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A Comparative Study Of Normal Concrete And Recycled Concrete
CHAPTER I
INTRODUCTION
Normal concrete
Recycled Concrete
1.1 General Any construction activity requires several materials such as concrete, steel, brick, stone,
glass, clay, mud, wood, and so on. However, the cement concrete remains the main
construction material used in construction industries. For its suitability and adaptability with
respect to the changing environment, the concrete must be such that it can conserve
resources, protect the environment, economize and lead to proper utilization of energy. To
achieve this, major emphasis must be laid on the use of wastes and byproducts in cement and
concrete used for new constructions. The utilization of recycled aggregate is particularly very
promising as 75 per cent of concrete is made of aggregates. In that case, the aggregates
considered are slag, power plant wastes, recycled concrete, mining and quarrying wastes,
waste glass, incinerator residue, red mud, burnt clay, sawdust, combustor ash and foundry
sand. The enormous quantities of demolished concrete are available at various construction
sites, which are now posing a serious problem of disposal in urban areas. This can easily be
recycled as aggregate and used in concrete.
The recycling and reuse of construction & demolition wastes seems feasible solution in
rehabilitation and new constructions after the natural disaster or demolition of old structures.
This becomes very important especially for those countries where national and local policies
are stringent for disposal of construction and demolition wastes with guidance, penalties,
levies etc.
And attempt has been made to find out feasibility of using recycled concrete instead of
reinforced concrete.
1.2 Objective of the study:
1) To find out feasibility of using recycled concrete instead of normal concrete.
2) To prepare a mix design ratio of 1:1.5:3 and test 3 sets of cylinders at 14,21,&28 days for
compressive strength using fresh reinforce concrete.
3) To prepare three sets of cylinders of recycled concrete using the same mix design ratio and
test the specimens at 14, 21, & 28 days for compressive strength.
4) To compare the compressive strength of normal concrete with recycled concrete at
different days.
5) To compare the cost of recycled and fresh concrete.
6) To assess the effect of demolished concrete on environment and friendly use of recycled
concrete.
7) To draw few recommendations based on the study.
1.3 Scope & Limitation of the study:In this study concrete waste collected from breaking of pile head is used. Only one mix
design ratio is used to prepare the cylinders. For time limitation and limited budget only six
sets of cylinders were prepared for testing. For further study waste concrete collected from
several demolished construction, different mix design ratio can be used.
Chapter ii
Literature review2.1 ConcreteConcrete is an artificial stone manufactured from a mixture of binding materials and inert materials
with water.
Concrete = Binding materials + Inert materials + Water.
Concrete is considered as a chemically combined mass where the inert material acts as a filler
and the binding material acts as a binder. The most important binding material is cement and
lime. The inert materials used in concrete are termed as aggregates. The aggregates are of two
types namely,
(1) Fine aggregate and
(2) Course aggregate.
Concrete is a composite construction material, composed of cement (commonly Portland
cement) and other cementitious materials such as fly ash and slag cement, aggregate
(generally a coarse aggregate made of gravel or crushed rocks such as limestone, or granite,
plus a fine aggregate such as sand), water and chemical admixtures.
The word concrete comes from the Latin word "concretes" (meaning compact or condensed),
the perfect passive participle of "concrescere", from "con-" (together) and "crescere" (to
grow).
Concrete solidifies and hardens after mixing with water and placement due to a chemical
process known as hydration. The water reacts with the cement, which bonds the other
components together, eventually creating a robust stone-like material. Concrete is used to
make pavements, pipe, architectural structures, foundations, motorways/roads,
bridges/overpasses, parking structures, brick/block walls, footings for gates, fences and poles
and even boats.
Concrete is used more than any other man-made material in the world. As of 2006, about 7.5
billion cubic metres of concrete are made each year-more than one cubic metre for every
person on Earth.
2.2 AggregatesFine and coarse aggregates make up the bulk of a concrete mixture. Sand, natural gravel and
crushed stone are used mainly for this purpose. Recycled aggregates (from construction,
demolition and excavation waste) are increasingly used as partial replacements of natural
aggregates, while a number of manufactured aggregates, including air-cooled blast furnace
slag and bottom ash are also permitted.
Decorative stones such as quartzite, small river stones or crushed glass are sometimes added
to the surface of concrete for a decorative "exposed aggregate" finish, popular among
landscape designers.
The presence of aggregate greatly increases the robustness of concrete above that of cement,
which otherwise is a brittle material and thus concrete is a true composite material.
Redistribution of aggregates after compaction often creates in homogeneity due to the
influence of vibration. This can lead to strength gradients.
2.2.1 Fine aggregateSand and Surki are commonly used as f ine aggregate in Bangladesh. Stone
screenings, burnt clays, cinders and fly-ash are sometimes used as a substitute for sand
in making concrete. The fine aggregate should not be larger than 3/16 inch (4.75mm) in
diameter.
2.2.2 Coarse aggregateBrick khoa (broken bricks), broken stones, gravels, Pebbles, clinkers, cinders etc. of
(he size of 3/16 to 2 inch are commonly used as coarse aggregate in Bangladesh. It
may be remembered that 3/16 inch is the d iv id ing l ine between f ine and coarse
aggregates.
2.2.3 Functions of Aggregates in ConcreteThe aggregate give volume to the concrete around the surface of which the binding material
adheres in the form of a thin Him. In theory the voids in the coarse aggregate is filled up with
line aggregate and again the voids in the Hue aggregate is filled up
With the binding materials. Final ly , the binding materials as the name involve
binds the individual units of aggregates into a solid mass with the help of water.
2.2.4 Qualities of AggregatesSince at least three quarters of the volume of concrete is occupied by aggregate. It is not
surprising that its quality is of considerable importance. Not only the aggregate l im i t the
strength o f t h e concrete, as weak aggregates can not produce a strong concrete, but also
the properties of aggregates greatly affect the durability and structural performance of the
concrete.
Aggregate was though, originally viewed as an inert material dispersed throughout the cement
paste largely for economic reason, yet it is possible, however, to take an opposite view
and to look on aggregate as a building material connected into a cohesive whole by
means of cement paste, in a manner similar to masonry constructions. In fact aggregates
are not truly inert and their physical, chemical and sometimes thermal properties influence the
structural performance of a concrete.
Aggregates are cheaper than cement and it is therefore, economical to put into the mix as much
as of the former and as little of the latter. But economy is not the only reason for using
aggregate: it confers considerable technical advantage on concrete, which has a higher
volume stability and better durability than the cement paste alone. The coarse aggregate should
be clean, strong, durable and well grades and should be free from impurities and deleterious
materials, such as salts, coal residue, etc.
2.3 CementCement is a cementing or binding material used in engineering construction. It is
manufactured from calcareous substance (compounds of calcium and magnesium) and is
similar in many respects to the strongly hydraulic limes but possessing far greater
hydraulic properties.
Portland cement is the most common type of cement in general usage. It is a basic ingredient
of concrete, mortar and plaster. English masonry worker Joseph Aspdin patented Portland
cement in 1824; it was named because of its similarity in color to Portland limestone,
quarried from the English Isle of Portland and used extensively in London architecture. It
consists of a mixture of oxides of calcium, silicon and aluminum. Portland cement and
similar materials are made by heating limestone (a source of calcium) with clay and grinding
this product (called clinker) with a source of sulfate (most commonly gypsum).
