N. P.

Rajamane, Head, Concrete Composites Lab; N Lakshmanan, Former Director and

Presently Project Advisor Structural Engg Research Centre, Chennai, and Nataraja M C, Professor,
SJ College of Engg, Mysore

General
The cement industry is the Indias second highest payer of Central Excise and Major contributor to
GDP. With infrastructure development growing and the housing sector booming, the demand for
cement is also bound to increase. However, the cement industry is extremely energy intensive.
After aluminium and steel, the manufacturing of Portland cement is the most energy intensive
process as it consumes 4GJ per tonne of energy. After thermal power plants and the iron and steel
sector, the Indian cement industry is the third largest user of coal in the country. In 2003-04,
11,400 million kWh of power was consumed by the Indian cement industry. The cement industry
comprises 130 large cement plants and more than 300 mini cement plants. The industrys capacity
at the beginning of the year 2008-09 was about 198 million tones. The cement demand in India is
expected to grow at 10% annually in the medium term buoyed by housing, infrastructure and
corporate capital expenditures. Considering an expected production and consumption growth of 9
to 10 percent, the demand-supply position of the cement industry is expected to improve from
2008-09 onwards.

Coal-based thermal power installations in India contribute about 65% of the total installed capacity
for electricity generation. In order to meet the growing energy demand of the country, coal-based
thermal power generation is expected to play a dominant role in the future as well, since coal
reserves in India are expected to last for more than 100 years. The ash content of coal used by
thermal power plants in India varies between 25 and 45%. However, coal with an ash content of
around 40% is predominantly used in India for thermal power generation. As a consequence, a
huge amount of fly ash (FA) is generated in thermal power plants, causing several disposal-related
problems. In spite of initiatives taken by the government, several non-governmental organizations
and research and development organizations, the total utilization of FA is only about 50%. India
produces 130 million tonne of FA annually which is expected to reach 175 million tonne by 2012.
Disposal of FA is a growing problem as only 15% of FA is currently used for high value addition
applications like concrete and building blocks, the remainder being used for land filling. Globally,
less than 25% of the total annual FA produced in the world is utilized. In the USA and China, huge
quantities of FA are produced (comparable to that in India) and its reported utilization levels were
about 32% and 40%, respectively, during 1995. FA has been successfully used as a mineral
admixture component of Portland pozzolan blended cement for nearly 60 years. There is effective
utilization of FA in making cement concretes as it extends technical advantages as well as controls
the environmental pollution.

Ground granulated blast furnace slag (GGBS) is a by-product from the blast-furnaces used to
make iron. GGBS is a glassy, granular, non metallic material consisting essentially of silicates and
aluminates of calcium and other bases. Slag when ground to less than 45 micron from coarser,
popcorn like friable structure, will have a specific surface of about 400 to 600 m2/kg (Blaine).
GGBS has almost the same particle size as cement. GGBS, often blended with Portland cement as
low cost filler, enhances concrete workability, density, durability and resistance to alkali-silica
reaction.

Alternative but promising gainful utility of FA and GGBS in construction industry that has emerged
in recent years is in the form of Geopolymer cement concretes (GPCCs), which by appropriate
process technology utilize all classes and grades of FA and GGBS; therefore there is a great
potential for reducing stockpiles of these waste materials.
 Importance of Geopolymer Cement Concretes
Producing one tonne of cement requires about 2 tonnes of raw materials (shale and limestone) and
releases 0.87 tonne (H 1 tonne) of CO2, about 3 kg of Nitrogen Oxide (NOx), an air contaminant
that contributes to ground level smog and 0.4 kg of PM10 (particulate matter of size 10 m), an
air borne particulate matter that is harmful to the respiratory tract when inhaled. The global
release of CO2 from all sources is estimated at 23 billion tonnes a year and the Portland cement
production accounts for about 7% of total CO2 emissions. The cement industry has been making
significant progress in reducing CO2 emissions through improvements in process technology and
enhancements in process efficiency, but further improvements are limited because CO2 production
is inherent to the basic process of calcinations of limestone. Mining of limestone has impact on
land-use patterns, local water regimes and ambient air quality and thus remains as one of the
principal reasons for the high environmental impact of the industry. Dust emissions during cement
manufacturing have long been accepted as one of the main issues facing the industry. The
industry handles millions of tonnes of dry material. Even if 0.1 percent of this is lost to the
atmosphere, it can cause havoc environmentally. Fugitive emissions are therefore a huge problem,
compounded by the fact that there is neither an economic incentive nor regulatory pressure to
prevent emissions.

The cement industry does not fit the contemporary picture of a sustainable industry because it
uses raw materials and energy that are non-renewable; extracts its raw materials by mining and
manufactures a product that cannot be recycled. Through waste management, by utilizing the
waste by-products from thermal power plants, fertiliser units and steel factories, energy used in
the production can be considerably reduced.This cuts energy bills, raw material costs as well as
green house gas emissions. In the process, it can turn abundantly available wastes, such as fly ash
and slag into valuable products, such as geopolymer concretes.

