Strength, permeability and shrinkage cracking of silica fume and metakaolin concretes

Using mineral admixtures as cement replacement substance in concrete has a tendency to increase by the future in order to provide greater sustainability in construction industry. This paper investigates the effectiveness of metakaolin (MK) and silica fume (SF) on the mechanical properties, shrinkage, and permeability related to durability of high performance concretes. Mechanical properties were evaluated by means of compressive and splitting tensile strength. Water sorptivity and gas permeability tests were carried out to find out the permeation characteristics of the concretes due to the incorporation of MK and SF. Shrinkage behavior of the concretes with and without mineral admixtures were dealt through measurements of free shrinkage strains and weight loss of the specimens due to drying. Moreover, crack formation and propagation of the restrained specimens were observed to better understanding the effect of MK or SF incorporation on the restrained shrinkage properties. For concrete production, replacement levels of 5% and 15% of MK or SF by the weight of cement were assigned. Water-to-cementitious (w/cm) material ratios of 0.25 and 0.35 were used in production of concrete. The design strength level ranging from75 to 86 MPa was achieved. Test results revealed that replacement level of MK and SF had significant effects on the mechanical and especially durability characteristics of high performance concretes.

► Influences of metakaolin (MK) and silica fume (SF) on the properties of high performance concrete were examined.
► Compressive and splitting tensile strength of concretes was enhanced as a result of MK and SF incorporation.
► Gas permeability and sorptivity of MK concretes demonstrated a similar trend as SF concretes.
► Utilization of MK and SF decreased considerably the free shrinkage strains due to drying.
► Initial crack formation and propagation of restrained shrinkage specimens were significantly affected from MK and SF.