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PARTIAL CEMENT REPLACEABLE MATERIALS
BY
A.RAGHU TEJA B.K.CHAITANYA
III/IV B.Tech(civil) III/IV B.Tech(civil)
[email protected] [email protected]
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CONTENTS
1. Abstract
2. Introduction
3. Experimental plan
a) part I
b) part II
4. Materials Required
5. Test results and discussions
6. Compressive strengths of mortars
7. Acidic resistance of mortars
8. Conclusions
9. References
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ABSTRACT
An experimental program is conducted to develop new kinds of pozzolana from
other agricultural wastes apart from rice husk and rice straw. The study
investigated the use of coconut husk, corn cob and peanut shell ash as cement
replacement materials. A series of tests were performed to determine the chemical
composition of coconut husk ash, corn -cob ash and peanut shell ash which are
referred to as CHA, CCA and PSA respectively. The mechanical properties of paste
and mortar containing different percentages of ash replacement were investigated.
``Experimental results revealed that coconut husk ash and corn cob ash cannot be
utilized as pozzolona while peanut shell ash can be classified as Class ‘C’ pozzolona
according to ASTM Standards. Corn cob ash mortars possessed higher compressive
strength. Among the four types of mortars tested for chemical attack, PSA mortars
showed higher resistance against acidic attack.
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INTRODUCTION
Many developing countries are attempting to develop substitutes for cement from locally
available raw materials like agricultural and industrial wastes. Fly ash (F.A) and rice-
husk ash (RHA) have already been proven to be economical as partial substitutes for
cement. These can replace cement up to 50 %. The researches carried out so far revealed
that reactive RHA could be produced by controlled burning of rice husk and grinding it to
a certain degree of fineness. Further more, RHA satisfies the minimum requirements of
ASTM class N, F and C pozzolona . Rice straw is another agricultural waste which is also
readily available in abundance in rice growing countries. But rice straw cannot be
considered totally as an agricultural waste since it can also be used in animal feeding,
mushroom production, paper manufacturing and pyrolosis. Rice straw ash (RSA) is also a
good partial substitute for cement. It was found that the compressive strength of RSA
concrete is slightly higher than ordinary Portland cement (OPC) and RHA concrete.
Other possible agricultural products which could be used as pozzolona are
coconut husk, corn cob and peanut shell. Coconut is readily available and abundant in
rural areas. Like rice straw, coconut husk is not totally regarded as agricultural waste
because it can be used for different purposes. Coconuts are the staff of life of tropics.
Some tropical people called it “THE TREE OF LIFE” because the meat and milk of the
nut give them food and drink; the trunk of the tree produces beautiful and durable wood
for their homes. Floor mats and clothing can also be made from the coconut husk ash.
The corn cob is about 16 % to 20 % by weight of the whole unshelled corn. Due
to the presence of many mechanical corn Sheller, a large volume of corn cob is produced
in one day operation and is normally utilized as fuel. One sack of dry corn cob weighs
approximately 25 kilogram.
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The shell of peanut is approximately 30 % by weight of a given amount of
unshelled peanut. Like corn, a mechanical Sheller has been developed for peanut. Peanut
shell can also be used as a fuel but most farmers dispose it in the field to improve the soil
condition for planting. Considering the abundance of coconut husk, and peanut shell in
rural areas, an attempt is made to utilize these three agricultural products as low-cost
construction materials. This research was conducted to investigate the potential of
coconut husk, corn cob, and peanut shell as partial substitutes for Portland cement. Figs
1-3 show different parts of coconut, corn and peanut respectively.
EXPERIMENTAL PLAN
The coconut husk ash, corn cob ash and peanut shell ash which are here in after
referred to as CHA, CCA, and PSA respectively will be obtained by burning the coconut
husk, corn cob and peanut shell in a ferrocement incinerator which .After burning the
ashes will be ground in the grinding machine .For simplicity, the time of grinding will be
kept constant at one hour through out the - experimental work.
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The experimental program is dived in to two parts as follows:
PART 1 - Properties of Coconut Husk Ash, Corn Cob Ash and Peanut shell
Ash
An investigation on the physical and chemical properties of CHA, CCA and
PSA is conducted in this part. The physical properties considered are the strength activity
index, specific gravity and fineness. The chemical composition of each type of ash is also
obtained. All testing procedures are based on ASTM standards.
