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UTILIZ TION OF RECYCLED ND W STE M TERI LSIN V RIOUS CONSTRUCTION PPLIC TIONS
BSTR CTMore production equals more waste, more waste creates environmental concerns of
toxic threat. An economical viable solution to this problem should include utilization of waste
materials for new products which in turn minimize the heavy burden on the nations landfills.
The amount of waste generated by public works and other construction projects reaches 83
million tons every year, and the amount of waste that is processed through reduction and
reuse at final disposal sites is 6.64 million tons (8%). Moreover, the amount of general waste
generated by domestic households and offices on an annual basis is 55 million tons, and 11
million tons (20%) of this is subject to final disposal. The annual amount of industrial waste
(excluding waste generated by the mining industry) is 235.8 million tons, and 11.79 million
tons (5%) of this is subject to final disposal. However, looking at this problem from the wider
viewpoint, there is also a contrary concept that all waste should be effectively reused and that
recycled materials should be accepted as widely as possible, by all industrial fields, in a
manner that transcends industrial demarcation lines.
Recycling of waste construction materials saves natural resources, saves energy,
reduces solid waste, reduces air and water pollutants and reduces greenhouse gases. In
addition to this, the effective use of recycled waste will act as a substitute for the materials
that are conventionally purchased new, and by adopting a policy such as this we will be able
to reduce the cost of materials, save energy and help conserve resources. This will also lead
to the possibility of reducing costs for companies, even though they will have to pay for therecycled materials. The construction industry can start being aware of and take
advantage of the benefits of using waste and recycled materials. Studies have investigated
the use of acceptable waste, recycled and reusable materials and methods. The use of fly ash,
slag, glass, plastic, rice husk ash, tire scraps, asphalt pavement and concrete aggregate in
construction is becoming increasingly popular due to the shortage and increasing cost
materials. This study presents an initial understanding of the current strengths and
weaknesses of the practice intended to support construction industry in developing effective
policies regarding uses of waste and recycled materials as construction materials.
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INTRODUCTION
As the volume of waste and by-product materials generated in our society
and the cost of disposal continue to increase, there is increased pressure and incentive to
recover and recycle these materials for use in secondary applications. Because the
construction of pavements requires large volumes of materials, highway agencies have
become participants in these recycling efforts. From a pavement engineering perspective,
recovered materials should be used in such a manner that the expected performance of the
pavement will not be compromised. Waste and by-product materials, however, differ vastly
in their types and properties and, as a result, in the pavement applications for which they may
be suited. Experience and knowledge regarding the use of these materials vary from material
to material as well as from state to state. To recover these materials for potential use,
engineers, researchers, generators, and regulators need to be aware of the properties of the
materials, how they can be used, and what limitations may be associated with their use.
The primary purpose of this guideline document is to assist those who have an interest
in using or increasing their understanding of the types of waste and by-product materials that
may be recovered and used in pavement construction applications. It is intended to provide
the potential user or reviewer with sufficient information on each material included in this
document so that he or she will have an understanding of the nature of the material, whereother information may be obtained, and what issues need to be evaluated when considering
its use. It is also intended to provide the reader with general guidance on engineering
evaluation requirements, environmental issues, and economic considerations for determining
the suitability of using recovered materials in pavement applications.
Their study revealed that a significant amount of material wastage can be reduced by
the adoption of prefabrication and the rates of reused and recycled waste materials are
relatively higher in projects that adopt prefabrication. In addition to a reduction of
construction waste generation, identified and discussed other advantages of applying
prefabrication in the building and construction activities. This include enhance integrity on
the building design and construction, reduction unskilled workers, reduce construction cost,
fixed design at the early stage of design, better supervision, promote safer and more
organized construction site and improve environmental performance through waste
minimization. Further, from the results of the survey, one issue companies felt need
addressing is the creation of a separation process on site oppose to an accumulation of all
waste in one pile. A solution to this problem would be planning recycling into the pre
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construction plans in advance. Integrated Solid Waste Management is the selection and
application of suitable techniques, technologies management programs to achieve specific
waste management objectives and goals.
Several researchers from governmental and academia agencies investigated several
green materials technologies that reduce environmental effects and use recycled materials in
infrastructures applications. The researchers developed several green material technology
programs, which maintain or improve current practices in construction engineering and
ensures green products or methods arising from these programs would be cost effective and
would confer benefits on society, the economy and the environment.
