USE OF RICE HUSK ASH AS AN ADMIXTURE OF

PORTLAND CEMENT IN CONCRETE

BS CIVIL ENGINEERING, BATCH 2017

SUBMITTED BY

1. SHAKEEL HUSSAIN 2017-CV-062

2. IFTIKHAR ALI 2017-CV-064

3. AHMED HUSSAIN 2017-CV-094

4. EHSAN ALI 2017-CV-096

5. AAMIR MEHDI 2017-CV-103

PROJECT SUPERVISORS

Ms. Hira Shakeel Ms. Madiha Shamim

Lecturer Lecturer

DEPARTMENT OF CIVIL ENGINEERING

SIR SYED UNIVERSITY OF ENGINEERING AND TECHNOLOGY
UNIVERSITY ROAD, KARACHI
 CHAPTER 1

INTRODUCTION

1.1GENERAL
Rice husks ashes are best alternative which substitute cementing material instead of
ordinary Portland cement. RHA can be intermingling with OPC for improving the
strength and durability of concrete. The RHA and egg shell material reduces the cost of
construction.
Rice husk ash act as a Pozzolanic material which have reactive high silica or alumina,
which have little or no binding property, but when this pozzolanic materials react with
lime in the presence of water, it will set and become harden like ordinary Portland
cement. In this study the ordinary Portland cement is replaced by RHA at different
proportion such as 6.5%, 7.2%, 10%, and 15% to study different strength properties,
saturated water absorption of concrete and comparison of strength at different age of
curing.
At the temperature 550 to 800 Celsius amorphous silica is produced and after that (at
high temperature) crystalline silica is formed. The properties of amorphous silica are
different from crystalline silica. The rice husk is produced during milling process of
paddy. The outer covering of paddy grain is surrounded by the by product known as
husk. When burning of this rice husk is done in proper manner in furnace, the rice husk
ash is obtained. In the burning process of rice husk, this husk has approximately 75%
organic volatile substance and remaining 25% by weight is transform into ash.

1.2 Introduction To Our Project

The project that we selected is basically a material testing project. This project deals
with the study of the binding properties of rice husk ash (RHA) to use it as an admixture
to ordinary Portland cement (OPC) to increase the durability and strength of concrete.
In this project we tested 15 cubes and 15 cylinders at 0, 6.5, 7.2, 10 and 15% ratios of
rice husk ash (RHA) on 7, 14 and 28 days of curing. The highest compressive strength
for the concrete was obtained at 10% of rice husk ash on 28 days of curing. The flexural
test of the beams were also tested at 0, 6.5, 7.2, 10 and 15% of rice husk ash on 7, 14
and 28 days of curing. The maximum strength was obtained on 10 % of rice husk ash
on 28 days of curing. While slump test was also carried out to check the workability of
the concrete with different rice husk ash. This test was done to check the effect of the
RHA on the workability of the concrete. As the shows that it decreased with increase
of RHA proportion.
1.3 Objective:
The aims of present investigation are:

 To study the effect of rice husk ash and egg shell (powder) as an admixture in
concrete.
 To investigate strength like compressive, flexural strength at different ages of
concrete.
 To determine the optimum level of replacement of ordinary Portland cement
with rice husk ash and egg shell (powder).
 To determine the workability of Rice husk ash and egg shell (powder) concrete.
To conduct durability study on Rice husk ash concrete with mineral admixtures.

1.4 Scope:
 To obtain Mix proportions of concrete by ASTM method.
 To conduct Compression and tensile testing on concrete using OPC and by
using RHA and egg shell (powder) with varying content on standard
specimens.
 To conduct Flexural strength test on concrete with or without RHA and egg
shell (powder) on standard specimens.
1.5 Methodology

Study of literature

Sample collection (RHA)

Mix design

Casting of specimens

Curing of specimens

Testing of specimens

Analysis of concrete tensile, flexural and compressive

Strength at different ages

Analysis of optimum level of RHA

Comparison of concrete with or without RHA

Results and graphical representation of results

Conclusion and recommendation

 CHAPTER 2

LITERATURE REVIEW

2.1 Introduction:
Pozzolanas are often used to blend with OPC or to partially replace OPC. Pozzolanas
are natural or artificial materials which contain Silicon dioxide and/or alumina. They
are not cementitious themselves but when finely ground and mixed with lime, the
mixture will set and harden at ordinary temperature in the presence of water, like
cement (ASTM 618-94a cited in Neville 2003). An example of the well-known
pozzolana is RiceHusk Ash (RHA). Rice husk is an agro-waste material that is
produced all over the world. According to Zheng (1996), Tashima, etal 2009, about 100
million tons of rice husks is produced annually all over the world. Approximately, 20kg
of rice husk are obtained from 100kg of rice. Rice husks contain organic substance and
of inorganic materials. RHA is obtained by the combustion of rice husk. RHA is 20%
by weight of rice husk and serve no economic purpose for either agriculture or industrial
usage (Mehta, 1977; Dahiru and Zubairu, 2008). Prasad et al (2000) reported that RHA
contains 87 % to 97% of silica with small amount of alkalis and other trace elements.
Tashima et al (2005) also indicated that RHA contains about 92.99 5 silica. RHA is a
highly reactive pozzolanic material suitable for use in lime-pozzolana mixes and for
OPC replacement. Based on the temperature range and the duration of burning of the
husk, crystalline and amorphous forms of silica are obtained. The crystalline and
amorphous forms of silica have different properties and it is important to produce ash
with correct specifications for specific end use (Muthadhi et al, 2006). Generally, the
amorphous forms of silica is composed of silica tetrahedral arranged in a random three-
dimensional network without regular lattice structure. Due to disordered arrangement,
the structure is open with holes in the network where electrical neutrality is not satisfied
and the specific surface area is also large. This helps to increase the reactivity, due to
large area available for reaction to take place (Shomglin et al, 2001). On the other hand,
the structure of crystalline silica is built by repetition of a basic unit, the silicon
tetrahedron in an oriented three-dimensional framework. The factors influencing the
ash properties are the incinerating conditions (temperature and duration), rate of
heating, geographic location, fineness and crop variety. Among these, the incinerating
conditions make great impact on the quality of the final product (Muthadhi et al, 2006).
In general, lower temperature and prolonged duration will result in amorphous ash. The
reactivity of the RHA depends on the non-crystalline (amorphous) silica content and its
specific surface. Theamorphous silica is obtained by burning the ash at temperatures of
650oC to 700oC (UNIDO, 1984). Muthadhi et al (2006) reported that amorphous silica
is obtained at temperature in the range of 500oC to 700oC and the duration of firing
varies from a few hours to a day producing ash that is white in colour. Uncontrolled
combustion of rice husk, for example, when used as a fuel or heap burning, may occur
at temperature above 800oC producing ash that is lilac pink in colour and predominantly
containing crystalline silica, which is less reactive.Research on producing rice husk ash
(RHA) did not start recently. Metha (1977) reported on the use of RHA in blended
cement. Since then a lot of studies have been reported, these include Cook et al (1977),
Okpala(1987), Yogenda and Jagadesh (1988), Okpala(1993), Metha and Pit (1996).
Other recent researches on RHA in concrete and mortar have been reported by Cisse
and Laguerbe (2000).
Asif Farooq and Mr. Misba Danish mentioned the following researchers and also
comment on their work about the partial replacement of rice husk ash (RHA) with
cement.
2.2 Case Study
2.2.1 Chai Jaturpitakkul and Boonmark Roongreung (2003): In this
study they suggested new cementitious materials, they use 50% rice husk ash and 50%
calcium carbide residue. This mixture shows cementing properties and the pozzolani
reaction between these two mixtures was identified, without OPC in the mixture. In this
study the different properties such as compressive strength and flow were investigated
while using this mixture. The setting time of this mixture paste is greater than OPC
mortar. At the age of 28 days with the ratio of RHA and CCR of 50:50 with OPC the
highest compressive strength was obtained. This mixture of RHA and CCR has the
highest potential to be used as a cementing material for mortar’s compressive strength.
2.2.2 Deepa G. Nair, K.S. Jagadish , Alex Fraaij (2006):
This study shows the RHA was produce by the different types of field oven the property
were discussed in this paper. The performance of this oven has discussed for classifying
different methods to produce most reactive pozzolanic material to use as a substitude
for the cementitious material. Investigation for the long term strength of RHA with lime
or cement was carried out.

