Embed Size (px)
Citation preview
Effect of fine aggregate replacement with fly ash on the mechanical properties of concrete
ABSTRACTThe utility of flyash as partial replacement in concrete mixes is on rise these
days. Flyash is a waste product which is generated in thermal power stations. The
quantity of fly ash produced from thermal power plants in India is approximately 105
million tons each year, and its percentage utilization is less than 13%. Majority of fly
ash produced is of Class F type. The use of these materials would reduce the disposal
problems now faced by the thermal power stations and industrial plants. During the
last few years, some cement companies have started using fly ash in manufacturing
cement, known as 'Pozzolana Portland cement', but the overall percentage utilization
remains very low, and most of the fly ash is dumped at landfills.
Fly ash is generally used as replacement of cement, as an admixture in
concrete, and in manufacturing of cement. Whereas concrete containing fly ash as
partial replacement of cement poses problems of delayed early strength development,
concrete containing fly ash as partial replacement of fine aggregate will have no
delayed early strength development, but rather will enhance its strength on long-term
basis. In this investigation flyash is used as sand replacement material. The material
mix of proportion 1:1.45:2.46:0.5. Each category comprises of various percentages of
sand replacement material in increasing order i.e. 46%, 47%, 48%, 49%, 50%, 51%,
52%, 53%, 54%, and 55%. The workability is maintained constant for all mixes.
Strength characteristics such as compressive strength flexural strength split tensile
strength of concrete mixes are found out for seven and twenty eight days curing
period and results are analyzed
1.0 INTRODUCTION
The demand for cement as well as other primary building material is increasing in
the country because of growth in economy, population and living standards. Cement
production in the country is estimated to be around 90 million tonnes per annum and is
expected to be growing at 10% per annum (1)
Cement concrete has established itself as the most preferred material of construction
owing to its versatility, ease in production and use (1). However, three aspects are
gaining emphasis in the use of concrete. The first one is the durability aspect. The
importance of durability is amply reflected in the revised code of practice on concrete IS
456-2000. The second aspect is the economy in construction by improved design and
cost reduction in cost of materials. The third aspect relates to energy conservation and
environment protection. These three factors can be uniquely addressed by the use of fly
ash in concrete.
The present production of fly ash in our country is around 100 million tonnes per annum
of which about 20% is being gainfully utilized. The utilization of fly ash in concrete
making, though, is negligible. Concrete owes its unique position as the structural
material to the fact, that it is economically highly resistant to fire, wind, water and
earthquakes. The demand is likely to increase in the future to match the growing
population, housing, transportation and other amenities. However, on many occasions
individual materials as such may not serve the specific purpose. Concrete can be
called as a composite material. For reducing the cost of concrete, greater use of
pozzolonic materials like flyash and blast furnace slag was suggested. The use of
these materials as the substitute material in concrete would reduce the disposal
problems now faced by thermal power plants and industrial plants and at the same
time achieving the required strength of concrete.
In the present investigation, flyash has been used as a partial replacement of sand.
Flyash is a finely divided residue resulting from the combustion of ground or
pulverized bituminous coal or sub-bituminous coal. It is available in large quantities
in the country as a waste product from a number of thermal power stations and
industrial plants using pulverized coal or lignite as fuel as fuel for the boilers. The
effective use of flyash for partial replacement of sand as an admixture in cement
mortar and concrete has established in the country in recent years. Greater utilization
of flyash will lead to not only saving such construction material but also assists in
solving the problem of disposal of this waste product. The recent investigations have
also indicated the necessity to provide proper collection methods for flyash so as to
yield flyash of quality and uniformity, which are prime requirements of flyash for use
construction materials.
