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Center for
By-Products
Utilization
RECYCLED MATERIALS IN CONCRETE
INDUSTRY
By Tarun R. Naik and Rakesh Kumar
Report No. CBU-2003-08
REP-503
March 2003
A CBU Report
Department of Civil Engineering and Mechanics
College of Engineering and Applied Science
THE UNIVERSITY OF WISCONSIN - MILWAUKE
2
1.0 INTRODUCTION
Concrete industry is the single largest consumer of the natural resources available in the
world. Each year, it consumes 12.6 billion tons (11.4 billion metric tones) of raw materials that
include 1.6 billion tons of cement, 10 billion tons of sand and rock, and 1 billion tons of mixing
water (Mehta, 2001). Adverse effects on ecology are not beyond imagination.
On the other hand, enormous quantity of by-product materials is generated from industries,
domestic, and agricultural activities. These by-products or so-called waste materials possess lots of
environmental problems. Large amounts of by-products generated from industrial and domestic
sources are currently landfilled due to non-availability of economically attractive use options.
Landfilling is undesirable because it causes not only huge financial burdens to producers of by-
products, but also makes them responsible for unknown future environmental liabilities.
Additionally, due to shrinking landfill space, increased environmental restrictions, cost of
landfilling, and realization of the facts that natural resources are limited, are driving forces for
exploring more new ways to utilize them. Recycling of by-product materials generated from
various sources, for their utilization in concrete industry provide one of the innovative solutions to
the above problems. Use of a variety of by-product materials as supplementary cementing materials
is growing time to time. Fly ash, silica fume, granulated blast furnace slag, rice –husk ash etc., have
already been established as mineral admixtures in cement-based industry. By-product materials can
be utilized for raw materials, substitute for basic ingredients of concrete, and for additional
ingredient that may impart better strength and durability properties.This chapter briefly describes
various by-product materials generated from industrial, agro-based, . and post-consumer activities
along with their possible recycling for the utilization in concrete industry. These by-product
materials include coal combustion by-products, wood ash, pulp and paper industry by-products,
3
foundry by-products, metallurgical by-products material, municipal solid waste materials, used tires,
plastics, glass, recycled concrete pavements for aggregates, recycled asphalt pavement for asphalt,
construction and demolition debris, cement kiln dust, rice-husk ash, wheat straw ash etc. For each
by-product material, production, properties, and potential applications in manufacture of
construction materials and the environmental impact are briefly addressed. Additionally, future
recycling and research needs are also discussed.
2.0 MATERIALS
2.1 COAL-COMBUSTION BY-PRODUCTS
In most of the countries coal- fired thermal power plants are the major source of generation of
electricity. Coal-fired power plants derive energy by burning coal in their furnaces. These
power plants generally use either pulverized coal-fired furnaces or cyclone furnaces (Murarka
1987). The cyclone furnaces burn relatively coarse coal particles, less than 13 mm, at very high
temperature. The pulverized coal-fired furnaces use fine coal particles with particle size passing
No. 200 sieve. During the process of combustion in pulverized coal-fired furnaces, the volatile
matters and carbon burn off and the coal impurities fuse and remain in suspension. These fused
substances solidify when flue gas reaches low temperature zones to form predominantly
spherical particles called fly ash. The remaining matters, which agglomerate and settle down at
the bottom of the furnace, are called bottom ash. The pulverized coal-fired furnaces employ
either a dry bottom or wet bottom to collect bottom ash. Amount of bottom ash can range from
20 to 25% of total coal combustion by-products for dry bottom collection system. Fly ash
constitutes a major component (75 - 80%) of by-product material in pulverized coal-fired power
plants. The combustion of coal in cyclone furnaces occurs by continuous swirling in a high
4
intensity heat zone (Murarka 1987). This causes fusing of fly ash particles into a glassy slag,
called boiler slag, which drop to the bottom of the furnace. The boiler slag constitutes the major
component of the cyclone boiler by-product (70 to 85%). The remaining combustion by-
products exit along with the flue gases. Clean coal ash is defined as the ash derived from plants
involving the use of SOx and NOx control technologies.
More than half of U.S. electricity is supplied by coal burning power plants. Coal burning,
combined with pollution control technologies such as low NOx, FGD, SO2 control technologies,
generate huge amount of by-product materials. Currently, in U.S. more than 107 million metric tons
of coal combustion products (CCPs) are being generated per year (ACAA 2001; Kalyoncu 2001). .
Fly ash is the major component (58%) of CCPs produced, followed by flue gas desulfurization
(FGD) material (24%), bottom ash (16%), and boiler slag (2%) (Kalyoncu 2001). Fly ash is a
heterogeneous mixture of particles varying in shape, size, and chemical composition. The particle
types may include carbon from un-burnt coal, fire-polished sand, thin-walled hollow spheres and
fragments from their fracture, magnetic iron containing spherical particles, glassy particles, etc. Fly
ash is predominantly composed of spherical particles, which can be less than 1 µm to more than 1
mm in size. The nitrogen adsorption surface area of fly ash varies in the range of 300 to 500 m2/kg.
The density of fly ash normally varies between 1.6 and 2.8 g/cm3. Major mineralogical component
of fly ash is a silica-aluminate glass containing Fe2O3, CaO, and MgO. It also contains certain other
oxide minerals. According to ASTM C 618, Class F fly ashes contain less than 10% total CaO,
whereas Class C fly ashes normally show total CaO content greater than 10%. Class C fly ashes can
even show cementitious behavior in the presence of water. The properties of coal ashes are presented
in Table 1. The particle size distribution of fly ash and bottom ash is presented in Fig. 1.
. Currently, over 17 million metric tons of bottom ash and 2.3 million metric tons of boiler
5
slag are being produced, respectively (Kalyoncu 2001). Bottom ash and slag are generally non-
spherical and are composed of particles ranging from 2 μm to 20 mm. Bottom ash particles are
rounded in shape but can be also angular. They have porous structures. Boiler slag is composed of
angular particles with a glassy appearance. The size distribution of bottom ash and boiler slag is also
shown in Fig. 1. Specific gravity for bottom ash and slag varies between 2.2 and 2.8. Their bulk
densities range from 737 to 1586 kg/mt3 (Murarka 1987).
Wet scrubbers or flue gas desulfurization (FGD) systems are most commonly used to control
power plant SO2 emissions and they produce wet by-products. . Currently, about 25.9 million
metric tons of FGD material is being produced in the United States (Kalyoncu 2001). The residue
from such systems consists of a mixture of calcium sulfite and sulphate, CaCO3, and fly ash in water.
The fly ash amount in FGD material varies from . 10% to 50% depending up on whether or not fly
ash was collected prior to the FGD system. Particle size distribution for FGD sludge is shown in
Fig. 2. Recent increased concern over SO2 emissions from power plants has resulted in development
of several advanced SO2 control systems that produce dry by-products. Therefore, these new
processes avoid the complexity and operating problems encountered when handling large volumes of
liquid or semi-liquid wastes produced in the case of wet FGD systems. In addition, no dewatering is
needed prior to utilization or landfilling. However, these processes require costlier sorbent
materials. The advanced systems include Atmospheric Fluidized Bed Combustion (AFBC), Lime
Spray Drying, Sorbent Furnace Addition, Sodium Injection, and other clean coal technologies such
as integrated coal classification combined cycle process (IGCC), etc. The solid by- products
generated by these processes have some physical and chemical properties significantly different
from those for conventional coal ashes.
The AFBC process produces coal ash, sulfur reaction products, and calcined limestone
6
reaction products. The sulfur reaction products are primarily composed of calcium sulfate and
7
Table 1: Typical Chemical and Physical Properties of Fly Ash From Different Coal Burning
Power Plants (ACI 226 Committee 1987)
Fly Ash
Source
Chemical Properties, Percent
Physical Properties
LOI
(1)
CaO
SiO2
Al2O3
Fe2O3
Mg
O
Na2O
K2O
No. 325
sieve
retention,
percent
Blaine
fineness
m2/kg
Specific
gravity
Less than 10 percent CaO (Class F)
FA-4
FA-5
FA-7
FA-8
FA-13
FA-14
FA-15
FA-16
FA-17
FA-18
No. 3
D-Precip
D-Mech
1.0
0.9
1.8
2.6
4.2
3.0
2.5
4.0
0.4
4.3
7.2
3.9
6.4
6.7
0.7
1.7
2.4
1.7
1.9
1.3
1.6
7.5
2.2
3.2
1.0
1.0
58.5
60.1
56.0
49.0
45.0
47.7
52.7
50.6
49.8
43.6
64.4
52.9
54.9
19.9
27.8
25.7
21.8
19.6
29.5
28.6
27.6
21.6
26.0
24.7
30.1
27.6
5.6
3.8
8.3
17.9
23.9
9.7
5.8
8.2
7.0
16.6
3.9
7.3
10.4
1.7
1.0
1.1
1.0
0.9
0.7
1.0
1.0
1.7
0.9
1.5
1.1
0.9
1.5
0.3
0.3
0.4
0.4
0.3
0.3
0.4
2.8
0.3
-
0.4
0.3
1.3
2.8
2.8
2.7
2.3
1.9
2.4
2.5
0.7
1.9
-
2.9
2.4
17
18
22
20
24
28
17
4
24
17
2
8
30
379
262
282
282
236
287
351
508
316
337
-
643
333
2.31
2.18
2.28
2.45
2.45
2.30
2.38
2.49
2.27
2.24
-
2.33
2.15
More than 10 percent CaO (Class C)
FA-1
FA-2(a)
FA-9(a)
FA-
10(a)
FA-
11(a)
A
F
G
I
0.9
1.9
0.5
0.5
0.4
0.4
0.7
0.6
0.3
25.5
15.5
11.6
28.2
16.9
17.3
24.9
11.7
29.0
36.3
38.8
50.5
35.9
51.4
35.7
23.1
48.9
31.1
17.7
13.4
17.7
17.1
16.9
20.3
13.3
21.3
17.0
6.7
22.5
6.6
5.6
5.8
5.8
9.6
3.7
5.6
4.6
1.5
3.4
5.1
3.5
4.3
7.5
2.7
3.8
1.6
0.5
3.5
1.8
0.6
6.5
7.3
6.4
3.2
0.6
1.9
1.2
0.5
0.8
0.8
0.6
0.9
0.4
15
16
11
16
21
11
12
38
15
417
355
315
390
288
418
324
318
604
2.65
2.74
2.44
2.70
2.52
2.67
2.86
2.31
2.74
(1) LOI = Loss on ignition.
8
Fig. 1 Particle size distribution for fly ash and bottom ash (Summers et al. 1983)
9
sulfite, and calcium oxide. The calcined limestone reaction forms primarily calcium sulfate.
Chemical composition of the AFBC residues is given in Table 2. The chemical composition of the
AFBC fly ash is similar to that of Class C fly ash except SO3 and SiO2 contents. AFBC SO3 content
is higher and SiO2 content is lower relative to the conventional Class C fly ash.
The spray dryer by-products (Table 2) consist of primarily spherical fly ash particles coated
with calcium sulfite/sulphate, fine crystals of calcium sulfite/sulphate, and unreacted sorbent
composed of mainly Ca(OH)2 and a minor fraction of calcium carbonate. The spray dryer by-
products are higher in concentrations of calcium, sulfur, and hydroxide, and lower in concentrations
of silicon, aluminum, iron, etc. compared to the conventional Class C fly ash.
The Lime Furnace Injection (LFI) by-products (Table 2) are made up of primarily coal ash,
calcium sulfite and sulfate, and unreacted lime. By-products generated by LFI contain 40 to 70% fly
ash, 15 to 30% free lime, and 10 to 35% calcium sulfate by weight.
The calcium injection process produces by-products (Table 2) similar to that of LFI and
calcium spray dryer because of similarities in sorbents and injection methods used. The sodium
injection process differs from the calcium injection in regards to type of sorbent used. This process
uses a sodium-based sorbent such as sodium bicarbonate, soda ash, trona, or nahcalite (ICF
Northwest, 1988). By-products generated by this process include fly ash particles coated and
intermixed with sodium sulfite/sulfate, and unreacted sorbent. The IGCC process produces by-
products similar to the SO2 control processes.
10
Fig. 2 Particle size distribution for FGD sludge (Summer et al. 1983)
11
Table 2: Clean Coal By-Products Chemical Composition in Percent by Weight (a)
(ICF Northwest 1988)
Sample No. A12O3
CaO
Fe2O3
MgO
K2O
SiO2
Na2O
SO3
AFBC:
TVO3 (bed)
TVO4 (char)
TVO5 (ash)
SFO6 (comp.)
2.72
7.29
15.04
6.12
45.07
30.79
22.64
39.13
4.77
13.20
18.88
17.11
0.62
0.48
0.51
0.54
0.31
0.78
1.93
0.72
3.17
7.97
15.26
6.04
0.27
0.05
0.34
0.29
6.50(b)
20.00
17.25
12.00 Spray Dryer:
ARO7
STO7
LRO7
HSO5
APO7
NVO4
RSO5
AVO6
25.20
12. 60
21.20
24.90
24.90
15.00
19.00
18.00
21.73
31.22
26.88
20.02
17.67
21.32
28.50
19.03
3.26
10.92
6.11
6.51
3.11
4.83
15.34
9.23
0.84
2.93
2.33
2.62
0.65
1.53
2.85
4.62
1.69
1.45
0.74
0.75
1.35
0.60
0.42
1.46
21.17
15.60
17.72
21.30
25.72
20.42
15.96
24.52
3.29
1.76
2.08
1.81
2.05
6.58
2.12
9.17
17.50
12.00
12.25
10.25
18.25
14.00
13.75
11.50 Lime Furnace Injection:
SRO7 (lime)
SRO9 (limestone)
OLO3 (limestone)
OLO4 (limestone)
OLO8 (limestone)
16.40
17.20
17.80
17.10
29.80
28.83
29.15
36.13
40.00
16.80
14.20
16.48
13.17
11.91
16.86
2.50
0.82
0.63
0.70
0.67
2.84
2.96
1.11
1.08
2.12
17.72
19.33
15.75
16.18
27.86
1.77
1.64
0.48
0.51
1.02
12.50
11.25
6.25
5.50
3.50 Calcium Injection:
AHO6
AA1O-01
AA1O-02
9.07
31.37
31.37
40.57
15.39
13.99
2.17
8.86
8.86
0.56
1.13
1.13
0.82
3.37
3.37
10.27
29.95
27.81
0.59
1.24
1.27
NA
NA
NA Sodium Injection:
NXO4
NBO4
28.90
30.50
4.54
4.40
2.50
6.60
1.16
0.70
0.77
1.45
25.18
33.94
24.78
12.89
12.00
7.75
(a) All elements expressed as their oxides, but may occur in other forms.