PART 2 - Compressive strengths and Acidic Resistances of Mortars
{a} The compressive strengths at different ages of mortars containing different types of
ash are determined. Four different mixes for OPC, CHA, CCA and PSA mortars having a
consistency equivalent to 105 % -- 115 %. Flow values are tested for 0 – 40 %
replacement by weight of cement. The samples are tested after curing for periods of 3, 7
and 28 days
{b} The resistance against acidic attack of mortars is determined by immersing the
tested specimen in 10 % HCL and 10 % sulphuric acid solution for 30 days and the
losses of weight are obtained. This was conducted for CHA, CCA, PSA, and RHA
mortars under saturated surface and oven dry conditions.
MATERIALS REQUIRED:
Coconut Husk, Peanut shell and corn cob .
CEMENT
Ordinary Portland cement. This was selected in order to compare the testing results with
previous researches on rice husk and rice straw ash.
MIXING WATER
Ordinary tap water was used for all mortars and pastes
FINE AGGREGATE
Natural river sand passing sieve number 30 and retained on sieve number 100 was used
through out the experiment.
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TEST RESULTS AND DISCUSSIONS:
PART 1 – Properties of Different types of Ashes.
Chemical Analysis of Ashes
The ash obtained by burning coconut husk in the ferrocement incinerator was
found to posses a darkish grey color. The ash produced is only 2.8 % by weight of the
unburnt coconut husk. This means that burning 25 kg of coconut husk which is the
capacity of the small ferrocement incinerator produces only 0.7 kg of ash in one hour.
The color of ash produced by corn cub is also darkish gray and its weight is only 1.43 %
of the unburnt corn cob it takes approximately two hours to burn 75 kg of corn cob.
Peanut shell when burnt in the same incinerator produces a brownish color ash which is
12% by weight of the unburnt peanut shell. The burning of 45 kg of peanut shell requires
approximately 5 hours. The maximum recorded temperature inside the ferrocement
incinerator was 750 degree Centigrade
The chemical analyses`of these ashes were performed by the laboratory of Siam
City Cement Co; Ltd. Factory located in Saraburi, Thailand. The results of chemical
analysis are shown in Table. These properties were also compared with different
pozzalanas namely rice husk ash, rice straw ash and sugar cane bagasse ash in Table 2. In
Table 3, a comparison of these ashes is made with the ASTM requirements for class N, F
and C pozzalans.
It can be observed from Table 1 that PSA has higher SiO2 , CaO contents which
are major composition of hardened cement gel than those of CHA and CCA. The
hardend cement gel than those of CHA and CCA. The hardened cement gel is composed
of Tricalcium silicate (C3S) , Dicalcium silicate(C2S), Tri calcium Alluminate (C3A),
Tetra calcium Alumino Ferrite (C4AF). Among these three ashes, PSA also has the lower
total amount of minor compounds namely Mgo,Mno,Cl respectively. The oxides of
sodium and potassium, Na2O, K2O, known as alkalis. They have been found to react with
some aggregates; the products of the reaction could lead to the disintegration of the
concrete. It has also been observed that the affect of the rate of the gain of strength.
Therefore the presence of large amount of these two alkalis requires special attention. As
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observed from the table, PSA shows lesser amount of these two alkalis than CHA and
CCA. Another which affects the strength is the loss of ignition. It was found that greater
amount of ignition loss results in loss of strength. Considering this factor, PSA is found
to be better than CHA and CCA.
Comparing with other pozzolanas, the silica content of PSA is lower than that of rice
husk ash.
TABLE 1:
Chemical composition Coconut
Husk Ash
(CHA)
Corn cob
Ash
(CCA)
Peanut shell
Ash
(PSA)
Ordinary
Portland
Cement(OPC)
Silicon dioxide
Aluminium oxide
Iron oxide
Calcium oxide
Magnesium oxide
Sodium oxide
Potassium oxide
Sulphate
Chloride
Manganese oxide
Loss on ignition
25.68
1.74
2.65
4.08
5.38
8.40
31.23
0.71
0.61
0.05
29.80
37.26
1.09
2.78
2.10
3.15
0.04
37.09
0.75
0.12
0.08
16.18
44.57
15.12
7.56
7.69
1.65
0.12
6.06
1.10
----
0.27
9.75
21.30
4.96
3.10
66.61
1.81
0.21
0.50
2.27
-----
-----
0.74
Physical properties
Blaine fineness
Specific gravity
2823.00
2.23
1036.00
2.21
5292.00
2.56
------
------
The test results for strength activity index of PSA and CCA mortars are tabulated
in table3. The results showed that the strength activity index of peanut shell ash with
Portland cement at 28 days is 95.02% and its water requirement is 99.6%. It can be
observed therefore that the addition of PSA to Portland cement reduces the amount of
water required for a given slump. Similar test was performed with ages of 3 and 7 days to
determine the early strength activity of PSA. The strength activity of PSA with Portland
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cement at ages 3 and 7 days is 117.34% and 106.4% respectively. It can be seen that PSA
has a greater early strengths compared to OPC at the ages of 3 and 7 days but becomes
lower at the age of 28 days. The high early strength of PSA is due to the presence of high
alumina. One feature of high alumina cement is its high rate of strength development.
