Pozzolans for Sustainable Concrete- A Review

Pozzolans for Sustainable Concrete- A Review

G. A. Habeeb*
H. B. Mahmud
Dept. of Civil Engineering, Faculty of Engineering,
Dept. of Civil Engineering, Faculty of Engineering,
University of Malaya
University of Malaya
Lembah Pantai, 50603 Kuala Lumpur.
Lembah Pantai, 50603 Kuala Lumpur.


Abstract- Pozzolans are finely divided materials used in

concrete in relatively large amounts and mainly used as cement

replacement in order to enhance early and long term

performance. The use of these materials to some extent reduces
the cost of concrete production. This paper reviews the

significance of using natural and industrial waste materials

posing pozzolanic properties as a cement replacement material

in the concrete industry. The paper attempts to provide a

better understanding of using these materials and the concerns

rose from the massive cement production and the need for
alternative binders. A brief description of these materials is

provided and their effects on the properties of concrete are also

shown.


I. INTRODUCTION


Concrete is a composite material consists mainly of
Figure 1. CO2 emissions due to world cement production [1]
aggregates dispersed in a cement paste matrix. The paste

itself consists of hydration products (calcium hydroxide,

calcium silicate hydrate, calcium monosulphoaluminate and
II. DEVELOPMENT OF DURABLE GREEN
ettringite, etc.), un-reacted cement, pores and water. The use
CONCRETE
of concrete in construction is relatively new compared to the
use of steel and stone.
Green concrete is environmental/eco friendly and can be
In the construction industry, concrete is the most used
obtained by utilizing the industrial by-products such as fly
material. The cost of concrete is relatively high due to the
ash and silica fume, agricultural wastes such as rice husk
manufacturing cost of its main component, the ordinary
ash, or using natural pozzolans as cement replacement
Portland cement (OPC). In addition to that, reports showed
materials, in order to make resource/cost saving concrete
that from 1880 to 1996, the world’s annual consumption of
structures. In addition, green concrete will usually enhance
Portland cement rose from 2 million to 1.3 billion tons. This
concrete durability. The use of these materials in concrete
was associated with major environmental costs. Cement
will contribute in solving the disposal problems of these
manufacturing is considered the third largest CO2 producer
materials, which are normally considered as by-product or
and for over 50 % of all industrial CO2 emissions where for
wastes, and relatively reducing the cost of concrete
every one ton of cement produced, 1 to 1.25 ton of CO2 is
production, in addition to imparting special properties to
released to the air [2]. Figure 1 shows the rising global CO2
concrete that would not be achieved by the use of OPC
emissions from cement production over the last forty years
alone [3].
[1]. Furthermore, to produce one ton of cement, 1.6 ton of

natural resources are consumed [1]. In addition to that,
III. POZZOLANIC MATERIALS
cement is a highly energy consuming process requiring
around 4 GJ of energy per ton cement [3].
The American Society of Testing and Materials (ASTM)
To deal with this major issue, the American Concrete
defines pozzolan as a siliceous or alumino-siliceous material
Institute (ACI) board of direction formed a task group on the
that in itself possesses little or no cementitious value but that
sustainable development and its mission was “to encourage
in finely divided form and in the presence of moisture will
development and application of environmentally friendly,
chemically react with alkali and alkaline earth hydroxides at
sustainable concrete materials, design, and construction” [2].
ordinary temperatures to form or assist in forming
This would be achieved by the use of the sustainable
compounds possessing cementitious properties [4]. Some
materials, such as, fly ash, ground granulated blast furnace
pozzolans are natural and others are industrial by-products
slag (GGBFS), rice husk ash (RHA), natural pozzolans and
and both contain silica in amorphous form and that would
silica fume. Finally, the need for cement replacement
react with calcium hydroxide (C-H) to form more
material is due to two main factors, i.e. the design for
cementitious calcium silicate hydrate (C-S-H) and
durable concrete and to reduce the use of cement by
contribute to the concrete strength. These materials include
replacing with pozzolanic materials.
volcanic ash, diatomaceous earths, condensed silica fume,

pulverized fly ash, natural pozzolan and rice husk ash. It

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International Conference for Technical Postgraduates (TECHPOS),"Towards Advancement of Engineering Research - Global Challenges", Kuala
Lumpur, Malaysia. 2009.
contains some form of amorphous reactive silica which may
VIII.
EFFECT OF POZZOLANS ON
combine with lime in presence of water to form C-S-H [5].
MICROSTRUCTURE OF CONCRETE
Slags are the by-products of the production of the iron,
Concrete microstructure is the type, amount, size, shape,
slag consists mainly of calcium and alumino-silicate.
and the distribution of the various phases present in the
Granulated blast furnace slag is the type mainly used in
concrete solid constitute. It can be seen from a cross-section
large scale in the cement industry. However, due to its
in the material with the aid of a microscope [12]. It is well
cementitious properties and the presence of silica, slags may
known now that using pozzolans may increase the strength
also possess pozzolanic activity [6]. Adding pozzolans to
and improve durability through the improvement in the
concrete influence mixture proportioning, rheological
interfacial transition zone (ITZ) due to the pozzolanic
behaviour of fresh concrete, degree of hydration of cement
reaction and the finer pore size distribution [17].
paste, strength and permeability of the produced concrete

[7].



IV. THE EFFECT OF POZZOLANS ON FRESH
IX. CONCLUSION
PROPERTIES
1.
The use of pozzolanic materials would contribute
The slump test is most widely used method for evaluating
to the reduction of the major environmental concerns raised
concrete fresh properties both in the laboratory and the
from cement production.
construction site, due to its availability and ease of operation
2.
Most of the commonly used pozzolans are
and portability. Adding pozzolans as cement replacement
considered as industrial waste materials and thus, their use
materials to concrete would usually reduce the slump and
will solve the disposal problems of these materials.
increase the water demand due to the high fineness of these
3.
The workability is generally reduced when
materials such as silica fume, rice husk ash, and metakaolin
pozzolans is used. However, some pozzolans such as fly ash
[8, 9]. However, fly ash and GGBFS is proven to enhance
and ground granulated blast furnace slag can enhance the
the fresh properties and a reduction in the water demand are
workability significantly.
also reported[6].
4.
Adding pozzolans as cement replacement materials

to concrete would produce concrete with equivalent or
V. THE EFFECT OF POZZOLANS ON STRENGTH
enhanced strength as compared to the control OPC concrete.
5.
Durability of the blended cement concrete is
Adding pozzolans as cement replacement materials in
generally improved by reducing the porosity and increasing
concrete would usually enhance the strength of the produced
the resistance to harmful solutions.
concrete. For example, silica fume, RHA and metakaolin
6.
The drying shrinkage is usually increased upon the
would contribute to the early and later age strength
addition of pozzolans due to the fine particle size of these
enhancement [3, 6]. However, adding other pozzolans such
materials.
as, fly ash and GGBFS would contribute to the strength
7.
Using pozzolans would improve the interfacial
enhancement at later ages only and the strength would be
transition zone (ITZ) due to the pozzolanic reaction and the
comparable to the control OPC concrete [6].
finer pore size distribution.


VI. THE EFFECT OF POZZOLANS ON DURABILITY
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International Conference for Technical Postgraduates (TECHPOS),"Towards Advancement of Engineering Research - Global Challenges", Kuala
Lumpur, Malaysia. 2009.
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