(b) SO3 content of the uncrushed sample; the crushed sample had a SO3 content of 23.9%.
12
From the above description, it is evident that most SO2 control processes generate a by-product
similar to the conventional fly ash. But due to sorbent addition, fly ash is modified to a significant
extent. The modified fly ash contains fly ash particles coated with sorbent and sorbent reaction
products, and smaller non-fly ash particles composed of reacted and unreacted sorbents. The solid
by-products generated by these processes exhibit some physical and chemical properties
significantly different than those of conventional coal ashes (ICF Northwest 1988; ICF Technology,
Inc. 1988).
2.1.1 Applications of Coal-Combustion By-Products
The current utilization rate of CCPs is around 35%. However, in 2001, FGD material has
shown the highest gain in the rate of utilization among all the major CCP components (ACAA 2001;
Kalyoncu 2001). Among CCPs, fly ash utilization is in the largest quantities and it has widest range
of applications. About 60% of fly ash is used in construction applications followed by structural fills
and waste stabilization. The data on production and various applications of coal combustion by-
products in 2001 is given in Table 3. The most widely accepted use of fly ash is in making concrete.
However, in keeping with the primary emphasis of this chapter, only emerging materials using fly
ash is discussed.
2.1.1.1 Fly Ash
With a view to save a significant amount of energy and cost in cement manufacturing, fly ash
can be utilized as a major component of blended cements, exceeding 50% of total blended cement
mixture (Naik and Singh 1995). Fly ash can be used as either a raw material in the production of the
cement clinker, interground with the clinker, or blended with the finished cement.
13
Table 3: Coal combustion product production and consumption in 2001
(Thousand metric tons)
Fly ash Bottom ash Boiler slag FGD material Total CCPs
Production 61800 17100 2300 25900 107000
Consumption
Agriculture 20 20 -- 100 140
Blasting grit and
roofing granules
-- 40 1350 -- 1390
Cement clinker
raw feed
940 710 -- 440 2090
Concrete-grout 11200 710 -- 440 12400
Flowable fill 730 10 -- -- 740
Mineral filler 100 10 10 -- 120
Mining
application
740 110 -- 130 980
Road base and
subbase
930 550 -- 40 1520
Snow and ice
control
-- 770 20 -- 790
Soil modification 670 100 -- -- 770
Structural fills 2910 1050 10 170 4140
Wallboard -- -- -- 5650 5650
Waste
stabilization and
solidification
1310 60 -- 40 1410
Other 410 1610 260 280 2550
Total 20000 5750 1650 7300 34700
Individual use, % 32.3 33.7 71.70 2820 xx
Cumulative use,
%
32.3 32.6 33.70 32.40 32.40
xx Not applicable
-- Zero
14
Fly ash can be used in manufacture of Controlled Low Strength Materials (CLSM) as a
replacement of regular concrete sand up to 100% (Naik et al. 1990; Naik et al. 1997a,b,f). Flowable
slurry made with fly ash is suitable for base support and backfilling of foundations, bridge
abutments, buildings, retaining walls, utility trenches, etc.; for filling abandoned tunnels, sewers, and
other underground facilities; and as embankments, grouts, etc.
Both sintered (fired) and unfired (cold bonded) processing methods can be used to
manufacture lightweight aggregates using fly ash (Courts 1991; Hay and Dunstan 1991). For
manufacture of lightweight aggregate, first fly ash is pelletized. Thereafter, it is sintered in a rotary
kiln, shaft kiln, or traveling gate at temperature from1000 to 12000C.
Naik et al. (1994) developed mixture proportions for paving roadway concrete using large
amounts of fly ash. These mixtures were composed of 50% Class C fly ash and 40% Class F fly ash
as a replacement of portland cement. Test results revealed that high volumes of Class C and Class F
fly ashes could be used to produce high-quality concrete pavements with excellent performance.
Fly ash with and without silica fume can be used in manufacture of high-performance
concrete (Naik et al. 1997d). High-performance concrete mixtures containing up to 30-40% fly ash
can be proportioned to attain both high-strength and high-durability related properties. Past studies
(Naik and Singh 1995; Naik et al. 1995) have substantiated that concrete containing large amounts
(more than 50%) of either Class C or Class F fly ash can be proportioned to meet strength and
durability requirements for structural applications.
Recent studies by Naik and Ramme (1990) have substantiated that superplasticized Class C
fly ash concrete with low water-to-cementitious materials ratio can be proportioned to meet the very
early-age strength as well as other requirements for precast/prestressed concrete products. The
maximum cement replacement with the fly ash was reported to be 30% for such high-early strength
15
concrete application.
Fly ash can be used in large amounts as a fine filler material as well as a pozzolan in roller
compacted concrete (Schrader 1994). In manufacture of autoclaved cellular concrete, fly ash can be
used as a replacement of 30 to 100% of silica sand (Pytlik and Saxena 1991). Cenospheres derived
from fly ash are an ideal filler material for manufacture of polymer matrix composites (Hemmings
and Berry 986; Quanttroni et al. 1993). The inclusion of fly ash improves mechanical properties,
elastic modulus, permeability, and reduces thermal conductivity and expansion. In fresh concrete it
reduces bleeding and heat of hydration.
2.1.1.2 Bottom Ash/Boiler Slag
Extensive studies by Naik and his associates (Naik et al.1992; Wei 1992) and elsewhere have
revealed that bottom ash can be used as lightweight aggregates. Large size bottom ash can be used
as coarse aggregate and small size bottom ash can be used as fine aggregate sand. Naik and his
associates demonstrated feasibility of using bottom ash in manufacture of masonry products as a
partial replacement of coarse as well as fine aggregates (Wei 1992). Recent studies (Kula et al.
2001; Targan et al. 2002) indicate that bottom ash with the pozzolanic nature can be used for the
replacement of portland cement separately or along with fly ash. Bottom ash can also be used as a
low–cost replacement for more expensive sand for concrete production, as a fine aggregate in high-
performance lightweight concrete (Afshin and Matsufuji 1998). Bottom ash used in CLSM slurry
can enhance insulating ability of the fill. The same is true for boiler slag. The most popular use of
coal boiler slag is in architectural concrete as aggregates. The major applications of bottom ash are
in structural fill, ice control, and road base and subbase. Other uses of bottom ash include concrete,
mining applications, and cement clinker raw feed, as fine aggregate in asphalt paving mixtures.
Owing to its abrasive properties, boiler slag is used mostly in the manufacturing of
16
blasting grit. It can also be used in hot-mix asphalt as fine aggregate because of its superior
hardness, affinity for asphalt, and dust free surface, which aid in asphalt adhesion and resistance
to stripping.
2.1.1.3 Clean Coal Ash
Relatively little work has been done concerning the utilization of clean coal ash. FGD
material is mostly used in the manufacturing of wallboard. Today, cement based industries account
for 15% utilization of FGD materials ( Kalyocu 2001). Stabilized FGD sludge can be used in
construction of stabilized road base. It can be used as a raw material for production of cement. FGD
can be used as gypsum for manufacture of wallboards. The advanced SO2 by-products have a
potential for use in structural fill, mineral filler in asphalt, synthetic aggregates, concrete, mineral
wool, ceramic products, masonry products, etc. (ICF Technology, Inc. 1988, ICF Northwest 1988).
Naik et al. (1997a) carried out an extensive laboratory investigation to characterize clean coal ash
by-products in order to establish their applications in cement-based materials. Based on laboratory
investigations, they reported that significant amounts of clean coal ash by-products can be used in
concrete as well as masonry products. Naik et al. (1997b) have also established mixture proportions
and production technologies for clean coal ash in CLSM as a replacement of sand and/or
conventional fly ash. The production and consumption of coal combustion by-products are shown in
Figure 3 as per the data of year 2001.
17
0
20
40
60
80
100
120
Fly ash Bottom ash Boiler slag FGD
materials
Total
MIL
LIO
N M
ET
RIC
TO
NS
Production
Consumption
Fig. 3 Production and consumption of coal ash combustion products in the USA in 2001
(Kalyoncu 2001).
18
2.2 WOOD ASH
Wood ash is the residue generated due to combustion of wood and wood products (chips, saw dust, bark, etc.). Approximately one
million dry tons of wood ash is generated annually in the Wisconsin State of the U.S.A. alone (Naik and Kraus 2003). Wood ash is composed of
both inorganic and organic compounds. The physical and chemical properties of wood ash, which determine its beneficial uses, are dependent up
on the species of the wood and the combustion methods that includes combustion temperature, efficiency of the boiler, and supplementary fuels
used. Ash content yield decreases with increasing combustion temperature (Etiégni and Campbell 1991). Density of wood ash decreases with
increasing carbon content. Typically, wood ash contains carbon in the range of 5-30% (Campbell 1990). The major elements of wood ash
include calcium (7-33%), potassium (3-4%), magnesium (1-2%), manganese (0.3-1.3%), phosphorus (0.3-1.4%), and sodium (0.2-0.5%). The
chemical and physical properties depend up on the type of wood, combustion temperature, etc. (Campbell 1990; Misra et al. 1992). An elemental
metal, and other analyses for various types of wood are shown in Table 4.
2.2.1 Application of Wood Ash
The majority of wood ash is either landfilled or land applied. In Europe, wood ash is used as a feedstock for cement production and road
base material (Greene 1988). Wood ash can be used in manufacture of low-strength concrete and controlled low-strength materials (Fehrs
19
Table 4: Elemental Metals and Other Analyses for Ash from Wood (mg/kg)
Elemental
Metal
Regulatory
Limits
(U.S.EPA)
Normal Wood
Fuel
Particle/
Plywood
Creosote-
Treated
Pentachlorophenol-
Treated
Construction/
Demolition
Wood
CCA-
Treated
Aluminum N/A 4000 - 4500 4400 - 4800 3600 - 5000 3600 - 4200 4900 - 5800 3900 - 4500
Arsenic 41/75 42 - 53 22.5 - 26.9 51 - 64 24.3 - 27.7 78 - 98 8570 - 9390
Barium N/A 220 - 300 280 - 400 200 - 280 220 - 270 480 - 590 220 - 280
Cadmium 39/85 5.5 - 6.1 7.3 - 7.9 5.1 - 5.7 8.7 - 10.1 7.1 - 8.1 10.7 - 11.7
Chromium 1200/3000 12 - 14 12 - 15 14 - 17 19 - 23 34 - 39 1710 - 1850
Copper 1500/4300 41 - 46 50 - 59 49 - 52 52 - 61 71 - 93 2610 - 2820
Iron N/A 5900 - 6100 3700 - 4300 14900 - 17100 5000 - 5100 6900 - 7400 6400 - 6900
Lead 300/840 29 - 35 73 - 78 47 - 50 198 - 235 920 - 1010 58 - 73
Manganese N/A 2440 - 2750 2430 - 2740 2040 - 2140 2020 - 2230 2030 - 2230 2610 - 2720
Mercury 17-57 0.05 - 0.08 0.06 - 0.10 0.12 - 0.14 0.09 - 0.16 0.36 - 0.52 0.03 - 0.32
Molybdenum 18/75 5.6 - 6.7 7.6 - 8.2 4.0 - 5.4 4.8 - 6.1 6.9 - 8.0 8.6 - 11.4
Nickel 420/420 6 - 8 6 - 7 8 - 10 9 - 9 7 - 10 6 - 8
Selenium 36/100 0.53 - 064 0.55 - 0.64 0.74 - 0.81 0.55 - 0.65 0.84 - 0.97 1.18 - 1.45
Silver N/A 0.2 - 0.4 0.3 - 0.4 0.4 - 0.4 0.1 - 0.2 0.1 - 0.1 0.7 - 0.8
Zinc 2800/7500 380 - 420 530 - 610 450 - 510 540 - 590 1420 - 1520 520 - 620
PH 11.31 - 11.67 10.64 - 10.85 10.69 - 11.09 10.18 - 10.39 10.76 - 11.12 10.68 - 10.84
Alkalinity
(%)
12.0 - 13.2 13.4 - 14.6 10.2 - 11.6 9.1 - 11.3 11.7 - 12.5 11.1 - 12.2
20
1996). It can also be used as an admixture in concrete through proper mixture proportioning for
encapsulating heavy metals and other pollutants present in the ash. However, this technology is yet
to be developed. Based on an excusive laboratory and field study work Naik and his associates
(Naik 2002; Naik and Kraus 2003) have developed a technology for the manufacturing of flowable
slurry (Controlled Low Strength Material, CLSM) and medium strength structural grade concrete
incorporating the wood ash.
2.3 PULP AND PAPER INDUSTRY BY-PRODUCTS
The U.S. pulp and paper industry generates more than 14.6 million dry tons of solid residues
per year that includes wastewater treatment residual (5.83 milliom tons), ash (2.81 million tons), and
miscellaneous residues (5.91 million tons) (NCASI 1995). By-products from pulp, paper, and
associated products industry are mainly sludge from liquid waste treatment plants. Paper mill sludge
is primarily composed of very short fiber material, lignin-based compounds, and coagulant
chemicals. The sludge is usually lagooned, landfilled, or subjected to land cultivation (Naik 1989).