Each sector includes subsections of recyclable materials in relation to the construction
industry. The Transportation Sector waste that can be used as beneficial recycled materials
including tire rubber, reclaimed asphalt and recycled concrete aggregate. The Municipal
waste sector contains beneficial materials for the construction industry including roofing
shingles, glass, plastic and carpet. The Industrial waste sector contain beneficial materials
including Cement Kiln Dust, foundry sand, fly ash, silica fume and slag. Findings suggested
the need for better documentation of the use of recycled materials and that construction
industry need to develop effective policies regarding the use of waste and recycled materials
as construction materials. The main objective of this study is to investigate the effective use
of recycled and waste materials in various construction applications. Goals and objectives
include:
Review of studies of Recycled Materials in construction application. Survey of current practices of uses of waste and recycled material in construction. Connecting Researches and industry with an overview of what recycled materials are
available for different applications.
Better Documentations for green infrastructures benefits.
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M TERI LS ND METHODSFly ash
ABSTRACTFly ash is produced by thermal power plants while generating electricity by burning
pulverised coal and is a waste material. In India, the availability of fly ash is substantial since
the Indian coal contains as high as 40% ash much higher than the other countries. The
disposal of this waste material is a matter of great concern from the environmental and
ecological point of view. The safest and gainful utilisation of this material has been one of the
topics of research over the last few decades. This paper is aimed to highlight the various
applications of fly ash as building material such as lime / clay fly ash bricks, Portland
Pozzolana Cement, light weight aggregates replacing the conventional building material to
some extent.
INTRODUCTION
In India about 70% of electricity is produced by burning pulverised bituminous or sub
bituminous coal (lignite) which is producing about 75 million tonnes of fly ash; a solid waste
from 77 thermal power plants.". For a long time to come, India will have no option but to
generate electricity by burning coal. Considering 10% annual growth in electrical power
generation through thermal power plants, the annual fly ash generation is expected to exceed
100 million tonnes by 2000 AD. According to a general estimate, a coal based thermal power
plant of 1000 MW capacity generates about 1200 tonnes of fly ash per day. The disposal of
this solid waste is a matter of great concern today as it requires huge area of land at the power
plant site; the management has to give full thrust for the gainful utilisation of fly ash. Only a
very small percentage of fly ash (5 to 7%) generated in India is used for gainful applications
whereas the corresponding figure for the other advanced countries varies from 30 to 80%. In
some European countries the products like bricks, cement, concrete, mortars, light weight
aggregates etc. are being produced utilising 100% of fly ash. With the awareness regarding
the environment and ecological parameters, it is believed that in the years to come, at least
50% of the fly ash being generated by thermal power plants shall be used for manufacturing
building materials.
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The advantages of fly ash utilisation are
i) Saving of space for disposal
ii) Saving of natural resources
iii) Energy saving
iv) Protection of environment.
Fly ash is generally grey in colour, abrasive, acidic, refractory in nature and it is finely
divided residue from the combustion of pulverised coal possessing pozzolanic properties. The
chemical Composition of fly ash varies with the coal source.
Fly ash can be used for producing various products which may be used as building
materials; these are listed below -
1. In the production of clay-fly ash / fly ash-lime-gypsum (FAL-G) / Fly ash - sand time
building bricks.
2. In the production of sintered light weight bricks / aggregates.
3. As Pozzolana in the production of -
i) Portland Pozzolanic Cement (PPC)
ii) Ready-mixed fly ash concrete for use as a structural and in the production of precast
concrete building units
iii) As a part replacement of Portland cement in mortars and concretes at the construction site.
4. In the production of cellular light weight concrete
Classification of fly ash is given in ASTM C-618-89 on the basis of chemical
composition (Table 2A). Anthracite and bituminous or high ranking coals give low lime
class- F fly ash, used by all thermal power plants except Neyveli Lignite Corporation. Low
rank sub-bituminous or lignite coals give high lime (>10% CaO) fly ash of class-C (Table
2B). The mineralogical composition of fly ash indicates that a large quantity of glassy matter
is present along with various other crystalline phases. The glassy phase generally exceeds 50
wt% and can be as high as 90 wt%. The crystalline phases are mainly mullite and magnetite
with some amount of quartz and haematite.
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Table 2 A: Classification of fly ash as per ASTM: C - 618 - 89
R203= Fe203; LOI indicates So3+ Unburnt Carbon
Table 2 B: Typical Chemical Composition of Fly ash
Constituents Class F Class C
SiO2 34-60 25-40
AL2O3 17-31 8-17
Fe2O3 2-25 5-10
CaO 0.5-10 10-38
MgO 1-3 1-3L.O.I. 0-15 0-15
FLY ASH UTILISATION
1 Brick making
The clay brick used for construction purposes is the age old product and is being used
confidently by the consumers even today. With the fast urban development, the demands for
bricks have been increasing allowing brick industry to exploit top soil which is a social crime.
