Measured under ASTM C403 by pushing needles into mortar sieved from the concrete: initial set comes at 500 psi of penetration resistance and final set at 4,000 psi. At 70 F an ordinary mix reaches initial set in about 3 to 5 hours, and every 18 F (10 C) of temperature change roughly halves or doubles that time. Placing, vibrating and screeding all have to be done well before it.
Lab says initial set is about four hours with the retarder, so the last truck has to be here by two.
Also heard as
- set
- time of set
Do not mix it up with
- Kick: Kick is the crew word for a load setting faster than expected, usually well ahead of the lab's initial set time.
Related terms
Kick
To start setting, usually sooner than the crew expected; a load that kicks stiffens fast.
Retarder
An admixture that delays setting, used in hot weather, on long hauls and for big continuous placements.
Accelerator
An admixture that speeds up setting and early strength gain, mostly used in cold weather.
Cold joint
An unplanned seam left where fresh concrete was placed against concrete that had already begun to set.
Hydration
The heat-releasing reaction of cement with water that turns the paste into solid binder.