatentNo 5022 pp 1927ndash1940 1977

[38] K Scrivener R Snellings and B Lothenbach A PracticalGuide to Microstructural Analysis of Cementitious MaterialsCRC Press Boca Raton FL USA 1st edition 2017

[39] ASTM C 1552 Standard Test Method for DeterminingChloride Concentration using Chloride Ion-Selective ElectrodeAmerican Society for Testing and Materials Elsevier LondonUK 2005

[40] C Andrade C Castellote C Alonso and C Gonzalez ldquoNon-steady-state chloride diffusion coefficients obtained frommigration and natural diffusion testsrdquo Materials and Struc-ture vol 33 no 1 pp 21ndash28 1999

[41] M S Vekariya and J Pitroda ldquoBacterial concrete a new erafor the construction industryrdquo International Journal of En-gineering Trends and Technology (IJETT) vol 4 pp 9ndash162013

[42] H iyagarajan S Maheswaran M Mapa et al ldquoInvesti-gation of Bacterial activity on Compressive Strength of ce-ment mortar in different curing Mediardquo Journal of AdvancedConcrete Technology vol 14 no 4 pp 125ndash133 2016

[43] S A Abo-El-Enein A H Ali A H Ali F N Talkhan andH A Abdel-Gawwad ldquoApplication of microbial bio-cementation to improve the physico-mechanical properties ofcement mortarrdquo HBRC Journal vol 9 no 1 pp 36ndash40 2013

[44] H K Kim S J Park J I Han and H K Lee ldquoMicrobiallymediated calcium carbonate precipitation on normal andlightweight concreterdquo Construction and Building Materialsvol 38 pp 1073ndash1082 2013

[45] F Nosouhian D Mostofinejad and H HasheminejadldquoConcrete durability improvement in a sulphate environmentusing bacteriardquo Advances in Materials Science and Engi-neering vol 28 no 1 Article ID 04015064 2016


Chloride ions may also penetrate from external sources suchas seawater or deicing salts In the marine environment theingress of chloride is the most important problem [10 11]

Chloride is bound if it has reacted with cement and isfree if it is available in pore solution [10] Several chemicalinteractions between chloride and the cement constituentsdo affect the chloride penetration into the concretemortarbulk [5 12]e chemical reactions of chlorides with cementpaste start with calcium hydroxide and calcium aluminatehydrate depending on the cations in solution [13]

Chloride ingress in cement-based materials is mainlythrough capillary absorption permeation and diffusion[14] However it may also occur through a multiple of theaforementioned mechanisms Diffusion is the most preva-lent process [15] e ingress of chloridessulphates due tothe various transport mechanisms obeys different laws [16]Fickrsquos second law of diffusion is commonly applied toquantify the aggressive ion ingress due to the multipletransport phenomena

Chlorides react with C3A and the C4AF present in Portlandcement to produce Friedelrsquos salt Ca6Al2O6middotCaCl2middot10H2O orcalcium chloroferrite Ca6Fe2O6middotCaCl2middot10H2O respectively[5 14] No deleterious effect is associated with theseproducts e reaction between the C3A phase and freechlorides in hydrated cement leads to a reduction of Clminusfrom the pore solution [17] is lowers the risk of rebarcorrosion [18] Solutions with high concentrations ofCaCl2 or MgCl2 may cause chemical attack which maylead to a drop in pore water pH and disruption of thecement matrix [19] is is due to the consumption of thesparingly soluble Ca(OH)2 MgCl2 reacts with portlanditeas shown in

MgCl2(aq) + Ca(OH)2(s) + 2H2O(l)⟶ CaCl2 middot 2H2O(aq)

+ Mg(OH)2(s)(1)

