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There are many advantages of incorporating fly ash into a Portland cement concrete that have been demonstrated through extensive research and countless highway and bridge construction projects.

Road construction

Road construction (Photo credit: World Bank Photo Collection)

Benefits to concrete vary depending on the type of fly ash, proportion used, other mix ingredients, mixing procedure, field conditions and placement.

Some of the advantages of fly ash in concrete are:

•   Higher ultimate strength;

•   Improved workability;

•   Reduced bleeding;

•   Reduced heat of hydration;

•   Reduced permeability;

•   Increased resistance to sulphate attack;

•   Increased resistance to alkali-silica reactivity (ASR);

•   Lowered costs;

•   Reduced shrinkage; and

•   Increased durability.

Fly ash and lime can be combined with aggregate to produce a quality stabilized base course. These road bases are referred to as pozzolanic-stabilized mixtures (PSMs).

Typical fly ash contents may vary from 12 to 14 percent with corresponding lime contents of 3 to 5 percent.

Portland cement may also be used in lieu of lime to increase early age strengths. The resulting material is produced, placed, and looks like cement stabilized aggregate base.

Pozzolanicstabilized mixture bases have advantages over other base materials that are:

•  Use of locally available materials;

•  Provides a strong, durable mixture;

•  Increased energy efficiency;

•  Suitable for using recycled base materials; and

•  Can be placed with conventional equipment.

Fly ash is an effective agent for chemical and/or mechanical stabilization of soils. The properties of soil which can be change by using of fly ash are density, water content, plasticity, strength and compressibility performance of soils, hydraulic conductivity, and so on.

Typical applications include: soil stabilization, soil drying, and control of shrink-swell. Fly ash improve soil conditions by:

•  Eliminates need for expensive borrow materials;

•  Expedites construction by improving excessively wet or unstable sub grade;

•   By improving sub grade conditions, promotes cost savings through reduction in the required pavement thickness; and

•  Can reduce or eliminate the need for more expensive natural aggregates in the pavement cross-section.

Fly ash can be used as mineral filler in hot mixed asphalt (HMA) paving applications. Mineral fillers increase the stiffness of the asphalt mortar matrix, improving the resistance of pavements, and the durability of the mix. Fly ash will typically meet mineral filler specifications for gradation, organic impurities, and plasticity.

More than 12 million tons of coal fly ash are used in concrete products each year. The use of fly ash, a recovered resource, reduces the depletion of natural resources.

It also reduces the energy intensive manufacturing of portland cement. This reduction in energy leads to less emissions of greenhouse gases.

Source : International Journal of Environmental Science and Development, Vol. 1, No. 2, June 2010 and everything-about-concrete.com

(this article written for 1BINA.my)

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