Abstract
This study evaluated the performance of latex-modified fiber-reinforced concrete (RC) segments as a function of the substitution level of microsilica and type of reinforced fiber, to address the problem of corrosion of steel segments and steel-reinforced fiber segments, which are commonly used to shield tunnel-boring machine (TBM) tunnels in urban spaces. Our study compared macro synthetic, steel, and hybrid (macro synthetic fiber + polypropylene fiber) reinforcing fibers. The substitution levels of microsilica used were 0, 2, 4, and 6%. The target strengths were set at 40 and 60 MPa to test compressive strength, flexural strength, chloride ion penetration resistance, and impact resistance. Testing of latex-modified and fiber-reinforced segment concrete showed that the compressive strength, flexural strength, and chloride ion penetration resistance increased with an increasing substitution level of microsilica. These improvements were attributed to the densification of the concrete due to filling micropores with microsilica. Micro synthetic fiber was more effective in terms of improved compressive strength, flexural strength, and chloride ion penetration resistance than steel fiber. These results were due to the higher number of micro synthetic fibers per unit volume compared with steel fiber, which reduced the void volume and suppressed the development of internal cracks. The optimal microsilica content and fiber volume fraction of micro synthetic fiber were 6% and 1%, respectively. To evaluate the effects of the selected mixtures and hybrid fibers simultaneously, other mixing variables were fixed and a hybrid fiber mixture (combination of macro synthetic fibers and polypropylene fibers) was used. The hybrid fiber mixture produced better compressive strength, flexural strength, chloride ion penetration resistance, and impact resistance than the micro synthetic fibers.
Highlights
As underground tunnel construction in urban spaces usually causes severe environmental problems, complaints because of noise and vibration, and infrastructural effects, the shielded tunnel-boring machine (TBM) construction method is generally used for urban tunnel cutting [1, 2]
Is study evaluated the performance of microsilica, which can serve as a highly strengthening, noncorrosive polyolefin macro synthetic fiber substitute for the steel fibers and steel-reinforcing bars traditionally used in segment concrete
Microsilica was used to ensure durability and water tightness of the segment concrete; its properties are listed in Table 2. is study used crushed aggregate (25 mm maximum size) and fine aggregate having a density of 2.62 g/mm3. e physical properties of the coarse aggregate are listed in Table 3 [35]. e following reinforcing fibers were used: bundle-type steel fibers and micro synthetic fibers [34, 36]
Summary
As underground tunnel construction in urban spaces usually causes severe environmental problems, complaints because of noise and vibration, and infrastructural effects, the shielded tunnel-boring machine (TBM) construction method is generally used for urban tunnel cutting [1, 2]. Steel segments were used initially in TBM construction, but because concrete performance has improved, reinforced concrete (RC) segments are used widely because of the lower risk of corrosion and higher cost-effectiveness versus steel [3]. Possible solutions to the issue of corrosion of reinforcing steel bars and steel fibers include compacting concrete structures to improve water permeability resistance and using a stiffener that cannot corrode [10]. Is study evaluated the performance of microsilica, which can serve as a highly strengthening, noncorrosive polyolefin macro synthetic fiber substitute for the steel fibers and steel-reinforcing bars traditionally used in segment concrete. Previous studies have focused on the application of latexmodified reinforced segment concrete with blends of polyolefin and polypropylene fibers [34]. We evaluated the effects of hybrid fiber and microsilica use (mixture of macro synthetic fibers and polypropylene fibers)
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