Biocementation in OPC lowers chloride ingress andpermeability into the cement matrix [20] is is due to therefinement of the pore structure [5] Chloride ions penetratea pore system and form chloride salts which may crystallizewithin the pores inducing internal cracks [21] e cracksaffect the mechanical and durability properties of concretemortar [20 22 23]

e high alkalinity of the concretemortar introducedduring the bacteria MICP prevents the breakup of thepassive film [25 24] Its carbonation accompanied by thepresence of chloride ions lowers the alkalinity of pore waterRasheeduzafar et al [18] Dousti et al [21] and Rao andMeena [26] observed the amount of free chloride decreasewith increasing C3A and the amount of bound chloridedecreased with increasing OH-concentration from the ce-ment Given this the high corrosion of rebars exposed tochloride media can be assumed to be due to the low alka-linity of pore solution [21 22 27]

OPC based structures are well known for achieving highearly compressive and flexural strength due to large contentand early hydration of C3S [15 28 29] Despite the variousOPC concretemortar advantages it has a more open pore

structure than blended cement structures [3 15 30] OPC-made structures also have a high tendency to form cracksduring and after curing allowing aggressive substances topenetrate the structure Permeability or cracks are one of themain causes of deterioration of these structures and decreasein durability Treatment of cracks and pores are generallydivided into passive and active treatments Passive treat-ments can only heal the surface cracks while active treat-ments can heal both interior and exterior cracks [22 25]

Microbial concretemortar biologically produce calciumcarbonate (limestone) to seal pores that appear within itsmatrix or sealrepair cracks that appear on the structurersquossurface [25 31]esemicrobial deposits could also establishnucleation sites that enhance the early cement hydrationprocess leading to improved compressive and flexuralstrengths Microbial precipitation of calcium carbonatemainly occurs by hydrolyzing urea Urea hydrolysis is achemical reaction in which urea reacts with water andproduces ionic products as shown in the following equation

CO NH2( 11138572 + 2H2O Urease⟶

CO32minus

+ NH41+

(2)

When this reaction occurs in the presence of Ca2+CaCO3 (solid) is formed as shown in the following equation

Ca2++ CO3

2minus ⟶ CaCO3 (3)

When this reaction occurs inside a cementitious porousmaterial after settling it produces sediment a coating and abridge is formed sequentially around and between theparticles and increases interparticle linkage [31]

Specific types of the bacteria genus such as Bacillus alongwith a calcium-based nutrient such as calcium lactate orcalcium nitrate could be added to the ingredients of theconcretemortar when it is being mixed [21] e solublecalcium-containing nutrient is converted to insoluble cal-cium carbonate [22 32] e calcium carbonate solidifies onthe cracked surface thereby sealing it up

e densification of cementitious material due to mi-crobial reaction is important in reducing the permeability ofaggressive ionsis paper reports on findings of the flexuralstrength gain of MICP-containing Kenyan-made OPC andlowered diffusivity of chloride in such laboratory-mademortars

2 Materials and Methods

21 Cement Chemical Analysis In this study the ordinaryPortland cement (OPC 425N) KS EAS 18-12017 [33] andstandard sand ISO 6791989 [34] were used Flexuralstrength tests were carried out in accordance to ASTMC2931990 [35] 100 g sample of the test cement sample wasprepared and analyzed in the usual manner following KSEAS 18-12017 [33] Loss on ignition was done followingASTM D7348 2013 [37] e results are given in Table 1

Using Bogues formula [36] the average phase compo-sition for the test OPC is 65115plusmn 0854 14485plusmn 09133899plusmn 0013 and 10355plusmn 0018 for C3S C2S C3A andC4AF respectively


Tabl

e1

OPC

chem

ical

analysisresults

Sample

Cem

entcompo

sition

wwplusmnSD

Al 2O

3SiO2

SO3

Na 2O

K2O

CaO

MgO

Fe2O

3MnO

LOI

Avg

3643plusmn0010

22182plusmn0010

2695plusmn0021

0410plusmn0001

0975plusmn0006

64627plusmn0042

2084plusmn0025

3403plusmn0012

0173plusmn0001

1519plusmn0001














4Dappt1113872 1113873(12)

