Conbextra GP: General Purpose Shrinkage Compensated Grout

Product Description

Conbextra GP is a shrinkage-compensated, non-shrink cementitious grout supplied by Fosroc as a ready-to-use dry powder product. It is specifically formulated for general-purpose grouting applications where it is essential to eliminate shrinkage when completely filling voids or grouting between a base plate and substrate, such as the grouting of a stanchion base plate. The product can also be used for anchoring a wide range of fixings including masts and anchor bolts.

The addition of a controlled amount of clean water to Conbextra GP produces a flowing grout suitable for gap thicknesses ranging from 10mm up to 100mm in a single pour. The grout features graded fillers and chemical additives that impart controlled expansion in the plastic state while minimizing water demand, ensuring high early strength development.

Key Characteristics

Composition and Properties

• Type: Cementitious, cement-based formulation
• Maximum Aggregate Size: 0.7mm (for pumping applications)
• Fresh Wet Density: Approximately 2200 kg/m³ (depending on consistency used)
• Supply Format: 20kg moisture-resistant plastic bags
• Product Code: FC501020-20KG
• Shelf Life: 36 months from date of manufacture when kept in original, unopened bags

Expansion Characteristics

Conbextra GP incorporates a gaseous expansion system that compensates for shrinkage and settlement in the plastic state. This expansion process is a chemical reaction that occurs after mixing and requires placement within 20 minutes at 20°C to achieve full expansion benefits.

Performance Standards

Conbextra GP is classified as non-shrink according to ASTM C1107:2020, which establishes comprehensive testing methodologies and acceptance criteria for grout materials. The product also complies with AS 4020-2018 at an exposure level of 15,000mm² per litre.

Compressive Strength Properties

Conbextra GP demonstrates progressive strength development across multiple curing periods:

According to ASTM C1107:2020 specifications, Conbextra GP achieves compressive strengths of 31.6 N/mm² at 1 day, 52.9 N/mm² at 3 days, 61.5 N/mm² at 7 days, and 74.3 N/mm² at 28 days (tested at 3.8L water per 20kg).

Other Mechanical Properties

• Flexural Strength: 4.4 MPa (1 day), 8.7 MPa (7 days), 13.6 MPa (28 days)
• Indirect Tensile Strength: 3.5 MPa (1 day), 5.6 MPa (7 days), 6.1 MPa (28 days)
• Setting Time: 5.5 hours (initial set), 7.5 hours (final set)
• Flow Characteristics: 400-600mm (Flow Trough), 25-30 seconds (Flow Cone)
• Alkali Reactive Particles: Non-reactive (Rapid Mortar Bar Test)

Mixing and Yield Properties

Water Content Requirements

Conbextra GP requires specific water-to-powder ratios to achieve different consistency levels:

Grout Yield

The grout yield varies from 10.6 to 10.9 litres depending on water content and consistency achieved during mixing.

Application Guidelines

Preparation Requirements

The foundation surface must be free from oil, grease, or any loosely adherent material. If the concrete surface is defective or has laitance, it must be cut back to a sound base. Bolt holes or fixing pockets must be blown clean of any dirt or debris before grouting operations.

Placing Procedures

• Conbextra GP can be placed in thicknesses from 10mm up to 100mm in a single pour when used as an underplate grout
• Where the grouting gap exceeds the maximum thickness allowed, the grout can be bulked out with Conbextra Grout Aggregate to minimize exotherm heat buildup
• Filling/bulking out should not exceed a ratio of 2:1 grout:aggregate by weight
• Continuous grout flow is essential during placement to prevent air entrapment

Pumping Capability

Where large volumes need to be placed, Conbextra GP may be pumped using pumps capable of handling the maximum aggregate size of 0.7mm. This provides flexibility in application methods for larger grouting operations.

Flow Properties

Flow distances vary depending on gap depth and hydrostatic head applied:

Key Advantages

• High ultimate strength and low permeability ensure durability of hardened grout
• Gaseous expansion system compensates for shrinkage and settlement in the plastic state
• Versatile application methods: Can be dry packed, rammed, trowelled, poured, and pumped
• Pre-packaged material overcomes potential on-site mixing variations
• High early strength development without chlorides
• No metallic iron content to cause staining
• RCS (Respirable Crystalline Silica) Hazard Free - contains <0.1% RCS in accordance with Australian Inventory of Industrial Chemicals
• Non-shrink classification according to ASTM C1107:2020

Temperature Considerations

Low Temperature Working

When air or contact surface temperatures are 5°C or below on a falling thermometer, warm water (30-40°C) is recommended to accelerate strength development. For ambient temperatures below 10°C, formwork should be kept in place for at least 36 hours.

High Temperature Working

At ambient temperatures above 35°C, cool water (below 20°C) should be used for mixing prior to placement.

Safety and Storage

A Technical Data Sheet and Safety Data Sheet are available from the Fosroc website and should be read carefully before use. The product must be stored in original, unopened bags to maintain its shelf life of 36 months. Do not use if there are lumps in the product or if a loss of workability is experienced.

References

• [1] Fosroc_Conbextra_GP_TDS.pdf
• [2] Fosroc_Construction_Grout_TDS.pdf