Comportamiento y diseño de hormigones estructurales con áridos siderúrgicos EAF

Resumen

The use of the EAF steel slags as aggregate in the production of concrete has gained great interest with the increasing concern about the environment impact and the sustainability in the construction industry. The EAF steel slags are by-products from the steel production process with electric arc furnace. In many applications, they are an interesting alternative to preserve natural resources, decrease the energetic consumption, decrease emissions and the need for landfills. Traditionally, the use of this EAF steel slags in concrete has been limited to applications with low added value, with poor structural responsibility and with reduced content due to reservations regarding its technical viability and durability. The EAF steel slags are characterized by a high density (around 3550 kg/m³) in comparison with conventional natural aggregate, a high resistance to fragmentation and to abrasion. These reasons make the EAF steel slag a potentially interesting material to produce heavyweight concrete or concrete submitted to highly abrasive processes. The main objective of this Thesis is to evaluate the technical viability of structural concrete with EAF steel slags in substitution to 100% of the conventional coarse aggregate and 80% of the conventional fine aggregate. Such analysis takes into account the requirements of two applications in which the EAF steel slags contributes to an improved performance (structural walls with radiological protection and the road bearing layer of pavements). In order to achieve these objectives, the research is divided in three parts that cover the different stages in the concrete life cycle: production, performance in service and durability. In the first part, the physical, chemical and mineralogical characteristics of the EAF steel slags are analyzed in comparison with those from the reference aggregates (limestone and barite). A study of the influence of the mixing process in the grading curve and the surface characteristics of the aggregates is conducted. In the second part, the ideal mix to obtain a structural heavyweight concrete with EAF steel slag is determined. Likewise, the mechanical properties, the radiological shielding capacity, the slip/skid and abrasion resistance are studied and compared with equivalent concrete mixes with reference aggregates. Finally, the durability of the concretes is evaluated for the possible degradation processes that might occur in the applications considered. The results show that the mechanical properties of concrete with EAF are similar or higher than the measured for conventional concrete and, in all cases, are significantly higher than the obtained for concretes with barite. Although the radiological attenuation coefficients of the concretes with EAF slags are lower than that of concrete with barite, the differences in terms of the equivalent wall thickness are small. Moreover, concrete with EAF steel slags have similar slip/skid resistance and higher resistance to abrasion than conventional concrete. These results support the use of EAF steel slags as aggregate to produce heavyweight concrete with structural responsibility with radiological protection capacity. Collaterally to the main focus of the present study, it was found that the mixing process modifies the grading curve of the barite at a higher extent than in the case of the other aggregates. This is attributed to the highly crystalline structure and high friability of barite, which generates a weak interfacial transition zone with the cement paste and affects adversely the mechanical properties and the durability of concrete. The observations of the behavior of barite aggregate during the mixing process provide important guidelines for its use in the concrete.