The effect of fi̇ber combi̇nati̇on, fi̇ber volume and mi̇cro fi̇ber length on the electri̇cal resi̇sti̇vi̇ty of the hybri̇d steel fi̇ber rei̇nforced self-compacti̇ng concrete

Concrete, which is one of the commonly used building materials, is not a good conductive material despite its high mechanical properties. Many studies have been performed on the contribution of steel fibers to the concrete's electrical conductivity and mechanical properties. Within the scope of this thesis, 10 mixtures were designed to determine how the electrical resistivity of steel fiber reinforced self-compacting concrete (SFR-SCC) samples changes depending on different fiber combinations (single and binary hybrid), fiber ratio by volume (1%, 1.25%, 1.5%) and micro fiber length (6 mm and 13 mm). For this purpose, one non-fiber reference sample, three single fiber reinforced SCC with only macro steel fiber and six binary hybrid steel fiber reinforced SCC containing macro and two different types micro steel fibers were produced. In order to observe the effect of steel fiber combination and volume and micro steel fiber type on the electrical properties of SCC samples, the workability properties were adjusted by plasticizer and thus, all components of mixtures were kept constant except for the plasticizer. Fresh concrete tests (slump-flow, T500 and J-ring tests) were carried out as per EFNARC to determine the self-compactability of the mixtures while 90-day samples were tested to find the properties of electrical resistivity and heating of steel fiber reinforced SCC as well as the compressive, splitting tensile and flexural strenght. As a conclusion, with the increase of the steel fiber ratio, it was observed that there was a decrease in the slump-flow diameter (Dç), the J-ring slump-flow diameter (Dj) and time to 500 mm flow (T500) while the height difference (ΔH) values increased. On the other hand, when the inclusion of steel fiber volume into mixtures increased the splitting, flexural tensile strength and toughness values increased but the compressive strength generally affected negatively. Moreover, for all fiber ratios, the electrical resistivity of binary hybrid steel fiber reinforced SCC containing 13 mm micro steel fiber was lower than that of binary hybrid steel fiber reinforced SCC containing 6 mm micro steel fiber as well as its high conductivity and heating. In addition to all these, there were a good correlation between electrical resistivity-temperature rise and conductivity-temperature rise of the steel fiber reinforced SCC samples with R2=0.76 and R2=0.81, respectively. Keywords: SCC, Steel fiber, Workability, Mechanical properties, Electrical resistivity, Temperature rise