Curing of concrete is the process of maintaining requisite moisture and temperature in hardened concrete for continued hydration. The curing of concrete plays a prime role in maintaining the design strength and durability of concrete. This article explains the significance of curing, and the types of curing methods prevailing in construction sites.
Curing of concrete
Curing is the process that helps in maintaining moisture to allow fresh concrete to attain its desired strength in a planned manner through a hydration reaction. Concrete is a mixture of cement, aggregates, and water in fixed designed proportions calculated based on certain strength requirements. The primary factor in these proportions is the water to cement ratio (Water cement ratio). The water-cement ratio is to be maintained for hydration reaction. If the water evaporates quickly ,sufficient amount of water will not be available for the hydration process.
The curing of concrete helps to retain the concrete moisture until the hydration process is complete and concrete attains the requisite strength. American Concrete Institute (ACI) Committee 301 recommends a minimum curing period corresponding to concrete attaining 70 percent of the specified compressive strength. The curing time of 7 days/10 days as per IS codes and construction practices represent the time required to attain at least 70 % of the designed compressive strength.
Also Read : Concrete Mixing- Objectives and Types
Curing of concrete – Significance
Perfect curing is required to attain good strength and serviceability and is necessary due to the following reasons.
- By protecting the moisture loss, curing prevents concrete drying and maintains the recommended temperature range. Curing increases the strength and decreases the permeability of hardened concrete.
- Prevents cracks from developed due to thermal and plastic shrinkage.
- Helps in maintaining good bonding with reinforcement and ingredients.
- Provides a crack-free durable concrete with desired strength.
- Helps in attaining high serviceability performance by increasing abrasion resistance.
Curing time as per IS 456-2000
The Indian Standard IS 456 – 2000 recommends that the curing duration of concrete must be at least seven days in the case of ordinary Portland Cement, at least ten days for concrete with mineral admixtures or blended cement are used. It also recommends that the duration should not be less than ten days for concrete exposed to dry and hot weather conditions and 14 days with mineral admixtures or blended cement in hot and dry weather.
OPC cement = 7 Days (Normal conditions) and 10 Days ( Hot and dry weather)
Concrete with mineral admixture or blended cement (PPC cement) = 10 Days (Normal conditions) and 14 Days ( Hot and dry weather)
Concrete curing methods
The curing method and time primarily depend on structure type, site conditions, and ingredient parameters. Some of the curing methods adopted in constructions sites are as follows.
- Water curing
- Membrane Curing
- Steam curing
Water curing is the most popular and common method of curing concrete. This method maintains or retains water on the concrete surface by various methods. This includes ponding, sprinkling and fogging, and saturated wet coverings or left-in-place forms.
These methods prevent water loss from the concrete surface by continuous wetting of the exposed surface of the concrete.
The basic concept of membrane curing is reducing the loss of water from the surface of the concrete. Membrane curing methods uses curing compounds or impervious plastic sheets. Curing compounds are available in water-based and acrylic-based types. They form an impermeable membrane and reduces the loss of moisture.
The steam curing process accelerates the process of strength gaining by using heat and providing additional moisture. This speeds up the early hardening process. These methods are familiar in prefabricated structures and factory-made precast components for the speedy recovery of form works.
Steam curing keeps the surface moist and raises the concrete temperature to speed up the strength achievement rate.
Now a days curing activity is not taken seriously and this hampers the strength and quality. This is an activity to be done with utmost care to ensure design strength and serviceability of structures.