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ASSESSMENT OF BAMBOO CULM ASH FOR USE AS
AS AN ADDITIVE IN CONCRETE
by
SARA SOLEIMANZADEH
ERIC GIANNINI, COMMITTEE CHAIR
JIALAI WANG
PAUL G. ALLISON
A THESIS
Submitted in partial fulfillment of the requirements
for the degree of Master of Science
in the Department of Civil, Construction and Environmental Engineering
in the Graduate School of
The University of Alabama
TUSCALOOSA, ALABAMA
2015
Copyright Sara Soleimanzadeh 2015
ALL RIGHTS RESERVED
ii
ABSTRACT
Each year tens of millions of tons of bamboo are utilized commercially, generating a vast amount
of waste. One solution is to calcine this waste and use it as additive in concrete to keep it out of
landfills and save money on waste disposal. This research project identifies (1) the optimal
calcination condition of bamboo culm ash (BCAsh) and (2) the effect of various cement
replacement levels on mortar properties. After considering the amount of energy consumed and
the carbon content, burning at 700 °C [1292 °F] for 1.5 h was selected as the optimum condition.
Cement replacement levels between 0.5 and 5% were investigated by evaluating the effects on
heat of hydration and compressive strength of four mixes of BCAsh mortar. While the BCAsh
reduced the strength of the mortar only slightly, it did show a considerable retarding effect on
mortar hydration.
Keywords: Bamboo Culm Ash; Mineral Admixture; Retarding Effect; Heat of Hydration;
Agricultural Waste; Chemical Composition; Mortar.
iii
LIST OF ABBREVIATIONS
BCAsh
BLAsh
CH
LOI
K2O
SEM
SiO2
XRD
XRF
Bamboo Culm Ash
Bamboo Leaf Ash
Calcium Hydroxide
Loss On Ignition
Potassium Oxide
Scanning Electron Microscopy
Silicon Dioxide
X-Ray Diffraction
X-Ray Fluorescence
iv
ACKNOWLEDGMENTS
Although I worked diligently on this thesis, it would not have been possible without the
guidance and the help of several individuals who contributed and extended their valuable
assistance in the preparation and completion of this study.
I would like to express the deepest appreciation to my committee chair, Dr. Giannini. His
guidance, patience, supervision, and support truly helped the progression of this research.
I would also like to express my gratitude towards Dr. Charles A. Weiss, Jr., Mr. Kevin
Torres-Cancel and Dr. Feraidon Ataie for the valuable assistance during the experimental part of
this study. Their cooperation is indeed much appreciated.
Also, I would like to thank my committee members who have been very generous not only
with their time and energy, but also with their expertise. Thank you Dr. Jialai Wang and Dr. Paul
G. Allison for agreeing to serve on my committee. I would like to thank Dr. Back, Department
Head of Civil, Construction and Environmental Engineering, for the insights he has shared.
My thanks and appreciation also go to the Hale Empowerment and Revitalization
Organization (HERO) for the bamboo waste materials supplied.
Last but not least, I am so grateful to my family for their endless supports and prayers.
