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The decrease in concrete resistance and the expansion generated in reinforced concrete structures by direct exposure to fire at 400 °C maximum temperature serves as the basis for the present research. The aim is to improve these problems by the addition of steel fibers or of polypropylene fibers in concrete. From the results analysis of compression fracture tests on cylindrical concrete specimens, it can be concluded that concrete with addition of polypropylene fibers or steel fibers are a good alternative to traditional concrete, because both its strength, and its behavior in case of fire are improved, delaying the appearance of fissures and explosive concrete spalling. [ABSTRACT FROM AUTHOR]

This paper focuses on two low-energy systems - thermo-active building systems and energy foundations - both of which use concrete elements that are already required for structural reasons but which simultaneously work as heat exchangers. The aim of this work was to study the mechanical behaviour of these concrete elements due to the inclusion of polyethylene pipe heat exchangers cast directly into the concrete core and the influence of fluids flowing inside at a moderate temperature. Cylindrical and cubic specimens of two types of concrete (H-25 and H-30) were manufactured in order to study the influence of temperature through compression and pull-out tests and the influence of the embedded pipes in different positions using compression tests. The mechanical properties were found to decrease with an increase in temperature in both concrete types, with a sharper decline in the H-30 specimens. The pipe layout reduced the mechanical resistance of the structural elements regardless of the type of concrete used, with the most damaging position being perpendicular to the load. It is concluded that thermo-active reinforced concrete elements perform best when the polyethylene pipes are placed parallel to the load and the temperature of fluid in the pipes is lower than 70°C. [ABSTRACT FROM AUTHOR]

Highlights: [•] Models that relate mechanical properties with corrosion degree have been obtained. [•] The variation of yield stress and ultimate strength does not depend on the diameter. [•] Bar resistance reduction is lower than the one caused by section loss. [•] Deformation energy density undergoes higher decreases than yield stress or strength. [Copyright &y& Elsevier]

Highlights: [•] The corrosion process in reference specimens and LFS specimens is similar. [•] In reference specimens with 0.8% Cl−, the inhibitor reduces the corrosion rate. [•] Reference specimens with 1.2 and 2% Cl−, inhibitor does not reduce the corrosion rate. [•] In LFS specimens and Cl− of over 0.4%, the bars remain in an active state. [•] The surface inhibitors are not effective in states of advanced corrosion. [Copyright &y& Elsevier]

The mechanical and structural behavior of three stainless steel (SS) reinforcing bars (austenitic AISI 304, duplex AISI 2304 and new lean duplex AISI 2001) have been studied and compared with the conventional carbon steel (CS) B500SD. The study was conducted at rebar level, cross-section level and structural member level. The results demonstrate higher ductility performance for hot-rolled SS rebars than for CS, but lower ductility for cold-rolled SS rebars compared to CS. The experimental elastic modulus of SS rebars is lower than that of CS. [ABSTRACT FROM AUTHOR]