Why are expansion joints made in concrete structures

From sidewalks and driveways to big commercial buildings and bridges, concrete is a strong and adaptable material used in many different construction projects. To ensure longevity and structural integrity, concrete, like all materials, has limitations and characteristics that must be managed. The use of expansion joints is a crucial component of concrete construction.

Excavation joints are precisely positioned openings in concrete constructions. Although these gaps might not seem like much, they are essential to preserving the functionality and security of concrete surfaces. The primary purpose of adding expansion joints is to allow for the normal expansion and contraction of concrete due to variations in temperature, moisture content, and other environmental conditions. Concrete without these joints is prone to warping and cracking, which can result in unsightly damage and possibly expensive repairs.

Concrete swells in response to rising temperatures. It contracts when it gets colder. This cycle of expansion and contraction, particularly if the structure is large or subjected to large temperature variations, can result in a significant amount of internal stress within the concrete. By allowing the concrete to flow freely through these spaces, expansion joints help to avoid the accumulation of stress that can lead to cracking or other damage.

Furthermore, expansion joints aid in the isolation of specific concrete sections, which is advantageous in seismically active areas and places where uneven ground settling is possible. These joints can lengthen the life of the concrete installation and lower the possibility of structural damage by enabling separate sections to move independently.

All things considered, expansion joints are a basic but crucial component of concrete construction. They aid in controlling the inherent tendencies of the material, guaranteeing that structures stay sturdy, secure, and aesthetically pleasing for many years. Whether you’re working on a large-scale construction project or pouring a new driveway, knowing the value of expansion joints is essential for successful concrete work.

In order to prevent cracks and structural damage, expansion joints are essential in concrete structures because they allow the material to expand and contract with changes in temperature. Expansion joints contribute to the longevity and structural integrity of concrete structures, including roads, buildings, and other infrastructure, guaranteeing their continued safety and functionality.

Vertical temperature-shrinkage joints of buildings

SNiP stipulates that vertical expansion gaps must be arranged in both long-standing buildings and buildings with varying floor counts in individual sections.

• Temperature – to prevent the formation of cracks due to changes in the geometric dimensions of the building"s structural elements due to temperature differences (average daily and average annual) and concrete shrinkage. Such joints are brought to the level of the foundation.
• Sedimentation joints, preventing the formation of cracks that can form due to uneven settlement of the foundation caused by unequal loads on its individual parts. These joints completely divide the building into separate sections, including the foundation.

Both kinds of joints have the same designs. Two paired transverse walls are built to create the gap; these walls are filled with a material that reflects heat and waterproofed to keep precipitation out. The joint’s width must precisely match the building’s design, with a minimum of 20 mm.

The temperature-shrinkage joint step for frameless large-panel buildings is standardized by SNiP and is dependent on the following factors: the distance between transverse walls, the annual variation in average daily temperatures for a specific region, and the materials used in the panel manufacture (compressive strength class of concrete, mortar grade, and diameter of longitudinal load-bearing reinforcement). For Petrozavodsk, for instance, where there is an annual temperature difference of 60 °C, temperature gaps have to be placed 75 ÷ 125 m apart.

According to SNiP, the step of transverse temperature-shrinkage joints in monolithic structures and buildings built using the precast-monolithic method ranges from 40 to 80 m, depending on the structural features of the building. Such a configuration of seams not only makes the building structure more reliable, but it also makes it possible to cast the building’s individual sections gradually.

Be aware that, in individual construction, these kinds of gaps are rarely used because a private house’s wall is typically no longer than 40 meters.

The joints in panel or monolithic buildings are arranged similarly to those in brick houses.

Temperature joints of floors

The dimensions of floors in buildings with reinforced concrete structures can vary based on temperature variations, just like the dimensions of other elements. As such, expansion joints must be arranged when installing them.

The design documentation for the building’s construction specifies the materials for their manufacture, as well as their dimensions, locations, and installation technology.

These joints can occasionally be made to slide structurally. Two layers of galvanized roofing iron are placed beneath the floor slab in areas where it rests on load-bearing structures to ensure sliding.

Temperature expansion joints in concrete floors and cement-sand screeds

A concrete floor or cement-sand screed must be applied with all building structures (walls, columns, doorways, etc.) kept out of contact with the poured solution for the duration of its thickness. This space serves three purposes at once:

• At the stage of pouring and setting of the solution, it works as a shrinkage joint. Heavy wet solution compresses it, with the gradual drying of the concrete mixture, the dimensions of the poured sheet decrease, and the material filling the gap expands and compensates for the shrinkage of the mixture.
• It prevents the transfer of loads from building structures to the concrete surface and vice versa. The screed does not press on the walls. The structural strength of the building does not change. The structures themselves do not transfer loads to the screed, and it will not crack during operation.
• With temperature differences (and they necessarily occur even in heated rooms), this seam compensates for changes in the volume of the concrete mass, which prevents its cracking and increases its service life.

