Environmental-friendly durable concrete made with recycled materials for sustainable concrete construction

Abstract

Concrete is one of the most widely used construction materials in the world. However, the production of portland cement, an essential constituent of concrete, leads to the release of significant amount of CO2, a greenhouse gas; one ton of portland cement clinker production is said to creates approximately one ton of CO2 and other greenhouse gases (GHGs). Environmental issues are playing an important role in the sustainable development of the cement and concrete industry. For example, if we run out of limestone, as it is predicted to happen in some places, then we cannot produce portland cement; and, therefore, we cannot produce concrete and all the employment associated with the concrete industry goes out-of-business. Limestone powder is sometimes interground with clinker to produce cement, reducing the needs for clinker making and calcinations. This reduces energy use in the kiln and CO2 emissions from calcinations. A sustainable concrete structure is one that is constructed so that the total environmental impact during its entire life cycle, including during its use, is minimum. Concrete is a sustainable material because it has a very low inherent energy requirement, is produced to order as needed with very little waste, is made from some of the most plentiful resources on earth, has very high thermal mass, can be made with recycled materials, and is completely recyclable. Sustainable design and construction of structures have a small impact on the environment. Use of "green" materials embodies low energy costs. Their use must have high durability and low maintenance leading to sustainable construction materials. High performance cements and concrete can reduce the amount of cementitious materials and total volume of concrete required. Concrete must keep evolving to satisfy the increasing demands of all its users. Reuse of post-consumer wastes and industrial by- products in concrete is necessary to produce even "greener" concrete. Use of coal ash, rice-husk ash, wood ash, natural pozzolans, GGBFS, silica fume, and other similar pozzolanic materials can reduce the use of manufactured portland cement clinker; and, at the same time, produce concrete that is more durable. "Greener" concrete also improves air quality, minimizes solid wastes, and leads to sustainable cement and concrete industry.

Full text

Environmental-friendly durable concrete made with recycled materials
for sustainable concrete construction
T.R. Naik
UWM Center for By-Products Utilization, University of Wisconsin-Milwaukee, Milwaukee, WI, USA
G. Moriconi
Materials Science and Technology, Materials and Environment Engineering and Physics, Marche
Polytechnical University, Ancona, Italy
ABSTRACT: Concrete is one of the most widely used construction materials in the world. However, the
production of portland cement, an essential constituent of concrete, leads to the release of significant amount
of CO2, a greenhouse gas; one ton of portland cement clinker production is said to creates approximately one
ton of CO2 and other greenhouse gases (GHGs). Environmental issues are playing an important role in the
sustainable development of the cement and concrete industry. For example, if we run out of limestone, as it is
predicted to happen in some places, then we cannot produce portland cement; and, therefore, we cannot
produce concrete and all the employment associated with the concrete industry goes out-of-business.
Limestone powder is sometimes interground with clinker to produce cement, reducing the needs for clinker
making and calcinations. This reduces energy use in the kiln and CO2 emissions from calcinations. A
sustainable concrete structure is one that is constructed so that the total environmental impact during its entire
life cycle, including during its use, is minimum. Concrete is a sustainable material because it has a very low
inherent energy requirement, is produced to order as needed with very little waste, is made from some of the
most plentiful resources on earth, has very high thermal mass, can be made with recycled materials, and is
completely recyclable. Sustainable design and construction of structures have a small impact on the
environment. Use of “green” materials embodies low energy costs. Their use must have high durability and
low maintenance leading to sustainable construction materials. High performance cements and concrete can
reduce the amount of cementitious materials and total volume of concrete required. Concrete must keep
evolving to satisfy the increasing demands of all its users. Reuse of post-consumer wastes and industrial by-
products in concrete is necessary to produce even “greener” concrete. Use of coal ash, rice-husk ash, wood
ash, natural pozzolans, GGBFS, silica fume, and other similar pozzolanic materials can reduce the use of
manufactured portland cement clinker; and, at the same time, produce concrete that is more durable.
“Greener” concrete also improves air quality, minimizes solid wastes, and leads to sustainable cement and
concrete industry.
1 INTRODUCTION
Concrete is one of the most widely used construction
materials in the world. However, the production of
portland cement, an essential constituent of concrete,
leads to the release of significant amount of CO2, a
greenhouse gas. One ton of portland cement clinker
production creates one ton of CO2 and other
greenhouse gases (GHGs). Environmental issues
will play a leading role in the sustainable
development of the cement and concrete industry in
this century.
According to the World Commission on
Environment and Development: sustainability means
“Meeting the needs of the present without
compromising the ability of the future generations to
meet their own needs.” Sustainability is an idea for
concern for the well being of our planet with
continued growth and human development
[McDonough 1992].
For example, if we run out of limestone, as it is
predicted to happen in some places, then we cannot
produce portland cement and, therefore, we cannot
produce concrete; and, all the employers associated