In order to meet the increasing demand of brick, the fly ash based brick can be an alternative
with the improved engineering properties. Considering 25% based fly ash bricks at the
national level, it can be envisaged to consume 30 - 45 million tonnes of fly ash every year.
Bricks made of fly ash can be broadly classified into three groups
(i) Fly ashsand lime bricks
(ii) Fly ash - gypsum/lime/ cement bricks
(iii) Fly ash-clay (Sintered) bricks.
Class of
fly ash
Type of sourceSi02+R203
Min (%)
CaO
Min (%)
SO3
Max (%)
H2Oas
Moisture(%)
LOI
Max (%)
FBituminous
Anthracite70 - 5 3 6
CSub-bituminous
Lignite50 10 5 3 6
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The various suggested proportions of fly ash with sand, clay and lime/cement are as
follows -
Lime Based Bricks: 70% fly ash; 5-10% lime; 20-25% sand.
Cement Based Bricks: 70% fly ash; 10% Cement; 20% sand
Clay Bricks: 30% fly ash; 50% clay; 20% sand
Fal-G Bricks: 65% fly ash; 16% lime; 15% sand; 4% gypsum
It is important to know the end use of fly ash based bricks while considering them,
whether it is for load bearing Structure or for some other applications. If it is for load bearing
structure, then to what loads or these being used for partitions or single storey buildings.
Accordingly the specifications are fixed up for the bricks. Available technologies are capable
of supplying the bricks from strength of 50 kg/cm2 to > 180 kg/cm2.
In the case of clay-fly ash bricks, fly ash plays primarily the role of replacing the top
soil and thus silica and other constituents play a normal role. The presence of unburnt carbon
is very advantageous as it saves the fuel consumption during firing. In other words, the fly
ash with higher L.G.I is more useful for these applications. After mixing clay and fly ash in
proper proportion; extrusion and drying; the bricks are fired in Hoffman kilns.
Fly ash- lime-gypsum (FAL-G) or lime based bricks are made by using fly ash, low
cost course sand, gypsum and the lime sludge. Pond-ash from ash ponds can also be used by
mixing with locally available clay. It is better to use lime sludge 5 in place of fresh lime as it
is free from hard clinker and is available cheaply from acetylene plants-The manufacturing
process of FAL-G bricks involves thorough mixing of all the ingredients, conveying the mix
to the press and forming green bricks using press, stacking the bricks and curing them for
about 20 days. Bricks are ready to use after nearly 30 days from the date of manufacturing.
Fly ash-lime-sand bricks are made by mixing the ingredients in the appropriate
proportion using mechanical mixer with the addition of water. This prepared mixture is then
stored for few hours to complete the hydration of lime. Green bricks are formed by pressing
this mixture in a hydraulic press and kept for natural curing under a shed for approx. 24 hours
and then steam cured at pressures higher than 1 atm. for about 5 to 7 hours at a temp. of 135-
140C. Flow sheets are given in figure 1 and 2.
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Table 5: Typical properties of fly ash bricks and burnt clay bricks
Property Clay brick Fly ash brick
% Water absorption 21 15
App-Density (gm/cc) 1.44 1.80
Compressive strength(Kg/cm2) 19-42 58-78
There are certain distinct advantages of fly ash based bricks over the conventional red bricks
and these are
(i) Uniform and standard product size resulting in 10% less consumption of bricks per unit
construction.
(ii) Cement Consumption is less in cement and mortar.(iii) Compressive strength is more than conventional red bricks (> 100 kg/ cm2) and further
increase with the passage of time.
(iv) Less load on foundation due to light weight.
(v) Due to the property of less water absorption and no weathering effects, surfaces can be
left exposed without plastering and direct application of paint is also possible.
The available Indian standards for fly ash based building materials are given in table 6.
Table 6: Available Indian standards for fly ash based building materials
(1) Manufacturing of portland pozzolana cement BIS 1489 (I)-1991
(PPC) with fly ash
(2) Masonary cement BIS 3466-1988
(3) Fly-ash -lime -gypsum bricks BIS 12894 -1990
(4) Fly-ash as raw material for OPC BIS 269-1967
(5) Oil well cement with fly ash BIS 8229-1986(6) Autoclave aerated concrete blocks BIS 2185(3)-1984
(7) Use of fly ash in concrete BIS 3812-1981
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2 Portland Pozzolana Cement (PPC)
Pozzolans are the clay matter either natural or synthetic, which when ground with
lime or clinker and mixed with water, produce cementations compounds when highly reactive
fly ash is mixed with Portland cement clinker and ground with 5-6% of gypsum the resultantproduct is Portland Pozzolans Cement (PPC). PPC should not contain >25% fly ash. It has
much lower heat of hydration and is also fairly sulphate resistant. It liar all the physical
properties of OPC but has lower shrinkage and can be used for all construction work for
which OPC is used. The role of fly ash is predominan0' in the case of PPC as it engages the
free lime into mineralogical formulations akin to the cement as shown below, simultaneously
vetoing the availability of lime for deleterious after effects.