2.2.3 Gemma Rodri guez Sensale (2006):

The researcher in this study provide the knowledge about the improvement of the
compressive strength of the concrete with RHA at the age of 91 days. In this study two
different replacement of cement were used by rice husk ash 10% and 20%. Different
water/cement (w/c) ratios were used in this study (0.5, 0.40 and 0.32). The results
obtained from these ratios were compared with the specimens casted with OPC
concrete. The comparative study was carried out in the compressive, split tensile
strength and air permeability. The results shows that the rice husk ash gives a good
performance in compressive strength test. The results obtained from the split tensile
and air permeability shows that the burning temperature of rice husk ash should be in
control manner.
2.2.4 Gemma Rodriguez de sensale (2010):
The researcher Gemma Rodriguez de Sensale discuss about the effect on durability
aspects by the partially replacement of OPC (ordinary Portland cement) by rice husk
ash (RHA) and the investigation has done on the high performance cementious material.
Two RHAs (amorphous and partially crystalline optimized by dry-milling) and
different water cementitious materials ratio and different percentages of rice husk ash
(RHA) replacement levels are investigated in this study. The durability tests were
carried out, namely chloride ion penetration, alkali-silica expansion, sulfate and acid
resistance. While air permeability was also tested.The conclusion from the study was
that the incorporation of both RHAs in concrete explain different behaviors for chloride
ion penetration and air permeability depending on the water cementious materials ratio.
In mortars, it reduces the mass loss of specimens exposed to hydrochloric acid solution
and decreases the expansion due to sulfate attack and the alkali silica reaction.

2.2.5 Hwang Chao-Lung, Bui Le Anh-Tuan, Chen Chun-Tsun

(2011):
Hwang and the companion carried out a test on the influence of partially replacement
of cement by RHA derived from the South Vietnam produced by burning of rice husk
in the boiler. The rice husk ah was ground for one hour to improve its pozzolanic
reactivity. Hence, the strength of both the ground and non-ground rice husk ash (RHA)
were checked. While beside this other properties like compressive strength, concrete
electrical resistivity and ultrasonic pulse velocity were also investigated.While from the
results it was concluded that the non-ground rice husk ash (RHA) could be used as a
pozzolanic material.It was also concluded that the smallest particle size of ground rice
husk ash (RHA) increases the compressive strength of the concrete.
While the amount/ratio/percent of rice husk ash fo0r the better results concluded from
the results was 20% of the cement. At that percentage it did not adversely affects the
strength and durability of concrete.

2.2.6 Rahmat Madandoust, Malek Mohammad Ranjbar, Hamed

Ahmadi Moghadam, Seyed Yasin Mousavi (2011):
They studied the RHA’s effect on the properties of the concrete and durability aspect
were studied. To determine the appropriate percentage of rice husk ash (RHA) for
partial replacement of OPC, mixture with 0-30% rice husk ash and test were established
and the mechanical properties of the concrete were determined.
The percentage of decrease in compressive strength was considered for degree of
damage and chloride ions penetration as compare with control specimens.
The results shows that the partial replacement of cement by rice husk ash (RHA)
enhanced durability and homogeneity. But did not increase the early age of compressive
strength of concrete.
All the researchers reported on RHA as a partial replacement of OPC in concrete and
mortar have been positive and shown to be economical and also addressing the problem
of environmental pollution.
RHA could also be considered for use in concrete in small quantities as an admixture
to improve on the properties of fresh and hardened concrete, and if suitable would
replace the use of more expensive materials.

2.3 Compressive strength of cubes results of different age and

different replacement level of RHA

RISE HUSKS
7 DAYS 28 DAYS
ASH
( MPa) (MPa)
%

0 29.32 41.91

5 27.58 43.76

7.5 27.89 46.18

10 26.90 44.82

12.5 26.20 42.18

15 23.21 39.14

Table 1
 Graph.1 Influence of RHA on compressive strength

2.4 Flexural Strength

The Flexural strength results at the various ages such as 7,28 days and at the
replacement levels such as 0%, 5%, 7.5%, 10%, 12.5% and 15% of rice husk ash are
presented in Table

RHA 7 DAYS 28DAYS

% (Mpa) (MPa)

0 3.94 5.31

5 3.49 5.60

7.5 3.81 5.69

10 3.41 5.58

12.5 3.36 5.60

15 3.19 5.09

Table 2
 Graph 2 Influence of RHA on flexural strength

2.5 Splitting Tensile Strength

The Splitting Tensile strength results at the various ages such as 7,28 days and at the
replacement levels such as 0%, 5%, 7.5%, 10%, 12.5% and 15% of rice husk ash are
given in below table.

RHA 7 DAYS 28DAYS

% (Mpa) (Mpa)

0 2.22 3.128

5 1.90 3.118

7.5 2.092 3.316

10 1.98 3.28

12.5 1.90 3.075

15 1.650 2.911

Table 3
 Graph 3 Influence of RHA on split tensile strength

2.6 Egg Shell:

Eggshell is the hard outer shell of the egg. It mainly consists of calcium carbonate,
normal calcium. The rest is made up of proteins and other minerals. Calcium is an
essential mineral and is found in many foods, including dairy products, egg shell
chopper is used to process egg shell into egg shell powder. As for the production of egg
shell powder, this process: washing eggshell, drying egg shells and grinding egg shells.
Eggshell before chopping is broken into small pieces. Throughout the process, three
machines are required: a dryer for eggshell, a mill for eggshell, and a sieve for eggshell.
For eggshell washing machines, it can be customized to suit your needs.
Egg Shell Powder Production:

Figure 1

Crushing of egg shell

Figure 2
 Grinding of Eggshell

Figure 3

Egg shell powder after sieving

Figure 4
2.6.1 Chemical Composition of Egg Shell Powder:

CEMENT ESP
SiO2 21.8 0.08
Al2O3 6.6 0.03
Fe2O3 4.1 0.02
CaO 60.1 52.1
MgO 2.1 0.01
Na2O 0.4 0.15
K2O 0.4 -
SO3 2.2 0.62
Table 4

2.6.2 Previous Studies on egg shell:

Muneeb Ayoub Memon and Mian Jawaduddin:
Muneeb Ayoub Memon and Mian Jawaduddin done an experimental work on the
partial replacement of cement with egg shell.
Calcium-enriched eggshells are poultry waste with almost the same chemical
composition as limestone. Using eggshell waste instead of natural lime instead of
cement in concrete can bring many benefits, such as minimizing the use of cement,
protecting natural lime and using waste. Eggshell is a good accelerator for cement
binders. The eggshell and lime stone are almost same in chemical nature. To this end,
we can minimize the use of cement and waste disposal. Various researchers use
eggshell powder as a substitute for cement. Present research analyzed the fresh and
hardened characteristics of concrete comprising of ESP.
The researchers concluded following results from their work:
1. The compressive strength of concrete using egg shell powder as a substitute for
cement was reduced by 10%.
2. The flexural strength of concrete of an egg shell mixture increases with an
increase in the amount of egg shell powder added by 7.5%.
3. It reduced the permeability over a long period of time.

