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• As F-S powder content increases, the flexural crack spacing increases. • F-S concrete strength is an important factor ensuring the flexural capacity. • Concrete strength affects the ductility of RC beams. • F-S concrete with required strength can be applied in beams. Concrete containing ferronickel slag with blast furnace slag, namely composite ferronickel slag concrete or F-S concrete, is featured by low bond strength with horizontally-placed rebar compared with normal concrete of equal strength. This feature may affect the flexural capacity and deformational characteristic of F-S concrete beams, which needs to be investigated. Four under-reinforced beams were prepared and tested, including one normal concrete beam and three F-S concrete beams. The variable was the percentages of F-S powder content, i.e., 0%, 20%, 30%, and 40%. The experimental results showed that as F-S powder content increased, both the flexural capacity and ductility of RC beams decreased. For the flexural capacity analysis, directly increasing F-S powder content lowers concrete strength, thus reducing the flexural capacity. Regarding the deformational characteristic analysis, the RC beam is ideally simplified to the combination of the compressive concrete column model plus the tie bar model, and the influence of tensile rigidity effect with different bond level on the tie bar deformation is mainly studied. It is found that the lower bond stress just increases the flexural crack spacing, and changes the stress and strain distribution of rebar and concrete, but does not change the stress-mean strain relation of the rebar in the tie bar per unit length. The incorporation of F-S powder has no effect on the deformation of RC beams. Unexpectedly, the concrete strength is another important factor affecting the plastic rotation ability of RC beams. Whether increasing/decreasing the concrete strength will increase or decrease the ductility of RC beams, it is much determined by the given ratio of the longitudinal tensile reinforcement. In other words, while F-S concrete strength equals that of normal concrete, the ductility of the F-S concrete beam resembles that of normal concrete beam. F-S concrete can be applied in engineering structures, as long as it meets the design strength requirement as normal concrete does, irrespective of any F-S powder content. [ABSTRACT FROM AUTHOR]

• Bond quality of F-S concrete is inferior to that of normal concrete. • Bleeding has a severe impact on the bond quality of reinforcement-concrete. • A bond stress-slip relationship was proposed for F-S concrete. • An anchorage length modifying factor was proposed for F-S concrete. Thirty-six pullout tests, including twelve groups of three specimens, were performed to study the bond behavior of steel reinforcement in concrete containing ferronickel slag and blast furnace slag powder (F-S powder/concrete). Test parameters considered in this research were F-S powder replacement percentages (i.e., 0%, 10%, 20%, 30%, 40%, and 50%) and concrete strength grades (i.e., C30 and C35). Unexpectedly, the results showed that the bond quality of steel reinforcement in F-S concrete was inferior to that of normal concrete even with comparable concrete strength. The more F-S powder content, the greater the inferiority. Through investigating the underlying mechanism, it was found that bleeding adversely affected the reinforcement-concrete bond quality in F-S concrete. Based on the pullout test results, a bond stress-slip relationship and an anchorage length modifying factor were proposed for F-S concrete of C30 and C35 strength grade. The conclusions would help designers assess the suitability of a particular F-S concrete for use in a given structure. [ABSTRACT FROM AUTHOR]

• F-S concrete presents identical mechanical properties to conventional concrete. • The stress-strain curve characteristics were mainly related to F-S concrete strength. • The stress-strain constitutive equations were established for F-S concrete. This study investigated the mechanical properties of concrete of strength grade C30 and C35, containing different content (10%–50%) of a composite admixture of ferronickel slag and blast furnace slag powder (referred to as F-S powder and F-S concrete hereafter, respectively). The mechanical properties include axial compressive strength, elastic modulus, Poisson's ratio, splitting tensile strength, and the compressive stress-strain relationship. The difference in mechanical properties between F-S concrete and conventional concrete was analyzed. Test results indicated that the positive correlation of conventional concrete between the axial compressive strength, elastic modulus, splitting tensile strength, and cubic compressive strength was applicable to F-S concrete irresponsible of the specific F-S powder content. Both Poisson's ratio and the failure mode under compression for F-S concrete were identical to those of conventional concrete. The shape characteristics and fitting parameters of the stress-strain curve were mainly related to F-S concrete strength grade but had little connection with the specific F-S powder content. Furthermore, based on tested data, the stress-strain constitutive equations were established for F-S concrete, which provides a reference for the test analysis of large specimens and corresponding engineering application. [ABSTRACT FROM AUTHOR]