⎛⎜⎝ ⎞⎟⎠⎧⎪⎨

⎪⎩

⎫⎪⎬

⎪⎭ (4)


(a) (b)

(c) (d)


Sample cleaning

Sample stabilizing

Sample rinsing

Sample dehydration

Sample drying (CPD)

Sample mounting

Sample coating

SEM sample analysis





Dapp RT

ziFDmig

Int2

Δempty (5)
















(a) (b)

(c) (d)


(a) (b)

(c)











1200


1100

1000

900

800

700

600

500

400

300

200

100

0


Calcite CCaO3 06


178

06lowast

206

76lowast

292

52lowast

264

338

55lowast

363

55lowast

392

88lowast

401

04lowast

422

54lowast

456

17lowast 49

938

lowast

547

00lowast

30 40 50

Cou

nts

(a)

Figure 5 Continued





1600

1500

1400

1300

1200

1100

1000

900

800

700

600

500

400

300

200100

0




266

180

26lowast

208

25lowast

300

49lowast

341

36lowast

364

86lowast

394

36lowast

402

97lowast

423

93lowast

457

94lowast 50

111

lowast

548

25lowast


Cou

nts

(b)


1500

1400

1300

1200

1100

1000

900

800

700

600

500

400

300

200

1000



265

179

57lowast

207

75lowast

229

28lowast

293

47lowast

340

28lowast

364

56lowast

393

83lowast

402

22lowast

4237

4lowast

457

37lowast

470

39lowast 50

031

lowast

547

78lowast


Cou

nts

(c)






169 138 123 185 215 246

278236 208

264306

333

288260

233

315342

370

OPC-BM (BM)

OPC-BM (H2O)

OPC-H2O (BM)

OPC-H2O (LB)

OPC-LB (H2O)

OPC-LB (LB)

g

ain

flexu

ral s

tren

gth




00

200

400

600

800

1000

1200











CH3COO1minus



HCO31minus


+ H2O



(6)


34 Chloride Ingress






4 Conclusions





000002004006008010012014016018020

[Clndash ]

x 1

0ndash3 g

g ce

men

t mor

tar





000002004006008010012014016018020

[Clndash ]

x 1

0ndash3 g

g ce

men

t mor

tar







Data Availability




Acknowledgments


References




















































Tabl

e1

OPC

chem

ical

analysisresults

Sample

Cem

entcompo

sition

wwplusmnSD

Al 2O

3SiO2

SO3

Na 2O

K2O

CaO

MgO

Fe2O

3MnO

LOI

Avg

3643plusmn0010

22182plusmn0010

2695plusmn0021

0410plusmn0001

0975plusmn0006

64627plusmn0042

2084plusmn0025

3403plusmn0012

0173plusmn0001

1519plusmn0001














4Dappt1113872 1113873(12)

⎛⎜⎝ ⎞⎟⎠⎧⎪⎨

⎪⎩

⎫⎪⎬

⎪⎭ (4)


(a) (b)

(c) (d)


Sample cleaning

Sample stabilizing

Sample rinsing

Sample dehydration

Sample drying (CPD)

Sample mounting

Sample coating

SEM sample analysis





Dapp RT

ziFDmig

Int2

Δempty (5)
















(a) (b)

(c) (d)


(a) (b)

(c)











1200


1100

1000

900

800

700

600

500

400

300

200

100

0


Calcite CCaO3 06


178

06lowast

206

76lowast

292

52lowast

264

338

55lowast

363

55lowast

392

88lowast

401

04lowast

422

54lowast

456

17lowast 49

938

lowast

547

00lowast

30 40 50

Cou

nts

(a)

Figure 5 Continued





1600

1500

1400

1300

1200

1100

1000

900

800

700

600

500

400

300

200100

0




266

180

26lowast

208

25lowast

300

49lowast

341

36lowast

364

86lowast

394

36lowast

402

97lowast

423

93lowast

457

94lowast 50

111

lowast

548

25lowast


Cou

nts

(b)