2.3.1 Chemical composition of cement
Followings are the chemical compositions of cement:
* Lime (CaO) = 60-67%
* Silica (SiO2) = 17-25%
* Alumina (A12O3) = 3-8%
* Magnesia (MgO) = 0.1 -4%
* Sulphur trioxide (SO3) = 1 -3%
* Iron Oxide (Fe2O3) = 0.5-6%
* Soda and Potash alkalis = 0.5-1%
2.3.2 HardeningProcess of gaining strength by the mass of cement concrete is known as hardening. Tri-Calcium
Silicate (C3S) hydrated first and responsible for most of early strength of concrete. Strength
acquired during first 7 days is mostly due to hydration of €38. Di-Calcium Silicate (€28) starts
contributing strength after 7 days to a year.
2.3.3 SettingProcess of loosing plasticity is known as setting. Tri-Calcium Aluminates (CsA) responsible
for early setting of cement. C3A does not contribute any strength.
Tetra Calcium Alumino Ferrite (C4AF) does not play any significant roll in setting and
hardening properties. For delaying setting for 30 to 40 minutes add 1-3% gypsum powder in
cement. Initial setting of cement, 45 min to 8-10 hrs. Final setting time, 5to 20 hrs. Progressive
hardening time, 24 hrs to a year. Within 30 days 80-90% strength gain.
2.4 WaterCombining water with a cementitious material forms a cement paste by the process of
hydration. The cement paste glues the aggregate together, fills voids within it and allows it to
flow more freely.
Less water in the cement paste will yield a stronger, more durable concrete; more water will
give a freer-flowing concrete with a higher slump. Impure water used to make concrete can
cause problems when setting or in causing premature failure of the structure.
Hydration involves many different reactions, often occurring at the same time. As the
reactions proceed, the products of the cement hydration process gradually bond together the
individual sand and gravel particles and other components of the concrete, to form a solid
mass.
Reaction:
Cement chemist notation: C3S + H → C-S-H + CH
Standard notation: Ca3SiO5 + H2O → (CaO)·(SiO2)·(H2O)(gel) + Ca(OH)2
Balanced: 2Ca3SiO5 + 7H2O → 3(CaO)·2(SiO2)·4(H2O)(gel) + 3Ca(OH)2
2.4.1 Functions of water in concreteWater serves the following three purposes:
1.To wet the surface of aggregates to develop adhesion because the cement paste
adheres quickly and satisfactory to the wet surface of the aggregates than to a dry
surface,
2.To prepare a plastic mixture of the various ingredients and to impart workability to
concrete to facilitate placing in the desired position and
3.Water to also needed for the hydration of the cementing materials to set and harden
during the period of curing.
2.5 Advantage of concrete over other materials of constructionFollowings are the advantage of concrete over other materials of construction:
• Concrete is free from defects and flaws which natural stones are associated,
• It can be manufactured to desired strength and durability with economy.
• It can be cast to any desired shape.
• Maintenance cost of concrete structures is almost negligible.
• Concrete does not deteriorate appreciably with age.
2.6 Workability of ConcreteThe strength of concrete of given mix proportion is very seriously affected by the degree of
its compaction ; it is therefore, vital that the consistency the mix be such that the
concrete can be transported placed and finished sufficiently easily and without
segregation. A concrete satisfying these condition is said to be workable but to say
merely that workability determines the case of transportation, placement and finishing
and the resistance of concrete to segregation is too loose a description of this vital
property of concrete workability can be best defined as a physical property which is the
amount of useful external and internal works necessary to produce of compaction of
concrete.
Another term used to describe the state or fresh concrete is consistency. In a simple
language, the word consistency refers to the firmness of a form of a substance or to the
case with which it will flow. In case of concrete, consistency is sometimes taken to mean
the degree of witness within limits. Wet concrete are more workable than dry concrete,
concretes of the same consistency may vary in workability.
2.6.1 Factors affecting workabilityThe main factor is the water content of the mix, expressed in pounds per cube yard of concrete.
It is convenient, though approximate, to assume that for a given type and grading of aggregates
and workability of concrete. The water content is independent of the aggregate cement ratio.
On the basis of this assumption the mix proportions of concretes of different richness can be
estimated and the following Table 2.1 gives typical values of water content for different
slumps and maximum size of the aggregates.
Workability is also governed by the maximum size of the aggregates their grading, shape and
texture. Grading and water/cement ratio have to be considered together as a grading producing
most workable concrete for one particular value of water/cement ratio may not be the best for
another value of the ratio. In particular, the higher the water/cement ratio the finer the grading
required for the highest workability. In actual fact, for a given value of water/cement ratio, there
is only one value of the coarse/fine aggregates ratio that gives the highest workability.
Air entrainment also increases workability. In general terms, entrainment of 5 percent air
increases the compacting factor of concrete by about 0.03 to 0.07 and slump by 1/2 to 2 inch
but actual values vary with properties of the mix. Air entrainment is also effective in
improving the workability of the rather harsh mixes made with light weight aggregates.
The reason for the improvement of workability by the entrained air is probably that air bubbles
act as a fine aggregate of very low surface friction and considerable elasticity. It is also claimed
that the air entrainment reduces both segregation and bleeding.
Table 2.1: Approximate Water Content for different Slumps and Maximum sizes of
Aggregates
Maximum
size of
Water content in Ib per cu yd. of concrete
1-2 inch slump 3-4 inch slump 6-7 inch slump
Rounded
Agg.
Angular
Agg.
Rounded
Agg.
Angular
Agg.
Rounded
Agg.
Angular Agg.
3/8 320 360 340 380 390 4303/4 290 330 320 350 350 380
l!/2 270 290 290 320 320 350
2 250 280 280 300 300 330
3 230 260 260 280 270 310
2.6.2 Measurement of WorkabilityUnfortunately no test is known that will measure directly the workability, numerous attempts
have been made, however, to correlate workability with some easily measurable parameter.
But none of these is fully satisfactory although they may provide useful information within a
range of variation in workability. Water content for different size of aggregates is followed as
per Table 2.1 as shown above.
2.7 Factors controlling properties of ConcreteThe properties (Strength, durability, impermeability and workability) of concrete depend
upon the following parameters (factors):
1. Grading of the aggregates.
2. Moisture content of the aggregates.
3. Water/cement ratio.
4. Proportioning of the various ingredients of concrete.
5. Method of mixing.
6. Placing and compaction of concrete.
7. Curing of concrete.
2.7.1 Water/Cement ratioIn engineering practices, the strength of concrete at a given age and cured at a
prescribed temperature is assumed to depend primarily of two factors:
1.The water/cement ratio and
2.The degree of compaction.
The proportion between the amount of water and cement used in a concrete mix is termed as
the water cement ratio.
The water in the concrete does primarily the three functions:
1. To wet the surface of the aggregate,
2. To impart workability and
3. To combine chemically with cement.
When concrete is fully compacted, its strength is taken to be inversely proportional to water-
cement ratio. It may be recalled that the water-cement ratio determines the porosity of the
hardened cement paste at any stage of hydration.
Experiments have shown that the quality of water in a mix determines its strength and there is
a water/cement ratio which gives the maximum strength to the concrete. It will be found
that there is a certain percentage of water below which the water will not be sufficient to
hydrate the cement. The use of less water than that required will not give workability and will
produce porous and weak concrete. On the other hand if more water is used than that actually
required, the concrete will be weak.
2.8 Concrete Recycling: When structures made of concrete are demolished or renovated, concrete recycling is an
increasingly common method of utilizing the rubble. Concrete was once routinely trucked to
landfills for disposal, but recycling has a number of benefits that have made it a more
attractive option in this age of greater environmental awareness, more environmental laws,
and the desire to keep construction costs down.
