Construction and Building Materials 142 (2017) 92–100
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Construction and Building Materials
journal homepage: www.elsevier.com/locate/conbuildmat
Effect of bacteria on strength, permeation characteristics and
micro-structure of silica fume concrete
Rafat Siddique a, Abir Jameel a, Malkit Singh b,⇑, Danuta Barnat-Hunek c, Kunal d,1, Abdelkarim Aït-Mokhtar e,
Rafik Belarbi e, Anita Rajor f
a
Department of Civil Engineering, Thapar University, Patiala, Punjab, India
Punjab State Power Corporation Limited, Patiala, India
Faculty of Civil Engineering and Architecture, Department of Construction, Lublin University of Technology, Nadbystrzycka St. 40, 20-618 Lublin, Poland
d
School of Agricultural Biotechnology, Punjab Agricultural University, Ludhiana, Punjab, India
e
Department of Civil Engineering, University of La Rochelle, France
f
School of Energy and Environment, Thapar University, Patiala, Punjab, India
b
c
h i g h l i g h t s
Effect of bacteria on strength and permeation properties of concrete is presented.
Concrete is made with 0, 5, 10, and 15% silica fume as cement replacement.
Economic study of bacterial SF concrete is also covered.
a r t i c l e
i n f o
Article history:
Received 29 November 2016
Received in revised form 19 February 2017
Accepted 9 March 2017
Available online 19 March 2017
Keywords:
Bacteria
Concrete
Silica fume
Compressive strength
Sorptivity
Porosity
a b s t r a c t
Influence of bacteria on strength and permeation characteristics concrete incorporating silica fume (SF)
as a substitution of cement has been investigated in this study. The cement was partially substituted with
5, 10 and 15% SF and with constant concentration of bacterial culture, 105 cfu/mL of water. Cement was
substituted with silica fume in concrete by weight. At 28 d, nearly 10–12% increase in compressive
strength was observed on incorporation of bacteria in SF concrete. At 28 d, the compressive strength of
concrete increased from 32.9 to 36.5 MPa for SF, 34.8 to 38.4 MPa for SF5, 38.7 to 43.0 MPa for SF10
and 36.6 to 40.2 MPa for SF15 on addition of bacteria. Water absorption, porosity and capillary water rise
reduced in the range of 42–48%, 52–56% and 54–78%, respectively, in bacterial concrete compared to corresponding nonbacterial samples at 28 days. Reduction in chloride permeability of bacterial concrete was
observed and the total charge passed through bacterial concrete samples reduced by nearly 10% compared to nonbacterial concrete samples at 56 d of age. At 28 d, total charge passed through concrete
reduced from 2525 to 1993 C for SF, 1537 to 1338 C for SF5, 961 to 912 C for SF10 and 1186 to 1174
C for SF15 on addition of bacteria. Calcite precipitation on addition bacteria and confirmed by SEM
and XRD analysis is considered as the reason for improvement in properties of concrete. Economic study
of bacterial SF concrete has also been carried out in the present work. The Benefit/Cost Ratio of bacterial
SF concrete got reduced with the increase in SF quantity. Compared to control concrete, bacterial SF concrete containing 10% silica fume demonstrated highest benefit in improvement in its properties and corresponding highest Benefit/Cost Ratio.
Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction
⇑ Corresponding author.
E-mail addresses: siddique_66@yahoo.com (R. Siddique), abir47@gmail.com
(A. Jameel), bhangal_ms@yahoo.co.in (M. Singh), d.barnat-hunek@pollub.pl
(D. Barnat-Hunek), kunal_pau@yahoo.co.in ( Kunal), karim.ait-mokhtar@univ-lr.fr
(A. Aït-Mokhtar), rbelarbi@univ-lr.fr (R. Belarbi), anitarajor@yahoo.com (A. Rajor).
1
Participated in this work when worked in Department of Civil Engineering,
Thapar University till July 2015.
http://dx.doi.org/10.1016/j.conbuildmat.2017.03.057
0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.
Supplementary cementing materials (SCMs) are extensively
used in enhancing concrete properties. Waste/by-product materials used as SCM in concrete constructions not only check the environmental contamination but also enhance the concrete properties
in fresh as well as in hardened state. Silica fume (SF) is generated
by silicon metal or ferrosilicon alloys producing industry and has
R. Siddique et al. / Construction and Building Materials 142 (2017) 92–100
pozzolanic properties. High strength concrete are made with the
use of SF as supplementary cementitious materials. ACI Committee
[1], in its report has illustrated various possible application and
limitations of use of SF in concrete. Very high strength concrete
having 28-d compressive strength of 100 MPa and higher can be
produced with the use of SF as SCM material. Yogendran et al.
