Splitting Tensile Strength of Fiber Reinforced and Biocemented Sand Technical Note Splitting Tensile Strength of Fiber Reinforced and Biocemented Sand Sun Gyu Choi, Ph D 1; Tung Hoang2; E James Alleman, Ph D 3; and Jian Chu, Ph D 4 Abstract This technical note examines the splitting tensile strength properties of natural sand treated with polyvinyl acetate (PVA) fiber in combination with biocementation using the microbially induced calcite precipitation (MICP) process Ottawa 20 30 sand was mixed.
Trang 1Technical Note
Splitting Tensile Strength of Fiber-Reinforced
and Biocemented Sand Sun-Gyu Choi, Ph.D.1; Tung Hoang2; E James Alleman, Ph.D.3; and Jian Chu, Ph.D.4
Abstract: This technical note examines the splitting tensile strength properties of natural sand treated with polyvinyl acetate (PVA) fiber in combination with biocementation using the microbially induced calcite precipitation (MICP) process Ottawa 20-30 sand was mixed with PVA fiber at five different fiber ratios (0.0%, 0.2%, 0.4%, 0.6%, and 0.8% by weight) and then stabilized using urease-producing bacteria plus
that the splitting tensile strength and splitting secant elastic modulus increased with increasing in either calcium carbonate content or fiber ratio The use of PVA fibers together with MICP treatment could also increase the failure strain and the postfailure splitting tensile strength DOI:10.1061/(ASCE)MT.1943-5533.0002841 © 2019 American Society of Civil Engineers
Author keywords: Microbially induced calcite precipitation (MICP); Splitting tensile strength; Reinforced cemented sand; Calcium carbonate content; Polyvinyl acetate (PVA) fiber
Introduction
Ordinary portland cement (OPC) has been used for decades for
soil improvement or ground stabilization In recent years, an
alter-native material, biocement by microbial activity without traditional
cement, has been developed and applied in lieu of cement for soil
stabilization One of the biocementation processes is microbially
Burbank et al 2011;Chu et al 2012;O’Donnell and Kavazanjian
2015;Choi et al 2017b;Li et al 2018)
However, sand treated by biocement will suffer from the same
shortcomings as that treated by OPC, that is, OPC treated soil or
an important mechanical parameter in the design of geosystems,
additives to improve the mechanical properties of OPC One of
such studies involved the use of metallic (typically steel) or fiber
Xing et al 2008;Maher and Ho 1994;Song and Hwang 2004;Park
using biocementation with homopolymer polypropylene and
multifilament fiber An increase in friction angle and effective
cohesion, as compared to clean sand performance, was observed after the soil had been treated with 0.3% of fiber and
carbon-ate content (measured on an additive weight basis) Choi et al (2016a) also studied biocemented sand with polyvinyl acetate (PVA) fiber as reinforcement A 30% increase in unconfined com-pressive strength and 160% in splitting tensile strength was ob-served after the sand had been treated using a 0.8% fiber ratio
carbonate buildup
Given that clean sand has no splitting tensile strength, the use
of fiber plus MICP will improve ductility and produce splitting ten-sile strength The splitting tenten-sile strength properties of fiber- and MICP-treated soils are affected by several factors, including the type of fibers, fiber ratio, and calcium carbonate content However, studies on the effect of fibers and biocementation on the splitting tensile strength of biocemented sand are still uncommon
In this technical note, a study on the splitting tensile strength
of PVA fiber reinforced, MICP biocemented sand is presented Tests with different fiber ratios of 0.0%, 0.2%, 0.4%, 0.6%, and
conducted After treatment, the splitting tensile strength and cal-cium carbonate content of the treated samples were measured
to establish a relationship between splitting tensile strength and processing factors such as fiber ratio and calcium carbonate content
Experimental Work Materials
The employed PVA fiber materials were 0.1 mm in diameter and
12 mm in length The basic technical properties of these PVA
Ottawa 20-30 sand was used for all tests, with a specific gravity
of 2.65 The grain size for the involved sand material ranged from 0.6 mm (sieve #30) to 0.85 mm (sieve #20), with a mean grain size
of 0.73 mm
1 Senior Researcher, Disaster Prevention Research Division, National
Disaster Management Research Institute, Ulsan 44538, Republic of Korea.
2 Lecture, Faculty of Bridge and Road Construction Engineering
Univ of Danang –Univ of Science and Technology, Danang 550000,
Vietnam.
3 Professor, Dept of Civil, Construction, and Environmental
Engineer-ing, Iowa State Univ., Ames, IA 50014.
4 Professor, School of Civil and Environmental Engineering, Nanyang
Technological Univ., Blk N1, 50 Nanyang Ave., Singapore 639798
(corresponding author) ORCID: https://orcid.org/0000-0003-1404-1834.
Email: CHCHU@ntu.edu.sg
Note This manuscript was submitted on October 4, 2018; approved on
March 28, 2019; published online on June 21, 2019 Discussion period
open until November 21, 2019; separate discussions must be submitted
for individual papers This technical note is part of the Journal of Materials
in Civil Engineering, © ASCE, ISSN 0899-1561.