Concrete aggregate collected from demolition sites is put through a crushing machine.
Crushing facilities accept only uncontaminated concrete, which must be free of trash, wood,
paper and other such materials. Metals such as rebar are accepted, since they can be removed
with magnets and other sorting devices and melted down for recycling elsewhere.
2.9 Recycled concreteConcrete is one of the most important construction materials. Approximately one ton of
concrete used per capita per year throughout the world. This enormous dependence on
concrete is a compelling economic justification to seek improvements and new applications
for a material that has been, in more ways than one, the foundation of major construction
works. (Lee and Shah, 1988.) According to Kriejger (1980), concrete recycling usually
involves cement concrete pavements along roadways. Meanwhile, advances in the design and
construction of concrete structures since World War II imply demolition and disposal
problems for the concrete components in these structures when they eventually reach the end
of their useful lives. The need to recycle concrete components may be more than just cost-
oriented. Advantages of recycling concrete pavements include reduced costs from aggregate
produced on the job; reduced disposal costs and environmental damage; and the conservation
of natural resources, i.e. aggregate and energy. Moreover, valuable landfill space is not used
up. Recycled coarse aggregates may be more durable than virgin materials because they have
already gone through years of freeze-thaw cycles. Conservation of natural resources includes
reductions in the use of petroleum-based products and Portland cement, in aggregate
quarrying and in iron ore mining. The fact that asphalt concrete, Portland cement concrete
and iron can be recycled completely without requiring disposal also indirectly contributes to
efforts for preserving the environment. The fact that recycling concrete has proved
advantageous in pavement and road building encourages its use in residential construction as
well. In the Netherlands, so much work is being done regarding the recycling of C&D waste
in order to produce aggregates that a framework for a certification system
2.10 Importance of recyclingRecycling is the process of changing old and used products into new products to reduce
pollution and prevent the waste of useful material.
Without recycling, some important metals would be entirely used up in the next 50 to 100
years. For example, there would be no more zinc by 2037 without recycling.
Normal landfills, where regular trash goes, give off many toxic and dangerous chemicals.
These include gases that contribute to acid rain. Especially important to the world today is the
release of methane and carbon dioxide. Both are greenhouse gases and contribute to climate
change.
It takes less energy to recycle old products than make new ones entirely from 'scratch'. For
instance, it takes little energy to recycle an aluminum can. However, it takes a lot of energy to
produce entirely new aluminum cans as it is expensive to extract aluminum from its ore.
It creates jobs and stimulates the economy. People have to drive trucks to pick up the
recycling and the recycling plants employ lots of workers.
2.11. Uses of recycled concrete Smaller pieces of concrete are used as gravel for new construction projects. Sub-base gravel
is laid down as the lowest layer in a road, with fresh concrete or asphalt poured over it. The
Federal Highway Administration may use techniques such as these to build new highways
from the materials from old highways. Crushed recycled concrete can also be used as the dry
aggregate for brand new concrete if it is free of contaminants. Larger pieces of crushed
concrete, such as riprap, can be used for erosion control With proper quality control at the
crushing facility, well graded and aesthetically pleasing materials can be provided as a
substitute for landscaping stone or mulch. Wire gabions (cages), can be filled with crushed
concrete and stacked together to provide economical retaining walls. Stacked gabions are also
used to build privacy screen walls (in lieu of fencing)
2.12 Benefits of Recycling concreteThere are a variety of benefits in recycling concrete rather than dumping it or burying it in a
landfill.
Keeping concrete debris out of landfills saves landfill space.
Using recycled material as gravel reduces the need for gravel mining.
Using recycled concrete as the base material for roadways reduces the pollution involved in
trucking material.
Recycling Concrete is becoming an increasingly popular way to utilize aggregate left behind
when structures or roadways are demolished. In the past, this rubble was disposed of in
landfills, but with more attention being paid to environmental concerns, concrete recycling
allows reuse of the rubbl while also keeping construction costs down.
2.13 Uses of recycled concrete aggregate1. Using recycled concrete is an accepted source of aggregate into new concrete by ASTM
and AASHTO.
2. It is of high quality and meeting or exceeding all applicable state and federal
specifications.
3. Recycled aggregates are lighter weight per unit of volume, which means less weight per
cubic yard, resulting in reduced material costs, haul costs, and overall project costs.
4. It is currently being used in concrete and asphalt products with better performance over
comparable virgin aggregates.
5. It means minimization of environmental impacts in an Urban Quarry setting.
6. It Offers a way to reduce landfill waste streams.
7. It weighs ten to fifteen percent (10%-15%) less than comparable virgin quarry products
(concrete).
8. It provides for superior compaction and constructability.
2.14. Recycled and Reuse of Construction & Demolition Wastes in Concrete:
The recycling and reuse of construction & demolition wastes seems feasible solution in
rehabilitation and new constructions after the natural disaster or demolition of old structures.
This becomes very important especially for those countries where national and local policies
are stringent for disposal of construction and demolition wastes with guidance, penalties,
levies etc.
2.14.1. International StatusThe extensive research on recycled concrete aggregate and recycled aggregate concrete
(RAC) as started from year 1945 in various part of the world after second world war, but in a
fragmented manner. First effort has been made by Nixon in 1977 who complied all the work
on recycled aggregate carried out between 1945-1977 and prepared a state-of-the-art report
on it for RILEM technical committee 37-DRC. Nixon concluded that a number of researchers
have examined the basic properties of concrete in which the aggregate is the product of
crushing another concrete, where other concentrated on old laboratory specimens. However, a
comprehensive state-of-the-art document on the recycled aggregate concrete has been
presented by Hansen & others in 1992 in which detailed analysis of data has been made,
leading towards preparation of guidelines for production and utilization of recycled aggregate
concrete.
It has been estimated that approximately 180 million tones of construction & demolition
waste are produced each year in European Union. In general, in EU, 500 Kg of construction
rubble and demolition waste correspond annually to each citizen. Indicatively 10% of used
aggregates in UK are RCA, whereas 78,000 tons of RCA were used in Holland in 1994. The
Netherland produces about 14million tons of buildings and demolition wastes per annum in
which about 8 million tons are recycled mainly for unbound road base courses. The 285
million tons of per annum construction waste produced in Germany, out of which 77 million
tons are demolition waste. Approximately 70% of it is recycled and reused in new
construction work. It has been estimated that approximately 13 million tons of concrete is
demolished in France every year whereas in Japan total quantity of concrete debris is in the
tune of 10-15 million tons each year. The Hong Kong generates about 20 million tons
demolition debris per year and facing serious problem for its disposal. USA is utilizing
approximately 2.7 billion tons of aggregate annually out of which 30-40% are used in road
works and balance in structural concrete work. The rapid development in research on the use
of RCA for the production of new concrete has also led to the production of concrete of high
strength/performance. Indian Status there is severe shortage of infrastructural facilities like
houses, hospitals, roads etc. in India and large quantities of construction materials for creating
these facilities are needed. The planning Commission allocated approximately 50% of capital
outlay for infrastructure development in successive 10th & 11th five year plans. Rapid
infrastructural development such highways, airports etc. and growing demand for housing has
led to scarcity & rise in cost of construction materials. Most of waste materials produced by
demolished structures disposed off by dumping them as land fill. Dumping of wastes on land
is causing shortage of dumping place in urban areas. Therefore, it is necessary to start
recycling and re-use of demolition concrete waste to save environment, cost and energy.