v
CONTENTS
ABSTRACT ................................................................................................ ii
LIST OF ABBREVIATIONS…………………………………………….iii
ACKNOWLEDGMENTS ......................................................................... iv
LIST OF TABLES ..................................................................................... vi
LIST OF FIGURES .................................................................................. vii
1. INTRODUCTION ...................................................................................1
2. RESEARCH SIGNIFICANCE…………………………………………3
3. EXPERIMENTAL PROCEDURE ..........................................................4
3.1. Materials ...............................................................................................4
3.2. Microstructural characterization ...........................................................5
3.3. Mortar preparation and testing ..............................................................6
4. EXPERIMENTAL RESULTS AND DISCUSSION ..............................7
4.1. Mass loss percentage and loss on ignition ............................................7
4.2. Microstructural properties .....................................................................8
4.3. Optical properties ................................................................................12
4.4. Effect of bamboo ash on heat of hydration .........................................13
4.5. Effects of BCAsh on mortar setting time ............................................14
4.6. Effect of bamboo ash on Mortar Strength...........................................17
5. FURTHER RESEARCH .......................................................................18
6. CONCLUSIONS....................................................................................19
REFERENCES ..........................................................................................20
vi
LIST OF TABLES
Table 1–Physical and chemical compositions of cement and BCAsh…….........................9
Table 2–Maximum power and initial and final setting time of five mixes of mortar ……15
vii
LIST OF FIGURES
Fig. 1–Mass loss % vs. time for oven dry bamboo ash............................................................... …7
Fig. 2–Bamboo culm ash ............................................................................................................... .8
Fig. 3–XRD pattern of BCAsh..................................................................................................... .10
Fig. 4–SEM image for the sample burnt at different temperatures and durations ........................ 11
Fig. 5–SEM image for sample analysis in ImageJ ....................................................................... .12
Fig. 6–Particle size distribution for samples of different temperature .......................................... 12
Fig. 7–Effects of different replacement levels of BCAsh on the rate of reaction of mortar……..13
Fig. 8–Effects of different replacement levels of BCAsh on degree of hydration of mortar……14
Fig. 9–Effects of different replacement levels of BCAsh on the initial setting time of mortar….16
Fig. 10–Effects of different replacement levels of BCAsh on the final setting time of mortar….16
Fig. 11–Effects of different replacement levels of cement with BCAsh on 7-day and 28-day
compressive strengths of mortars.………………………………………………………………..17
1
1. INTRODUCTION
In recent years there has been increasing interest in utilizing agricultural waste ashes in concrete
[1, 2]. If the waste can be reused and recycled, natural resources are used efficiently, waste is kept
out of landfills, and waste disposal costs are saved [3, 4]. Utilization of the waste as a cement
replacement material not only reduces the economic and environmental problems associated with
the waste disposal [5], but also reduces the CO2 emissions during cement manufacture [6]. CO2
emissions due to portland cement production are approximately 0.87 tons per ton of cement [7].
Therefore, partial replacement of cement with bamboo culm ash (BCAsh) in concrete or mortar
has twofold effect: (1) reducing the waste and the problems associated with them and (2) reducing
the cement content in concrete and its negative economic and environmental impacts [2, 8, 9].
Several natural waste products such as rice husk ash, sawdust, sugar cane straw ash, and sugar
cane bagasse ash are already in use in concrete as mineral admixtures to improve concrete
properties in fresh and/or hardened state [10-14]. Another potential source is bamboo waste
generated during the annual industrial processing of approximately 20 million tons of bamboo [4]
for diverse applications including construction materials, bamboo furniture, and even the high-
tech industry [15-17]. These wastes are either disposed of in landfills or burnt, ultimately harming
the environment [18] by polluting the air and occupation of useful lands [19]. In addition, the
biodegradation of bamboo, which is a natural lignocellulosic composite [20], emits methane, with
an atmospheric heating effect of 72 times higher than that of CO2 [19]
2
Studies about the utilization of bamboo leaf waste are still very few and no research is available
on waste obtained from the culm, or hollow stem, of bamboo plants. Villar-Cociña, et al [18]
studied the pozzolanic behavior between calcium hydroxide (CH) and bamboo leaf ash (BLAsh)
and concluded that the ash contains silica with a completely amorphous nature and a high
pozzolanic activity. Asha, et al. [21] examined the possibility of using BLAsh as partial
replacement for portland cement in concrete. According to the results, replacement levels of 5, 10,
and 15% (by mass of cement), reduced the 28 day compressive strength of the concrete by 11%,
21%, and 41% respectively. They considered the incomplete hydration of BLAsh at the age of 28
days the main cause of the strength reduction. On the other hand, the acid resistance and chloride
resistance improved considerably at 10% replacement of cement with BLAsh. Therefore, they
suggested that concrete containing BLAsh is desirable where durability is a major concern rather
than a high strength. Singh, et al. [22] examined 20% (by mass) replacement of cement with
BLAsh in mortar and found that the hydration properties and 28 day compressive strength were
comparable to those of a 100% portland cement mortar.
Although all the research on BLAsh produced promising results, no study could be found on the
utilization of BCAsh as an admixture in concrete or mortar. Therefore, in this research, the
potential of BCAsh as a mineral admixture in mortar and its effect on fresh and hardened properties
of mortar were evaluated. To achieve this goal, the optimal calcination condition of bamboo culm
ash (BCAsh) was first evaluated. Then, the effect of various cement replacement levels on heat of
hydration, setting time, and the strength of mortar were assessed. The chemical composition,
external morphology, and texture of BCAsh were also analyzed using scanning electron
microscopy (SEM), X-ray diffraction (XRD) and X-ray fluorescence (XRF) techniques.
