Name: concrete shrinkage as water evaporates
Uploaded: 2024-11-07T14:48:42.000Z
Duration: 1 min 21 s
Channel: JoVE

When hardened concrete is exposed to unsaturated air, the free water present in its capillaries evaporates out of the pores.
This causes the movement of water adsorbed on the large surface area of calcium silicate hydrates present in the cement paste into the dried-out capillaries. This water eventually evaporates out of the concrete.
As a result, the volume of the cement paste reduces with time, causing contraction in concrete, known as drying shrinkage.
However, some drying shrinkage is reversible if the concrete is exposed to external moisture. The cement paste absorbs the moisture and undergoes wetting expansion.&#160;
The irreversible portion of drying shrinkage results from the rearrangement of particles as gel pores collapse and the formation of&#160; Si-O-Si bonds within the cement gel upon removing adsorbed water.
If the concrete member subjected to drying shrinkage is free to move, it will experience an increase in strain with time while the stress will remain zero.
Alternatively, if the member is restrained during drying shrinkage, the strain will be zero, and tensile stresses will develop in the member over time.

drying shrinkage

Drying Shrinkage

When hardened concrete is exposed to air with a relative humidity of less than 100 percent, it begins to lose the free water within its capillaries. As this water evaporates, the water initially adsorbed onto the calcium silicate hydrates migrates towards these now empty spaces and eventually evaporates as well. Over time, as more water leaves, the volume of the concrete decreases, a phenomenon known as drying shrinkage.
A portion of this drying shrinkage can be reversed; if the concrete is later exposed to moisture, it can reabsorb water and expand slightly. However, not all shrinkage is reversible. Permanent changes occur as new physical and chemical bonds form between the hydrates in the cement paste when they lose water. The extent and reversibility of drying shrinkage are influenced by factors such as the duration of wetting and drying periods, the relative humidity of the air, and the composition of the concrete, along with the degree of hydration at the onset of drying shrinkage.
The behavior of concrete under drying shrinkage also varies depending on whether it can move freely. In unrestrained concrete, the material experiences deformation over time without developing stress within it. However, if movement is restricted, no deformation is observed. Instead, tensile stresses build up as the concrete tries to shrink but is held in place.

When hardened concrete is exposed to unsaturated air, the free water present in its capillaries evaporates out of the pores.
This causes the movement of ...

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JoVE Core

Civil Engineering

Unit 1

Elasticity, Creep, and Shrinkage in Concrete

elasticity-creep-and-shrinkage-in-concrete

KEY TERMS AND CONCEPTS

concrete shrinkage as water evaporates

Concrete shrinkage happens when hardened concrete loses water to air with a relative humidity below 100 percent. Free water in the capillaries evaporates first. Then water that was adsorbed, or held on the calcium silicate hydrates, moves into these empty spaces and evaporates too.

As more water leaves, the concrete volume decreases. This is called drying shrinkage. Some of this change can be reversed. If the concrete later meets moisture, it can take in water again and expand slightly.

Not all of the shrinkage goes away. Some permanent change occurs because new physical and chemical bonds form between the hydrates in the cement paste as they lose water. How much drying shrinkage happens, and how much can be reversed, depends on the length of wetting and drying periods, the air’s relative humidity, the concrete’s composition, and how hydrated it was when drying shrinkage began.

The effect also depends on whether the concrete can move freely. In unrestrained concrete, the material deforms over time without stress building inside it. If movement is restricted, the concrete does not visibly deform. Instead, tensile stresses develop as the concrete tries to shrink but is held in place.

Concrete Shrinkage as Water Evaporates

elasticity in concrete

Concrete Stress-Strain Modulus Methods

Concrete shows a non-linear stress-strain response when it is loaded in uniaxial compression or tension at moderate to high stress levels. As the load is removed, the stress-strain path does not return along the same line. This creates a hysteresis loop and shows that concrete is not perfectly elastic. The modulus of elasticity is used to describe stiffness. In many materials, it is taken from the slope of the linear part of the stress-strain curve. Concrete does not have a simple linear...

dynamic modulus of elasticity of concrete

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Sonic Testing of Concrete Beams

Sonic testing of concrete beams is used to measure the dynamic modulus of elasticity. This value describes how a concrete specimen deforms under impact or other dynamic loads. It is usually higher than the static modulus of elasticity, which is measured under slow, steady loading. A common test uses a concrete beam that is either 6 x 6 x 30 inches or 4 x 4 x 20 inches. The beam is clamped at its center. Vibrations start at one end with an electromagnetic exciter unit powered by a...

creep in concrete

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Concrete creep is the time-dependent increase in strain under a sustained load. It is different from shrinkage, swelling, and thermal expansion, which are other time-based changes in concrete. When concrete stays under constant stress, its shape can slowly change over time. The main cause of creep is the loss of physically adsorbed water from calcium silicate hydrate in the hydrated cement paste. Concrete also shows a non-linear stress-strain relationship, which adds to this behavior.