2.0 LITERATURE SURVEY
Though numbers of significant results have been reported on the use of Class
F fly ash in concrete but there is not much literature available on the use of Class F fly
ash as partial replacement of fine aggregates. Maslehuddinet carried out investigations
to evaluate the compressive strength development and corrosion-resisting
characteristics of concrete mixes in which fly ash was used as an admixture (equal
quantity of sand replacement). Concrete mixtures were made with fly ash additions of
0%, 20%, and 30% and water–cement ratios of 0.35, 0.40, 0.45, and 0.50. Based on
the test results, they concluded that addition of fly ash as an admixture increases the
early age compressive strength and long-term corrosion-resisting characteristics of
concrete. The superior performance of these mixes compared to plain concrete mixes
was attributed to the densification of the paste structure due to pozzolonic action
between the fly ash and the calcium hydroxide liberated as a result of hydration of
cement.
Ghafoori carried out investigations on a series of laboratory-made roller
compacted concretes (RCC) containing high-calcium dry bottom ash as a fine
aggregate. Concrete specimens of six different proportions (cement content of 188–
337 kg/m3 and coarse aggregate content of 1042–1349 kg/m3) were prepared at their
optimum moisture content and fabricated in accordance with ASTM C 1170
Procedure A. Specimens were tested for compression, splitting tension, drying
shrinkage, and resistance to abrasion and rapid freezing and thawing. Based on the
test results, they concluded that good strength, stiffness, drying shrinkage and
resistance to wear, and repeated freezing and thawing cycles can be obtained with
compacted concretes containing bottom ash.
Hwang examined the effects of fine aggregate replacement on the rheology,
compressive strength, and carbonation properties of fly ash and mortar. Rheological
properties, compressive strength, and rate of carbonation of mortars of water to
Portland cement ratio of 0.3, 0.4, and 0.5, in which the fine aggregate was replaced
with fly ash at 25% and 50% levels. Test results showed that rheological constants
increased with higher replacement level of fly ash and that, when water to Portland
cement ratio was maintained, the strength development and carbonation properties
were improved.
Bakoshi used bottom ash in amounts of 10–40% as replacement for fine aggregate.
Test results indicate that the compressive strength and tensile strength of bottom ash
concrete generally increases with the increase in replacement ratio of fine aggregate
and curing age. The freezing–thawing resistance of concrete using bottom ash is
lower than that of ordinary concrete and abrasion resistance of bottom ash concrete is
higher than that of ordinary concrete.
3.0 EXPERIMENTAL WORK
3.1 Outline
The experimental investigation consisted of designing fly ash concrete mixes
following rational methods combined with efficiency factor considerations to
obtain the optimum fly ash content for a requisite 28-day strength and workability.
3.2 Materials
Cement: Ordinary Portland Cement of 53 grade confirming to IS 12269 was used
in the investigation
Fine Aggregate: Natural sand was used. The specific gravity was found to be 2.65
and sieve analysis confirmed to zone II.
Coarse Aggregate: Crushed stone aggregate of maximum size 20mm was used
Specific gravity was found to be 2.65
Flyash: Fly ash obtained from Nashik Thermal Power Station was used in the
investigations. The chemical and physical properties are given in Table 2.
