SAFETY
In the dynamic field of construction, shotcreting plays a pivotal role, offering a versatile and efficient method for applying concrete. However, it's imperative to prioritize safety due to the inherent risks of the shotcreting process. This webpage is dedicated to outlining the best practices and guidelines for ensuring safety in shotcreting operations.
Adhering to Regulations and Training
- Compliance with Safety Regulations: It's essential to adhere strictly to statutory and site-specific Occupational Health and Safety regulations.
- Training and Competency: Operators and personnel must be thoroughly trained and competent in their roles, including statutory and industry inductions, as well as site-specific training.
Personal Protective Equipment (PPE)
- Essential Gear: All personnel must wear safety helmets, approved footwear, and high-visibility vests.
- Protection from Rebound and Dust: Use of approved dust masks, respirators, eye, and ear protection is crucial, especially for sprayers and personnel near the shotcreting operation.
- Skin Protection: Barrier creams or other skin protection methods are necessary due to the irritating nature of wet cement and chemicals used in shotcrete.
- Appropriate Clothing: Long sleeves and pants are recommended for sprayers to protect against splashes and debris.
Equipment and Operational Safety
- Remote-Controlled Equipment: Utilizing remote-controlled equipment can significantly enhance safety by keeping operators away from unsupported ground and minimizing exposure to rebound and dust.
- Proper Lighting: Adequate lighting is critical, especially in underground environments, to ensure safe and effective spraying.
- Restricting Access: Limit access to the shotcreting area with signage and barricades to prevent unauthorized entry.
Pre-Spraying Safety Checks
- Inspecting the Site: Before beginning shotcreting, thoroughly inspect the site for misfired explosives, loose ground, water seepage, and signs of ground movement.
- Equipment Set-Up: Ensure that the shotcrete machine is correctly positioned and ready for operation after a comprehensive inspection and risk assessment.
Stability of Fresh Shotcrete
When new shotcrete is sprayed it will usually rely on either bond to the substrate or support of reinforcing bars or mesh to remain in place until it is hardened. In some cases this may not be sufficient to maintain stability with the result that the shotcrete may fall out or slide to the base of the wall or slope where it was placed. This can present a safety risk to the sprayer or other workers and must be considered carefully before work commences.
In the case of overhead spraying, fall outs of fresh shotcrete are one of the most serious risks faced by operators involved in the spraying of linings. For this reason, several measures are usually applied to prevent fall-outs or the consequences of fall-outs. Firstly, the surface of the ground is thoroughly scaled to remove loose rocks that may initiate a fall-out. This could include high pressure water jetting or hydro-scaling of the ground surface. Secondly, the ground surface must be left damp prior to spraying of concrete to aid in the development of bond to the ground. Thirdly, an exclusion zone is normally placed around a freshly sprayed area to allow strength (and associated adhesion to the substrate) to develop before human re-entry is permitted under the newly sprayed area. A common requirement is that the shotcrete must develop a minimum compressive strength of 1 MPa and bolting must be completed with cover plates installed before an area can be considered ‘safe’ for re-entry. However, variations on these requirements may apply especially in soft ground tunnelling.
For shotcrete sprayed on walls and slopes, set accelerator is usually not used so the shotcrete may be considerably softer and setting times longer than is typical of overhead spraying in tunnels and mines. Thin layers of low slump shotcrete are typically sprayed to stabilize slopes, and these may be reinforced with fibres or mesh. The slump must be relatively low (under 80 mm) to avoid sloughing or sliding of the shotcrete down-slope before the work is finished. Rigid mesh with numerous tie-down points can assist in maintaining stability. For vertical walls, mesh or reinforcing bars are normally used to provide a framework to support the weight of wet shotcrete as it is screeded, floated, or otherwise worked to the final surface finish requirements all of which must be done while it is wet. There is always a risk that the shotcrete may fall out or collapse while being worked. This is most commonly addressed by using low slump shotcrete, a rigid framework of support, and careful manual work. Special attention to safety is required when working walls over 2 metres high.
Maintaining a safe shotcreting environment requires diligent adherence to safety regulations, proper training, use of protective equipment, and cautious operation. By following these guidelines, shotcreting can be performed efficiently without compromising the safety and well-being of those involved.
