Emphasizing the Safety, Health and Hazards Related to Using of Sprayed Concrete in Underground Mining Works

Sprayed concrete is a traditional building material, but at the same time it represents a highly
innovative technology. The development of sprayed concrete includes material science and advances
spraying equipment technology. The performance and characteristics of sprayed concrete depend
mainly on the condition of its application, equipments, experience and competence of the crew
performing the sprayed concrete operation. This paper presents some aspects regarding a sprayed
concrete operation that may have multiple hazards due to the equipment, pressure value and the
projection of rebound. In addition, the use of sprayed concrete in underground mining works, involve
an adequate ventilation in the application area. Special attention has to be given to chemical
admixtures and complementary products use in the constituent materials and finally, in the
composition of sprayed concrete. Using this technique in order to mobilize at maximum the strength
that develops in consolidated rocks around the underground work, lead to smaller loads that act on
permanent support and thus more economic and practical support system results. The particularity of
the support made from mortar or spraying concrete consists in the participation of the rocks
themselves to achieve the bearing strength. Thus, the rocks, from the object of the support, became
themselves a means of support, basically rocks are self-supporting. In the new formed system,
sprayed concrete - rock, the latter has a decisive role in supporting the underground works. The
mixture spilled on the surface of rocks adheres very well and strengthens in a short time, having a
resistance and impermeability superior to conventional concrete. The sprayed concrete is
impermeable to water infiltrations at pressures of less than 0.6 to 0.8 MPa and can be used as a
temporary and permanent support. Sprayed concrete is an artificial conglomerate obtained by setting
the homogeneous mixture of aggregates, binder and water in certain proportions. In smaller
proportions, other powdered materials are also found in the sprayed concrete composition and a
number of substances which modify, in the desired sense, some physical-mechanical characteristics.
From the spraying operation can be linked different hazards due to both technical and technological
factors, as well as the human factor. As regards the underground personnel who are directly involved
in the application of sprayed concrete, they must wear protective equipment at all times and ensure
adequate ventilation in the application area, because spraying creates dust, mist and other
substances that can contaminate the air. At the same time, there is a risk to be protruding
reinforcement fibers in sprayed concrete on the contour of underground work and may constitute real
dangers, as they can injure the personnel. To avoid this potential risk (hazard) a simple solution is to
initially apply a thin layer of unreinforced sprayed concrete. Special attention must to be given to
safety requirements and operation instructions provided by the equipment manufacturer and the
materials supplier. Admixtures and water reduction admixtures in particular, but also complementary
products, are generally considered to be harmful to humans and to the environment. Accelerators
based on silicate have a high alkali content and require personal protection against skin and eye
irritation; risk of alkali silicate reaction and leaking water soluble portions occurs. Accelerators based
on aluminates (alkaline) are caustic and require personal protection against skin and irritations. Alkalifree
accelerators are preferred because they are less hazardous and provide a better working
environment.