The chemical composition of a typical sludge is composed of moisture (75%), solids (25%), ash
(7.8%), nitrogen (740 ppm), kjeldahl nitrogen (sum of organic and ammonia nitrogens) (740 ppm),
potassium (20 ppm), phosphorus (102 ppm), calcium (2670 ppm), magnesium (234 ppm), sulfur
(15 ppm), boron (0.5 ppm), chloride (185 ppm), iron (1280 ppm), manganese (3.0 ppm),
molybdenum (4.2 ppm), zinc (170 ppm), nickel (1.1 ppm), lead (5.3 ppm), mercury (0.1 ppm),
chromium (4.2 ppm), copper (7.0 ppm), organic carbons (12.0%), and PCB (2.5 ppm) (Thomas et al.
1987).
21
2.3.1 Applications of Pulp And Paper Industry By-Products
About 300 kg of sludge is produced for every tonne of paper produced (Kirk et al. 1978).
Thomas et al. (1987) successfully developed a material composed of portland cement mixed with the
sludge produced by the treatment of wastewater from a paper recycling plant. The material
developed had a compressive strength on the order of 10 MPa, and tensile strength on the order of 3
MPa. Such a material can be successfully used in masonry blocks, wallboards and panels, shingles,
fire retardants, panels, filler material for fireproof doors, etc. The developed material had a fracture
toughness approximately twice that of conventional concrete. Springer et al. (1996) manufactured
blocks in a laboratory from 100% recycled pulp fiber. The wood fiber composite was compressed
and dried to produce the block. The product was recommended for non-structural applications and
meant to compete with materials such as office partitions, shelving, and ceiling tiles. Soroushian et
al. (1995) used recycled fibers for production of thin sheet cement products. Test results showed
improvement in flexural strength and toughness but at reduced stiffness.
Patented methods (GGC 1995; O'Connor and Nechvatal 1996) are available to produce good
quality lightweight aggregates using paper mill sludges. A study showed that a blend of bark ash
(8%) and Class F ash (92%) could be used as a replacement of 20% portland cement (Collins and
Ciesielski, 1994). The blended ash mixture results exhibited performance similar to unblended Class
F fly ash. Péra and Ambroise (2002) have reported that when the pulp and paper mills sludges are
calcined under 7000C then these sludges show interesting pozzolanic properties that can be used in
development of high-strength and colored concrete. Further, calcinations of the sludges over 7500 C
result in a self-cementing material which can be used to replace portland cement in several
applications such as in controlled low strength materials, masonry blocks and autoclaved products.
An extensive study carried out by Naik (2002) on strength and durability of concrete
22
containing residual solids from pulp and paper mills has revealed that the addition of residual solids
in concrete enhances its durability properties in aggressive environments.
2.4 FOUNDRY BY-PRODUCTS
Foundry by-products result from the metal molding and core-making processes in metal
casting industry (foundry). Metal casting industries use sand molds to cast materials into desired
shapes. Cores are used in the sand molds to shape the casting to be cast by the molten metal
materials. Since sand grains do not naturally adhere each other, binders must be included to cause
sand grains to stick together and retain shape during the introduction of the molten metal into the
mold. Two types of binder systems namely green sand and chemically bonded systems are used in
metal casting. The remainder is generated primarily by melting operations (as cupola slag) with
minor contributions from cleaning of castings and dust collectors. The foundry by-products include
used (spent) foundry sand, slag, dust, etc. Approximately 100 million tons of sand is used in the U.S.
3000 foundries. Out of that, 6 – 10 million tons are discarded annually (www.foundryrecycling.org).
The reutilization rate of foundry sand is only about 0.5 million tones per year. The commonly used
green sands for molds making are composed of four major materials: sand, clay, sand additives, and
water. Sand usually constitutes 50 to 95% of the total materials in a molding (Edey and Winter
1958). Clay acts as a binder for the green sand. The major types of clay used are Bentonites
(western and southern), Fireclays, and other clays such as Illite and Halloysite. Amount of clays
varies from 4 to 10 percent of the green sand mixture. Core sands are employed to produce desired
cavity shapes in which molten metal is cast. Core sands are composed primarily of silica sand with
small percentages of either organic-type or inorganic-type binders. The organic binders include oil,
synthetics, cereal proteins, etc. The inorganic binders include portland cement, fly ash, and sodium
23
silicate.
Other by-products from foundries are: slag, which is primarily composed of metal oxides,
sand from recycled castings, coke ash, melted refractories, and other materials. Slag is usually
removed from the furnaces by conditioning them through the use of fluxes or flocculants. The
fluxes used include fluorspar, limestone, and soda ash. Silica is also one of the flocculants used.
The furnaces, or cupolas, emit exhausts carrying suspended dust particles, which are captured by
particulate collection systems such as a baghouse or wet scrubbers. These particulate matters are
called cupola dust.
Depending on the binder systems used the sands from foundry have different physical
and environmental characteristics. A few studies have evaluated physical and chemical
properties of foundry sand (AFS 1991; Naik and Singh 1994; Naik and Singh 1997 a,b). The
properties of used foundry sand varies due to factors such as type of foundry processing
equipment used, types of additives used for mold making, number of times sand is recycled, and
type and amount of binder used (Naik 1989). The sieve analysis results for foundry sands and
regular concrete are shown in Table 5. The sieve analysis grading curves for regular concrete
sand and foundry sand is shown in Fig. 4. The physical properties are shown in Table 6. The
results reveal that used foundry sand is much finer and does not fall within the ASTM limits.
When foundry sand was used as a 30% replacement of regular concrete sand, the resulting
grading curve for the composite sand materials was close to the upper limit of ASTM (Fig. 5).
Used foundry sands are finer and higher in unit weight, compared to regular concrete sand (Naik
et al. 1994d). The used foundry sand is composed of metallic elements in addition to silica,
which is also found in regular concrete sand. Spent foundry sand particles are weaker than
regular concrete sand particles because they are subjected to a complex form of heating and
24
cooling loadings, especially thermal fatigue loading. Spent sand does not meet ASTM C 33
requirements for fine aggregate. Oxide analysis of a spent foundry sand by AFS (1991) showed
SiO2 (87.9%), Al2O3 (4.7%), Fe2O3 (0.9%), CaO (0.1%), MgO (0.3%), SO3 (0.1%), N2O (0.2%),
K2O (0.3%), TiO2 (0.2%), and LOI (5.2%).
Some physical properties of foundry slags were determined by Naik et al. (1996b). The
results showed lower unit weight of foundry slag (1280 kg/m3) compared to normal weight
aggregate (2400 kg/m3) but higher than the structural lightweight aggregate (1120 kg/m
3). The SSD
absorption was slightly lower for foundry slag relative to the structural lightweight aggregate. The
soundness of foundry slag was equivalent to the structural lightweight aggregate.
2.4.1 Application of Foundry By-Product Materials
2.4.1.1 Foundry Sands
Large volumes of foundry sands are currently being used in geotechnical applications such as
road bases, structural fills, embankments, general fills and landfills (Richter et al.1999; Ji and Wan
2001; Patridge 1999; www.foundyrecycling.org). The use of high quality sand in foundry industry
makes the by-product an excellent aggregate for cement-based manufactured products, flowable fill,
asphalts, and concrete products (Javed et al. 1994; Richter et al.1999; Regan et. al 1997;
www.foundyrecycling.org).
Extensive investigations at the UWM Center for By-Products Utilization, University of
Wisconsin-Milwaukee (Naik and Patel 1992; Naik et al. 1994d; Naik and Singh 1994c) have
revealed that foundry sand can be used in concrete as a replacement of regular concrete sand up to
30-35% by weight to meet strength requirements for structural-grade concrete. Some preliminary
work reported by AFS (1991) indicated replacement of regular concrete sand by used foundry sand
25
up to about 8% by weight.
26
Table 5: Sieve analysis results for sand (ASTM C 136) (Naik and Singh 1997a)
Sand 1: Regular Concrete Sand
Sand 2: Clean Foundry Sand (FS1)
Sand 3: Used Foundry Sand (FS2)
Sieve
Size
Percent Retained on each
Sieve
Cumulative Percent
Retained
Cumulative Percent Passing
Required
ASTM
C33* Sand 1
Sand 2
Sand 3
Sand 1
Sand 2
Sand 3
Sand 1
Sand 2
Sand 3
Cumulative
Passing (%)
#4
0.1
0.0
0.0
0.1
0.0
0.0
99.9
100
100
95-100
#8
12.8
0.0
0.0
13.0
0.0
0.0
87.0
100
100
80-100
#16
13.6
0.0
0.0
26.6
0.0
0.0
73.4
100
100
50-85
#30
18.9
0.1
0.5
45.5
0.1
0.5
54.5
99.9
95.5
25-60
#50
32.2
41.4
46.1
77.7
41.5
46.6
22.3
58.5
53.4
10-30
#100
16.6
54.6
47.1
94.2
96.1
93.7
5.8
3.9
6.3
2-10
* For use in concrete.
27
Table 6: Physical Properties of Sand (Naik and Singh 1997a)
Sand 1: Regular Concrete Sand
Sand 2: Clean Foundry Sand (FS1)
Sand 3: Used Foundry Sand (FS2)
As
Received
Moisture
Content,
%
Unit
Weight,
kg/m3
Bulk
Specific
Gravity
Bulk
Specific
Gravity,
SSD
Apparent
Specific
Gravity
SSD
Absorption,
%
Void,
%
Fine
-ness
Mod
-ulus
Clay
Lumps &
Friable
Particles,
%
Soundness
of
Aggregates,
%
Material
Finer than
#200 (75
µm) Sieve
ASTM
C 566
C 29
------------------------------C 128------------------
C 29
C
136
C 136
C 88
C 117
Sand 1
0.39
1840
2.43
2.47
2.52
1.0
25.0
3.57
0.2
10.0
1.40
Sand 2
0.19
1730
2.38
2.50
2.70
4.9
33.8
2.33
0.1
54.9
0.17
Sand 3
0.25
1784
2.44
2.57
2.79
5.0
34.8
2.32
0.4
10.5
1.08
28
Fig. 4 Sieve analysis envelope for regular concrete sand & foundry sands
29
Fig. 5 Sieve analysis envelope for foundry sand combined with regular concrete sand
30
The test results showed some loss in concrete strength due to the use of spent foundry sand. More
recently, investigations by Domann (1997) at the UWM Center for By-Products Utilization have
shown that this loss can be compensated through the use of Class C fly ash in foundry sand concrete.
Emery and MacKay (1991) reported that up to 15% used foundry sand could be used as
replacement of fine aggregate in Hot Mix Asphalt (HMA). A laboratory study by Javed et al.
(1994) on waste foundry sand in asphalt concrete advocated a replacement level of 15% for regular
sand by foundy sand without any compromise in performance of asphalt concrete mixture. Recently,
Naik et al. (1996b) established suitability of used foundry sand in manufacture of masonry products.
Their results revealed that 35% spent foundry sand could be used as a replacement of regular
concrete sand in manufacture of masonry products such as blocks, blocks, and paving stones.
Naik and his associates (Naik and Singh 1994c; Naik and Singh 1997 a,b) developed mixture
proportions and production technologies for foundry sand in flowable slurry materials for field
applications. Test data have shown that excavatable flowable slurry materials can be manufactured
using foundry sand as a replacement of fly ash or fine aggregate up to 85% (Naik and Singh 1997
a,b). The strength requirement for this material ranged from 0.30 MPa to 0.60 MPa at 28 days.
Bhat and Lovell (1997) study on flowable fill containing foundry sand as a substitute of natural sand
has indicated lower potential for corrosivity. Their tests on toxicity revealed that some foundry
sands are environmentally safe if used in flowable fill.
2.4.1.2 Foundry Slag
Foundry slag is a glass like amorphous material exhausted from melting furnace of iron
foundry and treated as industrial waste (Uehara and Sakurai 1996). An investigation by Naik et al.
(1996b) demonstrated that foundry cupola slag is appropriate for manufacture of coarse semi-
31
lightweight aggregate for use in cement-based materials. Their results also demonstrated that the
foundry slag could be used as a replacement of normal weight aggregate (in the 50-100% range) in
manufacture of structural-grade concrete.
2.5 METALLURGICAL BY-PRODUCT MATERIALS
2.5.1 Iron Blast Furnace Slag
The American Society of Testing and Materials (ASTM 1999) defines blast furnace slag as
“the non-metallic product consisting essentially of calcium silicates and other bases that is developed
in a molten condition simultaneously with iron in a blast furnace. The iron and steel industry does
not routinely measure slag output; therefore, actual annual ferrous slag production data in the U.S.
do not exist (Kalyoncu 2000b). The data collected by the U.S. Geological Survey (USGS) indicates
data blast furnace slag production ranges from about 220 to 370 kilograms per metric ton of pig iron
produced. Lower grade ores yield much higher slag fraction. Iron blast furnace slag is produced
during the manufacture of pig iron in a blast furnace. Four types of blast furnace slags, namely air-
cooled, expanded, granulated, and pelletized are produced, depending up on the type of cooling and
processing used. Air-cooled slags are produced when slag is cooled under ambient air conditions.
Expanded slag is produced through controlled cooling with water or steam. Granulated slag is
produced when slag is quenched with water. The pelletized slag is produced due to cooling of slag
by water and air. In U.S.A., approximately 12 million tons of blast furnace slag was produced in
2000, out of which about 75% was air cooled slag (Kalyoncu 2000b). The principal constituents of
the blast furnace slags are silica, alumina, calcia, and magnesia, which accounts for 95% of the
composition (Miller and Collins 1976; Kalyoncu 2000b).
