Engineers, supers and testing techs talk in breaks: 7-day breaks, 28-day breaks, the hold, a low break. Seven-day results usually land around 65 to 75 percent of the 28-day strength for a straight cement mix and lower for heavy SCM blends, so a weak 7-day number is an early warning. A low 28-day break sets off cores, extra holds and arguments about who added water.
Seven-day breaks came in at 2,600 on a 4,000 mix, call the plant and ask what changed.
The hold is a spare cylinder kept unbroken until the 28-day results are in, then broken to check a suspect low result or at 56 days for information.
Also heard as
- breaks
- cylinder break
- 7-day
- 28-day
Related terms
Cylinder
A cast concrete test specimen, usually 4 by 8 in or 6 by 12 in, crushed to measure compressive strength.
Compressive strength
The crushing load concrete can carry per unit area, the main property specified and tested for concrete.
f'c
Symbol for specified compressive strength, the design strength the engineer requires, usually at 28 days.
Core
A cylinder of hardened concrete drilled out of a structure to test its strength or inspect its condition.