Conbextra C: Dual Shrinkage Compensated Cementitious Grout

Product Overview

Conbextra C is a general-purpose, dual shrinkage compensated, non-shrink cementitious grout supplied as a ready-to-use dry powder. When mixed with a controlled amount of clean water, it produces a flowing shrinkage compensated grout suitable for gap thicknesses ranging from 10mm to 100mm. The product is designed to deliver high flow characteristics along with dual shrinkage compensation properties.

Product Composition & Description

Conbextra C is a blend of Portland cement, specially graded fillers, and chemical additives that work together to impart controlled expansion in both the plastic and hardened states. The formulation minimizes water demand, ensuring high early strength and long-term durability. The graded filler composition is specifically designed to assist uniform mixing and produce a consistent, flowable grout while minimizing segregation and bleeding over a wide range of application consistencies.

Key Material Property: Maximum aggregate size for pumping is 0.3mm.

Key Advantages

• Dual expansion system compensates for shrinkage in both the plastic and hardened states
• Non-shrink according to ASTM C1107:2020 standard
• High ultimate strength and low permeability ensure durability of the hardened grout
• Hydrogen-free gas expansion mechanism
• Chloride-free formulation
• Flexible application methods — can be dry packed/rammed, trowelled, flowed, and pumped
• No metallic iron content, preventing rusting
• RCS (Respirable Crystalline Silica) Hazard Free — contains <0.1% RCS in accordance with Australian Inventory of Industrial Chemicals
• Prepackaged material overcomes potential on-site mixing variations

Typical Applications

Conbextra C is used for general grouting of gaps from 10mm to 100mm where high flow is required along with dual shrinkage compensation. Applications include:

• Baseplates and soleplates of machines
• Structural steel column baseplates
• Voids between precast concrete and infilling blockwork

Technical Specifications

Compressive Strength (AS 1478.2:2005)

Consistency	1 Day	7 Days	28 Days
Stiff	45 MPa	60 MPa	70 MPa
Plastic	35 MPa	50 MPa	60 MPa
Flowable	25 MPa	45 MPa	55 MPa

Flexural Strength (Modulus of Rupture)

• 1 Day: 5.0 MPa
• 7 Days: 9.5 MPa
• 28 Days: 9.6 MPa

(Tested to AS 1012.11 - 2000)

Indirect Tensile Strength

• 1 Day: 2.7 MPa
• 7 Days: 4.4 MPa
• 28 Days: 4.8 MPa

(Tested to AS 1012.10.2000)

Fresh Wet Density

• 2100 kg/m³ (depending on consistency used)

(Tested to ASTM C185:2020)

Flow Characteristics

• 400 - 600mm (Flow Trough test)

(Tested to AS 1478.2:2005)

Setting Time

• Initial set: 300 minutes
• Final set: 360 minutes

(Tested to ASTM C953:2017)

Thickness Specifications

• Minimum thickness: 10mm
• Maximum thickness: 100mm

Standards Compliance

• AS 1478.2-2005 Appendix E: Test for Early Volume Change
• AS 1478.2-2005 Table 4.1.2.2: Test for Consistency
• ASTM C1107:2020: Non-shrink specification

Volume Change (ASTM C1107:2020 Test Results)

Measurement	Result
Flow Consistency (ASTM C939:2016a)	>145%
Volume Change at Early Age - Final Setting (ASTM C827:2016)	+0.40%
Volume Change of Hardened Grout - Moist Cured (ASTM C1090:2015)
- 1 day	+0.01%
- 3 days	+0.02%
- 7 days	+0.02%
- 28 days	+0.03%
- 28 days + 28 days in air	+0.01%

Compressive Strength (ASTM C1107:2020)

Time Period	Strength
1 day	23.3 N/mm²
3 days	38.0 N/mm²
7 days	45.1 N/mm²
28 days	56.2 N/mm²

(All tests conducted at 25°C ± 2°C. Tests conducted at water addition rate of 3.6L per 20kg)

Mixing Requirements

Water Addition Rates

Required Consistency	Water Addition (litres per 20kg bag)	Yield (litres of mixed material)
Stiff	2.6 - 3.4	10.4
Plastic	3.4 - 3.6	10.7
Flowable	3.6 - 3.9	10.8

Mixing Equipment

A forced-action mixer is essential. Mix for 3 to 5 minutes at slow speed (400-500 rpm) in a suitably sized drum using appropriate equipment such as a 140mm helical mixing paddle fitted to a heavy-duty 1600W mixer.

Procedure: Accurately measure the selected water content into the mixing bucket. While mixing, slowly add the total contents of the Conbextra C bag and mix continuously for 3 to 5 minutes, ensuring a smooth, even consistency is obtained. Always add the powder to the water — not water to powder.

Larger Volumes

Larger quantities require a high shear vane mixer. Do not use a colloidal impeller mixer. To enable continuous grouting operations, sufficient mixing capacity and labour must be available. A grout holding tank with gentle agitation provision may be required.