3.3 Design Parameters
The design parameters adopted are given in table 2. Control mixes are
proportioned as per guidelines provided in IS 10262-1982.The proportions for
control concrete are far each grade of concrete investigated are given in table 3,
4& 5
Physical test Results obtained
IS: 8112-1989 specifications
Fineness (retained on 90-mm sieve)Fineness: specific surfaceNormal consistency
Vicat time of setting (min) Initial FinalCompressive strength (MPa)7 days28 daysSpecific gravity
8.528530%
120215
13.72921.283.15
10 max225 min
30 min minimum600 min maximum
13.4 minimum20.0 minimum
Table 1
Physical properties of Ordinary Portland Cement
Chemical analysis Class F flyash (%)
Silicon dioxide, SiO2Aluminum oxide, Al2O3Ferric oxide, Fe2O3SiO2+Al2O3+Fe2O3Calcium oxide, CaOMagnesium oxide, MgOTitanium oxide, TiO2Potassium oxide, K2OSodium oxide, Na2OSulfur trioxide, SO3LOI (100o C)Moisture
55.325.75.385.95.62.11.30.60.41.41.90.3
Table 2Chemical composition of fly ash (3)
Property Fine aggregate Coarse aggregate
Specific gravityFineness modulusSSD absorption (%)Void (%)Unit weight (kg/m3)
2.652.250.8636.21690
2.656.611.1239.61615
Table 3Physical properties of aggregates
Fine aggregates Coarse aggregates
Sieve size % Passing Requirement IS:383-1970
Sieve size % Passing Requirement IS:383-1970
4.75 mm2.36 mm1.18 mm600 mm300 mm150 mm
92.2086.3576.8566.7613.563.21
90-10085-10075-10065-7912-400-10
40 mm20 mm16 mm
12.5 mm10 mm
4.75 mm
100.0095.0086.0076.0027.8506.00
10095-10085-9075-8025-550-10
Table 4Sieve analysis of aggregates
4.0 CONCRETE MIX DESIGN BY INDIAN STANDARDS METHOD (GRADE M20) (11)
1. DESIGN SPECIFICATIONSa) Characteristic compressive strength required at the end of 28 days = 20 MPab) Maximum size of aggregates = 20 mm c) Degree of workability = 0.85 cfd) Degree of quality control = Faire) Type of exposure = Mild
2. TEST DATA FOR MATERIALSa) Cement used – Ordinary Portland Cement satisfying
requirements of IS: 269-1976
b) Specific Gravity of cement= 3.15
c) (i) Specific Gravity of coarse aggregates= 2.65
(ii) Specific Gravity of fine aggregates = 2.65
d) Water Absorption (i) Coarse aggregates =0.5%
(ii) Fine aggregates =1.0%
e) Free Surface Moisture (5) (i) Coarse aggregates = 0.5% (ii) Fine aggregates = 5%
f) Sieve Analysis (8) (i) Coarse aggregates
(ii) Fine aggregates
Fine aggregates Coarse aggregates
Sieve size % Passing Requirement IS:383-1970
Sieve size % Passing Requirement IS:383-1970
4.75 mm2.36 mm1.18 mm600 mm300 mm150 mm
92.2086.3576.8566.7613.563.21
90-10085-10075-10065-7912-400-10
40 mm20 mm16 mm
12.5 mm10 mm
4.75 mm
100.0095.0086.0076.0027.8506.00
10095-10085-9075-8025-550-10
Table 5
3. TARGET MEAN STRENGTH OF CONCRETE
For a tolerance factor of K=1.65 and Standard Deviation= 5.6, the target mean strength for the specified characteristic cube strength= [20+ {5.6x1.65}] =29.24 MPa
4. SELECTION OF WATER CEMENT RATIO
The water cement ratio required for the target mean strength of 29.44 MPa is 0.47< 0.65 prescribed of Mild Exposure.
5. SELECTION OF WATER CONTENT
Water content per cubic metre of concrete = 215kgSand content is 45%
6. DETERMINATION OF CEMENT CONTENT
Water cement ratio= 0.50Water = 215.00
Cement = = 430 kg/m3
7. DETERMINATION OF COARSE AND FINE AGGREGATES CONTENT
For fine aggregates
V= [W+ ]
0.98= [215+ ]
fa = 654 kg/m3
For coarse aggregates
V= [W+ ]
0.98= [215+ ]
Ca= 1056 kg/m3
FINAL MIX PROPORTION
For 1 m3
Water Cement Fine aggregates Coarse aggregates215 liters 430 kg 654 kg 1056 kg
Mix Proportion0.5 1 1.46 2.8
FLY ASH CEMENT CONCRETE MIX (7)
Type of mix
Water Cement Fine aggregates Coarse aggregatesFlyash Sand
0.5 1 1.46 2.8PLAIN 10.776 21.552 00.000 32.327 60.3446 P 10.776 21.552 14.871 17.450 60.3447 P 10.776 21.552 60.3448 P 10.776 21.552 15.517 16.812 60.3449 P 10.776 21.552 15.871 16.350 60.3450 P 10.776 21.552 16.160 16.160 60.3451 P 10.776 21.552 16.350 15.871 60.3452 P 10.776 21.552 16.812 15.517 60.3453 P 10.776 21.552 60.34
54 P 10.776 21.552 17.450 14.871 60.34100 P 10.776 21.552 32.327 00.000 60.34
6.0 TEST PROGRAMME
Sand is very expensive to procure and apart from this, depending on its source,
it may require additional treatment such as washing to remove some undesirable
substances and organic matters that may impair the strength of concrete.
