Construction and Building Materials 55 (2014) 462–469
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Bio-bricks: Biologically cemented sandstone bricks D. Bernardi a, J.T. DeJong b, , B.M. Montoya c, B.C. Martinez d ⇑
a
ENGEO Incorporated, Walnut Creek, CA, USA Department of Civil and Environmental Engineering, University of California, Davis, CA, USA c Department of Civil, Construction, and Environmental Engineering, North Carolina State University, Raleigh, NC, USA d Geosyntec Consultants, Oakland, CA, USA
b
h i g h l i g h t s
A novel technique to manufacture bio-bricks using a biologically mediated natural cementation process is presented. Results show that bio-bricks bio-bricks can have compressi compressive ve strengths up to 2 MPa. P-wave velocity measurements show bio-brick stiffness to be relatively uniform and high. Bio-bricks are comparable to bricks prepared with the more conventional cement and hydraulic lime additives.
a r t i c l e
i n f o
Article history: Received 24 September 2013 Received in revised form 9 January 2014 Accepted 11 January 2014 Available online 14 February 2014 Keywords: Bricks Calcite precipitation Microbially induced calcite precipitation Compression Compression strength Stiffness
a b s t r a c t
The cementation of sand into sandstone through microbial activity is a novel technology with a wide range of possible applications. The cementation process involves the introduction of bacteria and nutrients ents to sand, sand, and throug through h bacter bacterial ial proces processes ses calcit calcite e precip precipitat itationbinds ionbinds partic particles les togeth together, er, ultima ultimatel tely y crecreating a sandstone material. This technology could provide a new, more sustainable building material in the form form of ‘‘bio‘‘bio-bri bricks cks’’. ’’. This This paper paper descri describes bes the treatm treatment ent techni technique que as well well as result results s from from testin testing g after after brick manufacturing. Bricks were tested to determine compression (p-wave) wave velocity, unconfined compression strength, and calcite concentration. P-wave velocity, stiffness, strength, and calcite content of bio-bricks all increase with further treatment of bacteria and cementation media. Results show that bio-brick bio-bricks s can have strengths strengths ranging from 1 MPa to 2 MPa. Bio-bricks Bio-bricks are comparable comparable in terms of stress stress and stiffness to bricks prepared with the more conventional cement and hydraulic lime additives. 2014 Elsevier Ltd. All rights reserved.
1. Introduction The global use of resources and emphasis on sustainable infrastructure is a growing societal issue civil engineers must address [21].. The international population is growing at an unprecedented [21] rate, and in response, response, civil infrastructure infrastructure must must expand and be rehabilitate bilitated d in a sustaina sustainable ble manner. manner. The The demand demand on natural natural resource resources s is far greaterthan greaterthan thesupplyin both both develo developedand pedand develo developin ping g councountries [1] [1].. Sustainable Sustainable development development must consider the energy and material material flows flows through the construction, construction, maintenance, maintenance, dismantling, dismantling, and material disposal related to a project [28] [28].. Meeting the societal demands demands with locally available available resources resources and minimal material and energy energy promot promote e a sustaina sustainable ble approa approach ch to develo developm pment. ent. Biologic Biological al processe processes s have been harnesse harnessed d for a multitud multitude e of engineering applications applications [9,10] [9,10],, DeJon DeJong g et al. al. [11] [11].. Bio-geochemical Bio-geochemical
⇑ Corresponding author. Address: Department of Civil and Environmental Engineering, University of California, One Shields Ave., Davis, CA 95616, USA. Tel.: +1 530 754 8995.
E-mail address:
[email protected] (J.T.
[email protected] (J.T. DeJong). http://dx.doi.org/10.1016/j.conbuildmat.2014.01.019 0950-0618/ 2014 Elsevier Ltd. All rights reserved.
