The new commercially available Micro-Composite Multi-Structural Formable (MMFX) steel is a high strength and highly corrosion-resistant steel. Use of MMFX steel could lead to potential savings due to its unique characteristics. Many state transportation departments have begun to use MMFX steel as a direct replacement for conventional Grade 60 steel. However, the higher strength and lack of well-defined yield point of MMFX steel alter the structural behavior of bridge decks reinforced with MMFX steel bars. Therefore, three concrete bridge decks with a span-to-depth ratio of 12.5 were tested up to failure using concentrated loads intended to simulate the effects of truck wheel loadings. The first and second bridge decks were reinforced with the same amount of MMFX and conventional Grade 60 steel, respectively. The third bridge deck was reinforced with MMFX steel reduced by 33 percent in an attempt to utilize its high strength characteristics. The results of the experimental program and the analytical modeling demonstrated that bridge decks reinforced with 33 percent less MMFX steel developed the same ultimate loadcarrying capacity and deflection at service load as those reinforced with Grade 60 steel.
In addition, the effect of bending on the tensile strength of MMFX steel bars was experimentally investigated. Experimental results demonstrated that debonded MMFX bent bars have a reduced ultimate strength by 6 percent. However, bonded bent bars developed the full strength as those of straight bars.
The high corrosion-resistance of MMFX steel bars claimed by the manufacturer was validated by using very severe test conditions. The corrosion test results confirmed that that MMFX steel has a lower corrosion rate compared to conventional Grade 60 steel.
