Conbextra UW – Underwater Cementitious Grout

Product Overview

Conbextra UW is a formulated anti-wash-out specialist grout specifically designed for underwater grouting applications. It is supplied as a ready-to-use powder that requires only the on-site addition of water to produce a free-flowing, non-shrink grout with exceptional resistance to cement phase wash-out when placed in submerged or slow-moving water environments.

Key Features and Advantages

Conbextra UW offers several distinctive advantages for underwater applications:

• No significant wash-out risk: Exhibits exceptional resistance to 'washing-out' of the cement phase when placed in stationary or slow-moving water
• Effective water displacement: Displaces water effectively to ensure proper grouting in submerged conditions
• Non-shrink properties: Complies with ASTM C1107:2020 non-shrink specification
• Shrinkage compensation: Class A gaseous expansion system compensates for shrinkage and settlement in the plastic state
• High strength development: Delivers high early and ultimate strength
• Chloride-free formulation: Safe for use in corrosion-sensitive applications
• RCS hazard-free: Classified as hazardous-free for Respirable Crystalline Silica, containing <0.1% RCS
• Convenient packaging: Pre-packaged format requiring only on-site water addition

Product Composition and Description

Conbextra UW is a blend of cement, graded fine aggregate, and chemical additives that impart:

• Controlled expansion characteristics
• Water reduction properties
• Non wash-out resistance characteristics

The carefully selected aggregate grading minimizes segregation and bleeding while optimizing flow characteristics. The product's maximum aggregate size for pumping is 0.3mm, allowing it to flow effectively through pumping equipment.

Technical Properties and Performance

Compressive Strength (AS 1478.2:2005)

Consistency	Water Addition	1 Day	7 Days	28 Days
Flowable	4.4 L	25 MPa	44 MPa	53 MPa

Additional Mechanical Properties

• Flexural Strength: 3.4 MPa (1 Day), 7.3 MPa (7 Days), 8.8 MPa (28 Days)
• Indirect Tensile Strength: 1.7 MPa (1 Day), 3.5 MPa (7 Days), 4.1 MPa (28 Days)
• Tensile Bond Strength to submerged concrete: 2.1 MPa
• Setting Time: 5.0 hours initial set, 7.5 hours final set
• Fresh Wet Density: 2050 kg/m³ (depending on consistency used)
• Flow Characteristics: 400mm (Flow Trough)
• Alkali Reactive Particles: Non-reactive (Rapid Mortar Bar Test)

Application Thickness Specifications

Specification	Above Water	Below Water
Minimum Thickness	10mm	10mm
Maximum Thickness	80mm	150mm

The underwater environment's heat sink effect allows thicknesses up to 150mm in single pour applications beneath water, compared to 80mm when used above water.

Mixing and Preparation

Water Addition: 4.4 litres per 20kg bag produces flowable consistency

Yield: 11.6 litres of mixed material per 20kg bag (accounting for wastage allowance)

Mixing Equipment

A forced-action mixer is essential for proper preparation. Mix for 3 to 5 minutes at slow speed (400-500 rpm) using appropriate equipment such as a 120/140mm helical mixing paddle fitted to a heavy-duty 1600W mixer. Always add the powder to the water, ensuring a smooth, even consistency is achieved.

For larger volumes, a high shear vane mixer is required. A colloidal impeller mixer must not be used.

Placement and Application Methods

Free Flow Grouting

The grout should be poured continuously to ensure proper flow and prevent air or water entrapment.

Pumped Grouting

Conbextra UW can be pumped through flexible tubing with a minimum diameter of 50mm to the lowest point in the formwork. Care must be taken at the start of the grouting operation to restrict grout flow and prevent water entrapment. The tube may be raised to reduce back pressure but should not be raised above the grout surface level.

Placement timing: Place the grout within 20 minutes of mixing to gain full benefit of the expansion process. Continuous grout flow is essential to prevent air or water entrapment.

Aggregate Enhancement for Thicker Sections

For applications requiring thicknesses up to 200mm above water and 400mm underwater, Conbextra UW can be bulked out using Conbextra Grout Aggregate:

• Maximum ratio: 10kg of Conbextra Grout Aggregate per 20kg bag of Conbextra UW
• Typical yield increase: approximately 4 litres per 10kg of aggregate added
• Mixing method: Use a concrete mixer; add aggregate slowly to mixed grout and mix for a further 2 minutes
• Important note: Do not exceed the top-end water content specified on the Technical Data Sheet
• Flow reduction: The addition of aggregate will reduce flow characteristics

Curing Requirements

Underwater/Submerged applications: No curing is required in intermittently or totally submerged situations.

Above-water applications: When cast above water, exposed areas should be thoroughly cured using:

• Concure curing membrane
• Continuous water application
• Wet hessian covering

Storage and Shelf Life

Shelf life: 36 months from date of manufacture when stored in original, unopened bags in dry conditions

Storage conditions: Store in original, unopened moisture-resistant plastic bags. If stored in high temperature and high humidity locations, the shelf life may be reduced.

Quality indicators: Do not use if lumps are present in the product or if loss of workability (requiring additional water) is experienced.

Supply and Packaging

Product	Product Code
Conbextra UW 20kg	FC501030-20KG

Conbextra UW is supplied in 20kg moisture-resistant plastic bags.

Application Limitations

• Must not be applied below 5°C
• Substrate surface must be properly prepared, free from oil, grease, and loosely adherent material
• For permanently immersed substrates: sand-blasting or high-pressure water jet cleaning recommended
• For non-immersed or intermittently immersed substrates: scabbling or bush hammering may be appropriate alternatives

Typical Applications

Conbextra UW is used for free flow or pumped grouting in the following underwater and tidal zone environments:

• Bridge columns
• Quay pillars (wharf piles)
• Concrete piling
• Slipways
• Dams
• Other submerged structural elements

Equipment Cleaning

Due to its water-resisting properties, equipment used for Conbextra UW requires more rigorous cleaning than with standard cementitious grouts. Hot water is recommended for cleaning purposes. Cured material can only be removed mechanically.

Health, Safety, and Documentation

A Safety Data Sheet (SDS) is available from the Fosroc website and must be read carefully prior to use. Application or performance data may change from time to time as the product is refined and improved.

In emergency situations, contact any Poisons Information Centre (phone 13 11 26 within Australia) or consult a doctor for advice.

References

• [1] Fosroc_Conbextra_UW_TDS.pdf