Fast Slow
C3S + H ---------> C-S-H + CH Pozzolana + CH + H-------- > C-S-H
(Portland cement) (Portland Pozzolana Cement)
The heat of hydration and strength development in PPC is low in comparison with
OPC, The Pozzolanic reaction is lime consuming instead of lime producing, which has an
important bearing on the durability of hydrated paste in the acidic environment. The pore-size
distribution certainly plays an important role in PPC in improving the strength and
impermeability of the system by filling up the large capillary space. Hence, the use of fly ash
at blending stage needs careful screening and selection. In order to get maximum lime
reactivity, fly ash must have adequate fineness as well as higher glass content.
CONCLUSIONS
In various. Countries abroad, products such as bricks, PPC, sintered aggregates etc-
are being manufactured utilising the fly ash which is a waste material. Although there is no
dearth of the technology in India but still our industries do not have much confidence in the
indigenous know-how and the import of technology from abroad in going on, thus
discouraging the indigenous R&D efforts. The fly ash disposal can be, usefully made if the
local entrepreneurs preferably from nearby thermal power plants come forward to install
brick making plants using fly ash. Fly ash bricks because of greyish in colour are hesitated by
the customers (public) to switch over from the usual reddish burnt clay bricks. Moreover,
because of high strength, the masons are also reluctant in using the same. However, for better
utilisation of fly ash bricks and other building materials, more publicity should be given to
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the actual users. Government agencies also should come forward in using such materials in
its construction work. The increased utilisation of such materials will definitely help in the
reduction of the usage of the conventional raw materials like clay/ shales, thus saving
valuable natural resources. In brief, in order to have the efficient utilisation of fly ash based
building materials, the need of the hour is
(i) The development of coal - ash based marketable products having potentiality for bulk
utilisation.
(ii) The development of environment-friendly ash-disposal methodology.
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RICE HUSK ASH
IntroductionRice husk ash is a by-product from the burning of rice husk. Rice husk is extremely
prevalent in East and South-East Asia because of the rice production in this area. The rich
land and tropical climate make for perfect conditions to cultivate rice and is taken advantage
by these Asian countries. The husk of the rice is removed in the farming process before it is
sold and consumed. It has been found beneficial to burn this rice husk in kilns to make
various things. The rice husk ash is then used as a substitute or admixture in cement.
Therefore the entire rice product is used in an efficient and environmentally friendly
approach. In this article we will be exploring the common processes of burning rice husk and
the advantages of using the burnt ash in cement to facilitate structural development primarily
in the East and South-East Asian regions. We will be investigating prior research from
various sources, as well as prepare specimens of our own to perform a range of strength tests.
Disposal
Disposal of rice husk ash is an important issue in these countries which cultivate large
quantities of rice. Rice husk has a very low nutritional value and as they take very long to
decompose are not appropriate for composting or manure. Therefore the 100 million tons of
rice husk produced globally begins to impact the environment if not disposed of properly.
One effective method used today to rid the planet of rice husk is to use it to fuel kilns. These
kilns help to produce bricks and other clay products that are used in daily life. Burning the
rice husk is an efficient way to dispose of the rice cultivation by product while producing
other useful goods. After the kilns have been fired using rice husk, the ash still remains. As
the production rate of rice husk ash is about 20% of the dried rice husk, the amount of RHA
generated yearly is about 20 million tons worldwide .
Burning
The rice husk ash is a highly siliceous material that can be used as an admixture in
concrete if the rice husk is burnt in a specific manner. The characteristics of the ash are
dependent on the components, temperature and time of burning (Hwang, 185). During the
burning process, the carbon content is burnt off and all that remains is the silica content. The
silica must be kept at a non-crystalline state in order to produce an ash with high pozzalonic
activity. The high pozzalonic behaviour is a necessity if you intend to use it as a substitute or
admixture in concrete. It has been tested and found that the ideal temperature for producing
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such results is between 600 C and 700 C. The following graph shows the curve for
obtaining reactive cellular rice husk ash with certain burning temperatures and time fired. If
the rice husk is burnt at too high a temperature or for too long the silica content will become a
crystalline structure. If the rice husk is burnt at too low a temperature or for too short a period
of time the rice husk ash will contain too large an amount of un-burnt carbon.
