Ian's Guide to Industrial Manufacturing

Why Curing Is Critical When Making Concrete

Many construction projects rely extensively on concrete. This material has excellent hardened properties, and is effective in situations where you need something that's durable, strong and resistant to harsh environments (like salty or humid air). Concrete gets these properties from a process known as curing. Learn more about curing, and find out how this process helps create the most durable, long-lasting concrete.

Concrete composition

Concrete is essentially a mixture of air, Portland cement, various crushed rocks (aggregate) and water. Manufacturers mix Portland cement with water to create a paste, and then mix this paste with fine and coarse particles of rock. A chemical reaction (hydration) subsequently takes place, which allows the mixture to harden, forming the rock-like material that you will recognise as concrete.

A typical concrete mix has:

  • 10-15 percent cement
  • 60-75 percent coarse and fine aggregate
  • 15-20 percent water
  • 5-8 percent air

Manufacturers create strong, durable concrete by carefully mixing and proportioning these ingredients. For example, a mixture that doesn't have enough paste to fill the gaps around the aggregate particles will result in a porous concrete. A mixture that has too much cement mix will create a smooth surface, but the concrete is likely to crack easily. High-quality concrete comes when the water-cement ratio is as low as possible. 

The benefits of curing

To make sure your concrete is as strong as possible, you need to control the amount of moisture the hardening concrete loses. You also need to keep the concrete within a reasonable temperature range. This process is known as curing. Curing can also prevent cracks in the concrete, and can cut the amount of cement you need in the overall mixture. In turn, this process can also help you save money and lower your carbon footprint because cement production uses a lot of energy.

The most critical period for curing is immediately after you place the concrete because the sun's heat and the wind can quickly dry out concrete. Indeed, concrete that dries naturally without curing will generally only have half the strength of cured concrete.

Curing methods

Construction companies generally use three curing methods:

Moist curing keeps water in the concrete during the early hardening period. If you're curing a flat surface, you can use small sand dikes to flood the concrete surface. You can also use lawn sprinklers or hoses to continuously spray or fog the concrete surface. Alternatively, you can keep the concrete surface moist with water-saturated materials.

A method called sealing stops water evaporating from the hardening concrete. You can use various materials for this purpose, including plastic sheets, liquid membrane-forming compounds and impervious paper. The material you use will vary according to the surface area, your budget and the weather conditions.

Steam curing accelerates the concrete's strength by applying heat and moisture to the concrete. You can cure concrete with steam, either at high or atmospheric pressure. If you follow the process correctly, you can boost the concrete's strength in 3 days to the same level that would normally occur after 28 days, so this method is particularly useful when you are short of time.

The impact of weather

The prevailing weather conditions can significantly impact the results of curing. During normal weather, most curing methods will work, as long as you keep the concrete temperature above 5 degrees. In hot temperatures, the main problem is that the concrete will quickly lose moisture. In these conditions, you will need to moist cure the concrete throughout the entire curing period.

Cold weather curing is difficult because it's hard to keep the concrete at the right temperature for hydration. In this case, steam curing often works well, particularly on smaller areas, as you apply moisture and heat simultaneously.

That aside, curing normally lasts for at least seven days. Steam curing can shorten this period to three days.

Curing is an essential part of working with concrete. Without this process, the finished product is often not durable and won't have the strength you need for your construction project. If you are not confident in your ability to correctly cure the concrete, the best option is often to work with a precast concrete contractor.