processes that induce mineral precipitation have been utilized for many applications, including improving the strength and stiffness of soil [8,32,20] as an alternative to traditional chemical grouting which which can be environm environmenta entally lly hazardou hazardous s [17] [17].. Microbi Microbially ally induced induced calcit calcite e precip precipita itatio tion n (MICP (MICP)) can be used used for a varie variety ty of other other appl appliications including environmental environmental remediation remediation [13] [13],, improved improved duradurability bility and remedia remediation tion of concrete concrete [25,7], [25,7], calciu calcium m remov removal al in wastewater [15] [15],, and carbon sequestration [26] sequestration [26].. Although Although various forms of MICP are availabl available e using using differen differentt bacterial and precursors, the form of MICP treatment used for this research utilized natural soil bacteria to metabolize urea, increasing the pH of the pore pore water water,, prom promoti oting ng miner mineral al precip precipita itatio tion. n. UreUreolytic olytic bacteria bacteria are prevalen prevalentt in natural natural soils; soils; they increase increase the alkalinity of the soil by hydrolyzing the urea to produce ammonia and carbon dioxide. This induces calcite precipitation primarily at particle–particle contacts, which increases the strength and stiffness ness of the sand. sand. The amoun amountt of calcit calcite e cement cementati ation on is propo proportio rtiona nall to the concentrati concentrations ons of chemicals chemicals supplied supplied (e.g. urea and calcium) calcium) and the numbe numberr of treatm treatmen ents ts perfo perform rmed ed.. The The reacti reaction on netwo network rk for for the net urea hydrolysis reaction and formation of calcite is:
D. Bernardi et al. / Construction and Building Materials 55 (2014) 462–469 NH2 2þ
Ca
CO NH2 þ 3H2 O ! 2NHþ þ HCO þ OH 4 3
þ HCO3 þ OH ! CaCO3 þ H2 O
Current methods for brick manufacturing vary widely, but most methods include high energy processes of compression under high stresses and/or baking at high temperatures. The most common method of brick manufacturing is by firing clay at high temperatures. Red clay bricks are typically placed in wood molds and dried in the sun for 2–3 days and then baked in the oven for 24 h at temperatures up to 1200 C [6]. Engineering properties and physical characteristics differ between red clay bricks primarily due to the clay source andfiring temperature. For example, Lower Oxford Clay based bricks have a 28 day unfired strength of 3.5 MPa and a fired strength above 20 MPa [22] (and other references in Table 1). Alternatives to red clay bricks include sand–lime bricks, which are manufactured using water, sand, and lime mixed together, compacted together at a pressure of 20 MPa and then autoclaved for up to 9 h at temperatures of up to 190 C (Fang et al. [12]). Another method uses clay in addition to lime, cement, and a manufacturing byproduct such as ground granulated blast furnace slag. The bricks are cured at room temperature, yielding strengths between 2.7 and 5 MPa [23]. Other methods of manufacturing earth-based building materials consists of adobe, cob, rammed earth, and compressed earth bricks [29,24]. The range of strengths and modulii for these and other bricks are summarized in Table 1. This paper summarizes a research program undertaken to develop a natural, bio-mediated process for the manufacturing of bio-bricks (Bernardi [4]). The materials, treatment methods, and measurement techniques are presented first. Bricks produced using the novel technique are compared against cement and lime treated bricks. Results assessing the treatment uniformity within individual bricks, as measured and indicated by shear and compression wave velocity, are presented. The correlation between cementation level (precipitated calcite concentration) and wave velocities is then investigated. A comparison of brick strength between the three brick types is presented, followed by correlations between compressive strength and velocity measurements. 2. Materials and test methods 2.1. Soil The sand used for productionof allbricks was silica rich #1masonrysand, quarried in Chico, California. Thissand was used because it is moderately graded, locally produced, and available in large quantities. Salient sand characteristics are presented in Table 2.
2.2. Bacteria and growth conditions The soil bacteriumutilized in this studywas Sporosarcina paseurii (ATCC 11859). Cultures were grown in an Ammonium-Yeast Extract media (ATCC 1376) as described in Mortensen and DeJong [20] (0.13 M Tris Buffer, 10 g of (NH4)2SO4, and 20 g of yeast extract per liter of deionized water). The bacteria were inoculated in the growth media and incubated aerobically in a 30 C water bath shaken at 200 rpm for approximately 24 h. Bacteria were incubated until samples obtained an optical density near 1.0 using a spectrophotometer (600 nm wavelength). The Table 1
Strength of other bricks and materials.
Table 2
Sand characteristics. Material
D50 (mm)
C u
C c
Gs
emin
emax Mineralogy
#1 Masonry sand
0.42
2.6
1.2
2.6
0.5
0.8
Quartz
sand was inoculated with the bacteria by percolating the bacterial solution through the sand top-down, which was retained for 4 h in the soil before treatments with cementation media began.
2.3. Cementation media A urea-calcium medium was used to drive calcite precipitation. The cementation media consisted of urea (200 mM), calcium chloride (100 mM), and nutrient broth (0.5 g/L). The nutrient broth, which contains beef extract and peptone, was used to enable bacteria reproduction within the brick mold.
2.4. Brick mold Three identical brick molds were fabricated from PVC plastic, with each mold containing five bricks with dimensions of 91 mm by 58 mm by 200 mm (similar dimensions as standard red clay bricks, Fig. 1, Bernardi [4]). The mold is assembled with screws andsilicone sealant with drain holes at the mold base to enablefluid to percolate through. The mold base enables saturation of the mold during bacterial treatment and relatively unobstructed flow during cementation treatment. Three plastic screens with different opening sizes (3.360 mm, 0.711 mm, and 0.178 mm) were placed at themoldbase to prevent soil lossduring treatment. The sand is then placed, three additional screens were placed on top of the sand, and a low confining stress (10 kPa) applied with a rubber band. Coarse gravel is placed on top to prevent erosion of the sand when the treatment solution is added.
