RHA Paper - S.P.alam- UVCE - Bangalore - 160108

Paper by: Mr. Syed Parveez Alam, M.E. 4th Semester,

Construction Technology, University Vishveshwaraya College of Engineering

Bangalore – 560 056.

Dec 2007

Processed Rice Husk Ash procured from : Mr. Narayan P. Singhania,

N K Enterprises Jharsuguda ,Orissa - 768201

[email protected]

1

SYNOPSIS Increase in the Cost of Conventional building materials and to provide a

sustainable growth; the construction field has prompted the designers and

developers to look for ‘alternative materials’ for the possible use in civil

engineering constructions. For this objective, the use of industrial waste products

and agricultural byproducts are very constructive. Large amounts of wastes

obtained as byproducts from many of the industries can be the main sources of

such alternate materials. These industrial wastes and agricultural byproducts such

as Fly Ash, Rice Husk Ash, Silica Fume, and Slag etc can be used as cementing

materials because of their pozzolanic behavior, which otherwise require large

tracts of lands for dumping. Thus the concrete industry offers an ideal method to

integrate and utilize a number of waste materials, which are socially acceptable,

easily available, and economically within the buying powers of an ordinary man.

Presence of such materials in cement concrete not only reduces the Carbon dioxide

(CO2) emission, but also imparts significant improvement in workability and

durability.

During the last three decades, great strides have been made in improving

the performance of concrete as a construction material. In the light of

implementation of stringent measures to meet the standards in the production of

construction materials and disposal of wastes, the use of industrial and agricultural

byproducts lead to reduction of the costs of materials also. In the present

investigation, a feasibility study is made to use Rice Husk Ash and Silica Fume as

an admixture to Cement Concrete, and an attempt has been made to investigate the

strength parameters of concrete (Compressive, Split tensile and Flexural strength)

made with partial replacement of cement by Rice Husk Ash and Silica Fume. The

aim of present investigation is to compare the strength behavior of Rice husk ash

concrete and silica fume concrete.

v

For control concrete, IS method of mix design is adopted and considering

this a basis, mix design for replacement method has been made. Three different

replacement levels namely 5%, 10% and 15% are chosen for the study concern to

replacement method. Large range of curing periods starting from 3days to 91days

is considered in the present study. Though the study is mainly concerned to

compressive strength behavior, studies regarding split tensile strength and flexural

strength are also taken up.

The experimental observations has shown that, as the age advances, the

Compressive Strength, Tensile Strength and Flexural Strength of both Rice Husk

Ash and Silica Fume concrete gradually increases at all the percentage

replacement levels, and With the increase in the Percentage replacement with Rice

Husk Ash, the Compressive strength and Tensile strength of Rice Husk Ash

concrete is found to be gradually decreased at the early ages up to 7 days, however

there is an increase in the compressive strength and Tensile strength with the

increase in the Cement Replacement Level from 28 days to 91days w.r.t Control

concrete. With the increase in the Percentage replacement with Silica Fume, the

Compressive strength of Silica Fume concrete is found to be increased gradually at

all the ages up to 10% replacement, however there is a decrease in the

compressive strength with the further increase in the Silica Fume replacement

level. The flexural strength behavior of both Rice Husk Ash and Silica Fume

concrete was found to be better than that of flexural strength of Control concrete at

all the ages as well as at all the replacement levels. It can be concluded that Silica

Fume could be suitably replaced with Rice Husk Ash.

vi

CHAPTER 3 AIM AND SCOPE OF PRESENT INVESTIGATION

3.1GENERAL

Recognizing the need for the utilization of Industrial waste products and

Agricultural by-products in concrete, the present investigation is taken up with an

aim to establish or to understand the behavior of Rice husk ash & Silica fume

concrete under Compressive, Tensile and Flexural loads.

The behavior of Rice husk ash (RHA)& Silica fume (SF) Concrete can be

understood better, when a relative study is made. To facilitate this, comparison of

Control concrete or ordinary concrete specimens were tested under the same

conditions as RHA & SF concrete specimens were considered in the present

investigation.

Further to continue the investigation, M20 grade Control concrete is

designed using IS method of design mix, where cement is replaced with three

percentages of RHA & SF. Totally Three hundred and fifteen specimens were

casted and tested.

3.2 AIM OF PRESENT STUDY

The aim of the present investigation is:

a) To study different strength properties of Rice husk ash concrete with age in

comparison to Control concrete.

b) To study different strength properties of Silica fume concrete with age in

comparison to Control concrete.

c) To study the relative strength development with age of Rice husk ash

concrete with Control concrete of same grade.

d) To study the relative strength development with age of Silica fume concrete

with Control concrete of same grade.

14

3.3 SCOPE OF PRESENT STUDY

The Experimental investigation is planned as under:

1. To obtain Mix proportions of Control concrete by IS method.

2. To conduct Compression test on RHA, SF & Control concrete on standard

BIS specimen size 150 x 150 x 150 mm.

3. To conduct Split tensile test on RHA, SF & Control concrete on standard

BIS specimen size 150 mm diameter and 300 mm height.

4. To conduct Flexural test on RHA, SF & Control concrete on standard BIS

specimen size 100 x 100 x 500 mm.

3.3.1 Parameters Considered

a) Constant parameters:

i. 53 Grade Cement

ii. 20mm and down size Aggregate

iii. Grade of Concrete- M20

iv. Water binder ratio (Depending on mix design)

b) Variable Parameters:

i. Curing period – 3days, 7days, 28days, 56days and 91 days.

ii. Size of specimen (Depending on the test under consideration)

iii. Cement replacement levels adopted in replacement method (5%, 10%

&15%)

The details of investigations carried out and results obtained are presented in

subsequent chapters.

15

CHAPTER 5

EXPERIMENTAL INVESTIGATIONS

5.1 GENERAL

This chapter deals with the Mix design procedure adopted for Control

concrete and the studies carried out on properties of various materials used

throughout the Experimental work. Also the details of method of Casting and

Testing of Specimens are explained.

5.2 MIX DESIGN

Mix design can be defined as 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.

The purpose of designing as can be seen from the above definitions is two-fold.

The first object is to achieve the stipulated minimum strength and the second

object is to make the concrete in the most economical manner.

Various Mix design methods are available for Control concrete, each and

every method has its own methodology to arrive at the final concluding results.

The proportions obtained in one method may not match with another method even

though the characteristics of the materials used in both the methods are same.

5.2.1 Control Concrete mix design

I.S. method of Mix design procedure is followed as per IS 10262-1982 for

Control concrete, Rice husk ash concrete and Silica fume concrete (replacement

method only) for M20 grade. An example is illustrated for M20 grade of concrete

in Appendix-A.

34

5.3 MATERIALS

5.3.1 CEMENT

Cement used in the experimental work is ORDINARY PORTLAND

CEMENT of 53 grade conforming to IS: 12269-1987. The physical properties of

the cement obtained on conducting appropriate tests as per IS: 269/4831 and the

requirements as per IS 12269-1987 are given in Table 5.1

Table 5.1 Physical Properties of Cement

Sl.No Properties Obtained

Values

Requirement

as per

IS: 12269-1987

1 Fineness 2.5% Not more than 10%

2 Soundness 1.5 mm Not more than 10 mm

3 Setting Time:

a) Initial

b) Final

170.00 min

260.00 min

Not less than 30 min

Not more than 600 min

4 Compressive Strength:

a) 3 days

b) 7days

c) 28 days

40.50N/mm2

51.00N/mm2

67.50N/mm2

Not less than 27N/mm2



4 Standard Consistency 28.50% ----------

6 Specific gravity 3.1 ----------

35

5.3.2 RICE HUSK ASH

Rice Husk Ash used in the present experimental study was obtained from

N.K Enterprises Jharsuguda, Orissa. Specifications, Physical Properties and

Chemical Composition of this RHA as given by the Supplier are given in

Table5.2, 5.3 and 5.4.

Table 5.2 Specifications of Rice Husk Ash

Sl No. Parameter Value

1 SiO2-Silica 85% minimum

2 Humidity 2% maximum

3 Mean Particle Size 25 microns

4 Colour Grey

5 Loss on Ignition at 8000 C 4% maximum

Table 5.3 Physical Properties of Rice Husk Ash


1 Physical State Solid-Non Hazardous

2 Appearance Very fine powder

3 Particle Size 25 microns-mean

4 Colour Grey

5 Odour Odourless

6 Specific Gravity 2.3

36

Table 5.4 Chemical Composition of Rice Husk Ash


1 Silica-SiO2 > 85%

2 Carbon < 4%

3 Moisture Max 2.0%

4 Loss on Ignition Max 4.0%

5 Water Soluble 6.40%

5.3.3 SILICA FUME

Micro silica 920-D, a dry powder available in densified form as supplied by

Elkem India Pvt Ltd, Navi Mumbai, is used in the present experimental study.