with the concrete industry go out-of-business, along
with their employees.
Over 5 billion ton of non-hazardous by-product
materials are produced each year in USA (2002). At
an average disposal cost of $30 per ton, it would
cost $150 billion to throw it all away. These by-
products are from agricultural sources, domestic
sources, industrial sources, and materials processing
sources.
2 ENVIRONMENTAL ISSUES
The production of portland cement releases CO2 and
other greenhouse gases (GHGs) into the atmosphere.
Total CO2 emissions worldwide were 21 billion tons
in 2002, Table 1.
Table 1. CO2 emissions by industrialized countries
in 2002 [Malhotra 2004].
Country/Union Percent CO2
USA 25
EU 20
Russia 17
Japan 8
China > 15
India > 10
Environmental issues associated with the CO2
emissions from the production of portland cement,
energy demand (six-million BTU of energy needed
per ton of cement production), resource conservation
consideration, and economic impact due to the high
cost of portland cement manufacturing plants
demand that supplementary cementing materials in
general and fly ash in particular be used in
increasing quantities to replace portland cement in
concrete [Malhotra 1997, 2004].
Fly ash is a by-product of the combustion of
pulverized coal in thermal power plants. The dust-
collection system removes the fly ash, as a fine
particulate residue from the combustion gases before
they are discharged in the atmosphere.
For each ton of portland cement clinker, 3 to 20
lbs. of NOx are released into the atmosphere. In
2000, the worldwide cement clinker production was
approximately 1.6 billion tons [Malhotra 2004].
Yomiuri Shimbun [The Daily Yomiuri 2004]
reported from Kobe, Japan that: “The Hyogo
prefecture government on (Oct. 1, 2004) banned
automobiles with emissions of nitrogen oxide (NOx)
and particulate matter that exceed levels set in a law
concerning these emissions from traveling in certain
parts of the prefecture.”
Thermal mass of concrete contributes to
operating energy efficiency and reduced cooling
costs, under certain climatic conditions. Longer
lasting concrete structures reduce energy needs for
maintenance and reconstruction. Made to order
concrete means less construction waste. Concrete is
a locally available material; therefore, transportation
cost to the project site is reduced. Light colored
concrete walls reduce interior lighting requirements.
Permeable concrete pavement and interlocking
concrete pavers can be used to reduce runoff and
allow water to return to the water table. Therefore,
concrete is, in many ways, environmentally friendly
material. As good engineers, we must use more of it
[Malhotra 2004].
In view of the energy and greenhouse gas (GHG)
emission concerns in the manufacturing of portland
cement, it is imperative that either new
environmentally friendly cement-manufacturing
technologies be developed or substitute materials be
found to replace a major part of the portland cement
for use in the concrete industry [Malhotra 2004].
2.1 Coal combustion products (CCPs)
It is important to develop recycling technology for
high-volume applications of coal combustion
products (CCPs) generated by using both
conventional and clean-coal technologies. Many
different types of CCPs are produced; for example,
fly ash (Class F since 1930s, and Class C since early
1980s), bottom ash, cyclone-boiler slag, and clean-
coal ash (since late 1980s, ash derived from
SOx/NOx control technologies, including FBC and
AFBC or PFBC boilers, as well as dry- or wet-FGD
materials from SOx/NOx control technologies). In
general some of these CCPs can be used as a
supplementary cementitious materials and use of
portland cement, therefore, can be reduced.
The production of CCPs in USA is about 120
million tons per year in 2004 (from about 55% of
total electricity & steam production). Cyclone-boiler
slag is 100% recycled. Overall recycling rate of all
CCPs is about 40 %. High-sulfur coal ashes, such as
Class F fly ash and especially clean-coal ashes are
underutilized. For 2002, in USA, Fluidized Gas
Desulphurization (FGD) Gypsum: 11.4 MT (million
tons) produced, 7.8 MT used (70%); FGD wet-
Scrubbers: 16.9 MT, 0.5 MT (3%); FGD Dry-
Scrubbers: 0.9 MT, 0.4 MT (45%); and, A/FBC
Ash: 1.2 MT, 0.9 MT (75%). Overall, 30.4 MT
produced, 9.6 MT used (32%).

