EFFECT OF FLY ASH ON THE FRESH AND

EFFECT OF FLY ASH ON THE FRESH AND HARDENED PROPERTIES OF CONCRETE Asena SİVASLIOĞLU

Fly ashes are used in concrete technology for purposes of taking advantage of pozzolanic properties, providing economy and preventing environmental pollution.

Workability and Water Demand Fly ash improves the workability of the concrete and ruduces water demand but fly ash must not used like an additive, it has to take the place of cement. Their particles are spherical. Fine-grained ones help for workability, coarse grained ones help to reduce water.

Bleeding and Segregation Highly fine-grained fly ashes decreases the segregation by increasing the cohesion so prevent shrinkage.

Setting Time Fly ash needs Ca(OH)2 which nascency from cement, so setting time may be longer but some situations can change it. These are listed below; o High lime fly ash can be self-binding o Fly ashes can be include sulphate which may react with portland cement.

Heat of Hydration Air Content Hydration Especially effects concrete badly, it causes cracks. Using fly ash instead of cement helps to decrese the harmful heat of hydration. F types fly ashes increase need for air entrainer in concrete.

The Effect of Fly Ashes on The Strength of Concrete The effect of fly ashes on the strength is lower in early ages, this effect gradually increase while concrete getting older because pozzolanic reaction starts later.

Ø Fly ashes which include low percentage lime known as F types fly ashes, this type of ashes effect the strength slower than others first but after then becomes faster.

Sulfate Attack Pozzolans prevent the reaciton with sulfate by using Ca(OH)2 so make sulfate resistance of concrete higher than before. Except ones. made by lignite Alkali-aggregate Reaction The fly ashes include low percentage lime helps to decrease the alkali aggregate reaction.

Freeze-thaw Resistance There are two ideas about it; 1. The concrete include %20 fly ash (high-lime) more durable. 2. Fly ash has no effect, the important one is air entrainer.

Permeability Fly ash concretes has more permeability in early ages but later permeabilty becomes lower. Carbonation It has no effect on carbonation.

REFERENCES Ø COIN Project report no 18 Sigrun Kjær Bremseth (Norcem) Fly ash in concrete a literature study of the advantages and disadvantages Ø Post Gradue Thesis, ITU Emrah Gürbüz C-Type Fly Ashes Ø Effect of Fly ASH on Properties of Concrete P. R. Wankhede V. A. Fulari Assistant Professor IBSS College of Engineering, Amravati Ø Semsi Yazici & Hasan Sahan Arel Department of Civil Engineering, Engineering Faculty, 35100 ˙Izmir, Turkey ―Effects of fly ash fineness on the mechanical properties of concrete‖.