Ground granulated blast furnace slag (GGBS)

What is GGBS and How it is Manufactured?

Ground granulated blast furnace slag (GGBS) is a by-product from the blast-furnaces used to make iron. furnaces are fed with a controlled mixture of iron-ore, coke and limestone, and operated at a temperature of about 1,500°C.The granulated slag is further processed by drying and then grinding in a vertical roller mill of rotating ball mill to a very fine powder, which is GGBS.

Hardened concrete

Compressive strength and strength development:

The rate of hydration reaction of GGBS concrete is temperature dependent.GGBS has a higher activation energy than OPC and therefore their higher their reaction rate is more sensitive to temperature change. As the temperature increases the rate of gain of strength in GGBS blend concrete is greater than OPC concrete. The influence of temperature on strength development is of significance when considering the behaviour of concrete in-situ.In such situation, the rate of strength development and ultimate strength may be appreciably different from that indicated by standard cured cubes.

Tensile Strength & Elastic Modulus

Compared to concrete produced with only OPC, the GGBS blend produced concrete tend to have a slightly higher tensile strength and elastic modulus for a given compressive strength.

Surface Finish

Generally, GGBS makes it easier to achieve a good surface finish. In addition, the colour of concrete will be lighter than concrete produced with only OPC.

Durability

Durability of concrete is related to its permeability or diffusion to liquids and gases and its resistance to penetration by ions such as Cl and SO3+. Generally speaking, provided the concrete is well cured GGBS blended concrete is likely to be more durable than similar concrete produced with only OPC.

Alkali-Silica Reaction

Use of GGBS blend with OPC is one of the ways to reduce the Alkali-Aggregate Reaction when aggregate used in concrete is alkali reactive. Use of GGBS with OPC reduces the total alkali content in the cementitious material. Thereby, deterioration of concrete due to alkali-aggregate reaction could be avoided.

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Sulphate Resistance

Concrete containing GGBS are acknowledged to have higher resistance to attack from sulphates than those made with only OPC. This is due to overall reduction in C3A level of concrete and to the inherent reduction in permeability.

Chloride Ingress

blended concrete is significantly more resistant to the ingress of chloride ions in concrete apart from reduced permeability.OPC used with GGBS blend chemically binds the chlorides with slag hydrates effectively reducing the mobility of chlorides thereby reducing the reinforcement corrosion risk.

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Alkalinity

Despite the reduction in Ca(OH)2 caused by secondary slag hydration reactions the pH of paste remains at a level which is well in excess of that which would affect the passivity of the reinforcing steel.

GGBS – A sustainable material for Green building construction

Replacing the Portland cement by help in reducing CO2 emissions and in conserving non-renewable resources of limestone.GGBS blended concrete is significantly more resistant to the ingress of chloride ions in concrete apart from reduced permeability.