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Yuleba Minerals Pty Ltd is and Australian company mining a high grade silica deposit in south west Queensland
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Shot Crete Shotcrete is, in effect, a version of a cast-in-place concrete wall. Rather than placing concrete into forms, however, a fresh mix is sprayed onto wall, roof or other panels.
A nozzle man applies concrete from a pressurized hose to encompass the reinforcement and build up the wall thickness, forming structural shapes that include walls, floors, roofs, and other assemblies.
This material has also been called “gunite” in reference to the nozzle or “gun” used to shoot material at the form face. Any surface suitable for accepting fresh concrete can be used: wood, steel, and polystyrene are common. Finishes are often applied directly to the concrete while it is still wet.
Advantages Shotcrete structures have advantages, they are strong, durable, resistant to disasters, fires, mould, insects and vermin, and have low permeability, good thermal mass, and create tight envelopes.
Although the hardened properties of shotcrete are similar to conventional cast-in-place concrete, the nature of the placement process provides additional benefits, such as very fast erection, particularly on complex forms or shapes, including curved walls and arches.
Shotcrete is a cost effective building method due to the speed of construction and minimal equipment requirements.
Installation One reason that shotcrete systems are installed so quickly is that the formwork is often lightweight. They are easy to handle and make erecting the shape simple. It may be possible to do this primarily with manual labour and very limited equipment.
In most shotcrete systems, dowels from the floor slab provide attachment at the base of the walls. For insulated panels, each segment is attached to at least two dowels. At the top edges, the panels are connected to ones on either side of them.
For the plain mesh systems (no polystyrene core), rebar is attached to the floor dowels and then wire mesh is hung off the rebar. One proprietary system uses a top beam to position and brace the rebar and form a clean edge at the roofline.
All shotcrete methods involve spraying material onto the forms. There are two ways to do this: a wet mix and a dry mix. The end result is the same on the wall, but the mixing equipment is slightly different.
•Wet Mix - All ingredients, including water, are thoroughly mixed and introduced into the delivery equipment. Wet material is pumped to the nozzle where compressed air is added to provide high velocity for placement and consolidation of the material onto the receiving surface.
• Dry Mix - Pre-blended dry or damp materials are placed into the delivery equipment. Compressed air conveys material through a hose at high velocity to the nozzle, where water is added. Material is consolidated on the receiving surface by the high-impact velocity.
The basic concrete mix contains cement, aggregates, and water. Natural aggregates and sand are easy to pump and form the basis of Yuleba Minerals SP2, SP3 and SP4 shotcrete product range and According to the American Shotcrete Association, properties of both wet and dry process shotcrete can be further enhanced through the addition of other ingredients, such as:
• Silica Fume - Provides reduced permeability, increased compressive and flexural strength, increased resistance to alkali and chemical attack, improved resistance to water washout, reduced rebound levels, and allows for thicker single pass applications.
• Air-Entraining Admixtures - Improve pump ability and adhesion in wet-process shotcrete and freeze-thaw durability in both wet and dry processes.
• Fibres - Control cracking, increase toughness values and improve impact resistance and energy absorption.• Accelerators - Improve placement characteristics in adverse conditions, allow for thicker single pass applications, increase production capabilities and reduce the occurrence of fallouts on structures subjected to vibration.
Yuleba Minerals (www.yulebaminerals.com.au ) manufactures its products at its quarry in the Surat Basin around the Roma and Miles townships and distribute shotcrete throughout the Emerald, Mackay, Blackwater (Bowen Basin) and the NSW mining areas including the Gunnedah and Hunter Valley.
