recycle & reuse of waste material in civil
TRANSCRIPT
COLLEGE OF ENGINEERING PUNE
Abstract:-
The purpose of this paper is to
transmit information on the state of practice
for recycling and reuse of concrete materials
from building demolitions.
Civilization also produces waste
products. Disposal issue of the waste
products is a challenge. Some of these
materials are non-biodegradable and often
leads to waste disposal crisis and
environmental pollution. The present article
seeks the possibilities of whether some of
these waste products can be utilized as
highway construction materials.
Use of waste material in construction is an
issue of great importance in this century.
Utilization of waste glass and rubber
particles in concrete addresses this issue.
The combination of waste glass with
portland cement (Glascrete) offers an
economically viable technology for high
value utilization of the industrial waste.
Glascrete has attractive appearance due to
the smooth and colorful glass aggregates,
which makes it suitable for various
architectural and decorative applications.
Also, the reduction of portland cement
production will reduce carbon dioxide
(CO2) emissions, reduce energy
consumption and reduce the rate of global
warming.
By weight, concrete makes up the
largest portion of the solid waste stream.
Billions of tons of concrete have been used
since World War II to construct buildings,
bridges, dams, roads, and other structures.
When the useful life of these structures is
over, the materials from which they were
built will find their way into the waste
stream as rubble. Thousands of structures on
those installations will be removed. A
survey of all installations identified 8,000
buildings, totaling 50 million square feet, as
candidates for removal. If these buildings
are removed using traditional demolition
techniques, hundreds of thousands of tons of
waste will be generated and disposed of in
landfills.
Industrial waste in
highway construction: -
Introduction: -
Civilization also produces waste
products. Disposal issue of the waste
products is a challenge. Some of these
materials are not biodegradable and often
leads to waste disposal crisis and
environmental pollution. The present article
seeks the possibilities of whether some of
these waste products can be utilized as
highway construction materials.
Traditionally soil, stone aggregates,
sand, bitumen, cement etc. are used for road
construction. Natural materials being
exhaustible in nature, its quantity is
declining gradually. Also, cost of extracting
good quality of natural material is
increasing. Concerned about this, the
scientists are looking for alternative
materials for highway construction, and
industrial waste product is one such
category. If these materials can be suitably
utilized in highway construction, the
pollution and disposal problems may be
partly reduced.
The following table presents a partial
list of industrial waste materials that may be
used in highway construction:
Waste product Source Possible usage
Fly ash Thermal power station Bulk fill, filler in bituminous mix,
artificial aggregates
Blast furnace slag Steel industry Base/ Sub-base material, Binder in
soil stabilization (ground slag)
Construction and
demolition waste
Construction industry Base/ Sub-base material, bulk-fill,
recycling
Colliery spoil Coal mining Bulk-fill
Spent oil shale Petrochemical industry Bulk-fill
Foundry sands Foundry industry Bulk-fill, filler for concrete, crack-
relief layer
Mill tailings Mineral processing industry Granular base/sub-base, aggregates in
bituminous mix, bulk fill
Cement kiln dust Cement industry Stabilization of base, binder in
bituminous mix
Marble dust Marble industry Filler in bituminous mix
Waste tyres Automobile industry Rubber modfied bitumen, aggregate.
Glass waste Glass industry Glass-fibre reinforcement, bulk fill
Nonferrous slags Mineral processing industry Bulk-fill, aggregates in bituminous
mix
China clay Bricks and tile industry Bulk-fill, aggregates in bituminous
mix
Material acceptability criteria: -
Roads are typically constructed from
layers of compacted materials, and generally
its strength decreases downwards. For
conventional materials, a number of tests are
conducted and their acceptability is decided
based on the test results and the
specifications. This ensures the desirable
level of performance of the chosen material,
in terms of its permeability, volume
stability, strength, hardness, toughness,
fatigue, durability, shape, viscosity, specific
gravity, purity, safety, temperature
susceptibility etc., whichever are applicable.
There are a large number tests suggested by
various guidelines/specifications; presently
the performance based tests are being
emphasized, rather than the tests which
estimate the individual physical properties.