1500

1400

1300

1200

1100

1000

900

800

700

600

500

400

300

200

1000



265

179

57lowast

207

75lowast

229

28lowast

293

47lowast

340

28lowast

364

56lowast

393

83lowast

402

22lowast

4237

4lowast

457

37lowast

470

39lowast 50

031

lowast

547

78lowast


Cou

nts

(c)






169 138 123 185 215 246

278236 208

264306

333

288260

233

315342

370

OPC-BM (BM)

OPC-BM (H2O)

OPC-H2O (BM)

OPC-H2O (LB)

OPC-LB (H2O)

OPC-LB (LB)

g

ain

flexu

ral s

tren

gth




00

200

400

600

800

1000

1200











CH3COO1minus



HCO31minus


+ H2O



(6)


34 Chloride Ingress






4 Conclusions





000002004006008010012014016018020

[Clndash ]

x 1

0ndash3 g

g ce

men

t mor

tar





000002004006008010012014016018020

[Clndash ]

x 1

0ndash3 g

g ce

men

t mor

tar







Data Availability




Acknowledgments


References
































































4Dappt1113872 1113873(12)

⎛⎜⎝ ⎞⎟⎠⎧⎪⎨

⎪⎩

⎫⎪⎬

⎪⎭ (4)


(a) (b)

(c) (d)


Sample cleaning

Sample stabilizing

Sample rinsing

Sample dehydration

Sample drying (CPD)

Sample mounting

Sample coating

SEM sample analysis





Dapp RT

ziFDmig

Int2

Δempty (5)
















(a) (b)

(c) (d)


(a) (b)

(c)











1200


1100

1000

900

800

700

600

500

400

300

200

100

0


Calcite CCaO3 06


178

06lowast

206

76lowast

292

52lowast

264

338

55lowast

363

55lowast

392

88lowast

401

04lowast

422

54lowast

456

17lowast 49

938

lowast

547

00lowast

30 40 50

Cou

nts

(a)

Figure 5 Continued





1600

1500

1400

1300

1200

1100

1000

900

800

700

600

500

400

300

200100

0




266

180

26lowast

208

25lowast

300

49lowast

341

36lowast

364

86lowast

394

36lowast

402

97lowast

423

93lowast

457

94lowast 50

111

lowast

548

25lowast


Cou

nts

(b)


1500

1400

1300

1200

1100

1000

900

800

700

600

500

400

300

200

1000



265

179

57lowast

207

75lowast

229

28lowast

293

47lowast

340

28lowast

364

56lowast

393

83lowast

402

22lowast

4237

4lowast

457

37lowast

470

39lowast 50

031

lowast

547

78lowast


Cou

nts

(c)






169 138 123 185 215 246

278236 208

264306

333

288260

233

315342

370

OPC-BM (BM)

OPC-BM (H2O)

OPC-H2O (BM)

OPC-H2O (LB)

OPC-LB (H2O)

OPC-LB (LB)

g

ain

flexu

ral s

tren

gth




00

200

400

600

800

1000

1200











CH3COO1minus



HCO31minus


+ H2O



(6)


34 Chloride Ingress






4 Conclusions





000002004006008010012014016018020

[Clndash ]

x 1

0ndash3 g

g ce

men

t mor

tar





000002004006008010012014016018020

[Clndash ]

x 1

0ndash3 g

g ce

men

t mor

tar







Data Availability




Acknowledgments


References






















































Dapp RT

ziFDmig

Int2

Δempty (5)
















(a) (b)

(c) (d)


(a) (b)

(c)











1200


1100

1000

900

800

700

600

500

400

300

200

100

0


Calcite CCaO3 06


178

06lowast

206

76lowast

292

52lowast

264

338

55lowast

363

55lowast

392

88lowast

401

04lowast

422

54lowast

456

17lowast 49

938

lowast

547

00lowast

30 40 50

Cou

nts

(a)