Average compressive strength of cubes

% of ESP 0 2.5 5 7.5 10
DAYS
3 17.82 18.89 19.38 20.7. 19.60
7 23.73 24.22 25.75 26.35 25.95
28 28.37 29.14 30.1 30.93 30.13
Table 5
Average flexural strength of beam
% of ESP 0 2.5 5 7.5 10
DAYS
3 3.50 3.65 3.80 4.00 3.88
7 4.50 4.65 4.78 4.96 4.86
28 5.55 5.65 5.80 6.10 5.90
Table 6

Graph 4 Compressive strength of cube

Graph 5 Flexural strength of cube

2.3 Chemical Analysis of RHA and cement:
The silica content is one of the most important constituents of cement. The silica content
of the RHA was found to be 87.2 %, which indicate higher silica content then in cement
shown in table 7.

Table 7

2.4 Physical properties of procured Rice Husk Ash (RHA):

Physical properties of procured Rice Husk Ash (RHA)

Physical State Solid – Non Hazardouz

Appearance Very fine powder

Particle Size 25 microns –mean

Color Grey
Specific Gravity 2.3
Table 8
 CHAPTER 3
METHODOLOGY
3.1 Use of RHA and ESP in OPC for improvement of workability:
They carried slump test of the concrete with different ratios of RHA and egg shell to
check the effect of the eggshell on the workability of the concrete. As from the table
given below it is concluded that the workability of the concrete gradually decreased
with the increase in the percentage of the egg shell replacement.

Figure 5

Slump test results of different replacement level

S.NO % OF ESP SLUMP RESULT

(mm)
1 0 88
2 2.5 76
3 5 65
4 7.5 54
5 10 45
Table 9
 Graph 6 Slump Test

A certain process is adopted for the eggshell to make it usable. In first it the egg shell
can be washed with normal water, it removes the thin membrane of the eggshell aside
from cleaning the impurity. After washing step it can be dried up (sun dry), the duration
of drying should be one to five days. Then it should be crushed into small pieces by
using hammer or simply by hand and then it can be grinded and sieved.

3.2 Types of slump

There are three types of slump that may occur in a slumps test, namely, true slump,
shear slump and collapse slump. True slump refers to general drop of the concrete mass
evenly all around without disintegration. Shear slump indicates that the concrete lacks
cohesion. In our case we got true slump at 10% mix of Rha and zero slump at 15% mix
of RHA in concrete as shown in figures below.
 Figure 6

3.2.1 Collapse Slump

In a collapse slump the concrete collapses completely. A collapse slump will generally
mean that the mix is too wet or that it is a high workability mix, for which slump test is
not appropriate. It means the water-cement ratio is too high, i.e. concrete mix is too wet
or it is a high workability mix, for which a slump test is not appropriate.

3.2.2 Shear Slump

In a shear slump the top portion of the concrete shears off and slips sideways. OR

If one-half of the cone slides down an inclined plane, the slump is said to be a shear
slump. The shear slump indicates that the result is incomplete, and concrete needs to be
retested for valid results.

1. If a shear or collapse slump is achieved, a fresh sample should be taken and the
test is repeated.
2. If the shear slump persists, as may the case with harsh mixes, this is an
indication of lack of cohesion of the mix.

3.2.3 True Slump

In a true slump the concrete simply subsides, keeping more or less to shape

1. This is the only slump which is used in various tests.

2. Mixes of stiff consistence have a Zero slump, so that in the rather dry range no
variation can be detected between mixes of different workability.

However, in a lean mix with a tendency to harshness, a true slump can easily change to
the shear slump type or even to collapse, and widely different values of slump can be
obtained in different samples from the same mix; thus, the slump test is unreliable for
lean mixes.
3.3 Applications of Slump Test
 The slump test is used to ensure uniformity for different batches of similar
concrete under field conditions and to ascertain the effects of plasticizers on
their introduction.
 This test is very useful on site as a check on the day-to-day or hour- to-hour
variation in the materials being fed into the mixer. An increase in slump may
mean, for instance, that the moisture content of aggregate has unexpectedly
increases.
 Other cause would be a change in the grading of the aggregate, such as a
deficiency of sand.
 Too high or too low a slump gives immediate warning and enables the mixer
operator to remedy the situation.
 This application of slump test as well as its simplicity, is responsible for its
widespread use.

3.4 Workability of Concrete and Factors Affecting Workability

The ease with which the concrete ingredients can be mixed, transported, placed,
compacted, and finished with minimum homogeneity loss. The property of fresh
concrete which is indicated by the amount of useful internal work required to fully

compact the concrete without bleeding or segregation in the finished product.

Figure 7
3.4.1 Factors Affecting Workability of Concrete
i. Water content in the concrete mix.
ii. Amount of cement & its Properties.
iii. Aggregate Grading (Size Distribution).
iv. Nature of Aggregate Particles (Shape, Surface Texture, Porosity etc.).
v. Temperature of the concrete mix.
vi. Humidity of the environment.
vii. Mode of compaction.
viii. Method of placement of concrete.
ix. Method of transmission of concrete.

3.6 How to improve the workability of concrete

 Increase water/cement ratio.

 Increase size of aggregate.
 Use well-rounded and smooth aggregate instead of irregular shape.
 Increase the mixing time.
 Increase the mixing temperature.
 Use non-porous and saturated aggregate.
 With addition of air-entraining mixtures.
 CHAPTER 4

PRODUCTION OF RHA AND MIX DESIGN OF SAMPLES

4.1 Production of Rice Husks Ash

The RHA produce from the burning of husk in boiler at controlled temperature that
fulfils the physical characteristics and chemical composition of mineral admixtures.
The pozzolanic behavior of RHA depends upon the silica crystallization phase, silica
content and size and surface area of ash. The amount of carbon content in RHA should
be smallest. If the carbon contain is more in RHA the strength of concrete will be less.
RHA is produce by burning of rice husk at control temperature that has amorphous
silica content and large surface area. Appropriate furnace and the good grinding method
is necessary for combustion and grinding RHA to obtain the excellent quality of ash.

4.1.1 BURNING PROCESS OF RICE HUSK

The rice husk is burn into Ferro cement furnace or sometimes in boilers to produce
RHA at controlled temperature. In furnace air ducts are provide which play two role,
one is supply air to husk in combustion process and other is act as passages for fire. Air
ducts are controlling commotion temperature. Electric fans are attached to air ducts
which control the combustion temperature. Air ducts also reduce the carbon content in
RHA, if there are no air ducts the carbon content will be more in ash and the strength
of concrete will be low. In the burning process of RHA the temperature of boiler or
furnace is around 700-800̊c for 24 hours. After the 24 hours the temperature is about 52̊
c. After the 48 hours the temperature of ash is about 25̊ c. At 700-800̊ c temperate the
silica is remain in amorphous silica, above this temperature the amorphous silica is
converted into crystalline silica which is not useful in concrete. The air is providing into
air ducts at the rate of velocity 12 meter per second. After burning the physical
appearance of rice husk ash is shown in figure
 Figure 8 Rice Husk ash

4.1.2 Grinding Process Of Rice Husk ash

The grinding process should be done in proper manner in the loss angeles abrasion
machine. The finer pozzolanic ash is superior. Fineness of rice husk ash is necessary
because it influence the rate of reaction and the rate of gain in concrete strength.