2.5. Preparation and treatment programs 2.5.1. MICP treatment method The bacterial solution was added to the sand by percolation (i.e. unrestrained flushing of fluid from top to bottom). The treatment method implemented was selected in order to ensure bacteria attachment at particle contacts within the permeable sandmatrix. Effluent consisting of the bacterial solutionwas cycled through the sand two additional times to improve bacteria attachment throughout the sample, and during the second cycle the mold was sealed to create fully saturated conditions. Treatment media was added to the sand by percolation. Three brick molds were treated for different amounts of time. Since the bio-bricks were going to be compared to lime and cement treated bricks that were cured for up to 28 days, an equivalent treatment time was devised. Treatments ranged from 1 to 5 times per day, depending on permeability reduction from the treatment, so an average of 3 treatments per day was defined as equivalent to one day of curing of conventional bricks. The molds were treated at 7 days (21 treatments), 14 days (42 treatments), and 28 days (84 treatments). A 12 h retention was usually allowed overnight before treatment started the following day. All treatments contained the cementation media (Table 2). pH readings were made of the influent solution and the immediate effluent of each brick with the use of pH strips (displaying pH in the range of 6.5–9.0). Occasionally excess calcite precipitation on the injection face of the bricks reduced permeability sufficiently that the mold was partially disassembled and the screens cleaned. Once the required treatments were completed, two pore volumes of deionised water with50 mM sodium chloride were percolated through to rinse excess chemicals from the pore space. The mold was then disassembled and thebricks were oven dried overnight in a 77 C oven.The brick dimensions were measured and the mold was weighed again to estimate changes in dry density and void ratio. 2.5.2. Lime treatment method Lime bricks were prepared by combining dry sand with varied volumes of hydraulic lime. The evaluated percents of hydraulic lime to sand by volume were 20%, 25%, 30%, 40%, and 50% for each set of five bricks (these correspond to percentages by weight of about 10.1%, 12.7%, 15%, 20.9%, and 26.7%). These mixtures bracket the strengthsthatwere expected from the bio-bricks ( 2 MPa) andwereselected in part frommanufacturer recommendations. The limeused was fromthe manufacturer St. Austier and is a natural hydraulic lime (NHL5) with approximately 20–30% clay included as the silica source. The lime and the sandwere measured, dry mixed, and then water was added until proper workability was achieved ( 250 mL of water per brick). The sand–lime mixture was placed in approximately 2.54 cm lifts and tamped 50 times using the steel overburden stress tamper. The overburden stress was then applied the same way as the bio-brick treatment. The three brick molds were used to make batches of bricks to be tested at different curing times. The bricks set for 2 days and then cured for 7, 14, and 28 days in a constant humidity chamber ( 95% humidity, 13.3 C). After curing was complete, the brick molds were disassembled and bricks dried for up to 2 days in a 77C oven before testing.
Bricks
Strength (Mpa)
Elastic modulus (MPa)
Autoclaved bricks Red clay bricks Compressed earth block Rammed earth Adobe Sandstone Limestone
20 >20 0.7–3.1 0.75–1.5 1.2–1.8 70 10–70
– – 200 72–102 100–300 45,000 –
[12,14,5,18,30,3,27,16] .
463
D. Bernardi et al. / Construction and Building Materials 55 (2014) 462–469
464
Overburden Stress Rip Rap Top Filter Screens
Brick Divider Bottom Filter Screens and Drain Holes
Fig. 1. Image of assembled brick mold (left image with one side removed for display purposes).
2.5.3. Cement treatment method Cement bricks were prepared by combining dry sand to various volumes of type II/V cement according to ASTM C150. The cement was added in quantities of 5%, 10%, 15%, 20%, and 25% by volume for each respective brick in a batch (corresponding to percents by weight of about 3.7%, 7.4%, 11.2%, 15.3%, and 19.3%). The cement amount selected was to bracket the expected strengths of the bio-bricks. The cement and sand were measured and manually mixed together dry and then water was added until a proper consistency for workability was achieved ( 250 mL per brick). The mixture was then placed in approximately 2.54 cm lifts and tamped 50 times using the overburden stress tamper. An overburden stress was applied. The bricks set for one day and then cured for 7, 14, and 28 days in a constant humidity chamber ( 95% humidity, 13.3 C). After curing was completed, the bricks were dried for up to 2 days in a 77C oven before testing.
2.6. Measurement methods 2.6.1. Compression wave velocity Seismic wave measurements are effective in monitoring the incremental cementation that occurs with MICP [8,9,31]. As cementation occurs the contacts between particles become increasingly stiff, which results in an increase in bulk stiffness and faster transmission of seismic waves. Compression seismic waves (p-waves) were used post-treatment to assess cementation uniformity along the brick length for the bio-bricks, hydraulic lime, and cement bricks. The equipment, settings, and techniques used are specified by Weil et al. [31]. A pair of 0.5 MHz Panametrics V101-RB ultrasonic transducers were powered by an HP 33120A Function Generator and received by a Fluke PM3384oscilloscope. The transmitted signal was a +10 V, 60 kHz square wave and the received signal was subjected to a 1 kHz high pass filter to remove background noise and a 30 dB gain. Five equidistant locations along the brick lengths were measured. All of the p-wave measurements were performed across the brick width ( 91 mm). Vacuum grease was used to provide coupling between the transducer faces and brick surfaces.