Trang 2The materials used for biocementation included: (1)
urease-producing bacteria (UPB), S pasteurii (American Type Culture
Collection, ATCC 11859), (2) urea, and (3) calcium chloride
The growth medium for culturing S pasteurii was made of a yeast
medium for 2 days The urea and calcium chloride were both
Specimen Preparation
Test specimens were prepared with the following mix recipes:
32.4 g of Ottawa sand, PVA fiber addition at 0.0%, 0.2%, 0.4%,
0.6%, and 0.8% (by weight of sand, respectively), and 7% of
dis-tilled water (by weight) to easily mix the fiber uniformly in the sand
column These materials were mixed together by hand and placed
into clear acrylic, 5-cm diameter and 10-cm height (10 layers)
uniformly distribution of fiber in the sand column, each layer
(Park 2011) At the bottom of the specimen, a layer of gravel and
scrub sponge was used More details regarding these sample
sand specimen was initially formed, UPB, urea, and calcium
chlo-ride were then injected using the following steps First, 10 mL of
for 3 h and then drained from the bottom Second, 500 mL of the
column by pump for 20 h After completing this 24-h processing
sequence, the column specimens were then drained and repeated
until a total of seven such cycles had been completed to precipitate
Testing
A total of 15 column specimens were prepared using the
aforemen-tioned method and then used for splitting tensile strength tests
strength equipment With each fiber ratio (0.0%, 0.2%, 0.4%, 0.6%,
and 0.8%), three duplicate tests were carried out As expected,
these specimens would typically fracture in a vertical fashion After
each test, 5 g of the sample were taken from the center portion of
the tested specimen for calcium carbonate determination using a
washing and elution method that has been previously documented
(Zhao et al 2014;Montoya and DeJong 2015;Choi et al 2017a)
Testing Results
Engineering Properties
strength, and secant elastic modulus results obtained from the
split-ting tensile strength tests on biocemented specimens with PVA
fiber ratios of 0.2%, 0.4%, 0.6%, and 0.8%, respectively All the
specimens showed biocement to produce splitting tensile strength
speci-mens were very brittle These specispeci-mens failed at strain levels
the other plots reveal a pattern in which the failure strain levels
tended to increase in relation to higher fiber ratio levels Similarly,
the splitting tensile stress levels within the postpeak region also
additionally, samples in higher fiber ratio tended to induce higher residual strength in this study
Relationship of calcium carbonate contents and splitting tensile
carbonate content and fiber ratio on tensile strength It can be seen
ad-ditions in calcium carbonate content for tests with five different fiber ratios In general, the splitting tensile strength also increases with the increase in fiber ratio The average splitting tensile strength
The relationships between splitting secant elastic modulus and calcium carbonate content and fiber content are also shown in
Table 1 Test results
Test ID
Fiber (%)
Calcium carbonate content (%)
Splitting tensile strength (kPa)
Splitting secant elastic modulus (E s
50, MPa)
Fig 1 Strain-stress behaviors of samples versus different fiber ratio
Trang 3modulus (Es
elastic modulus in general also increases by increasing the calcium
carbonate content and fiber ratio
Comparison and Analysis
with fiber and biocement having a higher calcium carbonate
con-tent ranging from 4.8% to 10.4% By combining the data from the
two studies, the influence of calcium carbonate content and fiber
ratio on the splitting tensile strength over a wider calcium carbonate
content range can be established In general, the splitting tensile
strength increases with calcium carbonate content The effect of
fiber content on the splitting tensile strength is only pronounced
when the calcium carbonate content is relatively high, or in other
words, when the splitting tensile strength is relatively high Thus,
the proportions of the contributions by calcium carbonate content
and fiber content are different depending on the slitting tensile
strength achieved
For example, for fiber reinforced, biocemented specimens with
low calcium carbonate (less than 4%), the splitting tensile stress in
Fig 2 Relationships of calcium carbonate content, fiber ratio, and splitting tensile strength: (a) individual data; and (b) average of tensile strength by different fiber ratio
Fig 3 Relationships of calcium carbonate content, fiber ratio, and splitting secant elastic modulus: (a) individual data; and (b) average of splitting secant elastic modulus by different fiber ratio
Fig 4 Relationships of calcium carbonate, splitting tensile strength, and fiber ratio
Trang 4strain-stress curves dropped quickly after failure as reported by
much to the improvement of a sudden failure On the other hand,
for fiber-reinforced, biocemented sand with high calcium carbonate
content (10.4% or higher), the splitting tensile stress does not
de-crease so drastically after failure and therefore, the fiber may have
contributed to the prevention of a sudden decrease in the postpeak
tensile stress
Combining the effects of calcium carbonate content and fiber
ratio, the dependence of splitting tensile strength on both calcium
cal-cium carbonate content (4% or lower), the influence of fiber ratio
on splitting tensile strength is much lower compared with that for
high calcium carbonate content
Microstructure PVA Fiber, Biocemented Sand
Scanning electron microscope (SEM) images were taken for
se-lected samples after drying at 60°C The SEM images for a sample
are coated with calcium carbonate, which also bound the sand
grains as well as the fibers together and the PVA fibers are
em-bedded in the sand grains to act as reinforcement The PVA fibers
are also bound together by calcium carbonate and bridge across
con-tribute toward the increase in the shear strength The calcium
Conclusions
The splitting tensile strength and the elastic modulus of Ottawa
sand treated with biocementation plus PVA fibers were studied
us-ing experiments The followus-ing conclusions can be drawn:
1 The splitting tensile strength of biocemented sand increases with
increasing calcium carbonate content Inclusion of PVA fiber
also increases the splitting tensile strength However, the effect
of fiber content on the splitting tensile strength is only
pro-nounced when the calcium carbonate content is higher than 6%
ratio of 0.4% appears to be optimal for the tested sand
2 The use of PVA fiber increases the ductility of biocemented soil
as indicated by an increase in the value of failure strain by 130%
and the splitting elastic modulus by 133%
Acknowledgments This study forms part of a collaboration between Nanyang Tech-nological University, Singapore, and Iowa State University We would like to acknowledge that part of this study is supported
Research Fund on Sustainable Urban Living, Singapore
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