Estudo da influência do teor de umidade na resistência ao fogo de placas maciças pré-fabricadas de concreto

Abstract

From the validity of the Brazilian performance law, parameters other than durability have been studied by designers and researchers in Brazil. Fire safety has been a major concern among professionals, although it still is not known by most of the market. In case of accidents, the building must have means of allowing the users to evacuate safe and rapidly, while providing easy access to the actions of firefighters and security of assets. According to the values of fire safety, the resources for hindering the principles of fire and propagation, as well as the fire-resistance rating (FRR), are defined with respect to the specificities of each system designed. The concrete, as a material with low thermal conductivity, presents a good performance against fire when compared to other structural systems. However, this composite, when submitted to high temperatures, has its mechanical properties altered. With the civil construction’s tendency of industrialization, the use of prefabricated concrete pieces has been seen as an alternative to use on buildings, although their behavior in fire situations is not so widespread in the technical field. Among the influence factors that can impair the fire resistance of these pieces are the moisture content and the internal pressure. These factors, combined or isolated, provoke pathological manifestations originated from high temperatures, such as spalling, cracking, loss of moisture, deformations, and others. Still, a blank in the technical field is the age of cure for performing the tests that evaluate FRR of concrete elements. The curing age of 28 days is used as a parameter, based on standards that orientate the tests for evaluating compressive strength of cylindrical specimens. The fire resistance tests are then performed from this this parameter. The concrete already presents satisfactory compressive strength at lower curing ages, however, the moisture content of the pieces is still very high, thus hindering the performance during the fire resistance tests. That way, designers choose to modify projects, increasing the covering of the armors, making additions to concrete, etc. Therefore, this research aimed to evaluate the influence of moisture content and internal pressure on prefabricated concrete pieces, considering only the samples’ curing age as a variable and proposing a method for quantifying moisture content and internal pressure. The test was performed in a standardized vertical oven, and the specimens were tested with 7, 14, 28, 56 and 84 days of curing, all cured outdoors, thus displaying different moisture contents. Based on the test results, the samples with 84 days of curing, which displayed the smallest moisture contents, presented better performance regarding high temperatures, indication the influence of this factor.