7 Day
0
p o T ) 5 m m c o r ( k F c 10 e i r c B n f a o 15 t s i D
(a) Brick 1 Brick 2 Brick 3 Brick 4 Brick 5
20
2.6.2. Unconfined compressive strength Unconfined compression testing wasperformed on all bricks in accordance with ASTM C67-07a [2]. Tests were performed on a GeoTac Sigma-1 Triax machine with a 4.5 Mg (10 kip) load frame. Bricks were cut in thirds instead of halves, as recommended in the ASTM standard, to better assess brick spatial variability. All bricks were cut with a wet masonry saw to minimize disturbance. The dimensions of both faces of each brick section undergoing loading were taken, as well as the average depth of the brick. All surfaces of the testing apparatus were cleaned and the specimenswere placed without sulfur or gypsum capping because surfacesof thebricks were flat, smooth, and parallel. The load was seated on the specimen and testing initiated. The test was strain controlled with a rate of 2% strain/min ( 0.045 cm/ min). Tests were performed until failure and the maximum stress was recorded [2].
0
1000
2000
3000
4000
P-wave Velocity (m/s) 14 Day p o T ) m m c o r ( F k c e i r c B n f a t o s i D
0
(b)
5
Brick 6 10
Brick 7 Brick 8 Brick 9
15
Brick 10
2.6.3. Calcite measurements Calcite concentration measurements were performed following the methods described in Mortensen and DeJong [20] and Martinez et al. [19]. Samples were obtained from the middle of each brick section after compression testing. The dry weight of the sample was taken, then acid washed with 5 M HCl, and dry weights obtained again after acid washing to determine the amount of cementation that occurred.The sand used does contain a smallpercentage of fines whichis lost when undergoing this treatment, so the calcite test was also performed with un-treated sand to determine the average loss of fines and any calcite existing in the soil. This was determined to be approximately 0.88% of the sample, so the values presented are adjusted for the loss in fines.
20 0
1000
2000
3000
4000
P-wave Velocity (m/s)
3.1. Small-strain properties and uniformity
28 Day p o T ) m m c o r ( F k c e i r c B n f a o t s i D
3. Results and discussion
0
The compression wave (p-wave) velocities along the length of the brick are plotted in Fig. 2 with the ranges, average, and coefficient of variability presented in Table 3. P-wave velocity for
(c)
5
Brick 11 Brick 12
10
Brick 13 15
Brick 14
Table 3
Brick 15
Minimum, maximum, average, and coefficient of variation for p-waves of bio-bricks.
20 0
1000
2000
3000
4000
P-wave Velocity (m/s) Fig. 2. P-wave velocities of bio-bricks at (a) 7 day, (b) 14 day, and (c) 28 day treatment.
Treatment time (Days)
Average V p (m/s)
Min V p (m/s)
Max V p (m/s)
COV (%)
7 14 28
1560.8 2269.9 3062.7
1383.6 2008.0 2723.4
2591.5 2591.5 3576.5
6.0 6.9 6.6
D. Bernardi et al. / Construction and Building Materials 55 (2014) 462–469
brick (range of 177 m/s), but the top portion exhibits the highest compression wave velocity with a slight decrease toward the brick base. The trend of p-wave for the 14 day bio-brick batch have a range of 262 m/s and is slightly higher at the top of the brick than at the bottom of the brick, indicating more cementation occurring in the top of the brick and gradually decreasing throughout the brick length (Fig. 6b). The p-wave velocities for the 28 day biobrick batch have a range of 339 m/s. The top of the brick possesses a high p-wave velocity with a decrease toward the upper third to the brick center. P-wave velocity then increases again towards the brick base, which results in a p-wave velocity being comparable to the top of the brick. The biased cementation at the brick top is most likely due to a majority of the bacteria being present at the top of the brick (since bacteria were initially flushed top-down). P-wave velocities of lime and cement bricks for the range of treatment levels and time periods showed consistent spatial uniformity and increasing velocity as expected. Representative results
0
p o T ) 5 m m c o r ( 10 F k c e i r c B n f 15 a o t s i D 20
(a) 20% Lime 25% Lime 30% Lime 40% Lime 50% Lime 0
1000
2000
3000
4000
P-wave Velocity (m/s) 0
p o T ) 5 m m c ( o r F k c 10 e i r c B n f a o 15 t s i D
(b) 5% Cement 10% Cement 15% Cement 20% Cement 25% Cement
20 0
1000
2000
3000
Table 4
4000
Minimum, maximum, average, and coefficient of variation for strength values of biobricks.
P-wave Velocity (m/s) Fig. 3. P-wavevelocitiesof lime and cementtreated bricksafter28 daycuring time.
7 Day
200
(a)
) 150 a P k ( s 100 s e r t S 50
465
Treatment time (Days)
Average strength (kPa)
Min strength (kPa)
Max strength (kPa)
COV (%)
7 14 28
69.1 441.3 1645.4
43.3 115.5 910.9
121.7 934.7 2286.6
37.0 48.7 26.4
Table 5
Minimum, maximum, average, and coefficient of variation for E 50 modulus values of bio-bricks.