Figure 5 Continued





1600

1500

1400

1300

1200

1100

1000

900

800

700

600

500

400

300

200100

0




266

180

26lowast

208

25lowast

300

49lowast

341

36lowast

364

86lowast

394

36lowast

402

97lowast

423

93lowast

457

94lowast 50

111

lowast

548

25lowast


Cou

nts

(b)


1500

1400

1300

1200

1100

1000

900

800

700

600

500

400

300

200

1000



265

179

57lowast

207

75lowast

229

28lowast

293

47lowast

340

28lowast

364

56lowast

393

83lowast

402

22lowast

4237

4lowast

457

37lowast

470

39lowast 50

031

lowast

547

78lowast


Cou

nts

(c)






169 138 123 185 215 246

278236 208

264306

333

288260

233

315342

370

OPC-BM (BM)

OPC-BM (H2O)

OPC-H2O (BM)

OPC-H2O (LB)

OPC-LB (H2O)

OPC-LB (LB)

g

ain

flexu

ral s

tren

gth




00

200

400

600

800

1000

1200











CH3COO1minus



HCO31minus


+ H2O



(6)


34 Chloride Ingress






4 Conclusions





000002004006008010012014016018020

[Clndash ]

x 1

0ndash3 g

g ce

men

t mor

tar





000002004006008010012014016018020

[Clndash ]

x 1

0ndash3 g

g ce

men

t mor

tar







Data Availability




Acknowledgments


References




















































(a) (b)

(c) (d)


(a) (b)

(c)











1200


1100

1000

900

800

700

600

500

400

300

200

100

0


Calcite CCaO3 06


178

06lowast

206

76lowast

292

52lowast

264

338

55lowast

363

55lowast

392

88lowast

401

04lowast

422

54lowast

456

17lowast 49

938

lowast

547

00lowast

30 40 50

Cou

nts

(a)

Figure 5 Continued





1600

1500

1400

1300

1200

1100

1000

900

800

700

600

500

400

300

200100

0




266

180

26lowast

208

25lowast

300

49lowast

341

36lowast

364

86lowast

394

36lowast

402

97lowast

423

93lowast

457

94lowast 50

111

lowast

548

25lowast


Cou

nts

(b)


1500

1400

1300

1200

1100

1000

900

800

700

600

500

400

300

200

1000



265

179

57lowast

207

75lowast

229

28lowast

293

47lowast

340

28lowast

364

56lowast

393

83lowast

402

22lowast

4237

4lowast

457

37lowast

470

39lowast 50

031

lowast

547

78lowast


Cou

nts

(c)






169 138 123 185 215 246

278236 208

264306

333

288260

233

315342

370

OPC-BM (BM)

OPC-BM (H2O)

OPC-H2O (BM)

OPC-H2O (LB)

OPC-LB (H2O)

OPC-LB (LB)

g

ain

flexu

ral s

tren

gth




00

200

400

600

800

1000

1200











CH3COO1minus



HCO31minus


+ H2O



(6)


34 Chloride Ingress






4 Conclusions





000002004006008010012014016018020

[Clndash ]

x 1

0ndash3 g

g ce

men

t mor

tar





000002004006008010012014016018020

[Clndash ]

x 1

0ndash3 g

g ce

men

t mor

tar







Data Availability




Acknowledgments


References




























































1200


1100

1000

900

800

700

600

500

400

300

200

100

0


Calcite CCaO3 06


178

06lowast

206

76lowast

292

52lowast

264

338

55lowast

363

55lowast

392

88lowast

401

04lowast

422

54lowast

456

17lowast 49

938

lowast

547

00lowast

30 40 50

Cou

nts

(a)

