The document summarizes the results of an experimental study on the shear strength properties of mixtures containing fly ash, electroplating waste sludge, and cement. Undrained unconsolidated triaxial compression tests were performed on cylindrical specimens at different curing periods. The following key results were reported: 1) The maximum shear strength of 2.48 MPa was achieved for a mixture containing 47% fly ash, 45% waste sludge, and 8% cement after 90 days of curing, compared to only 0.10 MPa for fly ash alone. 2) Increasing the waste sludge content and curing time improved the shear strength and shear strength parameters of the mixtures. The mixture with 60% fly

1. International Journal of Civil Engineering and OF CIVIL
Technology (IJCIET), ISSN 0976 – 6308
INTERNATIONAL JOURNAL 2, February (2014),ENGINEERING
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pp. 25-32 © IAEME
AND TECHNOLOGY (IJCIET)
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STRENGTH OF FLY ASH MIXED WITH WASTE SLUDGE
Dr. Malik Shoeb Ahmad
Civil Engineering Department, Z.H. College of Engineering & Technology
Aligarh Muslim University, Aligarh-India
ABSTRACT
The strength of fly ash-electroplating waste- cement mix were determined by undrained
unconsolidated (UU) triaxial shear tests conducted on cylindrical specimens of diameter 39 mm and
length 84 mm, prepared for fly ash and different combination of fly ash-waste sludge-cement mixes.
The tests were carried out at different curing periods of 7, 28 and 90 days. The shear strength
parameters and undrained shear strength of fly ash and mix blends were determined. The outcome of
the test results was quite encouraging in terms of undrained shear strength and shear strength
parameters. The maximum gain in shear strength was obtained at 90 days of curing for the mix
47%FA+45%S+8%C (2.48 MPa) as compared to fly ash (0.10 MPa) for the same curing period.
KEYWORDS: Fly Ash; Shear Strength; Waste Sludge, Triaxial Shear Test.
1.
INTRODUCTION
The demand of power is increasing day by day. Major part of the power is supplied by Thermal
Power Plants where coal is used as fuel and a large quantity of fly ash emerges in the process. Fly ash
creates different environmental problems like leaching, dusting and takes huge disposal area.
Transforming this waste material into a suitable construction material may minimize the cost of its
disposal and in alleviating environmental problems. Fly ash has become an attractive construction
material because of its self hardening character which depends on the availability of free lime in it.
The variation of its properties depends on nature of coal, fineness of pulverization, type of furnace,
and firing temperature. According to ASTM C 618[1] classification, fly ashes fall in two types; Class
C and Class F. Class C fly ash high in calcium content undergoes high reactivity with water even
without addition of lime [2]. Class F fly ash contains lower percentages of lime. It lacks adequate
shear strength for use in geotechnical applications and requires stabilization with lime or cement and
some admixtures to accelerate shear strength gain in short period. The fly ash studied in the present
25

2. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 25-32 © IAEME
investigation belongs to Class F. Various studies on application of fly ash as bulk fill material are
available [3-5] which demonstrated the possibility of utilizing huge amount of fly ash in construction
of embankments, dykes, and road subgrade. [6] demonstrated the use of fly ash as foundation medium
reinforced with jute-geotextiles. They showed through unconfined compression test results that lime
stabilization enhanced the strength of stabilized fly ash at elevated temperature or with long curing
period. [7] reported the unconfined compressive strength and undrained triaxial strength for fly ash.
Undrained shear strength parameters of solid waste incinerator fly ash stabilized with lime and cement
were reported by [8]. The shear strength of geofibre reinforced fly ash was investigated by [9-10] but
the strength characteristics of Class F fly ash mixed with waste sludge and cement have not received
much attention by the previous researchers.
2.
TEST MATERIALS
In this study, the materials used are Fly ash; Electroplating Waste Sludge; Lime and Cement.
2.1
FLY ASH
Fly ash was procured from Harduaganj thermal power plant located at 16 km from Aligarh
City, Uttar Pradesh, India. This power plant consist of 440 MW pulvarised coal units, producing 25
trucks of fly ash and bottom ash per day which is about 1500 tonnes fly ash and 500 tonnes of
bottom ash. For the present investigation, dry fly ash from hoppers is collected in polythene bags.
2.1.1
Physical Properties
Colour= Grey, Percent finer= 88%, Size of the particle= 0.002-0.30mm, Maximum dry
density (MDD)= 9.30 kN/m3, OMC= 27.5%, Specific gravity = 2.02, Surface area= 3060 cm2/g
Unburnt carbon= 11.80% and Classification = ML as per IS: 1498-1987.
2.1.2
Chemical Composition
The chemical composition of fly ash are SiO2= 54.0, Al2O3= 24.0, Fe2O3= 12.0, CaO = 2.0,
MgO= 1.0, SO3= 0.3 and Loss on Ignition (Percent by Weight) = 1.5 %.
2.2
ELECTROPLATING WASTE SLUDGE
The electroplating waste sludge was collected in the form of filter cake, comprises of 70%
solid waste and 30% waste water. The solid waste includes chemicals, heavy metals and metallic
dust. Heavy metal analysis was carried out using GBC-902 atomic absorption spectrophotometer
(AAS). The heavy metals concentration in the electroplating waste sludge was found as Nickel= 610,
Chromium= 630, Zinc= 800, Cadmium= 025, Copper= 300 and Lead = 005 ppm.
2.3
Lime
The finely powered white coloured lime was used as precipitator having the chemical
composition such Assay= 95, Chloride = 0.01, Sulphate=0.2, Aluminium, iron and insoluble
matters=1.0, Arsenic=0.0004 and Lead =0.001%.
2.3
Cement
The cement used in this study was OPC-43 grade. The test on cement was conducted in
accordance with IS: 269-1989. The physical properties of cement are Specific surface cm2/gm=
3175, Soundness in mm = 3.30, Compressive strength in MPa at 3 & 7 days = 14.3 & 23.5, Setting
time (minutes) = 100(Initial) & 290(Final), Specific gravity = 3.13 and Normal consistency (water in
% of cement by weight) = 27.5.
26

3. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 25-32 © IAEME
3.
PREPARATION AND TESTING OF SPECIMENS
The preparation and testing of specimens for triaxial compression tests has been carried out in
accordance with the IS: 2720 (Part 11–1993). The standard Proctor compaction tests were carried out
using equipment and procedure as specified in IS: 2720 (Part 7–1987) equivalent to (ASTMD 698–
2000a) to obtain Maximum Dry Density (MDD) and Optimum Moisture Content (OMC) of fly ash
and fly ash-waste sludge mixes. The OMC of the fly ash was obtained as 27.5% which also satisfies
the IS: 456 (2000) requirements (i.e., 25% water by weight of cement is to be added to cement
mortar for chemical reactions).
First of all the lime precipitated electroplating waste sludge was dried in oven for 24 hours,
pulverized and sieved through 425µ IS sieve. Fly ash was dried in oven for 24 hours and sieved
through 425µ IS sieve. A known quantity of fly ash, fly ash–waste sludge, fly ash-cement and fly
ash–waste sludge–cement mix were taken and water equal to OMC was added. The material was
thoroughly mixed to achieve uniform mixing of water. The wet mix was then placed in split mould
for casting the remolded cylindrical specimens having diameter as 39 mm and length 84 mm, for
triaxial compression test as described in the IS: 2720 (Part 11–1993).
4.
RESULTS AND DISCUSSION
The results of triaxial compression tests (UU-test) on aged/cured specimens of fly ash, fly
ash-waste sludge, fly ash–8% cement and fly ash–waste sludge–8% cement are shown in Table. The
tests were conducted under confining pressures of 0.05, 0.10 and 0.15 MPa at 7 and 28 days of
curing. The results show that:
(i)
(ii)
(iii)
(iv)
(v)
(vi)
(vii)
(viii)
(ix)
The confining pressures have a significant effect on deviator stresses. The deviator stresses
at failure after 90 days of aging are 0.171 MPa, 0.235 MPa and 0.253 MPa at confining
pressures of 0.05 MPa, 0.10 MPa and 0.15 MPa respectively.
The shear strength of fly ash improves on aging. The improvement in shear strength is of the
order of 12.5% and 25% at 28 and 90 days of aging respectively (Fig. 1).
The average undrained cohesion values have been observed as 0.04 MPa and 0.043 MPa at
28 and 90 days of aging respectively. The gain in the cohesion due to aging is 33% and 43%
respectively, when compared with 7 days of aging.
The shear strength of the mix increases with increase in the waste sludge content and curing
periods. Amongst all the combinations of mixes, 60%FA+40%S mix exhibits highest shear
strength of 1.53 MPa at 28 days of curing, which is 17 times more than the shear strength of
fly ash at the same curing period.
The average peak friction angle (¢) for the mix 60%FA+40%S has been increased
significantly from 150 (fly ash) to 330 at 7 days of curing.
The similar trend has also been observed at 28 days of curing i.e., the value of average peak
friction angle (¢) increased from 15.20 (fly ash) to 410 of this mix.
The value of average undrained cohesion (c) of this mix has been observed as 1.13 MPa at
28 days of curing, which is 2725% more than the value of cohesion of fly ash for the similar
curing period.
The increase in the shear parameters of this mix, clearly demonstrates the existence of an
interaction effect that involves the confining pressure and curing periods on the peak
strengths.
Amongst all combinations of the mixes, mix 50%FA+50%S has the lowest shear strength
0.74 MPa at 28 days of curing.
27

4. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 25-32 © IAEME
(x)
(xi)
(xii)
(xiii)
(xiv)
(xv)
(xvi)
(xvii)
(xviii)
(xix)
The addition of cement has increased the deviator stress and shear strength parameters due
to availability of cement for pozzolanic reaction.
The rate of gain of shear strength of the mix 92%FA+8%C is 0.59 MPa which is 556% more
than the fly ash (0.09 MPa) at 28 days of curing. The gain in the shear strength continues
further at 90 days of curing (Fig. 2).
The average peak friction angle (¢) of the mix has been increasing significantly from 15.20
(fly ash) to 390 at 28 days of curing. The gain in the ¢ value is observed as 157%.
The value of average undrained cohesion (c) of the mix has been observed as 0.41 MPa at 28
days of curing, which is 925% more than that of fly ash.
The gain in the average values of peak friction angle and undrained cohesion has been
continued further at 90 days of curing as well.
It is envisaged from the test results that the contribution of waste sludge with cement in fly
ash at longer periods of curing is significant. Amongst all the combinations of mixes,
47%FA+45%S+8%C mix exhibits maximum shear strength of 2.15 MPa at 28 days of
curing, which is 24 times more than the fly ash.
The shear strength of this mix at 90 days of curing has been observed as 2.48 MPa, which is
25 times more than the fly ash at 90 days of curing (Fig. 3).
The percent gain in average undrained cohesion (c) of this mix with respect to fly ash at 28
days of curing is 3350%. Whereas, the increase in c value at 90 days is 4272%.
The average peak friction angle (¢) of this mix has been increased significantly from 15.20
(fly ash) to 420 at 28 days of curing. The gain in the (¢) value observed as 176%. The
improvement in the (¢) value continues at 90 days (500), which is 190% more than fly ash.
The decrease in the shear strength of this mix might also be attributed due to the presence of
excess amount of sulphate and lime added with the waste sludge in the mix, causing
development of shrinkage cracks due to formation of ettringite and progressive carbonation
reaction which eventually leads to depletion of portlandite. Subsequently decalcification of
C-S-H results in deterioration in the strength of the mix. The failure pattern of the samples is
shown in Fig. 4.
1.6
0.30
0.05 MPa
0.25
0.05 MPa
0.10 MPa
1.4
0.10 MPa
0.15 MPa
0.15 MPa
Deviator Stress (MPa)
Deviator Stress (MPa)
1.2
0.20
0.15
0.10
0.05
1.0
0.8
0.6
0.4
0.2
0.0
0.00
0.00
1.00
2.00
3.00
4.00
5.00
0.0
2.0
4.0
6.0
Axial Strain (%)
Axial Strain (%)
Fig. 1: Stress-Strain Behaviour of
Fly ash at 90 days of Curing
Fig. 2: Stress-Strain Behaviour of
92%FA+8%C at 90 days of Curing
28
8.0

5. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 25-32 © IAEME
4.0
0.05 MPa
3.5
0.10 MPa
0.15 MPa
Deviator Stress (MPa)
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0.0
1.0
2.0
3.0
4.0
Axial Strain (%)
5.0
Fig. 3:Stress-Strain Behaviour of
47%FA+45%S+8%C at 90 days of Curing
Fig. 4: Specimen after Failure
Table: Shear Strength Behaviour of Fly ash, Fly ash-Waste Sludge, Fly ash-Cement and Fly
ash-Waste Sludge-Cement Mix
Mix
Curin
g
Period
(days)
(1)
(2)
7
Fly ash
28
90
7
70%FA+30%S
28
7
65%FA+35%S
28
Confin
ing
Pressu
re
(MPa)
(3)
0.05
0.10
0.15
0.05
0.10
0.15
0.05
0.10
0.15
0.05
0.10
0.15
0.05
0.10
0.15
0.05
0.10
Failur
e Load
(N)
Deviator
Stress
(MPa)
Average Angle of
Shearing
Resistance
(degree)
Average
Undrained
Cohesion
(MPa)
Average
Shear
Strength
(MPa)
(4)
99
155
187
202
272
287
214
294
316
1422
1488
1567
1676
1845
1910
2012
2165
(5)
0.081
0.125
0.150
0.161
0.217
0.230
0.171
0.235
0.253
1.105
1.156
1.218
1.302
1.434
1.484
1.563
1.682
(6)
(7)
(8)
15.1
0.03
0.08
15.2
0.04
0.09
17.2
0.043
0.10
21.2
0.57
0.76
28.9
0.66
0.92
28.0
0.85
1.14
0.15
0.05
0.10
0.15
2234
2535
2616
2765
1.736
1.970
2.033
2.149
29.4
0.97
1.32
29

6. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 25-32 © IAEME
(1)
(2)
7
60%FA+40%S
28
7
55%FA+45%S
28
7
50%FA+50%S
28
7
92%FA+08%C
28
90
7
62%FA+08%C+
30%S
28
90
(3)
(4)
(5)
0.05
0.10
0.15
0.05
0.10
0.15
0.05
0.10
2295
2378
2605
2408
2714
2876
2324
2409
1.783
1.848
2.024
1.871
2.109
2.235
1.806
1.872
0.15
0.05
0.10
0.15
0.05
0.10
0.15
0.05
0.10
0.15
0.05
0.10
0.15
0.05
0.10
0.15
0.05
0.10
0.15
0.05
0.10
0.15
0.05
0.10
0.15
0.05
2458
2587
2603
2713
1479
1544
1596
1270
1356
1378
763
1003
1107
1134
1426
1578
1270
1569
1736
1780
1987
2132
2430
2690
2860
3120
1.910
2.010
2.023
2.108
1.158
1.209
1.259
1.010
1.083
1.101
0.593
0.779
0.860
0.881
1.109
1.226
0.987
1.220
1.349
1.383
1.544
1.657
1.888
2.090
2.222
2.424
0.10
3456
2.686
0.15
57%FA+08%C+
35%S
7
28
90
3786
2278
2378
2634
3462
3552
3894
3506
4067
4319
1.775
1.848
2.052
2.690
2.760
3.026
2.766
3.160
3.356
(7)
(8)
33.7
1.00
1.35
40.5
1.13
1.53
20.1
0.93
1.19
19.9
0.98
1.26
18.7
0.52
0.69
19.6
0.57
0.74
35.3
0.34
0.50
39.0
0.41
0.59
41.0
0.45
0.71
35.4
0.67
0.97
38.8
0.87
1.26
46.2
1.04
1.53
36.2
0.90
1.26
40.0
1.20
1.71
48.8
1.41
1.96
2.942
0.05
0.10
0.15
0.05
0.10
0.15
0.05
0.10
0.15
(6)
30

7. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 25-32 © IAEME
(1)
(2)
7
52%FA+08%C+
40%S
28
90
7
47%FA+08%C+
45%S
28
90
7
42%FA+08%C+
50%S
28
90
5.
(3)
(4)
(5)
0.05
0.10
0.15
0.05
0.10
0.15
0.05
0.10
0.15
0.05
0.10
0.15
0.05
0.10
0.15
0.05
0.10
0.15
0.05
0.10
0.15
0.05
0.10
0.15
0.05
0.10
0.15
3053
3281
3441
4136
4237
4612
4356
4788
5198
3218
3357
3678
3489
3716
3978
3819
4387
4578
718
805
961
922
1194
1287
1067
1269
1339
2.372
2.550
2.674
3.214
3.292
3.602
3.385
3.720
4.039
2.584
2.729
2.939
2.829
3.028
3.234
3.051
3.505
3.658
0.588
0.658
0.787
0.766
0.978
0.973
0.880
1.037
0.973
(6)
(7)
(8)
37.0
1.19
1.65
42.6
1.38
1.97
50.0
1.65
2.29
39.0
1.30
1.80
42.0
1.61
2.15
50.0
1.88
2.48
30.0
0.30
0.46
33.4
1.19
1.43
25.2
0.38
0.56
CONCLUSIONS
The following conclusions may be drawn from the test results of these studies.
(i)
(ii)
(iii)
(iv)
(v)
The mix containing 70%-55% fly ash and 30%-45% waste sludge has been showing good shear
and bearing strength characteristics.
Addition of small percentage of cement (8%) along with waste sludge to fly ash enhances the
shear and bearing strengths at early stage of curing.
The shear and bearing strengths of fly ash were increased to manifolds on addition of waste
sludge and cement to it.
The shear strength parameters ‘c’ and ‘φ’ of fly ash have been increased to 4272% and 191%
respectively, for 47%FA+45%S+8%C mix at 90 days of curing.
Amongst all combinations of mixes, mix 42%FA+50%S+8%C exhibits lowest shear strength
of 1.43 and 0.56 MPa at 28 and 90 days of curing respectively.
31

8. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 5, Issue 2, February (2014), pp. 25-32 © IAEME
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