Other than influence the rate of reaction, fineness also influences water–cement ratio,
shrinkage, creep. The finer RHA particles yield larger surface area and increases
strength of concrete. Chemically reactive very fine RHA would fill empty columns in
concrete in an optimum manner. The particles of RHA retained on 45 m sieve should
not be more than 12.0%. Therefore, to get the required fineness, proper grinding of
burnt ash is very important. In 90 min of grinding, fineness of 5 kg burnt husk obtained
by combustion method met the standard requirements.
 Figure 9 Los Angeles machine for grinding of RHA

4.1.3 Material Production

The production of RHA was obtained by burning the rice husk in a Ferro cement
furnace. Only ash that lies within the middle third of the furnace taken for grinding as
it was considered as quality ash. Figure show the sequence of operation in producing
finely ground RHA for the present investigation.

a) Rice husk b).Dumping of rice husk

c). Ferro cement furnace d). After burning in kiln

e).Los Angeles machine f). After grinding- RHA

Figures 10

4.2 Standard Method for Preparing Samples

4.2.1 Gradation of Sand as per ACI Standard
Grading refers to the distribution of particle sizes present in an aggregate. The grading
is determined in accordance with ASTM C 136, “Sieve or Screen Analysis of Fine and
Coarse Aggregates.” A sample of the aggregate is shaken through a series of sieves
nested one above the other in order of size, with the sieve having the largest openings
on top and the one having the smallest openings at the bottom. These wire cloth sieves
have square openings. A pan is used to catch material passing the smallest sieve.
 Figure 11

4.2.2 Fineness modulus

Using the sieve analysis results, a factor called the fineness modulus is often computed.
The fineness modulus is the sum of the total percentages retained on each of a specified
series of sieves, divided by 100. The specified sieves are the 75.0, 37.5, 19.0, and 9.5
mm (3, 1.5, 3/4, and 3/8 in.) and 4.75 mm, 2.36 mm, 1.18 mm, 600 µm, 300 µm, and
150 µm (No. 4, 8, 16, 30, 50, and 100). Note that the lower limit of the specified series
of sieves is the 150-mm (No. 100) sieve and that the actual size of the openings in each
larger sieve is twice that of the sieve below. The coarser the aggregate, the higher the
fineness modulus. For sands used in concrete, the fineness modulus generally ranges
from 2.3 to 3.1.

4.2.3 Specific Gravity of Fine Aggregate

Fine aggregate is dried to a constant mass at 100 to 110 C (212 to 230 F), cooled in air
and immersed in water for 24 hr. Excess water is drained off and the sample is spread
on a flat surface exposed to a gently moving current of warm air. The sample is stirred
frequently until it approaches a free flowing condition and then a portion is placed in a
mold and tamped. If surface moisture is still present, the fine aggregate will retain its
molded shape after the mold is lifted. Drying is continued with testing at frequent
intervals until the tamped fine aggregate slumps slightly upon removal of the mold.
This indicates that it has reached a saturated surface-dry condition. Next, about 500 g
of the surface-dried material is placed in a jar or flask, and water is added to fill it to its
calibrated capacity. The total mass of the jar, specimen, and water is determined. The
fine aggregate is then removed from the jar, oven-dried and its mass determined.
Finally, the mass of the jar filled with water to its calibrated capacity is determined. The
specific gravity values are then calculated as follows:
 A
Bulk specific gravity = B+C−D
B
Bulk specific gravity SSD = B+C−D
Where
A = mass of oven-dry sample in air;
B = mass of saturated surface-dry mass in air
C = mass of saturated sample.
4.2.4 Specific Gravity of Coarse Aggregate
Test methods for finding specific gravity of aggregates are described in ASTM C 127,
“Specific Gravity and Absorption of Coarse Aggregate,” and ASTM C 128, “Specific
Gravity and Absorption of Fine Aggregate.” Coarse aggregate is thoroughly washed,
dried to constant mass at 100 to 110 C (212 to 230 F), cooled in air and immersed in
water for 24 hr.* It is then removed from the water and dried to a saturated surface-dry
state with a large absorbent cloth. Care is taken to avoid evaporation of water from the
aggregate pores during this operation. The mass of the sample in air is determined and
then it is placed in a sample container for determination of its mass in water. The mass
of the sample in water will be less than that in air and the loss in mass is equal to the
mass of the water displaced. Therefore, the loss in mass is the mass of a volume of
water equal to the aggregate volume. After the mass in water is determined, the sample
is oven-dried and its mass determined again. The bulk specific gravity and bulk specific
gravity SSD, are calculated as follows.
A
Bulk specific gravity = B−C
B
Bulk specific gravity SSD = B−C
Whereas,
A = mass of oven-dry sample in air;
B = mass of saturated surface-dry mass in air
C = mass of saturated sample.

4.3 MIX DESIGN CALCULATION RESULTS AND ANALYSIS OF

RESULTS:

4.3.1 Mix Design:

The process of selecting suitable ingredients of concrete and determining
their relative proportions with the object of producing concrete of certain minimum
strength and durability as economically as possible.

ASTM C387/C387M FOR 1:2:4 MIX RATIO OR M15 GRADE OF

CONCRETE.
4.3.2 CALCULATION FOR MATERIAL:-
 FOR CUBE:-
Dimension = 6”x6”x6”
= 0.5’x0.5’x0.5’
Volume of cube = 0.5’x0.5’x0.5’
= 0.125 ft3
Density of concrete = 144 lb/ft3
Mass = Density x volume
= 144 x 0.125
= 18 lbs 1 Kg = 2.204 lbs
Mass = 18/2.204
= 8.16 Kg
Wastage (15%) = 0.15 x 8.16
= 1.224 Kg
Total mass = 1.224 + 8.16
= 9.384 Kg
Mix design ratio = 1:2:4
Cement = 1/7 x (9.384) = 1.34 Kg
Fine aggregate = 2/7 x (9.384) = 2.68 Kg
Coarse aggregate = 4/7 x (9.384) = 5.36 Kg
 FOR CYLINDER:-
Diameter = 6” = 0.5’
Height = 12” = 1’
Volume of cylinder =Ω x(d2 x h)
4
= 0.196 ft3
Density of concrete = 144 lb/ft3
Mass = Density x volume
= 144 x 0.196
= 28.224 lbs. 1 Kg = 2.204 lbs.
Mass = 28.224/2.204
= 12.8 Kg
Wastage (15%) = 0.15 x 12.8
= 1.923 Kg
Total mass = 1.923 + 12.8
= 14.72 Kg
Mix design ratio = 1:2:4
 Cement = 1/7 x (14.72) = 2.10 Kg
Fine aggregate = 2/7 x (14.72) = 4.2 Kg
Coarse aggregate = 4/7 x (14.72) = 8.11 Kg
Water cement ratios=0.55 Kg

4.3.3 MIX PROPORTIONING OF RICE HUSK ASH (RHA)

CONCRETE:
4.3.3.1 FOR CUBE
In this method, five replacements of cement i.e., 6.5%, 7.2%, 10%, and 15% with
Rice husk ash (RHA) are done, whereas the total binder content remains the same.
The mix proportions considered for each replacement by replacement method by
RHA are presented in tables.