32
2.5.1.1 Application of Iron Blast Furnace Slag
Uses of blast furnace slag ranges from building and road construction to waste stabilization.
Air-cooled slag is appropriate for use as conventional aggregate in concrete, asphalt, and road bases.
Expanded slag is used as lightweight aggregate material for concrete. Granulated slag is appropriate
for manufacture of cement. Pelletized is used as a lightweight aggregate and in manufacture of
cement. In 2000, 8.9 million tons of blast furnace slag was used in various applications such as
concrete products, railroad ballast, concrete aggegate, asphaltic concrete aggregate, road bases,
roofings built-up and shingles, fill etc. the U.S.A.(Kalyoncu 2000b).
2.5.2 Steel Slags
Steel slag is the residue of steel production process. It is generated when lime flux reacts
with molten iron ore, scrap metal, and other materials charged in a steel furnace. It consists of
silicates and oxides of unwanted elements in steel chemical composition. Generally, steel slag is air
cooled. Steel slags shows differences in physical and chemical properties depending on the raw
materials and process (Xuequan et al. 1999). Typical physical properties of steel slag are given in
Table 7. Approximately 13 million tons of steel slag was produced in 2000 in the U.S. out of which
5.1 million tons were used in various application ( Kalyoncu 2000). Steel slag has expansive
behavior, resulting in volume change of up to 10% that can cause difficulties with products containg
steel slag (Ahmed 1991; www.rmrc.unh.edu/Resources/PandD/UserGuidelines/UserGuide/ssal.htm).
2.5.2.1 Application Of Steel Slags
The Netherlans uses 100% of steel slag (Eighmy and Magee 2001) while the Germany uses
about 97% of the produced steel slag as aggregate for road construction, ways, earthworks,
33
armourstones for hydraulic structures (Motz 2001). Steel slag can be processed into a coarse or fine
aggregate materials for use in dense and open graded hot mix aspalt concrete pavements (Rossini-
Lake et al. 1995; Kandahal and Hoffman 1982; Collins and Ciesielski 1994) and in cold mix or
surface treatment applications ( Noureldin and McDaniel 1990). The steel slag containing asphaltic
mixture has shown improved skid resistance properties (Jones 1996).
2.5.3 NON-FERROUS SLAGS: COPPER, LEAD, ZINC, NICKEL, AND PHOSPHOROUS
Non-ferrous slags are generated due to thermal processing of non-ferrous ores such as
copper, lead, zinc, nickel, and phosphate (Collins and Ciesielski 1994). About 9 million tonnes of
ferrous slags are generated each year. Copper and phosphate slags constitute the major portion of
non-ferrous slags, 3.6 million tonnes each per year. The non-ferrous slags that can exhibit
cementitious and pozzolanic behavior are copper, nickel, and lead (Malhotra 1993). Work is still in
progress to establish potential uses of these slags in cement-based materials on a rational basis. Non-
ferrous slags have been used in aggregates (OECD 1977). However, due to potential leachate
problems, aggregates made with non-ferrous slags must be evaluated prior to their use.
34
Table 7: Typical Physical Properties of Steel Slag
Property Value
Specific Gravity 3.2 - 3.6
Unit Weight, kg/m3
(lb/ft3)
1600 –1920
(100 – 120)
Absorption Up to 3%
The study on utilization of zinc in two forms: ground and un-ground for the replacement of
cement and natural sand, respectively in concrete has shown insignificant leaching problem
regardless of the use in replacing cement and/or natural sand. . But, the use of both ground and un-
ground zinc to replace cement (15%) and natural sand (20%) together releases Pb (lead) higher than
the individual separate replacements, however, the Pb concentration was far lower than the limit
(Monosi et al. website reference).
2.6 MUNICIPAL SOLID WASTE MATERIALS
2.6.1 Sewage Sludge
Sewage sludge is a by-product of sewage treatment plants that contains nutrients, organic
matter, and contaminants such as metals and synthetic organics discharged into the sewers from
homes, industries, and businesses and leached from pipes (Cornell Guide 2003). The sewage sludge
is also known as biosolids (NRC 2002; USEPA 1999). The composition of sewage sludge mainly
depends on the characteristics of the wastewater influence entering the wastewater treatment plant
and treatment processes used. The total solid content of sewage sludge includes the suspended and
35
dissolved solid. It is less expensive to transport sewage sludge with high solids content than to
transport liquid sewage sludge. Liquid sewage sludge has a solids content of 2 to 12 percent while
dewatered sewage sludge has a solid content of 12 to 40 percent of solids. Dried or composed
sewage sludge contains solids over 50% (EPA 1995). Total solid content depends on the type of
sewage sludge (primary, secondry or tertiary). Initial solid content of primary sludges varies
between 3 and 7%, which contain 60 to 80% organic matter (Outwater 1994). The solid content of
secondary sludges vary from 0.2 to 1.5% with organic matter ranging between 35 to 50%. The dried
solid sludge typically has moisture in the range of 18 to 24%. The sludge is primarily composed of
nitrogen and phosphorus containing organics. Depending up on the source of the wastewater, the
sludge can have heavy metals, organic carcinogens, and pathogens including bacteria, viruses,
protozoa, etc. A dried sludge shows values ranging between 1.6 to 1.7, 8.1 to 8.5, and 59 to 61 for
specific gravity, pH, and loss on ignition, LOI (Tay and Show 1992).
2.6.1.1 Application of Sewage Sludge
Rapid urbanization in many countries has resulted in a drastic increase of wastewater sludge.
Due to land scarcity and stringent environmental control regulations, sludge disposal by landfilling is
no longer appropriate. Therefore, future trends in sludge management are towards minimization and
reutilization as useful resources. Various studies (Tay and Show 1997; Cenni et al. 2001; Ferreira et
al. 1996) suggest to use sludge as non-conventional construction materials for the manufacturing of
bricks, lightweight aggregate etc. Municipal sludge in combination with fly ash and paper mill
sludge can be used to manufacture lightweight aggregate through a sintering process (O'Connor and
Nechvatal 1996). Sludge has also been used to produce lightweight aggregate in Japan using the
sintering process (Baeyens and Puyvelde 1994). These aggregates can be used in the manufacture of
36
lightweight concrete and masonry products. Fired clay bricks can be manufactured using sludge up
to 40% of clay replacement (Tay and Show 1992).
2.6.2 Sludge Ash
More than 150 wastewater treatment plants incinerate sewage sludge, producing sludge ash
in the range of 0.5-0.9 million tonnes (Collins and Ciesielski 1994). Sludge ash is primarily
composed of silt size particles and free of organic matters. The bulk density values for wastewater
can be found in the range of 480 - 870 kg/m3. The particle density varies between 0.9 and 1.1 kg/m
3.
Four major oxides found in sludge ashes are SiO2 (14.4 - 57.7%), CaO (1.8
- 36.9%), Al2O3 (4.6 - 16.4%), and Fe2O3 (3.4 - 24.4%) (Tay and Show 1992). When polymers are
used as flocculating and dewatering agents, lime becomes a minor constituent of the ash. Whereas,
lime becomes a major component when it is used as a flocculating and dewatering agent instead of
polymers.
Up to 10% of sludge ash can be used as a filler in concrete without significantly affecting
strength of concrete (Tay and Show 1992). Sludge ash can be used in asphaltic concrete mixtures as
a partial replacement of mineral filler (Sayed et al. 1995). A technology for producing sludge as
pellets has been developed. These sludge ash pellets can be used as a partial replacement of coarse
aggregate (up to 35%) without compromising performance of concrete (Collins and Ciesielski 1994).
2.6.3 Incineration Ash
In 1999, more than 230 million tons of Municipal Solid Waste (MSW) was generated in the
United States. Currently, in the United State, 28% of MSW is recovered and recycled or composted,
15% is burned at combustion facilities, and the remaining 57% is disposed of in landfills (USEPA
37
2000). Recycling, including composting, divereted 64 million tons of material away from landfills
and incinerators in 1999, up from 34 million tons in 1999. Burning MSW can generate energy while
reducing the amount of waste by up to 90% in volume and 75% in weight. In 1999, 96,000 tons of
MSW was burnt per day at 102 combustors of the United States (USEPA 2000;
www.epa.gov/epaoswer/non-hw/muncpl/facts.htm). The ash produced by incineration of MSW at
incineration plant is generally known as Municipal Solid Waste Incineration (MSWI) ash (Rémond
et al. 2002 a,b). Both fly ash and bottom ash are generated. More than 90% (by mass) of incinerator
residue consist of bottom ash, which is similar to the slag-like material (Pera et al. 1997).
Incineration ash consists of glass, metals, ash, ceramics, and un-burnt materials (OECD 1977). ,.
Un-burnt materials found in Municipal Solid Waste (MSW) ash include cans, wires, organics, etc.
that are not fully reduced during the combustion process. Therefore, incineration ashes need to be
screened prior to their use in construction materials. Composition of the incineration ash derived
from several sources in the USA is shown in Table 8. Chemical composition of the incineration ash
varies greatly with source, type of incinerator used and, operating conditions of incineration.
Chemical compositions of incineration ashes are shown in Table 9. Incineration fly ash can be used
for manufacture of synthetic aggregate by fusion or vitrification. Various studies regarding
incorporation of municipal solid waste incineration fly ash (Rémond et al. 2002a, Ferreira et al. 96,
Collivignarelli and Sorlini 2002; Mangialardi 2001) and bottom ash (Pera et al. 1997) in cement
paste, mortar, and concrete are reported. A study (Mulder 1996) in the Netherlands showed that fly
ash, after pretreatment (washing), can be used in cement-based construction materials. Collivinarelli
and Sorlini (2002) reported that incineration fly ashes washed and milled and then stabilized by
cement-lime process could be used for the substitution of natural aggregate (200 – 400 kg/m3) in the
manufacturing of concrete. They further reported a drastical reduction in the leachate material in
comparison with the raw incineration fly ash. An extensive study by Rémond et al. (2002a)
38
indicated that municipal solid waste incineration fly ashes this material have high content of soluble
salts (mainly chlorides and sulphates) and heavy metals (abundant Zn and Pb). The incorporation of
MSWI fly ash in mortar up to 15% (optimum 10%) in relation to cement mass, has shown increase
in strength after 7, 28, and 90 days in spite of delay in early setting time of the mortars (Rémond et
al. 2002a).
39
Table 8: Incinerator Residue (Ash and Clinker) Analysis (OECD 1977)
Component
A
B
C
Range
Ave.
Range
Ave.
Range
Ave.
Glass
Ferrous metals
Ash (including fly
ash)
Ceramic and stone
Non-ferrous
metals
45.1-55.2
23.6-32.8
15.9-18.6
1.2-2.3
4.1-1.2
50.1
28.2
17.2
1.6
2.6
53.3-52.4
27.0-36.6
13.1-19.4
1.4-2.9
0.7-1.1
48.4
31.5
17.0
2.2
1.0
59.9*
40.9
59.9*
0.1
0.1
59.9*
40.9
59.9*
0.1
0.1
* Glass and ash fractions were indistinguishable.
A. Two continuous travelling grate incinerators.
B. Four batch incinerators.
C. One rotary kiln incinerator.
40
Table 9: Chemical Composition of German and Swiss Incineration Residues (OECD 1977)
Component
Germany
(range), %
Switzerland
(average), %
Si02
Fe202
Al203
Ca0
K20
Na20
Zn0
S03
Mg0
C
Ti02
Mn0
P205
41.8-57.7
5.5-18.2
7.8-17.9
9.2-12.0
1.1-1.6
2.6-7.4
-
0.69-6.4
1.2-2.0
0.14-0.38
0.2-0.5
-
0.2-1.2
50
13
10
15
1
6
-
-
2
-
1
-
2 (unburnt)
41
2.7 USED TIRES
In 2001, approximately 273 million scrap (used) tires were generated in the United State.
Today, in the U.S., markets exist for 76% of these scrap tires from 17% in 1990. Civil engineering
projects used 40 million scrap tires in 2002 in the U.S.A. About 42% of all scrap tires are as a
combustion fuel using new technologies having pollution control equipments. 9% of scraped tires
are recycled through the use of ground rubber, while about 12% are retread annually
(www.epa.gov/epaoswer/non-hw/muncpl/tires.htm 2002). Even with all these reuse and recycling
efforts, almost quarter of the scrap tires end up in landfills each year. Over the years, more than 800
million scrap tires have accumulated in stockpiles. Stockpiled tires create an ideal atmosphere for
breeding mosquitoes and are also a habitat for rodents. Currently, landfills in many states restrict the
burial of whole tires in municipal landfills due to several factors including: tires are not
biodegradable and cannot be easily compacted, resulting in more space requirements; and, they
"float up" to the surface due to settlement of other materials surrounding it and buoyancy effects of
gases trapped by the tires. This, in turn, exposes landfill to insects, rodents, and birds. Used tires
must be shredded before landfilling. The cost of shredding can from $65 to $85 per ton.
The raw materials in tyres include natural and synthetic rubber, carbon black, nylon,
polyester and even Kelvar cord, sulphur, oils and resins, and other chemicals (www.profit-from-
waste.com/crumb.html). Tire rubber with fiber and steel belting comprise the major elements of
tires currently being used. Of all the possible methods of tire disposal the creation of rubber crumb
potentially offers the most effective environmental solution, as the material that can be used in a
variety of other products. Tire rubber is ground to a particulate form before using in asphaltic
concrete mixtures. This form of tire rubber is termed crumb rubber modifier (CRM) because its
42
inclusion modifies properties of the asphaltic material. The composition of CRM depends greatly
up-on the original chemistry of the tire rubber and contamination. Chemical composition of CRM is
shown in Table 10. In 1999, more than 500 million pounds of crumb rubber was used in North
America (www.profit-from-waste.com/crumb.html 2003).
