B.E. CIVIL ENGINEERING PROJECT PROPOSAL

PROPERTIES OF RECYCLED COARSE AGGREGATES

IN CONCRETE

Submitted By

SHIVA KRISHNA CHENNA

(160110732052)

Project Guide

Dr. K. JAGANNADHA RAO SIR

Professor, Structural Engineering

DEPARTMENT OF CIVIL ENGINEERING

CHAITANYA BHARATHI INSTITUTE OF TECHNOLOGY

HYDERABAD.

Table of Contents

S.NO CONTENT PAGE NO.

1. Title Page 1

2. Table of Contents 2

3. Objective of Project 3

4. Literature Review 3

5. References 21

OBJECTIVE OF THE PROJECT

The main object of the Project is to study the behaviour of

concrete when RECYCLED COARSE AGGREGATES are

replaced by CONVENTIONAL AGGREGATES.

LITERATURE REVIEW

INTODUCTION

WHY RECYCLED AGGREGATES

1. Sustainable practices are desirable

2. Reuse and conserve natural resources

3. Cost savings over traditional methods

Use of RA in concrete and asphalt showed comparable

performance over virgin aggregates

CHALLENGES FOR USE OF RCA

1. Resistance to change

2. Lack of experience

3. Inadequate codes, specifications and standards

4. Inconsistent aggregate grading

5. Lower and variable quality

Collection Of Aggregates From Construction Waste

AGGREGATE PROPERTIES

Residual adhered mortar on aggregate is a main factor affecting

the properties of density, porosity and water absorption of RCA.

The density of Recycled Coarse Aggregates is generally lower

than Natural Aggregate due to the adhered mortar that is less

than the underlying rock. The relative density of RCA is 7-9%

lower than NA.

COMPRESSIVE STRENGTH

Most researches recommended that without changes to the mix

involving adjustments to the w/c ratio, up to 25% or 30% of coarse

aggregate can be replaced with RCA before the ceiling strength is

comprised.

TENSILE STRENGTH

Splitting tensile strength is less effected by RCA than

Compressive strength. Splitting tensile strength of RCA is

comparable to NA also. In some cases RCA performs more

superior to NA in case of tensile strength and the improvement is

due to increased absorption of mortar attaché to RCA and also

the ITZ zone (which is a zone of concrete weak in compression),

which creates a good bond between aggregates and adhered

mortar.

MODULUS OF RUPTURE AND ELASTICITY

Modulus of rupture, a measure of flexural strength and modulus of

elasticity (young’s modulus), a measure of concrete stiffness are

often predicted from compressive strength but these relationships

do not represents RCA concrete and NA concrete. RCA performs

better in modulus of rupture than NA at high water cement ratio.

For RCA replacement of 15%-50%, there is only 13% reduction in

Modulus of rupture.

MODULUS OF ELASTICITY

The main factor effecting the modulus of elasticity of RCA

concrete if modulus of elasticity of aggregates itself. Improvement

of tensile strength with the addition of RCA would usually be

associated with an improved elasticity, however the RCA are

more prone to deform than NA, the weakness of the aggregates

reduces the modulus of elasticity of RCA.

DEFLECTIONS

Based on service loads RCA reinforced concrete beam performs

less well than conventional concrete beams. However the change

in aggregate does not have enough influence on deflection to

discourage RCA use in concrete beams and it is found that under

a load of 40% of failure load mid span deflections are greater for

RCA beams than for NA beams.

SHAPE AND GRADATION

The shape of the aggregate piece is influence on the workability

of the concrete, that the method of producing RCA and the type of

crusher that is used in this process is influenced on the shape of

RCA produced. NA is generally an angular shape with smooth

sides and initially described the plant produced RCA as grainy in

texture and later discussed that the RCA has more rounded,

spherical shape which seemed to improve the workability. The

residual mortar on RCA can smooth out the hard edges of the

original aggregate. This allows the new mortal to flow later round

the aggregates. The effect of the aggregates shape on workability

and strength parameters of concrete.

CONCLUSIONS

RCA can be lower quantity aggregate and have a negative

influence on concrete material properties, the large scale testing

showed that, when looking at a complete structural member, RCA

can still be used to create a structural concrete. Since the

performance of RCA concrete beams are still within standard

specifications, it is likely a variable option for structural use. Since

the qualities if RCA are highly varied among different sources.

REFERENCES

1. www.cement.org/tech/cct_aggregates_recycled.asp

2. http://en.wikipedia.org/wiki/Concrete

3. http://en.wikipedia.org/wiki/Concrete_recycling

4. http://www.ccanz.org.nz/images