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DESIGN OF CONCRETE
MIXTURES WITH
RECYCLED CONCRETE
AGGREGATES
DONE BY
FENIL JOSE
S7 CE
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INTRODUCTION
This seminar focus on the use of Recycled Concrete
Aggregate as a replacement for natural coarse aggregatein normal strength structural concrete application
o RCA - defined as minimum 90- 95 % crushed concrete
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ADVANTAGES
Possible to reduce the demand for new aggregate
Keep the construction cost down
To avoid the exploitation of natural aggregate
save time
no shortage of material
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CONCRETE MIXTUREDESIGN METHODS
3 METHODS
DIRECT WEIGHT REPLACEMENT
EQUIVALENT MORTAR REPLACEMENT
DIRECT VOLUME REPLACEMENT
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DIRECTWEIGHT REPLACEMENT
Simple method
Weight of C.A in concrete kept constant
W/C constant
Reduction in F.A is made
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EQUIVALENT MORTAR REPLACEMENT
RCAtreated as two phase material (RNA & RM)
Vol. of residual mortar is accounted
Vol. of total mortar is constant
VRM+ VFM (EMR) = VFM (NAC)&
VRNA + VNA (EMR) = VNA (NAC)
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DIRECT VOLUME REPLACEMENT
Natural aggregate in the concrete mixture replaced
by same volume of RCA
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Aggregate from 16 places are used in this study
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AGGREGATEPREPARATION
Dry sieving ( 2.36 mm)
Washing & grading
Dried in oven at 110 c for 24 hrs
Soaked in water for 18 -24 hrs
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PREPARATIONOFCONCRETECUBES
& CYLINDERS
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TESTS
SLUMP TEST
COMPRESSIVE STRENGTH
MODULUS OF ELASTICITY
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TEST RESULTS
SLUMP TEST
o Direct Volume Replacement method provide similar
workability that of natural aggregate concrete
o Direct Volume Replacement method provide a smaller
slump than Natural Aggregate concrete
o Due to the reduced fresh mortar Equivalent Mortar
Replacement mixtures become unworkable at small
amount of replacement (20 %)
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COMPRESSIVE STRENGTH
o A significant distinction can not be made between
DWR, DVR, EMR methods
o Depending up on the RCA quality , it is possible to
produce concrete with comparable strength as the
target NA concrete
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MODULUS OF ELASTICITY
o For the RCA mixtures based on NA-PG target ,there is
no discernible change in Esecas R is increase
o Where as for the mixtures based on NA-CL target , a
significant decrease in Esec is observed with increase
in R
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FINDOUTSOFTHISSTUDY
o Workability of fresh RCA concrete is affected by the mixture designmethods. DVR produce similar slump of natural concrete mix.
o Compressive strength & Modulus of elasticity of RCA
concrete are not significantly affected by the mix design methods
o Compressive strength & Elastic modulus depends up on quality ofRCA
o Greater effect of RCA on modulus of elasticity than on compressive
strength
o By ensuring the quality of RCA better concrete can produce withmaximum replacement
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A CASE STUDY IN INDIA
In this study concrete waste from demolished structure
(near Nehru park ,bhandarar , pune ) is used.