Today use of other pozzolans, such as rice-husk
ash, wood ash, GGBFS, silica fume, and other
similar pozzolanic materials such as volcanic ash,
natural pozzolans, diatomite (diatomaceous earth),
calcined clay/shale, metakaolin, very fine clean-coal
ash (microash), limestone powder, and fine glass can
reduce the use of manufactured portland cement, and
make concrete more durable, as well as reduce GHG
emissions. Chemical composition of ASTM Type I
portland cement and selected pozzolans is given in
Table 2.
Table 2. Chemical composition of CCPs.
Oxides,
%
Port-
land
cement
St.
Helen’s
ash
VPP
Class F
ash
Colombia
Unit #1
fly ash
P-4
Class C
ash
SiO2 20.1 62.2 48.2 44.8 32.9
Al2O3 4.4 17.6 26.3 22.8 19.4
CaO 57.5 5.7 2.7 17.0 28.9
MgO 1.6 2.2 1.1 5.1 4.8
Fe2O3 2.4 5.6 10.6 4.2 5.4
TiO2 0.3 0.8 1.2 1.0 1.6
K2O 0.7 1.2 2.3 0.4 0.3
Na2O 0.2 4.6 1.1 0.3 2.0
Mois-
ture
0.2 0.4 0.4 0.1 0.8
LOI 1.1 0.6 7.9 0.3 0.7
3 SUSTAINABILITY
Entire geographical regions are running out of
limestone resource to produce cement. Major
metropolitan areas are running out of sources of
aggregates for making concrete. Sustainability
requires that engineers consider a building’s “life-
cycle” cost extended over the useful lifetime. This
includes the building construction, maintenance,
demolition, and recycling [ACI 2004, Coppola et al.
2004, Corinaldesi et al. 2002b, Corinaldesi &
Moriconi 2004b, Moriconi 2003].
A sustainable concrete structure is one that is
constructed so that the total societal impact during
its entire life cycle, including during its use, is
minimum. Designing for sustainability means
accounting in the design the full short-term and
long-term consequences of the societal impact.
Therefore, durability is the key issue [Moriconi
2003]. New generation of admixtures/additives are
needed to improve durability.
To build in a sustainable manner and conduct
scheduled & appropriate building maintenance are
the keys that represent the “new construction
ideology” of this millennium. In particular, to build
in a sustainable manner means to focus attention on
physical, environmental, and technological
resources, problems related to human health, energy
conservation of new and existing buildings, and
control of construction technologies and methods
[Coppola et al. 2004, Corinaldesi & Moriconi 2004a,
2004b, Corinaldesi et al. 2005b].
Traffic tunnel being built in Akita, Japan (2001 –
2007) is expected to cost about 625 million USD
(about 70 billion Yens). If it is not constructed as a
durable infrastructure, with a minimum life-cycle
cost, then say 45 years from now it would cost 700
billion Yen. 2004 cost is 5 USD (550 Yens) per
person in Japan (Population: 127.6 million, in May
2004; down 50,000 from a year ago [The Japan
Times 2004]. If the population of Japan, as expected
in 2050 is 100 million, then it would cost 7,000 Yen
per person to re-build this tunnel. Would it be re-
built?
4 CONCRETE
Concrete is environmentally very friendly material.
As good engineers, we must use more of it in
construction [Malhotra 2004]. Concrete has been
used for over 2,000 years. Concrete is best known
for its long-lasting and dependable nature. However,
additional ways that concrete contributes to social
progress, economic growth, and environmental
protection are often overlooked. Concrete structures
are superior in energy performance. They provide
flexibility in design as well as affordability, and are
environmentally more responsible than steel or
aluminum structures [Cement Association of Canada
2004].
“The concrete industry will be called upon to
serve the two pressing needs of human society;
namely, protection of the environment and meeting
the infrastructural requirement for increasing
industrialization and urbanization of the world. Also
due to large size, the concrete industry is
unquestionably the ideal medium for the economic
and safe use of millions of tons of industrial by-
products such as fly ash and slag due to their highly
pozzolanic and cementitious properties. It is obvious
that large-scale cement replacement (60 - 70 %) in
concrete with these industrial by-products will be
advantageous from the standpoint of cost economy,
energy efficiency, durability, and overall ecological
profile of concrete. Therefore, in the future, the use