The high rate of strength gained is due to C3A which has the highest rate of strength
development, resulting in the formation of CAH10 a small quantity of C2AH8 and alumina
gel. The strength activity index of corn cob ash at 28 days is 38.96% with a water
requirement of 102.4%. The addition of CCA in portland cement increases the amount of
water requirement. It can also be seen from table that its strength activity indices at ages
3 and 7 days are only 39.69% and 43.08% respectively. The low compressive strengths of
CCA are probably due to its high amount of alkalis and loss of ignition as in table2.
TABLE 2:
Chemical
composition
CHA CCA PSA SCBA RHA RSA
Silicon dioxide 25.68 37.26 44.57 65.8 92.05 65.94
Aluminium
oxide
1.74 1.09 15.12 5.5 0.94 0.99
Iron oxide 2.65 2.78 7.56 3.3 0.81 0.65
Calcium oxide 4.08 2.10 7.69 4.2 0.27 4.27
Magnesium
oxide
5.38 3.15 1.65 1.7 0.27 1.97
Sodium oxide 8.40 0.04 0.12 0.6 0.06 0.23
Potassium oxide 31.23 37.09 6.06 7.5 1.72 11.66
Sulphate 0.71 0.75 1.10 2.0 0.13 0.45
Chloride 0.61 0.12 ----- ----- ----- -----
Manganese
oxide
0.05 0.08 0.27 ----- ----- -----
Loss on ignition
29.80 16.18 9.75 9.4 3.19 13.46
Physical properties
Percent of ash
after burning
2.8 1.43 12 3.2 18-20 15
Blaine fineness 2823 1036 5292 15040 14300 12860
Specific gravity 2.23 2.21 2.56 2.308 2.085 2.240
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TABLE 3:
PART 2:Compressive Strength & Acidic Resistance Of Mortars
Compressive strength of Mortars:
Table 4 shows the comparison of compressive strengths at different ages of OPC,
CHA,CCA, PSA mortars having percentage of cement replacement. It can be observed
that among three types of ashes investigated in this study, coconut husk ash exhibits very
low compressive strengths as compared to corn cob ash and peanut shell ash. Evidently
the use of peanut shell ash as cement replacement up to 40% in mortar results in a high
strength matrix. It is of interest to note that for CCA mortars, the compressive strengths at
different ages of samples increase as the percentage of cement replacement is increased
from 20% to 40%. On the contrary, the compressive strengths of PSA mortars decrease as
the percentage of cement replacement is increased.
Property Pozzolona Class#
CHA CCA PSA
Chemical properties
N P C
Moisture content(%) 3.0 3.0 3.0 -- -- --
Loss of ignition % 10.0 12.0 6.0 29.80 16.18 9.75
SiO2+Al2O3+Fe2O3
(%)
2.65 2.78 7.56 3.3 0.81 0.65
SO3 4.0 5.0 5.0 0.71 0.75 1.10
MgO 5.0 5.0 5.0 5.38 3.15 1.65
Na2O 1.50 1.50 1.50 8.40 0.04 0.12
Physical properties
Fineness: Amount retained
On sieve no:325(%)
34 34 34 0.60 33.20 4.20
Pozzolanic activity index
With Portland cement at
28 days.
75 75 75 -- 38.96 95.02
Water requirement max % of
control
115 105 105 -- 102.5 99.6
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Acidic resistance of Mortars:
Resistance against sulphate attack:
Hardened concrete when present in sulphate solution results in expansion and
disruption of concrete. This phenomenon is called ‘sulphate attack.’ Attack of cement can
thus take place when sulphate reacts with Ca (OH)2 and with calcium aluminate hydrate.
