Investigation of the Mechanical Properties and Durability of Concretes Produced with Microsilica and Crystalline Admixtures

In order to enhance the durability of reinforced concrete structures and their protection against corrosion, the addition of various durability enhancing concrete admixtures to the composition of the mixtures is a catalytic factor, in addition to proper concrete mix design and correct execution of the concreting process. This durability enhancing concrete admixtures include permeability reducing admixtures, such as crystalline admixtures, as well as silica fume (microsilica). Crystalline admixtures reduce permeability, which is one of the key factors leading to premature concrete wear and corrosion of the reinforcement, sealing capillary pores and cracks through the crystal growth mechanism under the presence of moisture. Correspondingly, microsilica as a strong pozzolanic material has the ability to reduce porosity and create a denser structure in hardened concrete, acting equally beneficial on long-term durability. The durability testing of the specimens of the first experimental part was carried out through appropriate laboratory tests involving the determination of the compressive strength of each mixture, the depth of penetration of water under pressure and the deterioration of concrete, either due to carbonation or due to chloride ingress. Results indicate that addition of crystalline admixture enhances the durability of concrete against carbonation and chloride induced corrosion. These durability indicators are further enhanced when crystalline admixtures are used in combination with silica fume.