Central Pollution Control Board has estimated current quantum of solid waste generation in
India to the tune of 48 million tons per annum out of which, waste from construction industry
only accounts for more than 25%. Management of such high quantum of waste puts
enormous pressure on solid waste management system. In view of significant role of recycled
construction material and technology in the development of urban infrastructure, TIFAC has
conducted a techno-market survey on 'Utilization of Waste from Construction Industry'
targeting housing /building and road segment. The total quantum of waste from construction
industry is estimated to be 12 to 14.7 million tons per annum out of which 7-8 million tons
are concrete and brick waste. According to findings of survey, 70% of the respondent have
given the reason for not adopting recycling of waste from Construction Industry is "Not
aware of the recycling techniques" while remaining 30% have indicated that they are not
even aware of recycling possibilities. Further, the user agencies/ industries pointed out that
presently, the BIS and other codal provisions do not provide the specifications for use of
recycled product in the construction activities.
In view of above, there is urgent need to take following measures:- Sensitization/
dissemination/ capacity building towards utilization of construction & demolition waste.
Preparation and implementation of techno-legal regime including legislations, guidance,
penalties etc. for disposal of building & construction waste. Delineation of dumping areas for
pre-selection, treatment, transport of RCA. National level support on research studies on
RCA. Preparation of techno-financial regime, financial support for introducing RCA in
construction including assistance in transportation, establishing recycling plant etc.
Preparation of data base on utilization of RCA. Formulation of guidelines, specifications and
codal provisions. Preparation of list of experts available in this field who can provide
knowhow and technology on totality basis. Incentives on using recycled aggregate concrete-
subsidy or tax exemptions. Realizing the future & national importance of recycled aggregate
concrete in construction, SERC, Ghaziabad had taken up a pilot R&D project on Recycling
and Reuse of Demolition and Construction Wastes in Concrete for Low Rise and Low Cost
Buildings in mid nineties with the aim of developing techniques/ methodologies for use
recycled aggregate concrete in construction. The experimental investigations were carried out
in Mat Science laboratory and Institutes around Delhi/GBD to evaluate the mechanical
properties and durability parameters of recycled aggregate concrete made with recycled
coarse aggregate collected from different sources. Also, the suitability in construction of
buildings has been studied. The properties of RAC has been established and demonstrated
through several experimental and field projects successfully. It has been concluded that RCA
can be readily used in construction of low rise buildings, concrete paving blocks & tiles,
flooring, retaining walls, approach lanes, sewerage structures, sub base course of pavement,
drainage layer in highways, dry lean concrete(DLC) etc. in Indian scenario. Use of RCA will
further ensure the sustainable development of society with savings in natural resources,
materials and energy. Experimental Investigations. In the present paper, an endeavor is made
so as to compare some of the mechanical properties of recycled aggregate concrete (RAC)
with the natural aggregate concrete (NAC). Since the enormous quantity of concrete is
available for recycling from demolished concrete structures, field demolished concrete is
used in the present study to produce the recycled aggregates. The concrete debris were
collected from different (four) sources with the age ranging from 2 to 40 years old and broken
into the pieces of approximately 80 mm size with the help of hammer & drilling machine.
The foreign matters were sorted out from the pieces. Further, those pieces were crushed in a
lab jaw crusher and mechanically sieved through sieve of 4.75 mm to remove the finer
particles. The recycled coarse aggregates were washed to remove dirt, dust etc. and collected
for use in concrete mix. The fine aggregate were separated out, and used for masonry mortar
& lean concrete mixes, which is not part this reported study. But these were found to suit for
normal brick masonry mortar and had normal setting and enough strength for masonry work.
Concrete Mixes The two different mix proportions of characteristic strength of 20 N/ mm2
(M 20) and 25 N/mm2 (M 25) commonly used in construction of low rise buildings are
obtained as per IS 10262 - 1982 or both recycled aggregate concrete and natural aggregate
concrete. Due to the higher water absorption capacity of RCA as compared to natural
aggregate, both the aggregates are maintained at saturated surface dry (SSD) conditions
before mixing operations. The proportions of the ingredients constituting the concrete mixes
are 1:1.5:2.9 and 1:1.2:2.4 with water cement ratio 0.50 & 0.45 respectively for M-20 & M-
25 grade concrete. The ordinary Portland cement of 43 grade and natural fine aggregates
(Haldane sand) are used throughout the casting work. The maximum size of coarse aggregate
used was 20 mm in both recycled and natural aggregate concrete. The total two mixes were
cast using natural aggregate and eight mixes were cast using four type of recycled aggregate
concrete for M-20 & M-25. The development of compressive strength is monitored by testing
the 150-mm cubes at 1, 3, 7, 14, 28, 56 and 90 days. In one set 39 cubes were cast for each
mix. The cylinder strength and corresponding strain & modulus of elasticity were measured
in standard cylinder of 150x300 mm size at the age of 28 days. The prism of size
150x150x700 mm and cylinder of size 150x300mm were cast from the same batches to
measure Flexural strength and splitting tensile strength respectively. This paper reports the
results of experimental investigations on recycled aggregate concrete. Properties of Recycled
Concrete Aggregate Particle Size Distribution The result of sieve analysis carried out as per
IS 2386 for different types of crushed recycled concrete aggregate and natural aggregates. It
is found that recycled coarse aggregate are reduced to various sizes during the process of
crushing and sieving (by a sieve of 4.75mm), which gives best particle size distribution. The
amount of fine particles (<4.75mm) after recycling of demolished were in the order of 5-20%
depending upon the original grade of demolished concrete. The best quality natural aggregate
can obtained by primary, secondary & tertiary crushing whereas the same can be obtained
after primary & secondary crushing incase of recycled aggregate. The single crushing process
is also effective in the case of recycled aggregate. The particle shape analysis of recycled
aggregate indicates similar particle shape of natural aggregate obtained from crushed rock.
The recycled aggregate generally meets all the standard requirements of aggregate used in
concrete. Specific Gravity and Water Absorption The specific gravity (saturated surface dry
condition) of recycled concrete aggregate was found from 2.35 to 2.58 which are lower as
compared to natural aggregates. Since the RCA from demolished concrete consist of crushed
stone aggregate with old mortar adhering to it, the water absorption ranges from 3.05% to
7.40%, which is relatively higher than that of the natural aggregates. The Table 4 gives the
details of properties of RCA & natural aggregates. In general, as the water absorption
characteristics of recycled aggregates are higher, it is advisable to maintain saturated surface
dry (SSD) conditions of aggregate before start of the mixing operations. Bulk Density the
ridded & loose bulk density of recycled aggregate is lower than that of natural aggregate
except recycled aggregate-RCA4, which is obtained from demolished newly constructed
culvert. Recycled aggregate had passed through the sieve of 4.75mm due to which voids
increased in ridded condition. The lower value of loose bulk density of recycled aggregate
may be attributed to its higher porosity than that of natural aggregate. Crushing and Impact
Values The recycled aggregate is relatively weaker than the natural aggregate against
mechanical actions. As per IS 2386, the crushing and impact values for concrete wearing
surfaces should not exceed 45% and 50% respectively. The crushing & impact values of
recycled aggregate satisfy the BIS specifications except RCA2 type of recycled aggregate for
impact value as originally it is low grade rubbles. Compressive Strength the average
compressive strengths cubes cast are determined as per IS 516 using As expected, the
compressive strength of RAC is lower than the conventional concrete made from similar mix
proportions. The reduction in strength of RAC as compare to NAC is in order of 2- 14% and
7.5 to 16% for M-20 & M-25 concretes respectively. The amount of reduction in strength
depends on parameters such as grade of demolished concrete, replacement ratio, w/c ratio,
processing of recycled aggregate etc. Splitting Tensile & Flexural Strength. The average
splitting tensile and flexural of recycled aggregate are determined at the age 1, 3, 7, 14, & 28
days varies from 0.30 -3.1 MPa and 0.95- 7.2 MPa respectively. The reduction in splitting
and flexural strength of RAC as compared to NAC is in order of 5-12% and 4 -15%
respectively. Modulus of Elasticity The static modulus of elasticity of RAC has been reported
in Table 4 and found lower than the AC. The reduction is up to 15% .The reason for the
lower static modulus of elasticity of RCA is higher proportion of hardened cement paste. It is
well establish that Ec depends on Ec value of coarse aggregate, w/c ratio & cement paste etc.