3
2. RESEARCH SIGNIFICANCE
This research is a necessary first step in evaluating the potential of BCAsh as an additive in
concrete and facilitating its future use in construction applications. This study addresses the
concerns for the problems associated with bamboo waste disposal, the large amount of cement in
concrete/mortar, and the negative environmental impacts of both of these practices. It introduces
a new natural byproduct to be utilized and opens the door for further research, namely, studying
the effect of BCAsh on other aspects of concrete/mortar such as durability properties in which
many of the other natural materials have already played an important role.
4
3. EXPERIMENTAL PROCEDURE
3.1. Materials
Waste bamboo shavings were collected from a manufacturer of bamboo-framed bicycles in
Greensboro, Alabama. The waste was from a mix of three different species of bamboo:
Phyllostachys Edulis (Moso Bamboo), Phyllostachys Nigra (Giant Gray Bamboo), and
Phyllostachys Viridis (Pigskin Bamboo). Bamboo waste samples were calcined at 50 °C [122 °F]
temperature intervals between 500 and 700 °C [932 and 1292 °F] for durations between 1.0 and
2.5 h. Bamboo culm waste was oven dried at 110 °C [230 °F] for 24 h prior to calcination to avoid
variations in moisture content affecting yield calculations. At each temperature, 200 g [0.44 lb.] of
shavings were burned in stainless steel crucibles in a laboratory furnace. Then, the obtained ash
was ground using a micronizing mill for 1.0 h. Finally, the ground ash was sieved below 90 μm
[0.0035 in.] fineness to obtain ash with particle size of equal to or smaller than that of cement. The
sand and cement used in mortar were ASTM C109 [23] cube test sand and ASTM C150 Type II
cement. The chemical analysis and LOI of the cement used in this study are listed on Table 1.
Potable water from the local water supply network was used as the mixing water.
The ash samples were placed in containers labeled according to the temperature and time at which
they were provided. The mass of the samples was measured before and after they were placed in
the furnace. The mass loss percentage and loss on ignition (LOI) of each sample were measured
to determine the yield and the content of unburned carbon respectively. Based on the results and
5
by considering the energy usage, the optimal burning condition was selected. LOI was measured
for each sample by burning the samples at 950 °C [1742 °F] for 15 minutes per ASTM C114 [24].
3.2. Microstructural characterization
A conventional high vacuum scanning electron microscopy (SEM) was used to observe the
morphology of the BCAsh. The accelerating voltage applied to the electron gun as well as the spot
size and magnifications can be found on the data bar displayed on each SEM image presented in
the results section of this paper.
In addition, five SEM images were obtained from the samples burned at different conditions and
the images were analyzed in ImageJ software to estimate the particle size distribution of each
sample. Samples burned at 600 °C [1112 °F] and 700 °C [1292 °F] for duration of 1.5 h were
analyzed by both XRF and XRD to find the chemical composition and mineralogical properties of
the ash. Mr. Kevin Torres-Cancel a research physical scientist in the U.S Army Corps of Engineers
performed the XRF analysis. The XRD analysis was conducted by Dr. Charles A. Weiss, Jr., a
senior research geologist in the Engineer Systems and Materials Division, Geotechnical and
Structures Laboratory, and Engineer Research and Development Center.
In preparation for XRD analysis, a portion of the sample was passed through a 45-μm (No. 325)
sieve. Random orientation powder mounts of bulk samples were analyzed using XRD to determine
the mineral constituents present in each sample. XRD patterns were gathered from an X-Pert Pro
Multipurpose Powder Diffractometer system that used standard techniques for phase identification
(Panalytical, Inc.). The run conditions included Co-Kα radiation, scanning from 2 to 70 º 2θ with
a step size less than 0.02 º and collection of the diffraction patterns accomplished using the PC
6
based Windows version of X-Pert Pro Data Collector, and analysis of the patterns using the
Jade2010 program (Materials Data, Inc.).