The Physical properties and chemical composition of Silica fume as given by the

Supplier are given in Table 5.5 and 5.6

Table 5.5 Physical Properties of Silica Fume


1 Bulk density D (kg/m3) 600-700

2 Bulk density U (kg/m3) 200-350

Table 5.6Chemical Composition of Silica Fume


1 SiO2 (Silicon dioxide, amorphous) 85.0%

2 H2O 1.0%

3 C (Carbon) 2.5%

4 LOI (Loss on Ignition) 4.0%

37

5.3.4 FINE AGGREGATE

Fine aggregate was purchased which satisfied the required properties of

fine aggregate required for Experimental work and the sand conforms to zone III

as per the specifications of IS 383: 1970.

a) Specific gravity = 2.64

b) Fineness modulus = 2.71

c) Clay content = 1.65%

5.3.5 COARSE AGGREGATE

Crushed granite of 20 mm maximum size has been used as coarse

aggregate. Two different sizes of coarse aggregates were used 85 percentage of

coarse aggregate passing 20mm sieve size and 15 percent of coarse aggregate

passing 12.5 mm sieve sizes were used, the sieve analysis of combined aggregates

confirms to the specifications of IS 383: 1970 for graded aggregates.

a) Specific gravity =2.7

b) Fineness Modulus = 6.816

5.3.6 CHEMICAL ADMIXTURE (Super plasticizer)

For basic tests on Rice husk ash and Silica fume, Poly carboxylic ether

based Glenium-51 type Super plasticizer is used.

5.3.7 Water

Clean Potable water as obtained from Civil Engg.Dept.Jnanabharathi was

used for mixing and curing of Concrete.

38

5.4 METHODOLOGY OF TEST

5.4.1 Mixing

Uniform mixing of concrete should be ensured to get correct test results of

the specimen. For Control concrete, initially the mixing tray1 is properly cleaned

with water; coarse aggregate is weighed for required quantity as per mix

proportioning and grade of concrete and poured in to the mixing tray1. Sand is

weighed and poured into another mixing tray2, which is completely dry. Cement is

weighed and uniformly spread on the surface of sand in to tray2 and uniform

mixing is ensured. Required proportion of super plasticizer is measured and mixed

with measured quantity of water. Mixed cement and sand from tray2 is uniformly

spread on the coarse aggregate in tray1, dry mixing is carried out, later water

mixed with super plasticizer is added to the dry mix, mixing is ensured up to a

minimum of 5 minutes until uniform colour of concrete is seen. Immediately the

concrete is measured for slump and placed in moulds as per procedure.

For Rice husk ash (RHA) concrete, the above-explained procedure is

followed except that before adding cement to sand, RHA is thoroughly blended

with cement, the blended mixture of RHA and cement is later mixed with sand and

further procedure is followed.

5.4.2 Casting and Curing of Cube Specimens

5.4.2. A) Casting of Cube specimens for compression test

The steel cube moulds were coated with oil on their inner surfaces and were

placed on a granite platform. The amount of cement, sand, coarse aggregates

required for 15 cubes were weighed. The materials were first dry mixed then

mixed with 1/3rd amount of total water. Super plasticizer mixed with left amount

of water is now added and mixed thoroughly to get a homogeneous mix. Slump

test is conducted to measure the degree of workability of mix. Concrete was

39

poured in to the moulds in three layers; each layer was uniformly tamped by a

tamping rod with 25 numbers of blows. The top surface was finished using a

trowel. Plate 1 shows photographic view of cube specimens cast in position &

Plate 2 Shows the Casted Cube Specimens.

5.4.2. B) curing of cube Specimens

Moulds were safely demoulded causing no damage to the specimen and

immediately concrete cube specimens were kept in curing tank, completely

immersed in water for curing. Plate 3 shows the cube specimens immersed in

water tank for curing.

5.4.3 Casting and Curing of Cylinder Specimens

5.4.3. A) Casting of Cylinder specimens for split tensile test

The steel cylinder moulds were coated with oil on their inner surfaces and

were placed on a granite platform. The amount of cement, sand, coarse aggregates

required for 15 cylinders were weighed. The materials were first dry mixed, then




poured in to the moulds in four equal layers; each layer was uniformly tamped by

a tamping rod with 35 numbers of blows. The top surface was finished using a

trowel. Plate 1 shows photographic view of cylinder specimens cast in position &

Plate 2 Shows the Casted Cylinder Specimens.

5.4.3. B) Curing of cylinder Specimens


immediately concrete cylinder specimens were kept in curing tank completely

immersed for curing up to desired period. Plate 3 shows the cylinder specimens

immersed in water tank for curing.

40

5.4.4 Casting and Curing of Prism Specimens

5.4.4. A) Casting of Prism specimens for flexural test

The steel prism moulds were coated with oil on their inner surfaces and

were placed on a granite platform. The amount of cement, sand, coarse aggregates

required for 15 prisms were weighed. The materials were first dry mixed then




poured in to the moulds in two equal layers; each layer was uniformly tamped by a

tamping rod. The top surface was finished using a trowel. Plate 1 shows

photographic view of Prism specimens cast in position & Plate 2 Shows the

Casted Prism Specimens.

5.4.4. B) Curing of Prism Specimens


immediately concrete Prism specimens were kept in curing tank completely

immersed for curing up to desired period. Plate 3 shows the Prism specimens

immersed in water tank for curing.

5.4.5 Tests on Fresh concrete

To measure the degree of workability, slump test was conducted. The test

results of slump test are given as below.

Sl.No. Concrete Type and Grade Slump in mm

1 Control Concrete- M20 Grade 55

2 RHA Concrete- M20 Grade 58

3 SF Concrete- M20 Grade 63

41

PLATE 1-CASTING OF CUBE, CYLINDER AND PRISM SPECIMENS

43

PLATE 2-CASTED CUBE, CYLINDER AND PRISM SPECIMENS

45

PLATE 3-CURING OF CUBE, CYLINDER AND PRISM SPECIMENS

46

5.4.6 Tests on hardened concrete

5.4.6. A) COMPRESSION TEST

Compressive strength of concrete

The compressive strength of concrete i.e., ultimate strength of concrete is

defined as the load which causes failure of the specimen divided by the area of the

cross section in uniaxial compression, under a given rate of loading. To avoid

large variation in the results of compression test, a great care is taken during the

casting of the test specimens and loading as well. It is however realized that in an

actual structure, the concrete at any point is in a complex stress condition and not

in uniaxial compression. However it is customary to conduct the test in uniaxial

compression only. Concrete under triaxial state can offer more resistance and will

fail only after considerably large deformations. The use of 150mm cubes has been

made as per I.S.I. code of practices IS 456. The advantage of selection of IS 516 –

1959 (24) cube, as the standard test specimen is that two plane and parallel

surfaces can always be found between which the load can be applied.

Compression testing machine is used to test the concrete cubes. The compression

strength is calculated using the formula

AreaLoadstrengthnCompressio = N/mm2

Testing of cube specimens

At each desired curing periods, cube specimens were taken out of water and

kept for surface drying. The cubes were tested in a 200T capacity compressive

testing machine to get the compressive strength of concrete. Plate 4 shows the

testing of cube specimen in progress.

47

5.4.6. B) SPLIT TENSILE TEST

Split tensile strength

The split tensile strength of concrete can be obtained indirectly by

subjecting a concrete cylinder to the action of a compressive force along two

opposite ends of a base plate of compression testing machine as shown in figure

5.1.

Due to the compressive force, the cylinder is subjected to a large magnitude

of the compressive stress near the loading region. The large portion corresponding

to a depth of about 87% and length of the cylinder is subjected to a uniform tensile

stress acting horizontally. This tensile stress (St) is taken as an index of the tensile

strength of concrete and is given by the formula.

FIG 5.1: ARRANGEMENT FOR INDIRECT TENSILE TEST

⎟⎠⎞

⎜⎝⎛=

dlP

sp 637.0σ

Where

mminofcylinderLengthlmmincylinderofDiameterd

KNinrupturegcauLoadP

mmNinconcreteofstrengthtensileindirectThesp

===

=

sin

/ 2σ

48

The load has to be applied to the cylinder through a packing plate of rubber

or plywood. The packing plate should be of a width of not more than 13mm and

thickness 3mm.

Testing of cylinder specimens

At each desired curing periods, the cylinder specimens were taken out of

water and kept for surface drying. The cylinders were tested in a 200T capacity

compressive testing machine to get the split tensile strength of concrete. Each

specimen is carefully placed in position, so that loading is uniformly distributed

over the length of the specimen, in split tensile test; the specimen is supported

with two timber pieces on top and bottom of the specimen to uniformly distribute

the load. Load is applied without shock and increased continuously until no

greater load can be sustained. Maximum load applied on the specimen is recorded.