[2] suggested that with respect to improvement in strength properties of high strength concretes (28 d compressive strength ranging from 50 to 70 MPa),use of 15% SF was the optimal substitution
level. Maximum improvement in compressive strength of concrete
incorporating SF as SCM occurs between 7 and 28 d of curing period [3]. Zhou et al. [4] concluded that replacement of 10–15%
cement with silica fume in high strength concretes with higher
water binder ratio (28-d compressive strength between 80 and
115 MPa) has more influence on its compressive strength. The
use of SF has great effect on durability properties of concrete as
well, significant reduction in porosity and chloride permeability
of SF concrete have shown [5–11].
The durability properties of concrete can further be enhanced
by applying bacterial induced carbonate precipitation (BICP) techniques in addition to use of SCM’s. The concept of utilization of
microbiologically induced calcite (CaCO3) precipitation was first
introduced by Ramakrishnan et al. [12] and they used it in repairing the cracks and fissures in concrete. They observed that bacteria
when used in concrete, continuously precipitated calcite layer over
already existing concrete layer. The precipitated calcite layer was
insoluble in water, impermeable and was adhered to the existing
surface of concrete in the form of scales. Bacterial technique when
used in fresh concretes results in calcite precipitation in voids and
consequently improves the strength and lowers permeability of
concrete. De Muynck et al. [13] reported that surface calciteprecipitation reduced water absorption in the range of 65–90% depending on specimen porosity. They also observed decrease in
sorptivity and permeability of concrete specimens due to surface
precipitation of calcite by the bacterium. Wiktors and Jonkers
[14] and Wang et al., [15] observed that gas and water permeability of bacterial concrete reduced after activation of the bacteria and
filling the cracks with the deposited CaCO3 crystals.
For the researchers, the incorporation of bacteria in concrete
manufacturing is an important research area these days. Various
researches have reported the improvement in durability properties
of concrete on implementation of bacterial techniques [16–19]. In
the present study, influence of bacteria addition in silica fume concrete on its strength and permeation properties has been investigated. In addition to properties of concrete, economic study of
bacterial silica fume concrete has also been carried out.
93
pH was maintained equal to 6.8. The prepared solution was
autoclaved at 121 °C for 15 min then cooled down to room
temperature. Then 1 g of glucose was added to the solution. The
solution was steamed for one hour and subsequently, 20% aqueous
100 ml of urea was added to it. Following the sterilization of finally
obtained solution by filtration, the slants were prepared. The
isolated organisms splashed on the surface of the media was incubated at 37 °C and then media colour change from yellow to pink
was observed. The isolate AKKR5 were studied for urease activity.
2.3. Study of bacteria
The bacterial strain morphology was determined using gram
staining method. After staining the bacterial smear slide with crystal violet for 1–2 min, it was flooded with Gram’s iodine for 1–
2 min to remove colour, slide was slowly washed with acetone
for 2–3 s. After decolourization, the slide was rinsed with water
and then flooded with safranin counter stain for 2 min. Thereafter,
the bacterial smear slide was first washed with water and then air
dried.
XRD spectrums of bacterial samples were taken with the help of
X’Pert PRO diffractometer and scanning 2 theta between 5° and
60°. The phases present in bacterial samples were identified with
the help of X’pertHighScorePlus software.
2.4. Materials
Ordinary Portland cement (OPC) conforming to BIS: 8112-1989
[20] an equivalent to ASTM C - 150 – Type I [21] was used. Properties of SF were examined according to BIS 15388-2003 [22] and are
given in Table 1. Coarse aggregate with nominal size of 12.5 mm
having bulk density 1650 kg/m3 was used in this work. Physical
properties of coarse aggregates and fine aggregates are presented
in Table 2.
2.5. Mix composition
Control concrete mix having 28-d compressive strength of
33.0 MPa was designed as per BIS: 10262-1982 [23]. Silica fume
(5, 10 and 15% by weight) was used as partial replacement of
cement. Constant concentration of bacterial culture (105 cfu/mL
of water) was used in all the bacterial concrete mixes. The bacterial
growth curve was prepared by observing optical density at 600 nm
and cell concentration was determined from it. Mixes proportion
details are presented in Table 3. The addition of bacteria has no
effect on the slump value of concrete. As such slump results of
BSF concrete are not presented in the Table 3.