0 0
2
4
6
Strain (%) 14 Day 1000
Treatment time (Days)
Average E 50 (kPa)
Min E 50 (kPa)
Max E 50 (kPa)
COV (%)
7 14 28
5782.4 15019.5 83915.5
3140.6 4525.0 27433.8
13868.5 29964.7 131398.3
49.2 47.4 36.5
(b)
) 750 a P k ( s 500 s e r t S 250
40% Lime
2000
0 0
2
4
6
Strain (%) 28 Day
0
2000
0
(c)
) a P k ( s 1000 s e r t S
(a)
) a P k ( s 1000 s e r t S
2
6
6
20% Cement
2000
0 0
4
Strain (%)
2
4
6
Strain (%) Fig. 4. Representative stress strain curves of bio bricks tested in unconfined compression.
bio-bricks exceeds 3500 m/s with an average coefficient of variation within a single brick of 6.5%. The trend of the p-wave velocity for the 7 day bio-brick indicates uniformity within the center of the
(b)
) a P k ( s 1000 s e r t S 0 0
2
4
Strain (%) Fig. 5. 28 Day stress strain curves of 40% line and 20% cement bricks tested in unconfined compression.
D. Bernardi et al. / Construction and Building Materials 55 (2014) 462–469
466
after 28 days of curing for all of the lime and cement treated bricks are shown in Fig. 3 (with further details in Bernardi [4]). An increase in curing time resulted in very little change in p-wave velocities; on average p-wave velocities increased by 250 m/s for both lime and cement bricks. The average coefficient of variability within a single brick for the lime bricks was 12.8% while the cement bricks were 15.8%.
3.2. Compressive strength and secant modulus Stress strain curves of bio-bricks were obtained from compression testing on five bricks at each treatment interval, with representative stress strain curves presented in Fig. 4. The peak strength of the stress strain curve and the modulus (computed as a secant elastic modulus based on the strain required to mobilize
Table 6
Constants for statistical fits of strength and modulus plotted with p-wave velocity. Admixture
X -axis
Y -axis
MICP
P-wave P-wave P-wave Calcite content Calcite content
Strength E 50 Calcite content Strength E 50
P-wave P-wave P-wave Percent mass Percent mass
Strength E 50 Percent mass Strength E 50
P-wave P-wave P-wave Percent mass Percent mass
Strength E 50 Percent mass Strength E 50
Lime
Cement
A
B
C
R2
0 423 5 5265 6527
0.0016 0.0018 0.0004 0.0232 0.2052
2.45 5.61 1.55 8.49 8.1
0.75 0.38 0.83 0.75 0.38
140 16,010 50 0 0
0.0010 0.0006 0.0003 0.1038 0.0957
4.69 9.54 3.84 3.84 7.78
0.65 0.34 0.81 0.75 0.70
70 1570 9 400 24,345
0.0011 0.0014 0.0004 0.1144 0.0978
4.14 7.00 2.05 5.90 10
0.83 0.63 0.97 0.87 0.53
Bio-Bricks
(a) 3000 ) a P k ( h t g n e r t S
200000
7 Day
) a P 150000 k ( s u 100000 l u d o M 50000
R 2 = 0.76
14 Day
2000
28 Day
1000
7 Day
R 2 = 0.38
14 Day 28 Day
0 5
E
0 0
1000
2000
3000
0
4000
0
P-wave Velocity (m/s)
1000
2000
3000
4000
P-wave Velocity (m/s)
Lime Bricks
(b) 1000 ) a P k ( h t g n e r t S
100000
) a P k ( s u l u d o M
7 Day
750
14 Day 28 Day
500
R 2 = 0.65 250
7 Day
75000
R 2 = 0.34
14 Day 28 Day
50000
25000
0 5
E
0 0
1000
2000
3000
0 0
4000
1000
2000
3000
4000
P-wave Velocity (m/s)
P-wave Velocity (m/s)
Cement Bricks
(c) 4000
250000
) a P 3000 k ( h t 2000 g n e r 1000 t S
7 Day
) a P 200000 k ( s 150000 u l u d 100000 o M 50000
R 2 = 0.83
14 Day 28 Day
7 Day
R 2 = 0.63
14 Day 28 Day
0 5
E
0 0
1000
2000
3000
P-wave Velocity (m/s)
4000
0 0
1000
2000
3000
4000
P-wave Velocity (m/s)
Fig. 6. 28 Day strength and E 50 modulus versus p-wave velocity for (a) bio-bricks, (b) lime bricks, and (c) cement bricks.
D. Bernardi et al. / Construction and Building Materials 55 (2014) 462–469
50% of the peak strength, E 50) was computed for each brick section tested. The average and range of strengths and modulii as well as the coefficient of variation are presented in Tables 4 and 5, respectively. The 7-day treatments of bio-bricks have a relatively low strength and modulus exhibiting a ductile failure (Fig. 4a). After 14 days of treatment the bio-bricks increase in both strength and modulus with a transition between ductile and brittle behavior that can be seen between the top and middle/bottom segments (Fig. 4b). Upon further treatment to 28 days, the strength and modulus continue to increase throughout the brick with the top of the brick being stronger than both the middle and bottom. The bottom of the brick becomes stronger than the middle portion of the brick at this treatment level, which coincides with the p-wave data (Fig. 3c). All brick segments exhibit brittle failure after 28 days of treatment (Fig. 4c). Overall, strengths and modulii both increase with continued treatment. The average strength increases from 69 kPa to 1600 kPa, while the average modulus increases from 5782 kPa to over 83,900 kPa from 7 to 28 days of treatment. Representative stress strain curves for 40% lime and 20% cement bricks cured at 28 days are plotted in Fig. 5 for comparison. Lime and cement bricks show a general trend of the top and middle brick segments having a higher strength and modulus than the bottom brick segment. Lime bricks exhibit ductile failure exclusively, while cement exhibits ductile failure at a low admixture percent (10% and lower) while changing to brittle failure above 10% concentration. Strength and modulii for lime and cement systematically increased with increase in admixture (Bernardi [4]). Strength and modulii for lime bricks remain low relative to the strength gain of both bio-bricks and cement bricks. The lime bricks tested at 50% lime content had a maximum strength of 0.98 MPa and a maximum secant modulus of 544 MPa, which is less than that claimed by the manufacturer (compressive strength of 2.2 MPa, elastic tangent modulus of 10,800 MPa). The source of the difference was investigated with additional tests, but could not be identified. Compression strengths and modulii for cement bricks tend to increase more rapidly with increasing percent of admixture. Strengths and modulii of bio, lime, and cement bricks are plotted versus p-wave velocity in Fig. 6. A three constant single exponential growth equation as shown in the plots was fitted to each data set:
467
while the tangent secant modulus, E 50, of bio-bricks only reach up to 130 MPa.
