In normal concrete work, the maximum compressive strength that can possibly be obtained is generally reckoned to be about 7,500 psi for a 28-day cylinder. It would be interesting to know if there is a conceivable maximum limit using materials and techniques available.
The limit at the moment seems to be 16,000 psi, although this can be obtained only under laboratory conditions. Using crushed rock or granite aggregates in an aggregate/cement ratio of 3:1 and pressure compaction, 6-inch cubes with a 14,000 psi strength at between 28 and 36 days can be obtained without any great difficulty. It would appear that the achievement of maximum density depends on the development of some radically new type of vibrator, possibly ultrasonic.