For shrinkage cracks and leakages, the concrete mix is not the only responsible thing.
For the shrinkage cracks it mostly observed and recorded as improper supervision in doing concrete placing, compaction, finishing & curing etc.
If those things are taken care by the execution team, this problem can be solved.
As a QA QC Engineer, you shall train your execution team to do the proper placing, compaction, finishing and curing etc, if they still don't do or don't understand its significance and your management is serious about this issue, you have the authority to terminate such peoples who does not take things seriously, you can even terminate Project Manager if you found him involved in such act or has behavior issue towards Quality.
This issue is deemed as a classical problem of construction industry and its not taken seriously in many organizations at least here in India, in order to achieve a good concrete finish that too a crack free, requires lot of efforts in all activity involved in concrete. might be organizations are not paying right amount or its a huge resistance from contractor to do right at first time as he need to invest more to deploy good, skilled and required number of people to complete a task in proper way.