Engineering Performance
The performance of rice husk ash cement is important to investigate to be sure that it
can be used in place of a normal batch of cement. All projects must be considered on a
separate basis beforehand, but there are some common characteristics of rice husk ash cement
that may be beneficial to certain locations, situations, or projects.
Structural IntegrityThe use of pozzolanas as alternatives for the commonly used Portland cement have
been used in the past few decades either for cost reduction, performance & durability
enhancement or environmental reasons. Malhorta and Mehta state that pozzolanas are defined
as siliceous or siliceous and aluminous materials which in themselves possess little or no
cementing property, but will in a finely dispersed form in the presence of water chemically
react with calcium hydroxide at ordinary temperature to form compounds possessing
cementations properties. When water is added to a mixture with pozzolanic material it acts as
cement, in some instances providing a stronger bond than cement alone. The cost reduction is
especially important for the areas of Africa, South America, and South-East Asia where the
poverty level and wealth of the areas are low. This can allow for cheap building material
without the loss of performance, which is crucial for any developing nation to continue to
grow.
Corrosion Performance
The addition of rice husk ash to a concrete mixture has been proven to increase
corrosion resistance. It has a higher early strength than concrete without rice husk ash. The
rice husk ash forms a calcium silicate hydrate gel around the cement particles which is highly
dense and less porous. This will prevent the cracking of the concrete and protect it from
corrosion by not allowing any leeching agents to break down the material. The study done by
Song and Saraswathy found that the incorporation of RHA up to 30% replacement level
reduces the chloride penetration, decreases permeability, and improves strength and corrosion
resistance properties.
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Effect of Humidity
The effects of humidity can result in a drastic change in the final behavior of the
concrete. The comparative tests performed and documented by Jauberthie between specimens
stored in dry and wet conditions have shown that at high humidity conservation the mortar
gains strength by virtue of the well developed pozzolanic reaction (Jauberthie, 243). This
added strength is only under compression forces, specimens are more brittle under a smaller
flexural load than specimens stored at 50% relative humidity. The following table explains
the figures that were found from the experiment. As for climates of South-East and East Asia,
the high humidity levels indicate that there will be a higher compressive strength, but more
brittleness in the concrete produced. That is unless it is stored in a facility with regulated
humidity levels. For the use of concrete with rice husk ash mixtures, it would be
recommended to use it for columns or structural walls which tend to support compressive
forces.
Experiment
Casting
To complete an analysis of our own, we produced four batches of concrete with
varying amounts of rice husk ash substituted for Ordinary Portland Cement. There was a
control group with no rice husk ash, one with 15% substitution, 30% substitution, and 40%
substitution. We mixed the samples and did the testing at the Center for Vocational Building
Technology (CVBT) in Nong Khai, Thailand. This is important because it fits the conditions
of more rural and developing countries, where cement is expensive and rice cultivation is
widespread. The technique and procedure used was replicated of that used by the villagers at
the same building factory. This gives us more accurate results compared to the products used
in these areas.
We used the CVBTs standard mix proportions they use for paving slabs without dye.
For each batch 6kg of standard OPC, 16.1 kg of sand, 17.42 kg of 3/8 aggregate, 53 mL of
super plasticizer, and 2.7 L of water was mixed together. The super plasticizer added was
equal to 1% of the weight of cement in the mix. To find the amount of water necessary, first
the moisture content of the sand was calculated. For the third and fourth batch, the concrete
was not workable so more water was added to the mix. 500 mL of extra water was added in
each batch in order to achieve a constant slump throughout the experiment. The following
figure from Ganesans article shows the percentage of cement replacement level versus
standard consistency.
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It indicates that the water required for standard consistency linearly increases with an
increase in RHA content. As ashes are hygroscopic in nature and the specific surface area of
RHA is much higher than cement, it needs more water (Ganesan, 1680). For this reason, extra
water was added to the 30% RHA and 40% RHA batches. Infused with the water was a super
plasticizer, known as F2 at this specific site. This ingredient is used to reduce the amount of
water needed to produce a sufficiently low viscosity, by producing charged ions that repel
each other in the mix. The repulsion of the charged ions helps the particles in the concrete
mix slide past one another respectively on a microscopic level. The molds were set on a
vibrating table once the concrete was placed in them. The vibrating causes the concrete to
better fill the molds and allows the air to escape producing a form without voids. The lack of
air voids increases the strength of the product.
