THE EFFECT OF RICE HUSK ASH ON STRENGTH AND PERMEABILITY OF
CONCRETE
IntroductionThe production of cement is costly, consumes
high energy, depletes natural resources and emits huge amounts of greenhouse gases (1 ton of cement production emits approximately 1 ton of CO2). Consequently, environmental degradation, pollution and health hazards problems associated with cement industries, have come under scrutiny.
So, now a day’s many people are trying to use industrial and agricultural wastes in concrete. These wastes otherwise pose several environmental problems.
ObjectivesTo investigate compressive strength
properties of concrete containing different percentage of Rice Husk Ash
To investigate the permeability properties of concrete containing different percentage of Rice Husk Ash
To determine the optimal replacement of cement with Rice Husk Ash, by comparing the results of compressive strength and permeability tests.
Methodology (Detail of Tests)
Name of test
Size of specim
en(mm)
No. of mix
No. of specimen for each mix
Total no. of
specimen
Compressive
strength test
150×150×150
4 (0%, 15%, 25%,
35%)
6 (3-7 Days, 3-28
Days)
24
Permeabilit
y Test
150x150x1
504 (0%,
15%, 25%, 35%)
6 (3-7 Days, 3-28
Days)
24
All the specimen were cast with M25
mix
The specimen
were taken out from the mould after
24 hours and cured for 7/28 days.
Specimen of cubes were tested for
‘Compressive Strength’
and ‘Coefficient
of Permeability’ and the final results
were analysed to
find the optimal
percentage replacement of cement with Rice Husk Ash
(RHA)
Methodology
Material used in the experimental investigation
Cement
Water
Coarse Sand
Rice Husk Ash
Coarse Aggregate
Continue……..
Ordinary Portland Cement of grade – 43 (source J.K Cement)
Rice Husk Ash used in the study has been obtained from NK Enterprises, Singhania House, Jharsuguda, Orissa, India
Water- Tap water was used in concrete masonry
Rice Husk Ash OPC
Fine Aggregates
Coarse Aggregates
Rice Husk Ash Rice husk is one of the main agricultural residues
obtained from the outer covering of rice grains during the milling process. Rice Husk Ash is obtained from burning of Rice Husk, which is the by-product of rice milling. It is estimated that 1,000 kg of rice grain produce 200 kg of Rice Husk after burn.
The rice husk ash had no useful application and had usually been dumped into water streams and caused pollution until it was known to be a useful mineral admixture for concrete.
Test on cement• Standard Consistency of the cement paste
= 29.5 • Initial setting time of cement = 115min• Final setting time of cement = 220min• Specific gravity of cement = 3.38Test on fine
aggregates• Fineness modulus of fine aggregates =2.50• Specific gravity of fine aggregates= 2.65
Test on coarse aggregates
• Specific gravity of coarse aggregates= 2.61
• Fineness modulus of coarse aggregates =7.68
Mix Design for M25 Grade Concrete
Table of final mix proportion (Wt. in Kg)/m3 concrete
Cement
Fine Aggrega
te
Coarse Aggrega
te
Water Cement
ratio
1 1.3 2.9 0.45
Preparation, casting and curing of concrete cubes
Testing Methods
Compressive strength test
Cube failure after compression test
Compression testing machine
Permeability
Permeability of concrete generally refers to the rate at which water or other aggressive substance (sulphates, chlorides ions, etc.) can penetrate concrete.
Low permeability of concrete to moisture and gas is the first line of defence against: frost damage, acid attack, sulphate attack, corrosion of steel embedment and reinforcements, carbonation, alkali-aggregate reaction, and efflorescence.
Methods For Testing Permeability(IS 3085:1965)
Constant flow Method
Darcy’s law has been used to determine the co-efficient of permeability.
The equation used is
Ks=
Where, Ks - Coefficient of saturated permeability (m/s)
Q - Volume of flow rate (m3/s) A -Cross-sectional area (m2) L -Specimen thickness in the direction of flow
(m) H - Head of water causing flow (m)
Permeability test
Permeability apparatus Permeability mould
Water reservoir and pressure controler
Air Chamber
Continue……
Permeability test Set-Up (Schematic)Typical Details of Permeability Cell
Sealing of specimen
(1) Filling pieces of jute rope (2) Filling mixture of lac & wax
(3) Filling Epoxy injection grout (4) Applying Sikadur 31 compound(Epoxy Grout)
Leakage testing & Running the test
Fill the water reservoir and apply the desired pressure (10 Kg/cm2) and note the initial gauge reading.
After steady state of flow is reached, put the empty beaker below the mould and note the time and pressure on the gauge
Note the discharge passed in a particular time interval and at an average pressure on gauge.
From the Darcy's law find the coefficient of permeability.
