- Blast furnace granulated slag
is a by-product of the metallurgical industry. By its origin, slag is a burnt residue of waste iron ore, which contains compounds similar in chemical composition to the minerals of portland cement clinker. These compounds are formed due to high-temperature treatment and subsequent rapid cooling. One of the strong arguments favouring this material for cement production is its hydraulic properties. The binding properties of blast furnace granulated slag are activated in the course of grinding in cement mills and as a result of chemical interaction with clinker minerals and gypsum.
in the aquatic environment becomes chemically active towards certain elements of portland cement clinker and chemically reacts with its minerals. Eventually, strong compounds are formed in the contact zones.
The reasons to choose cement with mineral additives:
Higher frost resistance, water impermeability and durability of concrete
Concretes made with cement with additives have a denser structure. When cement with granulated blast furnace slag is used, both clinker and slag are involved in the setting process, so the reaction results in more complex minerals than cement without additives. Meanwhile, fine limestone fills the voids between cement grains, improves the reaction between them and the water, and promotes the formation of denser cement stone by reducing the total porosity.
Even greater strength over the years
In the initial stages, blast furnace slag cement gains strength slightly more slowly than ordinary portland cement. However, after two weeks, strength gaining is accelerated. From the 7th month, it increases to 50% of the declared strength class (depending on the blast furnace granulated slag content in the cement).
Lower risk of cracks during the construction of solid structures
The presence of blast furnace granulated slag in cement helps to reduce the hydration temperature, decreasing the temperature difference during the construction of solid structures and, consequently, reducing the risk of cracking.
Lower risk of efflorescence
Cement with active mineral additives contains less soluble substances that, in the process of hydration (interaction of cement with water), migrate to the surface of the concrete product to form efflorescence.
More convenient pouring of concrete
The concrete based on cement containing blast furnace granulated slag sets more slowly due to blast furnace slag cement's slowed down the setting process and the lower hydration temperature. That is why it is recommended to use cement with slag in hot weather. Cement without additives quickly loses workability at high temperatures.
High resistance to aggressive environments
Blast furnace granulated slag increases the resistance of cement stone to aggressive environments: sulphate resistance, acid resistance, resistance to alkaline aggressions, seawater, carbonisation, etc. All this is due to a reduced content of Ca(OH)₂ and the hydration products of the aluminate phase of the portland cement clinker in the cement stone.
The cost of production of cement with additives is lower, so the price of such cement is lower.
Caring about the environment
Clinker production involves quarrying for minerals and then burning them, which leads to СО₂ emissions. The production of 1 t of clinker is accompanied by the release of 1 t of СО₂. When part of the clinker in cement is replaced with active mineral additives, it helps reduce СО₂ emissions and solve environmental problems such as global warming and depletion of natural reserves.