3.3. Mortar preparation and testing
Four mortar mixes with different cement replacement levels of 0.5, 1.0, 2.5 and 5.0% (by mass)
with BCAsh were made. The BCAsh was obtained at the optimal calcination condition (burning
at 700 °C [1292 °F] for 1.5 h). For the control mortar, the cement, sand and water mixing
proportions were respectively 1.0:2.75:0.50 (mass ratio). After mixing the mortar, 50.8 mm [2 in.]
cube specimens were molded, covered with plastic, and cured in a moist room at temperature of
23 °C [73.4 °F]. The 7-day and 28-day compressive strengths of the mortar mixes were determined
by testing three specimens from each mix and calculating the average of the three tests per standard
test method for compressive strength of mortars (ASTM C109).
In addition, 50 g [0.11 lb.] of each mortar mix was sampled and placed in an isothermal conduction
calorimeter to be tested for its heat of hydration. The temperature of the calorimeter was set to
23 °C [73.4 °F] during the test. Heat of hydration data was collected from the calorimeter for 72 h
to determine and compare the effect of different replacement levels on the hydration process of the
mortars.
Some retarders become less effective at temperatures higher than 23 °C [73.4 °F] [25]. Therefore,
the effect of BCAsh on the hydration process of mortar was also examined at higher temperatures
of 30, 40 and 50 °C [86, 104 and 122 °F]. The heat flow of four mortar mixes with cement
replacement level of 0, 0.5, 1.0 and 2.5% was measured at each temperature. The initial and final
setting time for each mortar was estimated by using the calorimetry curve, and the results were
compared to those of achieved at ambient temperature.
7
4. EXPERIMENTAL RESULTS AND DISCUSSION
4.1. Mass loss percentage and loss on ignition
The mass loss percentage of samples burned at different temperatures and durations can be seen
in Fig.1. According to the results, by increasing the time, mass loss percentage increased for all of
the samples except for the samples burned at 500 and 600 °C [932 and 1112 °F] for 2.5 hrs. For
the two mentioned samples, the mass loss percentages were 0.04 and 0.08% lower than those of
samples burned at the same temperatures for 2 hrs. However, since this insignificant deviation
from an expected data is most likely due to experimental error, the experiment will be repeated for
these two samples.
In general, there was a considerable difference with extending the burning time from 1 h to 1.5 h;
this likely indicates that 1 h was insufficient burning time. However, with burning for longer time
- up to 2.5 h - no significant changes could be observed. The obtained yield was between 2.3 to
4.5%. Clearly, the increase in time and/or temperature results in obtaining a lower amount of ash.
Fig. 1–Mass loss % vs. time for oven dry bamboo ash burnt at the temperature range of 500 to
700 °C [932 to 1292 °F] for 1 to 2.5 hrs.
95.5
96
96.5
97
97.5
98
1:00 1:30 2:00 2:30
Mas
s lo
ss %
Time (h)
700 ᴼC [1292 ᴼF]
650 ᴼC [1202 ᴼF]
600 ᴼC [1112 ᴼF]
550 ᴼC [1022 ᴼF]
500 ᴼC [932 ᴼF]
8
Samples burned at higher temperatures and for longer times had lower values of LOI. However,
the carbon content of the ash was not completely removed by burning at 500 to 650 °C [932 to
1202 °F] and the value of LOI was greater than 10%, the specified value in ASTM C618 [26] for
Class N pozzolanic materials. Samples calcined at 600 °C [1112 °F] for 2.5 h still had an LOI of
approximately 17%; burning for only 1.5 h at 650 °C [1202 °F] resulted in obtaining ash with a
relatively lower LOI, but still higher than the 10% limit in ASTM C618.
Ash with lower carbon content was obtained by burning the samples at 700 °C [1292 °F] for
durations of 1.5 to 2.5 h. It can be concluded that 700 °C [1292 °F] and 1.5 h are the minimum
temperature and time of burning in which the ash with an acceptable LOI of less than 10% can be
obtained. The sample burned at this condition had an LOI of 6%. Considering the amount of energy
consumption, costs and the environmental impact, these minimum burning time and temperature
were selected as optimum calcination condition. The ground BCAsh obtained at the optimum
condition is light gray in color and can be seen in Fig. 2.