Mixing Part Bags

Full bags are recommended; however, experienced applicators may mix half bags by weighing out the correct quantity and mixing with half the recommended water quantity. The contractor accepts responsibility for any off-ratio mixing risks. Agitate the dry product before weighing to minimize segregation, and use reliable scales.

Placement Instructions

Temperature Conditions

• At 23°C, place the grout within 20 minutes of mixing to gain full benefit of the expansion process

Placement Thickness

Conbextra C can be placed in thicknesses from 10mm up to 100mm in a single pour when used as an underplate grout.

Continuous Flow

Continuous grout flow is essential. Sufficient grout must be prepared before starting. The time taken to pour a batch must be regulated to the time to prepare the next one.

Pouring method: Pour from one side of the void to eliminate air or pre-soaking water being trapped under the baseplate. Pour across the shortest distance of travel. Maintain grout head at all times to achieve continuous grout front.

Bulking Out Option

Where the grouting gap exceeds the maximum thickness allowed, the grout can be filled/bulked out with Conbextra Grout Aggregate to minimize exotherm heat buildup. Filling/bulking should not exceed a ratio of 2:1 (grout:aggregate by weight). Alternatively, Conbextra Deep Pour is available for pours up to 500mm thick.

Bolt Pockets

Any bolt pockets must be grouted prior to grouting between the substrate and base plate.

Pumping

Where large volumes must be placed, Conbextra C may be pumped. A heavy-duty diaphragm pump is recommended. Screw feed and piston pumps may also be suitable. Maximum aggregate size for pumping is 0.3mm — ensure the selected pump is capable of handling this size.

Flow Properties Guide

The following flow distances (mm) are provided as a guide. Actual flow distances will vary depending on site conditions:

Gap Depth (mm)	Flowable 100mm head (mm)	Flowable 250mm head (mm)
10	320	1080
20	850	2300
30	1350	2700
40	2000	2700+
50	2700	2700+

Surface Preparation

Foundation Surface

The substrate surface must be:

• Free from oil, grease, or any loosely adherent material
• If defective or has laitance, cut back to sound base
• Abraded or roughened for maximum bond, preferably by mechanical means (needle gun, grit blasting, grinding)
• Bolt holes or fixing pockets blown clean of dirt and debris

Base Plate

• Must be clean and free from oil, grease, scale, paint, or any coating
• Air pressure relief holes should be provided to vent isolated high spots

Levelling Shims

If to be removed after hardening, treat with a thin layer of grease.

Formwork

• Must be leakproof — use foam rubber strip or construction silicone sealant beneath and between joints
• Should include outlets for pre-soaking
• Gap width between perimeter formwork and plate edge should not exceed 150mm on pouring side and 50mm on opposite side
• Advisable to have no gap at flank sides

Pre-soaking

• Fill the formed grouting area with clean water for minimum 2 hours before grouting
• Immediately before grouting, remove any free water by draining or vacuum
• Take particular care to blow out bolt holes and pockets

Curing and Finishing

Curing Method

On completion of the grouting operation, exposed areas should be thoroughly cured by:

• Use of Concure curing membrane, or
• Continuous application of water and/or wet hessian

Cleaning

Conbextra C should be removed from tools and equipment with clean water immediately after use. Cured material can be removed mechanically.

Limitations and Special Conditions

Low Temperature Working

• When air or contact surface temperatures are 5°C or below on a falling thermometer, grouting should be postponed
• For ambient temperatures below 10°C, maintain formwork in place for at least 36 hours
• Adopt normal winter precautions for cementitious materials

High Temperature Working

• At ambient temperatures above 35°C, use cool water (below 20°C) for mixing the grout prior to placement

Storage and Shelf Life

Conbextra C has a shelf life of 36 months from date of manufacture if kept in original, unopened bags. Refer to the manufacture date on packaging.

Do not use if:

• Lumps are present in the product
• Loss of workability occurs (requiring more water to be added)

Packaging and Supply

• Conbextra C 20kg: FC501040-20KG
• Supplied in 20kg moisture-resistant plastic bags

Safety Information

A Safety Data Sheet (SDS) is available from the Fosroc website. Read the SDS and Technical Data Sheet (TDS) carefully prior to use, as application or performance data may change from time to time.

In emergency: Contact any Poisons Information Centre (phone 13 11 26 within Australia) or a doctor for advice.

Product Disclaimer

This Technical Data Sheet summarizes the best knowledge of the product, including how to use and apply it based on information available at the time. Users should read this TDS carefully and consider the information in the context of how the product will be used, including in conjunction with any other product and the type of surfaces to, and the manner in which, the product will be applied.

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References

• [1] Fosroc_Conbextra_C_TDS.pdf
• [3] Fosroc_Conbextra_HS_TDS.pdf
• [5] Fosroc_Conbextra_GP_TDS.pdf
• [6] Fosroc_Conbextra_Deep_Pour_TDS.pdf