The tests and specifications, which are
applicable for conventional materials, may
be inappropriate for evaluation of non-
conventional materials, such as industrial
wastes. This is because the material
properties, for example, particle size,
grading and chemical structure, may differ
substantially from those of the conventional
materials. Thus for an appropriate
assessment of these materials, new tests are
to be devised and new acceptability criteria
are to be formed. However, with the advent
of performance based tests, it is expected
that the performances of the conventional as
well as new materials can be tested on a
same set-up and be compared. Figure-1
presents a flow chart to evaluate the
suitability of industrial waste for potential
usage in highway construction. Health and
safety considerations should be given due importance handling industrial waste
materials.
Suitability of industrial
wastes as highway
material: -
Limited information is
available on suitability of individual
industrial wastes for its utilization
in highway construction. The
following table (Table-2)
summarizes the advantages and
disadvantages of using specific
industrial wastes in highway
construction.
Conclusion: -
It appears that some of the
industrial waste materials may find
a suitable usage in highway
construction. However,
environmental consequences of
reuse of such materials needs to be
thoroughly investigated.
Glascrete: Portland Cement
Concrete with Waste Glass as
Aggregates: -
The partial replacement of natural
aggregate by waste glass in Portland cement
concrete is studied in this article. As
mentioned earlier, the main problem to be
confronted here is the alkali-silica
reaction(ASR) expansion. The research
showed that there are several approaches
that can effectively control the expansion of
ASR due to glass aggregate, in addition to
the conventional approaches used to
minimize ASR expansion of regular
Portland cement concrete, such as using
silica fume and various additives. First, the
particle size of glass aggregate was found to
have a major influence on ASR expansion.
Since the ASR reaction is clearly a surface-
area dependent phenomenon, one would
expect the ASR associated expansion to
increase monotonically with aggregate
fineness. However, there exists a size of the
aggregate at which the maximum expansion
occurs. This is called "pessimum" size. For
aggregate finer than the pessimum size, the
ASR expansion decreases with further
decrease in particle size. This means that the
ASR expansion increases with increasing
fineness of glass particles up to a certain
point and then decreases afterwards.
Types of glass were found to have a
significant effect on the ASR expansion..
Various types of glass aggregate were tested
including soda-lime glass (used in most
beverage containers), pyrex glass, and fused
silica. The maximum expansions of mortar
bars made with different glass aggregate
types differ by almost one order of
magnitude. Window glass, plate glass, and
windshield glass were found to cause
negligible ASR expansion in test.
Colors of glass are also important for
ASR expansion. Clear glass (the most
common kind in waste glass) was found to
be most reactive, followed by amber
(brown) glass. Green glass did not cause any
expansion. Depending on the size of glass
particle, green glass of fine particles can
reduce the expansion. This implies that
finely ground green glass has the potential
for an inexpensive ASR suppressant.
The green color comes from added
Cr2O3 in the glass. However, when
chromium oxide is added directly into the
concrete mix, the ASR expansion of the
concrete is not reduced. So, the ASR
suppressing mechanisms of Cr2O3 in green
glass needs to be further studied.
Rubber Modified Concrete (RMC):
A systematic experimental study was
performed recently for improving strength
and toughness of rubber modified concrete.
Two types of rubber particles of different
sizes (large and small) were used to study
the size effect on mechanical properties of
RMC. The average size of large particles is
4.12 mm, and the average size of small
particles is 1.85 mm. The test results
indicated that particle sizes used in this
study has no effect on compressive strength,
brittleness and toughness of RMC.
Low water-cement ratio significantly
increases the strength of rubber-modified
mortars (RMM). An 8% silica fume
pretreatment on the surface of rubber
particles can improve properties of RMM.
On the other hand, directly using silica fume
to replace equal amount (weight) of cement
in concrete mix has the same effect. In
general, the bond between rubber particles
and concrete can be enhanced by increasing
electrostatic interactions and/or facilitating
chemical bonding. In this study, rubber
particles were pretreated by coupling agents,
and the method was found to be very
effective to improve mechanical properties
of the RMC. Three coupling agents:
PAAM(polyacrylamide), PVA(Pressure
Ageing Vessel) and silane were tested.
Although PAAM is quite effective to
improve the interface strength between
rubber particles and cement matrix, it has
adverse effect on the workability of the
RMC when the rubber content is above 10%
of total aggregate by volume. Both PVA and
silane are very effective in improving the
compressive strength of the RMC. There is
no adverse effect on workability of the
RMC. PVA is more effective than silane for
improving the compressive strength of the
RMC. The overall results show that using
proper coupling agents to treat the surface of
rubber particles is a promising technique,
which produces a high performance material
suitable for many engineering applications.
