English to German Tech/Engineering Mechanics / Mech Engineering

Where sand is expensive, a minimum of sand should be used, conversely where aggregates are comparatively expensive for reason of run of pit sizes, necessity to crush, etc., a minimum of aggregate of highest cost are used.
Generally, where sand is expensive, sand is reduced and maximum aggregate size is increased and, conversely where sand is cheap and aggregates expensive, sand is increased.
We have used up to 42% sand and down to 26% with aggregate adjusted accordingly.
In some areas where certain sizes are short or of value for other purposes, ***blank or gap grading*** of the “short” sizes is practiced and has been found practical.
There is no relief from the monetary necessity to actually try the most economic mix versus theoretical designed mix, and make cylinders and beams to comparatively test them.