Fig. 2–Bamboo culm ash obtained at the optimal calcination condition
(burning at 700 °C [1292 °F] for 1.5 h)
4.2. Microstructural properties
Table 1 shows the chemical composition of the selected BCAsh samples determined by XRF. The
chemical composition was conducted on the samples which had LOI of less than 20%. The amount
of silica (SiO2) and potassium (K2O) were about 1.6% and 22% respectively. Since the BCAsh
9
doesn’t meet the ASTM C618 requirement for natural pozzolans of having SiO2+Al2O3+Fe2O3>
70%, BCAsh cannot be considered pozzolanic material for use in concrete.
The physical properties and chemical analysis of the cement and BCAsh calcined at 600 °C
[1112 °F] and 700 °C [1292 °F] are listed in Table 1.
Table 1–Physical and chemical compositions of cement and BCAsh
Type II
Cement
BCAsh
600 °C [1112 °F]
BCAsh
700 °C [1292 °F]
Loss of ignition, % 2.40 26.0 6.0
SiO2, % 20.1 1.63 1.61
Al2O3, % 4.07 0.04 0.042
CaO, % 63.74 0.93 0.78
MgO, % 2.53 1.38 1.11
SO3, % 3.17 0.36 0.33
P2O5, % - 5.59 5.46
K2O, % - 22.88 21.88
Cr2O3, % - 0.01 0.058
MnO, % - 0.028 0.044
Fe2O3, % 3.18 0.18 0.599
ZnO, % - 0.074 0.063
BaO, % - 0.027 0.0
CO2, % 1.4 66.13 67.38
Cl, % - 0.724 0.413
The mineralogies of the two BCAsh samples were determined using X-ray diffraction analysis
(Fig. 3). Both samples contained similar amounts of the same phase, principally K-rich and
carbonate phases including K2CO3, K2CO3 · 1.5 H2O, KCl, and K4H4(CO3)3· 1.5 H2O as well as
10
SiO2. This parallels the chemistry as shown in Table 1. There does not appear to be any appreciable
amorphous material in either sample [27].
Fig. 3–XRD pattern of BCAsh [27]. Upper Curve: 600 °C [1112 °F], Lower Curve: 700 °C
[1292 °F].
The SEM was used to obtain images of the microstructure of the samples burned at temperatures
of 500, 600 and 700 °C [932, 1112 and 1292 °F] for 1.0, 1.5 and 1.5 h respectively. In Fig. 4 it can
be seen that increasing the burning temperature has definite effects on the morphology of the
BCAsh. Increasing the temperature provides sufficient energy for the particles to fuse together and
remove the porosity. Accordingly, a change in the particle size distribution was also noticed. In
Fig. 5 the method of using the SEM images in ImageJ software to estimate the particle size
distribution of the samples is shown. Using this method, the particle size distribution of three
samples burned at different conditions was estimated and presented in Fig. 6. While the average
particle size of the ash was almost the same for all of the ash (~7-10 μm [2.7-3.9 x 10-4in]), with
11
increasing the temperature, a slight increase in grain size was observed. This change could be only
caused by increasing the temperature since the grinding time for all the samples was the same.
(a)
(b)
(c)
Fig. 4–SEM image for the sample burned at different temperatures and durations:
(a) 500 °C [932 °F] and 1 h, (b) 650 °C [1202 °F] and 1.5 h, (c) 700 °C [1292 °F] and 1.5 h.
12
Fig. 5–SEM image for sample analysis in ImageJ. The area of the highlighted particle is
measured: Left: 500 °C/1h [932 °F]. Right: 650 °C/2h [1202 °F].
Fig. 6–Particle size distribution for samples burned at 500 °C [932 °F] for 1 h, 650 °C [1202 °F]
for 1.5 h, and 700 °C [1292 °F] for 1.5 h. (1 μm equals to 3.4 × 10-5 inches)
4.3. Optical properties
The changes in the microstructure due to the increase of the temperature from 500 to 700 °C [932
to 1292 °F] was also reflected in the freshly-burned ash color changing from gray to light greenish.
