Research And Structural Application Of Polymer Modified Steel Fiber-cement-base Composites

Concrete used as well cover materials includes an urgent need to develop high performance possessing high strength, toughness, energy absorption, durability, etc. Reinforcement of concrete with short randomly distributed steel fibers leads to improvements in the tensile strength and tensile and compressive ductility of the material. This is due to the tendency of propagating micro-cracks in cementitious matrices to be arrested or deflected by fibers. The prepeak behavior and maximum tensile strength of the composite material depends on local bond characteristics at the fiber - matrix interface, the postpeak behavior is dominated by an average bond behavior in pullout action of fibers bridging the critical crack. Fiber -matrix interfacial bond strength is provided by a combination of adhesion, friction, and mechanical interlocking. In most cases, steel fibers are pulled out after debonding. Silica fume, silane coupling agents, polymer, or significantly long steel fibers have been used to over come the limitations. Polymer cement concrete has high tensile strength, ductile behavior, and impact resistance capability due to the formation of a three-dimensional polymer network through the hardened cement paste network. Due to the effect of void filling and bridging of cracks, the porosity decreases and pore radius refine for the polymer modified cement concrete. Furthermore, when added to concrete, polymers normally exhibit water-reducing qualities, because of the dispersing agents in the polymer latexes and the spherical shape of the polymer drops. The quality of the transition zone between cement and paste and other materials may be improved due to the adhesion effect of polymer. In order to improve the ductile behavior and flexural strength of steel fiber-reinforced cement concrete to be used as road well cover, a polymer styrene butadiene rubber emulsion was incorporated in steel fiber-reinforced cement concrete. Silica fume and fly ash were also added to concrete due to their ability of enhancing densification of the cementitious matrix.It is found that steel fibers show a strong reinforced effect on the flexural strength and the compressive strength. The compressive strength and flexuralstrength increase significantly as the content of steel fibers increase. The flexural strength increases significantly when 3~10wt% polymer incorporated, especially for concrete incorporating 10wt% SBR polymer, the flexural strength increase 25wt%. The compressive strength decrease when SBR incorporated. It is interesting to found that the flexural strength of steel fiber-reinforced cement concrete incorporating 5wt% polymer was the highest among all kinds concretes. Measurements of the mineralogy and microstructure by using scanning electron microscope demonstrates that polymer film can be found in concretes when incorporating 5, 10 wt% polymer, and polymer film act as bridges across pore and crack. The polymer film for concrete incorporating 10wt% SBR is thicker and more coherent as compared to that of the concrete incorporating 5wt%. Big pores, ettringites, and debonding between aggregate and cement can be observed in control steel fiber-reinforced concrete. The phase composition was characterized with Fourier transform infrared spectroscopy. It is found that there are interfacial interactions between polymer and the hydrations (such as C-S-H and calcium hydroxide) of cement, which will produce a high bonding strength between the reinforcement and cement matrix.In the engineering applications, as the polymer modify steel fiber concrete can largely improve bending strength, compression strength and deformability. We use it to meet the characteristic requirement of the complex stress status in sewer well lid, namely , in the high shearing stress district at the edge we use some reinforcing bar to respond to the request of shear force, utilize combining structure principle adopt high-strength glass fiber reinforced polymer which sticks to the well lid bottom to improve its structure integrality and ductility, for more than one year after its generation, this product is proved to be working in a good condition, which proved the polymer modify steel fiber concrete successfully and the well lids quality is reliable .