Investigations made on local raw material have led to identify Fly ash, Laterite fines
and Granite fines as good substitute for sand in concrete. In the present investigation
fly ash is used as partial replacement material in concrete. In this investigation an
attempt is being made to compare the strength of concrete for mix proportion 1: 1.45:
2.45:0.5 with concrete having;
1. 0% flyash as a partial replacement to sand. (Plain)
2. 46% flyash as a partial replacement to sand. (P 46)
3. 48% fly ash as a partial replacement to sand. (P 48)
4. 49% fly ash as a partial replacement to sand. (P 49)
5. 50% fly ash as a partial replacement to sand. (P 50)
6. 51% fly ash as a partial replacement to sand. (P 51)
7. 52% fly ash as a partial replacement to sand. (P 52)
8. 54% fly ash as a partial replacement to sand (P 54)
As a part of the comprehensive program compressive strength, flexural
strength, split tensile strength and modulus of elasticity of concrete were determined
for 7 and 28 days. Fly ash for partially replacing sand with their increasing
percentages .i.e. 0%, 46%, 48%,49%,50%,51%,52%, 54% using a nominal mix
proportion of 1: 1.45: 2.45:0.5. The proportioning of concrete mixes was done on
absolute weight basis. On the field the proportioning is done on absolute volume
basis.
Normal concrete was made with Ordinary Portland Cement (53) conforming to IS:
4031-1968. River sand free from organic matter and crushed stone aggregate of
20mm maximum size as per IS: 10262-1982(9) and flyash obtained Nashik Thermal
Power Station. The concrete was prepared in the laboratory. The cement, fly ash, sand
and coarse aggregate were first mixed in dry state to obtain uniform color.
The quantity of water calculated by conducting workability test (slump cone test) is
then added to the dry mix with a view to obtain uniform mix, workability being
constant. Calculated amount of water obtained by conducting workability test
according to IS: 1199-1959(10) was added and the whole concrete was mixed in wet
state. The concrete after mixing was filled into cubes, cylinder and beam moulds and
compacted on vibrating table. For determining compressive and split tensile strengths,
150mm size cubes and 150 x 300mm size cylinders were cased. The moulds with
standard internal dimensions were kept on table vibrator and the concrete was poured
into the moulds in three layers by poking with a tamping rod and vibrated by table
vibrator. The vibrator was vibrated for one minute and it was maintained constant for
all the specimens. For determining flexural strength and modulus of elasticity, 100 x
100 x 500mm-size beam and 150 x 300mm-size cylinder was cast.
Compressive strength, flexural strength and split tensile strength and water
permeability have been determined for 7 & 28 days curing period. All the above tests
have been conducted as per IS-516 - 1959 on 300 Tonne compression testing
machine. Cylinders are tested by placing the cylinder with its longitudinal axis in
horizontal position as per IS: 5816 - 1970. (6)
The moulds were removed after 24 hours. The specimens were kept immersed
in a clean water tank after marking the specimens with some notation. After curing
the specimens for a period of 7 and 28 days, the specimens were removed from the
tank and allowed to dry under shade. Later the specimens were tested for
Compressive strength, Tensile strength, and Flexural strength and Water permeability.
