Conbextra UW - Underwater Cementitious Grout

Product Overview

Conbextra UW is a specialized, water-resistant, flowing grout product specifically engineered for both underwater and above-water grouting applications. It is formulated as an anti-wash out specialist grout, designed to maintain structural integrity and performance in aqueous environments where exposure to water is a critical consideration.

The product is supplied as a ready-to-use powder in 20kg moisture-resistant plastic bags (product code: FC501030-20KG), requiring only the on-site addition of water for preparation. This formulation eliminates the need for complex mixing procedures on-site, streamlining the application process.

Key Features and Advantages

Conbextra UW offers numerous advantages for demanding underwater grouting applications:

• No Risk of Wash-Out: No significant 'wash-out' of the cement phase when placed underwater, with exceptional resistance to washing-out when placed in stationary or slow-moving water
• Water Displacement: Effectively displaces water to ensure proper grout placement
• Class A Classification: Features a gaseous expansion system that compensates for shrinkage and settlement in the plastic state
• High Strength Development: Demonstrates high early and ultimate strength, providing long-term structural performance
• Chloride-Free Formulation: Contains no chloride content, enhancing durability
• Pre-Packaged Convenience: Ready-to-use format requiring only on-site addition of water
• RCS Hazard Free: Classified not hazardous for Respirable Crystalline Silica, containing less than 0.1% RCS
• Non-Shrink Properties: Complies with ASTM C1107:2020 non-shrink standards

Product Description and Composition

Conbextra UW is a blend of cement, graded fine aggregate, and chemical additives which impart controlled expansion, water reduction, and non wash-out characteristics. The aggregate grading minimizes segregation and bleeding while assisting the flow characteristics of the material. The maximum aggregate size for pumping is 0.3mm.

Mechanical Properties and Strength Development

Compressive Strength

Conbextra UW demonstrates progressive strength development over time:

• 1 Day: 25 MPa (25.0 N/mm²)
• 7 Days: 44 MPa
• 28 Days: 53-67.6 MPa (depending on testing methodology)

Additional Mechanical Properties

• Flexural Strength: 3.4 MPa at 1 day, 7.3 MPa at 7 days, and 8.8 MPa at 28 days
• Indirect Tensile Strength: 1.7 MPa at 1 day, 3.5 MPa at 7 days, and 4.1 MPa at 28 days
• Tensile Bond Strength to Submerged Concrete: 2.1 MPa
• Fresh Wet Density: 2050 kg/m³ (depending on consistency used)
• Setting Time: 5.0 hours for initial set and 7.5 hours for final set
• Flow Characteristics: 400mm (Flow Trough)

Application Thickness Specifications

Conbextra UW accommodates a wide range of placement thicknesses depending on application conditions:

• Above Water Applications: Can be placed in thicknesses from 10mm up to 80mm in one pour
• Underwater Applications: The heat sink effect in underwater environments allows thicknesses of up to 150mm to be placed in one pour

Primary Applications

Conbextra UW is used for free flow or pumped grouting applications in underwater or tidal zones. Primary applications include:

• Bridge Columns: Structural elements in bridge infrastructure
• Quay Pillars: Components of marine quay structures
• Concrete Piling: Underwater pile repair and maintenance
• Slipways: Marine vessel launching and recovery infrastructure
• Dams: Water retention structures requiring underwater grouting

Mixing Process and Preparation

The mixing process describes the procedure for preparing Conbextra UW by gradually adding the powder to water with continuous mixing. The addition of a controlled amount of clean water produces a free-flowing non-shrink grout.

For flowable consistency, the water addition is 4.4 liters per 20kg bag, yielding approximately 11.60 liters of mixed material. Allowance should be made for wastage when estimating quantities required.

Adding Aggregate for Thicker Sections

For thicker sections up to 200mm above water and 400mm underwater, it is necessary to fill out Conbextra UW using Conbextra Grout Aggregate. The ratio of aggregate should not exceed 10kg Conbextra Grout Aggregate per 20kg bag of Conbextra UW. The typical yield increase is approximately 4 liters per 10kg of aggregate added.

Curing Requirements

Curing will not be required in intermittently or totally submerged situations. However, when cast above water, exposed areas should be thoroughly cured through the use of Concure curing membrane, continuous application of water, and/or wet hessian.

Storage and Shelf Life

Conbextra UW has a shelf life of 36 months from the date of manufacture if kept in the original, unopened bags. The product should not be used if there are lumps present or if a loss of workability is experienced, which may indicate moisture penetration or deterioration.

If stored in high temperature and high humidity locations, the shelf life may be reduced.

Application Limitations

Conbextra UW must not be applied below 5°C. Standard winter working precautions for cementitious materials should be adopted when ambient temperatures are low.

Standards Compliance

Conbextra UW complies with established standards for grout materials, including:

• ASTM C1107:2020: Non-shrink grout specification
• AS 1478.2:2005: Australian standard for grout testing and properties
• AS 1012 series: Standards for testing hardened concrete and strength determination

Test Results to ASTM C1107:2020

Additional test results meeting ASTM C1107:2020 specifications are available, demonstrating compliance with international quality standards for grout materials.

References

• [1] Fosroc_Conbextra_HS_TDS.pdf
• [2] Fosroc_Conbextra_UW_TDS.pdf
• [3] Fosroc_Conbextra_EP65_Plus_Underwater_TDS.pdf
• [5] Fosroc_Conbextra_Grout_Aggregate_TDS.pdf