Durability

The lifespan of traditional concrete can be reduced due to a range of external and internal pressures. Including GGBS in a concrete mix helps to protect from sources of damage and significantly improves the durability of concrete.

Sulfate attack

Concrete that has been made using traditional Portland Cement often suffers from cracks and weakening if exposed to soluble sulfates. This is due to the chemical reaction that takes place between the sulfates and compounds found in Portland Cement.

Sulfates naturally occur in the ground and, in severe cases of sulfate exposure, can pose a significant structural threat to concrete. Sulfate attack usually presents itself in one of three ways:

Ettringite: Tricalcium aluminate is found in Portland Cement and when exposed to sulfates, it reacts to form ettringite. This reaction results in chemical expansion, which in turn causes concrete to crack.

Thaumasite sulfate attack (TSA): Concrete’s strength and durability can also be undermined when sulfates and carbonates in concrete react at low temperatures (below 15°C). This reaction forms thaumasite, which gradually replaces the cement paste matrix of the concrete and results in structural weakness.

Alkali-Silica Reaction (ASR): Concrete structures exposed to moisture can be damaged due to the reaction between forms of silica found in concrete ingredients and alkali hydroxide. This reaction causes a gel to form, which swells as it absorbs water, leading to cracking and structural damage.

How GGBS helps:
The use of GGBS as a cement replacement is proven to improve the strength and resistance of concrete against sulfate attack by reducing water absorption and concrete permeability.  

 

Chloride attack

Due to the high alkaline environment created when hydrating cement during the construction of reinforced steel, protective oxide films are formed on the surface of steel reinforcements. However, this protective layer is eroded when exposed to chloride.

The permeable nature of certain types of cement, such as Portland Cement, makes concrete more vulnerable to chloride attack, as particles can penetrate concrete more easily. This results in the faster erosion of the protective film covering steel reinforcements and subsequent corrosion of steel reinforcements themselves.

How GGBS helps:
GGBS helps to create a denser concrete, which makes it more challenging for chlorides to penetrate the concrete and damage the protective film covering steel reinforcements.   

 

Thermal cracking

Thermal cracking in concrete can occur during the hydration of cement. Hydrating cement generates heat due to exothermic reaction and can lead to weakening of concrete and cracks. Thermal cracking can be especially problematic in mass concrete pours, when large amounts of heat energy are generated.  

How GGBS helps:
The use of GGBS helps to significantly reduce the heat of hydration during concrete pours and lowers temperature rises, reducing the risk of thermal cracking.

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Francis Flower (Northern) Ltd, Brigg Road, Scunthorpe, DN16 1AW