WHAT IS CURING AND WHAT DOES IT DO TO THE CONCRETE? When most people think of curing, they think only of maintaining moisture on the surface of the concrete. But curing is more than that — it is giving the concrete what it needs to gain strength properly. Concrete strength depends on the growth of crystals within the matrix of the concrete. These crystals grow from a reaction between Portland cement and water — a reaction known as hydration. If there isn't enough water, the crystals can't grow and the concrete doesn't develop the strength it should. If there is enough water, the crystals grow out like tiny rock-hard fingers wrapping around the sand and gravel in the mix and intertwining with one another. Almost sounds like a horror movie — our concrete baby has turned into a monster! The other important aspect of curing is temperature — the concrete can't be too cold or too hot. As fresh concrete gets cooler, the hydration reaction slows down. The temperature of the concrete is what's important here, not necessarily the air temperature. Below about 10 C, hydration slows down a lot; below about 4.5 C, it virtually stops. Hot concrete has the opposite problem: the reaction goes too fast, and since the reaction is exothermic (produces heat), it can quickly cause temperature differentials within the concrete that can lead to cracking. And cement that reacts too quickly doesn't have time for the crystals to grow properly so it doesn't develop as much strength as it should. Improper curing is considered as one of the significant reasons for concrete failures in columns, beams, slabs, pavements, etc, evident in the form of cracks, which are easily noticeable by the naked eyes. The vertical member like a column, in particular, is one of the most victimized RCC elements which must be carefully cured, as the entire load from the slabs and beams are supported by columns and transferred to the foundations. Unfortunately, adequate curing is not given much importance at most of the sites leading to reduction in the durability of the structure. Curing of concrete plays a major role in developing the microstructure and pore structure of concrete. Curing of concrete means maintaining moisture inside the body of concrete during the early ages and beyond in o rder to dev elop the d esired prop erties in t erms of stre ngth & du rability. A good curing pra ctice involves keeping the concrete damp until the concrete is strong enough to do its job. However, good curing practices are not always religiously followed in most of the cases, leading to a weak concrete. This article summarizes various aspects of curing of concrete which can be of valuable assistance in adopting good construction practices at site. Concrete strength gain - Concrete strength increase with age as moisture and a favourable temperature is present for hydration of cement. An experimental investigation was conducted by "Cement, Concrete & Aggregates Australia" (CCAA) and the same was published in their data sheet on "Curing of Concrete," which has been included in this article for reference. Figure-1 illustrates a comparison of the strength of concrete at 180 days of moist curing with various periods of moist curing (0, 3, 7, 14 & 28 days) and then allowing it to dry out. From the graph below, it can be observed that concrete allowed to dry out immediately, achieves only 40% of the strength of the same concrete water cured for the full period of 180 days.

What is Curing and What Does It Do to the Concrete

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WHAT IS CURING AND WHAT DOES IT DO TO THE CONCRETE?

When most people think of curing, they think only of maintaining moisture on the surface of the concrete.But curing is more than that — it is giving the concrete what it needs to gain strength properly. Concretestrength depends on the growth of crystals within the matrix of the concrete. These crystals grow from a

reaction between Portland cement and water — a reaction known as hydration. If there isn't enough water,the crystals can't grow and the concrete doesn't develop the strength it should. If there is enough water,

the crystals grow out like tiny rock-hard fingers wrapping around the sand and gravel in the mix andintertwining with one another. Almost sounds like a horror movie — our concrete baby has turned into amonster!

The other important aspect of curing is temperature — the concrete can't be too cold or too hot. As freshconcrete gets cooler, the hydration reaction slows down. The temperature of the concrete is what'simportant here, not necessarily the air temperature. Below about 10 C, hydration slows down a lot; belowabout 4.5 C, it virtually stops.

Hot concrete has the opposite problem: the reaction goes too fast, and since the reaction is exothermic(produces heat), it can quickly cause temperature differentials within the concrete that can lead tocracking. And cement that reacts too quickly doesn't have time for the crystals to grow properly so it

doesn't develop as much strength as it should.

Improper curing is considered as one of the significant reasons for concrete failures in columns, beams,

slabs, pavements, etc, evident in the form of cracks, which are easily noticeable by the naked eyes. The

vertical member like a column, in particular, is one of the most victimized RCC elements which must be

carefully cured, as the entire load from the slabs and beams are supported by columns and transferred to

the foundations. Unfortunately, adequate curing is not given much importance at most of the sites leading

to reduction in the durability of the structure.

Curing of concrete plays a major role in developing the microstructure and pore structure of concrete.

Curing of concrete means maintaining moisture inside the body of concrete during the early ages and

beyond in order to develop the desired properties in terms of strength & durability. A good curing practiceinvolves keeping the concrete damp until the concrete is strong enough to do its job. However, good

curing practices are not always religiously followed in most of the cases, leading to a weak concrete. This

article summarizes various aspects of curing of concrete which can be of valuable assistance in adopting

good construction practices at site.

Concrete strength gain - Concrete strength increase with age as moisture and a favourable

temperature is present for hydration of cement. An experimental investigation was conducted by

"Cement, Concrete & Aggregates Australia" (CCAA) and the same was published in their data sheet

on "Curing of Concrete," which has been included in this article for reference. Figure-1 illustrates a

comparison of the strength of concrete at 180 days of moist curing with various periods of moist

curing (0, 3, 7, 14 & 28 days) and then allowing it to dry out. From the graph below, it can beobserved that concrete allowed to dry out immediately, achieves only 40% of the strength of the same

concrete water cured for the full period of 180 days.