Comparison of fly ash, silica fume and metakaolin from mechanical properties and durability performance of mortar mixtures view point

• The contribution of silica fume and metakaolin to the strength was started as early as 3 days.
• For the fly ash this duration was 180 days.
• Mineral admixtures improved transport properties greater than mechanical properties.
• The presence of the mineral admixture and its type changed the ettringite morphology.

In this study the effect of cement replacement with fly ash, silica fume and metakaolin on the compressive strength, dynamic elastic modulus, chloride-ion penetration, water absorption, water sorptivity, and freeze–thaw and sulfate resistance of the mortar mixtures were comparatively investigated. In addition, micro-structural investigation was performed on some selected mortar mixtures, and regression analysis was applied on the sulfate resistance test results. It was observed that, the presence of the mineral admixture and its type changed the ettringite morphology. Besides, only ball-ettringite and a special type of ettringite were observed in the silica fume- and metakaolin-bearing mixtures, respectively. The needle-like and ball-ettringite formation were found in the fly ash mixtures. In the control mixture the needle-like, ball-ettringite and massive ettringite were detected. Overall test results revealed that the performance of the mixtures was arranged in descending order as silica fume-, metakaolin-, fly ash-bearing mixtures and the control one.