For each of the four batches two cubes and three slabs were produced. The cubes were
tested for failure by compression tests. They were constructed in standard size for Thailands
test procedures (15cm x15cm x 15cm). The cubes were tested at seven days and fourteen
days. Only two cubes were made for each batch because there was a limited supply of molds.
The paving slab testing is more pertinent towards the CVBT because slabs are their most
successful product. Because of this, it was agreed that bending tests on the paving slabs
would be the most pertinent assessment. Three slabs were constructed for each batch in order
to get a more accurate analysis than the compression cubes. The slabs were tested after seven,
fourteen, and twenty eight days of curing. The curing process used was one little nugget of
appropriate technology known solar-thermal high humidity curing. The specimens were
placed outside under a clear plastic sheet. The high heat in the region was of concern because
the drying process is sped up tremendously. In order to achieve normal curing process water
was added under the plastic daily, which caused moisture to accumulate inside the curing
chamber. Overall the process was faster, but low input, and produced acceptable results.
Testing
Compression Test
The compression tests for the concrete cubes were done at the Nong Khai Technical
College. Thai standard test procedures were used. All specimens were weighed at the time of
each respective test. The testing machine applies a constant uniform pressure to the cubes
until failure occurs. Failure was observed when the cube no longer could resist the force
applied to it without breaking apart.
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Bending Test
The bending tests for the concrete paving slabs were performed at the CVBT at seven,
fourteen, and twenty eight days after the casting. A triple point bending test was done. This
involves two metal rods with a diameter of 31mm placed symmetrically under the slab
separated by 15.3 cm. One rod the same size was placed on top in the middle of the slab to
apply a force. A hydraulic jack was placed on top to provide the force in order to break the
slabs. A constant force was applied slowly until failure when the slabs were completely
severed.
Results
Analysis
For the bending tests there is a direct correlation between the weights of the mix at the
time of testing to the percentage of rice husk ash substituted for Ordinary Portland Cement.
The more rice husk ash that is used in the mix, the lighter the finished concrete becomes.
There is one outlier for the 30% RHA substitution that seems lighter than it should be. This
could be because the slab may not have been vibrated enough to fill the voids. These air voids
can decrease the weight of the concrete. Also there is always human error that will account
for outliers because it is not possible to make multiple batches the same each time. The mix
proportions were kept at a constant except for the percentage of rice husk ash, but the time to
prepare and cast varied slightly. More batches and more specimens to test would have been
ideal and would have provided a more accurate indication of the correlation. The following
graph shows that the correlation still is strong even with the small sample size.
The graph below shows the strength curve of each batch for the paving slabs that were
tested using a triple point bending method. The dark blue line is the control batch with no rice
husk ash. There is a trend that the final strength after twenty-eight days is decreased with the
increase of rice husk ash substitution. The strength is not decreased significantly until the rice
husk ash substitution is greater than 30%. At 30% rice husk ash substitution the strength of
our batch produced was only decreased by only around 16% of the control batch. Depending
on the project and the areas code enforcement, thisshould be a sufficient strength. For the
compression test specimens the weight to rice husk ash percentage correlation follows the
same trend as the paving slab specimens. This further proves that the substitution of rice husk
ash will decrease the weight of the final project. Figure 3 shows the relationship for our
compression cube specimens.
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The following graph, figure 4, shows the strength curves for the compression samples.
There were only enough samples to test at seven and fourteen days, but the tests follow the
same trend as the paving slabs. The strength is decreasing as the percentage of rice husk ash
is increased. The strengths for batches 2 and 3 are close to the control batch; with the 30%
rice husk ash substituted less than 10% decrease from the first batch. The 40% rice husk ash
has a significant decrease in strength.
Recommendation
After completing our research and testing samples of our own, it is our
recommendation to use rice husk ash substitution for Ordinary Portland Cement up to 30%.
This will decrease the weight of the finished project, decrease the cost, and dispose of the rice
husk ash waste product. This is the best option where rice production is prevalent, including
most of Asia especially South East Asia. This area is mostly underdeveloped with higher
rates of poverty. The cheaper cost of concrete can lead to more secure and longer lasting
infrastructure. The use of rice husk to fuel brick kilns and complement cement in building
materials transforms it from prevalent waste product into an abundant resource.