Tires can be used for environmentally safe applications in whole, cut or stamped form in civil
engineering works such as highway crash barriers, sound absorbing walls, boat benders on harbors
walls (ASTM D6270 1998), as insulation in building foundations and road base materials ( SBC
No.99/008).
43
TABLE 10: Average Chemical Compositions of CRM (Baker Rubber, Inc. 1993)
Composition
Mean (%)
Standard Deviation (%)
Min. (%)
Max. (%)
Acetone Extract
17.2
5.8
11.4
15.1
Ash
4.8
0.3
5.0
5.1
Carbon Black
32.7
1.2
32.0
33.2
Rubber
Hydrocarbon
42.9
7.3
47.9
50.2
44
2.7.1 Used Tires In Portland Cement Concrete Systems
In the past, tire chips and CRM have been used in concrete. Generally, use of tire chips
causes drastic reduction in concrete compressive strength due to a poor bond between the tire
chips and the cementitious matrix. Eldin and Ahmed (1992) reported that concrete containing
tire chips or CRM exhibited acceptable workability and decreased unit weight compared to plain
portland cement concrete. However, the rubberized concrete showed a lower compressive and
tensile strength, and decreased resistance to freezing and thawing actions. This problem can be
solved through the use of micro-fine CRM in cement-based materials. Li et al. (1998) reported
reduction in compressive strength but improvement in ductile behavior with capability of
absorbing a large amount of energy under compressive and flexural loads in concrete containing
particles of scrap rubber tyre. They suggested that concrete containing rubber tyre particles
might be used in construction of driveways, sidewalks or road construction where strength is not
priority but greater toughness is preferred, and where vibration reduction is required (e.g. base
isolated structures and machine foundations).
2.7.2 Used Tires In Asphaltic Concrete Systems
The largest potential market for discarded tires is in rubberized roads and other asphaltic
construction materials. Used tires are reduced to crumb rubber by primarily using ambient
temperature grinding (0.25 mm to 40 Mesh), ambient granulating (0.25mm to 40 Mesh), cryogenic
grinding (0.25 mm to 100 Mesh), and wet grinding (40 Mesh to 100 Mesh) techniques.
Two different processes exist for introducing CRM in paving materials: wet and dry
processes. In wet processes, a modified asphaltic binder is manufactured by blending CRM with
asphalt-cement. The modified binder, asphalt-rubber binder (AR binder), has improved properties
45
relative to conventional asphalt-cement without CRM. The technologies that use wet processes are:
(1) the McDonald or batch technology; and, (2) the continuous blending technologies (Naik et al.
1994e).
In the batch technology, 15-22% CRM is blended with asphalt-cement in a blending tank,
and then transferred to a reaction tank where the materials are allowed to react for 45 minutes to 1
hour. The reaction tank has provisions to maintain a uniform blend as well as a constant temperature
for obtaining consistent, predictable results. The reaction temperature ranges from 177o to 232
oC.
This technology produces a thick elastic binder with improved properties compared to conventional
asphalt-cement. The continuous technology is very similar to that of the McDonald technology but
it differs in the process of mixing CRM with asphalt concrete. This technology produces an asphalt-
rubber binder by using a continuous mixing unit and a finer CRM. The finer CRM is used to shorten
reaction time between the CRM and asphalt-cement. The continuous mixing unit can be installed at
the HMA plant and then it can be interlocked into the conventional asphalt binder system. The CRM
contents vary between 5 and 20%. This new CRM-modified binder exhibited increased softening
point and decreased temperature susceptibility. Thus, service life of the material made with asphalt-
rubber cement is increased considerably compared to conventional asphalt cement-based materials.
The asphalt-rubber binder can be successfully applied in several materials including crack and joint
sealant, chip or seal coats, stress absorbing membrane (SAM), hot mix asphalt (HMA), etc.
The dry process involves adding of CRM directly into asphaltic concrete mixtures.
Typically, the CRM is pre-blended with the heated aggregate and then hot asphalt is added to the
mix for manufacture of the asphaltic concrete. The paving concrete made with this process is
generally termed as rubber-filled concrete. Some of the CRM particles react with the asphalt
during the process of mixture preparation. However, the reaction of the particles greatly depends
46
up-on their size. An increase in fineness increases reactivity of the particles. Therefore, the
amount of fine CRM present in the mixture determines the degree of modification of the asphalt
binder. The two technologies that use the dry process include: (1) the PlusRide system; and, (2)
the generic (TAK) system. The dry process system employs CRM as a partial replacement of
aggregate in asphaltic concrete mixtures. The rubberized material provides sound attenuation,
improved fatigue properties, and better skid resistance. The PlusRide process was developed in
the 1960's by the Swedish Companies Skega AB and AB Vaegfoerbaettringar (ABC). The
system was marketed by Paveteck Corp. of Seattle, Washington.
The generic system was developed by Takallou in 1986. For this system, CRM gradation
is designed to suit individual aggregate gradations for dense-graded asphaltic concrete mixtures.
Since this system employs the available "generic" aggregate gradation for individual localities, it
was named the "generic system." The size of CRM to be used in this system should be smaller
(by one sieve size) relative to the gap that will be created in the mineral aggregate. The CRM
used in the generic system is finer than that for the PlusRide system. The finer rubber particles
present in the generic system mixture also modify the asphalt-cement considerably due to their
high reactivity, while the coarser rubber particles act primarily as elastic aggregate in the HMA
mixture.
More recently, Naik and Singh (1994b) developed a modified generic system. This system
used a constant size of CRM irrespective of aggregate gradation of individual localities. This
concept was substantiated by using two Wisconsin DOT asphaltic concrete mixtures that were
modified by using a constant size CRM (180 μm). All asphaltic concrete mixtures containing up to
15% CRM exhibited excellent performance. This investigation revealed that this size CRM or lower
can be used in all generic asphaltic concrete mixtures, irrespective of mixture proportions and
47
gradation of aggregates.
Radziszewski and Kalabinska (1999) reported that addition of grained rubber as a modifier in
bituminous mixture not only improves properties of modified asphalt concrete but also increases
concrete fatigue life as many as 10-15 times. Another study by Gawel and Slusarski (1999) shows
that use of rubber in asphalt not only enhance durability and service life of pavement but it also
make possible to use thinner layer of asphalt concrete. Another benefit from using rubber, as asphalt
modifier is the possibility of using lower-grade asphalts in road making. Their study further suggest
s that with the proper selection of suitable asphalt grade and rubber content the suitable binder can be
obtained for the construction of roads for service in hot and cold climates.
2.7.3 Other Applications
Shredded tires can be used as lightweight aggregate materials for structural fill whose weight needs
to be reduced. Wood chips or saw dust have been used to accomplish this. Tire chips provide a
better alternative to wood chips because of better durability. Additionally, shredded tires can be
used as soil reinforcement.
The Oregon DOT conducted a project in which shredded tires were used as lightweight fill
(Ahmed 1991). The results were very encouraging. Application of waste tires as lightweight fill can
consume large volumes of used tires. However, leachate tests of tire chips exhibited the maximum
permissible concentration of barium, cadmium, chromium, lead, soleneum, and zinc (MPCA 1990).
Under basic conditions, the highest concentration was observed for Polynuclear Aromatic
Hydrocarbons (PAHs) and total Petroleum Hydrocarbon (TPH). To avoid these or other negative
environmental impacts, it was suggested that tire materials should be used in the unsaturated zone
(low water table) of the subgrade.
48
2.8 PLASTICS
2.8.1 Post-Consumer Waste Plastics
Post consumer waste plastic made up 21.5 million tons of MSW generation in 1997 in the
United State (USEPA 1999). The quantity has increased steadily and has estimated to be about 25
million tons in 2000. Plastic wastes constitute around 10.7% of total municipal solid waste
generation in 2000 in the United State (www.epa.gov/epaoswer/non-hw/muncpl/facts.htm). Around
5.2 percent of plastic waste was recycled in 1997 (USEPA 1999).
2.8.2 Application of Plastics
Naik et al. (1994a) evaluated the literature concerning use of polymers and used plastics in
cement-based materials. They concluded that very little work had been directed toward the use of
discarded plastics in advanced cement-based materials. Plastics can be divided in to two major
categories: thermosets and thermoplastics. A thermoset is a polymer that sets irreversibly when
heated. They areuseful for their strength and durability and hence, used mainly in automobiles and
construction applications. On the other hand, a thermoplastics is a polymer in which the molecules
are held together by weak bonds, creating plastics that soften when exposed to heat. Themoplastics
can esily be shaped and molded into products such as milk jugs, soda bottles, carpet fibres etc.
There are seven types of plastic waste: (1) polyethylene terephthalate (PET), commonly found in
soft drink bottles is the number one recycled resin today; (2) high-density polyethylene (HDPE), the
second most commonly recycled resin, is found in milk jugs and base cups on soft drink bottles; (3)
polystyrene (PS), commonly used in egg cartons, plates and cups, packaging “peanuts”; (4) low-
49
density polyethylene (LDPE), generally found in films and trash bags; (5) polypropylene (PP),
generally used in luggage and battery castings; (6) poly-vinyl chloride (PVC) used in flooring,
piping, etc. and (7) Linear low-density polyethylene (LLDPE) (www.epa.gov/garbage/plastic.htm
1/27/2003).
Research has been conducted recently with reclaimed PET resins derived from soda bottles
(Rebeiz et al. 1993; Rebeiz et al. 1994). The PET material was processed to produce a liquid resin
using facilities available at a commercial company. This process is not available for other types of
plastic and not economically feasible at the present time. For the investigations reported,
unsaturated polyester resins were obtained from several commercial sources. Each contained a
particular percentage of recycled PET. The amount of recycled PET varied between 15 and 40%.
These resins were pre-polymers with high viscosities (100-1890 cps). Styrene was added to reduce
the viscosity of the resins. Appropriate initiators and promoters were then added to the resins
immediately prior to mixing with the concrete aggregates in order to initiate and accelerate
polymerization (curing or hardening of the resin to a solid plastic state). For manufacture of polymer
concrete (PC), the resin and aggregate were mixed in a conventional concrete mixer for
approximately 3 minutes and the specimens were cast, vibrated, and allowed to cure at room
temperature for 3-9 days prior to testing. In general, inclusion of recycled PET had no detrimental
effects on the PC. Applications for which this type of PC for precast components, overlays, and
repair materials.
Use of post-consumer plastics as a flexible particulate filler in concrete should improve its
fracture toughness. However, due to the absence of a chemical bond between plastic filler and
cementitious matrix, the potential increase in toughness is generally not achieved. To solve this
problem, Naik et al. (1996a) introduced a chemical bond between plastic particles and cementitious
50
matrix using chemical treatments. Of the chemical treatments (water, bleach, and NaOH) used, the
alkaline bleach performed the best. However, beyond 0.5% addition of plastic particles, concrete
strength decreased substantially. They recommended that plastic should be processed to obtain high
aspect ratios for improving the performance of the plastic filler due to increased bond area and load
transfer capability.
Low-density polyethylene (LDPE) can be used to modify asphalt cement (Little 1993). The
modified asphalt LPDE-binder exhibited higher viscosity and stiffness relative to conventional
asphalt binder. In general, recycled LDPE polymer modified asphalt exhibited better performance
than unmodified asphalt.
2.9 GLASS
2.9.1 Post-Consumer Waste Glass
In 2000, approximately 13 million tons of waste glass was generated in the United States
(USEPA 2002). It constituted 5.5% of total MSW. It is found in MSW primarily in the form of
containers, but also in durable goods like furniture, appliances, and consumer electronics. About
26.3% of glass bottle were recovered for recycling in 2000. Most of the recovered glass went into
new glass containers, but a portion went to other uses such as fiberglass and glasphalt for highway
construction (USEPA 2002).
Waste glass must be color sorted and free of contamination prior to use in manufacturing
glass products. However, color sorting and cleaning are generally costly. Glass consists primarily
of silica or silica sand and smaller amounts of lime sand, and soda ash (Ahmed 1991). Three types
of glass, namely borosilicate, soda-lime, and lead glass are manufactured. The majority of glasses
manufactured in the USA are soda-lime variety. The chemical compositions of these glasses are
51
presented in Table 11.
2.9.2 Applications of Glass
Post-consumer waste glass can be used as a partial replacement of aggregate material for use
in road base application (Henry and Morin 1997) and fine aggregate in asphaltic concrete mixtures.
Chen and Su (2002) based on excusive laboratory studies which included Marshal stability value,
dry/wet moisture damage, skid resistance, light reflection, water permeability, and compaction
behavior revealed that glass waste is a viable material for asphalt concrete. When glass is used in
asphalt concrete the resulting asphaltic mixture is termed glasphalt. Huges (1990) showed, based on
laboratory results, that the maximum amount of glass in asphaltic material should not exceed 15%.
The maximum size aggregate should be less that 9.5 mm with no more than 6% passing No. 200
sieve. Murphy et al. (1991) reported similar results using relatively coarser crushed glass: 100% 9.5
mm passing with no more than 8% passing No. 200 sieve. There are several potential problems
concerning the use of glass in HMA. These include loss of adhesion between asphalt and glass, and
fracture of glass under studded tire traffic, which causes reveling problems, future recycling of
HMA, etc. Due to these problems, use of glass is preferred in surface of pavements (wearing
courses) that support low-speed and low-volume traffic.
Ducman et al. (2002) reported the manufacturing of expanded glass aggregate (lightweight
52
Table 11: Chemical Composition of Glass (Miller and Collins 1976)
Constituent
Borosilicate
Soda-Lime
Lead
SiO2 81
73
63
R2O3
2
1
1
Na2O
4
17
7
K2O
-
-
7
B2O3
13
Trace
-
CaO
-
5
-
MgO
-
3
-
PbO
-
-
22
53
aggregate) by using finely ground waste glass with suitable expanding agent and firing this mixture
at a temperature above softening point of glass. They further reported that the aggregate was highly
reactive and was an additional source of alkalis. However, there was no either expansion or cracks
in the mortar bar even at the age of 284 days. This was attributed to the porous structure of the
aggregate. For all glassy aggregate, the possibility of alkali-silica reaction can not be rulled out
especially in the case of aggregate based on waste glass, which may contain more than 70% silica.
