Metakaolin and fly ash alkali-activated mortars compared with cementitious mortars at the same strength class

Alkali activated and cementitious mortars belonging to R1 ≥ 10 MPa, R2 ≥ 15 MPa and R3 ≥ 25 MPa strength classes are tested and compared in terms of workability, dynamic modulus of elasticity, porosimetry and water vapour permeability. Capillary water absorption, drying shrinkage, resistance to sulphate attack and corrosion behaviour of embedded bare and galvanized reinforcements have also been investigated. In alkali activated mortars, drying shrinkage is higher than that of cementitious mortars but restrained shrinkage is lower due to lower modulus of elasticity. Water vapour permeability is more pronounced in alkali activated mortars, and capillary water absorption is lower in those prepared with fly ash. The high alkalinity of alkali activated mortars was seen to delay the onset of the passive state in particular for galvanized reinforcements, but after one month of curing they were found to reach the same corrosion rates of those embedded in cementitious mortars.