05-01-2013, 02:36 PM
GEOPOLYMER CONCRETE
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Abstract
Limestone and clay are the prime raw materials used in the manufacturing of Portland
cement and quarrying of them is becoming the source of environmental degradation. Past
few researches showed that in coming years limestone will be hardly available for cement
production. Besides that, carbon footprints due to cement production are causing global
warming. In addition to this, waste disposal is also becoming a global issue because of
scarcity and expensiveness of landfills
Polymeric concrete utilizes waste materials such as Fly Ash (FA) and Rice Husk Ash
(RHA) together with alkaline solution (NaOH & NaSiO2), which results in a green binder to
replace cement. This study focuses on complete elimination of Portland cement for
production of concrete. This study incorporates Fly Ash as base source material in
polymeric concrete. Polymeric concrete gives higher compressive strength and tensile
strength values for external exposure curing as well as better development of microstructure
for the same, compare to ordinary concrete
Introduction
Concrete usage around the world is second only to water. Ordinary Portland cement
(OPC) is conventionally used as the primary binder to produce concrete. The
environmental issues associated with the production of OPC are well known. The amount of
the carbon dioxide released during the manufacture of OPC due to the calcination of
limestone and combustion of fossil fuel is in the order of one ton for every ton of OPC
produced. In addition, the extent of energy required to produce OPC is only next to steel and
aluminium.
On the other hand, the abundant availability of fly ash worldwide creates opportunity to
utilize this by-product of burning coal, as a substitute for OPC to manufacture concrete.
When used as a partial replacement of OPC, in the presence of water and in ambient
temperature, fly ash reacts with the calcium hydroxide during the hydration process of
OPC to form the calcium silicate hydrate (C-S-H) gel. The development and application
of high volume fly ash concrete, which enabled the replacement of OPC up to 60% by
mass is a significant development. (Malhotra 2002; Malhotra and Mehta 2002),
In 1978, Davidovits (1999) proposed that binders could be produced by a polymeric
reaction of alkaline liquids with the silicon and the aluminium in source materials of
geological origin or by-product materials such as fly ash and rice husk ash. He termed
these binders as geopolymers.
Dept Of Civil Engg, BVBCET Page 1
Geopolymer Concrete
Materials in Geopolymer Concrete
Fly Ash
A waste material from power stations, fly ash has been used as a mineral admixture
component of Portland-pozzolans blended cement for nearly 60 years. This, the largest use
of fly ash, consumes about 10 percent of fly ash produced throughout the world. Another
10-15 percent is used for construction, building materials and beneficiation applications.
Remaining 75-80 percent is disposed of as waste.
According to the American Concrete Institute (ACI) Committee, fly ash is defined as
‘The finely divided residue that results from the combustion of ground or powdered coal
and that is transported by flue gasses from the combustion zone to the particle removal
system’ (ACI Committee 232 2004) ’ . Fly ash is removed from the combustion gases by
the dust collection system, either mechanically or by using electrostatic precipitators, before
they are discharged to the atmosphere. Fly ash particles are typically spherical, finer than
Portland cement and lime, ranging in diameter from less than 1 μm to no more than 150 μm.
The chemical composition is mainly composed of the oxides of silicon (SiO2),
aluminium (Al2O3), iron (Fe2O3), and calcium (CaO), whereas magnesium, potassium,
sodium, titanium, and sulphur are also present in a lesser amount. The major influence on
the fly ash chemical composition comes from the type of coal (Malhotra and
Ramezanianpour 1994).