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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