A feasible evaluation protocol to determine the reactivity of sulfide-bearing aggregates for use in concrete

• Autor(a) principal: Ana Paula Borges Marcelino
• Data de Publicação: 2020
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Repositório Institucional da UFMG
• Texto Completo: http://hdl.handle.net/1843/36519; https://orcid.org/0000-0001-8213-7729
• topic: Internal sulfate attack; Sulfide-bearing aggregates; Testing method; concrete; Engenharia de estruturas; Agregados (Materiais de construção); Concreto; Métodos de ensaio

There are many degradation mechanisms in reinforced concrete. They can be divided into degradation mechanisms of the structure itself, in deterioration of the reinforcement, and deterioration of the concrete. Sulfate attack belongs to the latter group. Internal sulfate attack is one of the most harmful deterioration mechanisms to concrete. Sulfide-bearing aggregates when oxidized release sulfates which are dispersed inside the hardened concrete leading to generalized expansion and cracking of the material. These effects could cause serious structural problems in concrete. The use of this type of aggregates in concrete production is increasing worldwide since sulfides are present in most rock lithology. Moreover, the natural reserves of rocks without sulfides are becoming depleted and scarce. Few scientific studies on the use of sulfide-bearing aggregates in concrete structures associated with the resistance of the technical community in using this material justify more investigations. The main contribution of this research is to evaluate the sulfide-bearing aggregate reactivity using the combination of different procedures with reduced cost and time. Aggregates derived from rocks of the Irapé hydroelectric power plant area in Minas Gerais were used. These rock samples contained sulfides in the order of 5% in their composition. Initially, the more reactive grain size was evaluated. Based on previous investigations, grain sizes between 0.15- and 4.80-mm were selected for the study. For each particle size, the quantities of pyrite (FeS2) and pyrrhotite (Fe(1-x)S) were first determined by the direct combustion test (LECO). The exposed surface of each sulfide was also quantified by the mineral liberation analysis (MLA) technique. Samples of each particle size were then immersed in an H2O2 solution and the released sulfate (from the sulfide oxidation) was quantified by turbidimetry, thus indicating in which particle size the sulfide reacted more. The results also showed that the larger the sulfide exposed surface and the smaller the aggregate particle size are, the more effective is its oxidation and consequently more reactive the aggregate. With these results, the particle sizes 0.15- to 2.40-mm were defined as the most likely to be oxidized: thus, it should be discarded for use in concrete. Particle sizes larger than 4.80 mm may not be reactive for the analyzed material; however additional tests will be needed to verify their possible use in concrete.