Plate 5 shows the testing of cylinder specimen in progress.

49

PLATE 4- COMPRESSION TEST IN PROGRESS

PLATE 5- SPLIT TENSILE TEST IN PROGRESS

50

5.4.6. C) BENDING /FLEXURE TEST

MODULUS OF RUPTURE

Modulus of rupture is defined as the normal tensile stress in concrete, when

cracking occurs in a flexure test (IS 516-1959). This tensile stress is the flexural

strength of concrete and is calculated by the use of the formula, which assumes

that the section is homogeneous.

⎟⎠⎞

⎜⎝⎛= 2bd

plfb

Where, = modulus of rupture, N/mmfb 2

= Measured depth in mm of the specimen at the point of failure b

= Length in mm of the span on which specimen was supported l

= Max. Load in KN applied to the specimen p

The symmetrical two point loading creates a pure bending zone with

constant bending moment in the middle third span and thus the modulus of rupture

obtained is not affected by shear, as in the case of single concentrated load acting

on the specimen. The concrete test specimen is a prism of cross-section 100mm x

100mm and 500mm long. It is loaded on a span of 400mm. Modulus of Rupture is

useful as design criterion for concrete pavements and for evaluating the cracking

moment (Mcr), which is the moment that causes the first crack in a prestressed

concrete or partially prestressed concrete beam.

The modulus of rupture can be calculated by simple strength of materials

knowledge. If P is the load, which causes fracture of the prism specimen in KN

then the modulus of rupture is given by the following formulas.

a) If the fracture occurs within the middle third of the span the

⎟⎠⎞

⎜⎝⎛= 2bd

plfb

[When ‘a’ is greater than 20.0cm for 15.0 cm specimen or greater than 13.3

cm for a 10.0 cm specimen]

51

b) If the fracture occurs outside the middle third but deviating by not

more than 5 percent of the span length, then

⎟⎠⎞

⎜⎝⎛= 2

3bd

pafb

[When ‘a’ is less than 20.0 cm but greater than 17.0cm for 15.0cm

specimen or less than 13.3 cm but greater than 11.0cm for a 10.0cm

specimen]

Where l = span in mm

a = distance between line of fracture and the nearest support in mm

b = average breadth of the specimen in mm.

d = average depth of the specimen in mm.

c) If fracture occurs by more than 5 percent outside the middle third,

the results of the test should be rejected.

[If ‘a’ is less than 17.0 cm for a 15.0cm specimen, or less than 11.0cm

for a 10.0cm specimen, the result of the test shall be discarded]

Testing of Prism specimens

At each desired curing periods, the Prism specimens were taken out of

water and kept for surface drying. The prisms were tested in Flexure testing

machine by arranging two point loading system. Each specimen is carefully placed

in position. Load is applied without shock and rate of increase in loading is

maintained. Maximum load applied on the specimen is recorded at the point of

failure of the specimen and flexural strength is calculated. Plate 6 shows the

testing of prism specimen in progress.

52

PLATE 6- FLEXURAL TEST IN PROGRESS

53

PLATE 7- VIEW OF TESTED SPECIMENS

54

CHAPTER 6

RESULTS AND DISCUSSIONS

6.1 GENERAL

This chapter deals with the presentation of test results, and discussions

on Compressive, Tensile and Flexural strength development of Control

concrete, Rice husk ash concrete and Silica fume concrete at different curing

periods.

The present investigation is based on the IS method for Control

concrete. For Rice husk ash (RHA) and Silica fume (SF) concrete, replacement

method is considered. Trial mix proportions have been obtained for M20 grade

Control concrete from the mix design. By conducting trial mixes, an optimized

proportion for the mix is obtained for M20 grade Control concrete.

Compressive strength behavior of RHA and SF concrete designed by the

replacement method are studied, where in the effect of age and percentage

replacement of cement with RHA and SF on compressive strength is studied in

comparison with that of M20 grade Control concrete. In addition Split tensile

strength and Flexural strength studies are also carried out.

6.2 Mix Proportioning

6.2.1 Mix proportioning of Control concrete.

According to IS method of mix design, the proportions of Control

concrete were first obtained; trial mixes were carried out to determine the

strength at 3, 7 and 28days, and the results obtained are shown in figure 6.1 and

6.2, Where in the compressive strength obtained for M20 grade trial mixes are

represented against age. The target mean strength required by M20 grade

concrete is also marked in the figure 6.1and 6.2.

As the cube compressive strength at 28days obtained was higher than

the target mean strength as shown in figure 6.1, the trials were conducted based

on reduced cement content. The compressive strength at different ages of M20

55

grade Concrete under trial mix and final mix are dissipated through bar chart in

figure 6.2. The final mix proportions arrived at is shown in table 6.1.

The slump was measured to know the range of workability, which was

desired to be between 25 to 70 mm. But the slump obtained was 0 mm in the

trial mix; hence super plasticizer was used to obtain the required slump.

Different mixes were tested for slump and the optimum (least) dosage, which

gave the required slump, was noted and the same was used in the final mix.

Comparison of compressive strength at 28days of trial and final mix are

shown in figure 6.2, where in the target mean strength required is also

indicated. It can be seen how closely the compressive strength of the final mix

at 28 days correlates with the target mean strength for the M20 grade concrete.

Final mix proportions adopted for M20 grade Control concrete are given

in table 6.1.

TABLE 6.1: Final Mix Proportions of Control concrete

Grade

Of

Concrete

Cement

In kgs

Fine

Aggregate

In kgs

Coarse

Aggregate

In kgs

Water

in Ltrs

Super

Plasticizer in

Ltrs

M20 1 2.42 3.63 0.55 0.50%

Quantity

per cum 310 750.23 1125.35 170.5 1.55

56

FIG. 6.1: COMPRESSIVE STRENGTH V/S AGE OF CONTROL

CONCRETE

FIG. 6.2: COMPARATIVE BAR CHART FOR CONTROL CONCRETE

57

6.2.2 Mix Proportioning of Rice husk ash (RHA) Concrete

In this method, three replacements of cement i.e. 5%, 10%and 15% with

Rice husk ash (RHA) are done, where as the total binder content remains the

same.

The mix proportions considered for each replacement considered by

replacement method with RHA are presented in tables 6.2, to 6.4.

TABLE 6.2: MIX PROPORTIONS OF RICE HUSK ASH

CONCRETE FOR 5% REPLACEMENT

Grade

Of

Concrete

Cement

In kgs

Rice

Husk

Ash

In kgs

Fine

Aggregate

In kgs

Coarse

Aggregate

In kgs

Water

In

Ltrs.

Super

Plasticizer

in Ltrs.

M20 0.95 0.05 2.42 3.63 0.55 0.55%

Quantity

per cum 294.5 15.5 750.23 1125.35 170.5 1.62



Grade

Of

Concrete

Cement

In kgs

Rice

Husk

Ash

In kgs

Fine

Aggregate

In kgs

Coarse

Aggregate

In kgs

Water

In

Ltrs.

Super

Plasticizer

in Ltrs.

M20 0.90 0.1 2.42 3.63 0.55 0.65%

Quantity

per cum 279 31 750.23 1125.35 170.5 1.81

58



Grade

Of

Concrete

Cement

In kgs

Rice

Husk

Ash

In kgs

Fine

Aggregate

In kgs

Coarse

Aggregate

In kgs

Water

In

Ltrs.

Super

Plasticizer

in Ltrs.

M20 0.85 0.15 2.42 3.63 0.55 0.75%

Quantity

per cum 263.5 46.5 750.23 1125.35 170.5 1.97

6.2.3 Mix Proportioning of Silica fume (SF) Concrete

In this method, three replacements of cement i.e. 5%, 10%and 15% with

SF are done, where as the total binder content remains the same.

The mix proportions considered for each replacement considered by

replacement method with SF are presented in tables 6.5, to 6.7.

TABLE 6.5: MIX PROPORTIONS OF SILICA FUME CONCRETE

FOR 5% REPLACEMENT

Grade

Of

Concrete

Cement

In kgs

Silica

Fume

In kgs

Fine

Aggregate

In kgs

Coarse

Aggregate

In kgs

Water

In

Ltrs.

Super

Plasticizer

in Ltrs.

M20 0.95 0.05 2.42 3.63 0.55 0.60%

Quantity

per cum 294.5 15.5 750.23 1125.35 170.5 1.77

59


FOR 10% REPLACEMENT

Grade

Of

Concrete

Cement

In kgs

Silica

Fume

In kgs

Fine

Aggregate

In kgs

Coarse

Aggregate

In kgs

Water

In

Ltrs.

Super

Plasticizer

in Ltrs.

M20 0.90 0.1 2.42 3.63 0.55 0.75%

Quantity

per cum 279 31 750.23 1125.35 170.5 2.09


FOR 15% REPLACEMENT

Grade

Of

Concrete

Cement

In kgs

Silica

Fume

In kgs

Fine

Aggregate

In kgs

Coarse

Aggregate

In kgs

Water

In

Ltrs.