The combination of high silica content and the amorphous structure of glass that as an aggregate, it
is potentially deleterious and may react expansively with quite low levels of cement alkalies (St.
John et al. 1998).
Glass can be used as a partial replacement of aggregates in cement-based materials as well as
replacement of cement. Glass is known to activate alkali-silica reaction (ASR) in cement-based
materials. The resulting expansions due to ASR cause reduction in strength and have a very negative
impact on durability. Thus, the use of glass as an aggregate in cement-based materials is dependent
up on solving the problem associated with ASR (Meyer et al. 1996 a,b). There are several ways to
solve ASR problems in cement-based materials. The most commonly used method is to add a
pozzolanic material such as fly ash, silica fume, ground blast furnace slag, etc. Other methods
include use of chemical ASR inhibitors such as lithium compounds (Meyer et al. 1996b). These .
investigations described other methods such as grinding glass to very small sized particles, treating
glass with LiOH, or curing concrete with CO2 to suppress ASR reaction to a significant extent.
Meyer et al. (1996 a,b) reported that grinding of glass to small size particles (finer than 300 µ m) is
the most promising and economical way to combat the ASR expansions. Recent research by polley
et al. (1998) has demonstrated that concrete containing glass as a sand replacement can display
greater degrees of expansion during alkali-silica reaction tests however, this problem can be avoided
54
by inclusion of pozzolans. A comparative study on potential of alkali-silica reaction (ASR) of glass
aggregate used in Portland cement mortar and in water-glass activated fly ash (WAFA) by Xie et al.
(2003) reported less ASR expansion in WAFA mortar even up to 100% of replacement by glass
aggregate. The study further reported no effect of color of glass on WAFA mortar. .
The recent study by Shao et al (2000) on partial replacement of cement by finely ground
waste glass obtained from recycled fluorescent lamps reported that waste glass finer than 38 micron
could be used for the replacement up to 30% of cement in concrete. They further concluded that
waste glass if ground finer than 38 micron, did exhibit a pozzolanic behavor. The strength activity
indices of concrete with 30% cement replacement by 38-micron glass were 108%, exceeding the
75% as recommended by ASTM C618. They observed expansion in mortar bars just half of that in
controlled concrete. The lime activity, strength development, and reduction in expansion were
indicative of pozzolanic activity of glass waste. Their study further revealed higher strength
development in glass concrete in comparison to ASTM Class F fly ash but lower than concrete
containing silica fume. The chemical composition of soda-lime glass used in the study along with
fly ash and silica fumes are given in Table 12.
Similar results were absorbed by Dyer and Dhir (2001) in their study for use of glass cullet as
cement component. In their study, they used glass powder that passed through a 600 µm sieve to
ensure no large particles remained. White, green, and Amber glass cullet was used. Based on the
results they suggested that the pozzolanicity of finely ground glass cullet (GGC) could be exploited
by using it as a cement component in concrete. They further reported reduction in expansion due to
alkali-silica reaction of mortars containing GGC which was attributed to the rapid pozzolanic rate of
Table 12: Chemical compositions of soda-lime glass, Class F fly ash, and silica fume (% weight)
55
Soda-lime glass Class F fly ash Silica fume
SiO2 72.8 40.71 96.5
Al2O3 1.4 17.93 0.5
Fe2O3 - 29.86 2.0
SiO2 + Al2O3 + Fe2O3 74.2 88.50 99.0
CaO 4.9 2.80 0.80
MgO 3.4 1.09 0.90
SO3 - 1.27 0.20
K2O 0.3 1.56 2.0
Na2O 16.3 0.73 0.40
P2O5 - 0.17 -
TiO2 - 0.85 -
B2O3 1.0 - -
Color white grey dark
56
reaction of finely ground GGC than the slower alkali-silica reaction.
2.10 RECYCLED CONCRETE PAVEMENT FOR AGGREGATE
Pavement rehabilitation and reconstruction generates large quantities of reclaimed materials,
recycling into new paving mixtures, paving materials are the predominant application. Recycling of
pavement materials has become a viable alternative to be considered in road maintenance and
rehabilitation. Conservation of resources, preservation of the environment, and retention of existing
highway geometrics are some of the common benefits of using recycled pavements materials.
Work related to recycling of portland cement concrete (PCC) pavement materials use in
construction materials have been conducted for over 20 years. The aggregate present in recycled
PCC are generally strong and thus they have potential for reuse in manufacture of concrete (Kim et
al. 1992). Generally, the use of crushed concrete pavement as an aggregate could reduce
compressive strength, ranging between 15 to 40% (Bloomquist et al. 1993). However, previous
investigations (Marks 1984; Ahmed 1991) reported adequate performance of pavement made with
recycled PCC as aggregate. Use of recycled pavement as aggregate could cause increased cracking
compared to pavement made with conventional virgin aggregate.
Crushed aggregates derived from PCC pavements are more angular than conventional
crushed stone as a result of the cement mortar sticking to the aggregate surface (Bloomquist et al.
1993). However, concrete containing crushed PCC pavement exhibits satisfactory workability and
durability. Due to the presence of the mortar at the aggregate surface, flexural strength of concrete
made with recycled PCC pavement can be higher than concrete made with virgin aggregates.
Additionally, recycled PCC pavement can be used as unbound coarse aggregates for base course
materials, and as aggregate for asphaltic concrete.
57
2.11 RECYCLED/RECLAIMED ASPHALT PAVEMENT (RAP)
In the United States of America, more than 50 million tons of asphalt paving materials are
milled annually for the recycling into new asphalt paving mixtures (Taha et al. 1999). . Of these,
about 20-50% of the material is recycled in hot mix asphalt. However, recycled asphalt pavement
can also be used in hot mixes, cold mixtures, and in-place mixtures (Tia 1993). This material can
also be used as unbound aggregate bases and subbases, etc. (Collins and Ciesielski 1994). Maher et
al. (1997) evaluated the use of recycled asphalt pavement (RAP) in roadway base and subbase
application and reported higher modulus and stiffness for RAP than the dense graded aggregate base
normally used in the state of New Jersey. Ahmed (1991) reviewed various investigations completed
by the Iowa DOT and Kansas DOT. Experience gained in Iowa revealed that recycling of asphalt
pavement in new asphalt pavement is a technically and economically viable alternative to the
disposal of asphalt pavements. Experience by the Kansas DOT showed a similar trend.
Three asphalt recycling processes that can use at least 80% RAP are: cold in-place
recycling, hot in-place recycling, and hot central plant recycling by means of the proprietary
CYCLEAN process (Tia 1993). In this process of recycling, operation is performed by a train of
equipment that mills, screens, crushes, and mixes the recycled materials. This train is supported by
the remaining pavement after the top has been milled off for recycling. Good subgrade stability is
required to support the train (Jahren et al. 1999). Generally, in cold in-place recycling, the materials
are utilized as stabilized base course. This base course is covered with a chip seal or overlaid with a
hot or cold surface. This process is not suitable for pavements when subgrade is weak or for
pavements that have excessive patching already existing.
In most cases, hot in-place recycling (HIR) process is used to fix surface defects. This
58
process involves reworking of the surface of an asphalt pavement to a depth of less than 50 mm
using machinery such as heater-planer, hot milling, etc. The HIR process involves heating the
existing pavement surface, scarifying, adding rejuvenator, fine aggregates, or beneficiating hot-mix
(admixture) as required, mixing, reprofiling, and compacting this hot mixture in a continuos
operation. This method of recycling is cost-effective for rehabilitation of pavements exhibiting a
variety of surficial nonstructural distresses. In situ hot-mix recycling, including hot in-place
recycling (HIR) and cold in-place recycling (CIR), is proving to be an economical rehabilitation
technique that conserves granular materials and energy and results in zero waste (Kazmierowski et
al. 1999).
The hot central plant recycling involves processing of RAP by sizing, heating, and mixing in
a central plant with other materials such as aggregate, bitumen, or recycled agents (Tia 1993). The
resulting asphalt mixture is laid and compacted in accordance with standard specification for
conventional asphalt. The hot central plant recycling produces the best mixture quality among the
three methods discussed above. Due to emission problems, the typical maximum RAP is in the
range of 30 to 50%. The CYCLEAN process employs a microwave technology to solve the
emission problem and can recycle more than 80% RAP.
2.12 CONSTRUCTION AND DEMOLITION (C&D) DEBRIS
The materials generated every time a building, road, and bridge is constructed, remolded, or
demolished are termed as construction and demolition debris. About 136 million tons of building-
related C&D debris was generated in the United States in 1996 (USEPA 1998). The majority of this
material comes from building demolition and renovation. Demolition debris is composed of wood,
plaster, concrete, asphalt cement, roofing materials, glass, plastics, metal, insulating materials, etc.
59
The roofing waste is composed of 36% asphalt, 22% hard rock granules (minus No. 10 to No. 60),
80% fillers (minus No. 100 size), and smaller amounts of coarse aggregate (Paulsen et al. 1988).
2.12.1 Application of Construction and Demolition Debris
Concrete from demolition debris presents a great opportunity for concrete industry to
improve its resource productivity by using coarse aggregate derived from it (Mehta 2001).
Manufacture of aggregate from recycled concrete requires crushing, grading, and separation of
undesirable constituents. Use of recycled concrete is economically and technically feasible where
good source of aggregate is scarce and disposal cost is high. Concrete separated from demolition
debris can be used not only as an aggregate in portland cement concrete but also in asphaltic
concrete mixtures (Mabin 1993).
Literature (Rasheeduzzafar and Khan 1984) confirms that the cement mortar attached to the
aggregate particles preliminary determines the performance of concrete made with recycled
aggregate. Studies (Rasheeduzzafar and Khan 1984; Ravindrarajan et al. 1987; Hansen and Narud
1987; Sagoe-Crenstil et al. 2001; Tavakoli and Soroushin 1996a; Gómez-Soberón 2002) conducted
on strength and performance of concrete made with recycled concrete aggregate report typical
reduction of the order of 10 per cent in compressive strength and up to a 70 per cent increase in
drying shrinkage. The magnitude of the increase in drying shrinkage depends on the properties of
the original concrete and the mortar content adhered to the recycled aggregate (Tavakoli and
Soroushin 1996b). Furthermore, recycled-concrete aggregate, particularly the recycled masonry
aggregate, has a higher porosity than natural aggregate. Therefore, with a given workability, the
water requirement for making fresh concrete is high as a consequence of that mechanical properties
of hardened concrete are adversely affected. This problem can be overcome by using blends of
60
recycled and natural aggregate or by using water-reducing admixtures and fly ash in concrete
(Corianaldesi et al. 2001).
2.13 CEMENT KILN DUST
Cement manufacturing plants generate about 30 million tons of CKD worldwide per year
(Dhir et al. 1999). The US cement industry generates about 15 million tons of cement kiln dust
(CKD) per year (PCA 1992). Due to high alkaline content, large quantities of CKD can‟t be reused
in cement manufacturing (Bhatty 1994).
2.13.1 Application of Cement Kiln Dust
The primary value of cement kiln dust (CKD) is its cementitious property. The chemical
composition of a typical CKD in presented in Table 13. Depending on the concentration of free
lime (CaO), CKD can be highly cementitious. Because of its cementitious and alkaline
properties CKD has many applications such as soil stabilization, waste treatments, soil
amendment, as fertilizers and in chemical processing to recover alkali salts based on its high
potassium contents, mine backfilling, glass making, coagulant in waste-water treatments, and
absorptive agent for oil spillages etc. (Bhatty 1994; Wu 1995; Kumar et al. 2002; Baghadi et al.
1995). It can also be agglomerated or palletized to produce an artificial aggregate for special
61
Table 13: Chemical Composition of a typical CKD (Kumar et al. 2002)
Compound Percentage composition
CaO 47.8
SiO2 11.4
Al2O3 3.0
Fe2O3 2.1
MgO 0.7
Na2O 0.3
K2O 1.3
SO3 1.8
LOI 30.6
62
applications. In Japan, an oil-absorbing artificial aggregate is reportedly manufactured using CKD,
which is used to improve the rutting resistance of asphalt concrete pavements by absorbing the
lighter fractions of excess asphalt cement binder during hot weather (USDOE 2001). Due to
cementitious property CKD can be used in cement based materials for the replacement of cement.
Shoaib et al.(2000) investigated the effect of cement substitution by cement kiln dust on the
mechanical properties of concrete. They used three different types of cement namely, ordinary
portland cement (OPC), blast furnace slag cement (BFSC), and sulfate resistance cement (SRC) in
their investigation. Based on the results of mechanical properties of concrete with various content of
cement substituted by CKD, Shoaib et al.(2000) reported a decrease in the ultimate compressive as
well as tensile strengths for OPC concrete samples with increasing per cent of CKD; a slight increase
in strength for BFSC and some enhancement in concrete samples containing SRC. The study
suggested that the upper limit for substitution as 30% for SRC, 20% for BFSC, and 10% for OPC.
Their study suggests that direct replacement of cement by CKD is more effective for BFSC and
SRC. Al-Harthy and Taha (2002) studied the effect of cement by-pass dust on fresh and engineering
properties of concrete where OPC was replaced between 5% and 30% by weight of cement, based on
results they have reported that substitution of cement with CKD does not lead any strength gain.