Without RHA
FOR THREE CEMENT FINE COARSE WATER TOTAL
CUBES AGGREGATE AGGREGATE RATIO PRICE
QUANTITIY(kg) 4.023 8.045 16.092 2.21
PRICE RS. 52.22 10 20.11 82.33
Table 10 (a)

Mix proportions of rice husk ash concrete for 6.5 % replacement of cement
FOR THREE RHA CEMENT FINE COARSE WATER TOTAL
CUBES AGGREGATE AGGREGATE RATIO PRICE

QUANTITIY(kg) 0.26 3.76 8.045 16.09 2.21

PRICE RS. 1.3 48.5 10 20.11 79.9
Table 10 (b)

Mix proportions of rice husk ash concrete for 7.2 % replacement of cement
FOR THREE RHA CEMENT FINE COARSE WATER TOATAL
CUBES AGGREGATE AGGREGATE RATIO PRICE

QUANTITIY(kg) 0.29 3.73 8.045 16.09 2.21

PRICE RS. 1.45 48.49 10 20.11 80
Table 10 (c)
 Mix proportions of rice husk ash concrete for 10 % replacement of cement
FOR THREE RHA CEMENT FINE COARSE WATER TOATAL
CUBES AGGREGATE AGGREGATE RATIO PRICE
QUANTITIY(kg) 0.40 3.62 8.045 16.09 2.21
PRICE RS. 2 47.06 10 20.11 79
Table 10 (d)

Mix proportions of rice husk ash concrete for 15 % replacement of cement

FOR THREE RHA CEMENT FINE COARSE WATER TOATAL
CUBES AGGREGATE AGGREGATE RATIO PRICE
QUANTITIY(kg) 0.60 3.42 8.045 16.09 2.21
PRICE RS. 3 44.46 10 20.11 77.57
Table 10 (e)

4.3.3.2 FOR CYLINDER

In this method, five replacements of cement i.e., 6.5%, 7.2%, 10%, and 15% with Rice
husk ash (RHA) are done, whereas the total binder content remains the same. The mix
proportions considered for each replacement by replacement method by RHA are
presented in tables.
Without RHA
FOR THREE CEMENT FINE COARSE WATER TOTAL
CYLINDER AGGREGATE AGGREGATE RATIO PRICE
QUANTITIY(kg) 6.30 12.6 25.25 3.402
PRICE RS. 81.9 16.7 31.56 130.16
Table 11 (a)
Mix proportions of rice husk ash concrete for 6.5 % replacement of cement
FOR THREE RHA CEMENT FINE COARSE WATER TOTAL
CUBES AGGREGAT AGGREGATE RATIO PRICE

QUANTITIY(kg) 0.41 5.9 12.6 25.25 3.404

PRICE RS. 2.05 76.7 16.7 31.56 127.01
Table 11 (b)
Mix proportions of rice husk ash concrete for 7.2 % replacement of cement
FOR THREE RHA CEMENT FINE COARSE WATER TOATAL
CYLINDER AGGREGATE AGGREGATE RATIO PRICE
QUANTITIY(kg) 0.45 5.85 12.6 25.25 3.402
PRICE RS. 2.25 76.05 16.7 31.56 126
Table 11 (c)
 Mix proportions of rice husk ash concrete for 10 % replacement of cement
FOR THREE RHA CEMENT FINE COARSE WATER TOATAL
CYLINDER AGGREGATE AGGREGATE RATIO PRICE
QUANTITIY(kg) 0.63 5.67 12.6 25.25 3.402
PRICE RS. 3.15 76.05 16.7 31.56 123
Table 11 (d)
Mix proportions of rice husk ash concrete for 15 % replacement of cement
FOR THREE RHA CEMENT FINE COARSE WATER TOATAL
CYLINDER AGGREGATE AGGREGATE RATIO PRICE
QUANTITIY(kg) 0.945 5.35 12.6 25.25 3.402
PRICE RS. 4.7 70 16.7 31.56 122.96
Table 11 (e)
 CHAPTER 5

TESTING PROCEDURE AND SAMPLE PREPARATION

5.1 CASTING OF TEST SPECIMENS: (AS ASTM C387/C387M)

5.1.1 PREPARATION OF MATERIALS
All materials shall be brought to room temperature, preferably 27±3º C before start the
results. The cement samples, on arrival at the laboratory, shall be carefully mixed dry
either by hand or in an appropriate mixer in such a manner as to ensure the maximum
possible blending and uniformity in the material, care is being taken. The cement shall
then be stored in a dry place, preferably in air-tight metal containers. Samples of
aggregates for each batch of concrete shall be of the desired grading and shall be in an
air-dried condition. In general, the aggregate shall be separated into fine and coarse
portion and recombined for each concrete batch in such a way as to produce the desired
grading. ASTM sieve NO#4 shall be normally used for separating the fine and coarse
fractions, but where special grading are being investigated, both fine and coarse
aggregate shall be separated into different sizes as shown in figures below.
Water is the essential constituent of the concrete, it actively participates in the
chemical reaction with cement. It helps to form the strength giving cement gel. The
normal tap water (drinking water) is used in this project for the casting of specimen.
The room temperature was normal during the preparation of material for the
specimens (cubes, cylinders and beams).

Figure 12 Rice Husk

5.1.2 COMPRESSIVE STRENGTH OF CUBE:
5.1.3 Standards:
ASTM C387/C387M

5.1.4 APPARATUS:
1. Sieves
2. Balance
3. Mould
4 Oven
5. Trowel
6. Mixing tray
7. Mould oil
8. Compressive testing Machine

5.1.5 PROCEDURE:
 Take cement, Fine, and coarse aggregate by weight and mix them
vigorously.
 Add water as per desired water cement ratio.
 Clean the iron mould and apply oil to the inner surface of the moulds.
 Fill the mould with concrete in 03 equal layers.
 Compact each layer by compacting rod.
 Level top surface of the concrete with trowel.
 The specimen shall be stored in clean water at 25 to 290 C; until the time of
test.
 Just prior to testing, the specimen shall be capped with sulphur mixture.
 Remove the specimen from the water after curing up to desired period.
 Perform testing while specimen will be wiped clean and any lost material
should be removed.
 Align the axis of the specimen with the plate of the CTM.
 The load shall be applied slowly without shock and continuously until the
resistance of the specimen breaks down and no greater load can be
sustained.
 The maximum load applied to the specimen shall be recorded.
5.2 COMPRESSIVE STRENGTH OF CYLINDER:
5.2.1 Standards:
ASTM C387/C387M

5.2.2 APPARATUS:
1 Sieves
2 Balance
3. Mould
4. Oven
5. Trowel
6. Mixing tray
7. Mould oil
8. Compressive testing Machine

5.2.3 PROCEDURE:
 Take cement, Fine, and coarse aggregate by weight and mix them
vigorously.
 Add water as per desired water cement ratio.
 Clean the iron mould and apply oil to the inner surface of the moulds.
 Fill the mould with concrete in 03 equal layers.
 Compact each layer by compacting rod.
 Level top surface of the concrete with trowel.
 The specimen shall be stored in clean water at 25 to 290 C; until the time of
test.
 Just prior to testing, the specimen shall be capped with sulphur mixture.
 Remove the specimen from the water after curing up to desired period.
 Perform testing while specimen will be wiped clean and any lost material
should be removed.
 Align the axis of the specimen with the plate of the CTM.
 The load shall be applied slowly without shock and continuously until the
resistance of the specimen breaks down and no greater load can be
sustained.
 The maximum load applied to the specimen shall be recorded.
5.3 FLEXURAL STRENGTH OF CONCRETE:
Flexural strength of concrete is the measure of the tensile strength of concrete and to
resist failure in the bending it is a measure of an un-reinforced concrete beam or slab.

With a span length at least three times the depth, flexural strength of concrete is
measured by loading 6 x 6 inch (150 x 150mm) concrete beams. As Modulus of Rupture
in MPa, the flexural strength is expressed and by standard test methods ASTM C78
(third-point loading) or ASTM C293 (center-point loading) it is determined.