The modulus of elasticity is critical parameter for designing the structures, hence more
studies are needed.
2.15. DurabilityThe following parameters were studied to assess the influence of recycled aggregates on
durability of concrete.
Carbonation Freeze-Thaw Resistance CarbonationCO2 from the air penetrates
into the concrete by diffusion process. The pores (pore size>100nm) in the concrete in which
this transport process can take place are therefore particularly crucial for the rate of
carbonation. The carbonation tests were carried out for 90 days on the specimens
(150x150x150mm) of recycled aggregate concrete and natural aggregate concrete in
carbonation chamber with relative humidity of 70% and 20% CO2 concentration. The
carbonation depths of recycled aggregate concretes for different grade were found from 11.5
to 14mm as compared to 11mm depth for natural aggregate concrete. This increase in the
carbonation depth of RAC as compared to NAC, attributed to porous recycled aggregate due
to presence of old mortar attached to the crushed stone aggregate.
2.16. Freeze-Thaw ResistanceIn the freeze-thaw resistance test (cube method), loss of mass of the concrete made with
recycled aggregate was found sometimes above and below than that of concrete made with
natural aggregate. The results were so close that no difference in freeze thaw resistance (after
100 cycles) could be found. The literature also found that the effect of cement mortar
adhering to the original aggregate in RAC may not adversely affect the properties of RAC.
2.17. ConclusionRecycling and reuse of building wastes have been found to be an appropriate solution to the
problems of dumping hundred of thousands tons of debris accompanied with shortage of
natural aggregates. The use of recycled aggregates in concrete prove to be a valuable building
materials in technical, environment and economical respect Recycled aggregate posses
relatively lower bulk density, crushing and impact values and higher water absorption as
compared to natural aggregate. The compressive strength of recycled aggregate concrete is
relatively lower up to 15% than natural aggregate concrete. The variation also depends on the
original concrete from which the aggregates have been obtained. The durability parameters
studied at SERC(G) confirms suitability of RCA & RAC in making durable concrete
structures of selected types. There are several reliable applications for using recycled coarse
aggregate in construction. However, more research and initiation of pilot project for
application of RCA is needed for modifying our design codes, specifications and procedure
for use of recycled aggregate concrete.
CHAPTER III
TESTING AND ANALYSIS OF MATERIALS3.1 GeneralTo select the appropriate materials for concrete to get better strength as well as
workability following laboratory test has been recommended by ASTM.
• Gradation of Coarse and fine aggregates
• Aggregate crushing value (ACV) of coarse aggregate
• Flakiness Index of coarse aggregate
• Unit weight of coarse and fine aggregate
• Specific gravity and water absorption of coarse and fine aggregate
• Fineness modulus of fine aggregate
3.2 Testing of wet concreteTo confirm the workability and expected strength following test for wet concrete is widely used
at construction site
• Workability test.
• Slump test.
• Compaction factor..
• Spreading table.
• Two point test.
• Air content
• Setting time.
• Density
• Yield
3.3 Laboratory TestPrior to commencement of Concrete mix design we should know the physical properties of
materials. To know the physical properties of the materials following laboratory tests has been
conducted in the laboratory.
3.3.1 Grading of Coarse aggregateTo get the better workability as well as strength the coarse aggregate should confirm with the
specified limit of ASTM, which shown in Table 3.1 & 3.2. If we follow the proper grading the
proportion of paste and aggregate will be good combination which will give us better strength
and workability.
Table 3.1: Grading of Coarse aggregate
Sieve size(mm)
Individu al Wt. Retained (gm)
Cumulative Wt. Retained (gm)
Cumulative % retained
Cumulative % Passing
Specified Limit(% Passing)
25 0 0 0 100 100
20 118 118 2.58 97.42 90-100
12.5 3093 67.71 67.71 32.29 20-55
10 883 3976 87.13 12.87 5-20
5 (#4) 487 4463 97.80 2.87 0-5
0.075 (#200) 4522 4524 99.10 0.90 0-1.5
Pan 41 - - - -
Total 4563 - - - -
Remarks: The cumulative percent passing is within the range of the specified limit. So, the test
result is considered satisfactory.
Table 3.2: Grading of Coarse aggregate : (Recycled Concrete)
Sieve size (mm)
Individual Wt. Retained (gm)
Cumulative Wt. Retained(gm)
Cumulative % retained
Cumulative % Passing
Specified Limit (% Passing)
25 200 200 4.86 95.1 90-100
20 310 510 14.71 85.29 90-100
12.5 2920 3630 98.9 1.1 5-20
Pan 38 - - - -
Total 3468 - - - -
Remarks: The cumulative percent passing is within the range of the specified limit. & some
results are very near to the specified limit. So the test result is considered satisfactory.
3.3.2 Aggregate crushing value (ACV)The aggregate crushing value gives a relative measure of the resistance of an aggregate to
crushing under a gradually applied compressive load. With aggregate of an aggregate
crushing value higher than 30, the result may be anomalous. The standard aggregate
crushing test shall consist of aggregate passing the 14mm B.S Test Sieve and retained on the
10mm B.S Test Sieve. The specified value of ACV of ASTM shown in Table 3.3 & 3.4
Table 3.3: Aggregate Crushing value (ACV) Test (Stone chips)
Test No. 1 2 Specified Limit
Weight of surface dry Aggregate before test, A, gm. ( Aggregate Passing a 14.00 mm Sieve and Retained on a 10.00 mm Sieve) 2875 2860
Less than 30%
Weight of Aggregate Passing through 2.36 mm (# 8) Sieve after test. B gm. B gm. 722 706
Maximum load ( at 10 minutes duration ) KN 400 400
BAggregate Crushing value, ACV = — x100 % A
25.11 24.69
Average (Mean) Aggregate Crushing Value, (ACV), %
25.00
Remarks: The value for ACV test can not be greater than 30%, we get 25 %, which is less
than the specified limit. So, the result is satisfactory.
Table 3.4: Aggregate Crushing value (ACV) Test (Recycled concrete)
Test No. 1 2 Specified Limit
Weight of surface dry Aggregate before test, A,gm. ( Aggregate Passing a 14.00 mm Sieve and Retained on a 10.00 mm Sieve)
3050 3170
L
Weight of Aggregate Passing through 2.36 mm (# 8) Sieve after test. B gm 880 920 Less than 30%
Maximum load ( at 1 0 minutes duration ) KN 400 40030%
Aggregate Crushing value, ACV = ( B/A) * 1 00% 28.85 29.02
Average (Mean) Aggregate Crushing Value, (ACV),% 28.93
Remarks: The value for ACV test can not be greater than 30%, we 28.93 %, which is less
than the specified limit. So, the result is satisfactory.