The products of reactions which are the gypsum and calcium sulphoaluminate, having
considerably greater volume than the compounds they replace, so that the reactions with
sulphates lead to expansion and disruption of concrete.
Sulphate attack can also be reduced by the addition or even partial
replacement of cement by pozzolana. The effect of this is the reduction of free Ca
(OH)2 and rendering the alumina bearing phase inactive, but sufficient time must be
allowed for the pozzolanic activity to be developed before the concrete is exposed to the
sulphates. Another effect of pozzolana addition is the increase in impermeability of the
concrete. In table the values of percentage weight loss of different mortars are shown
after they were immersed in sulphate solution of 30 days. It can be seen in this table that
the resistance to sulphate attack increases in the following order:
1. Corn cob ash mortar
2. Ordinary Portland cement mortar
3. Rice husk ash mortar
4. Peanut shell ash mortar.
TABLE 4:
This trend
occurs also
for
specimen
under oven
AGE
Type of mortar Compressive
Strength(MPa)
Strenth activity
Index(%)
3-day Control mix
Peanut shell ash
Corn cob ash
18.34
21.52
7.28
100
117.34
39.69
7-day Control mix
Peanut shell ash
Corn cob ash
23.28
24.77
10.03
100
106.4
43.08
28-day Control mix
Peanut shell ash
Corn cob ash
30.11
28.61
11.73
100
95.02
38.96
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dried condition. However, specimen under oven dried condition, the mortars are more
resistant to sulphate attack than under saturated surface dry condition. This is because
hydration in the former part is accelerated and thus speeds up the pozzolanic activity.
Cement with high alumina content is indeed highly satisfactory to resist
sulphate attack. PSA contains 15% Al2O3 content and probably this leads to its higher
resistant to sulphate attack among the four types of mortars investigated. This resistance
to sulphates is due to the absence of Ca(OH)2 in hydrated high alumina cement and also
to the protective influence of the relatively inert alumina gel formed during hydration.
Resistance against acidic attack:
Acid solutions attack concrete by dissolving Ca(OH)2 and removing part of the
set cement, thus causing surface erosion. Cement having alumina content is not acid
resisting but can with stand well very dilute solutions of acid with pH greater than 3.5 to
4.0, found in industrial effluents, but not with HCl, HF or HNO3.
TABLE 5:
%loss of weight
Type of solution
Condition
Of
Specimen
Type
Of
mortar 10% HCl 10%H2SO4
Saturated
Surface
Dried
condition
OPC
RHA
PSA
CCA
5.23
4.26
8.94
15.04
73.74
48.59
46.26
75.46
Oven
Dried
condition
OPC
RHA
PSA
CCA
2.07
0.42
5.24
4.18
52.75
46.53
24.83
62.12
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From the table it can be observed that the resistance to acidic attack increases in the
following order:
1. Corn cob ash mortar
2. Peanut shell ash mortar
3. Ordinary Portland cement mortar
4. Rice husk ash mortar
It was that RHA is highly resistant to acid among the four mortars. This is due to the
higher silica content of RHA which reduces the free lime content of hydrated cement. It
can be seen also that OPC is more resistant to acid than PSA. Improved resistance against
acidic attack can then be obtained by treating the mortar in oven dried condition as
depicted from table 5.
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Conclusions:
1. The burning of peanuts shell produces a brownish ash while coconut husk and
corn cob produce grayish white ash.
2. Peanut shell ash has the highest silica content and lowest ignition loss among the
three raw materials and contains 15.12% Al2O3. According to ASTM standard,
only PSA can be classified as pozzolana class C respectively while corn cob ash
and coconut husk ash do not meet the requirements of pozzolana.
3. The strength activity index with Portland cement after 28 days of PSA is 95.02%
having a water requirement of 99.6% whereas CCA has a strength activity index
of 38.96% and a water requirement of 102.4%.
4. Peanut shell ash mortars have high early strengths compared to ordinary Portland
cement mortars. This is due to the presence of high amount of alumina in PSA.
5. PSA-cement mortar shows greater resistance to sulphate attack than OPC and
RHA but it has lower resistance to HCl attack than OPC and RHA.
References:
1. Journal of ferrocment: vol.25 No.1
2. Ranasinghe ,Arjuna 1985. Use of Rice straw ash as pozzolana . Asian institute of
technology, Bangkok.
3. Neville, A.M 1986. Properties of concrete .London: pitman publishing Ltd.
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