3.3. Relation to calcite/admixture concentrations Results showing percent of calcite along the length of the biobricks are presented in Fig. 7. Trends of calcite concentration along the length of the bricks seem to be counterintuitive at first, indicated a smaller amount of calcite at the top of the brick where the higher strength occurs (Fig. 7a). The 14 day bio-bricks are slightly more varied than the 7 day, with a couple of bricks containing higher calcite at the top of the brick and gradually decreasing along the brick. Bricks 9 and 10 of Fig. 7b are exceptions containing a low calcite percentage at the top relative to what is expected to occur. For the 28 day batch in Fig. 7c the calcite content variability is fairly narrow at the top of the brick, widens in the middle, and then narrows again towards the bottom of the brick. This data is consistent with the p-wave and strength data collected for the 28 day bio-bricks where the values of all these properties are higher in the top and bottom portions of the brick than in the center. The trends of calcite, particularly observed in the 7 and 14 day data, with increasing calcite along the brick length that are not congruent with the p-wave data are attributed to a measurement error associated with the calcite measurement technique. As mentioned previously, 0.88% of the sample consists of fine soil particles that could be washed out during the calcite
7 Day
0
p o T ) 5 m m ( c o r k F c 10 e i r c B n f a o 15 t s i D
Brick 1 Brick 2 Brick 3 Brick 4 Brick 5
(a)
20 0
5
10
15
20
20
20
Calcite Content (%) 14 Day 0
y ¼ A þ eðBxþC Þ
ð1Þ
The constants for each fit are presented in Table 6. Constant A is chosen to anchor a p-wave velocity between 150 and 300 m/s based off of values from previous research on dry sand with 100 kPa of confinement. The R 2 values for strengths versus p-wave are above 0.65 while the R2 for modulus versus p-wave are higher than 0.34. The plots of modulus generally have a higher data spread, resulting in lower R 2. In all cases, brick strength and modulus generally increase with an increase in p-wave velocity. Bio-bricks range in strengths from 1.0 to 2.2 MPa, lime reaches as high as 1.0 MPa, and cement has a maximum strength of 2.5 MPa. Other brick materials made of earth and sustainable material such as adobe and rammed earth (Table 1) have strengths ranging from 0.7 MPa to 3.1 MPa. A more conventional building material such as fired red clay brick has strengths above 20 MPa, much higher than bio-bricks. The p-wave velocities of bio-bricks are comparable to sandstone. Natural sandstone and limestone have an unconfined compressive strength of up to 70 MPa, which is much higher than any material tested herein. A direct comparison of the tangent secant modulus reported herein cannot be directly compared to the elastic modulus values in Table 1 as these values are for small strain elastic modulus. For example, the materials in Table 1 can have an elastic modulii up to 300,000 MPa
p o T ) 5 m m ( c o r F k c 10 e i r c B n f a o 15 t s i D
Brick 6 Brick 7 Brick 8 Brick 9 Brick 10
(b)
20 0
5
10
15
Calcite Content (%) 28 Day 0
p o T ) 5 m m ( c o r k F c 10 e i r c B n f a o 15 t s i D
Brick 11 Brick 12 Brick 13 Brick 14 Brick 15
(c)
20 0
5
10
15
Calcite Content (%) Fig. 7. Percent calcite for bio-brick for (a) 7 day, (b) 14 day, and (c) 28 day treatment times.
D. Bernardi et al. / Construction and Building Materials 55 (2014) 462–469
468
measurement. These same fine particles could have first migrated downwards inside the bricks during treatment, resulting in higher fines content near the brick base than at the top. When the calcite measurement is then performed and the average value of 0.88% subtracted to correct for the average fines content this likely results in an overcorrection for fines near the specimen top (resulting in too low of a calcite estimate) and an under correction near the base (resulting in too high of a calcite estimate). Unfortunately the experimental program did not allow this issue to be explored further. The relationship between calcite content, p-wave velocity, strength, and modulus are presented in Fig. 8. A trendline using Eq. (1) above was fit to all three relationships. In general, p-wave velocity, strength, and modulus increase with calcite content with R2 values of 0.83, 0.75, and 0.38, respectively. The p-wave velocity was again anchored to the range of 150–300 m/s as explained previously. The plot of calcite content versus strength was best fit when anchored to a calcite content of approximately 3.4%, which was then used for the graph of modulus. Similar trends were observed between the lime and cement admixture concentration versus p-wave velocity, strength, and modulus (Bernardi [4]). Like the bio-bricks, plots of percent of mass of admixture with p-wave velocity and strength yield a higher R 2 values than when plotted with modulii.