3.3.3 Flakiness IndexThis test is based on the classification of aggregate particles as flaky when they have a thickness
(smallest dimension) of less than 0.6 of their nominal size, this size being taken as the mean
of the limiting sieve apertures used for determining the sieve fraction in which the particle
occurs. The flakiness index often aggregate sample is found by separating flaky particles and
expressing their mass as a percentage of the mass of the sample tested. The test is not
applicable to material passing a 6.3mm B.S Test Sieve and retains on a 63mm B.S Test Sieve.
The flakiness index test as shown in Table 3.5.
Table 3.5: Flakiness Index (F.I) Test (Stone chips)
Aggregate SizeTested weight (gm)
Wt. Retained(gm)
Wt.Passing (gm)
% Flaky (Individual) Specified Limit
50 mm -37.5 mm - - - -
Less than 30%
37.5 mm -28 mm - - - -28 mm -20 mm 100 100 0 020 mm - 14 mm 2080 1705 375 18.03
14 mm- 10 mm 1535 1225 310 20.2010 mm -6.3 mm 1285 1002 283 22.02
6.3 mm Not tested 210Total Wt. ( gm ) 5210 968
Calculation: Flakiness Index =
F.I = (968/5210) x 100%
F.I = 18.58 %
Remarks: The percentage of flaky should not exceed the range of 30%. We get both individual
and total Percentage of flaky less than 30%. So, the result is satisfactory.
Table 3.6: Flakiness Index (F.I) Test (Recycled concrete)
Aggregate SizeTested weight (gm)
Wt. Retained(gm)
Wt.Passing (gm)
% Flaky (Individual) Specified Limit
50 mm -37.5 mm - - - -
Less than 30%
37.5 mm -28 mm 620 510 110 17.7428 mm -20 mm 2715 2118 597 21.98
20 mm - 14 mm 1080 880 200 18.51
14 mm- 10 mm 615 135 480 78.0410 mm -6.3 mm - - - -
6.3 mm Not tested 180Total Wt. ( gm ) 5210 1387
Calculation: Flakiness Index =
Total Wt. passing through gauges x 100%
Total Wt. of Test Sample
F.I = (1387/5210) x 100%
F.I = 26.26 %
Remarks: The percentage of flaky should not exceed the range of 30%. We get both individual
and total Percentage of flaky less than 30%. So, the result is satisfactory.
3.3.4 Grading of fine aggregateThe grading of fine aggregate to be done to maintain the better property of aggregate in
concrete mix . It has been seen that if the fine aggregate is in ASTM specified limit those have
given better workability and strength. The specified limit of ASTM for grading of fine
aggregate is shown in Table 3.6 & 3.7.
Table 3.7: Grading of Sylhet Sand
Sieve size (mm)
Individual Wt. Retained (gm)
Cumulative Wt. Retained (gm)
Cumulative % Retained
Cumulative % Passing Specified Limit ( % Passing)
10 0 0 0 100 100
5.0 22.0 22.0 1.45 98.55 95-100
1.2 509 531 34.70 65.30 45-80
0.300 691 1222 79.85 20.15 10-30
0.15 194 1416 92.56 7.44 2 - 1 0
0.075 89 1505 98.35 1.65 0-3Pan 25 - - - -
Total 1530 - - - -
Remarks: The cumulative percent passing is within the range of the specified limit. So, the test
result is considered satisfactory.
3.3.5 Fineness Modulus of fine aggregate (F.M)The term fineness modulus is a ready index of coarseness and fineness of the materials. It
is an empirical factor obtained by adding the cumulative percentages of aggregates retained on
each of the standard sieve and dividing some arbitrarily by 100. The fineness modulus test as
shown in Table 3.8.
Table 3.8: Fineness Modulus of Sand (F.M)
Total Wt. passing through gauges x 100%
Total Wt. of Test Sample
Sieve size(mm)
IndividualWt.Retained(gm)
CumulativeWt.Retained(gm)
Cumulative% Retained
Cumulative% Passing
Specified Limit(% Passing)
10 1005.0 (#4) 10 10 1.39 100
2.4 (#8) 96 106 14.72 1001.2 (#16) 135 241 33.47 95-100
0.600(#30)
142 383 53.19 85-100
0.300(#50)
118 501 69.58 50-80
0.150(#100)
104 605 84.03 5-25
Pan 115 256.38
Total 720 F.M = 256.38/100= 2.56
Remarks: For Cement concreting works F.M of fine aggregate should be minimum 2.50. We
get F.M 2.56. So, result is satisfactory.
3.3.6 Specific Gravity and water absorption of Coarse & Fine aggregate
Specific gravity of materials expresses the weight of that material with comparison with water. Specific gravity of a material is the ratio of weight of that material in air to the weight of losses of that material in water. Water absorption of materials shows the percentage of void attain in the material, i.e. how many water it can absorb. Determination of Specific gravity and water absorption are shown in Table 3.9 & 3.10.
Table 3.9: Specific Gravity and Water absorption of Coarse Aggregate (Stone chips)
SI. No. Description Test Result1 Weight of Sample in SSD condition, A 1841.20gm
2 Weight of Sample in Oven dry condition, B 1 830.70 gm
3 Weight of Sample in Water, C 1151.6 gm
4 Water absorption {(A-B)/B}*100 0.574 %
5 Bulk Specific gravity (SSD condation) {A/(A-C)} 2.67
6 Bulk Specific gravity (Oven dry condation) {B/(A-C)} 2.655
7 Apparent Specific gravity {B/(B-C)} 2.696
Remarks: For Cement concreting works the specified limit for Sp.Gr.of Coarse aggregate
(stone chips) should be minimum 2.60 and Water absorption should not exceed 1 %. We get
Sp. Gr. 2.67 and Water absorption 0.574 %. This is incompliance with the specified limit. Thus
the result is satisfactory.
Table 3.10: Specific Gravity and water absorption of Fine aggregate (Sylhet Sand)
SI. No. Description Test Result1 Weight in air saturated dry sample (SSD), A 100 gm
2 Weight in air of oven dried sample, B 98.40 gm
3 Weight of Pycnometer bottle filled with water, C 620.60 gm4 Pycnometer bottle + Sample, D 681.4 gm
5 Absorption (A — B)/B*100 1.626%
6 Bulk Specific gravity(SSD) A/(A + C-D) 2.551
7 Bulk Specific gravity(Oven dry) B/(A + C-D) 2.5108 Apparent Specific gravity B/(B + C-D) 2.617
Remarks: For Cement concreting works the specified limit of Sp.Gr.of Fine aggregate should
be minimum 2.50 and Water absorption should not exceed 2 %. We get Sp. Gr. 2.551 and
Water absorption 1.626 %. This is incompliance with the specified limit. Thus the result is
satisfactory.