Result and Discussion
Type of
MixRHA (Kg) OPC (Kg)
Compressi
ve
Strength
(MPa)
Average
Compress
ive
Strength
(MPa)
Percentage
Improvement
w.r.t. M0 Mix
M0
(0%)
19.84
21.24
20.56
20.55 ----
M1
(15%)
24.40
24.91
25.46
24.92 17.54
M2
(25%)
24.76
21.05
21.50
22.44 8.42
M3
(35%)
19.00
18.10
17.16
18.08 -13.66
Values of Compressive Strength (7-days curing)
Continue……
Type of
MixRHA (%)
Compression
Strength
(MPa)
Average
Strength
(MPa)
Ratio of
RHAC/OPC
Percentage
Improvement
w.r.t. OPC
M0 0%33.41
31.23
30.30
31.64 ---- ----
M1 15%34.26
34.56
35.00
34.61 1.09 8.58
M2 25%33.35
33.20
31.80
32.78 1.03 3.47
M3 35%30.20
29.78
28.98
29.65 0.93 -6.71
Values of Compressive Strength (28-days curing)
Compressive Strength of different mixes (7 & 28 days)
M0 M1 M2 M30
5
10
15
20
25
30
35
40
20.55
24.92
22.44
18.08
31.64
34.61
32.78
29.65
7 days
28 days
Concrete Mix
Co
mp
ressiv
e S
tre
ng
th (
MP
a)
Permeability test results
Mix
Sampl
e
Discharge
Q (ml)
Time
T (Hrs)
Head of
water
H (m)
Co-efficient of
permeability,
K(m/sec) X 10-12
Avg.
K(m/sec) X
10-12
M0 16
18
18 68.67
71.12
23.97
26.04
25.01
M1 12
14
18 73.58
76.03
16.78
18.94
17.86
M2 7
10
18 66.22
78.48
10.88
13.11
12.00
M3 15
16
18 68.67
73.58
22.47
22.37
22.42
Values of coefficient of permeability for 7-days water curing
Coefficient of permeability of RHAC at 7-days water curing
M0 M1 M2 M30
5
10
15
20
25
30
25.01
17.86
12
22.42
Concrete Mix
Coe
ffic
ien
t of
Per
mea
bili
ty (
10-1
2 m
/s)
Continue……
Mix
Sampl
e
Discharge
Q (ml)
Time
T (Hrs)
Head of
water
H (m)
Co-efficient of
permeability,
K(m/sec) X 10-12
Avg.
K(m/sec) X
10-12
M0 8
10
18 63.77
63.77
12.91
16.13
14.52
M1 6
7
18 68.67
71.12
8.99
10.13
9.56
M2 4
4
18 73.58
71.12
5.6
5.77
5.69
M3 9
8
18 66.22
68.67
13.98
12.0
13.00
Values of coefficient of permeability for 28-days water curing
Coefficient of permeability of RHAC at 28-days water curing
M0 M1 M2 M30
2
4
6
8
10
12
14
16
14.52
9.56
5.69
13
Concrete Mix
Coe
ffic
ien
t of
Per
mea
bili
ty (
10-1
2 m
/s)
Coefficient of Permeability of all mixes at both 7 and 28-days water curing
M0 M1 M2 M30
5
10
15
20
25
30
25.01
17.86
12
22.42
14.52
9.56
5.69
137 days
28 days
Concrete Mixes
Coe
ffic
ien
t of
Per
mea
bili
ty (
10-1
2 m
/s)
Permeability of concrete is influenced primarily by following factors:
The nature of the hardened cement paste Porosity and interconnectivity of pores in the
cement paste and micro-cracks in the concrete.
w/c ratioDegree of hydrationThe degree of compactionThe type and quantity of constituent
materials. (fine cement tends to reduce permeability, well graded aggregate tends to decrease permeability)
Conclusions
The coefficient of permeability of RHAC is significantly lower than that of OPC for all percent changes.
The coefficient of permeability of RHAC decreases for 15 % & 25 % replacement but it starts increasing at 35% replacement for cement.
The permeability of OPC and RHAC decreases with increase in curing period of samples.
The addition of RHA had a significant effect on the compressive strength of concrete. Compressive strength of concrete increases with the addition of RHA upto a certain level, after which it decreases.
Optimal cement replacement level (by RHA) is 25%, for which the compressive strength is maximum.
Continue……. The compressive strength is maximum at 15%
replacement and then it starts decreasing for both 7 and 28 days cured specimens.
With 25% replacement the compressive strength of cubes is nearly equal but slightly above then the OPC mix concrete specimens, but at 35% replacement the strength is less then the OPC mix for both 7 and 28 days cubes.
The compressive strength of OPC & RHAC increases with increase in curing period of samples.
The permeability of all mixes decreases with increase in compressive strength as compared to control concrete mix accept at 25% replacement.
Continue…….The results obtained from this study
indicates that up to 25% of RHA could be advantageously blended with cement without adversely affecting the strength and permeability properties of concrete.
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