Conbextra GP: General Purpose Shrinkage Compensated Grout

Overview

Conbextra GP is a general-purpose, high-flow, Class A shrinkage-compensated cementitious grout supplied by Fosroc as a ready-to-use dry powder. It is specifically designed for eliminating shrinkage when completely filling voids and for grouting between base plates and substrates in a wide variety of construction and industrial applications.

Product Description

Conbextra GP is a cement-based, non-shrink cementitious grout manufactured on a formulation that incorporates graded fillers and chemical additives. The product is engineered to produce controlled expansion in the plastic state while minimizing water demand, which ensures high early strength development. The formulation features a maximum aggregate size of 0.7mm, making it suitable for both conventional pouring and pumping operations.

The addition of a controlled amount of clean water to the dry powder produces a flowing grout suitable for various application consistencies and thicknesses.

Key Specifications

Gap Thickness Requirements

• Minimum thickness: 10mm
• Maximum thickness: 100mm
• Designed for single-pour applications within this range

Supply Format

• Packaging: 20kg moisture-resistant plastic bags
• Product code: FC501020-20KG
• Shelf life: 36 months from date of manufacture when kept in original, unopened bags

Grout Yield

The yield varies based on consistency and water content ratios:

Consistency	Water Addition (litres per 20kg bag)	Yield (litres of mixed material)
Stiff	2.9 - 3.6	10.6
Plastic	3.6 - 3.8	10.7
Flowable	3.8 - 4.0	10.8
Fluid	4.0 - 4.1	10.9

Classification & Standards Compliance

Conbextra GP is classified as a Class A shrinkage-compensated grout designed to eliminate shrinkage when completely filling voids. The product complies with:

• ASTM C1107:2020 - Non-shrink grout specification
• AS 1478.2:2005 - Australian standard for grout consistency and properties
• AS 4020-2018 - Exposure level of 15,000mm² per litre compliance

The product is certified as RCS (Respirable Crystalline Silica) Hazard Free, containing less than 0.1% RCS.

Mechanical Properties

Compressive Strength (AS 1478.2:2005)

Consistency	Water Addition (L/20kg)	1 Day	7 Days	28 Days
Stiff	2.9 - 3.6	34 MPa	50 MPa	75 MPa
Plastic	3.6 - 3.8	33 MPa	45 MPa	70 MPa
Flowable	3.8 - 4.0	32 MPa	43 MPa	65 MPa
Fluid	4.0 - 4.1	30 MPa	40 MPa	60 MPa

ASTM C109:2020b Test Results

• 1 day: 31.6 N/mm²
• 3 days: 52.9 N/mm²
• 7 days: 61.5 N/mm²
• 28 days: 74.3 N/mm²

Flexural Strength (AS 1012.11-2000)

• 1 day: 4.4 MPa
• 7 days: 8.7 MPa
• 28 days: 13.6 MPa

Indirect Tensile Strength (AS 1012.10:2000)

• 1 day: 3.5 MPa
• 7 days: 5.6 MPa
• 28 days: 6.1 MPa

Additional Properties

• Setting Time (AS 1012.18:1996): 5.5 hours (initial set), 7.5 hours (final set)
• Fresh Wet Density: 2200 kg/m³ (depending on consistency)
• Flow Characteristics (AS 1478.2:2005): 400-600mm (Flow Trough); 25-30 seconds (Flow Cone)
• Alkali Reactive Particles: Non-reactive (RTA T363)

Primary Applications

Conbextra GP is suitable for:

• Base plate grouting - Grouting of stanchion and machine base plates to concrete substrates
• Anchoring fixings - Securing masts, anchor bolts, and other structural connections
• General void filling - Grouting between base plates and substrates where shrinkage elimination is essential
• Precision grouting - Applications requiring dimensional stability and reliable strength development

Key Advantages

• Non-shrink property - Gaseous expansion system compensates for shrinkage and settlement in the plastic state
• High ultimate strength - Achieves excellent long-term compressive strength, ensuring durability
• Low permeability - Provides excellent resistance to water penetration and chemical attack
• Versatile placement methods - Can be dry packed, rammed, trowelled, poured, or pumped
• Pre-packaged consistency - Overcomes potential on-site mixing variations
• Early strength development - High early strength without requiring chlorides
• No staining risk - Contains no metallic iron content
• RCS hazard-free - Safe handling and application

Application Methods

Mixing

A forced-action mixer is essential for proper preparation:

• Mix for 3 to 5 minutes at slow speed (400/500 rpm)
• Use a 120-140mm helical mixing paddle fitted to a heavy-duty 1600W mixer
• Accurately measure water content into the mixing bucket
• Add powder slowly to water while mixing continuously
• Achieve smooth, even consistency

Placement

• Place grout within 20 minutes of mixing at 20°C to gain full benefit of the expansion process
• Continuous grout flow is essential to prevent air or water entrapment
• Pour from one side of the void to eliminate trapped air or pre-soaking water
• Maintain grout head at all times to achieve continuous grout front
• Maximum thickness in single pour: 100mm

Pumping

Conbextra GP may be pumped for large volumes:

• Maximum aggregate size: 0.7mm
• Use only pumps capable of handling this aggregate size

Curing

• Apply curing membrane (Concure), continuous water application, or wet hessian
• For temperatures below 10°C, keep formwork in place for at least 36 hours
• For temperatures above 35°C, use cool water (below 20°C) for mixing

Temperature Considerations

Low Temperature Working

• When air or contact surface temperatures are 5°C or below, use warm water (30-40°C) to accelerate strength development
• Maintain standard winter working precautions for cementitious materials

High Temperature Working

• At temperatures above 35°C, use cool water (below 20°C) for mixing to prevent premature setting

Surface Preparation

Foundation Surface

• Must be free from oil, grease, and loosely adherent material
• Cut back defective surfaces or laitance to sound base
• Abrade or roughen surfaces by mechanical means (needle gun, grit blasting, grinding)
• Blow clean all bolt holes and fixing pockets of dirt and debris

Base Plate Preparation

• Must be clean and free from oil, grease, or scale
• Provide air pressure relief holes to vent isolated high spots

Formwork Requirements

• Construct to be leakproof using foam rubber strip or silicone sealant
• Keep gap width between formwork and plate edge to minimum: 150mm maximum on pouring side, 50mm on opposite side
• No gap recommended at flank sides where practical

Pre-soaking

• Fill grouting area with clean water for minimum 2 hours before grouting
• Removes standing water by draining or vacuum immediately before pouring
• Improves grout flow and adhesion at concrete interface

Cleaning & Maintenance

• Remove grout from tools and equipment with clean water immediately after use
• Cured material can be removed mechanically

Storage & Handling

• Shelf life: 36 months from manufacture date in original, unopened bags
• Do not use if lumps appear in product
• Do not use if workability loss is experienced (requiring additional water)
• Store in dry conditions at ambient temperature

Safety & Documentation

A Safety Data Sheet (SDS) and Technical Data Sheet (TDS) are available from the Fosroc website. Guidelines for on-site sampling and compressive strength testing are also provided by Fosroc.

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References

• [1] Fosroc_Conbextra_GP_TDS.pdf
• [2] Fosroc_Construction_Grout_TDS.pdf
• [3] Fosroc_Conbextra_C_TDS.pdf
• [5] Fosroc_Conbextra_HS_TDS.pdf
• [6] Fosroc_Conbextra_HF_TDS.pdf