However, small additions up to 10% do not seem to have a significant adverse effect on strength,
especially at low water-to-cement ratios. Udoeyo and Hyee (2002) also reported a decrease in
strength of CKD concrete compared to reference concrete however, percentage reduction in strength
was minimal when up to 20% of OPC was replaced by CKD. Batis et al. (1996) investigated the
corrosion behavior of reinforcing steel in concrete containing CKD as a part replacement of portland
cement and concluded that replacement of portland cement with CKD lead to an increase in steel
corrosion resistance. In another study, the rebars corrosion performance of different mortar
63
specimens containing blast furnace slag and cement kiln dust simultaneous in portland cement, Batis
et al.(2002) have suggested that when BFS and CKD are added in proper ratio in OPC cement then
the compressive strength and corrosion resistance increases. Konsta-Gdoutos et al.(2002) evaluated
the performance of cement-kiln dust-slag cement and reported that CKD provides the environment
necessary to activate slag. Similar observations were also made by Shoaib et al. (2000), Konsta-
Gdoutos et al.(2002), further concluded that alkali concentration, fineness, and the presence of
sulfate play an important role during activation and initial hydration of slag. A comparative study by
Ramakrishnan (1986) on the properties of concrete made with 5% blend of CKD versus the
properties of corresponding concrete made with portland cement has revealed that blended cement
does not adversely affect most of the hardened concrete properties. However, addition of CKD
slightly retarded the setting time of cement. Nocuń-Wczelik (2000) studied some properties such as
setting time, strength parameters and corrosion resistance in sulfate environment of cement mortars
containing CKD from 10% to 50% by weight of cement. Based on the investigation he has reported
that cement with 10% or 25% of CKD admixture meets the standard requirements and shows good
corrosion resistance.
2.14 RICE-HUSK ASH
Rice-husk is an agricultural based by-product material. It constitutes about 20% of the
weight of rice. It contains about 50% cellulose, 25-30% lignin, and 15-20% of silica. When rice-
husk is burnt rice-husk ash is generated. On burning, cellulose and lignin are removed leaving
behind silica ash. The controlled temperature and environment of burning yields better quality of
rice-husk ash as its particle size and specific surface area are dependent on burning condition.
Completely burnt rice-husk is grey to white in color, while partially burnt rice-husk ash is blackish.
64
Rice-husk ash (RHA) is a very fine pozzolanic material (Mehta 1992). The average particle size of
rice-husk ash ranges from 5 to 10 µm and the specific surface area ranges from 20 to 50 m2/g (Zhang
et al. 1996). The physical and chemical properties of a typical RHA is shown in Table 14. The
ground rice-husk ash is of better quality in comparison with ungrounded one (Cisse and Laquerbe
2000). A well-burnt and well-ground rice-husk ash with most of its silica in an amorphous form is
very active and can considerably improve the strength and durability of cement-based materials.
Except RHA, no other pozzolanic materials including silica fume has the ability to contribute to the
early ages such as 1 and 3 days strength of portland cement concrete (Mehta 1992).
2.14.1 Application of Rice-Husk Ash
Due to pozzalanic, homogeneous size distribution of nanometric (very finer) particles, and
very high siliceous properties of rice-husk ash, several efforts have been made to utilize RHA in
cement-based materials including cement (Mehta 1992; Zhang and Malhotra 1996; Ismail and
Waliuddin 1996; Cisse and Laquerbe 2000; Chandrasekhar et al. 2002; Ajiwe and Okeke 2000).
Zhang and Malhotra (1996) used rice-husk ash as a supplementary cementitious material for 10%
replacement of cement (by weight) in the manufacturing of high-performance concrete and reported
higher compressive strength and higher resistance to chloride-ion penetration for concrete containing
RHA in comparison with the control portland cement concrete at the same water-to-cementitious
material ratio. Study by Wada et al (1999) has shown higher compressive strength of RHA mortar
and concrete than the control mortar and concrete. They have further reported excellent strength
development at the early stages even without steam curing for RHA mortar and concrete.
65
Table 14: Physical and Chemical Properties of a Typical RHA (Mehta 1992)
Physical Properties
Specific gravity 2.06
Passing 45µm, % 99.0
Chemical Analysis, %
SiO2 87.2
Al2O3 0.15
Fe2O3 0.16
CaO 0.55
MgO 0.35
Na2O 1.12
K2O 3.68
P2O5 0.50
TiO2 0.01
SO3 0.24
Cl 0.45
C 5.91
LOI 8.55
66
Modification of pore size distribution in RHA mortar from higher to smaller range of pores in
comparison with controlled mortar was also reported. Mehta (1989) observed that RHA not only
reduces the mass loss of concretes exposed to hydrochloric acid solution but also reduces the
expansion due to sulfate attack and alkali-silica reaction. Manufacturing of cement from rice-husk
ash is also reported (Ajiwe et al. 2002). The performance of concrete slab with cement from rice
husk ash was reported to of similar standard to commercial cement. Ismail and Waliuddin (1996)
studied the effect of replacement of cement by rice-husk ash in the range of 10% to 30% on the
strength of high-strength concrete above 70 MPa and reported that strength of high-strength concrete
decreased when cement was partially replaced by RHA at the same workability. Better performance
of sandcrete blocks containing rice-husk ash in comparison with classic mortar blocks had reported
by Cisse and Laquerbe (2000). They further reported that pozzolanic acitivity of rice-husk ash is
responsible for the better strength and performance of sandcrete blocks. In addition, the use of rice-
husk ash enables production of lightweight sandcrete with insulating properties, at reduced cost.
Attempts were made to manufacture of microsilica substitute from rice-husk ash
(Chandrasekhar et al. 2002; Real et al. 1996). The microstructural study of the interfacial zone of
RHA concrete indicated a reduction in porosity, the Ca(OH)2 amount, and width of interfacial zone
between aggregate and cement paste compared with the controlled portland cement specimens.
These are the reasons behind higher compressive strength in rice-husk ash concrete compared to
controlled one (Zhang et al. 1996). The improvement of concrete properties up on addition of RHA
may be attributed to the formation of more C-S-H gel and less portlandite in concrete due to the
reaction between RHA and the Ca+, OH
- ions or Ca(OH)2 (Yu et al. 1999).
67
2.15 WHEAT STRAW ASH (WSA)
Wheat is the main agricultural product grown worldwide. It is estimated world cereal
production is about 880 million tons, of which about 550 million tons is wheat straw. The amount of
wheat straw production is 2.8 tons per hectare (Atchison 1973). The straw consists of C. H. O, N,
Si, Fe, Al, Ca, Mg, Na, K, P, Cu, Mn, and Zn in various proportions. Straw has varying amounts of
water, protein, oil, extractive material fiber, pentosan, cellulose, lignin and ash (Biricik et. al 1999).
The physical and chemical properties of wheat straw ashes are given in Tables 15 and 16,
respectively.
2.15.1 Application of Wheat Straw Ash
Biricik et al. (1999) have concluded that (i) wheat straw has 8.6% ash and the silica content
of the ash is 73%, (ii) the pozzolanic properties obtained at 670oC are higher than those obtained at
570oC, and (iii) ash obtained from the wheat straw can be used as a pozzolanic material. A well-
burnt and well-ground wheat straw ash is very active as a pozzolanic material.
Al-Akhras and Abu-Alfoul (2002) have used wheat straw ash for the replacement of sand uo
to 10.9% by weight in autoclaved mortars and reported increase in compressive, tensile, and flexural
strength of mortar specimens in comparison with control mortar. They further, observed a more
packed structure of mortars containing 7.3% wheat straw ash compared to control paste specimens.
68
Table 15: Physical Properties of Wheat Straw Ash (Biricik et. al. 1999)
Pozzolana K5 K6
Specific Gravity (Kg/m3) 2.31 2.41
Fineness (residue %)
90 m
200 m
5.4
3.0
2.6
1.6
Specific Surface Blaine (cm2/g) 4850 5520
K5, ash production at 570oC; K6 ash production at 670
oC
69
Table 16: Chemical Properties of Wheat Straw Ashes (Biricik et al. 1999)
Compound K5 (%) K6(%)
SiO2 (soluble) 50.78 54.24
SiO2 (insoluble) 22.28 29.56
Al2O3 3.90 4.55
Fe2O3 1.75 1.05
CaO 8.12 12.54
MgO 2.80 2.39
SO3 1.91 1.49
K 5.85 --
Na 1.83 --
Ca 3.05 --
LOI 8.79 7.22
Silica module 9.69 9.69
Alumina module 4.33 4.33
70
2.16 OTHER MATERIALS
Several other materials including steel scraps, lime wastes, copper slag, sawdust ash, etc. can
be used in construction materials. Steel scrap can be composed of steel cans, appliances,
automobiles, construction equipment, bridges, etc. The recycling of steel scrap is well established.
Thus, steel scrap generated from automobiles or other sources can be used in new construction
materials. The other by-products materials, especially non-metals derived from automobiles, have
substantial potential for use in cement-based materials. Fluff generated from automobile shredding
plants is still mostly discarded in landfills.
Various lime wastes including carbide lime is produced during the manufacture of acetylene
(Collins and Ciesielski 1994). The manufacturing process may produce either sludge or powdery
by-product material depending up on whether or not water is used. Carbide lime exhibits both
physical and chemical properties analogous to hydrated lime. Thus, this waste can be used in soil
stabilization as well as mineral filler in asphaltic concrete mixtures.
Copper slag is a by-product material from the process of manufacturing of copper. In
Canada, copper slag has been used for many years in road abse construction, railroad ballast, and as
an engineered fill (Douglas and Mainwaring 1985). Mobasher et al. (1996) have demonstrated the
potential of using copper slag in concrete mixes. Recent study by Al-Jabri et al. (2002) has
demonstrated the possibility of using copper slag together with cement by-pass dust as a
cementitious material. Study by Udoeyo and Dashibil (2002) on the use of sawdust ash in
concrete as a replacement for ordinary portland cement has revealed that it is possible to replace
cement up to 10 – 20% by sawdust ash for making a concrete of 20 MPa strength. This is due to the
pozzolanic activity of sawdust ash.
3.0 ENVIRONMENTAL IMPACT ASSESSMENT OF MATERIALS MADE WITH BY-
71
PRODUCTS
3.1 LEACHATE TEST METHODS
Four different leachate methods, EP-Toxicity method, TCLP method, American
Foundrymen's Society (AFS) method, and ASTM method, are generally used to characterize various
waste materials (Greer et al. 1989). A comparison of these methods is presented in Table 17.
The Extract
medium and a liquid to solid ratio of 20:1, to determine toxicity of a solid waste. The leachate from
this test is analyzed for arsenic, barium, cadmium, chromium, lead, mercury, selenium, and silver. If
these parameters exceed 100 times the drinking water standards criteria then the waste is categorized
as an EP hazardous waste.
The TCLP test is carried out to evaluate mobility of both inorganic and organic contaminants
in liquid, solid, and multi-phase waste system. In this test, the leaching medium to be used depends
on the alkalinity of the solid phase of the waste. A sample of the waste is extracted with an
tested to see whether or not it exceeds the thresholds established by the Environmental Protection
Agency.
The AFS test employs deionized water as a leaching medium. This method provides an
indication of the release of certain chemical parameters over a period of time (AFS 1991).
The ASTM test method employs one elution, which is agitated for 18-hour period. The
sample is then allowed to settle for 5 minutes after which a vacuum or pressure filter is used to filter
the liquid through a 0.45 μm filter. The resulting filtrate is analyzed for concentration of certain
constituents.
72
Table 17: Comparison of Laboratory Leaching Tests (Greer et al. 1989)
Item EP-Toxicity TCLP AFS ASTM
Leaching
Medium
Deionized Water, 0.5
N Acetic Acid
Added to adjust pH
Acetate Buffer
Deionized
Water
Deionized
Water
Liquid to
Solid Ratio
20 to 1
20 to 1
5 to 1
20 to 1
Contact
Time
24 hours
18 hours
24 hours
48 hours
72 hours
18 hours
Method of
Mixing
Continuous Rotation
at 30 RPM
Continuous
Rotation at 30
RPM
Invert 15 time
in 24 hours
Continuous
Rotation at 29
RPM
Filtering
Once 0.45 μm
Once 0.7 μm
glass Once 0.45 μm
Once 0.45 μm
Number of
Elutions
1
1
3
1
73
Several investigators compared ASTM leach test data with that of either drinking water
standard or local groundwater standard to judge quality of the leachate. For example, some
researchers (Naik and Singh 1994c; Naik et al. 1997c; Pfughoeft-Hassett 1993; American
Engineering Testing, Inc. 1992), have compared ASTM leach data with both drinking water
standards and/or Ground Water Quality Standards as shown in Table 1 8.
Most coal combustion by-products are non-toxic. Leach tests (Pflughoeft-Hassett et al.
1993) on fly ash have exhibited all elements below the RCRA limits and most of them below
primary drinking water standards. Leachate characteristics of fly ash, spray dryer by-product
material, and bottom ash/boiler slag, exhibited a similar trend (American Engineering Testing, Inc
1992). More recently, this trend was also substantiated by Naik et al. (1997c).
Pulp and paper mill sludge may not have any significant environmental impact. For
example, when paper mill sludge is used in lightweight aggregate, pollutants present in the sludge
are either burnt or encapsulated in the manufactured aggregate matrix.
End uses of treated wood ash are limited because of the presence of heavy metals and other
contaminants. In many cases, treated wood ash fails to pass the TCLP regulatory limits. Use of
wood ash in low-strength concrete encapsulates most of the heavy metals. TCLP concentrations of
wood ash containing CLSM were found to be lower than that of the dry wood ash alone (Fehrs
1996). However, a reverse trend was also true, possibly due to contribution to the TCLP of the
cement used.
Use of small amounts of sewage sludge (10% or less) in cement-based materials should
not have any adverse effects due to encapsulating behavior of cement-based materials. Use of
sewage sludge in manufacture of cintered lightweight aggregate should also not cause any negative
effects.