of by-product supplementary cementing materials
ought to be made mandatory” [Malhotra 2004].
5 SUSTAINABLE CONCRETE SOLUTIONS
Concrete is a strong, durable, low environmental
impact, building material. It is the cornerstone for
building construction and infrastructure that can put
future generations on the road towards a sustainable
future [Cement Association of Canada 2004].
Benefits of concrete construction are many, for
example [Cement Association of Canada 2004]:
concrete buildings – reduce maintenance and energy
use; concrete highways – reduce fuel consumed by
heavily loaded trucks; insulating concrete homes –
reduce energy usage by 40% or more; fly ash,
cement kiln dust, or cement-based
solidification/stabilization and in-situ treatment of
waste for brownfield redevelopment; and,
agriculture waste containment – reduces odor and
prevents groundwater contamination. The concrete
industry must show leadership and resolve, and
make contribution to the sustainable development of
the industry in the 21 century by adopting new
technologies to reduce emission of the greenhouse
gases, and thus contribute towards meeting the goals
and objectives set at the 1997 Kyoto Protocol. The
manufacturing of portland cement is one such
industry [Malhotra 2004].
6 PORTLAND CEMENT
Portland cement is not environmentally very friendly
material. As good engineers, we must reduce its use
in concrete [Malhotra 2004]; and, we must use more
blended cements, especially with chemical
admixtures.
Clinker production is the most energy-intensive
stage in cement production, accounting for over 90%
of total energy use, and virtually all of the fuel use.
Processing of raw materials in large kilns produces
portland cement clinker. These kiln systems
evaporate the inherent water in the raw materials
blended to manufacture the clinker, calcine the
carbonate constituents (calcinations), and form
cement minerals (clinkerization) [Worrell &
Galtisky 2004].
6.1 Blended cements
The production of blended cements involves the
intergrinding of clinker with one or more additives;
e.g., fly ash,bnb granulated blast furnace slag, silica
fume, volcanic ash, in various proportions. The use
of blended cements is a particularly attractive
efficiency option since the intergrinding of clinker
with other additives not only allows for a reduction
in the energy used (and reduced GHG emissions) in
clinker production, but also directly corresponds to a
reduction in carbon dioxide emissions in
calcinations as well. Blended cement has been used
for many decades around the world [Worrell &
Galtisky 2004].
6.2 Concrete and the use of blended cements
Although it is most common to make use of
supplementary cementing materials (SCM) in the
replacement of cement in the concrete mixture,
blended cement is produced at the grinding stage of
cement production where fly ash, blast furnace slag,
or silica fume are added to the cement itself. The
advantages include expanded production capacity,
reduced CO2 emissions, reduced fuel consumption
and close monitoring of the quality of SCMs
[Cement Association of Canada 2004].
“Kyoto Protocol (UN Pact of 1997, requires to
reduce GHGs, including CO2).” It is now ratified.
USA has not ratified it. “The Russian Government
approval allowed it to come into force worldwide.”
By 2012, emissions must be cut below 1990 levels
(in Japan by 6.0 + 7.6 = 13.6% by 2012) [The Daily
Yomiuri 2004].
In Japan “(Per) household…5,000 yen green tax”
per year is planned (starting April 2005). This
includes “3,600 yen in tax per ton of carbon.” “The
revenue would be used to implement policies to
achieve the requirements of Kyoto Protocol.” A
survey released (on Oct. 21, 2004) showed that 61%
of those polled are in favor of the environmental
tax.” [The Japan Times 2004].
Rate of CO2 emission and global warming is
shown in Figure 1. In last 2 yrs. CO2 has increased
at a higher rate than expected [Corinaldesi &
Moriconi 2004b].
6.3 Foundry by-products
Foundry by-products include foundry sand, core
butts, abrasives, and cupola slag. Cores are used in
making desired cavity/shapes in a sand mold in
which molten metal is cast/poured. Cores are
primarily composed of silica sand with small
percentages of either organic or inorganic binders.

Figure 1. CO2 emission and global warming [Kawakami & Tokushige 2004].
Green sand for making molds is composed of
four major materials: sand, clay (4 to 10%),
additives, and water. Sand usually constitutes 50 to
95% of the total materials. Foundries in USA
generate approximately 15 million tonnes of by-
products annually. Wisconsin alone produces nearly
1.1 million tonnes (1.25 million tons) of foundry
byproducts, including foundry sand and slag. Most
of these by-products are landfilled. Landfilling is not
a desirable option because it not only causes huge
financial burden to foundries, but also makes them
liable for future environmental costs, problems, and
restrictions associated with landfilling. Furthermore,
the cost of landfilling is escalating due to shrinking
landfill space and stricter environmental regulations.
One of the innovative solutions appears to be high-
volume uses of foundry by-products in construction
materials [Moriconi 2003]. Table 3 provides
physical properties of foundry sand.

