GGBS particularly useful in basements, denser, lower permeability, more watertight, and extra protection against aggressive groundwater soils.
GGBS particularly useful in basements, denser, lower permeability, more watertight, and extra protection against aggressive groundwater soils.
35% vs 20% SiO2 40% vs 65% CaO 10% vs 5% Al2O3
Chloride ions are bound into chloroaluminates far more effectively than Portland cement pastes Lower permeability limits ingress of chlorides At 50% and greater, diffusivity of chloride ions becomes insignificant - Substitution levels of 70% to 80% often used To prevent the penetration of chloride ions a dense, impermeable concrete needs to be produced. This can be achieved by using Ground Granulated Blast furnace Slag (GGBS). When GGBS cement hydrates, dicalcium silicate and tricalcium silicate are formed. However, the reaction also produces other secondary hydrates, which effectively fill the cement paste pores. This is because there is an excess of reactive alumina and silica in the material. Both these compounds are free to react with the excess calcium hydroxide, which is present in the pores of cement paste to form further calcium silicate and calcium aluminate hydrates. These block the pores and reduce the permeability of the cement paste. In addition, GGBS cements are able to bind the penetrating chlorides into chloro-aluminates far better than cement pastes containing pure Ordinary Portland Cement or Sulphate Resistant Portland Cement. This reduces the danger of chloride attack still further. Sulphate Resistant Portland Cement has a reduced binding ability because of the low tricalcium aluminate content. GGBS cement has a slower rate of hydration than Ordinary Portland Cement helps in reducing the permeability of concrete as cracking due to temperature rise is minimised.
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