1
(a)
e max
0.8
o i t a 0.6 R d i 0.4 o V
e min 7 Day 14 Day
0.2
28 Day
0 0
1000
2000
3000
4000
P-wave Velocity (m/s) 2.25
) m / 2 g M ( y t i 1.75 s n e D 1.5 y r D
3
(b)
7 Day 14 Day 28 Day
d max
d min
1.25 0
1000
2000
3000
4000
P-wave Velocity (m/s) Fig. 9. Final dry density versus p-wave velocity for bio-bricks.
3.4. Void ratio and dry density The average final void ratio and final dry density after treatment to the designated time increments are presented versus p-wave velocity in Fig. 9. The data plotted was calculated using the ) 20 % ( t 15 n e t n o 10 C e t i 5 c l a C
7 Day
R 2 = 0.83
14 Day 28 Day
(a)
4. Conclusions
0 0
1000
2000
3000
4000
P-wave Velocity (m/s) 3000 7 Day
) % ( 2000 h t g n e r 1000 t S
R 2 = 0.75
14 Day 28 Day
(b)
0 0
5
10
15
20
20
Calcite Content (%) 150000
) a P k ( 100000 s u l u d o 50000 M
7 Day
R 2 = 0.38
14 Day 28 Day
(c)
0 5
E 0 0
dimensions and mass of the full dry bio-bricks after treatment and the average p-wave velocities for an entire brick. The average initial void ratio for each bio-bricks was 0.51, and the initial dry density was 1.72 Mg/m3. As evident, the void ratio following MICP treatment decreases to about 0.33, a value significantly less than the minimum void ratio for the untreated sand. The total dry density of the bricks increases with treatment up to a value of about 1.9 Mg/m3. The relatively small increase in density compared to the reduction in void ratio is attributed to the low dry density of precipitated calcite relative to that of the silica sand particles.
5
10
15
Calcite Content (%) Fig. 8. Calcite content plotted with (a) p-wave velocity, (b) strength, and (c) E 50 modulus.
The novel MICP bio-brick manufacturing technique developed herein can produce compressive strengths that exceed2.0 MPa. Results from 7, 14, and 28 day treatment schemes indicate that the strength and stiffness is scalable, enabling customization to project and site specific requirements. The strengths obtained after these different treatment durations followed trends similar to sand-based bricks treated with lime (27% by weight) and cement (12–18% by weight), though treatment with cement increased strength more consistently with respect to concentration of admixture. The stress–strain behavior became more brittle with increasing cementation level, eventually exhibiting behavior after 28 day treatment consistent with that for lime and cement admixture bricks. Secant elastic modulus corresponding to 50% mobilized strength, capturing the stiffness upon initial loading, increased from 5300 kPa after 7 days of treatment up to 83,900 kPa after 28 days of treatment. The secant elastic modulus also increased with cement admixture concentration and to a lesser extent when lime was used. Compression wave, or p-wave, velocity is effective in mapping the extent and uniformity of calcite cementation along the length of the bricks, with p-wave values after 28 days of treatment exceeding 3500 m/s and being comparable to sandstone and limestone rock. Variability within individual bio-bricks averaged about 6.5% in terms of coefficient of variation (COV), indicating high specimen uniformity. In comparison, lime and cement treated bricks had average COV values of 11.1% and 6.4%, respectively. P-wave
D. Bernardi et al. / Construction and Building Materials 55 (2014) 462–469
velocity also correlated directly with admixture concentration, secant elastic modulus, and strength for MICP, lime, and cement additives. Correlations developed generally followed exponential growth trends, with R 2 values greater than 0.6. For the bio-bricks specifically, estimates of calcite, secant elastic modulus and strength could be predicted with an accuracy of about ±30%. Overall this research has demonstrated the strong potential of manufacturing sand-based bricks using a natural microbial process. This is attractive given its simplicity, low embodied energy in materials, and scalability. Further research is needed to obtain a more accurate estimate on cost, durability, and net carbon footprint of MICP brick production relative to more conventional methods.
Acknowledgements Funding provided by the United States National Science Foundation (#072746). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the writer(s) and do not necessarily reflect the views of the National Science Foundation.
