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Improvement for Construction of Concrete-Wall with Resistance to Gas-Explosion 时间:2018-09-12 12:14 来源:未知作者:admin 点击: 次 Abstract:The research was initiated to investigate the performance of fiber-reinforced concrete for protecting people or assets in the building against the explosion or debris missiles. The fiber-reinforced concrete has the difficulty with being applied in the actual construction conditions with the normal ready-mixed concrete system. The fibers for the protection performance require high toughness to endure the huge energy from an explosion, but the large amount of the fiber is required. The required amount of fibers can result in decreased workability and insufficient dispersion of fibers. It has been difficult to apply fiber-reinforced concrete on field placing with the ready-mixed concrete system of plant mixing, delivering, and placing. This research carried out the investigation of properties of combined fiber of steel and polymeric fiber to improve workability and agitating in the mixer. Based on the preliminary experimental test results in a laboratory, combined fiber-reinforced concrete was applied on the actual field construction of chemical plant. According to the results from the laboratory tests and application in the real construction project, it is expected to introduce the combined fiber for desirable mechanical performance with less adverse effect on workability of the mixture.
1. Introduction
Against terrorism or warfare, structures or facilities with special purpose should have sufficient protecting performance for shock wave or debris missiles from bombing or explosion. In addition to the special purposed facilities, many people who work at the plants where handling explosive substances such as explosive gas or massive structures should be protected against explosion. Generally, to secure the enough protecting performance against these kinds of forces, the wall should be constructed thicken enough with normal strength-ranged reinforced concrete. For the lateral stress caused by earthquake or explosion, fiber-reinforced concrete (FRC) is known as a solution with its high energy absorption capacity and high tensile strength [1]. Comparing to the normal concrete without fiber reinforcement, FRC has high tensile strength and toughness. Generally, for FRC, the fiber content is a key of improving mechanical properties of the material [2].
On the contrary, addition of fiber in concrete mixture causes reduction of workability with increasing both viscosity and yield stress. Because of poor yield stress, FRC with increased fiber content has been reported a fiber ball effect during the mixing process and unfavorable consolidating performance. Therefore, as a method of achieving the maximum mechanical performance without workability issue, slurry infiltrated fiber concrete was introduced [3, 4]. Likewise, for FRC, the fiber content should be balanced between mechanical properties and workability.
The reinforcing fibers for improving the performance of cementitious materials have different roles or performances depending on their aspect ratios (length-to-diameter ratio), materials, or shapes (straight, bent, or hooked). Especially, regarding the materials, the reinforcing fiber can be categorized into metallic and polymeric fibers. First, metallic fiber, mainly steel fiber, increases the toughness of the mixture. The metallic fiber itself has a high tensile strength and elastic modulus; thus it provides increasing tensile strength and elastic modulus while it is pulled out from the cement matrix. Since the metallic fiber has a higher tensile strength than cement matrix, the fail behavior of metallic fiber is pulling out of the fibers, so there are various geometries of the metallic fibers such as hooked, bent, or various cross sections. Otherwise, polymeric fibers, such as polypropylene, polyethylene, or nylon fibers, have a relatively lower tensile strength and elastic modulus than metallic fiber. Hence, the polymeric fiber cannot improve the mechanical properties of the mixture as the metallic fiber does; however, because of the advantage of good dispersion inside of the fresh state cementitious materials, it contributes on improving mechanical properties of the mixture. Especially, the polymeric fiber can be produced with the high aspect ratio with thin diameter, and because of flexibility of the shape, it does not decrease the workability of the mixture rather than metallic fiber. The hybrid fiber or cocktailed fiber means the combined fibers of different types to achieve synergetic effect. For instance, Banthia et al. and Markovic et al. reported improved mechanical properties of FRC with two fibers with different materials [5, 6], and Peng et al. reported two different polymeric fibers with different aspect ratios and melting points for improved performance of preventing spalling damage of high-performance concrete mixture [7]. These studies were showing improvement in desired properties of FRC with combined fibers or hybrid fiber with decreased fiber content for the achievement of improved workability. Therefore, combining different types of fibers has been used as a solution of decreased workability by decreasing fiber content with equivalent performances [8].