3.3.7 Unit weight of Coarse and Fine aggregate:
This test method covers the determination of unit weight in a compacted or loose condition of
fine and coarse aggregates. The test may also be used for determining mass or volume
relationship for conversion and calculating the percentage of void in aggregates. This test
method confirms to the ASTM standard requirements of specification C29. The unit weight
test is shown in Table 3.11 & 3.12.Table 3.11: Unit Weight of Coarse aggregate (Stone chips)
SI. No. Description Sample1 Sample2 Sample3 Average Unit Wt. (gm/cc)
1 Wt. of empty Mould (gm) 5100 5100 5100
1.6202 Wt. of Mould + Sample (gm) 16598 16613 16598
3 Wt. of Sample (gm) 11498 11513 11498
4 Volume of Mould (cc) 7102 7102 7102
5 Unit Weight (gm/cc) 1.619 1,621 1.620
Remarks: The Unit weight of coarse aggregate (stone chips) should be minimum 1.60
gm/cc. We get 1.620 gm/cc. Thus the result is satisfactory.
Table 3.12: Unit Weight of Coarse aggregate (Recycled concrete)
SI. No. Description Sample1 Sample 2 Sample 3 Average Unit Wt. (gm/cc)
1 Wt. of empty Mould (gm) 5100 5100 5100
2 Wt. of Mould + Sample (gm)
15598 15613 14998
3 Wt. of Sample (gm) 10498 10513 9898 1.450
4 Volume of Mould (cc) 7102 7102 7102
5 Unit Weight (gm/cc) 1.478 1,480 1.393
Remarks: The Unit weight of coarse aggregate (Recycled concrete) should be minimum
1.60 gm/cc. We get 1.450 gm/cc. Thus the result is not satisfactory.
Table 3.13: Unit Weight of Fine aggregate (Sylhet Sand)
SI.No. Description Sample 1 Sample 2 Sample 3 Average Unit Wt. (gm/cc)
1 Wt. of empty Mould (gm) 5100 5100 5100
1.5522 Wt. of Mould + Sample (gm) 16123 16130 16117
3 Wt. of Sample (gm) 11023 11030 11017
4 Volume of Mould (cc) 7102 7102 7102
5 Unit Weight (gm/cc) 1.552 1.553 1,551
Remarks: The Unit weight of fine aggregate (Sylhet sand) should be minimum 1.50 gm/cc.
We get 1.552 gm/cc. Thus the result is satisfactory.
3.4 Mix Design:Calculation of materials:
Cement =300 kg/³
Water = 174 kg/m³
Coarse aggregate = 1053 kg/m³
Air voids = 2%
Now on Absolute volume basis
Cement = 300/(3.15x1000)= 0.095 m³
Water = 174 kg or liter =0.174 m³
Coarse aggregate = 1053/(2.67x1000)=0.394 m³
Air voids =2% = 0.020 m³
Total = 0.683m³
Volume of fine aggregate = 1-0.683 =0.317 m
Dry weight of sand = 0.317x2.55x1000 = 809 kg
Trial batch weight for one m3 mix is as follows:
Cement =300kg
Water = 174 liters or kg
Fine Aggregate = 809 kg
Coarse Aggregate = 1053 kg
Total wt. of batch = 2336 kg.
Field conditions normally exist where the aggregates contain some absorbed moisture, but
generally this percentage is less than the total absorbed amount. During rainy season
aggregates will contain more moisture where this should be checked before starting the work
and batch weights shall be adjusted.
In this example, moisture content of Fine Aggregate is 4% and the Coarse Aggregates is 0.5%.
Also in this example weight of coarse and fine aggregates would have to be increased due to
their moisture content.
Weight of coarse aggregates = 1053 +1053 x 0.005 = 1058.265 kg.
Weight of fine aggregates = 809 + 809 x 0.04 = 842 kg.
The coarse aggregate will absorb additional water because it contains only 0.5% water = 2-
0.5 = 1.5% from the mixing water whereas sand will contribute = 4-1 = 3% surface free
water.
The estimated requirement for added water therefore becomes: 174 + J053 x 0.015 - 809 x
0.03 = 166 kg.
The estimated batch weights for one m3 of concrete are
Water = 166 Liters
Cement = 300kg.
Coarse aggregate (moist) =1058 kg.
Fine aggregate (moist) = 842 kg.
Therefore total adjusted wt. of mix = 2366 kg,
Table 3:14. Mix Design Data sheet (basis 1 m³):
Tar
get S
treng
th (p
si)
Cem
ent c
onte
nt (k
g)
Wat
er (k
g)
W/C
ratio
Vol
ume
of C
.A m
³
Wei
ght o
f C.A
(kg)
Absolute volume m³
Vol
ume
of F
.A m
³
Wt.o
f F.A
(kg)
Uni
t wt.
ofco
ncre
te, k
g/ m
³
Cem
ent
Wat
er
C.A
Air
Vol
ume
with
out F
.A
3000
300 174 0.58
0.65 1053 0.095 0.174 0.394 0.02 0.683 0.317 8.9 2336
Photo 3.1: Concrete mixing
Photo 3.2: Making of cylinder
Photo 3.2: Cylinder Sample of curing
CHAPTER IV
RESULTS AND DISCUSSIONS4.1 GeneralAfter preparing the test specimen the sample is removed from the cylinder mould and
immersed in a water tank for curing. Thirteen, twenty & twenty seven days later six set of
specimens are taken out from the water tank for conducting the compressive strength test.
The 18 specimens are tested by compressive testing machine. The test results of the 6 sets of
concrete cylinders are shown in the Table 4.1, 4.2 & 4.3.
Table 4.1: Test Results for 14 days fresh concrete & recycled concrete
Type
of c
oncr
ete.
Sl.N
o.
Age
. On
the
date
of
test
(da
ys)
Sam
ple
iden
tific
atio
n on
mar
k
Spec
imen
are
a (s
q.in
)
Max
imum
load
(lb)
Cru
shin
g st
reng
th
(psi
)
Avg
. cru
shin
g str
engt
h (p
si)
Type
of f
ailu
re
Fres
h co
ncre
te
1 14 PBMMP1 12.42 34527.6 27802836.67
combined
2 14 PBMMP1 12.55 36395 2900 Combined
3 14 PBMMP1 12.67 35856.1 2830 Combined
Rec
ycle
d co
ncre
te
1 14 UTTARA-05 12.30 23247.0 18901846.67
Combined
2 14 UTTARA-05 12.42 22977.0 1850 Combined3 14 UTTARA-05 12.42 22356.0 1800 combined
Photo 3.3 : Cylinder Sample for testing
Type
of c
oncr
ete.
Sl.N
o.
Age
. On
the
date
of
test
(da
ys)
Sam
ple
iden
tific
atio
n on
mar
k
Spec
imen
are
a (s
q.in
)
Max
imum
load
(lb)
Cru
shin
g st
reng
th
(psi
)
Avg
. cru
shin
g str
engt
h (p
si)
Type
of f
ailu
re
Fres
h co
ncre
te 1 21 SYMYB1 12.30 44058.6 3582
3640.67
combined
2 21 SYMYB1 12.42 45829.8 3690 Combined
3 21 SYMYB1 12.42 45333.0 3650 Combined
Rec
ycle
d co
ncre
te 1 21 UTTARA-05 12.30 29889.0 2430
2370.00
Combined
2 21 UTTARA-05 12.42 29559.6 2380 Combined
3 21 UTTARA-05 12.42 28566.0 2300 combined
Table 4.2: Test Results for 21 days fresh concrete & recycled concrete.
Table 4.3: Test Results for 28 days fresh concrete &recycled concrete.
Type
of c
oncr
ete.
Sl.N
o.