74
Table 18: Leachate Characteristics of the Class F Fly Ash Mixtures with and without Foundry
Sand (Naik et al. 1997e)
Parameter S1-(P)
(mg/l)
S4-2(P)
(mg/l)
S7-2(P)
(mg/l)
S8-2(P)
(mg/l)
S9-2(P)
(mg/l)
Drinking
Water
Standards
(mg/l)
GWQS*
Enforcement
Standard,
(mg/l)
Prevention
Action Limit,
(mg/l) Foundry Sand,(%)
0
70(FS1)
50(FS2)
70(FS2)
85(FS2)
-
Aluminum
8.2
7.6
6.8
5.3
5.3
Antimony
0
0
0
0
0
Boron
0.065
0.053
0.065
0.062
0.034
Cobalt
0
0
0
0
0
Iron
0
0
0
0
0
0.30**
0.15**
Nickel
0
0
0
0
0
Potassium
12
6.6
9.3
13
13
Barium
0.79
0.43
0.88
0.62
0.48
1.0
2.0**
0.4**
Calcium
100
88
120
89
90
Magnesium
0
0
0
0
0
0.05**
0.025**
Manganese
0
0
0
0
0
Molybdenum
0.13
0
0.09
0.13
0.06
Silica
3
3.5
3.1
4.3
4
Sodium
8.1
4
3.7
3.6
3.4
Zinc
0
0
0
0
0
5**
2.5**
Arsenic
0
0
0
0
0
0.05
0.05
0.005
Chromium
0.036
0.036
0.018
0.023
0.021
0.05
0.10
0.01
Lead
0
0
0
0
0
0.05
0.015
0.0015
Selenium
0.008
0.005
0.01
0.015
0.007
0.01
0.05
0.01
Cadmium
0
0
0
0
0
0.01
0.005
0.0005
Mercury
0
0
0
0
0
0.002
0.0002
pH at 25
0C
11.3
11.4
11.3
11.2
11.2
Chloride
0
0
0
1
1
250**
125**
Conductivity at 25
0C
(μMho)
1150
852
1154
886
887
Sulfate
20
20
16
14
14
Alkalinity as CaCO3
290
220
280
230
210
Total Dissolved
Solids
324
256
354
255
278
Total Hardness as
CaCO3
250
220
300
222
225
Total Phosphorus
0.03
0.02
0
0
0.02
Note: A zero indicates a value below detection limit (BDL)
* GWQS = Ground Water Quality Standard (Public Health-Related)
** GWQS related to public welfare.
75
Leachate test results on MSW incineration ash show heavy metals such as lead and cadmium
exceeding regulatory limits (Collins and Ciesielski 1994). However, when fly ash was combined
with bottom ash, majority of samples did not exceed the limits. Additionally, when such ash was
used in concrete, the resulting material can meet the regulatory requirement if proper mixture
proportions are used.
Past investigations (Ham et al. 1993; MacRunnels 1994; Naik et al. 1997e) have revealed that
most by-product materials generated from iron, steel, and aluminum casting operations are
environmentally friendly. They met most drinking water parameters and were non-hazardous per
Resource Conservation and Recovery Act (RCRA) criteria. However, Boyle et al. (1981) reported
that cupola dust of grey iron foundries were EP toxic with respect to cadmium, chromium, and/or
lead.
All blast furnace slags and scrap-iron slags do not contain significant concentration of
polluting constituents. However, leachate derived from non-ferrous slags can have a negative
environmental impact. Therefore, it is desirable to study the environmental impact of non-ferrous
slag before using them in construction materials.
In most cases, plastics should not have any significant environmental impact when used in
polymer concrete compared to the virgin polymer concrete. Due to encapsulation of plastics in
cementitious matrix, its use in cement-based material should not cause any significant environmental
impact.
Most types of glass do not contain material that can have any adverse environmental impact.
Based on TCLP test, the glass is not classified as an EP toxic material (Eykholt 1996). However,
leachate from lead glass may have negative environmental impact on ground water quality due to the
presence of lead. Use of glass containing lead in structural- grade concrete may be acceptable due to
76
encapsulation characteristics of the concrete; allowing addition of the leaded glass in concrete
without any significant impact.
Use of recycled PCC pavement, as aggregate in concrete does not appear to have adverse
environmental impact. Use of crushed concrete aggregate derived from construction and demolition
debris in portland cement concrete mixtures, or asphaltic concrete mixtures, should not have any
adverse environmental impact.
Conventional hot mix asphalt plants fail to meet local air quality when RAP exceeds 50%;
especially for opacities. Generally, a binder derived from old asphalt pavement is hard and brittle,
and degradation in aggregate may also occur (Tia 1993). Due to these deficiencies, it is desirable to
blend RAP with soft asphalt or a rejuvenating agent, and a coarse aggregate in order to produce
binder of desired rheological properties. Application RAP in hot mix asphaltic should not have any
significant difference in chemical constituent of the metal from those observed from virgin asphalt
mixture.
4.0 FUTURE OF RECYCLING AND RESEARCH NEEDS
In order to solve waste disposal problems, it is essential to develop high-volume use
technologies for each by-product generated from various sources. High-volume use technologies for
conventional fly ash in cement-based material have already been developed. However, long-term
strength and durability of field performance of high-volume fly ash (HVFA) concrete is yet to be
fully established. Further research is needed to develop blended cement technology using more than
50% of conventional coal ash of total blended cement mixture. High-volume use technologies in
cement-based materials for clean coal ash are lacking. Therefore, more research is needed to
develop different effective and economical uses of clean coal ash in cement-based materials.
77
More research is needed to develop end uses of wood ash in cement-based materials. Further
research should be directed toward establishing mixture proportions for cement-based materials to
encapsulate heavy metals and other contaminants found in treated wood ash.
Research is needed to establish optimum content of paper mill sludge in cement-based
materials without compromising strength and durability performance. Lightweight aggregates made
with papermill sludge should be tested for long-term strength and durability performance. Similarly,
aggregates made with sewage sludge should also be tested for appropriate strength and durability
properties prior to their commercial applications.
More research is needed to establish optimum sewage sludge content in cement-based
materials. Further research is needed to establish optimum amounts of incineration ash in cement-
based materials.
It is possible that most of foundry-generated sand can be used in CLSM, low-strength
concretes, and structural-grade concretes. However, long-term performance of foundry sand
containing concrete needs to be evaluated. Very limited work has been conducted concerning use of
foundry slag as a coarse aggregates. Therefore, additional research is needed to evaluate strength
and durability performance of concrete incorporating foundry slag before developing specifications
for this material to be used in cement-based materials.
Additional research is needed to establish performance of very fine gradation of CRM in a
modified generic system. Research is needed to establish recycling of post-consumer plastics, such
as polystyrene (PS), low-density polyethylene (LDPE), polypropelene (PP), and poly-vinyl chloride
(PVC). Long-term performance related research is needed to develop uses of PET and HDPE and
other plastics as aggregates in cement-based materials.
Research concerning use of post-consumer glass as aggregate in concrete needs to be
78
conducted to establish optimum mixture proportions for using fly ash or other pozzolanic material to
combat ASR. Long-term strength and durability of concrete made with aggregate derived from
recycled pavements needs to be established also. More research is needed to develop separation and
recycling of various constituents of demolition debris.
Extensive research findings on utilization of CKD in cement-based materials are being
reported in published literatures. However, the work done so far is limited and further research on
long-term durability aspects of concrete, microstrucrural, ASR, and corrosion related studies are
needed to develop confidence among user.
Very limited works on utilization of rice-husk ash in cement-based construction materials are
reported. Further research on long-term durability aspects of concrete, ASR, microstrucrural, and
corrosion related studies are needed to establish the beneficial use of this material in construction
industry.
5.0 SUMMARY AND CONCLUSIONS
Large volumes of by-product materials generated from industrial, post-consumer, and
agricultural activities are landfilled. The amount of waste generation is increasing, while landfill
space is decreasing. Additionally, due to stricter environment regulations, it is difficult to obtain
approval for developing new disposal facilities. Thus, cost of disposal is escalating. Recycling not
only saves on huge disposal costs, but also conserves natural resources, and in some cases it provides
technical and economic benefits.
Various uses of by-products generated from industrial, post-consumer, and agricultural
sources exist. The cost effective and proven technologies are already available for the utilization of
by-product materials which include coal combustion by-products, wood ash, paper industry by-
79
products, MSW materials, foundry by-products, metallurgical by-product materials, used tires,
plastics, glass, recycled portland cement concrete pavement, recycled asphalt pavement, construction
and demolition debris, cement kiln dust, rice-husk ash, wheat straw ash etc. As engineering
materials, these by-products can add value while helping conserve the national as well as global
natural resources. Uses of these by-products in cement-based construction industry in the form of
raw materials, substitute materials, new source of materials, modifier material are as follows:
1. Among coal combustion by-products, fly ash utilization is the largest due to its wide range of
applications.
2. About 60% of total utilization of fly ash is in the construction industry.
3. Fly ash can be used in manufacturing of Controlled Low Strength Materials as a replacement
of regular concrete sand up to 100%.
4. Fly ash can be used as a major component of blended cement, exceeding 50% of total
blended cement mixture.
5. Fly ash can be used in manufacture of lightweight aggregates.
6. Significant amounts of fly ash can be used in the manufacturing of high-performance
concrete (HPC) in the range of 15 to 35% depending up on type of fly ash.
7. More than 50% of cement can be replaced with fly ash in the manufacturing of
superplasticized structural-grade concrete.
8. Fly ash can be used as a cement replacement up to 30% in manufacture of precast/prestressed
concrete products.
9. Fly ash can be used as a fine filler as well as a pozzolan in roller compacted concrete.
10. Fly ash can be used as a replacement of 30 to 100% silica sand in the manufacturing of
80
autoclaved cellular concrete.
11. Fly ash can be used as filler in polymer matrix composites as well as metal matrix
composites.
12. Bottom ash/boiler slag can be used as both fine and coarse lightweight aggregates.
13. Bottom ash of pozzolanic nature can be used for the replacement of cement.
14. Boiler slag can be used in hot-mix asphalt as fine aggregate to enhance resistance to
stripping.
15. Clean-coal ash can be used as a raw material in production of cement. FGD can be used as a
gypsum for the manufacturing of wallboards. It can also be used in concrete as well as
cement-based masonry products.
16. Wood ash can be used in the manufacturing of CLSM.
17. Paper mill by-products, especially sludge, can be used in the manufacturing of lightweight
aggregate. A blend of bark ash and Class F fly ash can be used in concrete as a replacement
of cement.
18. Blocks can be made using 100% recycled pulp fiber for non-structural applications.
19. Sewage sludge can be used in the manufacturing of lightweight aggregate. It can also be
used in clay bricks as a replacement of clay up to 40%.
20. Up to 10% of sewage sludge ash can be used as a filler in concrete. It can also be used in the
manufacturing of lightweight aggregate.
21. Foundry sand can be used as a replacement of regular concrete sand in portland cement
concrete. Foundry sand can be used as a replacement of natural fine aggregates in the
manufacturing of asphaltic concrete, cement-based manufactured products, CLSM, etc.
22. Foundry slag can be used as semi-lightweight coarse aggregate.
81
23. Air-cooled iron blast furnace slag can be used as an aggregate. Granulated iron blast furnace
slag is suitable for manufacture of cement. Pelletized iron blast furnace slag can be used as
lightweight aggregate and in the manufacturing of cement.
24. Blast furnace slag can also be used in concrete products, railroad ballast, road bases, in
CLSM.
25. Non-ferrous slags can be used as an aggregate.
26. Steel slag can be used aggregate for road construction,,armourstones for hydraulic structures.
27. Steel slag can be processed into aggregate materials for the use in dense and open graded hot
mixed asphalt pavements.
28. Sewage sludge can be used as non-conventional construction materials for the manufacturing
of bricks, lightweight aggregate.
29. Incineration ash can be used in the manufacturing of synthetic aggregate. However,
pretreatment is required before it can be used in concrete.
30. Rubber tire particles may be used in concrete where strength is not priority but greater
toughness is preferred such as driveways, sidewalks etc.
31. Used rubber tire can be used as a modifier in bituminous mixture.
32. Post consumer plastics, especially PET, can be used in the manufacturing of polymer
concrete.
33. Low-density polyethylene can be used to modify asphalt cement, similar to that of CRM.
34. Glass can be used as a partial replacement of aggregate in portland cement concrete as well
as asphaltic concrete.
35. Glass finer than 38 micron can be used for the replacement of cement.
36. Recycled portland cement pavement is appropriate for the manufacturing of aggregates for
82
use in new portland cement concrete as well as asphaltic concrete.
37. Recycled asphalt pavement can be used as replacement of asphalt in asphaltic concrete
mixtures.
38. Concrete derived from demolition debris can be used as coarse aggregate in portland cement
concrete or asphaltic concrete.
39. Problems of higher porosity or more water absorption by recycled concrete can be overcome
by using blends of recycled and natural aggregate or by using water-reducing admixtures and
fly ash in concrete.
40. Cement kiln dust can be used for the manufactured of artificial aggregate for special purpose
such as oil-absorbing aggregate for the improvement of the rutting resistance of asphalt
concrete pavement.
41. Cement kiln dust can be used for substitution of cement in concrete. It can be used to
replace up to 30% of SRC, 20% for BFSC, and 10% for OPC.
42. Replacement of portland cement with CKD can lead to an increase in steel corrosion
resistance of the concrete rebars.
43. Rice-husk ash can be used to replace cement for improvement of the strength and durability
of cement-based materials. Improvement in strength at early ages 1 and 3 days are also
possible.
44. Rice-husk ash can be used for the manufacure of economical lightweight sandcrete blocks
with insulating properties.
45. Rice-husk ash can be even used in place to condensed silica fume in concrete.
46. Wheat straw ash can be sued for the replacement of sand in concrete. It can also be used to
replace cement up to less than 10% by weight of cement.
83
47. Lime waste, especially carbide lime, can be used in soil stabilization as well as filler in
asphaltic concrete mixtures.
84
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