2. Experimental program
2.1. Isolation and identification of bacteria
Alkaliphilic/alkalitolerant bacteria which can tolerate high pH
was secluded from rhizospheric soil and from marble sludge. The
specimens were put in sterilized solution made using NaCl
(0.85%), properly diluted and plated on enrichment medium containing glucose (10.0 g/L), peptone (10.0 g/L), yeast extract (5.0 g/
L), KH2PO4 (1.0 g/L), agar (15 g/L) and pH was attuned to 10.5 with
1 N NaOH solution.
2.2. Urease test
Urea agar medium was prepared using Peptone (1.0 g/L),
sodium chloride (5.0 g/L), 0.2% phenol red, potassium dihydrogen
phosphate (2.0 g/L),agar (20.0 g/L), and distilled water (1000 ml).
The above constituents were dissolved in distilled water and the
2.6. Casting, curing and testing of specimens
Cubes (150 mm) were cast for compressive strength and water
absorption measurement. Cylinders (100 200 mm) were made
for permeability [24] and sorptivity [25] tests. Compressive
strength was measured as per BIS: 516-1959 [26]. Water absorption and porosity measurement were done as per ASTM C 642-13
[27]. Concrete samples were studied with Scanning Electron
Microscope (SEM).Specimens were first dried and then studied at
accelerating voltage range of 20 kV by a SEM (JEOL, JSM 6510
LV). The concrete samples for SEM and XRD analysis were got from
the inner core of the broken cube specimens. XRD spectra of powdered concrete samples were taken with the help of X’Pert PRO
(PANalytical) diffractometer and scanning 2 theta between 5°
and 60°. Phases in concrete were identified with the help of
X’pertHighScorePlus software. All experiments were done in
triplicate.
94
R. Siddique et al. / Construction and Building Materials 142 (2017) 92–100
Table 1
Chemical composition of Silica fume.
Compound
% By mass
SiO2
Al2O3
Fe2O3
CaO
MgO
Na2O
K2O
Loss on Ignition
Colour
Specific Gravity
91.92
1.05
1.11
1.35
0.61
0.6
1.73
1.27
Light grey
2.3
3. Results and discussion
Fig. 1. XRD analysis of bacterial precipitate.
3.1. Urease test
BSF0
40
SF5
BSF5
30
SF10
20
BSF10
SF15
10
BSF15
BS
F1
5
SF
15
BS
F1
0
SF
10
BS
F5
SF
5
0
BS
F0
Compressive strength test results are presented in Figs. 2 and 3.
At 28-day strength of specimen SF5, SF10 and SF15 was 34.84 MPa,
38.72 MPa and 36.63 MPa respectively, compared to 32.85 MPa of
control concrete (SF0). With age (28 to 56 d), all specimen sexhibited was invariably higher strength as compared to their 28 d compressive strength. This was due to continuous hydration of cement
and pozzolanic action of silica fume in concrete. At 56 d, strength
of mixes SF5, SF10 and SF15 was found to be 5.13%, 17.75%, and
10.04% higher than control concrete specimen SF0 (36.55 MPa).
Loss in strength of concrete (SF15) at all ages may be due to reduction in hydration product with increase in SF quantity in matrix,
which resulted decrease in formation of CSH gel.
Studies by Yogendran et al. [2]; Fidjestol [28]; Wild et al. [29];
Sakr [30]; Toutonji and Korchi [31]; Yunsheng et al. [32] revealed
that concrete mixes with silica fume (10–15%) exhibited better
strength than control concrete. The compressive strength increment in bacterial concrete specimens (BSF0, BSF5, and BSF10) as
compared to concrete specimens (with similar SF replacement)
specimens was found to be 11.25%, 10.28%, 11.13%, respectively
(Fig. 2). Improvement in strength of concrete with bacteria might
be due to deposition of the calcite in the pores, subsequently reduction in pores and compact microstructure obtained [16]. The findings of present investigation are similar to those reported by
SF0
SF
0
3.2. Compressive strength
Compressive strength (MPa)
50
The isolate AKKR5 was studied for urease activity, and XRD
(Fig. 1) of bacteria precipitate have indicated formation of calcite.
Concrete mixtures
Fig. 2. Compressive strength of bacterial silica fume concrete at 28 d.