Figure 13
The specimen size and type of loading does impact the measured flexural strength and
comparisons or requirements should be based on the loading configuration and same
beam size. It is also observed that with larger beam specimens, a lower flexural strength
of concrete will be measured.

Depending on the type, size, and volume of coarse aggregate flexural MR (Modulus of
Rupture) is about 10 to 20 percent of compressive strength and for given materials and
mix design, the best correlation for a specific material is obtained by laboratory tests.
The modulus of rupture determined by third point loading is lower than the MR
determined by center point loading sometimes as much as 15 percent.
5.3.1 APPARATUS:

There are the following apparatus used for determining the flexural strength of concrete
as given below;

1. Beam Mould
2. Tamping Bar
3. Flexural Testing Machine

Figure 14

5.3.2 PROCEDURE:
There are the following steps in the procedure of flexural strength of concrete as given
below;

1. By filling the concrete into the mold in 3 layers of approximately equal thickness,
prepare the test specimen and by using the tamping bar, tamp each layer 35 times.
Over the entire cross-section of the beam mold and throughout the depth of each
layer, tamping should be distributed uniformly.
2. Then clean the bearing surfaces of the supporting and loading rollers, and from the
surfaces of the specimen where they are to make contact with the rollers remove
any loose sand or other material.
3. For providing support and loading points to the specimens, circular rollers
manufactured out of steel having cross-section with a diameter of 38 mm will be
used. The length of the rollers shall be at least 10 mm more than the width of the
test specimen and a total of four rollers shall be used. The distance between the
inner rollers shall be d and the distance between the outer rollers (i.e. span) shall
be 3d and the inner rollers shall be equally spaced between the outer rollers.
4. The specimen stored in water shall be tested instantly on removal from water and
at right angles to the rollers, the test specimen shall be placed in the machine
 correctly centered with the longitudinal axis of the specimen. The mold filling
direction shall be normal to the direction of loading for molded specimens.

5. For the 15 cm specimens and at a rate of 180 kg/min for the 10 cm specimens, the
load shall be applied at a rate of loading of 400 kg/min.

Figure 15

5.3.3 CALCULATION:
The flexural strength fb is given by;
Fb = pl/bd2 (when a > 13.0cm for 10cm specimen or a > 20.0cm for 15.0cm
specimen)
Or
Fb = 3pa/bd2 (when a < 13.3 cm but > 11.0cm for 10.0cm specimen or a < 20.0cm
but > 17.0 for 15.0cm specimen)
Where,

a is the distance between the nearer support and the line of fracture.

b is the width of specimen in cm.

d is the failure point depth in cm.

l is the supported length in cm.

p is the max. Load in kg.

5.4 SAFETY & PRECAUTIONS:

1. At the time of the test, use hand gloves.

2. Switch off the machine after the test.
3. Grease all the exposed metal parts.
4. To the base & top plate, keep the guide rods firmly fixed.
5. Before testing & after testing equipment should be cleaned.

5.5 PROBLEMS WITH FLEXURAL:

To specimen preparation, handling, and curing procedure flexural tests are extremely
sensitive and beam specimens are very heavy and there will be yield lower strengths by
allowing a beam to dry. Beams must be tested while wet and must be cured in a standard
manner. A sharp drop in flexural strength is produced due to a short period of drying.

For control and acceptance of concrete, the concrete industry and inspection agencies
are much more familiar with traditional cylinder compression tests and for design
purposes flexural can be used.

Figure 16 (a) Grinding process of RHA by Los Angelos machine

Figure 16 (b) Sieving RHA by sieve#200

Figure 16 (c) Sieved RHA

Figure 16(d) Sieved Fine and Coarse Aggregate

Figure 16 (e) Preparing mortar for specimen

 Figure 16 (f) Casting specimen

Figure 16 (g) Casted cubes and cylinders

 Figure 16 (h) Beams being casted

5.6 WEIGHING

A weighing balance is an instrument which is used to determine the weight or mass of

an object. Available in a wide range of sizes with multiple weighing capacities they are
essential tools in laboratories etc

5.7 MIXING CONCRETE

Thorough mixing of the materials is essential for the production of uniform concrete.
The mixing should ensure that the mass become homogeneous, uniform in colour and
consistency. There are two methods adopting for mixing concrete one is hand mixing
and other is machine mixing. In this study the mixing of materials is done by hand.

5.8 COMPACTION OF TEST SPECIMENS: (AS PER IS: 516-1959)

Compaction of concrete is the process adopted for expelling the entrapped air from the
concrete. In the process of mixing, transporting and placing of concrete air is likely to
get entrapped in the concrete. The lower the workability, higher is the amount of air
entrapped. In other words, stiff concrete mix has high percentage of entrapped air and,
therefore, would need higher compacting efforts than high workable mixes. Therefore,
it is imperative that 100% compacting of concrete is one of the most important aim to
be kept in mind in good concrete making practices.
5.8.1 COMPACTION BY VIBRATION
When compacting by vibration, each layer shall be vibrated by means of an electric or
vibrator or by means of a suitable vibrating table until the specified condition is
attained.

5.8.2 PLACING MOULDS ON THE VIBRATING TABLE

This is the special case of formwork vibrator, where the vibrator is clamped to the table
or table is mounted on springs which are vibrated transferring the vibration to the table.
They are commonly used for vibrating concrete cubes. Any specimen kept on the table
gets vibrated. This idea adopted mostly in laboratory and in the making small but
precise prefabricated R.C.C members. The vibrating table is shown in figure

Figure 17 vibrating table

5.9 CURING OF TEST SPECIMENS: (AS PER ASTM: C 150)

The test specimens shall be stored on the site at a place free from vibration, under damp
matting, sacks or other similar material for 24 hours + ½ hour from the time of adding
the water to the other ingredients. The temperature of the place of storage shall be within
the range of 22 to 32º C. After the period of 24 hours, they shall be marked for later
classification, removed from the moulds and, unless required for testing within 24
hours, stored in clean water at a temperature of 24 to 30º C until they are transported to
the testing laboratory. They shall be sent to the testing laboratory well packed in damp
sand, damp sacks, or other suitable material so as to arrive there in a damp condition
not less than 24 hours before the time of test. On arrival at the testing laboratory, the
specimens shall be stored in water at a temperature of 27 ± 2º C until the time of test.
Curing of test specimens are shown in figures
\

Figure 18 (a) Cubes & Cylinders for Curing

Figure 18 (b) Beams specimen for curing

Figure 18 (c) Specimens placed for curing

 Figure 18 (d) Beam specimens in curing tank

5.10 TESTS AND RESULTS

The details of our project carried out on the test specimens to study the strength-related
properties of concrete using Rice husk ash. The strength- related properties such as
compressive strength, splitting tensile strength, and flexural strength were studied.

5.10.1 TESTS

5.10.1 CUBE COMPRESSIVE STRENGTH

For cube compression testing of concrete, 6 inches cubes were used. All the cubes were
tested in saturated condition, after wiping out the surface moisture. The tests were
carried out after the specimen has been centered in the testing machine. Loading was
continued till the specimen fails and reading note down from the automatic universal
testing machine. The ultimate load divided by the cross sectional area of the specimen
is equal to the ultimate cube compressive strength. The load on the specimen is shown
in Figure 4.4.1(a).

fc = L/A

Where, fc = compressive strength in Mpa L= load in psi

A=area of the specimen = 𝑖𝑛2

5.10.2 CYLINDER COMPRESSIVE STRENGTH
ASTM C39 determines the compressive strength of cylindrical concrete specimens
such as molded cylinders. A compressive axial load is applied to molded cylinders or
cores until failure occurs. The compressive strength of the specimen is calculated by
dividing the maximum load achieved during the test by the cross-sectional area of the
specimen. The results of this test method are used as a basis for quality control of
concrete. The load on the specimen is shown in Figure 4.2.1(b).