Super

Plasticizer

in Ltrs.

M20 0.85 0.15 2.42 3.63 0.55 0.80%

Quantity

per cum 263.5 46.5 750.23 1125.35 170.5 2.11

6.3 Strength characteristics of Concrete

6.3.1 Compressive strength

Most concrete structures are designed assuming that concrete processes

sufficient compressive strength but not the tensile strength. The compressive

strength is the main criterion for the purpose of structural design. To study the

strength development of Rice husk ash (RHA) & Silica fume (SF) concrete in

comparison to Control concrete, compressive strength tests were conducted at

the ages of 3, 7, 28, 56 & 91days. The test results are reported in table 6.8 (A)

for Control concrete and in table 6.9 &6.10 for RHA & SF concrete

respectively.

60

6.3.1.1 Control concrete (CC): A) Effect of Age on compressive strength:

Table 6.8 (A) gives the test results of Control concrete. The 28 days

strength obtained for M20 grade Control concrete is 27.45MPa. The strength

results reported in table 6.8 (A) are presented in the form of graphical variation

(Fig 6.3), Where in the compressive strength is plotted against the curing

period.

TABLE 6.8(A): COMPRESSIVE STRENGTH OF CONTROL

CONCRETE

Compressive Strength of Control Concrete in N/mm2

Grade of

Concrete 3DAYS 7DAYS 28DAYS 56DAYS 91DAYS

M20 14.28 18.92 27.45 33.14 37.20

The strength achieved at different ages namely 3, 7, 28, 56 and 91 days

for Control concrete are also presented in bar chart in figure 6.4.From the

figure, it is clear that as the age advances, the strength of Control concrete

increases. The rate of increase being higher at curing period up to 28days.

However the strength gain continues at a slower rate after 28 days.

STRENGTH OF CONTROL CONCRETE ON AGEING

0

10

20

30

40

0 20 40 60 80 100

AGE IN DAYS

CO

MPR

ESSI

VE S

TREN

GTH

IN

N/m

m2

M20

FIG. 6.3: STRENGTH OF CONTROL CONCRETE AT DIFFERENT AGES

61

BAR CHART REPRESENTATION OF STRENGTH OF M20 GRADE CONTROL

CONCRETE AT DIFFERENT AGES

05

10152025303540

M20

Grade of Control Concrete

Com

pres

sive

St

reng

th in

N/m

m2

3 Days7 Days28 Days56 Days91 Days

FIG 6.4 COMPRESSIVE STRENGTH OF M20 GRADE CONTROL CONCRETE AT DIFFERENT AGES

Strength achieved by M20 Grade Control concrete at different ages as a

ratio of strength at 28days is reported in table 6.8 (B). From the table, it can be

seen that 3 days strength is found to be 0.52 times that of 28 days strength, for

7 days, the strength is found to be 0.69 times that of 28 days strength, for 56

days, the strength is found to be 1.21 times that of 28days strength, and for 91

days, the strength is found to be 1.36 times that of 28days strength.

TABLE 6.8(B): COMPRESSIVE STRENGTH AS A RATIO OF

28DAYS STRENGTH AT DIFFERENT AGES FOR CONTROL

CONCRETE

Grade of

Concrete 3DAYS 7DAYS 28DAYS 56DAYS 91DAYS

M20 0.52 0.69 1 1.21 1.36

62

6.3.1.2 RICE HUSK ASH (RHA) AND SILICA FUME (SF) CONCRETE

A) Effect of Age on compressive strength of concrete:

Figure 6.5 to figure 6.6 represents the variation of compressive strength

with age for M20 grade RHA and SF concrete, in each figure, Variation of

compressive strength with age is depicted separately for each replacement level

of RHA & SF considered, namely 5%, 10% and 15%. Along with the

variations shown for each replacement, for comparison similar variations is

also shown for Control concrete i.e., for 0% replacement.

In each of these variations, it can be clearly seen that, as the age

advances, the compressive strength also increases. The highest strength

obtained at a particular age for different replacement levels with RHA & SF is

reported in table 6.9 for the ages of 3days, 7days 28days, 56days and 91days

respectively.

TABLE 6.9: HIGHEST COMPRESSIVE STRENGTH OBTAINED AT

DIFFERENT AGES

Age

in

days

0% 5%RHA 10%RHA 15%RHA 5%SF 10%SF 15%SF

3 14.28 25.11 22.00 13.11 16.00 23.33 18.89

7 18.92 26.00 25.56 20.00 28.67 31.11 26.00

28 27.45 35.78 42.22 48.89 37.33 44.44 36.00

56 33.14 40.22 45.11 53.33 41.78 46.66 46.66

91 37.20 42.22 46.67 55.55 41.78 48.89 45.33

Percentage increase in strength with respect to Control concrete strength

(i.e.0%replacement) at 3days, 7days, 28days, 56days and 91days are calculated

and presented in table 6.10 to 6.14.

63

In each table, the change in strength for M20 grade RHA and SF

Concrete is presented separately and the following observations are made,

The maximum increase in the Compressive strength of RHA concrete

(i.e., 78.11%)has occurred at 28 days with 15% replacement with RHA,

whereas the compressive strength of RHA concrete is found to be

decreased by 8.19% at 3days with 15% RHA replacement.

With respect to the Control concrete, the maximum increase in

compressive strength of SF concrete has occurred at 10% replacement

level and at the age of 7 days, however there is a little increase in the

compressive strength at 3days with 5% SF replacement.

It can be clearly observed that at the age of 28 days, there is a gradual

increase in the compressive strength of RHA concrete for all the

replacement levels with respect to Control concrete.

At the age of 28days, there is a gradual increase in the compressive

strength of SF concrete up to 10% SF replacement with respect to

Control concrete, whereas the strength of SF concrete reduces with the

further increase in the percentage of SF replacement.

TABLE 6.10 INCREASE OR DECREASE IN STRENGTH OF

CONCRETE AT 3 DAYS W.R.T % REPLACEMENT OF RHA & SF

Percentage

ReplacementRice Husk Ash Silica Fume

0-5% 75.84 12.04

0-10% 54.06 63.38

0-15% -8.19 32.28

64



Percentage


0-5% 37.42 51.53

0-10% 35.09 64.43

0-15% 5.71 37.42



Percentage


0-5% 30.35 35.99

0-10% 53.81 61.89

0-15% 78.11 31.15



Percentage


0-5% 21.36 26.07

0-10% 36.12 40.79

0-15% 60.92 40.79

65



Percentage


0-5% 13.50 12.31

0-10% 25.46 31.42

0-15% 49.33 21.85

Strength development of concrete for different percentage replacements

with RHA & SF is presented in Table 6.15 to 6.16. In each table, by what

percentage the compressive strength increases with respect to previous age is

reported.

TABLE 6.15 PERCENTAGE INCREASE IN COMPRESSIVE

STRENGTH OF M20 GRADE RICE HUSK ASH CONCRETE W.R.T.

AGE

CRL

% Increase

between

3days-7days

% Increase

between

7days-28days

% Increase

between

28days-56days

% Increase

between

56days-91days

0% 32.50 45.08 20.73 12.25

5% 3.54 37.62 12.41 4.97

10% 16.18 65.18 6.85 3.46

15% 52.56 144.45 9.08 4.16

66

TABLE 6.16 PERCENTAGE INCREASE IN COMPRESSIVE

STRENGTH OF M20 GRADE SILICA FUME CONCRETE W.R.T. AGE

CRL

% Increase

between

3days-7days

% Increase

between

7days-28days

% Increase

between

28days-56days

% Increase

between

56days-91days

0% 32.50 45.08 20.73 12.25

5% 79.19 30.21 11.92 0.00

10% 33.35 42.85 4.99 4.78

15% 37.64 38.46 29.61 -2.85

From table 6.15, it can be clearly seen that, the strength is always higher

for Control concrete (i.e., 0% replacement) for initial period up to between 3-7

days up to 10% replacement with Rice Husk Ash (RHA), and for 15%

replacement with RHA, the strength is very much higher when compared with

that of Control concrete. The rate of strength development between 7-28days is

maximum when cement is replaced with 15% RHA. However there is a gradual

decrease in the strength between 28-56days and 56-91days, as the cement is

replaced with RHA up to a percentage of 10%. Thus from the table 6.15, it is

clear that the rate of strength development is maximum up to the age of 28 days

at all the replacement levels with RHA, and as the age advances from 28-91

days, the rate of strength development gradually decreases at all the

replacement levels.