Table 3. Physical properties of used foundry sand.
Property Value Test method
Specific gravity 2.39 ASTM D 854
Unit weight, kg/m3 2590 ASTM C 48
SSD absorption, % 0.45 ASTM C 128
Coefficient of
permeability
10-3 ASTM D 2434
6.4 Applications of used foundry sand [Naik &
Kraus 1999]
Foundry sand can be used as a replacement of
regular sand up to 45% by weight, to meet various
requirements of structural-grade concrete [Naik &
Kraus 1999]. Use of foundry sand in concrete may
result in some loss of concrete strength due to
increased water demand. However, proper mixture
proportioning can compensate this. Concrete of
compressive strength of 42 MPa has been produced
with the inclusion of foundry sand up to 45%
replacement of regular sand. Flowable slurry
(CLSM), incorporating used foundry sand as a
replacement of fly ash up to 85% has also been
produced [Naik & Kraus 1999].
Up to 15% used foundry sand can be used as
replacement of fine aggregate in Hot Mix Asphalt
(HMA). Bricks, blocks, and paving stones made
with up to 35% used foundry sand passed ASTM
requirements for compressive strength, absorption,
and bulk density. Environmental impact of the use
of Controlled Low Strength Materials (CLSM)
incorporating industrial by-products (coal fly ash,
and used foundry sand) has been reported [Naik &
Kraus 1999]. The results demonstrated that
excavatable flowable slurry incorporating fly ash
and foundry sand up to 85% could be produced. In
general, inclusion of both clean and used foundry
sand caused reduction in the concentration of certain
contaminants. The use of foundry sand in CLSM
slurry, therefore, provided a favorable
environmental performance. All fly ash slurry
materials made with and without foundry sand were
environmentally friendly materials [Naik & Kraus
1999].
6.5 Applications of foundry slag
Foundry (cupola) slag is appropriate for use as a
coarse semi-lightweight aggregate in cement-based
materials. It has been used as replacement of
aggregate in manufacturing of structural-grade
concrete [Naik & Kraus 1999].
6.6 Post-consumer glass
Approximately 10 million tonnes of post-consumer
glass is produced each year in USA. About 3.4
million tonnes is used primarily as cullet for glass
manufacturing. There are three types of glass:
borosilicate, soda-lime, and lead glass. The majority
of glass manufactured in USA is soda-lime variety.
Glass primarily consists of silica or silica sand.
6.7 Applications of post-consumer glass [Naik &
Wu 2001]
Crushed glass is highly reactive with cement (alkali-
silica reaction). But Class F fly ash was used as a
replacement of cement by mass of 45% or more,
which helped in controlling alkali-silica reaction.
However, ground waste glass was used as aggregate
for mortars and no reaction was detected with
particle size up to 100 µm, thus indicating the
feasibility of the waste glass reuse as fine aggregate
in mortars and concrete. In addition, waste glass
seemed to positively contribute to the mortar micro-
structural properties resulting in an evident
improvement of its mechanical performance
[Corinaldesi et al. 2005a]. Mixed colored glass can
be utilized in flowable self-compacting slurry or
concrete [Naik & Kraus 1999]. Addition of mixed
colored glass increased impermeability of concrete
as the age increased. It can be used as partial
replacement of sand in other cement-based materials
also.
Moreover, every year, in Western Europe, Glass
Reinforced Plastic (GRP) processing, widely used in
several fields from buildings to furniture to boats,
produces 40,000 tons of unusable scraps and fines of
GRP, which are generally disposed in landfill. The
feasibility of re-using such GRP materials, in the
form of fine powder (about 0.1 mm in size) to
produce blended cements was investigated [Tittarelli
& Moriconi 2005]. Mechanical strength threshold
acceptable by actual cement standards could be
satisfied by replacing up to 15% of cement with
GRP powder. The “GRP cements”, even if they
show lower mechanical strengths, could confer
lightness and some ductility to cementitious
products manufactured by them. Mortars
manufactured by using these cements were more
porous with respect to the reference mortar without
GRP, due to higher water/cement and due to the
absence of any noticeable binding capacity of GRP
powder. Nevertheless, their capillary water
absorption and drying shrinkage were lower than
that of the reference mortar without GRP.

6.8 Wood ash [Naik & Kraus 2003]
Wood ash is the residue generated due to
combustion of bark, wood, and scraps from
manufacturing operations (pulp mills, saw mills, and
wood products manufacturing plants), and from
CDW (construction and demolition wastes). Wood
ash is composed of both inorganic and organic
compounds. Yield of wood ash decreases with
increase in combustion temperature.
6.9 Applications of wood ash
Wood fly ash has substantial potential for use as a
pozzolanic mineral admixture and as an activator in
cement-based materials. Wood ash has been used in
the making of structural-grade concrete,
bricks/blocks/paving stones, flowable slurry, and
blended cements [Coppola et al. 2004]. Air-
entrained concrete can be achieved by using wood
fly ash up to 35%. Structural-grade concrete can be
made using wood fly ash and its blends with Class C
fly ash to achieve a compressive strength of 50 MPa
or higher. Physical and chemical properties of wood
ash are given in Tables 4 and 5, respectively.
Table 4. Physical properties of wood ash.
Property Fly ash Bottom ash
Specific gravity 2.32 - 2.76 1.55 - 1.75
Unit weight, kg/m3 365 - 920 663 - 977
Cement activity index 49 - 90 -
6.10 Pulp and paper mill residual solids [Naik et
al. 2004]
More than six million dry tonnes of residual solids
from primary clarifiers are generated each year in
USA. Pulp and paper mill sludge is composed of
cellulose fibers, clay, ash-bearing compounds,
chemicals, and moisture. 50% of residuals are
landfilled, 25% is incinerated, and the final 25% is
utilized in someway. Figure 2 shows wastewater
treatment process at a typical pulp and paper mill.
Figure 2. Pulp and paper mill wastewater treatment
process.
Table 5. Chemical composition of wood ash.
ASTM C 618 requirements for coal fly ash
Constituent, % Fly ash Bottom ash
Class N Class C Class F
SiO2 4.0 – 59.3 32.2 – 50.7 - - -
Al2O3 5.0 – 17.0 15.5 – 20.3 - - -
Fe2O3 1.0 – 16.7 4.7 – 20.8 - - -
SiO2+Al2O3+Fe2
O3
10.0 –72.2 56.9 – 93.4 70 minimum 50 minimum 70 minimum
CaO 2.2 – 36.7 4.2 – 22.2 - - -
MgO 0.7 – 6.5 0.9 – 4.8 - - -
TiO2 0.0 – 1.2 0.7 – 1.5 - - -
K2O 0.4 – 13.7 0.5 – 2.2 - - -
Na2O 0.5 – 14.3 0.5 – 1.3 - - -
SO3 0.1 – 15.3 0.1 – 0.7 5 maximum 5 maximum 5 maximum
LOI 0.1 – 15.3 1.4 – 33.2 10 maximum 6 maximum 6 maximum
Moisture content 0.1 – 21.5 0.2 – 0.9 3 maximum 3 maximum 3 maximum
Available alkali 0.4 – 20.4 - 1.5 maximum 1.5 maximum 1.5 maximum

