Special Class Concrete

Overview

“Special Class” concrete is a term applied to concrete with a nominated strength grade over 50MPa, or with other specified performance characteristics, for example early strength, or maximum shrinkage values lower than 1000 micro-strain.

Kerb and Gutter

Kerb and gutter concrete is manufactured specifically for slipform machine placement and adheres to local council and TfNSW specifications, including nominated strength grade or cementitious content.

Slipform machines will consolidate, form and finish a plastic concrete mass to a redescribed shape or geometric form as it is pulled through it.

Slipform placement can be reliant on high concrete production and delivery rates to ensure a seamless process.

The concrete used needs to have specific properties in order to achieve optimal results and a clean smooth finish.

Specifically for kerb and gutter slipforms, the concrete will generally need the below properties:

Zero slump
Jersey kerb – 30mm slump and 10-14mm aggregate

Early Strength Concrete

Early strength concrete is a special class where the application requires early strength development, generally when early serviceability, stripping of formwork or lifting is required.

Concretes such as these are manufactured using specialised formulas (specified under AS3972) in addition to specific admixtures, placticisers and aggregates.

Precast panels

Generally specified at a higher slump (e.g. 140mm+) to achieve a high quality off-form finish, precast concrete can be designed to achieve early age strength to meet specific lifting requirements.

Post Tensioned Concrete

Generally used in suspended slab work to meet early age strength requirements. The concrete is generally ordered at 22MPa at 4 or 5 days. 22MPa at 3 days is available if building programs require.

Cast-in-place Construction

Early strength development assists with the speed of construction by allowing early stripping of formwork, as well as building upwards without the risk of concrete failure.

Prescribed Mix Concrete

Prescribed concrete is a mix for which the purchaser prescribes the exact composition and constituents of the concrete.

The purchaser is responsible for ensuring that these proportions produce a concrete with the required performance. Effectively the purchaser selects the materials and mix proportions to satisfy the required strength and durability needs but does not specify these parameters.

The mix is ordered by its constituent materials and the properties or quantities of those constituents to produce a concrete with the required performance. The assessment of the mix proportions will form an essential part of the conformity (compliance) requirements if the purchaser so requires.

Here at Hunter Readymixed, we have the Quality Assurance systems in place to oversee the manufacture of prescribed concrete, as well as the post manufacture testing through Hunter Construction Group company Hunter Civilab. Please contact HRMC for advice.

Fibre Reinforced Concrete

Steel fibres or poly fibres can be added to the concrete mix design to assist with minimising early age concrete cracking (or shrinkage cracking) and to reduce the permeability of the concrete. Steel fibres are also used in lieu of steel re-enforcing mesh.

Strength and Cracking Applications

The introduction of fibres into the mix influences the cracking properties of concrete, where micro cracking is the initial process that gives way to larger structural cracks. Fibres can control micro cracking in a way that lessens or eliminates the occurrence of these subsequent larger cracks.

Permeability Applications

Another application of fibres in concrete can be to reduce permeability. Concrete is a naturally permeable product, but many applications call for a watertight or water-resistant product. Whether used in conjunction with waterproofing membranes or not, fibre reinforced concrete can serve a useful and specific purpose.

Ask us about the types of fibre reinforcing that might suit your application.

No Fines Concrete

Made for drainage applications, the concrete is designed without fine aggregates to make the concrete permeable so fluids can flow through the concrete.

No Fines Concrete can be used to absorb and direct runoff in stormwater applications, to capture water in tanks or natural water reservoirs, or to simply prevent surface pooling.

No Fines Concrete is generally supplied to a specified cement to aggregate ratio.

Flowable Concrete

Flowable concrete can have a wide range of strengths and characteristics.

The concrete is usually designed to be super flowable through the addition of specialised super-plasticising admixtures generally in combination with low water binder ratios to achieve high early compressive strength and good off form finish characteristics.

Includes concrete designed for applications such as:

Piling
Stabilised Thermal Backfill for encasing power cables
Filling Masonry blocks
Tremie (underwater) work
Structural concrete for bridge work.

Hunter Readymixed has a number of mixes available to suit any application.

Sprayed Concrete / Pool Mix

Sprayed concrete is a method by which concrete is sprayed into place. As such, the concrete itself is manufactured specifically for this purpose.

Other terms for this product include Shotcrete and Pool Mix. It is commonly used to form the shell of a concrete swimming pool and the walls and ceiling of underground tunnels.

Commonly specified as a high strength concrete (32MPa) using small aggregates (5-10mm), the desirable traits include adhesiveness, the ability to stand-up on contact and to achieve its initial set more quickly than normal class concretes.

Lightweight Concrete

Lightweight concrete is a mixture made with a coated polystyrene aggregate, which give it its characteristic low density.

HRMC can supply lightweight concrete in densities from 1.2-2.0 tonnes per cubic metre.
Lightweight concrete has a limited compressive strength and is used in specialised applications.

light weight polystyrene aggregate concrete

Precast Concrete

Precast concrete is predominantly a construction product and is made by casting concrete in a reusable form or mould.

Casting occurs in a controlled, indoor environment and thus has a range of advantages including better quality assurance and production is unaffected by weather.

Precast concrete is available for a range of applications, and in a range of thicknesses, strengths, shapes and colours amongst other options.

Hunter Construction Group company Hunter Precast is Newcastle and the Hunter’s pre-eminent precast concrete manufacturer and installer.

Visit Hunter Precast Website

Stabilised Sand/Cement

Cement Stabilised Sand is sand mixed with a small amount of both cement and water in a range of ratios as required for specific applications.

Commonly used for filling around pipes, bulk filling voids, or for soil and earth stabilisation on landscaping and earthwork projects.

Lean blend at 20:1 (sand:cement) available as standard.

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