Figure 19 (a) Compressive strength of cube test in compressive testing machine

Figure 19 (b) CTM machine (cylinder testing)

5.10.3 FLEXURAL STRENGTH OF BEAM
The standard sizes of beam specimen were 5x4x21 inches. The beam moulds conform
to ASTM C78/C78. Compacting of concrete will be done by vibration or by hand.
Curing: Test specimens shall be stored in water at a room temperature for 7 to 28 days.
The specimens shall be tested immediately on removal from the water while they are
still in the wet condition. The Flexure test was performed on two point loading system.
The load on specimen is shown in figure 4.2.1 b

Figure 19 (c) flexural testing machine

 CHAPTER 6

ANALYSIS OF RESULTS AND THEIR GRAGHICAL

REPRESENTATION

6.1 Compressive Strength of Cubes Results

The cube compressive strength results at the various ages such as 7,14, 28 days and at
the replacement levels such as 0%, 6.5%, 7.2%, 10%, and 15% of rice husk ash are
presented in Table 4.4.1 (a). The variations of compressive strength at 7, 14 and 28 days
with different percentage of RHA were plotted in the form of graphs as shown in
Figures 5.1 (a) and (b)

FOR CUBES

DAYS 7 DAYS 14 DAYS 28 DAYS

(PSI) (PSI) (PSI)
RHA %
0 2770 2829 3000

6.5 2170 2639 2670

7.2 2278 2639 2500

10 2361 2861 3472

15 2000 2311 2900

Table 12 (a)
 Graph RHA PERCENTAGE
Graph 7 Influence of RHA on compressive strength of cubes

RHA PERCENTAGE
Graph 8 Graph on influence of RHA on compressive strength of cubes
6.2 Compressive Strength of Cylinder Results
The cylinder compressive strength results at the various ages such as 7,14,28 days and
at the replacement levels such as 0%, 6.5%, 7.2%, 10%, and 15% of rice husk ash are
presented in Table 13. The variations of compressive strength at 7,14 and 28 days with
different percentage of RHA were plotted in the form of graphs as shown in Figures.

FOR CYLINDER

DAYS 7 DAYS 14 DAYS 28 DAYS

(PSI) (PSI) (PSI)
RHA %
0 1804 2759 3007
6.5 1556 2405 2441
72 1839 2511 2794
10 1875 1875 3100
15 1970 175 2110

Table 13

Graph 9 Graph on influence of RHA on compressive strength of cylinder

 Graph 10 Graph on influence of RHA on compressive strength of cylinder

RHA Percentage

From the tests results of cubes and cylinders it was observed that the maximum
compressive strength is obtained for mixes with 10 % RHA at age 28 days. For water-
cement ratios at 28 days age the optimum replacement level of cement by RHA is 10
%. At the age of 7 days of concrete the compressive strength of concrete is decrease
and the maximum strength of concrete at 7 days is with 0% replacement of cement by
RHA in concrete. Where RHA content is exactly what is required for reacting with the
calcium hydroxide present. This may be the reason as more and dense C-S-H gel acts
as an impervious layer which prevents the water to enter through it and thereby arrests
further hydration. Therefore excess RHA added beyond this limit decreases the strength
of concrete.

6.3 Flexural Strength of Beam

The flexural strength results at various ages such as 7, 14 and 28 days and at
replacement levels such as 0% , 6.5% , 7.2% ,10% and 15% of rice husks ash will
present in the Table 4.4.3 (a) below. The variations in flexural strength at the age of 7
days and 28 days with different percentage of RHA will plot as soon as possible in
Figures. The variations of Flexural tensile strength at 7,14 and 28 days with different
percentage of RHA plotted in the form of graphs .
RHA Percentage 7 DAYS 14 DAYS 28 DAYS

(PSI) (PSI) (PSI)

0% 492 605 770

6.5 % 506 696 812

7.2 % 552 745 825

10 % 570 745 833

15 % 462 546 738

Table 14

Graph 11 Influence of RHA on flexural strength of beam

 Graph 12 influence of RHA on flexural strength of beams

From the test results, it was observed that the maximum flexural strength of beam was
obtained for concrete mix with 10 % replacement of cement by RHA at 28 days. It was
also observed that the flexural strength increases with the increase in RHA content up
to 10 % beyond that the strength decreases. At the age of 7 days of concrete the flexural
strength of concrete is decrease and the maximum flexural strength of concrete at 7
days is without replacement of cement by RHA in concrete.

6.4 Slump Test (As Per ASTM C143/C143m)

The concrete slump test measures the consistency of fresh concrete before it sets. It is
performed to check the workability of freshly made concrete, and therefore the ease
with which concrete flows. It can also be used as an indicator of an improperly mixed
batch. The test is popular due to the simplicity of apparatus used and simple procedure.
The slump test is used to ensure uniformity for different loads of concrete under field
conditions.
A separate test, known as the flow table, or slump-flow, test, is used for concrete that
is too fluid (non-workable) to be measured using the standard slump test, because the
concrete will not retain its shape when the cone is removed.
6.4.1mix Design Calculation:-
Volume of the cone = h (R2+ Rr + r2) / 3
Upper diameter of cone = r = 4”
Lower diameter of cone = R = 8”
Height of the cone = h = 12”
V = h (R2+ Rr + r2) / 3
V = 351.8 in2
V= 351.8 / (12)3
V = 0.203 ft3
Density of concrete:
=m/V
M=xV
M = 0.203 x 144
M = 29.32 lbs
M= 29.32 / 2.204 = 14.373 kg
Total mass = 16.53 kg
Ratio = 1:2:4
Cement = (1/7) x 16.53 =2.3 kg
Fine = (2/7) x 16.53 =4.72 kg
Coarse = (4/7) x 16.53 = 9.4 kg
Mix ratio of RHA with respect to cement= 0.115kg, 0.150kg, 0.165kg, 0.23kg and
0.345kg

Standard Slump Test Table

Degree of workability Slump(inch)

No Slump 0
Very Low workability ¼”-1/2”
Low workability ¾”-1 ¼”
Medium workability 1 ½”-3”
High workability 3”-6”
Very high workability 61/4” to collapse

Table 15
6.4.2 Procedure
The test is carried out using a metal mould in the shape of a conical frustum known as
a slump cone or Abrams cone,that is open at both ends and has attached handles as
shown in figure 5.1.2(a). The tool typically has an internal diameter of 102 millimetres
(4 in) at the top and of 203.2 millimetres (8in) at the bottom with a height of 305
millimetres (12.0 in).The cone is placed on a hard non-absorbent surface. This cone is
filled with fresh concrete in THREE stages. Each time, each layer is tamped 25 times
with a 2 ft (600 mm)-long bullet-nosed metal rod measuring 5/8in (16 mm) in diameter
as shown in figure 5.1.1(c). At the end of the third stage, the concrete is struck off flush
with the top of the mould. The mould is carefully lifted vertically upwards, so as not to
disturb the concrete cone. Also the sequence of procedures are shown in the figures
below.

