Concrete is a three-phase material encompassing the cement matrix, aggregate and interfacial transition zones (ITZ) between the cement matrix and aggregate. The strength of concrete is affected by the properties of the ITZ that is developed between the aggregate and the mortar phase.

By using very fine and well-dispersed mineral additions, the initial W/C gradient around the aggregates is lowered and the ITZ is densified and strength will improved. The microstructure of the ITZ may be improved in the vicinity of calcareous aggregate, which reacts with calcium aluminates of Portland cement paste, forming calcium carbo-aluminates.

The properties of concrete microstructure can be analysed by SEM analysis which clearly indicates the ITZ at higher magnification. The cracks around the ITZ will be observed, and these cracks will be generated by the stress transformation which reduce the strength of concrete.

So, my recommendation is that please go through microstructure behaviour of concrete by using SEM analysis.

The paper entitled “Pulse velocity–strength and elasticity relationship of high volume fly ash induced self-compacting concrete” may gives the idea about microstructure of concrete.

Article Pulse velocity–strength and elasticity relationship of high ...

Dear Arup,

Please find the attached files for an in-depth explanation. I hope these files will help you in a better understanding of the issue.

Regards,

Pravin

ITZ is weak link among all three phase i.e. cement matrix, aggregate and interfacial transition zones (ITZ). Under loading, generally ITZ is failed first and that is why it very important. Microstructural analysis using methods like SEM will provide many information regarding status of ITZ and its effect on strength and durability of concrete. Selection of appropriate methodology is play a vital role in this type of study.