The advantages of the RMC :-
(1) The toughness and ductility of RMC are
usually higher than that of regular concrete,
which makes it suitable for many
applications;
(2) The density of RMC is lower than the
density of regular concrete;
(3) Comparing with other recycling
methods, such as using waste tires as fuel in
cement plants, RMC makes a fully use of
the high energy absorption feature of the
rubber particles.
The disadvantages of RMC : -
(1) The strength of RMC is usually lower
than the strength of regular concrete;
(2) The durability of RMC is not well
understood.
Alkali-slag concrete:-
Alkali-slag concrete is made from
slag powder and alkali component as main
constituents of cementitious material. The
slag powder may be one or a mix of the
following:
blast furnace slag, phosphorous slag,
titanium-containing slag, manganese slag,
basic cupola furnace slag, aqueous slag from
power plant, nickel slag, silica aluminate.
The alkali component as an activator
is a compound from the elements of first
group in the periodic table, so such material
is also called as alkali activated cementitious
material or cement. The common activators
are NaOH, Na2SO4, Na2CO3, K2CO3, KOH,
K2SO4, water glass, or a little amount of
cement clinker and complex alkali
component; therefore, its activity is more
than that of compound from the elements of
second group as commonly used in
traditional cementitious material. The ions
with strong ionic force formed during
dissociation of alkali metal compound,
promote the disintegration of slag powder
and hydration of the ions, and then, such
ions take part in the structure formation of
cement paste, so the cement has properties
of rapid hardening and early strength gain.
For such type of concrete there is less
Ca(OH)2 and high alkali hydrates in
hydration products of cement, in case of
high Al/Si ratio, there will be some mineral
of zeolite type resulting in its high resistance
to corrosion. Due to perfect pore structure,
small total pore volume, proper distribution
of pore diameters, dense structure and good
bond of interface between cement and
aggregate, the special concrete and concrete
with the strength of 20-120 MPa can be
obtained. The concrete mix has a good
workability with slump of 0-22 cm without
water reducing agents.
The concrete has a high hardening
rate with low heat of hydration, consisting of
only 1/2 to 1/3 of that for OPC; its
impermeability is 1.0-4.0 MPa; the frost
resistance reached 300-1000 cycles. There is
strong protection of reinforcement with
excellent corrosion resistance. It can be used
for various building elements and
monolithic concrete. For preparing the
cementitious material of concrete, only the
grinding is required with no calcinations. As
for the concrete aggregate, the aggregate
with large content of mud or fine particles,
heavy loam, sea sand, super fine sand,
machined sand,etc. can be used. It is a low
cost, energy saving, low resource
consumption material, which can promote
the recycling of the waste and make an
environmental concrete with clean
production of cement, environment friendly
and in good coordination with the
environment.
Recycled Concrete Aggregate
(RCA):-
Definition:-
Recycled concrete originates from
C&D debris that has been removed from
pavement, foundations, or buildings, and
that has been crushed to produce Recycled
Concrete Aggregate (RCA) .Recycled
concrete aggregates account for roughly 5
percent of the total aggregates market (more
than 2 billion tons per year) while the rest is
being supplied by natural aggregates.
Concrete Building Recycling Flow Process.
Physical Properties:-
Recycled concrete aggregate looks
like crushed stone. However, crushed
concrete has many physical properties that
vary from those of natural aggregates. In
general, crushed concrete particles are more
angular have a rougher surface texture than
natural aggregate. Roughly textured,
angular, and elongated particles require
more water to produce workable concrete
than smooth, rounded compact aggregate.
The lightweight, porous cement
mortar attached to recycled concrete
aggregates causes crushed concrete
aggregates to have a lower specific gravity
and higher water absorption than
comparatively sized natural aggregates. The
lower compacted unit weight of RCA
compared with conventional mineral
aggregates results in higher yield (greater
volume for the same weight), and is
therefore economically attractive to
contractors. Department Of Transportation
(DOT) specifications have shape
requirements for aggregates. For example, at
least 70% of the material should have two or
more crushed (flat) faces. Increased
angularity of the aggregate increases the
asphalt and concrete stability.
