Interface-durability correlations in concrete

The performance of concrete is dictated mostly by the characteristics of the transition zone. Internal bleeding leads to a higher effective water/cement ratio and hence a more open, porous structure at the cement/aggregate interface. Besides, more of AFt, AFm and CH phases and halides, sulphate, alkalis and other admixture components and less of C-S-H are found in this zone. These cause the deterioration of the reinforcing materials like steel, silicious aggregates, glass and natural fibres. The orientation of the crystalline phases parallel to the interface also weakens the mortar. The porosity and related effects are considerably modified by the use of plasticizers, fine pozzolanic additives and reduced water cement ratio. The mechanism of interfacial structure formation and their resulting effects on the reinforcement are discussed together with the possible precautionary measures.