6.11 Primary residual
Solids are removed at the primary clarifier by
sedimentation or dissolved air flotation. Such solid
residuals consist mainly of cellulose fibers,
moisture, and papermaking fillers (kaolinitic clay,
calcium carbonate, etc.). Table 6 provides typical
chemical composition of primary residuals. Figure 3
provides properties of steel, carbon, and cellulose
microfibers. Figures 4 and 5 show wood cellulose
fibers contained in fibrous residuals from pulp and
paper mills.
Table 6. Chemical composition of primary residuals.
Constituents, % Value
CaO 0.55 - 31.46
SiO2 9.29 - 21.78
Al2O3 3.37 - 19.13
MgO 0.2 - 1.7
TiO2 0.04 - 4.62
LOI 55.4 - 83.4
0
5
10
15
20
25
30
35
Length , L
(mm)
Diameter, D
(µm)
Specific
Gravity
Steel
Carbon
Wood Cellulose
(a) Physical properties
0
100
200
300
400
500
600
700
Aspect
Ratio, L/D
Tensile
Strength
(MPa)
Modulus of
Elasticity
(GPa)
Steel
Carbon
Wood Cellulose
(b) Mechanical properties
Figure 3. Properties of microfibers.
6.12 Applications of pulp and paper mill Residual
Solids [Naik et al. 2004]
Residual solids are used in mine reclamation,
farmland soil improvement, bulking agent for
composting, raw material for composting, filler in
recycled paperboard, oil absorbent granules, odor
absorbent granules, additives in cement manufacture
(or for a new source of pozzolan from de-inking
process solids), and to produce structural-grade
concrete. Residual solids reduced somewhat the
chloride-ion penetrability of concrete and enhanced
the salt-scaling and freezing and thawing resistance
of concrete.
Figure 4. Pulp and paper mill sludge, 500X
magnification.
Figure 5. Sludge fiber reinforcing a micro-crack in
concrete.

