Sulphate resistance and passivation ability of the mortar made from pozzolan cement with zeolite

Sulphate resistance and passivation ability of the mortars made from pozzolan cement of CEM IV/A (P) type according to European Standard EN 197-1 (zeolite blended cement with 60.82 mass% of PC clinker, 35.09 mass% of zeolite and 4.09 mass% of gypsum abbreviated as ZBC) and ordinary Portland cement (abbreviated as PC) are introduced. Resistance tests were performed in water and 5% sodium sulphate solution (both 20°C) for 720 days. The increased sulphate resistance of pozzolan cement relative to that of PC was found. The key quantitative insight into the hydrate phase behaviour is given by thermal analysis. This is due to pozzolanic reaction of zeolite with PC resulting in reduction of the formed Ca(OH) 2 opposite to the reference PC. Ability of pozzolan cements with 15 to 50 mass% of zeolite to protect steel against corrosion was verified in 20°C/85% RH-wet air within 180-day cure. Steel was not corroded in the mortars made with pozzolan cement containing up to 35 mass% of zeolite. Pozzolan cement of CEM IV/A (P) type containing 35 mass% of zeolite is a suitable cementitious material for concrete structures exposed to sulphate attack. Steel is protected against corrosion by this pozzolan cement in the same measure as the reference PC.