Accelerator
An admixture that speeds up setting and early strength gain, used mainly to shorten the vulnerable window in cold weather or to open a slab to traffic sooner.
What does accelerator mean?
Accelerators do not warm the concrete or prevent freezing; they compress the timeline so the concrete reaches a safe strength faster. Traditional calcium chloride accelerators are effective and cheap but introduce chlorides that promote corrosion of embedded steel, so non-chloride versions are used around reinforcement and in colored concrete. Faster setting also means a shorter finishing window, which catches crews off guard.
In practice
Winter flatwork often arrives with accelerator dosed at the plant, and the crew has noticeably less time to bull float and finish than they expect.