For each category of concrete mix two cubes, two cylinders, and two beams were cast
and tested for 7 and 28 days. A total of 45 specimens were tested.
7.0 RESULTS
The experimental results are tabulated as category wise as bellow. Graphs were also drawn for the experimental results.
Table 6: Strength values of 1: 1.45: 2.45:0.5 concrete mix with different percentage replacement of sand (fine aggregate) with fly ash for 7 days curing period
20 mm machine crushed aggregate
Type of mixw/c
Ratio% of sand
replaced with fly ash
Compressive strength N/mm2
Flexural strength N/mm2
Split Tensile strength N/mm2
PLAIN 0.50 0 13.729 2.042 1.71346 P 0.50 46 13.149 2.05 1.05147 P 0.50 47 21.218 3.053 2.22448P 0.50 48 21.896 3.025 2.25349P 0.50 49 22.05 3.124 2.31250P 0.50 50 21.952 3.126 2.32051P 0.50 51 22.983 3.213 2.30652P 0.50 52 23.557 3.215 2.2253P 0.50 53 23.31 3.152 2.23154P 0.50 54 23.306 3.125 2.1155P 0.50 55 23.204 3.126 2.16
Table 7: Strength values of 1: 1.45: 2.45:0.5 concrete mix with different percentage replacement of sand (fine aggregate) with fly ash for 28 days curing period20 mm machine crushed aggregate:
Type of mix
w/cRatio
% of sand replaced with
fly ash
Compressive strength N/mm2
Flexural strength N/mm2
Split Tensile strength N/mm2
PLAIN 0.50 0 21.28 4.02 2.3246 P 0.50 46 16.226 3.062 1.5547 P 0.50 47 29.231 4.321 3.12548 P 0.50 48 29.325 4.33 3.12149 P 0.50 49 29.318 4.325 3.25250 P 0.50 50 29.825 4.525 3.28
51 P 0.50 51 30.817 4.552 3.20252 P 0.50 52 30.925 4.654 3.15153 P 0.50 53 30.896 4.253 3.12554 P 0.50 54 30.892 4.551 3.10255 P 0.50 55 30.232 4.328 3.125
Compressive strength N/mm2 at the end of 7 days
05
10152025
Type of mix
com
pres
sive
stre
ngth
Compressive strength N/mm2 at the end of 28 days
05
101520253035
PLA
IN
46 P
47 P
48 P
49 P
50 P
51 P
52 P
53 P
54 P
55 P
Type of mix
Com
pres
sive
Stre
ngth
Flexural strength N/mm2 at the end of 7 days
0
0.5
1
1.5
2
2.5
3
3.5
PLA
IN
46 P
47 P
48P
49P
50P
51P
52P
53P
54P
55P
Type of mix
Flex
ural
Stre
ngth
Flexural strength N/mm2 at the end of 28 days
012345
Type of mix
Flex
ural
Stre
ngth
Split Tensile strength N/mm2 at the end of 7 days
0
0.5
1
1.5
2
2.5
PLA
IN
46 P
47 P
48P
49P
50P
51P
52P
53P
54P
55P
Type of mix
Split
Ten
sile
stre
ngth
Split Tensile strength N/mm2 at the end of 28 days
00.5
11.5
22.5
PLA
IN
46 P
47 P 48P
49P
50P
51P
52P
53P
54P
55P
Type of mix
Split
Ten
sile
St
reng
th
Table 8: Cost analysis for the M20 grade 1: 1.45: 2.45 of concrete for 1.00 cu.mSr.No
Type of concrete mixes
Cement Fly ash Sand Crushedmetal
Total
Cost per Kg (in Rs.) 2.6 0.30 0.42 0.43 -
1. PLAIN 1118 - 275 454 1847
2. 46 P 1118 90 149 454 1811
3. 47 P 1118 92 146 454 1810
4. 48P 1118 94 143 454 1809
5. 49P 1118 96 140 454 1808
6. 50P 1118 98 137 454 1807
7. 51P 1118 100 135 454 1807
8. 52P 1118 102 132 454 1806
9. 53P 1118 104 129 454 1805
10. 54P 1118 106 126 454 1804
11. 55P 1118 108 124 454 1804
Cost analysis for M20 mix for various proportions
178017901800181018201830184018501860
PLA
IN
46 P
47 P
48P
49P
50P
51P
52P
53P
54P
55P
Types of mix
Cost
in R
upee
s
RESULTS
The experimental results are tabulated as category wise as bellow. Graphs were also drawn for the experimental results.
