Conbextra HS: Ultra High Strength Flowable Grout

Product Overview

Conbextra HS is a high-performance, dual shrinkage compensated, ultra high-strength cementitious grout engineered specifically for precision grouting applications. As a ready-to-use dry powder, it requires only the addition of clean water to produce a free-flowing precision grout suitable for demanding structural applications.

Key Applications

Conbextra HS is designed for heavy-duty precision grouting of gaps ranging from 10mm to 125mm, with particular effectiveness in applications including:

• Baseplates and soleplates of large machines subject to moderate dynamic loads
• Crane rail soleplates, beams, columns, and structural building members
• Foundation grouting requiring high flow and high ultimate strength

Core Features and Advantages

Shrinkage Compensation

Conbextra HS incorporates a non-metallic dual expansion system (Class A and Class C) that compensates for shrinkage in both plastic and hardened states, meeting ASTM C1107:2020 specifications for non-shrink performance. The expansion mechanism is hydrogen-free gaseous, ensuring reliable volume stability.

Flow Characteristics

The product demonstrates excellent initial flow and flow retention suitable for both large and small grout pours. This outstanding flowability, combined with its controlled consistency options, enables efficient application across diverse job site conditions without extensive working or finishing requirements.

Strength Development

• Rapid strength gain facilitates efficient installation and rapid plant operation
• High ultimate strength and low permeability ensure long-term durability of hardened grout
• Progressive strength development across extended curing periods

Chemical Properties

• Chloride-free formulation suitable for sensitive applications
• RCS (Respirable Crystalline Silica) Hazard Free - classified as non-hazardous, containing <0.1% RCS in accordance with Australian Inventory of Industrial Chemicals
• Suitable for pumping or pouring over a wide range of application consistencies and temperatures

Technical Specifications

Product Composition

Conbextra HS is a blend of:

• Portland cements
• Graded fillers (minimizing segregation and bleeding)
• Chemical additives imparting controlled expansion in both plastic and hardened states

Maximum aggregate size for pumping: 1.0mm

Consistency Options and Yield

The product can be mixed to two primary consistency levels:

Consistency	Water Addition (per 20kg bag)	Yield (mixed material)
Flowable	2.7 litres	9.8 litres
Fluid	3.0 litres	10.1 litres

Compressive Strength Performance

At 23°C:

Consistency	8 hrs	12 hrs	1 Day	7 Days	28 Days	56 Days
Flowable	5 MPa	20 MPa	55 MPa	80 MPa	100 MPa	105 MPa
Fluid	—	13 MPa	40 MPa	70 MPa	85 MPa	90 MPa

At 30°C:

Consistency	8 hrs	12 hrs	1 Day	7 Days	28 Days	56 Days
Flowable	26 MPa	40 MPa	60 MPa	90 MPa	100 MPa	105 MPa
Fluid	20 MPa	30 MPa	50 MPa	80 MPa	85 MPa	90 MPa

Flow Properties

The following flow distances (in millimeters) are indicative and will vary based on site conditions:

Gap Depth (mm)	Flowable 100mm Head	Flowable 250mm Head	Fluid 100mm Head	Fluid 250mm Head
10	360 mm	1200 mm	900 mm	2500 mm
20	950 mm	2600 mm	1900 mm	3000 mm
30	1500 mm	3000 mm	3000 mm	3000+ mm

Flexural and Tensile Strength

• Flexural Strength (Modulus of Rupture): 5.8 MPa (1 day), 11.4 MPa (7 days), 13.7 MPa (28 days)
• Indirect Tensile Strength: Values documented across multiple curing intervals

Maximum Filling Ratio with Aggregate

When bulking out Conbextra HS with Conbextra Grout Aggregate, the maximum filling ratio should not exceed 2:1 (Grout:Aggregate by weight). Grout depths exceeding 125mm up to 500mm should be addressed through bulking or by using Conbextra Deep Pour as an alternative product.

Placement and Application Parameters

Gap Depth Limitations

• Maximum single pour: 125mm without alternatives
• Depths 125mm to 500mm: Require either bulking with Conbextra Grout Aggregate or use of Conbextra Deep Pour

Placement Requirements

• Place grout within 15 minutes of mixing to gain full benefit of expansion process
• Continuous grout flow is essential to ensure complete filling and minimize air entrapment
• Formwork must be leakproof as Conbextra HS is a free-flowing grout
• Optimal formwork gap widths: maximum 150mm on pouring side, 50mm on opposite side

Temperature Considerations

Low Temperature Working:

• When air or contact surface temperatures are 5°C or below (falling), use warm water (30-40°C) to accelerate strength development
• For ambient temperatures below 10°C, use flowable consistency and maintain formwork for minimum 36 hours

High Temperature Working:

• At ambient temperatures above 35°C, store mixed grout in shade
• Use cool water (below 20°C) for mixing

Mixing Requirements

A forced-action mixer is essential for proper mixing:

• Mix at slow speed (400-500 rpm) for 3-5 minutes
• Use appropriate equipment such as 140mm helical mixing paddle fitted to heavy-duty 1600W mixer
• Always add powder to water (not vice versa)
• Ensure smooth, even consistency

For larger volumes, a high-shear vane mixer is required; colloidal impeller mixers should not be used.

Standards Compliance

Fire Performance (AS1530.3-1999)

All flame spread indices measure 0 or minimal values:

• Ignitability Indices: 0
• Spread of Flame Index: 0
• Heat Evolved Index: 0
• Smoke Developed Index: 0-1

Testing Standards

• Compressive Strength: AS 1478.2:2005
• Flexural Strength: AS 1012.11:2000
• Indirect Tensile Strength: AS 1012.10:2000
• Expansion/Shrinkage: ASTM C1107:2020

Supply and Storage

Packaging: 20kg moisture-resistant plastic bags (Product code: FC502000-20KG)

Shelf Life: 36 months from date of manufacture when stored in original, unopened bags under proper storage conditions

Storage Conditions: Keep in original, unopened bags in dry conditions. Do not use if lumps are present or if workability loss is experienced (requiring excessive water addition).

Health and Safety

A Safety Data Sheet (SDS) is available from the Fosroc website and must be read carefully prior to use. In emergencies, contact the Poisons Information Centre at 13 11 26 (within Australia) or consult a doctor for advice.

References

• [1] Fosroc_Conbextra_HS_TDS.pdf
• [2] Fosroc_Conbextra_HF_TDS.pdf
• [3] Fosroc_Conbextra_HES_TDS.pdf
• [6] Fosroc_Conbextra_Deep_Pour_TDS.pdf