Similarly from table 6.16, it can be seen that, the strength is

always higher for Control concrete (i.e., 0% replacement) between 7-28 days at

all the replacement levels with Silica Fume (SF). Also there is a gradual

increase in the rate of strength development till 28 days at all the replacement

levels with Silica Fume. As the age advances from 28 to 91 days there is a

decrease in the rate of strength development at all the replacement levels with

Silica Fume.

67

VARIATION OF COMPRESSIVE STRENGTH WITH AGE AND PERCENTAGE OF RICE HUSK ASH

0

10

20

30

40

50

60

0 20 40 60 80 100

Age in Days

Com

pres

sive

Str

engt

h in

N/m

m2 CC+0% RHA

CC+5% RHACC+10% RHACC+15% RHA

FIG 6.5 EFFECT OF AGE ON COMPRESSIVE STRENGTH OF CONCRETE W.R.T DIFFERENT % REPLACEMENT OF RICE HUSK

ASH

VARIATION OF COMPRESSIVE STRENGTH WITH AGE AND PERCENTAGE OF SILICA FUME

0

10

20

30

40

50

60

0 20 40 60 80 100

Age in Days

Com

pres

sive

str

engt

h in

N/m

m2 CC+0% SF

CC+5% SFCC+10% SFCC+15% SF

FIG 6.6 EFFECT OF AGE ON COMPRESSIVE STRENGTH OF CONCRETE W.R.T DIFFERENT % REPLACEMENT OF SILICA

FUME

68

B) Effect of Percentage Replacement of cement with Rice Husk Ash (RHA)

and Silica Fume (SF) on compressive strength of concrete:

Figure 6.7 to figure 6.8 represents the variation of compressive strength

with percentage replacement of RHA & SF for M20 grade concrete, in each

figure, Variation of compressive strength with percentage replacement is

depicted separately for RHA & SF.

In each of these variations, it is easily seen that as the percentage

replacement is increased, the compressive strength also increases.

PERCENTAGE OF RICE HUSK ASH Vs COMPRESSIVE STRENGTH

0

1020

30

4050

60

0% 5% 10% 15% 20%

Percentage of Rice Husk Ash

Com

pres

sive

Stre

ngth

inN

/mm2

Strength at 3 DaysStrength at 7 DaysStrength at 28 Days Strength at 56 DaysStrength at 91 Days

FIG 6.7 EFFECT OF RICE HUSK ASH PERCENTAGE ON COMPRESSIVE STRENGTH OF CONCRETE

69

PERCENTAGE OF SILICA FUME Vs COMPRESSIVE STRENGTH

0

10

20

30

40

50

60

0% 5% 10% 15% 20%

Percentage of Silica Fume

Com

pres

sive

Stre

ngth

in

N/m

m2

Strength at 3 DaysStrength at 7 DaysStrength at 28 DaysStrength at 56 DaysStrength at 91 Days

FIG 6.8 EFFECT OF SILICA FUME PERCENTAGE ON COMPRESSIVE STRENGTH OF CONCRETE

Comparison between different replacements is made possible if the

water cement ratio is common. For better pictorial representation, the variations

are also represented in the form of bar charts in the figures 6.9, & 6.10.

Figure 6.9 to 6.10 gives the variation of compressive strength with

different percentage replacement of cement with Rice husk Ash & Silica fume

for M20 grade concrete. The graph is so developed that a common water

cement ratio is considered for different replacement, so that for a particular

water cement ratio how the variation is observed with different replacement.

70

M 20 Grade 0.55 w/c

0

10

20

30

40

50

60

0% 5% 10% 15% 20%

% Replacement 0f RHA

Com

pres

sive

Stre

ngth

inN

/mm2 28 days

56 days91 days

M20 Grade 0.55 w/c

0

10

20

30

40

50

60

5% 10% 15%

% Replacement of RHA

Com

pres

sive

Str

engt

h in

N/m

m2

28 days56 days91 days

FIG 6.9 EFFECT OF % REPLACEMENT OF RICE HUSK ASH ON COMPRESSIVE STRENGTH W.R.T WATER BINDER RATIO FOR

M20 GRADE CONCRETE

71

M20 Grade 0.55 w/c

0

10

20

30

40

50

60

0% 5% 10% 15% 20%

% Replacement of Silica Fume

Com

pres

sive

Str

engt

h in

N/m

m2

28 days56 days91 days

M 20 Grade 0.55 w/ c

0102030405060

5% 10% 15%

% R eplacement o f Silica F ume

28 days

56 days

91 days

FIG 6.10 EFFECT OF % REPLACEMENT OF SILICA FUME ON

COMPRESSIVE STRENGTH W.R.T WATER BINDER RATIO FOR M20 GRADE CONCRETE

From figure 6.9, it is clearly seen that 15% replacement with RHA has

resulted in higher strength particularly considering 28days age. Also from

figure 6.10 it can be clearly seen that 10% replacement with SF has resulted in

higher strength particularly considering 28days age; also the rate of strength

development has decreased when the cement is replaced with 15% SF.

72

6.3.2 Split tensile Strength:

In reinforced concrete construction, the strength of concrete in

compression is only taken into consideration. The tensile strength of concrete is

generally neglected, as it is relatively low in comparison to the compressive

strength. But there are certain structures; where in tensile strength of concrete

also finds a place during design like water retaining structures and concrete

pavements. Therefore, it is necessary to assess the tensile strength of concrete.

The use of pozzolanic material increases the tensile strength of concrete. The

procedure for the split tensile test has been explained in chapter 5.

6.3.2.1 Control concrete:

The 28 days tensile strength obtained for M20 Grade Control concrete is

2.68 N/mm2. Table 6.17 shows the tensile strength of M20 Grade Control

concrete with respect to age.

Variation of tensile strength with age is presented in figure 6.11. It is

clear from the figure that tensile strength of Control concrete increases at a

greater rate up to 28days and the increase is gradual for further increase in age.

TABLE 6.17: TENSILE STRENGTH OF CONTROL CONCRETE

Tensile strength of Control Concrete in N/mm2

3DAYS 7DAYS 28DAYS 56DAYS 91DAYS

M20 1.50 1.99 2.68 2.70 2.75

73

0

0.5

1

1.5

2

2.5

3

0 20 40 60 80 100

AGE IN DAYS

TENS

ILE

STR

ENG

TH IN

N/m

m2

M20 ControlConcrete

FIG 6.11: TENSILE STRENGTH V/S AGE IN DAYS

OF CONTROL CONCRETE

6.3.2.2 Rice Husk Ash (RHA) Concrete:

The 28 days tensile strength of M20 grade concrete with 5%, 10% &

15% RHA replacement are 2.62N/mm2, 2.83 N/mm2 and 2.83 N/mm2

respectively.

Table 6.18 shows the tensile strength of M20 grade concrete with 5%,

10% & 15% RHA replacement with respect to age. The values show that the

tensile strength of RHA concrete is higher than that of Control concrete. Fig

6.12 and 6.13 shows the variation of split tensile strength with age and effect of

RHA percentage for M20 grade concrete. It is very clear from the figure 6.12

that there is not much variation in tensile strength from 28 days to 91 days.

74

VARIATION OF TENSILE STRENGTH WITH AGE AND PERCENTAGE OF RICE HUSK ASH

0

1

2

3

4

0 20 40 60 80 100

AGE IN DAYS

TEN

SILE

ST

REN

GTH

IN

N/m

m2 CC+0% RHA

CC+5% RHACC+10% RHACC+15% RHA

FIG 6.12 EFFECT OF AGE ON TENSILE STRENGTH OF CONCRETE

W.R.T DIFFERENT % REPLACEMENT OF RICE HUSK ASH

PERCENTAGE OF RICE HUSK ASH v/s TENSILE STRENGTH

01234

0% 5% 10% 15% 20%

Percentage of Rice Husk Ash

Tens

ile S

tren

gth

in

N/m

m2 Strength at 3 days

Strength at 7 days

Strength at 28 days

Strength at 56 days

Strength at 91 days

FIG 6.13 EFFECT OF RICE HUSK ASH PERCENTAGE ON TENSILE

STRENGTH OF CONCRETE

Referring to figure 6.12, where tensile strength variation with age and

RHA percentage is shown, the variation as observed in case of Control

concrete, the rate of development of split tensile strength is higher at initial

ages between 3days to 7days and 7days to 28days. The values show that the

75

tensile strength of RHA concrete also increases with age for M20 grade

concrete and it varies gradually up to 91days.

Table 6.18 shows the split tensile strength of M20 grade RHA

concrete at different curing periods with different replacement levels. Variation

of split tensile strength with age is compared between Control concrete and

RHA concrete in figure 6.12. It can be clearly seen from the figure that, the

split tensile strength of RHA Concrete is less than that of Control concrete up

to 28 days for 5%, 10% and 15% RHA replacement levels, where as the 28

days tensile strength of RHA concrete is more than that of the Control concrete

for 10% and 15% RHA replacement levels. The tensile strength of RHA

concrete is found to be higher than that of Control concrete at the ages of

56days and 91days for all the replacement levels.