However, at each given temperature, regardless to the color of the obtained ash, after grinding, the
ash color changed to gray; a darker gray color was observed for lower burning temperatures and a
lighter gray color for higher burning temperatures. At each temperature, burning for 1 h resulted
0
10
20
30
40
50
-5 5 15 25 35
Freq
uen
cy (
%)
Equivalent spherical diameter (µm)
500 ᴼC [932 ᴼF]
650 ᴼC [1202 ᴼF]
700 ᴼC [1292 ᴼF]
13
in obtaining ash with nearly black color; this is probably caused by the presence of a higher amount
of carbon content. Some of the factors affecting the color of the ash found in some previous studies
[28] are unburned carbon, various metal ions, and the chemical composition of the material.
4.4. Effect of bamboo ash on heat of hydration
The isothermal calorimetric curves of five mortars measured for 72 hours at 23 °C [73.4 °F] can
be seen in Fig. 7. From these curves, the maximum power for all of the five mixes was obtained
and the values are presented in Table 2. The BCAsh used for this experiment was obtained at the
optimal calcination condition (burning at 700 °C [1292 °F] for 1.5 h). According to the results, the
highest power value for heat of hydration was for the replacement level of 1.0%; this was about
8.0% higher than the control (0% replacement) mix. For the mix with 5.0% replacement level, the
maximum power value was 19% lower than that of control mortar. From this result, it can be
concluded that a BCAsh replacement level of at least 5.0% is required to achieve a significant
reduction in the peak rate of heat generation during the hydration process. Fig. 8 shows the
cumulative heat of hydration of the five mortars. The cumulative heat of hydration at 7 days is
similar for all types expect 5% BCAsh which is lower than others by about 6%.
Fig. 7–Effects of different replacement levels of BCAsh on the rate of reaction of mortar at 23
°C [73.4 °F]
0.0
2.0
4.0
0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00
Po
wer
, W/g
Cem
Mat
Time since Start Time, hh:mm
Control
0.5%
1.0%
2.5%
5.0%
14
Fig. 8–Effects of different replacement levels of BCAsh on cumulative heat of hydration of
mortar at 23 °C [73.4 °F]
4.5. Effects of BCAsh on mortar setting time
The initial and final setting times estimated from the calorimetric curves for all of the five mixes
are presented in Table 2. Using the calorimetry curve, the initial setting time can be found by
finding the end point of the dormant period [29] and the final setting time coincides with the
acceleration-deceleration peak time [30].
According to the results, the initial and final setting times were considerably delayed by increasing
the replacement level. At 23 °C [73.4 °F], the 0.5% replacement of cement with BCAsh increased
the initial and final setting time by about 129 and 345 minutes respectively. The maximum increase
in final setting time was achieved by 5% replacement in which a 959 minutes increase in time was
observed. The initial and final setting times increase with an increase in BCAsh content, thereby
retarding the hydration process.
-100
400
900
1400
1900
2400
2900
3400
3900
4400
0 20 40 60 80 100 120 140 160 180
Ener
gy, J
Time since Start Time, h
Control
0.5%
1.0%
2.5%
5.0%
15
Table 2–Maximum power and setting time of five mixes of mortar at 23 °C [73.4 °F]
Mix No.
Replacement
level
Initial setting
time (min)
Final setting
time (min)
Maximum power
(W/g Cem Mat)
1 - 120 600 3.24
2 0.5% 249 945 3.35
3 1.0% 289 1020 3.50
4 2.5% 388 1260 3.45
5 5.0% 472 1559 2.63
Fig. 9 and 10 show the effects of different replacement levels of BCAsh on the initial and final
setting time of mortars tested at temperatures of 30, 40 and 50 °C [86, 104 and 122 °F]. According
to the results, the 0.5% BCAsh replacement level increases the initial setting time by 25% at 50
°C [122°F], which is less than the 108% increase at ambient temperature, but the effect is still
considerable. At 1.0% BCAsh and 2.5% BCAsh replacement levels, by increasing the temperature
from 23 to 50 °C [72 to 122 °F], the change in setting time decreases from 141 and 223% to 44
and 111%, respectively.
By increasing the temperature from 23 to 50 °C [72 to 122 °F], the effect of BCAsh in increasing
the final setting time reduces from 58 to 5% for 0.5% BCAsh, from 70 to 12% for 1.0% BCAsh
and from 110% to 16% for 2.5% BCAsh. According to these results, it is concluded that by
increasing the temperature, BCAsh become a less powerful retarder, but it is still very effective.