Ghosh et al. [33]. They revealed that bacteria deposited filler material which reduced the pore size, modified the microstructure and
enhanced its strength. Pei et al. [34] concluded that bacterial precipitated CaCO3, filled the voids in concrete, decreased porosity,
improved particle packing effectiveness, made concrete dense and
thereby increasing the strength. Maximum compressive strength
(46.85 MPa) of bacterial concrete (BSF10) was achieved with 10% SF.
3.3. Water absorption and porosity
Water absorption and porosity of concrete are illustrated in
Figs. 4 and 5, respectively. At 28 days, concrete mixes SF5, SF10
Table 2
Physical properties of fine and coarse aggregate.
Sr. No
Material
Water absorption (%)
Specific gravity
Fineness Modulus
1
2
Coarse aggregate
Fine Aggregate
1.14
0.86
2.7
2.68
6.38
2.58
Table 3
Concrete mix proportions.
Mixture No.
Control
SF5
SF10
SF15
BSF0
BSF5
BSF10
BSF15
Cement (kg/m3)
Silica fume (%)
Silica fume (kg/m3)
Natural sand (kg/m3)
Coarse aggregate (kg/m3)
W/C ratio
Water (kg/m3)
Bacteria cells (cfu/mL)
Slump (mm)
390
0
–
569
1164
0.5
185
–
90
370.5
5
19.5
569
1164
0.5
185
–
80
351
10
39
569
1164
0.5
185
–
70
331.5
15
58.5
569
1164
0.5
185
–
73
390
0
–
569
1164
0.5
185
105
–
370.5
5
19.5
569
1164
0.5
185
105
–
351
10
39
569
1164
0.5
185
105
–
331.5
15
58.5
569
1164
0.5
185
105
–
95
SF0
BSF0
SF5
40
BSF5
SF10
BSF10
20
SF15
SF5
2000
BSF5
SF10
BSF10
1000
SF15
BSF15
3
SF0
BSF0
SF5
2
BSF5
SF10
BSF10
1
SF15
BSF15
5
BS
F1
SF
15
SF
10
BS
F1
0
BS
F5
SF
5
0
BS
F0
SF
15
BS
F1
5
SF
10
BS
F1
0
BS
F5
SF
0
BS
F1
5
SF
10
BS
F1
0
BS
F5
SF
5
BS
F0
SF
0
SF
15
Concrete mixtures
Fig. 3. Compressive strength of bacterial silica fume concrete at 56 d.
SF
0
SF
5
0
Concrete mixtures
Water absorption (%)
SF0
BSF0
BSF15
0
Concrete mixtures
Fig. 4. Water absorption of bacterial silica fume concrete at 28 d.
8
SF0
BSF0
6
Porosity (%)
3000
BS
F0
Compressive strength (MPa)
60
Charge passed (Coloumbs)
R. Siddique et al. / Construction and Building Materials 142 (2017) 92–100
SF5
BSF5
4
SF10
BSF10
Fig. 6. Chloride permeability of bacterial silica fume concrete at 28 d.
Percentage decrease in the water absorption of bacterial concrete
at 28 d age were 41.84%, 48.47% and 43.53% for BSF5, BSF10,
BSF15, respectively, compared to concrete specimens SF5, SF10
and SF15. At the age of 56 d, the percentage reductions in water
absorption of BSF5, BSF10 and BSF15 specimens were 52.75%,
53.95% and 55.21%, respectively. Lowest water absorption of
0.85% and 0.75% was observed in concrete specimen BSF10 at
28 d and 56 d, respectively. This decrease in the water absorption
may be related with the precipitated crystals of calcite in voids
and disrupted the connectivity of pores [35]. Pei et al. [34] also
reported similar results of reduction in water absorption of concrete on use of B. subtilis. Porosity results are shown in Fig. 4. At
28 d, incorporation of SF as cement substitution in concrete
resulted in 17.04%, 27.38% and 24.82% reduction in porosity of concrete mixes containing 5% (SF5), 10% (SF10), and 15% (SF15) silica
fume content, respectively. Similar to water absorption results,
concrete specimen containing 10% SF content exhibited lower
porosity at 28 d and 56 d. The fine particles of silica fume filled
the voids and formed a denser matrix. On inclusion of bacteria,
the reduction in porosity of all the bacterial concrete specimens
BSF0, BSF5, BSF10 and BSF15was about 50 to55% compared to corresponding concrete specimens SF0, SF5, SF10 and SF15. With
respect to water absorption and porosity, 10% SF is optimum dose.
