ABSTRACT
Concrete is the most common
used material for construction and its design consumes almost the total cement
production in the world. The use of large quantities of cement produces
increasing CO2 emissions, and as a consequence of this is the green house
effect. A method to reduce the cement content in concrete mixes is the use of
silica fines. One of the silica fines with high potential as cement replacement
and as concrete additive is nano-silica (nS). However, the commercial nS is
synthesized in a rather complex way, resulting in high purity and complex
processes that make them non-feasible for the construction industry. In recent
years a new nano-silica is produced from olivine. This nS, as well as
commercially available nS, will be applied and tested.
This paper aims to present the
state of the art of nS application in concrete, and in various fields focusing
on its properties to render it suitable to be applicable. It includes importance
of nS, the nS production process, their addition effect and their application especially
in concrete.
INTRODUCTION:
A long time used material in concrete is for the first time fully replaced
by a nano material. It is well known in physics and chemistry that a well
designed and developed nano material produces better and cheaper cost results
than traditional materials, the
stabilization and reinforcement of matter properties at this level: a thousand
fold smaller than the older level: “micro” (0.000001 mt).
Micro silica has been one of the world’s most
widely used products for concrete for over
eighty years. Its properties allowed high compressive strength concretes; water
and chemical resistant concretes, and they have been part of many concrete
buildings that we see nowadays. Its disadvantage, though, has been its
relatively high cost and contamination, which affects the environment and the
operators’ health
In the middle of 2003, a product which could
replace micro silica seen the contaminant effects, having the better
characteristics and at a reasonable cost was on the design table. The goal:
silica fulfilling the environ-mental regulation: ISO-14001.
Atlast the challenge was fulfilled. Lab tests and
production tests proved that the nano silica did not contaminate (because of its state), but it also produced better
results than micro silica, and a litre bottle of the product was equivalent to
a barrel full of micro silica, extra cement and super plasticizing additives.
Nano silica giving concrete not only the high
initial and final resistance but in addition, plasticity, impermeability, minor
final cost of work, and cement savings of up to 40%. Also, it lowered the
levels of environmental contamination.
NEED FOR THE EMERGENCE OF NANO SILICA:
Silica
(SiO2) is present in conventional concrete as part of the normal mix. However,
one of the advancements made by the study of concrete at the nanoscale is that
particle packing in concrete can be improved by using nano-silica which leads
to a densifying of the micro and
nanostructure resulting in improved mechanical
properties. Nano-silica addition to cement based materials can also control the
degradation of the fundamental C-S-H (calcium-silicate hydrate) reaction of
concrete caused by calcium leaching in water as well as block water penetration
and therefore lead to improvements in durability.
CO2 emissions from the global cement industry
are significant and they are increasing. Global cement production is currently
around 1.6bn tonnes/yr, and through the calcinations of limestone to produce
calcium oxide and carbon dioxide, approximately 0.97 tonnes of CO2 is produced
for each tonne of clinker produced. Around 900kg of clinker is used in each
1000kg of cement produced so the global cement industry produces around 1.
tonnes of CO2 each year. This represents about 6% of the total worldwide
man-made CO2 production. This is another important consideration for the
development of nano silica. Endowment Selling .
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