Conbextra C - Dual Shrinkage Compensated Cementitious Grout

Overview

Conbextra C is a high-flow, dual shrinkage compensated, precision cementitious grout supplied as a ready-to-use dry powder formulation. Manufactured and distributed by Fosroc, this product is specifically engineered for general grouting applications where controlled expansion and dimensional stability are critical performance requirements.

Product Description

Conbextra C is a blend of Portland cement, specially graded fillers, and additives that impart controlled expansion in both the plastic (uncured) and hardened (cured) states while minimizing water demand. The low water demand ensures high early strength development, making it suitable for applications requiring rapid load transfer and structural performance.

The graded filler system is designed to assist uniform mixing and produce a consistent, flowable grout. The product features a maximum aggregate size of 0.3 mm for pumping applications, ensuring compatibility with various placement methods.

Key Applications

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

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

Technical Advantages

• Dual expansion system compensates for shrinkage in both the plastic and hardened states
• High ultimate strength and low permeability ensure the durability of the hardened grout
• Multiple placement methods - can be dry packed/rammed, trowelled, flowed, and pumped
• Hydrogen-free gas expansion - eliminates concerns about metallic expansion
• Prepackaged material overcomes potential on-site mixing variations
• Non-metallic iron content ensures no rusting issues
• 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 standard

Mechanical Properties

Compressive Strength

Compressive strength varies based on consistency and curing time:

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

According to ASTM C109:2020b testing (at water addition rate of 3.8 litres per 20 kg):

• 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 (Modulus of Rupture)

Time Period	Value (MPa)
1 Day	5.0
7 Days	9.5
28 Days	9.6

Indirect Tensile Strength

Time Period	Value (MPa)
1 Day	2.7
7 Days	4.4
28 Days	4.8

Additional Properties

• Fresh Wet Density: 2100 kg/m³ (depending on consistency used)
• Alkali Reactive Particles: Non-reactive (Rapid Mortar Bar Test - RTA T363)
• Flow Characteristics: 400 - 600 mm (Flow Trough) per AS 1478.2:2005

Standards Compliance

Conbextra C complies with the following standards:

• 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 cementitious grout specification
• AS 1012.11-2000: Flexural strength testing
• AS 1012.10:2000: Indirect tensile strength testing
• ASTM C185:2020: Fresh wet density testing
• RTA T363: Alkali reactive particles assessment

Mixing Specifications

Water Content and Yield

Consistency	Water Addition (Litres per 20 kg 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 Procedure

• For smaller volumes, use a forced-action mixer at slow speed (400/500 rpm)
• Mixing time: 3 minutes initial mixing, plus 2 minutes secondary mixing
• Always add powder to water, never the reverse
• For larger volumes, use a high-shear vane mixer (do not use colloidal impeller mixer)
• Water content must be accurately measured; do not exceed top-end water content specified on the Technical Data Sheet

Mixing Larger Volumes

A grout holding tank with provision for gentle agitation may be required to enable continuous grouting operations. Ensure sufficient mixing capacity and labor availability.

Placement Guidelines

• Placing time: Within 20 minutes of mixing at 23°C to gain full benefit of the expansion process
• Gap thickness: 10 mm to 100 mm in a single pour when used as underplate grout
• Continuous grout flow is essential to prevent air entrapment

Flow Properties

Flow distances at different gap depths (intended as a guide; actual distances vary with 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+

Bulking Out with Aggregate

For grouting gaps exceeding 100 mm, Conbextra C can be filled/bulked out with Conbextra Grout Aggregate in ratios not exceeding 2:1 (grout:aggregate by weight) to minimize exotherm heat buildup. Alternatively, Conbextra Deep Pour is available for pours up to 500 mm thick.

Pumping

Conbextra C may be pumped for large volume applications using:

• Heavy-duty diaphragm pump (recommended)
• Screw feed pumps
• Piston pumps

Maximum aggregate size for pumping: 0.3 mm

Curing Requirements

On completion of grouting, exposed areas should be thoroughly cured using:

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

Temperature Limitations

Low Temperature Working

• Below 5°C: Grouting should be postponed
• Below 10°C: Formwork must be kept in place for at least 36 hours; normal winter working precautions for cementitious materials should be adopted

High Temperature Working

• Above 35°C: Cool water (below 20°C) should be used for mixing prior to placement

Supply and Storage

Packaging: 20 kg moisture-resistant plastic bags

Product Code: FC501040-20KG

Shelf Life: 36 months from date of manufacture when kept in original, unopened bags

Storage Note: Do not use if lumps are present in the product or if loss of workability (requiring more water to be added) is experienced.

Safety and Documentation

• Safety Data Sheet (SDS): Available from the Fosroc website and should be read carefully prior to use
• Technical Data Sheet (TDS): Contains comprehensive application and performance data
• Emergency Contact: Poisons Information Centre (phone 13 11 26 within Australia)

Alternative Products

In applications where maximum flow properties and extended flow retention times are required, Conbextra HF should be considered as an alternative to Conbextra C.

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References

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