DISCUSSIONS
When sand is partially replaced by fly ash by 50% (50P) the compressive strength, tensile strength, flexural strength of concrete reaches its maximum. The maximum strength is reached due to better packing and ball bearing effect produced by the spherical flyash particles and interspatial forces which influences both the hydration and packing efficiency of concrete. The strength is increased because of the improved deflocculating of cement agglomerates resulting in an increased rate of CaOH generated and stimulated pozzolonic activity in the fly ash.The high modulus of elasticity is achieved due to the fact that a considerable portion of unreacted fly ash consisting of glassy spherical particles act as tines to fill the voids present in fine aggregate.The strength is increased due to increased cohesiveness, total absence of bleeding and decreases in voids.
CONCLUSIONS
1. It has been observed that as the percentage of flyash increases the compressive strength increases initially, on further increase in its percentage reduces its compressive strength. It can be seen that when sand is partially replaced by flyash by 52% (52P) the compressive strength reaches its maximum for both 7 & 28 days curing period. The maximum compressive strength of flyash concrete (52P) is increased by 71.58% and 45.32% when compared to plain concrete (P) for 7 and 28 days curing period.
2. It has been observed that as the percentage of flyash increases the tensile strength increases initially, on further increase in its percentage reduces its tensile strength.It can be seen that when sand is partially replaced by flyash by 52% (52P) the tensile strength reaches its maximum for both 7 and 28 days curing period. The maximum tensile strength of flyash concrete (52P) is increased by 57.4% and 13.23%, when compared to plain concrete (P) for 7 & 28 days curing period.
3. It has been observed that as the percentage of flyash increases the flexural strength increases initially, on further increase in its percentage reduces its flexural strength. It can be seen that when sand is partially replaced by flyash by 52% (52P) the flexural strength reaches its maximum for both 7 and 28 days curing period. The maximum flexural strength of flyash concrete (52P) is increased by 34.61% and 35.81% when compared to plain concrete (P) for 7 & 28 days curing period.
10.0 REFERENCES
1. Sridhar B. and Nagi Reddy, K. 3rd International Conference-“Flyash Utilization and Disposal” by CBIP PIV 99-102 in 2003.
2. Balamukund, K. 3rd International Conference-“Flyash Utilization and Disposal” by CBIP PIV 94-98 in 2003.
3. Srirama R. and Zafarullah S.M., 'Fly ash Utilization" in India symposium organized by A.P.S.E.B in March' 89.
4. IS 516-1959: Methods of test for strength of concrete.5. IS 383-1970: Specification for coarse and fine aggregates from natural source
for concrete.6. IS 1199-1959: Methods of sampling and analyze of concrete.7. IS3512-1981: Specification for fly ash for use as pozzolana and admixture.8. IS: 383-1970, Specifications for Coarse and Fine Aggregates from
natural Sources for Concrete, Bureau of Indian Standards, New Delhi, India.
9. IS: 10262-1982, Recommended Guidelines for Concrete Mix Design, Bureau of Indian Standards, New Delhi, India
10. IS: 1199-1959, Indian Standard Methods of Sampling and Analysis of Concrete, Bureau of Indian Standards, New Delhi, India.
11. IS: 516-1959, Indian Standard Code of Practice-Methods of Test for Strength of Concrete, Bureau of Indian Standards, New Delhi, India.
