| Steel fiber reinforced concrete(SFRC) is applied widely nowadays for its excellent performance, however, the weak interfacial adhesion between steel fibers and concrete matrix leads to the steel fiber hard to be effective on enhancing the strength and toughness. This paper is purposed to modify the concrete by styrene-butadiene emulsion and silica fume in order to improve the interfacial adhesion properties between steel fiber and concrete matrix, thus enhancing the mechanical properties of SFRC. So this research works were carried out: test macro-mechanical properties include compressive strength, splitting tensile strength and rupture strength; Steel fiber pullout tests were conducted with self-designed molds and fixtures to assess the influence of silica fume, polymer and their content on the interfacial bonding properties; researched the influence of fiber embedded angles, steel fiber surface morphology and strength rank and age of concrete matrix. at last, through the microhardness test, SEM test, XRD experiments and the low temperature nitrogen adsorption experiments to explain the mechanism of silica fume and polymer act on the interfacial bonding properties.The following conclusions were obtained by these experiments above:○1 Silica fume can improve the flexural, compressive and splitting tensile strength of concrete preferable, while the polymer reducing these mechanical properties; When only add steel fiber, these macroscopic mechanical properties of concrete can be inproved, but there is an optimal dosage for steel fiber which range from 0.6% to 0.9%.○2 Silica fume can improves the interface bonding strength dramatically between steel fiber and cement, but it prone to being pulled quickly when the Silica fume content over 9%, what’s worse Silica fume also inhibition elasto-plastic deformation of steel fiber and reduced ability to adapt to deformations of steel fiber reinforced concrete. Polymers can increase the limit displacement of steel fiber and make it almost unbreakable by weakening the interface bonding with more energy cost. At the same time, it can also improve the ability of steel fiber concrete to adapt to deformations.○3 When steel fibers embedded in an angle of 45°the Interfacial bond strength is maximum, but the sloped steel fibers are easy pulled of when mixes with silica fume, the greater it sloped the more obvious it can be observed. The interface bonding strength of convex ribbed is higher than smooth steel fibers and interfacial bond strength increases with the increase of concrete strength, which exist certain functional relationship between them.○4 Silica fume can increase the microhardness of interface area and narrow the gap between the mechanical properties of the cement matrix and the interfacial area. it can also promot the hydration reaction of cement and the formation of C-S-H, and inhibit the emerging of Ca(OH)2. Besides, it reduced the microscopic pore volume among the matrix and the interface zone to improve the interface bond properties. Although the polymer can reduce the microhardness gap between the interface area and matrix, and decrease the total volume of harmful pores with large aperture, it also leads to the increasment of the size and content of Ca(OH)2, the reducing of the microhardness of the matrix, thus the interfacial adhesion performance gets worse with the content increasing of polymer.○5 Works were conducted to contact the mechanical parameters of the interfacial region and the microstructure mechanical properties parameters of concrete, as the result, several functions about the relationship between interfacial bond strength, pull-out energy, microhardness, specific surface area, total pore volume and the compressive and flexural strength. Those functions not only reveal the influencement of characteristic parameters of the interface area to the compressive and flexural strength, but also provides a theoretical basis to predict the mechanical properties of the concrete in engineering. |
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