Full grout coupler for precast concrete

Description

Full grout coupler, also known as grouted sleeve joints or sleeve grouting joints, constitute a meticulously engineered composite assembly. They comprise specially machined sleeves, materials specifically formulated for grouting, and reinforcing bars. During installation, the reinforcement bars are firmly bonded to the sleeve through the injection of a rapid-setting, non-shrink grout. This method leverages the adhesive and interlocking properties between the materials. This jointing technique not only delivers robust performance and broad applicability but also offers an exceptionally straightforward installation process.

Example diagram for full grout coupler for precast concrete

Advantages of Full Grout Rebar Coupler

1. Excellent Structural Performance

• Provides high tensile and compressive strength, equal to or greater than the parent rebar.
• Ensures stable mechanical connection without slippage or thread failure.
• Suitable for high-strength and large-diameter rebar such as HRB500 or HRB600.

2. Easy and Efficient Installation

• No threading or heating required — simple insertion and grouting process.
• Allows for greater construction tolerance, ideal for precast assembly on site.
• Multiple joints can be grouted simultaneously, improving construction speed.

3. High Safety and Durability

• Dense grouting offers excellent corrosion resistance and long service life.
• Performs well under seismic conditions, widely used in earthquake-resistant structures.
• Connection quality can be easily tested for grouting density and strength.

4. Wide Application in Modern Construction

• Ideal for precast concrete structures such as columns, beams, and walls.
• Extensively used in bridges, tunnels, metro systems, high-rise buildings, and nuclear projects.
• Compatible with both vertical and horizontal grouting systems.

Parameter Table for Full Grout Coupler

Comparison of core parameters between half grouted sleeve and full grout coupler

How to install a full grout coupler

1. Precast Component Production Phase (Factory Fabrication)

1.1 Pre-Assembly of Sleeve Left End (Plug and Rebar Installation)

• Insert the rubber plug into the left end (pre-assembly end) of the full grout coupler, ensuring it fits tightly against the inner wall without looseness.
• Insert the rebar of the corresponding size through the central hole of the plug into the sleeve. The insertion depth must strictly follow the connection technical requirements for the specific rebar diameter (refer to the design insertion depth standards for different rebar sizes).

1.2 Rebar Bundling and Formwork Placement

• After inserting the rebar to the designed depth, bundle it with other rebars in the component as per the drawing to ensure the overall stability of the rebar cage.
• Place the bundled rebar cage (with pre-assembled sleeves) into the precast component formwork, adjusting its position to meet the design coordinates.

1.3 Positioning of Sleeve Right End and Fixture Installation

• Align the right end (site installation end) of the sleeve with the matching fixture installed on the formwork panel. Ensure the sleeve axis is consistent with the design direction and its end face is flush against the formwork edge.
• Install corrugated pipes at the grout inlet and vent port of the sleeve, which protect the interfaces during subsequent concrete pouring and prevent blockage by slurry.

1.4 Fixture Fixing and Concrete Pouring

• Secure the installed corrugated pipes to the formwork using matching magnetic suction positioning fixtures to prevent displacement or detachment during pouring.
• Pour concrete in accordance with the component’s concrete construction specifications, vibrate it densely, and cure it to the specified strength to complete the precast component production.

2. On-Site Installation and Connection Phase (Site Construction)

2.1 Component Alignment and Sleeve Coupling

• Lift the precast component to the installation position and align the open end (site installation end) of the full-grouting sleeve on the component with the reserved rebar protruding from the lower wall panel.
• Lower the component slowly to fully sleeve the reserved rebar from the lower layer into the sleeve, ensuring the component’s installation elevation and position meet design requirements.

2.2 Sealing/Grouting Bed Treatment

• Depending on the construction plan, seal the gap between the component and the lower structure (using dedicated sealing materials) or perform grouting bed operation at the component bottom to prevent subsequent grout leakage.

2.3 Grout Injection and Hole Plugging

• Inject the matching grout through the grout inlet of the sleeve. The grouting process should be continuous and slow to avoid air bubbles.
• Once grout overflows from the sleeve’s vent port, immediately plug the vent hole and grout inlet with dedicated plugs to ensure the grout is full and void-free inside the sleeve.

2.4 Grout Curing and Connection Formation

• Cure the grout as per its technical requirements (controlling ambient temperature and humidity). After the grout strength reaches the design-specified value, the longitudinal rebars at both ends of the sleeve are connected into a single unit, completing the full grout coupler connection construction.

Factors Affecting Quality During the Installation Stage of Fully Grout coupler

1. Quality of Reinforcement Installation for Component Connections

Deviations in reinforcement positioning (permitted deviation from centreline: 0–2 mm) or protrusion lengths failing to meet design requirements (permitted deviation: 0–15 mm) may result in components being difficult to position correctly or insufficient connection lengths. Reinforcement surfaces contaminated with mortar or exhibiting severe corrosion, alongside excessively narrow gaps at component joints serving as grout-filled cavities, will all compromise connection quality.

2. Pre-treatment and Sealing Quality of Grouting Areas

If the connection surfaces of components are not thoroughly cleaned, or if foreign matter or water accumulation is present, these contaminants may become mixed into the grout during injection. This can alter the grout’s properties or obstruct the grouting channels. Inadequate sealing of the grouting cavity may lead to accidental leakage of grout under high pressure during the later stages of injection. Such leakage could result in the failure of the entire component connection or even render the structure unusable.

3.Grout Mixing Quality

During grouting operations, the grout material must be mixed with water to form a slurry for use. Among the three components of the joint, the grout slurry is the only material processed by on-site personnel. Consequently, its processing quality represents one of the most significant risk factors for joint integrity. Failure to adhere to specified product requirements during mixing may result in poor slurry flowability, short working time, unstable expansion and strength properties, or even bleeding. The use of substandard slurry in grouting operations may lead to issues such as non-flowing, premature setting, shrinkage, or insufficient strength, ultimately causing joint failure.

4.Grouting Operations and Component Protection Measures

Improper grouting procedures or failure to execute operations according to correct methods may result in insufficient anchoring length at joint grout zones, leading to substandard connection quality. Inadequate protection of components post-grouting can cause displacement at joint interfaces after grout solidification, creating voids between the grout and sleeves/reinforcing bars. Alternatively, freezing of the grout before achieving specified strength, causing ice formation from free water within the material, will degrade joint performance and cause connection failure.

How to Select Grouting Sleeves

• Prioritise half grouted sleeves: When the precast plant can complete rebar threading in advance and on-site installation progress needs to be accelerated, semi-grouted sleeves offer better value for money.
• Prioritise full grout coupler: When high precision is required for rebar positioning, on-site adjustment is needed at both ends, or the project demands exceptional connection reliability (such as in high-rise buildings or long-span structures), fully grouted sleeves are more suitable.

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