The steel-polypropylene hybrid fiber reinforced concrete can take full advantages of macro-scale crack resistance and toughening effect on the concrete matrix of steel and polypropylene fibers. The shortcomings of concrete are improved and there is a wide prospect application in engineering. This paper summarizes the enhancement theories of hybrid fiber reinforced concrete to explain its strengthening mechanism. The research status is reviewed including mix proportion design, working performance of fresh concrete, mechanical behaviors, durability (impermeability, shrinkage and others), and engineering applications etc. Some further researches are forecasted. It would be very useful to apply and popularize steel-polypropylene hybrid fiber reinforced concrete.
Compared with ordinay concrete, weight of lightweight aggregate concrete could be lower 20%-40% under same bearing capacity. Mixed with some given steel fibers in it, crack resistance and flexural strength will be improved. Once lightweight aggregate concrete mixed with steel fibers meets the requirements of frost resistance, it could be applied to most civil engineerings in a cold area. In this paper, the frost resistance mechanism of steel fiber reinforced lightweight aggregate concrete is introduced. The research status of frost resistance of steel fiber reinforced lightweight aggregate concrete is reviewed including the effects of water cement ratio, aggregate, mineral admixture and amount of fiber, frost resistance experimatal methods and engineering applications etc. Some further researches are prospected.
Under the background of engineering application, a 3-D FE analysis was carried out to evaluate the loading performance of a two-hole pair-arch tunnel under-across the main canal of South-to-North Water Transfer Project. In fact, the tunnel was constructed in integral longitudinally without obeying the design requirement of parting within certain length. The analysis showed that the vertical deformation and tensile stress along the longitudinal axis are obviously affected by the loads from main canal, moreover, the tensile stress exceeds the limit of tensile strength of concrete, which may lead thoroughly cracks on top plate of tunnel. This analysis determined the crack zone which should be dealt with.
Combined with construction of large span steel truss in the bottom of an Archaized tower, stresses in key members, displacements in control nodes and temperature variation were monitored and measured before and after moving construction temporary constraints. The unloading process based on the rule which constraints were unloaded gradually from outer to inner and four steps were carried out in the field. Compared with measured and theoretical results, they can meet with each other perfectly. The mechanical sensibility of steel stresses with temperature changing were also revealed. Then the reasonable conditions of unloading for the steel truss were advised. The process and method given in this paper provides the basis for safely construction of the Archaized tower, which would be reference for similar load bearing transform of steel structrues.
The experiment has been carried out to study the sodium sulfate attack on carbonized concrete. The concrete specimens with strength grade of C50 were first carbonized for 28d in the carbonation box after standard curing, and then immersed into the sodium sulfate solutions of three different concentrations. When the immersed time were up to 30d, 90d, 180d, 270d and 360d, the sulfate-ion concentrations of every layer from the surface to the inside of concrete specimen were measured by the chemical titration method. Based on the test results, the sulfate-ion diffusion regularity and the reaction mechanism of carbonized concrete are analyzed. It can be concluded that the sulfate-ion diffusion regularity and the reaction mechanism of carbonized concrete is completely different from that of un-carbonized concrete, the diffusion of sulfate-ion occupies advantage in the pore water of carbonized concrete, which increases the depth of concrete specimen attacked by sulfate solution.
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