Figure 20 (a) slump cone or Abrams cone

Figure 20 (b) preparing mortar for specimen

Figure 20 (c) Casted cone specimen

 Figure 20 (d) Casted cone specimen

6.4.3 Slump of Concrete at Different Ratio Of RHA

Slump test results of different replacement level of RHA

RHA % Slump (inch)

0 3
6.5 3
7.2 3
10 2.8
15 0

Table 16 Slump test results

 Graph 13 (a) Influence of different percentages RHA on workability of concrete

Graph 14 Graph on influence of RHA on workability of concrete

Results
The workability of concrete at 10 % of rha is found to be medium as per slump
standard table.
6.5 Test Results Decision
The results confirmed the findings of [10], [11], [12], [14], that RHA reduced the
workability of concrete. From [13], [12], [39], it was also reported that a high water
demand and coarseness is a major characteristic of RHA caused by its high pozzolanic
activity and a high specific surface area, but can be mitigated by using RHA of between
4-8μm, with the addition of superplasticisers. As highlighted in the methods section,
this study used a 45μm sieve and no plasticisers were introduced to the mixes. This
could have been the reason for the low slumps observed. The results were however not
consistent with [12], [10], who reported that a high cement replacement with RHA at a
low WCR considerably increased the slump of mixes studied
 CHAPTER 07

CONCLUSION AND FUTURE RECOMMENDATIONS

7.1 Conclusion

7.1.1 Cube Compressive Strength

At the age of 7 days the compressive strength of concrete mixes containing rice husk
ash was less than that of mixes without rice husk ash. But at the age of 28 days the
compressive strength of concrete mixes containing various proportion of rice husk ash
was more than that of mixes without rice husk ash. This indicates that addition of rice
husk ask as partial replacement to cement causes an increase in strength at the age of
28 days of curing. Thus rice husk ash act as pozzolanic material. Hence the compressive
strength of concrete increases as the percentage of those mineral admixtures increases.
The 7 days compressive strength of the concrete mixes containing rice husk ash slightly
decreases. Cement replacement level of 10 % by rice husk ash in concrete mixes was
found to be the optimum level to obtain maximum compression strength at the age of
28 days at w/c ratio 0.55. At the age of 28 days compressive strength of rice husk ash
concrete increase. This indicates that addition of rice husk ash as the partial replacement
of cement causes increase strength. The pozzolanic property of rice husks play a key
role in gaining of compressive strength of concrete. Pozzolanic properties of material
is such type of properties that in itself possesses little or no cementitious value but will,
in finely divided form and in the presence of moisture, chemically react with calcium
hydroxide at ordinary temperatures to form compounds having cementitious properties.

7.1.2 Cylinder Compressive Strength

At the age of 7 days the compressive strength of concrete cylinder mixes containing
rice husk ash was less than that of mixes without rice husk ash. But at the age of 28
days the compressive strength of concrete mixes containing rice husk ash was more
than that of mixes without rice husk ash. This indicates that addition of rice husk ask as
partial replacement to cement causes an increase in strength at the age of 28 days of
curing. Thus rice husk ash act as pozzolanic material. Hence the compressive strength
of concrete cylinder increases as the percentage of those admixtures increases at certain
limit.

Also Fly ash and Rice husk ash is found to be superior to other supplementary materials
like slag, and silica fume. RHA used in this study is efficient as a pozzolanic material;
it is reach in amorphous silica. Due to low specific gravity of RHA which leads to
reduction in mass per unit volume, thus adding it reduces the dead load on the structure.
Used of Fly ash and Rice husk ash helps in reducing the environment pollution during
the disposal of excess Fly ash and Rice husk ash. Cement is costly material, so the
partial replacements of these materials by Rice husk ash reduces the cost of concrete.
7.1.3 Flexural Strength of Beam

The optimum replacement of cement by rice husk ash for rice husk ash concrete was
found to be 10 percent for achieving maximum value of flexural strength at the age of
28 days at w/c ratio 0.55. The flexural strength increases along with increase in
compressive strength.

7.1.4 Investigations on Setting Times of Cement Pastes

In the present investigation the setting times of cement pastes, with partial replacement
of cement by rice husk ash varying from 0% to 15%, are in the range conforming to
ASTM C403M-16. The setting times of cement paste slightly increases with 6.5% to
10% replacement of cement by rice husk ash. There will be no adverse effect on the
cement paste containing rice husk ash in cement. The rice husk ash can be used as
cementitious material in concrete as it barely affects the initial and the final setting
times of cement paste, and the results remain in range specified in ASTM C403M-16.

7.2 Pozzolanic Property of Rice Husks Ash

Reactivity of rice husk ash is basically due to the high amorphous silica content and
also due to large surface area governed by porous structure of particles. This makes rice
husk ash a very reactive pozzolanic material. In chemical reaction of Portland cement
in concrete, there is release of calcium hydroxide. Silica present in rice husk ash reacts
with this calcium hydroxide to form additional binder material called as calcium silicate
hydrate (C-S-H) similar to the C-S-H produced by Portland cement. It works as
additional binder that gives RHA concrete its improved properties.

7.3 Mechanism of rice husk ash in concrete

Mechanism of rice husk ash in concrete can be studied basically under three roles:

7.3.1 Mechanism of rice husk ash in concrete

The presence of filler like rice husk ash in the Portland cement concrete mixes causes
reduction in volume of large pores. RHA acts as filler due to its fineness. It fits into the
spaces between grains in same way like cement grains fill the spaces between fine
aggregates grains and sand fills the spaces between particles of coarse aggregates.

7.3.2 Reaction with free-lime (From hydration of cement):

CH crystals present in Portland cement pastes are a source of weakness. Cracks can
easily propagate through or within these crystals without any significant resistance.
This affects the strength, durability and other properties of concrete. Rice husk ash
which is siliceous material reacts with CH results in reduction in CH content in addition
to forming strength contributing cementations products which in other words can be
termed as ‘‘Pozzolanic Reaction’’. Cement paste–aggregate interfacial refinement: In
concrete the transition zone between the aggregate particles and cement paste plays a
significant role in the cement-aggregate bond. Rice husk ash addition influences the
thickness of transition phase in mortars and the degree of the orientation of the
Chrystal’s in it. The thickness compared with mortar containing only ordinary Portland
cement decreases.

Hence mechanical properties and durability is improved because of the enhancement in

interfacial or bond strength. Mechanism behind is not only connected to chemical
formation of C–S–H(i.e. pozzolanic reaction) at interface, but also to the microstructure
modification (i.e. CH) orientation, porosity and transition zone thickness) as well.

7.4 Environmental Impacts of Using RHA

According to a survey which was taken in 2015 the production of rice husks in Pakistan
is approximately 2000 ton per year so due to which it not only reduces the consumption
of cement due to blending but also solves the waste disposal problems.

7.5 Future Recommendation

The following are the suggestions for future work.
1. This experimental work focused only a particular type of cement replacement
materials. Hence, investigations can be made on different types of cement replacement
materials (Blast furnace slag, silica fume, fly ash) to study the strength and durability-
related properties.
2. Studies could be conducted for other properties such as creep, shrinkage,
carbonation resistance, microstructure etc.
3. Investigations may be carried out for pre-stressed concrete.
4. Investigations may be carried out for fire resistance of concrete.

7.6 Cost
In our given project replacing of cement by rice husk (RHA) about 10%, the overall
cost of the work is decreased by 3 %. It is the excellent opportunity to make the concrete
at low price and the cost of construction will be low. In our report the replacing of
cement by rice husk (RHA) about 10 %, the overall cost of the work is decreased by 3
%. It is the excellent opportunity to make the concrete at low price and the cost of
construction will be low. Also at 10% of RHA we got maximum compressive strength
concrete.
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THE END