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.