The 28 days tensile strength of M20 grade RHA concrete obtained is

found to be decreasing by 2.24% for 5% RHA replacement and found to be

increased by 5.59% for 10% and 15% replacement with RHA with respect to

Control concrete. But for at 56days and 91 days, RHA concrete strength is

higher by 4.81% and 8% for 5% RHA replacement, 28.51% and 31.27% for

10% RHA replacement and 25.92% and 33.82% for 15% RHA replacement

with respect to Control concrete.

TABLE 6.18: TENSILE STRENGTH OF RICE HUSK ASH CONCRETE

Tensile strength of Rice Husk ash Concrete in N/mm2


5% 1.27 1.69 2.62 2.83 2.97

10% 0.99 1.77 2.83 3.47 3.61

15% 0.71 1.42 2.83 3.40 3.68

76

6.3.2.3 Silica Fume (SF) Concrete:

The 28 days tensile strength for M20 grade concrete with 5%, 10% &

15% SF replacement are 3.68N/mm2, 3.33 N/mm2 and 3.26 N/mm2

respectively.

Table 6.19 shows the tensile strength of M20 grade concrete with 5%,

10% & 15% SF replacement with respect to age. The values show that the

tensile strength of Control concrete is higher than that of SF concrete for 10%

and 15% SF replacement level up to 7 days and there after the tensile strength

is increasing with the age compared to Control concrete. However the tensile

strength of Silica fume concrete is more than that of the Control concrete at 5%

Silica Fume replacement at all the ages. Fig 6.14 and 6.15 shows the variation

of split tensile strength with age and effect of Silica fume percentage for M20

grade concrete. It is very clear from the figure 6.14 that there is no much

variation in tensile strength from 28 days to 91 days.

VARIATION OF TENSILE STRENGTH WITH AGE AND PERCENTAGE OF SILICA FUME

0

1

2

3

4

5

0 20 40 60 80 100

AGE IN DAYS

TEN

SILE

STR

ENG

TH

IN N

/mm

2 CC+0% SFCC+5% SFCC+10% SFCC+15% SF

FIG 6.14 EFFECT OF AGE ON TENSILE STRENGTH OF CONCRETE

W.R.T DIFFERENT % REPLACEMENT OF SILICA FUME

77

PERCENTAGE OF SILICA FUME v/s TENSILE STRENGTH

00.5

11.5

22.5

33.5

44.5

0% 5% 10% 15% 20%PERCENTAGE OF SILICA FUME

TEN

SILE

STR

ENG

TH IN

N/m

m2

Strength at 3 daysStrength at 7 daysStrength at 28 daysStrength at 56 daysStrength at 91 days

FIG 6.15 EFFECT OF SILICA FUME PERCENTAGE ON TENSILE

STRENGTH OF CONCRETE

Referring to figure 6.14, where the tensile strength variation with age is

shown for different percentage replacements with SF, the variation as observed

in case of Control concrete is that, the rate of development of split tensile

strength is higher at initial ages between 3days to 7days and 7days to 28days.

The values show that the tensile strength of M20 grade SF concrete also

increases with age and it varies gradually up to 91days.

Table 6.19 shows the split tensile strength of M20 grade Control

concrete and Silica Fume concrete at different curing periods. Variation of split

tensile strength with age is compared between Control concrete and Silica fume

concrete in figure 6.14. It is clearly seen from the figure that, the strengths of

M20 grade Control concrete are less than that of SF concrete at all the ages for

5% replacement with SF.

The tensile strength of M20 grade SF concrete is found to be higher than

that of Control concrete at the ages of 28 days, 56days and 91days for all the

replacement levels.

78

The 28 days tensile strength of M20 grade Silica Fume concrete

obtained is found to be increasing by 37.31%, 24.25% and 21.64% for 5%

replacement with respect to Control concrete. Also at 56days and 91 days,

Silica fume concrete strength is higher by 46.67%, and 49.45% for 5%

replacement with SF, 41.48% and 46.54% for 10% replacement with SF and

20.74% and 23.27% for 15% replacement with SF with respect to Control

concrete.

TABLE 6.19: TENSILE STRENGTH OF SILICA FUME CONCRETE

Tensile strength of Silica Fume Concrete in N/mm2


0% 1.50 1.99 2.68 2.70 2.75

5% 1.84 2.48 3.68 3.96 4.11

10% 1.13 2.05 3.33 3.82 4.03

15% 1.27 1.42 3.26 3.26 3.39

6.3.3 Flexural Strength:

It is seen that strength of concrete in compression and tension (both

direct tension and flexural tension) are closely related, but the relationship is

not of the type of direct proportionality. The ratio of the two strengths depends

on general level of strength of concrete. In other words, for higher compressive

strength, concrete shows higher tensile strength, but the rate of increase of

tensile strength is of decreasing order. The use of pozzolanic material increases

the tensile strength of concrete. The results of flexural strength test are

tabulated in table 6.20 and the corresponding graph is shown in fig 6.16.

6.3.3.1 Control Concrete:

Fig 6.16 shows the variation of flexural strength of Control concrete

with respect to age for M20 grade. It is clear from the figure 6.16 that, the

flexural strength increases at a greater rate up to 28days and the increase is

gradual for further increase in age.

79

TABLE 6.20: FLEXURAL STRENGTH OF CONTROL CONCRETE

Flexural strength of Control Concrete in N/mm2


M20 2.87 4.44 5.02 6.15 7.10

0

1

2

3

4

5

6

7

8

0 20 40 60 80 100

AGE IN DAYS

FLE

XURA

L ST

REN

GTH

IN N

/mm

2

M20 CONTROLCONCRETE

FIG 6.16: FLEXURAL STRENGTH V/S AGE IN DAYS OF

CONTROL CONCRETE

6.3.3.2 Rice Husk Ash (RHA) Concrete:

Table 6.21 gives the details of flexural strength of M20 grade Rice husk

ash concrete at different curing periods and at different cement replacement

levels with Rice husk ash. Variation of flexural strength with respect to age and

percentage of RHA, and effect of RHA percentage on Flexural strength of M20

grade concrete is depicted in figure 6.17 and 6.18 respectively. The rate of

development of flexural strength is higher at 7days to 28days and 28days to

56days. At later age between 56days and 91days only a marginal increase is

observed. At 28days, there is very less variation in flexural strength of RHA

concrete at the replacement levels, where as there is a comparative increase in

flexural strengths of RHA concrete at higher curing periods.

80

The 28 days flexural strength of M20 grade RHA concrete obtained is

found to be increasing by 119.12%, 104.18% and 124.10% respectively for 5%,

10% and 15% replacement levels with respect to Control concrete.

At 56 days increase in flexural strength by 95.12%, 66.67% and 82.92%

is observed for RHA concrete for 5%, 10% and 15% replacements with respect

to Control concrete. And at 91 days increase in strength is observed by

104.22%, 76.05% and 61.97% for 5%, 10% and 15% replacements with respect

to Control concrete.

Table 6.22 gives the flexural strength of Control concrete and Rice husk

ash concrete with respect to different age of curing. Flexural strength of the

concrete keeps on increasing with the increase in curing period, which is

clearly depicted in figure 6.17. Both the strength values of Control concrete and

Rice husk ash concrete for M20 grade are plotted in the figure.

VARIATION OF FLEXURAL STRENGTH WITH AGE AND PERCENTAGE OF RHA

0

5

10

15

20

0 50 100

AGE IN DAYS

FLEX

UR

AL

STR

ENG

TH IN

N/m

m2

CC+0% RHACC+5% RHACC+10% RHACC+15% RHA

FIG 6.17 EFFECT OF AGE ON FLEXURAL STRENGTH OF

CONCRETE W.R.T DIFFERENT % REPLACEMENT OF RICE HUSK ASH

81

PERCENTAGE OF RICE HUSK ASH v/s FLEXURAL STRENGTH

02468

10121416

0% 5% 10% 15% 20%

PERCENTAGE OF RICE HUSK ASH

FLEX

UR

AL

STR

ENG

TH IN

N

/mm

2Strength at 3 daysStrength at 7 daysStrength at 28 daysStrength at 56 daysStrength at 91 days

FIG 6.18 EFFECT OF RICE HUSK ASH PERCENTAGE ON FLEXURAL STRENGTH OF CONCRETE

Table 6.23 gives the details of 28 days compression, tension, and

flexural strength of Control concrete and Rice husk ash concrete with different

cement replacement levels for M20 grade. All the percentage replacement

levels considered are compared in bar chart in fig 6.19 for both Rice husk ash

concrete and Control concrete and for all the three percentage replacement

levels considered.