Chemical Properties:-
Concrete recycled from buildings
may be contaminated by sulphates from
plaster and gypsum wallboard, which creates
a possibility of sulphate attack if the
recycled aggregates used in concrete are
accessible to moisture.
One of the main issues surrounding
the use of recycled concrete aggregate in
concrete production is the potential for
reaction between the RCA and alkaline
water. Alkali-silica reaction results in
volumetric expansion, in which there is a
high probability of internal fracturing and
premature deterioration of the concrete.
Where alkali-silica reactivity is of concern,
the potential for deterioration should be
evaluated.
Chloride ions from marine exposure
can also be present in RCA. Because of the
use of deicing salts as a mechanism to
control development of ice on pavement,
there is a strong possibility that chloride ions
will be present in recycled concrete
aggregate. The presence of chloride ions in
Portland cement concrete can adversely
impact the reinforcing steel within concrete.
Reinforcing steel in the presence of chloride
ions will react to form iron oxide or rust. If
the formation of iron oxide persists, there is
a high probability of delamination of the
concrete structure. Since total elimination of
all deleterious contaminants is not practical,
experimentation is required to determine
acceptable levels and to eliminate
unnecessary processing cost while providing
a quality product.
CRUSHED CONCRETE AGGREGATE
Effect of Recycled Aggregate on Concrete Properties:-
Some properties of concrete from
recycled aggregates can deviate from those
of comparable concrete mixes with natural
aggregates. These differences need not
impair the suitability of recycled concrete.
Investigations on crushed concrete from
demolition work have proven that it is
possible to produce high-grade aggregate
with reused concrete. High quality can be
produced by pre-separation, processing, and
screening of the content for impairing
constituents.
Uses of RCA:-
i. Granular Base:-
A base course is defined as the layer
of material that lies immediately below the
wearing surface of a pavement. The base
course must be able to prevent overstressing
of the subgrade and to withstand the high
pressures imposed on it by traffic. It may
also provide drainage and give added
protection against frost action when
necessary.
Recycled aggregates can be (and are)
used as granular base and sub-base in road
construction. In many applications, recycled
aggregate will prove to be superior to
natural aggregate for use as granular base.
An estimated 85 percent of all cement
concrete debris that is recycled is used as
road base due to its availability, low
transport cost, and good physical properties.
ii. Embankment Fill:-
Crushed rock fill is specified where
necessary to control embankment erosion, to
prevent capillary action from saturating
embankments, and to prevent the entrapment
of water by the embankment. RCA is not
commonly used to construct fill
embankments because, in most cases, the
cost of the aggregate will be significantly
higher than that of common fill. Recycled
concrete aggregate in embankments or fill
may not make the best use of the high
quality aggregates associated with RCA.
Where no other applications are readily
available, RCA can be satisfactorily used in
this application. It requires minimal
processing to satisfy the conventional soil
and aggregate physical requirements for
embankment or fill material. Desirable
attributes of RCA for use in embankments
or fill include high friction angle, good
bearing strength, negligible plasticity, and
good drainage characteristics. The design
requirements for RCA in embankment
construction are the same as for
conventional aggregates. There are no
specific standard specifications covering
RCA use as embankment or fill and design
procedures are the same. Fines should be
screened out before this type of use.
iii. Railway Ballast:-
Ballast is a select material placed on
the subgrade to distribute the load of the
tract and trains to prevent overstressing of
the subgrade and to restrain the track
laterally, longitudinally, and vertically under
the dynamic loads imposed by trains and the
thermal stresses induced in the rails by
changing temperatures. Ballast also provides
adequate drainage of the track. Ballast
produced for use on main lines is generally
governed by standard specifications.
Ballast should meet the gradation
requirements specified in the AREA Manual
for Railway Engineering, chapter 1, part 2.
It is very desirable that the gravel
contain a large volume of crushed stones.
Otherwise, the ballast will not hold the ties
in place under high-speed traffic, increasing
maintenance costs. One requirement of good
ballast is that it quickly drain water away
from the track.
iv. Drainage and Filter Material:-
A relatively small volume of
aggregate production goes to provide
drainage or filter media for various
applications, including sub-drains for
buildings, dams, and other engineered
structures, as well as filters for sewage and
water treatment. Recycled aggregates are not
commonly used for filter or drainage
material because of concerns about
durability, particularly with respect to
chemical attack from impurities in the
groundwater or leachate being filtered.
