Sprayed concrete is a conventional construction material, but it reflects a highly advanced process at the same time. The development of sprayed concrete requires material science and developments in technology for spraying equipment. The performance and characteristics of sprayed concrete depend, in particular, on the state of its application, the equipment, the experience and the competence of the sprayed concrete team. This paper presents several aspects of a sprayed concrete operation that, due to the machinery, pressure value and the rebound projection, could have several hazards. In addition, proper ventilation in the field of application requires the use of sprayed concrete in underground mining works. Particular attention must be paid to the use of chemical admixtures and supplementary products in the constituent materials and, ultimately, in the sprayed concrete composition. Using this technique to mobilise the strength that forms in concentrated rocks around underground work to the limit, contributes to lower loads acting on permanent support and thus results in a more economic and realistic support system. The specificity of the support created from mortar or spraying concrete is that the rocks themselves are involved in achieving the bearing strength. Thus, from the object of the support, the rocks are a means of support themselves, literally rocks are self-supporting. The latter has a decisive role in promoting underground work in the newly developed framework of sprayed concrete-rock. With a resistance and impermeability superior to standard concrete, the mixture poured on the surface of rocks adheres very well and strengthens in a short time. At pressures of less than 0.6 to 0.8 MPa, the sprayed concrete is impervious to water penetration and can be used as a temporary and permanent support. Sprayed concrete is an artificial conglomerate obtained in some quantities by deciding the homogeneous mixture of aggregates, binder, and water. In smaller quantities, the sprayed concrete composition and a number of substances are also found in other powdered materials which change certain physical-mechanical characteristics in the desired sense. Due to both technical and technological variables, as well as the human factor, various hazards can be related from the spraying process. As far as underground workers who are directly involved in applying sprayed concrete are concerned, they must wear protective equipment at all times and maintain proper ventilation in the region of application, as spraying produces dust, mist and other contaminants that can contaminate the air. At the same time, there is a chance of protruding reinforcement fibres on the contour of underground work in sprayed concrete and can pose real dangers as they may harm the workers. A easy solution is to initially add a thin layer of unreinforced sprayed concrete to prevent this possible danger (hazard). Security specifications and operating instructions issued by the manufacturer of the equipment and the supplier of the materials must be given special attention. In particular, admixtures and admixtures for water reduction, but also complementary products, are commonly considered to be harmful to humans and the environment. Silicate-based accelerators have a high alkali content and need personal protection against irritation of the skin and eyes; there is a chance of alkali silicate reaction and water soluble portions leakage. Aluminate (alkaline)-based accelerators are caustic and require personal protection against skin and irritation. Since they are less risky and have a safer working environment, Alkalifree accelerators are favoured. The methods of spraying used have various effects on the working environment underground. Therefore, the use of the process of wet-mix spraying has a positive impact on the air quality of the working face and no air pollution has been found, if additions or alkaline-free accelerators are added in sprayed concrete, the working condition will dramatically improve. The sprayed concrete rebound consists mainly of aggregates, and its environmental effect is not significant. New sprayed concrete technology contributes greatly to environmental conservation and contributes to the safety of the entire working community. Advanced equipment allows underground workers to operate from safe distances to the work face and can mitigate the injuries that could arise or health issues as a result.

Author (s) Details

Mihaela Toderaş
University of Petrosani, Mining Engineering, Surveying and Constructions Department, 332006 Petrosani, Romania.

Ciprian Danciu
University of Petrosani, Mining Engineering, Surveying and Constructions Department, 332006 Petrosani, Romania.

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