Dear reader we have heard in previous posts about microstructure of concrete, here we will learn about a zone, an essential element of microstructure that control almost all properties of concrete which lies between aggregate and cement paste.
This zone is interfacial transition zone. In this discussion it plays important role, there lies microcracks in this zone. The extent and quantity of microcracks in this zone will be discussed in next post.
We know size of aggregate and its grading as well have influence on bleeding characteristics within concrete mixtures, thus influencing surrounding interfacial transition zone of aggregate.
During early age of concrete when hydration commenced for a while, the interfacial transition zone remain in week condition and have every possibility to be cracked. We know due to thermal shrinkage and drying shrinkage, differential strains are produced between aggregate particles and cement paste. The external superimpose load may also produce such strains.
The strains from these sources lead to crack in weak interfacial transition zone. This cracks generated in interfacial transition zone can not be seen with our naked eye. But don’t feel safe as they are sufficiently bigger than most of capillary cavities present in matrix of cement paste.
This system of microcracks is inter-connected by propagation process and increase permeability of system significantly. This is the microstructural cause of development of permeability.