6.13 Resource conservation
The production of one ton of portland cement
generates approximately one ton of green-house
gases (GHGs), such as CO2 and NOX and requires
1.6 tons of raw materials. These materials are
primarily good quality limestone and clay.
Therefore, for 1.6 billion tons of cement produced
annually, we need about 2.5 billion tons of raw
materials. CO2 and other GHG emissions can be
reduced by the use of other cementitious materials
(CM). Replacing 15% of cement worldwide by other
CM will reduce CO2 emissions by 250 million tons.
Replacing 50% of cement worldwide by other CM
will reduce CO2 emissions by 800 million tons. This
is equal to removing ¼ of all automobiles in the
world [Malhotra 2004].
A judicious use of natural resources, achieved by
the use of by-products and waste materials, and a
lower environmental impact, achieved through
reduced carbon dioxide emission and reduced
natural aggregate extraction from quarries; represent
two main actions that meet the requirements of
sustainable construction development. Recycled-
aggregate concrete containing large amounts of CM
is an example of construction material in harmony
with this concept, whereby sustainable construction
development is feasible with satisfactory
performance, in terms of both safety and
serviceability of structures, at lower costs and with
environmental advantages over ordinary concrete.
Moreover, when using recycled aggregates
appropriately, some important properties of the
hardened concrete such as ductility and durability
can be better engineered [Moriconi 2005b].
7 AGGREGATES
In addition to cement, water and aggregates are the
other primary constituents of concrete mixtures.
“Assuming an average of 0.6 water-cement ratio and
75% aggregate content by mass, nearly one billion
tonne (1 trillion liters) of drinking water and 8
billion tonnes of sand and gravel or crushed rock are
being consumed worldwide for concrete making
every year. Large quantities of additional water are
used as wash water for aggregate and ready-mixed
concrete trucks, and also for curing concrete. It is
evident that among the manufacturing industries, the
concrete industry is the largest consumer of natural
resources in the world. Furthermore, mining,
processing, and moving large quantities of cement-
making raw materials and concrete aggregates
consume a lot of energy besides leaving damaging
footprints on the ecology of riverbeds and forested
areas.” [Mehta 2004].
At more than 450 million tons per year, the
constrbuction and demolition waste (C&DW) stream
constitutes the largest waste stream in quantitative
terms within the European Union, apart from mining
and farm wastes [European Commission 2000]. If
one excludes earth and excavated road material, the
amount of construction and demolition waste
generated is estimated to be 180 million tons per
year. Roughly 75% of the C&DW is disposed to
landfill, despite its major recycling potential. This
represents very large quantities (more than million
tons per year) occupying existing landfills.
However, the technical and economic feasibility of
recycling has been proven, thus enabling certain EU
Member States (and in particular Denmark, The
Netherlands, and Belgium) to achieve recycling
rates of more than 80%.
At present, the South European countries (Italy,
Spain, Portugal, and Greece) recycle very little of
their C&DW. Their natural resources are of a
sufficient quality and quantity to meet the demand
for building materials at a moderate cost, thus
implying a delay in the market for recycled materials
to develop. Nevertheless, mainly for environmental
reasons, in this part of Europe, there is a growing
interest in the possibility to recycle these materials.
More recent data relative to the Italian market show
that almost 40% of C&DW was re-used or recycled
in 1998 verses of 9% in 1996. Unfortunately, more
up-to-date data are not yet available.
7.1 Recycled aggregates
In the current context of increasing waste production
and growing public awareness of environmental
problems, recycled materials from demolished
concrete or masonry can be profitably used in
different ways within the building industry. At
present, these materials are mainly used untreated as
obtained from demolition for excavation filling,
roadbeds, or floor foundation. However, if suitably
selected, ground, cleaned and sieved in appropriate
industrial crushing plants, the rubble from building
demolition could become useful for more ambitious
applications.
Several authors [Coppola et al. 1995, Dhir et al.
1998, Hansen 1992, Kasai 1988] have studied the
possibility of using recycled aggregates to prepare
structural concretes. A Technical Committee
(CEN/TC 154) have recently drawn an European
Standard (EN 12620 – “Aggregates for concrete

including those for use in roads and pavements”) in
which artificial or recycled aggregates are
considered beside natural aggregates for use in
concrete. These studies show that, in recycled-
aggregate concrete, mechanical strength loss occurs,
which is strongly dependent on the recycled
aggregate quality; in fact, this loss is completely
eliminated when recycled aggregates consist of
demolished concrete belonging to a strength class
equal to or higher than that of the new concrete in
which they will be used [Coppola et al. 1995].
Moreover, the fine recycled aggregate fraction is
particularly detrimental to both mechanical
performances and durability of concrete. Therefore,
the possibility of reusing this fraction in other ways
has recently been examined [Moriconi 2005a].
Recycled-aggregate fractions up to 15 mm,
although containing masonry rubble up to 25-30%,
proved to be suitable for manufacturing structural
concrete even if employed as a total substitution of
the fine and coarse natural aggregate fractions
[Corinaldesi & Moriconi 2001]. Moreover, the fine
fraction with particle size up to 5 mm, if reused as
aggregate for mortars, allowed excellent bond
strengths between mortar and bricks, in spite of a
lower mechanical performance of the mortar itself
[Corinaldesi et al. 2002a, Moriconi et al. 2003]. Also
the masonry rubble can be profitably treated and
reused for preparing mortars.
Finally, even for the finest fraction produced
during the recycling process, that is the rubble
powder, an excellent reuse was found, that is as
filler in self-compacting concretes [Corinaldesi et al.
2002c, 2005b, Corinaldesi & Moriconi 2003,
2004b].
7.2 Leaching issues
A research was conducted in order to verify the
possibility to use C&D debris as substitute for
natural aggregate in structural concrete production
[Sani et al. 2005]. The results obtained demonstrated
that such substitution modifies both structural and
leaching behavior. In general, the use of recycled
aggregate as a total replacement for natural
aggregate causes an increase of the total porosity
and a reduction in mechanical strength that can be
attenuated by fly ash addition. Although the total
porosity increases, the ion leaching rate expressed
for unit of specific surface area is lower and directly
related to the percentage of macro/meso-pores. The
calcium, sodium, and potassium analyses indicate
that different processes are operating, but also
suggest that the diffusion process is the most
relevant leaching mechanism. On the basis of these
first observations, the use of recycled aggregate
implies a reduction in the rate of calcium release, in
spite of a greater porosity of the concrete
microstructure. This effect could be ascribed to the
lower portlandite level, responsible for the soluble
calcium. From this point of view, the recycled
aggregate, if properly engineered, could have a
positive environmental effect and the recycled-
aggregate concrete may be suggested as more
environmentally sustainable.
8 THE HANNOVER PRINCIPLES ON DESIGN
FOR SUSTAINABILITY [McDonough 1992]
In 1991, City of Hannover, Germany commissioned
William McDonough and Michael Braungart to
develop a set of sustainability principles to guide
development associated with the EXPO 2000
World’s Fair in Hannover. The resulting document,
“The Hannover Principles - Design for
Sustainability” includes guidelines pertaining to
water, which are included below. While these
guidelines were developed for the World’s Fair, they
remain useful on a much broader scale.
The Principles are to be considered by designers,
planners, government officials, and all involved in
setting priorities for the built environment. They will
help form the foundations of a new design
philosophy underlying the future of proposed
systems and construction for the City, its region, its
global neighbors and partners in the world
exposition. World history offers many examples of
societies with environmentally sustainable structures
and communities that have endured for thousands of
years.
However, we have also pursued other paths that
have led to ecologically unsustainable practices. For
the development and improvement of humankind, it
is imperative to renew a commitment to living as
part of the earth by understanding development and
growth as processes which can be sustained, not
exploited to impractical limits. It is hoped that the
Hannover Principles will inspire an approach to
design that may meet the needs and aspirations of
the present without compromising the ability of the
planet to sustain an equally supportive future.
Hannover Principles by William McDonough
[1992]: Insist on rights of humanity and nature to
co-exist; recognize interdependence; respect
relationships between spirit and matter; accept
responsibility for consequences of design; create
safe objects of long-term value; eliminate the