These results are in accordance with the De Muynck et al. [18]
where 65–90% reduction in water absorption and porosity was
noticed in bacterial concrete.
SF15
2
BSF15
5
BS
F1
0
SF
15
BS
F1
SF
10
BS
F5
SF
5
BS
F0
SF
0
0
Concrete mixtures
Fig. 5. Porosity of bacterial silica fume concrete at 28 d.
and SF15 exhibited 17.04%, 27.38% and 24.82%, lower water
absorption in comparison to control mix. With increase in age from
28 d to 56 d, the water absorption reductions in control concrete
and SF concrete specimens were marginal. Concrete specimens
containing 10% SF exhibited minimum water absorption at 28 d
and 56 d.
Addition of bacteria cells (105 cfu/mL) played a significant role
in decreasing water absorption of SF concrete specimens. Metabolic activities by bacteria led to the precipitation of calcite in
pores. Precipitation of calcite in the pores, sealed the water ingress
which lead to decrease in water absorption of bacterial concrete.
3.4. Rapid chloride permeability test (RCPT)
RCPT results are given in Fig. 6. Silica fume concrete mixes
showed lesser permeability in comparison to the control (SF0). At
28 d, total charge passed through silica fume concrete mixes containing 5% (SF5), 10% (SF10) and 15% (SF15) was 1229, 840 and
1132 coulombs, respectively, compared to 2525 coulombs of control concrete (SF0).The decrease in the charge passed through concrete specimens was due to improved pore structure of the
hydrated matrix with the use of silica fume (Khan [8]; Ramezanianpour and Malhotra [10]; Shi [36]). With increase in age, it was
found that chloride ion penetration in all concrete mixes were
invariably lower at the age of 56 d compared to that at 28 d and
this was due to the continuous hydration of cement in concrete.
At 56 d, charge passed through silica fume concrete specimens
containing 5, 10 and 15% silica fume was 38.10, 57.69, and 43%
lower than that of control specimen.
At 28 d, bacterial concrete specimens BSF5, BSF10 and BSF15
displayed 12, 18 and 16% lower charge passed compared to that
for SF5, SF10 and SF15, respectively. The results obtained in the
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R. Siddique et al. / Construction and Building Materials 142 (2017) 92–100
Capillary water rise (mm)
0.015
SF0
BSF0
SF5
0.010
BSF5
SF10
BSF10
0.005
SF15
BSF15
BS
F1
5
SF
15
BS
F1
0
SF
10
F5
BS
SF
5
BS
F0
SF
0
0.000
decreased [15]. The biological precipitation of calcite resulted in
dense microstructure and decrease in capillary water uptake, chloride migration and water absorption (De Muynck et al. [18];
Nemati and Voordouw [37]; Tiano et al. [38]; Whiffinn [39]).
Reduction in sorptivity in concrete specimen SF10 was due to
formation of dense microstructure due to pozzolanic reaction of
SF. Addition of 10% SF by mass of cement in concrete caused maximum improvement in capillary water uptake performance and an
p
index of 3.42 mm/ h was a chieved. It is believed that Index values
p
less than 6.0 mm/ h represents excellent concrete performance
[40] which confirmed that the findings of this investigation similar
with the published literature. Chan and Ji [41] also confirmed that
addition of silica fume to concrete reduced sorptivity.
Concrete mixtures
Fig. 7. Sorptivity of bacterial silica fume concrete at 28 d.
present study are in good agreement with Chahal et al. [19]
wherein it is suggested that calcite deposition by bacteria reduced
the chloride permeability of bacterial concrete. Chloride permeability of silica fume concrete made with and without bacteria varied between low to very low as per ASTM C 1202.
3.5. Sorptivity
Fig. 7 shows that capillary water absorption of concrete were
significantly influenced by the addition of bacteria, and reduction
in the range of 50–70% in sorptivity coefficient of specimens were
observed both at 28 and 56 d. The minimum water capillary uptake
p
was observed in BSF10 (0.0021 mm/ s) at the age of 56 d. With
the addition of the bacteria in concrete, the microstructure of the
changed, therefore the water transport properties of the specimen
3.6. SEM analysis of concrete
SEM images of bacterial and nonbacterial silica fume concretes
are shown in Figs. 8–11. The SEM analysis revealed the presence of
calcite in the concrete samples incorporating bacteria. The formation of calcium silicate hydrate (CSH), portlandite (CH) and pores
was observed in all the concrete samples. In case of bacterial concrete, the precipitation of calcite (C) was visible in pores due to
which increase in strength and permeation properties were
observed. As shown in Fig. 9, compared to silica fume concrete,
the formation of CH crystals in bacterial silica fume concrete was
less and CSH gel is spread more homogeneously and densely over
the entire image. The calcite crystal are also visible in bacterial silica fume concrete (BSF5).
