Page 5 - Open-Access-July-2019

TECHNICAL PAPER

and plastering is done using cement mortar. In second method, significant change in concrete properties . To improve the
[8]
instead of resin, cement slurry is used as the bonding agent. In properties, various additives can be used. Previous studies
the third, meshes can be attached via mechanical means using showed that recycled aggregates can be used for structural
bolts or nails. The surface needs to be cleaned before attaching concrete members with the addition of flyash and condensed
wire mesh and thickness of confinement is limited to 25 mm. silica fume . The stress-strain behaviour of recycled aggregate
[9]
Use of Ferrocement laminates can enhance the load carrying concrete is similar to that of conventional concrete. Peak stress,
capacity and ductility of concrete specimens . Enhancement is peak strain and secant modulus increase with increase in the
[2]
more in small sized specimens. Also, study reveals that double strength grade of recycled aggregate concrete while elastic
layer of mesh can provide more effective confinement than modulus decreases with increase in percentage replacement
single layer of wire mesh . Ferrocement confinement on lower (0%, 30%, 50%, 70% and 100%) [10] . Only partial replacement is
[3]
grade concrete specimens showed more compressive strength currently in practice because the presence of old mortar makes
than confinement in higher grade concrete specimens . These these aggregates weak in strength.
[4]
laminates had an inhibiting effect on tensile cracks and crack
width will reduce after strengthening. Because of its excellent The use of recycled aggregates in pavements is well established.
crack resistance and durability, it can be effectively used as a A possible approach of using recycled aggregate in structural
crack repairing material. The restorability of about one- third compressive members is to confine recycled aggregate concrete
of the original strength of damaged specimen was reported members with various confinement materials as the compressive
[5]
for ferrocement . Many confinement models were developed performance of concrete can be significantly improved through
by researchers for predicting the stress-strain behaviour and confinement. Behaviour of confined specimens using fibre
ultimate load of ferrocement confined concrete beams and reinforced polymer laminates (CFRP and GFRP) were studied
column specimens. earlier. Confined recycled aggregate shows similar stress-strain
behaviour to that of confined natural aggregate concrete [11] .
Recycling is the most effective method for dealing with the
increasing volume of waste production for preservation of In this work, an attempt is made to study the behaviour of
the environment and for achieving sustainable development. reinforced concrete columns with recycled aggregate and
Recycling of old concrete is a simple process which involves external confinement using ferrocement laminate under
breaking, removing, and crushing the existing concrete compressive loading. To study mechanical properties of recycled
waste into a new material with a specified size and quality. aggregates, compression and flexure tests were carried out on
The commonly adopted methods for production of recycled standard test specimens with four replacement levels (25%, 50%,
aggregate include mechanical grinding, heating and scrubbing 75% and 100%) of natural aggregate with recycled aggregate. To
method, acid soaking method and other surface modification analyse the effect of confinement, reinforced concrete column
methods. Heating and scrubbing method enhances the specimens were confined externally with wire mesh and surface
properties of recycled aggregate concrete prominently . In was plastered by cement mortar. The experimental results were
[6]
this method, concrete rubble is crushed to 50 mm or less in verified with mathematical models available in the literature for
size. The crushed concrete rubble is heated to about 300ºC ferrocement confined columns with normal aggregate to see
with hot air. Hardened cement paste bonded to aggregate whether the same equations are applicable for ferrocement
weakens when dehydrated by heating. This weakened concrete confined columns with recycled aggregate. The effect of
rubble is ground by Los Angeles Abrasion testing machine ferrocement on retrofitting of reinforced concrete columns is
using steel balls. The processed product is separated into also studied.
coarse aggregate, fine aggregate, and powder with a sieve and
separator. 2. MAterIALs AND MetHODs

2.1 Materials
The bulk density and apparent density of recycled concrete
aggregates are lower than that of natural coarse aggregate The concrete mix was designed as per of IS 10262:2009 [12] and it
while water absorption, crush index and sediment percentage was prepared by using the following ingredients:
of recycled aggregates are higher . The proportion of
[7]
cement, sand and aggregate in recycled aggregate concrete 2.1.1 cement
is calculated based on the mix design code for conventional
concrete. Due to the presence of old mortar, water absorption 53 grade Ordinary Portland Cement (OPC) conforming to IS 269:
of recycled aggregate is high. Compressive strength of recycled 2015 [13] was used. The physical and chemical properties of the
aggregate concrete is less compared to conventional concrete. cement were tested. Specific gravity of 3.16, fineness (fraction
There is a significant reduction in strength of concrete made greater than 90 microns) of 4% and normal consistency of 34%
of 100% recycled aggregate while 25% replacement shows no were obtained.

The IndIan ConCreTe Journal | JulY 2019 19