References [1] American Society of Civil Engineers (ASCE). Policy statement 418: the role of the engineer in sustainable development; 2004. [2] ASTM. Standard test methods for sampling and testing brick and structural clay tile. American Society for Testing and Materials (ASTM), Standard C67; 2007. p. 12. [3] Baykasoglu A, Gullu H, Canakci H, Ozbakir L. Prediction of compressive and tensile strength of limestone via genetic programming. Exp Syst Appl 2008:111–23. [4] Bernardi DJ. Biologically Cemented Sandstone Brick, MSCE Thesis, Department of Civil and Environmental Engineering. University of California Davis; 2012. p. 53. [5] Bui Q, Morel J. Assessing the anisotropy of rammed earth. Constr Build Mater 2009;23:3005–11. [6] Custodio-Garcia E, Sebastian PJ, Campos-Alvarez J, Trevino-Palacios CG, Zarate EA, Cordova QA, et al. Solar conduction heat transfer in fired clay bricks. Sol Energy Mater Sol Cell 2005;88:169–78. [7] de Muynck W, Debrouwer D, de Belie N, Verstraete W. Bacterial carbonate precipitation improves the durability of cementitious materials. Cem Concr Res 2008(38):1005–14. [8] DeJong JT, Fritzges MB, Nusslein K. Microbially induced cementation to control sand response to undrained shear. J Geotech Geoenviron Eng 2006;11(132):1381–92. [9] DeJong JT, Mortensen BM, Martinez BC, Nelson DC. Bio-mediated soil improvement. Ecol Eng 2010;36:197–210. [10] DeJong JT, Soga K, Banwart SA, Whalley WR, Ginn T, Nelson DC, et al. Soil engineering in-vivo: harnessing natural biogeochemical systems for
469
sustainable, multi-functional engineering solutions. J R Soc Interface 2011;8:1–15. [11] DeJong JT, Soga KS, Kavazanjian E, Burns S, van Paassen L, Al Qabany A. Biogeochemical Processes and Geotechnical Applications: Progress, Opportunities, and Challenges. Geotechnique 2013;63(4):287–301. [12] Fang Y, Kang Q, Wen Q, Dai P. Utilizationof copper tailing forautoclaved sand– lime brick. Constr Build Mater 2011(25):867–72. [13] Fujita Y, Taylor JL, Gresham TLT, Delwiche ME, Colwell FS, McLing TL, et al. Stimulation of microbial urea hydrolysis in groundwater to enhance calcite precipitation. Environ Sci Technol 2008;8(42):3025–32. [14] Hall M, Djerbib Y. Rammed earth sample production: context, recommendations and consistency. Constr Build Mater 2004;18:281–6. [15] Hammes F, Seka A, Knijf S, Verstraete W. A novel approach to calcium removal from calcium-rich industrial wastewater. Water Res 2002;37(3): 699–704. [16] Hendry AW, Sinha BP, Davies SR. Design of masonry structures. Taylor and Francis e-Library; 2004. [17] Karol RH. Chemical grouting and soil stabilization. New York (NY): Marcel Dekker; 2003. p. 558. [18] Lima S, Varum H, Sales A, Neto VF. Analysis of the mechanical properties of compressed earth block masonry using the sugarcane bagasse ash. Constr Build Mater 2012;35:829–37. [19] Martinez BC, DeJong JT, Ginn TR, Montoya BM, Barkouki TH, Hunt C, et al. Experimental optimization of microbial-induced carbonate precipitation for soil improvement. ASCE J Geotech Geoenviron Eng 2013;139(4):587–98. [20] Mortensen BM, DeJong JT. Strength and stiffness of MICP treated sand subjected to various stress paths. In: Proceeding from ASCE geo-frontiers 2011 conference, Dallas, Texas; 2011. [21] National Research Council (NRC). Geological and geotechnical engineering in the new millennium: opportunities for research and technology innovation. Washington (DC): The National Academies Press; 2006. p. 206 . [22] Oti JE, Kinuthia JM, Bai J. Engineering properties of unfired clay masonry bricks. Eng Geol 2009;107:130–9. [23] Oti JE, Kinuthia JM, Bai J. Unfired clay bricks: from laboratory to industrial production. Proc Inst Civ Eng 2009(ES4):229–37. [24] Pacheco-Torgal R, Jalali S. Earth construction: lessons from the past for future eco-efficient construction. Constr Build Mater 2012;29:512–9. [25] Ramachandran SK, Ramakrishnan V, Bang SS. Remediation of concrete using micro-organisms. ACI Mater J 2001;1(98):3–9. [26] Renforth P, Manning DA, Lopez-Capel E. Carbonate precipitation in artificial soils as a sink for atmospheric carbon dioxide. Appl Geochem 2009;24(9):1757–64. [27] Ruffolo RM, Shakoor A. Variability of unconfiner compressive strength in relation to number of test samples. Eng Geol 2009;108:16–23 . [28] Russ TH. Site planning and design handbook. The McGraw-Hill Companies, Inc.; 2002. p. 443. [29] Silveira D, Varum H, Costa A, Martins T, Pereira H, Almeida J. Mechanical properties of adobe bricks in ancient constructions. Constr Build Mater 2012;28:36–44. [30] Tanacan L. Adobe construction: a case study in Turkey. Arch Sci Rev 2011;51.4:349–59. [31] Weil MH, DeJong JT, Martinez BC, Mortensen BM. Seismic and resistivity measurements for real-time monitoring of microbially induced calcite precipitation in sand. ASTM J Geotech Test 2011;35(2). [32] Whiffin VS, van Paassen LA, Harkes MP. Microbial carbonate precipitation as a soil improvement technique. Geomicrobiol J 2007(24):417–23.
