Internal Curing Concrete: Everything You Wanted to Know but Were Afraid to Ask
Define Internal Curing
When a concrete mixture is internally cured, a component that acts as a curing agent is introduced to it. It is possible to use saturated porous aggregates or superabsorbent polymers as the curing agent.
Define Superabsorbent Polymers
Concrete can also be internally cured by using superabsorbent polymers. If SAP comes into contact with water, it swells and becomes gel like. A superabsorbent polymer swell between 20 and 2000 times its own mass in water. Upon contact with other ionic substances, such as salt, the superabsorbent polymers release the absorbed water.
Workflow of Internal Curing
An internal curing of concrete depends on three main parameters: the volume of water supplied by lightweight aggregate, it’s desorption properties, and the spacing between lightweight aggregates.
Chemical shrinkage and auto shrinkage determine the volume of lightweight aggregate required. Water is required from lightweight aggregate by the difference between these two elements.
Curing internally requires large, well connected pores in the internal reservoir, which are larger than those found in cement paste.
The cement paste's capillary pores are refined during cement hydration, and their radius is smaller than that of lightweight aggregate pores. As a result, water can flow more easily between the aggregate and cement paste.
In hydrating mixtures, water movement determines the spacing of lightweight aggregates. It is recommended to use a greater quantity of lightweight aggregate if the mixture is highly impermeable.
Water in lightweight aggregates can travel up to one mm, so most of the cement paste will remain intact. Moisture movement within a mixture is affected by the amount of lightweight aggregate substituted for normal weight aggregate.
Purpose of Internal Curing
Lightweight aggregates such as expanded shale, slag, pumice, perlite, and clay are suitable for internal curing instead of normal strength aggregates.
It is important to note that internal curing of concrete does not replace surface curing, but it works in conjunction with it to produce better concrete. By using it, you can compensate for poor, plain concrete that commonly occurs on construction sites, and for rainy weather conditions that may negatively impact the strength development of concrete.
The humidity gradient and capillary pressure develop once the relative humidity is reduced as a result of chemical shrinkage and self-desiccation. During this process, suction is created that pulls water from the lightweight aggregates into the hydrating or drying cement paste, which assists in cement hydration.
As the cement paste hydrates, the pores get smaller and create more suction force, which draws more water from the reservoir. If the lightweight aggregate is not hydrated, or if the relative humidity of the hydrating cement paste is less than that of the internal reservoir, water movement will not stop.
Benefits of Internal Curing
As the concrete hydrates in the internal portion, external curing has a marginal effect on the hydration, whereas internal curing is specifically beneficial for concrete with a low water Cementitious ratio. By curing internally, concrete can reach its full potential economically and sustainably.
A pre-wetted absorbent material containing moisture is used in internally cured concrete. The moisture is dispersed throughout the concrete as the internal humidity drops below 100 percent to keep cement paste saturated, resulting in greater cement hydration. Concrete becomes stronger and more durable as a result of the proper Internal curing.
To learn more, watch the following video tutorial.
Video Source: American Concrete Institute
Uses of Internal Curing
Building bridges, pavements, and similar transportation infrastructure is highly beneficial and practical when internal curing is used. In addition to continuously reinforced concrete pavements, white toppings, ultra thin white toppings, and jointed plain concrete pavements, it is potentially applicable for the construction of a white topping.
Merits of Internal Curing
The internal curing process increases cement hydration within the concrete, resulting in increased strength, reduced permeability, reduced warping, increased resistance to cracking at a young age, and improved dimensional stability. The concrete has an improved resistance to freezing and thawing cycles, deicing chemicals, and chemical attacks as well as improved creep resistance.