Highlights of Recent Related Rice Husk Research
Since western-style buildings have become prevalent in SE Asia, elevated indoor temperature
due in part to solar heat gain has become a widespread problem, often remedied with energy-
intensive air conditioning. In 2007, C. Lertsatitthanakorn and S. Atthajariyakul of
Mahasarakham University, and S. Soponronnarit of King Mongkuts University of
Technology Thonburi (Thailand) studied the thermal performance of RHA based sand-
cement blocks as insulating thermal mass. They built a small room (5.75 square meter floor)
out of standard commercial clay brick, and another out of blocks composed of RHA, sand,
and cement at a ratio of 544:320:40. They took continuous temperature measurements inside
both for the Thai summer month of March, and found that the RHA blocks allowed 46 W less
heat transfer than the clay bricks. Also included in the study was an economic analysis of
potential energy savings.
In 2008, Sumin Kim of Soongsil University, (Seoul, Republic of Korea) Investigated
the effect of combining rice husk itself (not ash) with gypsum in the manufacture of drywall
boards. Kim found that at rice husk levels up to 30%, the modulus of rupture and modulus of
elasticity increased, but decreased at levels over 40%. Internal bonding strength increased for
RH levels up to 20%, but decreased at higher levels. At higher rice husk content, the product
absorbed less moisture, and became slightly more combustible, but up to 30% RH still met
Japanese Standards Association first class incombustibility requirements. The author
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concluded that 20% rice husk by weight is the ideal mixture for improving gypsum boards
while lowering costs and helping reduce the rice husk disposal issues.
A method has been developed by which the pozzolanic activity of a batch of ash can
be measured in 28 hours (as opposed to 7 or 28 days) by mixing a sample with Portland
cement, measuring the electrical conductivity of the solution, and comparing it to values from
the reaction of a solution with a known pozzolanic activity level. (Sinthaworn, Waste
Management, 2009) Rice husk can be co-combusted with coal to help clean up coal-fired
power plant emissions. 10% to 30% biomass appears to yield the lowest overall pollutant per
unit of energy ratio, though the co-firing may produce more ultra-fine particles, and increase
problems of slagging, fouling and formation of clinker in conventional systems. (Chao,
Bioresource technology, 2008) RHA can be added to soil to aid in compactibility. According
to Basha and Muntohar (Electronic Journal of Geotechnical Engineering, 2003), the plasticity
of soil is reduced when rice husk ash and/or cement is added, as is the maximum dry density,
and the optimum moisture content is increased. They state that considering plasticity,
compaction, and economy, the ideal soil additive mix is within 6-8% cement and 10-15%
RHA.
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Use of Waste Rubber Tyres in Construction of
Bituminous Road
ABSTRACT
The use of four wheeler, two wheeler vehicles etc. is increasing day by day. As a
result amount of waste tyres also increasing. Waste tyres in India are categorized as solid or
hazardous waste. It is estimated that about 60 per cent of waste tyres are disposed via
unknown routes in the urban as well as rural areas. This leads to various environmental
problems which include air pollution associated with open burning of tyres (particulates,
odor, visual impacts, and other harmful contaminants such as polycyclic aromatic
hydrocarbon, dioxin, furans and oxides of nitrogen) and aesthetic pollution. Therefore, it is
necessary to utilize the wastes effectively with technical development in each field. The
waste tyres can be used as well sized aggregate in the various bituminous mixes if it is cut in
the form of aggregate and can be called as rubber aggregate. This not only minimizes the
pollution occurred due to waste tyres but also minimizes the use of conventional aggregate
which is available in exhaustible quantity.
1. INTRODUCTION:
Now-a-days disposal of different wastes produced from different Industries is a great
problem. These materials pose environmental pollution in the nearby locality because many
of them are non-biodegradable. Traditionally soil, stone aggregate, sand, bitumen, cement
etc. are used for road construction. Natural material being exhaustible in nature, its quantity is
declining gradually. Also, cost of extracting good quality of natural material is increasing.
Concerned about this, the scientists are looking for alternative materials for highway
construction, by which the pollution and disposal problems may be partly reduced. Keeping
in mind the need for bulk use of these solid wastes in India, it was thought expedient to test
these materials and to develop specifications to enhance the use of waste tyres in road making
in which higher economic returns may be possible. The possible use of these materials should
be developed for construction of low volume roads in different parts of our country. The
necessary specifications should be formulated and attempts are to be made to maximize the
use of solid wastes in different layers of the road pavement.
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Post construction pavement performance studies are to be done for these waste
materials for construction of low volume roads with two major benefits (i) it will help clear
valuable land of huge dumps of wastes: (ii) it will also help to preserve the natural reserves of
aggregates, thus protecting the environment. Rubber tyres are user friendly but not
ecofriendly as they are non-biodegradable generally. The practice of disposing waste tyres in
landfills and open burning is becoming unacceptable because of rapid depletion of available
landfill sites and clear environment respectively.