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Concrete creep depends on the materials in the mix, the load applied, and the curing environment. In normal-weight aggregate concrete, the hardened cement paste is the main part that creeps. The aggregates are stiffer than the cement paste, so they resist stress-induced deformation more effectively. Aggregate properties can change how much a concrete member creeps. The stiffness of the aggregates is described by their modulus of elasticity. When aggregates make up a larger volume of the...

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Creep in concrete is the slow deformation that happens when a load stays on a structure for a long time. It can change how beams, columns, bridges, and other concrete members behave over time. Engineers must account for it when they design safe and durable structures. In reinforced concrete beams, creep increases deflection, which means the beam bends more than expected. That extra bending can widen cracks and may require added design measures. In slender columns under eccentric loads, creep...

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Concrete Shrinkage and Crack Risk

Concrete shrinkage is the loss of volume that happens when water leaves the mix or when cement reacts and carbonates. This contraction creates volumetric strain in the material. In practice, engineers often measure shrinkage as linear strain, which is about one-third of the volumetric strain. Fresh concrete can also shrink while it is still plastic. This plastic shrinkage can reduce the volume by about 1% of the concrete’s absolute volume. It usually happens when water evaporates from the...

Concrete shrinkage happens when hardened concrete loses water to air with a relative humidity below 100 percent. Free water in the capillaries evaporates first. Then water that was adsorbed, or held on the calcium silicate hydrates, moves into these empty spaces and evaporates too. As more water leaves, the concrete volume decreases. This is called drying shrinkage. Some of this change can be reversed. If the concrete later meets moisture, it can take in water again and expand slightly. Not...

carbonation shrinkage

Concrete Carbonation and Steel Corrosion

Concrete carbonation begins when atmospheric carbon dioxide enters the pores of concrete. If moisture is present, the gas forms carbonic acid. That acid reacts with calcium hydroxide in hydrated cement and produces calcium carbonate. This reaction causes carbonation shrinkage, which means the concrete loses some volume. The calcium carbonate can also fill pores, so permeability drops slightly. At the same time, the water released during the reaction can help any unreacted cement continue...

types of non-structural cracks in concrete

types-of-non-structural-cracks-in-concrete

Concrete Cracks from Shrinkage and Heat

Non-structural concrete cracks can form during placement, curing, and drying. The main groups are plastic cracks, early-age thermal cracks, and drying shrinkage cracks. Another surface pattern called crazing can also appear when finishing or curing is not done well. Plastic cracks form while the concrete is still fresh. Plastic shrinkage cracks usually appear within hours after pouring. The top of the concrete dries faster than the lower part, which creates tensile stress. The soft concrete...

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Preventing Thermal Cracks in Large Concrete

Large concrete pours can build up heat and crack as they cool. This is a key challenge in mass concreting, such as the placement of concrete in gravity dams. Heat from cement hydration, which is the chemical reaction that hardens cement, can create a temperature difference between the inside and outside of the concrete mass. That temperature gradient may lead to thermal cracks. To lower that risk, the concrete mix is adjusted before placement. Low-heat cement and pozzolans are used to reduce...

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Managing Heat in Concrete Placement

Hot weather changes how concrete sets and cures. High temperatures speed up hydration, which makes the mix set faster. That faster set can lower the long-term strength of the finished structure. Low air humidity creates another problem. Water leaves the fresh concrete more quickly, so workability drops. This can also increase plastic shrinkage, which is shrinkage before the concrete hardens, and raise the chance of crazing, a network of fine surface cracks. Several simple steps can reduce...

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Preventing Freeze Damage in Fresh Concrete

Fresh concrete can be damaged if it freezes before it sets. When the water in the mix turns to ice, it expands. That expansion disrupts setting, slows the chemical reactions needed for hardening, and can leave more pores in the finished concrete. Those extra pores weaken the final structure. If the concrete gains enough strength before freezing, the damage may be reduced. Cold-weather protection focuses on keeping the concrete warm during and after placement. Mixing with warm water and heated...

key terms and concepts

Learn how hardened concrete loses water, shrinks over time, and may regain some volume when rewet. See how restraint can create tensile stress.

Concrete Shrinkage as Water Evaporates | JoVE K12

JoVE Core Civil Engineering offers a foundational exploration of essential construction materials such as bricks, stones, steel, wood, and concrete, along with fluid mechanics topics like flow over immersed bodies, open channel flow, and dimensional modeling. It also covers key surveying concepts, including leveling, traverse adjustments, curve design, topographic mapping, and geospatial technologies (GPS & GIS). Science-in-action videos showcase laboratory research on materials, fluids, and surveying practices in real-world engineering systems.

civil engineering

Concrete Shrinkage as Water Evaporates

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