EXPERIMENTAL STUDY
3 types of aggregate is used in this experiment
Natural Coarse Aggregate
Natural Fine Aggregate
Recycled Concrete Aggregate
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Minimum size of the Natural Coarse Aggregate is 25 mm
Natural Fine Aggregate used is river sand
Natural Coarse Aggregate used is microtonalite
Concrete cubes & cylinders are prepared for 0%
25%,50%,75%,100% replacement of RCA
o Compressive strength & splitting tensile test for 7&28 daysare tested
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MIX DESIGN
Numerous trial mixes were done
OPTIMUM MIX PREPORTION
Cement - 400 kg/m3
Sand - 660 kg/m3
Gravel - 1168 kg/m3
Mix proportion by weight = 1:1.65:2.92
W/C ratio - 0.5
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MATERIALSREQUIREDFORTHEEXPERIMENT
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TREATMENT PROCESS FOR RCA
1.Washing
Aggregate collected by sieve analysis are washed bypressure washing for about 15 to 20 minutes
Aggregates are kept for sun drying about 30 minutes
2. Heating
Heated in an oven at 150 C for 1 hour
3.Cooling
cooled to room temperature
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CASTING PROCESS
Cubes & Cylinders are casted with 0 % ,25%,50%
75%,100% replacement of RCA
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CONCLUSION
This result obtained for W/C ratio 0.5 it may change with W/C
The compressive strength of the concrete containing
50 % RCA has strength in close proximity to that of normalconcrete
o Tensile splitting test shows that concrete has good tensile strengthwhen replace up to 50 %
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REMOVAL
1.Removal of reinforcement
2. Removal of contaminants by mechanical implements
3.Dry/Wet process
PLANT
* Open system
Closed system
Closed system is preferable -
It allow greater control over the maximum particle sizeproduced
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Screening
Eliminating dirt, gypsum, plaster
AGGREGATE QUALITY
Density :
RCA have density less than original aggregates
Water absorption
Higher water absorption of RCA due to old cement mortar
attached to the aggregate particle
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CONTAMINANTS
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EFFECT OF RCA ON CONCRETE
Compressive strength reduces from 5 to 24 %
compressive strength depends on the strength of theoriginal concrete & it is controlled by w/c ratio
If recycled fine aggregate is used with recycled coarse
aggregate strength of concrete reduced by 15 to 40%
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STRENGTH VARIATION
Concrete manufactured from recycled aggregates fromdifferent sources will have greater variations than
concrete manufactured from aggregates produced from
only one source
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Modulus of elasticity
Reduces 10 to 33 %
o Creep
Greater than concrete from natural aggregates 30 %
o Shrinkage
Greater than 20 -50 %
o Tensile strength
10 % reduction in the strength
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W/C ratio
w/c is valid for recycled aggregate concrete as it is for
concrete made with virgin material , but only the level
of strength development would be reduced
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MECHANICAL PROPERTIES OF RCA
WITH DEFORMED STEEL BAR
This study is intended to understand characteristics of
RCA and its bonding strength to deformed steel bar
Concrete specimens for two different mix proportion
with varying levels of replacement of RCA was made
while diameter of bars for two specimens were keptconstants
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EXPERIMENTAL VARIABLES
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PREPARATION OF SPECIMENS
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MATERIALS
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MIX PROPORTION
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CURING
Compressive strength , modulus of elasticity were
measured using the cylinder specimens which were
cured under water for 28 days
The pull out specimens were also cured under water
but all the exposed surface of the steel bar was covered
with an oil in order to minimize the corrosion
o It was then wet cured in the normal temperature using
the curing blanket which kept it consistently wet
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BOND STRENGTH MEASUREMENT
This experiment employed a modified testing scheme
Deformed bar not directly pulled out , in the right side
where bar fixing epoxy bulb was pulled out
In order to minimize the anticipated errors which
could occur due to deformation of metal parts in the
left hand side steel supports in the left side were fixedto the bottom of the floor using bolts
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CONCLUSION
In the occasion of replacing only C.A with the RCA ,
3 % decrease in bond strength is found
o
By replacing 30 % fines with RCA with C.A ,7%decrease in bond strength is found
o While replacing whole quantity 18 % decrease in bond
strength is found
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LIMITATION
Compressive strength concrete with RCA is reduces
to 5-24 %
o
Land & special machineries are required
o Higher drying shrinkage & creep
o Quality of material
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CONCLUSION
o Use of 30 % RCA does not affect the functional
requirements .
o Adopting more technical & improved methods in
preparation of RCA & also demolition of concrete
structures ,50 % RCA can used in concrete
o These results ( when RCA) is used give satisfactory
result s according to IS 2386