On site, it's tempting to think of curing as a purely material problem: mix design, water–cement ratio, cement type. But the environment around the fresh concrete is just as important.
If the air is hot, dry or windy, concrete can lose water too fast. If it's cold or near freezing, hydration slows and early strength stays low for longer. Over the life of the structure, those early curing conditions influence final compressive strength and stiffness, shrinkage and cracking risk, and durability under freeze–thaw, de‑icing salts and other exposures.
Temperature and humidity during curing: strength and freeze–thaw resistance
Concrete strength development depends on cement hydration, which is strongly temperature‑dependent. At low temperatures, hydration slows; at very low or negative temperatures, it can almost stop, leaving a porous, weak microstructure for a long time.
Recent studies of curing temperature and freeze–thaw performance show that:
- Lower curing temperatures (e.g. around 5 °C or below) lead to lower early compressive strength compared with standard curing at ~20 °C, because less hydration product has formed.
- Concrete cured at lower temperatures tends to have higher porosity and more harmful pore sizes, which reduces freeze–thaw resistance.
- During repeated freeze–thaw cycling, specimens cured at lower temperatures accumulate damage and mass loss faster, with worse scaling and microcracking.
A 2022 Materials and Structures study showed that cool, sub‑optimal curing conditions accelerate damage evolution under freeze–thaw, and that both temperature and relative humidity during early curing influence long‑term durability.
Hot weather, rapid drying and curing methods
At the other extreme, hot, dry, windy weather drives rapid evaporation from the surface of fresh concrete. This can cause plastic shrinkage cracking in the first hours, high internal moisture loss later, increased drying shrinkage and permeability, and reduced durability.
A 2013 study on curing methods under hot weather conditions compared wet burlap curing with several curing compounds. Key findings included:
- Curing compounds significantly improved durability (lower water absorption, reduced chloride permeability) compared with no curing, even in hot conditions.
- Among the compounds tested, bitumen‑based curing compounds gave the best performance, followed by coal tar epoxy and acrylic; water‑based compounds were less effective at moisture retention.
- An initial period of wet curing (e.g. two days under wet burlap) before applying curing compounds further enhanced durability and strength.
While compressive strength differences between curing methods were modest, durability differences were marked, underscoring that hot‑weather curing is about more than just 28‑day strength.
Internal humidity, shrinkage and internal curing
High‑strength concretes, with low water–cement ratios and dense microstructures, are especially sensitive to internal drying and autogenous shrinkage. Research on internal curing has shown that:
- In conventional high‑strength slabs without internal curing, internal relative humidity can drop by more than 40% over the first 28 days, which correlates with significant autogenous shrinkage and cracking risk.
- With internal curing, the drop in internal humidity is much smaller, keeping internal RH above 95% for longer and reducing autogenous shrinkage.
Why local weather knowledge is essential on site
Meteorology affects concrete curing through several mechanisms: temperature controls hydration rate and freeze–thaw durability; relative humidity and wind speed control evaporation from the surface, shrinkage and cracking risk; solar radiation adds heat to exposed slabs, increasing surface temperature and evaporation.
Using on‑site weather stations and forecasts to track air temperature, relative humidity, wind speed and solar load gives engineers and contractors the information needed to choose appropriate curing methods, schedule pours to avoid the worst evaporative conditions, and adjust stripping times and loading schedules based on real early‑age strength development, not just calendar age.
Ultimately, good concrete is as much about managing the environment as it is about managing the mix.
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