Age
. On
the
date
of
test
(da
ys)
Sam
ple
iden
tific
atio
n on
mar
k
Spec
imen
are
a (s
q.in
)
Max
imum
load
(lb)
Cru
shin
g st
reng
th
(psi
)
Avg
. cru
shin
g str
engt
h (p
si)
Type
of f
ailu
re
Fres
h co
ncre
te 1 28 BOPCB1 12.30 48954 3980
4043.34
combined
2 28 BOPCB1 12.42 50922 4100 Combined
3 28 BOPCB1 12.42 50301 4050 Combined
Rec
ycle
d co
ncre
te
1 28 UTTARA-05 12.52 33804 2700
2636.67
Combined
2 28 UTTARA-05 12.65 33522 2650 Combined
3 28 UTTARA-05 12.80 32768 2560 combined
4.2 Cost Analysis
4.2.1 Cost of 100 cft normal concrete using well graded crushed stone chips (cost based on PWD schedule)
A. Cost of Materials (1:1.5:3)1 3/4" down grade stone 82 Cft @ Tk. 130.00 Each = Tk.10,660.00 2 Sand (F.M.2.50) 41 Cft @ Tk. 40.00 Each = Tk. 1,640.00
3 Cement 22 bag @ Tk. 400.00 Each = Tk. 8,800.00 5 Water 1 L/S @ Tk. 5.00 Each = Tk. 5.00
6Carrying charge including storage screening, T& P & sundries in the plant area.
1 L/S @ Tk. 50.00 Each Tk 50.00
Total A- Tk.21,155.00
B. Cost of labour for 2500 Cft1 Head Mason 2 nos @ Tk.4,000.00 Each = Tk.8,000.00 2 Mason 4 nos @ Tk. 275.00 Each = Tk.1,100.00 3 Skilled labor 3 nos @ Tk. 250.00 Each = Tk. 750.00 4 Ordinary labor 3 nos @ Tk. 200.00 Each = Tk. 600.00
5Hire charge for vibrator machine with operator in/c. fuel & lubricants
1 L/S @ Tk.1,300.00 Each = Tk1,300.00
6Cost of Mixing charge by batching plant in/c. transit mixture truck & other necessary equipments
2500 Cft @ Tk. 25.00 Each = Tk.62,500.00
7 Cost of labor for curing 28days x 1/4 No 4 nos @ Tk. 150.00 Each = Tk. 600.00
Total B- Tk.74,850.00
So Rate per 100 Cft.
= Tk.2,994.00
Abstract of cost (For 100 Cft of work)
1 Cost of Materials Tk. 21,155.00
2 Cost labour, equipment, mixing charges by plant other n.c Tk 2,994.00
Total = Tk.24,149.00 Tk.24,149.00
Grand total = Tk.24,149.00
Rate per Cft. = Tk. 241.49
4.2.2 Cost of 100 cft recycled concrete using stone chips collected from
breaking of pile head (cost based on current market rate)
A. Cost of Materials (1:1.5:3)
1 3/4" pile head breaking stone(with crushing) 82 Cft @ Tk. 50.00 Each = Tk. 4,100.00
2 Sand (F.M.2.50) 41 Cft @ Tk. 40.00 Each = Tk.1,640.00 3 Cement 22 bag @ Tk. 400.00 Each = Tk.8,800.00 5 Water 1 L/S @ Tk. 5.00 Each = Tk. 5.00
6Carrying charge includingstorage screening, T& P & sundries in the plant area.
1 L/S @ Tk. 50.00 Each Tk 50.00
Total A- Tk.14,595.00
B. Cost of labour for 2500 Cft
1 Head Mason 2 nos @ Tk.4,000.00 Each = Tk.8,000.00
2 Mason 4 nos @ Tk. 275.00 Each = Tk.1,100.003 Skilled labor 3 nos @ Tk.250.00 Each = Tk 750.004 Ordinary labor 3 nos @ Tk.200.00 Each = Tk. 600.00
5 Hire charge for vibrator machine with operator in/c. fuel & lubricants 1 L/S @
Tk.1,300.00 Each = Tk.1,300.00
6Cost of Mixing charge by batching plant in/c. transit mixture truck & other necessary equipments
2500 Cft @ Tk. 25.00 Each = Tk.62,500.00
7 Cost of labor for curing 28days x 1/4 No 4 nos @ Tk.150.00 Each = Tk. 600.00
Total B- Tk.74,850.00 So Rate per
100 Cft. = Tk. 2,994.00
Abstract of cost (For 100 Cft of work)
1 Cost of Materials Tk.14,595.00
2 Cost labour, equipment, mixing charges by plant other n.c Tk. 2,994.00 Total = k.17,589.00
k.17,589.00 Grand total = Tk.17,589.00
Rate per Cft
= Tk. 175.89
4.3 Major findingsAfter testing the specimen of both normal concrete and recycled concrete, graphs of day vs
strength are plotted separately in fig 4.1, fig 4.2 and combined graph is also plotted in figure
4.3.
Figure 4.1 : Day vs strength graph of normal concrete
Figure 4.2 : Day vs strength graph of Recycled concrete
Figure 4.3 : Day vs strength graph of normal concrete and recycled concrete (Combined)
In 14 th day test average Cruising strength of recycled concrete varied from normal concrete by
34.9% and whereas 21st in day test it varied by 34.9% and in 28 th day it varied by 34.78%
and in an average strength of recycled concrete varied from normal concrete by 34.86% that is
35%.
In case of cost involved in preparation of 100 cft concrete it is reveled that material cost of
recycled concrete is 14,595 tk. where as materials cost of normal concrete is 21,155 tk. cost of
per cft recycled concrete 175.89 tk. and normal concrete is 241.5 tk. recycled concrete is
27.16% cost effective than normal concrete.
One of the Major challenge of our present society is protection of environment. Some of the
important element in this respect are reduction of consumption of energy and natural raw
materials and consumption of waste materials. The use of recycled aggregate from
construction and demolition waste is showing prospective application in construction as an
alternative to natural aggregates. It conserves natural resources and reduces the space required
for landfill disposal. This recycled concrete proves itself as environment friendly construction
materials
CHAPTER V
CONCLUSION AND RECOMMENDATION5.1 ConclusionsBased of the above study following conclusions can be done.
1) Recycling and reuse of building waste have been found to be and appropriate solution
to the problem of dumping of thousands ton of debris.
2) Recycling and reuse of construction waste also reduce disposal cost, reduce drainage
congestion and conserve the natural recourses both aggregate and energy.
3) Recycled course aggregate may be more durable than virgin material because they
have already gone through years of freeze thaw cycles.
4) Unit wt of recycled aggregate is less than natural aggregate which means less wt per
cubic ft resulting in reduced material cost and overall project cost.
5) The compressive strength of recycled aggregate concrete is 35% lower than natural
aggregate, so recycled concrete has proved advantageous was in pavement and road
buildings in landscaping and in retaining walls.
6) Use of recycled aggregate concrete proves to be a valuable building material in
technical and environmental aspect as well as in economical aspect by keeping
construction cost low.
5.2 RecommendationsRecycling concrete is becoming as increasingly popular way to utilize aggregate left behind
when structures or roadways are demolished. In the past that rubble was disposed of in land
fills, but with more attention being paid to environmental concerns concrete recycling allows
reuse of the rubble also keeping construction cost down
However more research and initiation of pilot project for application of recycled aggregate
concrete is needed for modification our design code specification and procedure for use of
recycled aggregate concrete.
REFERENCES1. Data Collected from “www.recycledconcrete.com”
2. Data collected from thesis paper of “A Comparative study of normal concrete and
chemical based concrete & different water cement ratio”.
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