Recycled fine aggregates are not
suitable for use in drainage layers beneath
the pavement because soluble mineral rich
in calcium salts and calcium hydroxide can
be transported with the water as it percolates
through and plugs sub-drains. If the RCA is
located above such porous drainage systems,
the calcium minerals tend to precipitate out
of solution and bind to the drainage
structure. The mineral deposits formed are
sometimes referred to as portlandite
deposits. Over time, the permeability of the
drainage system can be reduced. If the RCA
is intended for use as a drainage layer, then
the processed coarse aggregates should be
washed to remove the dust and fines.
v. Concrete Block:-
Concrete blocks are made by mixing
Portland cement, sand, and other aggregates
with a small amount of water and then
blowing the entire mixture into moulds. The
major component material of concrete block
(sand and various coarse aggregates)
account for as much as 90% of its
composition. Recycled material such as
crushed concrete and by-products of other
industrial processes such as blast furnace
slag, can be used for some portion of the
aggregate in block. Concrete block offers an
advantage because there is little waste.
Technical Issues:-
The processing of recycled concrete
materials is relatively simple, but requires
expensive, heavy-duty equipment, capable
of handling a variety of materials. The
technology basically involves crushing,
sizing, and blending to meet the required
product mix. Much C&D concrete contains
metal and waste materials that must be
detected and removed at the start of
processing by manual or magnetic
separation. Processing equipment must be
versatile yet efficient for a handling a
variety of materials of non-uniform size or
composition.
The crushing plants can be either a
portable type and located on the job site or a
stationary plant situated at an existing pit or
landfill. The main reasons for using portable
plants include the ease of moving the
equipment for cleaning and maintenance, as
well as the ability to go to the job site.
Portable plants must be small enough to fit
on existing roads and under overpasses.
Demolition project sites may also have
space limitations. Recycling concrete at a
demolition site is different than recycling on
a paving job or at a stationary plant; the
contractor usually has several pieces of
mobile equipment at the site, mostly
excavators with concrete breakers or
pulverizing attachments. Demolished
concrete is brought to the crushing operation
where it is reduced to the maximum size
called for in the specifications. Crushing is
usually performed in two steps: a primary
crusher reduces the larger incoming debris,
and a secondary crusher further reduces the
material to the desired particle size.
Magnetic ferrous metal recovery can take
place after both stages. The two main types
of equipment are jaw and impact crushers.
Jaw crushers are best suited to reduce large
or odd-shaped debris quickly from C&D
projects to a manageable size. Impact
crushers are more effective than jaw
crushers at freeing rebar encased in rubble.
CONCLUSION/FUTURE WORK:-
As natural resources diminish, the
demand for recycled concrete aggregate is
likely to increase, making concrete recycling
the economically and environmentally
preferable alternative to traditional “smash
and trash” demolition. Wherever good
natural aggregates are not locally available,
where natural aggregate costs exceed RCA
costs, or where disposal of existing concrete
pavement or concrete structures is
problematic, concrete recycling should be
evaluated.
In the future, procedures need to be
developed for the quality control of recycled
aggregates. Quality materials will also create
competitive markets and higher grade
outlets for secondary materials. Concrete
recycling appears to be profitable. In most
cases, it can meet demand requirements of
lower value product applications such as
road base, thereby freeing up higher quality
material for higher value applications. While
studies have shown that RCA can be used as
aggregate for new concrete, there is a need
to obtain long-term in-service performance
and life cycle cost data for concrete made
with RCA to assess its durability and
performance. If additional research supports
the use of concrete buildings – especially
barracks – then existing specification should
be revised to permit and encourage the use
of recycled concrete as aggregate, to
conserve existing supplies of natural
aggregates and to reduce the amount of solid
waste that must be disposed of in landfills.
Further research should focus on:
(1) The economic aspect of concrete
processing and recycling;
(2) The influence of contaminants in the
demolished concrete from buildings;
(3) The long-term feasibility of recycling;
(4) The durability of RCA in new concrete,
and its creep and shrinkage characteristics;
(5) The use of recycled fines.