Slag cement improves many of the strength and durability properties of hardened concrete.  Slag cement is a hydraulic binder that, like portland cement, reacts with water to form cementitious material (calcium-silicate hydrate or CSH).  It also, similar to a pozzolan, consumes by-product calcium hydroxide from the hydration of portland cement to form additional CSH.  The resulting cement paste is stronger and denser, thus improving the concrete.

A list of improvements to hardened concrete follows, with a link to individual Slag Cement in Concrete information sheets for further detail:

• Improved compressive and flexural strength (SCIC #14)
• Reduced permeability, and resistance to chloride intrusion and corrosion (SCIC #6)
• Ability to mitigate moderate to severe sulfate attack (even when used in combination with Type I cements - SCIC #7)
• Ability to mitigate alkali-silica reaction with reactive aggregates (even when used with higher-alkali cements - SCIC #8)
• Reduced thermal stress in mass concrete through lower heat generation (SCIC #9)