What are Concrete Joints & different joints sealant Products?
Joints between construction elements can be found in various elements of a structure, e. g. between precast concrete elements in facades, around windows and doors, between floors and walls, around storage tanks, or in concrete itself. So, what are those gaps or Lines on the concrete? The answer is Joints, but what exactly joints in concrete means? First of all;
Concrete is not a ductile material, which means it cannot be stretched or bent without breaking. But Concrete does move—it shrinks, it expands, and also different parts of a building move in different ways. This is where joints come into play. When concrete moves, if it is tied to another structure or even to itself, we get what's called restraint, which causes tensile forces and invariably leads to cracking. So, joints are used to prevent cracking of concrete.
The purpose of joint sealing generally is to:
- Prevent passage of media (air, water, chemicals, smoke etc.).
- Provide thermal and sound insulation.
- Enhance the visual appearance of the construction.
- permitting limited movement of the substrates & accommodate theses movement in joints
Will introduce you today to types of joints in concrete structures and different sealant types and different uses
Types of Concrete joints:
Construction joint is placed when the mass concreting works are done and cannot be completed on a single shot. The interface of hard concrete and fresh concrete is to be properly done so as the bonding should be perfect for load transferring and avoiding water leakage. This interface joint is known as Construction Joint. its main focus is on maintaining structural integrity.
Prior to pouring a new concrete slab next to an already completed piece, construction joints are installed.
Placed at regular intervals froming a weak plane, So cracks form at the joints but not in undesirable areas. Construction joints are provided in concrete pavements, slabs, walls, floors, dams, canal linings, bridge, retaining walls etc.
When concrete is placed, it decreases in size due to shrinkage, creep, and thermal movement, leading to hairline cracks in the concrete at the weak zone. Control joint is placed at the location of highest concentration of tensile stresses resulting from shrinkage are expected:
Expansion joints are used in concrete to prevent forming of expansive cracks as a result of temperature changes. When there is high temperature, the concrete expands in a confined boundary and cracks happens. Expansion joints are provided in slabs, pavements, buildings, bridges, sidewalks, railway tracks, piping systems, ships, and other structures.
Expansion joints allow for thermal contraction and expansion without stressing the elements.
Sealant Types and Uses
There are many different technologies of sealants on the market, and their properties vary:
Acrylic Emulsion Sealants
Water-based sealants, also known as latex, Such as U-fix AC40, popular in the construction industry for sealing gaps between moldings, doors, and windows. These sealants are easily applied and easy to clean, and they dry quickly. They are also paintable.
They have good adhesion to absorbent substances including wood, concrete, and plaster, as well as good adhesion to metals and glass, though not as good as silicones.
The 4 chemical types of sealants which display elastomeric properties are the following:
- Polysulfide sealants
- Silicone sealants
- Polyurethane sealants
- MS Polymer sealants
Excellent flexibility, even at low temperatures, with no shrinkage or UV deterioration; can be used underwater. Polysulfides are more expensive than comparable sealants and have greater quantities of volatile organic compounds (VOCs).
Except for the fact that they cannot be painted, silicone sealants are a good all-around sealant option. Silicon sealants are highly flexible and water-resistant. They’re also less prone to shrinking than most other sealants, and they stick to almost any material. They are having high temperature resistance and can be Mould Resistant.
There are two types of sealants:
- Acetoxy cure silicone suca as U-fix Silicon A, gives off an acetic acid when curing resulting in pungent vinegar like smell.
- Neutral Cure Silicone such as U-fix Silicon N, is relatively odourless releasing an alcohol during the curing process.
A polyurethane-based sealant may be your best choice for a durable sealant that adheres to practically everything such as U-fix PU30. These sealants create strong bonds between materials, they’re also abrasion resistant and provide more flexibility than many other sealant types, making them a favorite in the construction industry. Polyurethane sealants are rarely paintable, but they often come in tinted hues like grey, black, or white
General Properties of Polyurethane Sealants
- Good elongation at break: 250 to 600%,
- Low to high modulus: 0.25 to 1 MPa
- Excellent elastic recovery higher than 90%
- Excellent abrasion resistance and tear strength, their resistance to indentation makes them the best sealants for floor joints.
Hybrid Sealants/ MS sealants
Combine the high-performance characteristics of silicone and polyurethane while minimizing the weaknesses of each such as MS 25. For example, MS polymers possess the durability of polyurethane. It also has silicone’s weather and UV resistance while still standing up to abrasion.