TABLE 6.21: FLEXURAL STRENGTH OF RICE HUSK ASH

CONCRETE

Flexural strength of Rice Husk ash Concrete in N/mm2


5% 6.25 8.00 11.00 12.00 14.50

10% 8.00 8.75 10.25 10.25 12.50

15% 5.50 7.50 11.25 11.25 11.50

82


AND RICE HUSK ASH CONCRETE

Flexural strength of Control and Rice Husk ash Concrete in N/mm2


M20 CC 2.87 4.44 5.02 6.15 7.10

M20 CC+5%RHA 6.25 8.00 11.00 12.00 14.50

M20 CC+10% RHA 8.00 8.75 10.25 10.25 12.50

M20 CC+15% RHA 5.50 7.50 11.25 11.25 11.50

TABLE 6.23: 28 DAY COMPRESSIVE, TENSILE AND

FLEXURAL STRENGTH OF CONTROL CONCRETE & RICE HUSK

ASH CONCRETE

Strength

Type

Compressive

Strength in n/mm2

Tensile strength in

N/mm2

Flexural strength in

N/mm2

Percentage

replacement 0% 5% 10% 15% 0% 5% 10% 15% 0% 5% 10% 15%

Control

concrete 27.45 2.68 5.02

Rice husk ash

concrete 35.78 42.22 48.89 2.62 2.83 2.83 11.00 10.25 11.25

83

28 DAY COMPRESSIVE,TENSILE AND FLEXURAL STRENGTH OF CONTROL AND RICE HUSK ASH

CONCRETE

0

10

20

30

40

50

60

M20 CC,RHA CONCRETE

STR

ENG

TH IN

N/m

m2

0% RHA5% RHA10% RHA15% RHA

FIG. 6.19: BAR CHART FOR COMPRESSIVE, TENSILE AND

FLEXURAL STRENGTH OF CONTROL CONCRETE AND RICE HUSK ASH CONCRETE

6.3.3.3 Silica fume (SF) Concrete:

Table 6.24 gives the details of flexural strength of Silica fume concrete

at different curing periods and at different Cement replacement levels with SF.

Variation of flexural strength with respect to age and percentage of Silica fume

and effect of Silica fume percentage on Flexural strength of M20 grade

concrete is depicted in figure 6.20 and 6.21. The rate of development of

flexural strength is higher at 7days to 28days and 28days to 56days. At later

age between 56days and 91days only a marginal increase is observed. Up to

28days, the flexural strength for all the replacement levels, there is very high

variation in strength. Whereas, there is a comparative increase in flexural

strengths of SF concrete at higher curing periods.

The 28 days flexural strength of SF concrete obtained is found to be

increasing by 119.12%, 129.08% and 119.12% for 5%, 10% and 15%

replacements respectively with respect to Control concrete.

84

At 56 days, increase in flexural strength by 86.99%, 103.25% and

119.51% is observed for SF concrete for 5%, 10% and 15% replacements with

respect to Control concrete. At 91 days increase in strength is observed by

79.57%, 114.78% and 97.18% for SF concrete for 5%, 10% and 15%

replacements with respect to Control concrete at 91days.

Table 6.25 gives the flexural strength of Control concrete and Silica

fume concrete with respect to different age of curing. Flexural strength of the

concrete keeps on increasing with increase in curing period, which is clearly

depicted in the figure 6.20. Both the strength values of M20 grade Control

concrete and Silica fume concrete are plotted in the figure.

VARIATION OF FLEXURAL STRENGTH WITH AGE AND PERCENTAGE OF SILICA FUME

02468

1012141618

0 20 40 60 80 100

AGE IN DAYS

FLEX

UR

AL

STR

ENG

TH IN

N/m

m2

CC+0% SFCC+5% SFCC+10% SFCC+15% SF

FIG 6.20 EFFECT OF AGE ON FLEXURAL STRENGTH OF

CONCRETE W.R.T DIFFERENT % REPLACEMENT OF SILICA FUME

85

PERCENTAGE OF SILICA FUME v/s FLEXURAL STRENGTH

0

5

10

15

20

0% 10% 20%

PERCENTAGE OF SILICA FUME

FLEX

UR

AL

STR

ENG

TH IN

N

/mm

2Strength at 3 daysStrength at 7 daysStrength at 28 daysStrength at 56 daysStrength at 91 days

FIG 6.21 EFFECT OF SILICA FUME PERCENTAGE ON FLEXURAL STRENGTH OF CONCRETE

Table 6.26 gives the details of 28 days compression, tension, and

flexural strength of M20 grade Control concrete and Silica fume concrete with

different cement replacement levels. All the percentage replacement levels

considered are compared in bar chart in fig 6.22 for both Silica fume concrete

and Control concrete and for all the three percentage replacement levels

considered. All the three percentage replacement levels considered are

compared in bar chart in fig 6.22 for both Silica fume concrete and Control

concrete and for all the three percentage replacement levels considered. For any

percentage replacement level, it is seen that, the flexural strength is greater than

the split tensile strength, and the compressive strength is maximum for the

percentage replacement levels up to 10%. It is seen through the study that, the

Compressive strength of SF concrete is more than that of Control concrete for

all the replacement levels, where as Tensile and Flexural strength results are

also varying for the different replacement levels.

86

TABLE 6.24: FLEXURAL STRENGTH OF SILICA FUME CONCRETE

Flexural strength of Silica Fume Concrete in N/mm2


5% 5.25 8.75 11.00 11.50 12.75

10% 5.75 7.50 11.50 12.50 15.25

15% 3.00 7.25 11.00 13.50 14.00


AND SILICA FUME CONCRETE

Flexural strength of Control and Rice Husk ash Concrete in N/mm2


M20 CC 2.87 4.44 5.02 6.15 7.10

M20 CC+5%SF 5.25 8.75 11.00 11.50 12.75

M20 CC+10% SF 5.75 7.50 11.50 12.50 15.25

M20 CC+15% SF 3.00 7.25 11.00 13.50 14.00

TABLE 6.26: 28 DAY COMPRESSIVE TENSILE AND

FLEXURAL STRENGTH OF CONTROL CONCRETE & SILICA

FUME CONCRETE

Strength

Type

Compressive

Strength in N/mm2

Tensile strength in

N/mm2

Flexural strength in

N/mm2

Percentage

replacement 0% 5% 10% 15% 0% 5% 10% 15% 0% 5% 10% 15%

Control

concrete 27.45 2.68 5.02

Silica fume

concrete 37.33 44.44 36 3.68 3.33 3.26 11 11.5 11

87

28 DAY COMPRESSIVE, TENSILE AND FLEXURAL STRENGTH OF CONTROL AND SILICA FUME

CONCRETE

0

10

20

30

40

50

M20 CC,SF CONCRETE

STR

ENG

TH IN

N/m

m2

0% SF5% SF10% SF15% SF

FIG. 6.22: BAR CHART FOR COMPRESSIVE, TENSILE AND

FLEXURAL STRENGTH OF CONTROL CONCRETE AND SILICA FUME CONCRETE

88

CHAPTER 7 CONCLUSIONS

7.1 CONCLUSIONS

Based on the limited study carried out on the Strength behavior of Rice

husk ash and Silica fume Concrete, the following Conclusions are drawn:

1. At all the cement replacement levels with Rice husk ash; there is a gradual

decrease in the compressive strength at the early ages up to 7days. However as the

age advances, there is a gradual increase in the compressive strength of Rice husk

ash concrete.

2.The compressive strength of Silica fume concrete is found to be increased

gradually up to 10% replacement. However with further increase in age, the

compressive strength of Silica fume concrete is found to be increased gradually at

all the cement replacement levels.

3. During the initial ages of up to 7days,the split tensile strength of Rice husk ash

concrete is found to be decreased at all cement replacement levels, however with

the increase in age, there is a gradual increase in the split tensile strength of Rice

husk ash concrete, which is better than the split tensile strength of Control

concrete.

4.With the increase in the percentage replacement with Silica fume, the split

tensile strength of Silica fume concrete is found to be decreased at all the ages.

However with the advancement in age, the Split tensile Strength of Silica fume

concrete is found to be increased gradually at all the replacement levels.

5.At the initial ages, with the increase in the percentage replacement of both Rice

husk ash and Silica fume, the Flexural strength of both Rice husk ash concrete and

Silica fume concrete is found to be increased till 10% replacement. However, as

the age advances, there is an advancement in the Flexural strength of both Rice

husk ash concrete and Silica fume concrete.

89

6.From the study carried out here, it can be concluded that, it is possible to replace

the cement with Rice husk ash in concrete by 15% or even more without

compromising much of its Compressive strength. But it is possible to replace

cement with SF up to 10% only.

7.When compared to Silica fume the cost of Rice husk ash is less, hence it can be

used in place of Silica fume for reducing the cost of concrete and also for

obtaining the concretes of high strengths.