Geopolymer cement concretes (GPCC) are Inorganic polymer composites, which are prospective
concretes with the potential to form a substantial element of an environmentally sustainable
construction by replacing/supplementing the conventional concretes. GPCC have high strength,
with good resistance to chloride penetration, acid attack, etc. These are commonly formed by
alkali activation of industrial aluminosilicate waste materials such as FA and GGBS, and have a
very small Greenhouse footprint when compared to traditional concretes.
Basics of Geopolymers
The term geopolymer was first introduced by Davidovits in 1978 to describe a family of mineral
binders with chemical composition similar to zeolites but with an amorphous microstructure. Unlike
ordinary Portland/pozzolanic cements, geopolymers do not form calcium- silicate-hydrates (CSHs)
for matrix formation and strength, but utilise the polycondensation of silica and alumina precursors
to attain structural strength. Two main constituents of geopolymers are: source materials and
alkaline liquids. The source materials on alumino-silicate should be rich in silicon (Si) and
aluminium (Al). They could be by-product materials such as fly ash, silica fume, slag, rice-husk
ash, red mud, etc. Geopolymers are also unique in comparison to other aluminosilicate materials
(e.g. aluminosilicate gels, glasses, and zeolites). The concentration of solids in geopolymerisation
is higher than in aluminosilicate gel or zeolite synthesis.
Composition of Geopolymer Cement Concrete Mixes
Following materials are generally used to produce GPCCs:

i. Fly ash,
ii. GGBS,
iii. Fine aggregates and
iv. Coarse aggregates
v. Catalytic liquid system (CLS): It is an alkaline activator solution (AAS) for GPCC. It is a
combination of solutions of alkali silicates and hydroxides, besides distilled water. The role of
AAS is to activate the geopolymeric source materials (containing Si and Al) such as fly ash and
GGBS.

Formulating the GPCC Mixes

Unlike conventional cement concretes, GPCCs are a new class of materials and hence, conventional
mix design approaches are applicable. The formulation of the GPCC mixtures requires systematic
numerous investigations on the materials available.
Preparation of GPCC Mixes
The mixing of ingredients of GPCCs can be carried out in mixers used for conventional cement
concretes such as pan mixer, drum mixer, etc
Mechanical Properties
Compressive Strength: With proper formulation of mix ingredients, 24 hour compressive
strengths of 25 to 35 MPa can be easily achieved without any need for any special curing. Such
mixes can be considered as self curing. However, GPCC mixes with 28 day strengths up to about
60-70 MPa have been developed at SERC.

Modulus of Elasticity The Youngs modulus or modulus of elasticity (ME), Ec of GPCC is taken as
tangent modulus measured at the stress level equal to 40 percent of the average compressive
strength of concrete cylinders. The MEs of GPCCs are marginally lower than that of conventional
cement concretes (CCs), at similar strength levels.

Stress Strain Curves The stress-strain relationship depends upon the ingredients of GPCCs and
the curing period.

Rate of Development of Strength This is generally faster in GPCCs, as compared to CCs.

Reinforced GPCC Beams
Load carrying capacity of GPCC beams, are up to about 20% more of CC beams at similar concrete
strength levels. Cracking of concrete occurs whenever the tensile strength of the concrete is
exceeded. The cracking in reinforced concrete is attributable to various causes such as flexural
tensile stresses, diagonal tension, lateral tensile strains, etc. The cracking moment increases as
the compressive strength increases in both GPCC and CC beams.

Reinforced concrete structures are generally analyzed by the conventional elastic theory (Clause
22.1 of IS 456:2000) which is equivalent to assuming a linear moment-curvature relationship for
flexural members. However, in actual behaviour of beams, non-linear moment curvature
relationship is considered. The moment-curvature relation can be idealized to consist of three
straight lines with different slopes. The slopes of these line changes as the behaviour of the beam
is changed due to increasing load. Thus each straight line indicates different phases of beam
history. The moment-curvature relations of GPCCs and CCs are essentially similar.

The service load is generally considered as the load corresponding to a deflection of span/350 or
maximum crack width of 0.2 mm, whichever is less. The deflections at service loads for the GPCC
and CC beams are found to be almost same. Thus, at service loads, the behaviour of the GPCC and
CC beams are similar.

Ductility factor of the beams is considered as the ratio of deflection at ultimate moment (U) to
the deflection at yield moment (Y). The ductility factor decreases as the tensile reinforcement
increased. The ductility factor of GPCC beams could be marginally less than CC beams indicating
higher stiffness of GPCC beams. The crack patterns observed for GPCC beams are similar to the CC
beams.
Reinforced GPCC Columns
The concrete compressive strength and longitudinal reinforcement ratio influence the load capacity
of columns. The load carrying capacity increases with the increase in concrete compressive
strength and longitudinal reinforcement ratio. Crack patterns and failure modes of GPCC columns
are similar to those of CC columns.
Bond Strength of GPCC with Rebars
The bond strength of GPCCs with rebars are higher compared to CC. Thus developmental length of
steel bars in reinforced GPCC can be kept same, as in the case of reinforced CC. The bond
strengths of GPCC and PPCC are significantly more and conservative than the design bond stress
recommended in IS: 456-2000. The GPCCs possess satisfactory bond with embedded steel bars so
that the conventional design process of reinforced structural components can be applied
conservatively to GPCCs also.
Durability Aspects of GPCCS
The GPCC specimens have chloride permeability rating of low to very low as per ASTM 1202C.
GPCCs offer generaly better protection to embedded steel from corrosion as compared to CC. The
GPCC are found to possess very high acid resistance when tested under exposure to 2% and 10%
sulphuric acids.
Concluding Remarks on GPCCS
From the test data generated at SERC, it can be concluded that GPCCs are good candidates
materials of constructions from both strength and durability considerations. Geopolymer concrete
shows significant potential to be a material for the future; because it is not only environmentally
friendly but also possesses excellent mechanical properties. Practical recommendations on use of
geopolymer concrete technology in practical applications such as precast concrete products and
waste encapsulation need to be developed in Indian context.

Because of lower internal energy (almost 20% to 30 % less) and lower CO2 emission contents of
ingredients of geopolymer based composites compared to those of conventional Portland cement
concretes, the new composites can be considered to be more eco-friendly and hence their utility in
practical applications needs to be developed and encouraged.