EFFECT OF AIR COOLED BLAST FURNANCE SLAG AND METAKAOLIN ON COMPRESSIVE AND FLEXURAL STRENGHTH OF CONCRETE CONTAINING FLY ASH

Abstract

Concrete is the most commonly used construction material in the world. Concrete is extensively used in infrastructure projects. The concrete obtained by mixing cement, water and an inert matrix of sand and gravelundergoes a number of operations such as transportation, placing, compacting, finishing and curing.

Pozzolanic materials including flyash, metakaolin, slag, Rice Husk Ash and silica fume have been used in recent years as cement replacement material for developing HSC with improved workability, strength and durability with reduced permeability. Metakaolin, which is a relatively new material in the concrete industry is effective in increasing strength, reducing sulphate attack and improving air-void network. Pozzolanic reactions improve the microstructure of concrete and chemistry of hydration products by consuming the released calcium hydroxide (CH) and production of additional calcium silicate hydrate (C-S-H), resulting in an increased strength and reduced porosity and therefore improved durability.

Use of Metakaolin in construction industry as partial replacement of cement started in the 1960’s and the interest in this material has considerably increased in recent years. Metakaolin has pozzolanic properties bringing positive effects on resulting properties concrete. Pozzolanic properties cause chemical reaction of active components with calcium hydroxide (portlandite), which is formed as a product of cement hydration. This reaction leads to formation of binding phases of following types: secondary C-S-H gel, C4AH13, C3AH6, and C2ASH8 thereby increasing strength.

The Air cooled blast furnance slag (ACBFS) has also been used as partial replacement of coarse aggregates in the recent past . In the previous studies it has been confirmed that the concrete made with natural aggregates and with ACBFS has comparable compressive.