8. Rice husk ash is a viable alternative material to Silica fume in the production of

high strength concrete. The technical and economic advantages of incorporating

Rice husk ash in concrete should be exploited by the construction and rice

industries, more so for the rice growing nations of Asia.

90

7.2 SCOPE FOR FUTURE WORK

Other levels of replacement with Rice husk ash can be researched.

Some tests relating to durability aspects such as water permeability, resistance

to penetration of chloride ions, corrosion of steel reinforcement, resistance to

sulphate attack durability in marine environment etc.with Rice husk ash and

Silica fume need investigation.

The study may further be extended to know the behavior of concrete whether it

is suitable for pumping purpose or not as present day technology is involved in

RMC where pumping of concrete is being done to large heights.

Further research can be carried out with other mineral admixtures such as

GGBS, Metakaolin, Slag etc.

For use of Rice husk ash and Silica fume concrete as a structural material, it is

necessary to investigate the behavior of reinforced Rice husk ash and Silica

fume concrete under flexure, shear, torsion and compression.

91

CHAPTER 8 REFERENCES

8.1 REFERENCE

1. A.A. Boateng and D.A. Skeete, “Incineration of Rice Hull for use as a

Cementitious Material: The Guyana Experience,” Cement and Concrete

Research, Vol.20, 1990, pp.795-802.

2. Arpana,”Rice Husk Ash-Admixture to concrete,” 2nd National conference

on Advances in concrete Technology, February 26-27, 2004, pp.93-98.

3. Chai Jaturapitakkul and Boonmark Roongreung,”Cementing Material from

Calcium Carbide Residue-Rice Husk Ash,” Journal of materials in civil

Engineering ASCE, September-October 2003, pp. 470-475.

4. Concha Real, Maria D. Alcala, and Jose M. Criado, “Preparation of Silica

from Rice Husks,” Journal of American Ceramic Society, Vol.79, No.8,

1996, pp.2012-2016.

5. Deepa G. Nair, K.S Jagadish, Alex Fraaij, “Reactive Pozzolanas from Rice

Husk Ash: An alternative to cement for rural housing,” Cement and

Concrete Research 36(2006) 1062-1071.

6. Dr.Dilip Kumar Singha Roy and Amitava Sil, “Effect of partial

Replacement of Cement by Silica Fume on Strength parameters,” 2nd

National conference on Advances in concrete Technology, February 26-27,

2004, pp.80-84.

7. Dr.V.Bhaskar Desai, A.Ravi and B.Baladasu, “Some Studies on Reinforced

Cement Concrete with Partial Replacement of Cement by silica Fume,”

Advances in Concrete and Construction Technology, publication 3, pp.128-

135.

92

8. G.V.Rama Rao and M.V.Sheshagiri Rao,”High performance Concrete with

Rice Husk Ash as Mineral Admixture,”ICI Journal, April-June 2003, pp.17-

22.

9. Gemma Rodriguez de Sensale, “Strength Development of Concrete with

Rice- Husk Ash,” Cement & Concrete Composites 28 (2006) 158-160.

10. H.B.Mahmud, B.S.Chia and N.B.A.A. Hamid,”Rice Husk Ash-An

Alternative material in producing High Strength Concrete,” International

Conference on Engineering Materials, June 8-11, 1997, Ottawa, Canada,

pp.275-284.

11. Jose James and M. Subba Rao, “Characterization of Silica in Rice Husk

Ash,” American Ceramic Society Bulletin, Vol.65, No. 8, 1986, pp.1177-

1180.

12. Jose James and M. Subba Rao, “Reaction Product of Lime and Silica from

Rice Husk Ash,” Cement and Concrete Research, Vol.16, 1986, pp.67-73.

13. Jose James and M. Subba Rao, “Reactivity of Rice Husk Ash,” Cement and

Concrete Research, Vol.16, 1986, pp.296-302.

14. K.Ganesan, K.Rajagopal and K.Thangavelu,” Effects of the Partial

Replacement of Cement with Agro waste ashes (Rice husk ash and Bagasse

Ash) on strength and Durability of Concrete,” Proceedings of the

International Conference on Recent Advances in Concrete and Construction

Technology, December 7-9, 2005, SRMIST, Chennai, India pp.73-85.

15. L.V.A.Seshasayi, D.Ramaseshu and R.Shankariah, “Effect of Cement

replacements by fly ash and silica fume on compressive strength of

concrete,” Fly Ash, Silica Fume, Slag and Natural pozzolanas in concrete,

Volume 2, SP199-32, V.M Malhotra, pp.581-593.

16. M. Nehdi, J. Duquette, A. EI Damatty,” Performance of Rice Husk Ash

produced using a new technology as a Mineral Admixture in Concrete,”

Cement and Concrete Reasearch 33 (2003) 1203-1210.

93

17. M.J. Shannag,”High Strength Concrete containing natural Pozzolan and

Silica Fume,” Cement & Concrete Composites 22(2000) 399-406.

18. Mauro M. Tashima, Carlos A. R Da Silva, Jorge L. Akasaki, and Michele

Beniti Barbosa, “The Possibility of adding the Rice Husk Ash (RHA) to the

Concrete,” Conference, FEIS/UNESP, Brazil 2001.

19. Min-Hong Zhang and V. Mohan Malhotra, “High-Performance Concrete

Incorporating Rice Husk Ash as a Supplementary Cementing Material,”

ACI Materials Journal, November-December 1996, pp.629-636.

20. Moncef Nehdi, “Ternary and Quaternary Cements for Sustainable

Development,” Concrete International, April 2001, pp.35-41.

21. Ms.Nazia Pathan,”Use of Rice Husk Ash in making High Performance

Concrete,” National Seminar on Innovation Technologies in Construction

of Concrete Structures 7th & 8th Feb.2003, Dept. of Civil Engineering,

KITS, Ramtek, Maharashtra State.

22. N. Bouzoubaa and B. Fournier, “Concrete incorporating Rice Husk Ash:

Compressive Strength and Chloride-ion Penetrability,” Development of

Cement and Concrete (ICON), CANMET, Natural Resources Canada,

Ottawa, Canada.

23. N.P.Rajamane and D.Sabitha,”Effect of fly ash and silica fume on alkalinity

of cement mortars,” The Indian Concrete journal, March 2005, pp. 43-48.

24. N.R.D.Murthy, P.Rathish Kumar, Seshu D.R and M.V. Seshagiri

Rao,”Effects of Rice Husk Ash on the Strength and Durability of Concrete,”

ICI Journal July-September 2002, pp.37-38.

25. Nicole P.Hasparyk, Paulo J.M Monterio, and Helena Carasek,”Effect of

Silica Fume and Rice Husk Ash on Alkali-Silica Reaction,”ACI Materials

Journal, July-August 2000, pp. 486-491.

26. P.Kumar Mehta and Richard W.Burrows, “Building Durable Structures in

the 21st Century,” Concrete International, March 2001, pp.57-63.

94

27. P.Kumar Mehta, “Concrete Technology for Sustainable Development,”

Concrete International, November 1999, pp.47-53.

28. P.Kumar Mehta, “Greening of the Concrete Industry for Sustainable

Development,” Concrete International, July 2002, pp.23-28.

29. P.Kumar Mehta, “Reducing the Environmental Impact of Concrete,”

Concrete International, October 2001, pp.61-66.

30. P.S.S Narayana, P.Srinivasa Rao, B.L.P Swamy,” Studies on Cement

Replacement in Concretes by Micro Silica 920-D,” ACECON, September

2005, pp.22-25.

31. Pierre-Claude Aitcin, “Cements of Yesterday and Today Concrete of

Tomorrow,” Cement and Concrete Research 30(2000) 1349-1359.

32. V. Yogendran, B.W. Langan, M.N. Haque and M.A. Ward,” Silica Fume in

High-Strength Concrete,” ACI Materials Journal, March-April 1987,

pp.124-129.

33. V.M Malhotra,”Fly Ash, Slag, Silica Fume, and Rice-Husk Ash in

Concrete: A Review,” Concrete International, April 1993, pp.23-28.

34. Vesa Penttala,”Concrete and Sustainable Development,”ACI Materials

Journal, September-October 1997, pp.409-416.

95

8.2 BOOK

1. M.L Gambhir: Concrete Manual.

2. Rafat Siddique: Special Structural Concretes.

3. Concrete Technology and Design Volume 3, Cement Replacement

Materials: R.N Swamy.

8.3 CODES OF PRACTICE

1. SP: 23-1982, Hand Book on Concrete Mixes (Based on Indian Standards)

2. IS: 10262-1982, Indian Standards, Recommended Guidelines for concrete

mix Design.

3. IS: 516-1959, Indian Standards, Method of tests for Strength of Concrete.

4. IS: 12269-1987, Tests on Cement.

5. IS: 650-1966, Tests on Fine Aggregates.

6. IS: 2386-1963, Tests on Aggregates.

96

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