When is this schedule used?
- The early strength gain of many high performance mixes requires crushes before 24 hours.
- These mixes are used in a lot of construction applications requiring quick turnaround of formwork, or tensioning activities which are time-sensitive.
- Pre-24hr crushes generally involve keeping a lab open overnight and this can incur additional lab costs.
- Crushes can be omitted at your own discretion. It is common to remove any crushes falling on a Sunday, for example, due to lab opening hours.
How many samples are required?
28 samples (including 2 instrumented samples which should not be crushed)
General Crushing Guidance
A crushing schedule should be agreed in advance between the contractor and the appointed lab. The selection of a crushing schedule is the responsibility of the contractor, and this decision can be based on several factors, including:
- Application - certain applications will require understanding of the early strength gain of the concrete (eg. strength gain at <24 hours) whereas other applications will not.
- Mix type - Strength gain of the mix (eg. some high-performance mixes need crushes at <24 hours to characterise their initial strength gain)
- Lab availability - availability and opening hours of the lab (eg. some labs are not open on Sundays, so certain crushes can be removed from the schedule to accommodate this)
Crushes can be added or removed at the discretion of the contractor.
See 'crushing guidance' to compare our two example crush schedules.