Rebar anchoring adhesive

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عددی

Rebar anchoring adhesive is a compound that, after drilling and cleaning the hole in concrete, is injected into the cavity where the rebar is placed. Once the adhesive cures, the rebar becomes firmly and securely bonded to the concrete, allowing it to bear tensile and compressive loads similar to cast-in-place reinforcement. The 20th century is rightly known as the century of polymers. The construction industry is the largest consumer of polymeric materials, accounting for approximately 25 to 30 percent of total polymer usage. Epoxies, as one of the most important types of polymers, play a vital role in various applications such as bonding old concrete to new, protective coatings, injection systems, and more. One of the major uses of epoxy is in the rebar anchoring process, which serves as an effective method for installing starter rebars. According to EN 1504 standards, structural strengthening is defined as the use of systems and products aimed at increasing or restoring the load-bearing capacity of concrete structures.

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Properties of Rebar Anchoring Adhesive (Epoxy) Epoxy resins, after mixing and curing, form a three-dimensional network. These polymers are thermosetting and two-component, which, after a chemical reaction at room temperature, turn into a hard, adhesive, and durable compound. Some of the key features of epoxies include:

Very high adhesion to various surfaces
High mechanical strength
Good chemical resistance
Durability against corrosive environmental factors

Epoxy Adhesives for Rebar Anchoring Using epoxy adhesives to anchor rebars or bolts in hardened concrete—known as rebar or bolt anchoring—is widely used in the construction industry. This method applies to both structural and non-structural connections, strengthening and retrofitting structures, and more. Common applications of rebar anchoring include reinforcing concrete sections, enlarging foundations to improve load-bearing capacity, relocating columns due to architectural changes, stabilizing damaged elements, correcting construction defects or adapting to new usage conditions, and adding new structural elements. In some of these applications, achieving the desired structural performance requires adherence to specific design and execution standards. Cyclic and reversible loading can significantly affect the bond between rebars and concrete, especially if it reaches the yield point. Sudden failures due to rebar anchoring and splicing may result in bond degradation unless appropriate precautions are taken to prevent such issues.

Physical and Chemical Properties of Rebar Anchoring Adhesive

Physical Properties:

Appearance:
Two-component system, typically supplied in a dual cartridge containing resin and hardener (base and activator).
Color:
Usually gray, light gray, or off-white after mixing; may vary slightly depending on the brand.
Viscosity:
Relatively thick and gel-like to ensure adhesion to hole walls and prevent dripping.
Density:
Typically between 1.3 to 1.6 g/cm³, depending on whether it’s epoxy or hybrid-based.
Working Time:
Depending on the adhesive type and ambient temperature, provides 5 to 30 minutes for injection and rebar placement.
Curing Time:
Final curing time ranges from 30 minutes to 24 hours, based on adhesive type and environmental conditions.
Compressive Strength:
Very high, generally exceeding 70 MPa.
Tensile Bond Strength to Concrete:
Varies by adhesive type, typically between 12 to 25 MPa.

Chemical Properties:

Main Components:
Epoxy resin, polyester, vinyl ester, or hybrid compounds
Amine or peroxide hardeners (depending on the adhesive type)
Chemical Stability:
Highly resistant to moisture, alkalis, mild acids, chemicals within concrete, oil, gasoline, and saltwater.
Once fully cured, it becomes insoluble in water and retains its mechanical properties.
Thermal Resistance:
After full curing, capable of withstanding temperatures from -40°C to +80°C or higher, depending on the brand.
Reactivity:
When properly mixed, an exothermic chemical reaction occurs between the two components, leading to rapid hardening.
Shrinkage-Free:
After curing, the adhesive remains dimensionally stable without shrinkage, ensuring stronger bonding to concrete.
UV Resistance:
Generally designed for indoor use or embedded concrete applications; however, some brands offer limited UV resistance.

Steps for Using Rebar Anchoring Adhesive

Determine Hole Location and Specifications:
Identify the exact placement of the rebar according to the design or structural calculations.
The diameter and depth of the hole should match the rebar size and adhesive specifications (e.g., for 16 mm rebar, a depth of approximately 160 to 240 mm is recommended).
Drilling the Hole:
Use a hammer drill or rotary hammer to create the hole in concrete or stone.
The hole must be smooth and free of cracks.
Thorough Hole Cleaning:
This step is critical!
Using a wire brush and air blower (or compressed air):
- Brush the hole twice
- Blow out dust twice
  The hole must be completely dry, clean, and free of loose particles—otherwise, the adhesive won’t bond properly and strength will be compromised.
Adhesive Preparation:
Rebar anchoring adhesives are typically two-component (resin and hardener).
They are mixed and injected using a dual-cartridge gun with a mixing nozzle.
Cut the tip of the mixing nozzle before injection to ensure proper blending of components.
Injecting Adhesive into the Hole:
Inject the adhesive starting from the bottom of the hole and slowly withdraw the nozzle to fill about 2/3 of the hole volume.
Avoid trapping air bubbles in the adhesive.
Installing the Rebar:
Gently rotate and press the rebar or anchor bolt into the hole until it reaches the bottom.
No air or adhesive should escape from the opening.
Curing Time:
Initial curing time varies depending on adhesive type and ambient temperature—from 15 minutes to several hours.
Do not apply any load to the rebar until the adhesive has fully cured.