SEM micrograph of SF10 specimens (Fig. 10) shows dense
microstructure of concrete with CSH formation with negligible
amount of CH and lesser pores space, compared to control as well
(a)
(b)
CH
Voids
C
CSH
CSH
CH
Fig. 8. SEM micrograph showing (a) Control concrete (SF0) (b) Bacterial concrete (BSF0).
Fig. 9. SEM micrograph showing (a) Silica fume concrete (SF5) (b) bacterial Silica fume concrete (BSF5).
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R. Siddique et al. / Construction and Building Materials 142 (2017) 92–100
Fig. 10. SEM micrograph showing (a) Silica fume concrete (SF10) (b) bacterial Silica fume concrete (BSF10).
Voids
Voids
(a)
(b)
CSH
CSH
CH
Fig. 11. SEM micrograph showing (a) Silica fume concrete (SF15) (b) Bacterial Silica fume concrete (BSF15).
as other silica fume concretes. In bacterial silica fume concrete
specimen (Fig. 10) calcite precipitation were clearly seen which
shows densification of paste aggregate matrix which resulted in
decreased porosity and gain in strength (De Muynck et al. [18];
Ghosh et al. [33]; Pei et al. [34]). Zhang et al. [42] also reported that
bacteria served as pore filler sites during precipitation process.
SEM image examination revealed that bacterial concrete matrix
was more compact and dense compared to corresponding nonbacterial concrete specimens.
3.7. XRD analysis of bacterial concrete
XRD of bacterial and nonbacterial silica fume concrete specimens shows peaks of quartz (Q), calcium silicate hydrate (CSH),
calcite (C), Larnite (L) and ettringite (E). The X-ray diffractograms
of concrete specimens are shown in Figs. 12–15. The quantitative
analysis of powder concrete samples with and without bacteria
shows that calcite composition increased significantly in bacterial
silica fume concrete samples compared to non-bacterial concrete
samples. The hump from 28° to 33° as shown in Fig. 13 indicate
the presence of amorphous content in addition to crystalline
phases of calcite, portlandite and larnite.
4. Economics of bacterial concrete
The compressive strength and permeation properties and cost
involved in making one cubic meter of concrete have been considered for initial economic comparison of bacterial silica fume concrete with silica fume concrete. Optimum bacteria concentration
of 105cells/ml has been taken into account in the present study.
In each mix, 6 gm of bacteria was added. The prices of the different
materials used in manufacturing of concrete are taken as per the
prevailing Indian market rates and for comparison purpose, the
cost has been converted into US $ considering Rs. 67 (INR) equal
to 1 US $. The prevailing rates of materials taken the present study
are as under:
Rate of cement = Rs. 6 per kg (US $ = 0.089)
Rat of aggregates per m3 = Rs. 980/-(US $ = 14.62)
Rate of Bacteria = Rs. 80 per gm (US $ = 1.19)
Rate of Silica Fume = Rs. 45 per kg (US $ = 0.67)
The comparison of cost, permeability and compressive strength
of concrete using different ratio of silica fume and bacteria for one
cubic meter of concrete is shown in Table 4. The negative sign
represent percentage decrease and positive values reflect the
increase in percentage. However, negative sign in case of permeation properties and positive sign in case compressive strength of
concrete indicates improvement in its quality. The perfect concrete
mixtures are that do not enhance cost significantly with the inclusion of bacteria, but significantly improve compressive strength
and reduce permeability. It is known fact that decreases in permeability of concrete increases its life. However, the exact increase in
life of concrete in number of years with decrease in permeability
has not been established yet. Cusson et al. [43] has reported that
the service life of concrete bridge decks can increase over 100 years
with low permeability high performance concrete as compared to
only 20 years for normal concrete decks. The permeability for such
concrete reduced nearly 30% from the control concrete thus giving
favourable results. Jonkers et al. [44] found that if the bacteria add
50% to the concrete cost, it would increase the total cost of
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R. Siddique et al. / Construction and Building Materials 142 (2017) 92–100
6000
6000
5000
5000
4000
Q
Counts
3000
2000
2000
Q
1000
CS C
P
C
P
CSH
Q Q Q
1000
Q
Q PC
0
C
P Q Cb
C
T
20
30
P
Q
Q
Q
QP
0
10
20
30
40
50
60
10
40
50
60
2 Theta Angle
2 Theta Angle
Fig. 12. XRD diffractogram of control concrete at 28 d (P = Portlandite; Q = Quartz;
C = Calcite; CS = Calcium Silicate; CSH = Calcium Silicate Hydrate).