concept of waste; rely on natural energy flows;
understand the limitations of design; and, seek
constant improvement by the sharing of knowledge.
The Hannover Principles should be seen as a
living document committed to transformation and
growth in the understanding of our interdependence
with nature, in order that they may adapt as our
knowledge of the world evolves.
For sustainability consider actions on: materials
(use indigenous materials); land use (protect and
create rich soil); urban context (preserve open
spaces); water (use rainwater and gray-water);
wastes (recycle), air (create clean air); energy (use
solar & wind energy; recycle waste energy); and,
responsibility to nature (create silence) and the
future generations (eliminate maintenance).
9 OBSERVATIONS
Post-consumer wastes and industrial by-products
can be and must be used in concrete to make
“greener” concrete. Glass, plastics, tires, and wood
fibers can be used. Recycling of industrial by-
products is well established. Use of coal fly ash in
concrete started in the 1930s, and volcanic ash has
been recycled for several millenniums in mortar and
concrete (in Egypt, Italy, Mexico, India, and other
places). Recycling minimizes solid waste disposal,
improves air quality, minimizes solid wastes, and
leads to sustainable cement and concrete industry.
Use less portland cement. Use less water. Use
applications specific, high-quality, durable
aggregates [Malhotra 1997, 2004]. Use chemical
admixtures. Trade Emissions (refers to air emissions
economic mechanism to reduce global greenhouse
gases). Fundamental laws of nature say that we
cannot create or destroy matter; we can only affect
how it is organized, transformed, and used. Obey the
rules of nature: use only what you need and never
use a resource faster than nature can replenish it.
“We (over) extract from earth what the planet can
replace by an estimated 20%, meaning it takes 14.4
months to replenish what we use in 12. Sustainable
developments work to reduce that” [TIME Magazine
2002].
10 CONCLUSIONS
Generally, large volumes of by-product materials are
disposed in landfills. Because of stricter
environmental regulations, disposal cost is
escalating. Recycling not only helps in reducing
disposal costs, but also helps to conserve natural
resources, providing technical and economic
benefits. This is sustainability. Eliminate waste and
take life cycle responsibility/ownership. Think
Ecology, Energy, Equity, and Economy.
Acknowledge and balance these Es [McKay 2004].
Foundry sand can be used as a replacement of
regular sand in concrete, flowable slurry, cast-
concrete products, and other cement-based
materials. Foundry slag can be used as semi-light
weight coarse aggregate in concrete.
Glass can be used as a partial replacement of fine
aggregate in concrete. Wood ash can be used to
make structural-grade concrete, blended cements,
and other cement-based materials. Structural-grade
concrete can be made with pulp and paper mill
residual solids.
Sustainable design must use an alternative
approach to traditional design that incorporates these
changes in the designer’s mind-set. The new design
approach must recognize the impacts of every
design choice on the natural and cultural resources
of the local, regional, and global environments
[McDonough 1992]. “Save Our Climate” symbol
(Fig. 6) can be widely and freely used and is
designed “to act as a common and recognizable
thread in all communications concerning climate
change [Westwood 2004].
Figure 6. COP 9 saw the launch of a new
international climate symbol developed jointly by
WWF, UNEP, Greenpeace and the Dutch Ministry
of the Environment [Worrell & Galtisky 2004].
Wangari Maathai, 2004 Nobel Peace Laureate,
said “When we destroy our resources, when our
resources become scarce, we fight over them. And
many wars in the world are actually fought over
natural resources,” (in October 2004). She is known

as “the Tree Woman of Kenya” because she has
planted over 30 million trees since 1977.
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