What does an accelerator do in New Brunswick concrete?

An accelerator is an admixture added to concrete that speeds up the hydration reaction, causing the mix to set and gain strength faster than it normally would. In New Brunswick's climate, accelerators are most commonly used for cold weather pours — extending the usable construction season into late October and November when temperatures start dropping toward freezing.

The chemistry is straightforward. Concrete cures through a chemical reaction between cement and water called hydration. That reaction slows dramatically as temperatures fall — below 10°C it crawls, and below 0°C it can stop entirely, leaving the concrete permanently weakened. Accelerators counteract this by speeding up the reaction, generating more heat of hydration and pushing the concrete through its critical early strength gain before the cold can do damage. The target is getting the concrete above 3.5 MPa (roughly 500 PSI) as quickly as possible — that's the threshold below which freezing causes permanent structural damage.

Calcium chloride is the most common accelerator used in NB ready-mix operations. It's effective, affordable, and well-understood. A typical dosage is 1-2% by weight of cement. At 2%, it can cut initial set time nearly in half and significantly boost 24-hour strength. However, calcium chloride has an important limitation: it accelerates corrosion of steel reinforcement. For any reinforced concrete — foundations, structural slabs, retaining walls — non-chloride accelerators (such as calcium nitrite or proprietary non-chloride blends) are the correct choice, even though they cost more.

NB-Specific Considerations

In New Brunswick, accelerators are a tool — not a complete cold weather solution on their own. They work alongside other cold weather measures: heated mix water, heated aggregates, insulating blankets, and sometimes heated enclosures. The NB pouring window of May through October exists for good reason, and accelerators help push that window a few weeks in either direction, not eliminate the risk entirely.

One critical point: accelerators do not replace air entrainment. This is a mistake sometimes made on late-season NB pours. The accelerator helps the concrete gain strength before it freezes, but air entrainment (4-7% air content) is what protects the hardened concrete through 150+ annual freeze-thaw cycles for the life of the structure. Both are required for any exterior concrete poured in NB conditions — they serve completely different purposes.

Accelerators also reduce your working time. If you're placing a large driveway or patio slab, a faster-setting mix means the finishing window shrinks. Experienced NB concrete crews account for this by having enough hands on site to place, screed, float, and finish before the mix gets ahead of them.

Practical Guidance

If you're having concrete poured in September or October in NB, ask your ready-mix supplier and contractor directly whether an accelerator is being used, what type, and what other cold weather protection measures are planned. For any reinforced pour, confirm they're using a non-chloride accelerator. Insulating blankets should remain on the concrete for a minimum of 3-7 days depending on temperatures, and the concrete should not be exposed to freezing conditions during that period regardless of how fast it set.

Cold weather concrete in NB is absolutely doable — but it adds 25-40% to project costs when done properly. If your project can wait until May, that's almost always the better choice.

Need help finding a concrete contractor experienced with NB cold weather pours? New Brunswick Concrete can match you with local professionals for free through the New Brunswick Construction Network.