Mining and Ground Control

Yuleba Minerals produces a range of mining and ground control products;

Shote Crete

Shotcrete is usually an all-inclusive term that can be used for both wet-mix and dry-mix versions. In the pool construction trade however, the term “shotcrete” refers to wet-mix and “gunite” refers to dry-mix;

Shotcrete undergoes placement and compaction at the same time due to the force with which it is projected from the nozzle. It can be impacted onto any type or shape of surface, including vertical or overhead areas.

The dry mix method involves placing the dry ingredients into a hopper and then conveying them pneumatically through a hose to the nozzle. The nozzleman controls the addition of water at the nozzle. The water and the dry mixture is not completely mixed, but is completed as the mixture hits the receiving surface. This requires a skilled nozzleman, especially in the case of thick or heavily reinforced sections. Advantages of the dry mix process are that the water content can be adjusted instantaneously by the nozzleman, allowing more effective placement in overhead and vertical applications without using accelerators. The dry mix process is useful in repair applications when it is necessary to stop frequently, as the dry material is easily discharged from the hose.

Wet-mix shotcrete involves pumping of a previously prepared concrete, typically ready-mixed concrete, to the nozzle. Compressed air is introduced at the nozzle to impel the mixture onto the receiving surface. The wet-gun procedure generally produces less rebound, waste (when material falls to the floor), and dust compared to the dry-mix procedure. The greatest advantage of the wet-mix process is that larger volumes can be placed in less time.

Yuleba Minerals located near Roma and Chinchilla produces the SP series of shotcrete products which are supplied as a dry mix in 20kg bulk and mini bulk bags and can be wet or dry pumped the product has been formulated around a fine sand to minimise product loses from rebound. This makes the product ideal for spraying in and around steel reinforcing and where vertical and overhead spraying is required.

The SP2, SP3 and SP4 formulations provide a range of ultimate compressive strengths which allows the user to select a product to meet a specific need or application. The SP range of shot crete is used in underground coal mining for stoppings rib and roof support the product is available throughout the Bowen Basin, Emerald Mackay Queensland and Hunter and Gunnedah coal fields NSW.

Mine Ventilation

As a result of advances in materials technology, newer products have become available for the construction of ventilation controls, particularly for stoppings used in underground coal mines. Some of the newer materials were developed for the building and construction industry and were subsequently introduced into the mining industry. Another development was the use of fly ash as a component in the manufacture of lightweight blocks. Ventilation control devices such as stoppings, overcasts and under casts have traditionally been constructed of concrete block or steel panels. Efforts to reduce material and labour costs in the construction of stoppings have led to the introduction of newer lightweight materials for the construction of ventilation controls.

Traditional stoppings are usually constructed of hollow-core concrete blocks by dry stacking or by binding with mortar between the block joints. A difficulty with using concrete blocks is they are heavy. A typical 20.32-cm wide by 20.32-cm high by 40.64-cm long hollow core concrete block weighs on average about 18 kg. Today, comparable lightweight blocks weigh much less, which can be one third or less weight, or around 12 kg or less. The lightweight blocks are generally available in various sizes from 15.24 cm thick and 20.32 cm or 30.48 cm high and 60.96 cm long.

Some of the “non-traditional” or newer materials consist of lightweight blocks composed of various cement-type compounds or mixtures which may include fly ash or inorganic oxides such as calcium oxide and sand. Sometimes a small amount of plastic fibres are used in cement-type block mixtures to prevent micro cracks from developing into macro cracks. There are also block units made from autoclaved aerated concrete mixture. This type of unit is based on calcium silicate hydrates in which low density is acquired from reaction of the formulated materials to produce macroscopic voids in the finished product.

Other newer products are panels composed of gypsum or other mineral-type compounds, and plastic membrane and steel fabricated designs. Reduced labour and material costs 3may be derived from the use of lightweight blocks or the newer materials and designs, while the required safety may be derived from the use of lightweight blocks or the newer materials and designs, while the required safety properties are maintained. One factor in determining whether to use the “non-traditional” or newer materials would be the mine conditions and ventilation control factors. Will the stopping construction resist heaving and crushing? Are the newer materials readily available and affordable? Also, the most cost-effective ventilation controls are not necessarily those built in the shortest possible time. The steel and composite-type designs may require more effort to install. They are not advantageous for use where the openings are non-uniform, since additional materials and effort will be needed to close openings and gaps. Cost effectiveness is maximized by incorporating those qualities into ventilation controls that will minimize air loss.

Yuleba Minerals (www.yulebaminerals.com.au) produces a range of shotcrete or gunite products at its Roma quarry near the townships of Miles and Chinchilla that can be used by coal mines to spray concrete onto light structures forming a strong durable ventilation stopping. These products known as SP2,SP3 and SP4 are used widely by mines in the Bowen and Gunnedah basins reaching as far South as Angus Place and the Hunter Valley.