6000
Fig. 15. XRD diffractogram of bacterial Silica fume concrete (BSF15) at 28 d
(P = Portlandite; Q = Quartz; C = Calcite; Cb = Cristobalite; CSH = Calcium Silicate
Hydrate; T = Tilleyite).
construction by around 1 to 2% which will be much less than the
maintenance costs incurred. It was also concluded that the bacteria
could remain as dormant spore for a period up to 50 years without
media or water, which can again become active upon receiving
optimum conditions for its revival and growth which would be
beneficial for enhancing the durability by reducing the permeability through calcite production.
The Benefit/Cost Ratio for the samples is given in Tables 5 and 6
where in,
5000
4000
Counts
Q
3000
CSH
Counts
4000
3000
Q
2000
CQ
P/C
TC
Cb
P/Q
1000
CSH
P
Q
P
QP
0
10
20
30
40
50
60
2 Theta Angle
Fig. 13. XRD diffractogram of bacterial Silica fume concrete (BSF0) at 28 d
(P = Portlandite; Q = Quartz; C = Calcite; CSH = Calcium Silicate Hydrate;
Cb = Cristobalite; T = Tilleyite).
6000
5000
Counts
4000
3000
Q
P
Cb
C
CS
Q
1000
C
CSH
2000
P
Q
Q
P
Q
0
10
20
30
40
50
60
2 Theta Angle
Fig. 14. XRD diffractogram of bacterial Silica fume concrete (BSF10) at 28 d
(P = Portlandite; Q = Quartz; C = Calcite; CS = Calcium Silicate; CSH = Calcium
Silicate Hydrate; Cb = Cristobalite).
A = Value of specific property for mixture
B = Improvement of value with respect to control concrete
= 1 (Value of property of mixture/Value of property of Control
concrete)
C = Benefit for specific property. Calculated as product of (B)
and weightage factor.
Weightage factor is a measure of importance of specific property of concrete to bring them to same scale for calculations. In
the present case, all four properties compressive strength, permeability, water porosity and water absorption have been considered
equally important; therefore, highest weightage factor of 10 is
given to each.
Benefit/Cost Ratio of concrete is the ratio of sum of benefits (C)
for compressive strength, permeability, water porosity and water
absorption divided by its cost.
Compared to control concrete, bacterial silica fume concretes
showed increase in Benefit/Cost Ratio up to 10% replacement of
cement with silica fume and thereafter decrease in Benefit/Cost
Ratio was observed. Bacterial silica fume concrete BSF10 showed
highest Benefit/Cost Ratio. However, when compared to corresponding silica fume concrete mixture, bacterial silica fume concrete demonstrated decrease in Benefit/Cost Ratio with increase
in silica fume replacement level. This means that lesser benefits
in terms of improvement of properties of concrete were obtained
on addition of bacteria in concrete as the SF substitution level
increased. The addition of bacteria in concrete has demonstrated
increase in benefit in terms of improvement in properties of bacterial concretes with reference to both control concrete as well as
corresponding silica fume concrete mixtures. Since the cost factor
(Rs. 480.0) of bacterial component in all concrete mixtures was
constant, therefore, Benefit/Cost Ratio largely depended on cost
factor of silica fume component.
99
R. Siddique et al. / Construction and Building Materials 142 (2017) 92–100
Table 4
Comparison of cost, permeability and compressive strength of silica fume and bacterial silica fume concretes with control concrete and corresponding silica fume concrete.
Sr.
No.
Mix
1
2
Control
concrete
(SF0)
SF5
3
SF10
4
SF15
5
BSF0
6
BSF5
7
BSF10
8
BSF15
Cost in
INR (US
$)
Permeability
(Coulombs)
Compressive
Strength
(MPa)
Compared to control concrete
Compared to corresponding silica fume concrete.
