Estudo de concretos fabricados com agregado reciclado e fibras de polipropileno em situação de incêndio

Abstract

Numerous residues generated attributable to the changes in the population's standard of living may become alternative materials for concrete manufacture, occasionally these residues not only can lead to a lower cost of concrete production, but also add beneficial characteristics in its properties which may diminish the environmental damage and the accumulation of some residual materials in landfills. Amongst the alternative materials that can be used in concrete, there is glass from long neck bottles as a compelling choice once it is a material generated in a large scale by the industrial sector and not returnable because of the high cost of the reuse process. In this way, the possibility arises to explore crumbled glass as an alternative material by partially replacing natural sand in the production of concrete. In this research, it will be under study beyond its conventional properties, the behaviour of concrete in the exposé of adverse situations in which the concrete structure can be subjected throughout its useful life, for example, in a fire situation. In addition to be in favour of the minimization of glass disposal, this research aims to collab with the reduction of the harm caused by high temperatures in a structure through the incorporation of polypropylene fibres in the matrix of some concretes, which reduce the possibility of the spalling phenomenon befall, typical of concrete in a fire situation. The mechanical properties of resistance to axial compression and traction by diametrical compression, as well as water absorption by capillarity, were evaluated. Four mixes produced with CP-IV 32RS cement were studied, the first without glass and fibres (conventional), the second with 40% crumbled glass partially replacing natural sand and polypropylene fibres at a rate of 5 kg/m3, the third without adding fibres (only with 40% glass) and the fourth without glass (only with fibres at a rate of 5 kg/m3). Previously to the resistance tests, part of the specimens was heated in a muffle until they reached a temperature of 600°C, where they remained exposed to a constant temperature for 30 minutes, simulating a fire situation. The spalling phenomenon was not observed in none of the traits studied under the imposed heating conditions, which made it impossible to directly verify the efficiency of the fibres against the phenomenon. The results of the analysis of variance performed (ANOVA) revealed that the rate of 40% of crumbled glass replacing natural sand did not significantly influence the parameters of resistance and durability analysed. The addition of fibres also did not influence the strength parameters, however, the durability of the concretes may have been affected with the incorporation of fibres due to the more expressive increase in water absorption of concretes with fibres after exposure to 600°C. Temperature proved to be a significant variable for all investigated parameters, as it significantly influenced the loss of mechanical properties and increased water absorption in the studied mixes. Keywords: Concrete, fibres, glass, high temperatures.