What Is Non-Shrink Mortar?
Non-Shrinking Mortar is a material used as part of the wall or framework of a building and is a type of material called mortar.
Mortar is a material used when cement, sand, and water are mixed and allowed to harden. Generally, mortar has the property of shrinking when it hardens, but mortar that does not shrink when it hardens is called Non-Shrinking Mortar.
If water-containing mortar shrinks significantly as it sets, it can lead to cracking. Non-Shrinking Mortar prevents the mortar from cracking by suppressing shrinkage during setting.
Applications of Non-Shrinking Mortar
Non-Shrinking Mortar is used in three major applications
1. joint between steel column base and foundation
The base of a steel-framed building must be fixed to a foundation such as reinforced concrete. Non-Shrinking Mortar is injected into the joint to strengthen the bond between the steel frame and the foundation.
2. seismic reinforcement
Non-Shrinking Mortar is used for earthquake-resistant reinforcement of concrete buildings. Non-Shrinking Mortar is used at the anchor points that secure the concrete to the reinforcement, such as steel braces, as well as at the joints between the steel columns and the foundation. By strongly anchoring the reinforcement, it is possible to increase the seismic strength of the building.
3. Repair of concrete structures
Non-Shrinking Mortar is used to repair concrete structures by filling in cracks caused by deterioration. For example, it can be used for “ground improvement” of weakened ground due to excessive extraction of underground water sources, “reinforcement of cracks in concrete walls,” “prevention of bedrock delamination,” and “filling reinforcement” of aged RC structures.
Principle of Non-Shrinking Mortar
The principle of Non-Shrinking Mortar’s non-shrinking property is that it contains an expansion agent. Non-Shrinking Mortar contains a lime-based expander, etc., and has a slight expansive property.
By adding a material that expands to a mortar that shrinks, the material as a whole exhibits Non-Shrinking Mortar or slight expansion.
Types of Non-Shrinking Mortar
There are two types of Non-Shrinking Mortar: “grout” and “pad. Both are chosen according to the construction method.
1. grout type
Grout is a liquid material that is poured into a mold or other container and used to fill a certain space. Since grout has high fluidity, it is easy to fill gaps and is suitable for reinforcing structures.
2. pad type
Pads are used like ordinary mortar, spread out with a trowel. It is less fluid than grout and can be spread on vertical walls.
Other Information on Non-Shrinking Mortar
Non-Shrinking Mortar Method
Non-Shrinking Mortar is called “no-shrink” but it does not mean that it does not expand at all. Although the basic characteristics are watertight and no-shrinkage, a slight expansion may produce the maximum effect depending on the application. One construction method that takes advantage of Non-Shrinking Mortar’s expansive properties is the CFT method. In the hybrid high-rise CFT method, Non-Shrinking Mortar is used as the base material for filling steel pipes.
The principle of the CFT method is based on the mutual restraint (confinement effect) of the outward expansion force of the grouted mortar and the restraining force of the steel pipe. This method has been attracting attention in recent years because it is less expensive than the steel-filled method and, on top of that, has relatively high strength. However, the properties of Non-Shrinking Mortar are the same as those of concrete, and its strength is reduced by neutralization.
Concrete neutralization is a phenomenon in which concrete, which is inherently highly alkaline, approaches neutrality when carbon dioxide from the atmosphere enters the concrete. This phenomenon leads to corrosion of the reinforcing steel inside. In addition, since machine kneading is essential for construction, procurement of equipment is indispensable, and strength and durability are limited only to cases where the concrete is airtight.