Change
in cost
(%)
Change in
Chloride
Permeability (%)
Change in
Compressive
Strength (%)
Change
in cost
(%)
Change in
Chloride
Permeability (%)
Change in
Compressive
Strength (%)
3320
(49.5)
2525
32.9
–
–
–
–
–
–
4080
(60.9)
4841
(72.3)
5601
(83.86)
3800
(56.72)
4560
(68.1)
5321
(79.2)
6081
(90.8)
1537
34.8
22.89
39.13
5.77
–
–
–
961
38.7
45.81
61.94
17.30
–
–
–
1186
36.6
68.70
53.03
11.25
–
–
–
1993
36.6
14.5
21.0
11.2
14.5
21.0
11.2
1338
38.4
37.35
47.0
16.71
11.76
12.95
10.34
912
43.1
60.27
63.88
31.0
9.91
5.1
11.37
1174
40.3
83.16
53.51
22.49
8.57
1.0
10.11
INR = Indian Rupee.
Table 5
Benefit/Cost Ratio for bacterial silica fume concrete with reference to control concrete.
Property
Compressive Strength(MPa)
Permeability (Coulumbs)
Water Porosity (%)
Water Absorption (%)
Benefit
Cost (Rs.)
Benefit/Cost 100
Weightage Factor
10
10
10
10
BSF0
BSF5
BSF10
BSF15
A
B
C
A
B
C
A
B
C
A
B
C
36.6
1993
3.07
1.22
13.42
3800
0.35
0.11
0.21
0.55
0.47
1.12
2.1
5.5
4.7
38.4
1338
2.67
1.07
17.76
4560
0.39
0.17
0.47
0.60
0.53
1.67
4.7
6.06
5.33
43.1
912
2.36
0.85
22.31
5321
0.42
0.31
0.64
0.65
0.63
3.10
6.4
6.51
6.3
40.3
1174
2.41
0.99
19.72
6081
0.32
0.22
0.53
0.64
0.57
2.25
5.35
6.44
5.68
Table 6
Benefit/Cost Ratio for bacterial silica fume concrete mixtures with reference to corresponding silica fume concrete mixture.
Property
Compressive Strength(MPa)
Permeability (Coulumbs)
Water Porosity (%)
Water Absorption (%)
Benefit
Cost (Rs.)
Benefit/Cost X 100
Weightage Factor
10
10
10
10
BSF0
BSF5
BSF10.
BSF15
A
B
C
A
B
C
A
B
C
A
B
C
36.6
1993
3.07
1.22
13.42
3800
0.35
0.11
0.21
0.55
0.47
1.12
2.1
5.5
4.7
38.4
1338
2.67
1.07
12.14
4560
0.27
0.10
0.13
0.53
0.42
1.34
1.3
5.3
4.2
43.1
912
2.36
0.85
11.65
5321
0.22
0.11
0.05
0.52
0.48
1.14
0.51
5.2
4.8
40.3
1174
2.41
0.99
10.71
6081
0.17
0.10
0.01
0.53
0.43
1.01
0.1
5.3
4.3
5. Conclusions
i. Addition of bacteria in SF concrete enhances the compressive strength at all ages. Maximum 56-day strength of bacterial concrete was observed with 10% SF and was about 12%
more than that of the concrete with same silica fume
replacement.
ii. Calcite precipitation in pores by Bacterium caused lower
water absorption and porosity in concrete mixtures with
bacteria addition as compared to the mixtures without bacteria. The bacteria addition reduced water absorption and
porosity by 48–55% and 50–55%, respectively, in bacterial
concrete compared to corresponding nonbacterial concretes.
iii. Chloride permeability of SF concrete decreased on addition
of bacteria. The discontinuity of voids is reasons for lower
charge passed through the bacterial concrete specimens.
iv. Water intake of bacterial SF concrete through capillary voids
was lower than that of nonbacterial SF concrete.
v. Microstructure analysis demonstrated formation of calcite in
the form of calcium carbonate at 28 and 56 d. Calcite precipitation was more at 56 d and in all concrete mixes of concrete, calcite was present.
vi. The Benefit/Cost Ratio of bacterial silica fume concrete with
reference to corresponding silica fume concrete decreased
with increase in SF quantity as replacement of cement. In
comparison to control, bacterial silica fume concrete con-
100
R. Siddique et al. / Construction and Building Materials 142 (2017) 92–100
taining 10% silica fume demonstrated highest benefit in
improvement in its properties and corresponding highest
Benefit/Cost Ratio.
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