A unique damper tape, whose width is marginally greater than the screed’s height, is typically used to arrange these gaps. Using a construction knife, the excess solution is removed once it has solidified. If the final floor covering is not provided, shrinkage joints in concrete floors are installed with the polypropylene tape partially removed and the groove waterproofed with specialty sealants.

Large rooms (or those with a wall longer than 6 m) require the cutting of longitudinal and transverse temperature-shrinkage joints to a depth of ⅓ of the fill thickness, according to SNiP. Special tools are needed to create a temperature joint in concrete (a gasoline or electric joint cutter with diamond discs). Such joints should have a step of no more than six meters.

Take note! Shrinkage joints are placed throughout the entire depth of the screed when the underfloor heating elements are poured with mortar.

Expansion joints in foundation blind areas and concrete paths

The foundation blind areas, which are intended to shield the house’s base from the damaging effects of precipitation, can also be destroyed because of the year-round substantial temperature variations. Joints are positioned to account for the expansion and contraction of concrete in order to prevent this. These openings are created during the blind area’s formwork construction phase. Everywhere around the perimeter, transverse boards (20 mm thick) are fastened to the formwork in steps of 1.5 × 2.5 m. The boards are taken out once the solution has slightly set, and the grooves are waterproofed and filled with damping material once the blind area has dried completely.

Everything mentioned above also holds true for how parking spots close to your house or the configuration of concrete walkways on the street. Nonetheless, it is possible to raise the expansion gap step to 3 ÷ 5 m.

Materials for arranging joints

Materials meant for seam arrangement are subject to the same specifications (regardless of type and size). They should be quickly able to regain their original shape after being compressed, elastic, flexible, and easily compressible.

Damper tape

It is intended to offset the loads from building structures (walls, columns, etc.) and prevent the screed from cracking while it dries. You can arrange practically any screeds and concrete floors with this material because of its wide range of sizes (thickness: 3÷35 mm; width: 27÷250 mm).

Sealing cord

A common and simple material to use for expanding gap filling is a foamed polyethylene cord. On the construction market, it comes in two varieties:

• solid sealing cord Ø=6÷80 mm,
• in the form of a tube Ø=30÷120 mm.

The cord’s diameter should be ¼÷½ greater than the seam’s width. When the cord is inserted into the groove, it fills ⅔÷¾ of the available space and is compressed. For instance, 4 mm wide grooves cut in a screed can be sealed with a cord measuring Ø = 6 mm.

Sealants and mastics

Joints are sealed using a variety of sealants:

• polyurethane;
• acrylic;
• silicone.

They can be two-component (made by combining two components right before use) or one-component (ready to use). Sealant is applied over the laid cord of foamed polyethylene (or other damping material) if the joint is small; if it is large, sealant is applied to fill the gap.

External expansion gaps are sealed primarily with a variety of mastics (bitumen, bitumen-polymer, compositions based on raw rubber or epoxy with additives to impart elasticity). Over the damping material positioned in the groove, they are applied.

Special profiles

In modern construction, expansion joints in concrete are successfully sealed using special compensation profiles. These products have a variety of configurations (depending on the area of ​​application and the width of the seam). For their manufacture, metal, plastic, rubber are used, or several materials are combined in one device. Some models in this category must be installed during the pouring process. Others can be installed in the groove after the base has finally hardened. Manufacturers (both foreign and domestic) have developed a wide range of such devices, both for outdoor use and for indoor installation. The high price of the profiles is offset by the fact that this method of sealing gaps does not require their subsequent waterproofing.

Concrete structures’ longevity and durability depend heavily on their expansion joints. They prevent damage by enabling the concrete to expand and contract in response to temperature changes. Expansion joints allow for these movements, preventing cracking and other problems that could jeopardize the structural integrity.

Large concrete structures naturally settle and shift, and these joints aid in controlling this process. In the absence of them, the strain from these motions may cause structural weaknesses. An adequate spacing of expansion joints guarantees unhindered movement of the concrete.

In conclusion, expansion joints are a basic but crucial component of concrete construction. They are crucial to any concrete project because they support the structure’s long-term stability and strength. Builders can guarantee that their structures stay secure and operational for many years by incorporating expansion joints.

Video on the topic

Why do you need an expansion joint

Seam sealing device 🤝🇷🇺

Expansion joint | What is it for?

VISOR example of whether or not heat-shrinkable JOINTS are needed in a ROUGH concrete blind area?!

Why an Expansion Joint is Needed Examples