design of concrete mixtures with recycled concrete

8/12/2019 Design of Concrete Mixtures With Recycled Concrete

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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

design of concrete mixtures with recycled concrete

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