Concrete Expansion Joint Repair

Expansion joints

The main function of expansion joints is to damp a possible contact or friction due to movement between two construction elements. In addition, there exist also refraction or contraction joints, construction joints and combined action joints (refraction-expansion).

In relation to an industrial floor, they are known as expansion joints because they regulate compression deformations in the concrete. These are caused by internal expansions, caused by thermal variations, load fluctuations, or displacements of the concrete mass.

These joints are designed to prevent structural alteration of adjacent reinforced concrete elements, but independent of each other in terms of structural performance. In addition, expansion joints provide reciprocal insulation between the elements.

Concrete and reinforcing steel have similar coefficients of thermal expansion. They are exposed to thermal variations and both steel and concrete react collectively. The impacts of these variations are absorbed by the expansion joints.

Expansion joints can be classified according to their opening:

Open joints

These joints result from the determined calculation of the expansive displacements of the material composition between structural elements. The joints are not sealed, which makes them particularly susceptible to the accumulation of particles, deteriorating rapidly if they are not maintained periodically.

Sealed joints

Sealed joints represent the opposite of open joints. They maintain a separation between structural elements, which is sealed with an elastic and waterproof component. They are very resistant to humidity, temperature variations and erosion.

Why are expansion joints necessary in concrete

The main purpose of expansion joints is to prevent cracking between two different slabs. This ensures that vehicle traffic can circulate on an even, safe and unobstructed surface. It is the type of joint that faces the least problems on a concrete construction site, in comparison, for example, with refraction joints.

Refractive joints deal with stress changes in the core of concrete, which lead to the formation of cracks and fissures. This scenario is the most frequent, unlike the expansion joint scenario.

Technical reasons for expansion joints

The physicochemistry behind the joints in the concrete exposes clear effects of expansion and contraction in the dimensions of the concrete mass, initiated and affected by thermal variations. Even deformations due to overloads and differential displacements will always be present.

Each joint has a purpose, such as delaying the deterioration of a floor until the end of its lifespan. Expansion joints make wall-to-floor, wall-to-wall, wall-to-column systems, among others, harmonize synchronously, ensuring their individual integrities as structural elements, minimizing the probability of serious damage.

On the other hand, expansion joints in concrete are very important when it comes to bridge construction systems, industrial installations and precast structures. They will be exposed to high temperature fluctuations throughout their lifespan.

Expansion joints in bridge concrete must be designed to assimilate the dynamics of the structure. In particular, due to the large temperature fluctuations to which the pavement is exposed. It must preserve continuity of the g surface to satisfy the demands of comfort and safety of vehicle traffic.

Joint wear and associated problems

Like any other structural element, the expansion joints of a concrete floor are subject to progressive degradation over time. This leads to the expected wear, which in turn requires measures to repair the expansion joints.

The wear of the joints depends on the environmental influence. It is also associated with surface abrasion, since it is the factor that causes surface disintegration in its early stages.

The following types of abrasion exist in concrete joints:

Abrasion by transit

This is caused by the friction of different transport vehicles on a floor. The strength of the joints of the rigid floor depends on the characteristics of the sealer used. If the sealer is too soft, wear will lead to the formation of cracks and fissures, compromising the impermeability.

Abrasion by erosion

Sand particles carried by the wind flow impact the surface of the joints. The probability of wear by wind effects is very low, however, it is a matter of environmental conditions.

Abrasion by humidity

In some cases water can transport sand at high speeds, for example in heavy rainfall. As with erosion abrasion, moisture abrasion does not lead to short-term wear of joints, as it does not directly affect the adhesion of their components.

Chemical Abrasion

Finally, we have the abrasion caused by the interaction with chemical agents, such as some aggressive cleaning products. These can weaken the molecular structure of the sealer, causing it to break down, exposing the structural elements to further wear.

Solar radiation is another factor influencing the wear of joints. UV rays in particular alter the elastoplasticity of the sealing substances. Due to the long exposure period they become rigid and unable to absorb friction and reduce deformations.

We consider that wear during the lifespan of expansion joints leads to the following consequences:

Cracking

The most common consequence of joint wear is the formation of cracks and fissures. Cracks and fissures are the consequences of axial stresses in the concrete, triggered by overloads and temperature variations on the expansion joints.

Cracks usually appear in thin floors or slabs, making it difficult to dissipate and absorb the energy generated by axial and shear stresses. They can also be produced by improper construction works.

Some considerations for joint repair

In the case of concrete constructions, it is necessary, as a preliminary measure, to carry out an exhaustive cleaning of the joint to be repaired, especially if it is open. The presence of dirt and dust alters the effectiveness of the adhesion of the sealer on structural elements.

In most cases, sealed expansion joints are the best construction option. They offer good mechanical protection and waterproof structural elements.

The economic factor is important. However, investing in a state-of-the-art sealer will increase its lifespan and minimize maintenance periods. Elastomers have evolved technologically, becoming the ideal material for sealing expansion joints.