Figure 5 Continued





1600

1500

1400

1300

1200

1100

1000

900

800

700

600

500

400

300

200100

0




266

180

26lowast

208

25lowast

300

49lowast

341

36lowast

364

86lowast

394

36lowast

402

97lowast

423

93lowast

457

94lowast 50

111

lowast

548

25lowast


Cou

nts

(b)


1500

1400

1300

1200

1100

1000

900

800

700

600

500

400

300

200

1000



265

179

57lowast

207

75lowast

229

28lowast

293

47lowast

340

28lowast

364

56lowast

393

83lowast

402

22lowast

4237

4lowast

457

37lowast

470

39lowast 50

031

lowast

547

78lowast


Cou

nts

(c)






169 138 123 185 215 246

278236 208

264306

333

288260

233

315342

370

OPC-BM (BM)

OPC-BM (H2O)

OPC-H2O (BM)

OPC-H2O (LB)

OPC-LB (H2O)

OPC-LB (LB)

g

ain

flexu

ral s

tren

gth




00

200

400

600

800

1000

1200











CH3COO1minus



HCO31minus


+ H2O



(6)


34 Chloride Ingress






4 Conclusions





000002004006008010012014016018020

[Clndash ]

x 1

0ndash3 g

g ce

men

t mor

tar





000002004006008010012014016018020

[Clndash ]

x 1

0ndash3 g

g ce

men

t mor

tar







Data Availability




Acknowledgments


References























































1600

1500

1400

1300

1200

1100

1000

900

800

700

600

500

400

300

200100

0




266

180

26lowast

208

25lowast

300

49lowast

341

36lowast

364

86lowast

394

36lowast

402

97lowast

423

93lowast

457

94lowast 50

111

lowast

548

25lowast


Cou

nts

(b)


1500

1400

1300

1200

1100

1000

900

800

700

600

500

400

300

200

1000



265

179

57lowast

207

75lowast

229

28lowast

293

47lowast

340

28lowast

364

56lowast

393

83lowast

402

22lowast

4237

4lowast

457

37lowast

470

39lowast 50

031

lowast

547

78lowast


Cou

nts

(c)






169 138 123 185 215 246

278236 208

264306

333

288260

233

315342

370

OPC-BM (BM)

OPC-BM (H2O)

OPC-H2O (BM)

OPC-H2O (LB)

OPC-LB (H2O)

OPC-LB (LB)

g

ain

flexu

ral s

tren

gth




00

200

400

600

800

1000

1200











CH3COO1minus



HCO31minus


+ H2O



(6)


34 Chloride Ingress






4 Conclusions





000002004006008010012014016018020

[Clndash ]

x 1

0ndash3 g

g ce

men

t mor

tar





000002004006008010012014016018020

[Clndash ]

x 1

0ndash3 g

g ce

men

t mor

tar







Data Availability




Acknowledgments


References























































169 138 123 185 215 246

278236 208

264306

333

288260

233

315342

370

OPC-BM (BM)

OPC-BM (H2O)

OPC-H2O (BM)

OPC-H2O (LB)

OPC-LB (H2O)

OPC-LB (LB)

g

ain

flexu

ral s

tren

gth




00

200

400

600

800

1000

1200











CH3COO1minus



HCO31minus


+ H2O



(6)


34 Chloride Ingress






4 Conclusions





000002004006008010012014016018020

[Clndash ]

x 1

0ndash3 g

g ce

men

t mor

tar





000002004006008010012014016018020

[Clndash ]

x 1

0ndash3 g

g ce

men

t mor

tar







Data Availability




Acknowledgments


References




















































CH3COO1minus



HCO31minus


+ H2O



(6)


34 Chloride Ingress






4 Conclusions





000002004006008010012014016018020

[Clndash ]

x 1

0ndash3 g

g ce

men

t mor

tar





000002004006008010012014016018020

[Clndash ]

x 1

0ndash3 g

g ce

men

t mor

tar







Data Availability




Acknowledgments


References























































Data Availability




Acknowledgments


References




















































BiocementationInfluenceonFlexuralStrengthandChloride...

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