This significant increase in both initial and final setting time might be caused by the chemical
reactions that take place by addition of BCAsh to the composite which can be subjected to further
studies in this area.
16
Fig. 9–Effects of different replacement levels of BCAsh on the initial setting time of mortars
tested at temperatures of 30, 40 and 50 °C [86, 104 and 122 °F]
Fig. 10–Effects of different replacement levels of BCAsh on the final setting time of mortars
tested at temperatures of 30, 40 and 50 °C [86, 104 and 122 °F]
0
50
100
150
200
250
300
350
400
450
0 0.5 1.0 2.5
INIT
IAL
SET
TIN
G T
IME
(MIN
)
REPLACEMENT LEVEL (%)
23°C [73.4 ⁰F]
30°C [86 ⁰F]
40°C [104 ⁰F]
50°C [122 ⁰F]
0
200
400
600
800
1000
1200
1400
0 0.5 1.0 2.5
FIN
AL
SET
TIN
G T
IME
(MIN
)
REPLACEMENT LEVEL (%)
23°C [73.4 ⁰F]
30°C [86 ⁰F]
40°C [104 ⁰F]
50°C [122 ⁰F]
17
4.6. Effect of bamboo ash on Mortar Strength
The 7-day and 28-day compressive strengths of mortars were notably affected by the level of
replacement. As it can be seen in Fig. 11, a consistent reduction in the compressive strength of
mortars was observed as the amount of the BCAsh replacement level in the mortar increased. The
replacement level of 0.5, 1.0 and 2.5% reduced the compressive strength of the mortar respectively
by 5.0, 7.7 and 10.6% at 7 days and by 4.8, 9.5 and 11.8% at 28 days. However, since the final set
was increased significantly by increasing the BCAsh content, the lower rate of strength
development compared to the control mortar might be observed if the strength of the BCAsh
mortar is examined at ages later than 28 days.
Fig. 11–Effects of different replacement levels of cement with BCAsh on 7-day and 28-day
compressive strengths of mortars. Graph showing compressive strength (the average value ±
standard deviation of three specimens) of mortar samples. (1 MPa equals to 145 psi)
18
5. FURTHER RESEARCH
Since the delay in heat of hydration process suggests that setting of portland cement concretes
would be delayed, more experiments will be conducted to investigate this effect, such as the initial
and final setting time tests by Vicat Needle for different cement replacement levels. In addition,
further studies should be done on the chemical reactions that take place by addition of BCAsh to
the concrete resulting the significant retarding effect. The retarding effect of BCAsh on alkali-
activated materials (AAM) for which the normal retarders are not effective can be also examined.
Finally, since most of the other waste ashes have had lower long-term strength reduction effects
on concrete/mortar and BCAsh increased the final setting time of the mortar, the strength of the
mortars made with the same proportions and replacement level with this study at the age of 56 and
91 days will be tested and analyzed.
19
6. CONCLUSIONS
Bamboo shavings were burnt at 50°C [122 °F] intervals between 500 and 700 °C [932 and 1292
°F] for durations between 1.0 and 2.5 h to find the optimum burning condition. From this study,
the following conclusions can be made:
1. Increasing the burning time beyond 1.5 h did not have a considerable effect on yield.
2. Increasing the temperature had a noticeable effect on (1) carbon content reduction, (2)
morphology and (3) particle size.
3. As the burning temperature increases, the microstructure of the BCAsh becomes more
crystalline and the average particle size increases as well.
4. The optimum burning temperature and time were considered to be 700 °C [1292 °F] and
1.5 h, respectively.
5. The BCAsh could not be considered as a pozzolan because of the low amount of silica in
its chemical composition. The major oxide constituents of the ash are K2O and CO3.
6. The BCAsh did show a considerable retarding effect when used in mortars.
7. The initial and final setting time both increased with increasing BCAsh content.
8. By increasing the replacement level from 0.5 to 2.5%, The 7 day compressive strength of
mortars decreased by 5.0 to 10.6% and the 28 day compressivestrength of mortars
decreased by 4.8 to 11.8% compared to controls with 0% BCAsh.
9. This material could be considered for applications in which the retarding of the setting time
of the concrete/mortar is a higher priority than its strength.
20
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