Conbextra HF: High Flow Cementitious Precision Grout

Product Overview

Conbextra HF is a highly fluid, dual shrinkage compensated, cementitious non-shrink grout supplied as a ready-to-use dry powder. It is specifically designed for precision grouting applications requiring excellent flow characteristics and rapid strength development.

Key Features & Advantages

Conbextra HF offers several distinctive advantages that make it suitable for demanding applications:

• Excellent initial flow and flow retention – Suitable for both pumping and pouring applications
• Rapid strength gain – Facilitates efficient installation and operation of plant equipment
• High ultimate strength and low permeability – Ensures long-term durability of the hardened grout
• Hydrogen-free gaseous expansion – Provides controlled, non-metallic expansion
• Chloride free – Suitable for reinforced concrete applications
• RCS (Respirable Crystalline Silica) Hazard Free – Contains <0.1% RCS, classified as not hazardous
• Non-shrink properties – Complies with ASTM C1107:2020 standard specifications
• Dual shrinkage compensation – Controls expansion in both plastic and hardened states

Technical Composition

Conbextra HF is formulated as a blend of Portland cements, graded fillers and chemical additives which impart controlled expansion in both plastic and hardened states. The filler grading minimizes segregation and bleeding over a wide range of application consistencies. The low water requirement ensures high early strength and long-term durability.

Application Range & Uses

Conbextra HF is used for free flow precision grouting in a wide range of critical applications including:

• Critical machine base plates, sole plates and columns
• Pumped grouting applications
• Grouting applications where pouring access is restricted
• Precision gap filling requiring excellent flow properties

The product is designed for gap thicknesses of 10mm to 125mm in a single pour. For gaps exceeding 125mm up to 500mm, Conbextra Deep Pour or bulking with Conbextra Grout Aggregate may be considered.

Mechanical Properties

Compressive Strength (AS 1478.2:2005)

Consistency	Water Addition (litres/20kg)	1 Day (MPa)	7 Days (MPa)	28 Days (MPa)
Stiff	2.6-3.4	50	68	77
Plastic	3.4-3.6	38	53	64
Flowable	3.6-3.8	31	48	62
Fluid	3.8-4.0	27	46	60

Additional Strength Properties (AS 1478.2:2005)

• Flexural Strength (Modulus of Rupture): 3.2 MPa (1 Day), 9.5 MPa (7 Days), 10.0 MPa (28 Days)
• Indirect Tensile Strength: 2.5 MPa (1 Day), 4.5 MPa (7 Days), 4.7 MPa (28 Days)
• Setting Time: 5.5 hours (initial set), 7.5 hours (final set)
• Fresh Wet Density: 2200 kg/m³ (depending on consistency used)
• Alkali Reactive Particles: Non-reactive (per RTA T363 Rapid Mortar Bar Test)

ASTM C1107:2020 Test Results

Test Method	Standard	Result
Flow Consistency	ASTM C939:2016a	>145%
Setting Time	ASTM C953:2017	Initial: 300 mins / Final: 320 mins
Change in Height (Early Age)	ASTM C827:2016	+0.40%
Height Change (Hardened Grout, Moist Cure)	ASTM C1090:2015	+0.02% to +0.11% (varying by age)
Compressive Strength	ASTM C109:2020b	29.8 N/mm² (1 day) to 65.8 N/mm² (28 days)

Flow Characteristics

Flow Distance Guidance (AS 1478.2:2005):

• Flow Trough: 400 - 600mm
• Flow Cone: 19-25 seconds

The flow distances vary depending on gap depth and grout head applied:

Gap Depth (mm)	Flowable 100mm head (mm)	Flowable 250mm head (mm)	Fluid 100mm head (mm)	Fluid 250mm head (mm)
10	360	1200	900	2500
20	950	2600	1900	3000
30	1500	3000	3000	3000+
40	2200	3000+	3000+	3000+

Standards Compliance

Conbextra HF complies with the following standards:

• AS 1478.2-2005 Appendix E – Early Volume Change testing
• AS 1478.2-2005 Table 4.1.2.2 – Consistency classifications
• ASTM C1107:2020 – Non-shrink cementitious grout specification
• RCS Hazard Classification – Not hazardous for Respirable Crystalline Silica

Mixing & Consistency Options

Conbextra HF can be mixed to achieve four different consistency levels depending on application requirements:

Consistency	Water Addition (litres/20kg bag)	Yield (litres of mixed material)
Stiff	2.6 - 3.4	10.4
Plastic	3.4 - 3.6	10.7
Flowable	3.6 - 3.8	10.8
Fluid	3.8 - 4.0	10.9

Mixing Equipment Requirements

• Forced-action mixer essential – Mix for 3 to 5 minutes at slow speed (400/500 rpm)
• Typical equipment: 120/140mm helical mixing paddle fitted to heavy-duty 1600W mixer
• Larger volumes: High shear vane mixer (do not use colloidal impeller mixer)
• Always add powder to water, not vice versa

Placing & Application

• Placement window: Within 15 minutes of mixing to gain full benefit of expansion process
• Maximum thickness: 10mm to 125mm in a single pour as underplate grout
• Pumping capability: Heavy duty diaphragm pump recommended; screw feed and piston pumps also suitable
• Maximum aggregate size for pumping: 2.5mm
• Grout head maintenance: Essential to ensure continuous grout front and prevent air entrapment
• Pour method: From one side of void to eliminate air and pre-soaking water entrapment

Bulking Options

For grouting gaps exceeding 125mm up to 500mm thick, Conbextra HF can be:

• Bulked out with Conbextra Grout Aggregate (maximum ratio: 1 part aggregate to 2 parts grout by weight)
• Or alternatively, replaced with Conbextra Deep Pour product

Supply & Storage

Product Code: FC501050-20KG

Packaging: 20kg moisture-resistant plastic bags

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

Storage Conditions: Keep in dry conditions in original unopened packaging

Precautions: Do not use if lumps are present or if loss of workability is experienced

Temperature Considerations

Low Temperature Working

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

High Temperature Working

• At ambient temperatures above 35°C, mixed grout should be stored in shade
• Cool water (below 20°C) should be used for mixing

Curing & Finishing

• Curing method: Concure A99 curing membrane or wet hessian application
• Exposed areas: Should be thoroughly cured immediately after grouting completion
• Tool cleaning: Remove from tools and equipment with clean water immediately after use
• Cured material removal: Can be removed mechanically

Safety & Documentation

A Safety Data Sheet (SDS) is available from the Fosroc website and should be read carefully prior to use. In emergency situations, contact any Poisons Information Centre (phone 13 11 26 within Australia) or seek medical advice.

References

• [1] Fosroc_Conbextra_HF_TDS.pdf