The conventional bituminous mix includes stone aggregate and 3 to 5 percent bitumen
by weight of the aggregate. The scrap tyre rubber can be incorporated into bitumen, often
abbreviated as modified bitumen and granulated or ground rubber or crumb rubber can be
used as a portion of the fine stone aggregate. The use of waste in hot bituminous mixes
enhances pavement performance, protect environment and provide low cost and quieter
roads.
2. LITERATURE REVIEW:
Prof. Justo et al (2002), at the Centre for Transportation Engineering of Bangalore
University compare the properties of the modified bitumen with ordinary bitumen. It was
observed that the penetration and ductility values of the modified bitumen decreased with the
increase in proportion of the plastic additive, up to 12 percent by weight. Therefore the life of
the pavement surfacing using the modified bitumen is also expected to increase substantially
in comparison to the use of ordinary bitumen.
Shankar et al (2009), crumb rubber modified bitumen (CRMB 55) was blended at
specified temperatures. Marshalls mix design was carried out by changing the modified
bitumen content at constant optimum rubber content and subsequent tests have been
performed to determine the different mix design characteristics and for conventional bitumen
(60/70) also. This has resulted in much improved characteristics when compared with straight
run bitumen and that too at reduced optimum modified binder content (5.67 %). Mohd.
Imtiyaz (2002) concluded that the mix prepared with modifiers shows: - Higher resistance to
permanent deformation at higher temperature.
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3. METHODOLOGY:
Waste rubber tyres were collected from roads sides, dumpsites and waste-buyers. The
collected waste tyres were sorted as per the required sizes for the aggregate. The waste tyres
were cut in the form of aggregate of sizes ranging from 22.4 mm to 6.00 mm (as per IRC-
SP20) in the tyre cutting machine which is shown in picture 1.
Picture 1
The waste rubber tyres can be managed as a whole tyre, as slit tyre, as shredded or
chopped tyre, as ground rubber or as a crumb rubber product. The rubber of tyre usually
employed in bituminous mix, in the form of rubber particles are subjected to a dual cycle of
magnetic separation, then screened and recovered in various sizes and can be called as
Rubber aggregate. It was cleaned by de-dusting or washing if required. The rubber pieces
(rubber aggregate) were sieved through 22.4 mm sieve and retained at 5.6 mm sieve as per
the specification of mix design and these were added in bituminous mix, 10 to 20 percent by
weight of the stone aggregate. These rubber aggregate were mixed with stone aggregate and
bitumen at temperature between 1600c to 1700c for proper mixing of bituminous mix. As the
waste rubber tyres are thermodynamically set, they are not supposed to melt in the bitumen,
at the time of mixing of rubber aggregate, stone aggregate and bitumen in hot mix plant.
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4. RESULT:
The possible use of rubber particles from scrap tyres into concrete mix have already
given better result in sub-bases for highway pavements, highway medians, sound barriers and
other transportation structures. The addition of rubber aggregate in bituminous mix decreases
the quantity of stone aggregate by volume and increases the flexibility and flexural strength
of the carpet layer of the highways. Aggregate is the granular material used in bitumen
concrete mixtures, which makes up 90 to 95 percent of mixture weight and provide most of
the load bearing characteristics of the mix. Due to which the quantity of aggregate is
gradually decreasing which will need the alternative material as aggregate for the highway
construction.
5. SIGNIFICANCES:
The Rubber aggregate can be the better option for conventional aggregate for the
surface layer for highway. The rubber aggregate solves the problem of permanent
deformation and thermal cracking. When used for road construction it can withstand higher
temperature. Hence it is suitable for tropical regions. It can also resist the effect of water.
With all these, it is a good saving too. No toxic gas is produced. Disposal of waste tyres will
no longer be a problem. The use of waste tyres on the road has helps to provide better place
for buying the used tyres waste without causing disposal problem. At the same time, a better
road is also constructed. It also helps to avoid the general disposal technique of waste tyres
namely land-filling and open burning, which have certain burden on ecology.
6. CONCLUSION:
Addition of waste tyres as rubber aggregate modifies the flexibility of surface layer.
Optimum content of waste rubber tyres to be used is between the range of 5% to 20%.
Problem like thermal cracking and permanent deformation are reduce in hot temperature
region.
Rubber has property of absorbing sound, which also help in reducing the sound pollution of
heavy traffic roads.
Waste rubber tyres thus can be put to use and it ultimately improves the quality and
performance of road.
Conventional stone aggregate can be saved to a certain quantity.
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