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    Precio : Gratis

    Publicado por : dnfsdd814

    Publicado en : 27-10-21

    Ubicación : A Coruña

    Visitas : 9


        The use of doubled strips of rubber dam material for drains has become general in this

    clinic, especially for wounds that do not require irrigation. These have been found

    superior to tubing and the ordinary type of cigaret wicks because they are nonirritating to

    the wound and the capacity of the drain is increased as a result of the capillarity derived

    from the two opposed surfaces of the rubber dam material. On removal, these drains leave

    very little deformity in the tissue and they do not tend to plug the wound, as do wick or

    tube drains frequently.
        This type of material has the fault of stretching considerably and of sometimes

    breaking, a portion being left within the wound. To obviate this we have strengthened

    strips of rubber dam material by running a seam down the center with a sewing machine. This

    makes the rubber nonelastic and adds sufficiently to its tensile
        The proper assembly of underground precast concrete structures is often critical in the

    construction of underground structures. In particular, interfacial waterproofing between

    precast concrete segments is a key factor influencing use, safety, and life span. Current

    practice is to incorporate waterproofing rubber strips in the design. During the

    installation process, compressive stress is applied to the strip by post-tensioning to

    achieve performance. For this paper, lateral constraint compression tests were carried out

    on composite rubber seal strips that utilize putty. Special waterproofing and sealing test

    devices were designed to investigate corresponding relationships between water pressure and

    compressive stress (or strain). A relationship between water resistance pressure and

    compression stress and strain of the putty-based composite

    rubber strip was proposed based on the

    series tests and the control target of the minimum compression strain of the putty

    composite rubber strip was then suggested. Finally, full-scale waterproofing tests on

    tunnel joints were conducted. The experimental results provide a scientific reference for

    the engineering application and design of composite sealing rubber strips putty for

    underground post-tensioned precast concrete structures.
        Waterproofing is typically a key design goal for underground precast concrete

    structures (Ossai 2017). For modern tunnel structures, segments often require casting of

    high performance concrete with very low permeability (DAUB 2013). Therefore, the primary

    possible leakage point considered is the segmental joint (Yurkevich 1995; Lee and Ge 2001;

    Henn 2010; Wang et al. 2011; Wu et al. 2014; Fang et al. 2015; Soltani et al. 2018). For

    tunnel lining, one of the most significant factors impacting the overall behavior and

    structure response was the existence of the segmental joints for precast concrete units

    (Wood 1975; Koyama 2003). Due to the underground environment, repair after the leakage in

    the structure is very difficult. In general, design service life for underground structures

    ranges from 75 to 100 years. Structures within urban underground tunnel networks tend to

    deform due to the long-term dynamic load and impacts associated with surrounding buildings.

    Under working conditions, the largest deformation was frequently observed and entered into

    failure state at the joint (B?er et al. 2014; Huang et al. 2015; Hong et al. 2016).

    Therefore, waterproofing materials need to accommodate structural deformation.
        In present concrete construction, elastic rubber strips in sealing and waterproofing

    joints of assembling segments have been commonly used. For underground concrete structures,

    standard design for sealing joints uses Ethylene-Propylene-Diene Monomer (EPDM) polymer

    rubber strips arranged circumferentially on the end faces of the segment (Ding et al.

    2017). Putty-based composite rubber strips have great viscosity and elasticity, which can

    compensate to a certain degree for the adverse effect of the interface defects at joints.

    To evaluate the waterproofing ability at joints, special attention is directed to the

    sealant behavior of the EPDM sealing strips. A time-dependent constitutive model is

    proposed to assess the long-term waterproof ability of EPDM rubber used in segmental joints

    (Shi et al. 2015). At present, there are few requirements for rubber strips in the design

    specifications, and there is limited understanding of the relationship between applied

    forces and waterproofing performance. In addition, precast concrete structures incorporate

    a groove at the joint interface for the rubber strip positioning (Hu et al. 2009). The type

    of groove at the joint interface can limit extruded profile epdm rubber seal strip lateral deformation,

    which can increase pressure on the strip and improve waterproofing ability. The various

    types of grooves offer different degrees of constraint. Therefore, mechanical properties of

    rubber strips along with groove design at precast concrete structure joints are key

    elements in waterproof design. The joint open width is also regarded as a key performance

    indicator, since it is the weakest part of the shield segmental lining (Liao et al. 2008;

    Zhang et al. 2015). As the weakest and vulnerable point in the segmental lining, joints

    have been investigated in experiments (Ding et al. 2013; Liu et al. 2015; Kiani et al.

    2016), numerical analyses (Ding et al. 2004; Teachavorasinskun and Chub-uppakarn 2010) and

    case studies (Jun 2011; Basnet and Panthi 2018). Testing apparatus was designed to

    accurately monitor water leakage pressure of segmental joints under various combinations of

    opening and offsets (Ding et al. 2017). Molins and Arnau (2011) presented an in situ load

    test and 3D numerical simulation on a full-scale segmental lining for the Barcelona metro

    line. According to a case study in Shanghai, Huang et al. (2017) perceived that

    longitudinal joints of the metro tunnel have large open widths and lose waterproofing when

    disrupted by unexpected surcharges.
        In this paper, mechanical tests for compressive stress and strain of putty-based

    composite rubber strips along with waterproofing performance tests at the interface between

    putty-based composite rubber strips and concrete are conducted. These tests investigate

    influence of strip compressive force and the joint stretching value on waterproofing of

    sealing rubber strips. It attempts to establish a design model and proposed control target

    for mechanical and waterproofing properties of this new type of rubber strip. Waterproofing

    test of a full-scale tunnel joint is carried out. The research work of this paper provides

    a scientific reference for the engineering application and design of composite sealing

    rubber strips with putty for underground post-tensioned precast concrete structures.
        The putty-based composite silicone weather stripping extruded rubber strip was made up of Ethylene-

    Propylene-Diene Monomer polymer rubber (EPDM foam strip) and the external composite layer

    (putty paste) of high viscosity reactive polymer cement (butyl rubber). The primary reason

    for use of the composite was to take advantage of the external putty-based material’s

    properties of viscosity and superplasticity, which can heal mesoscopic cracks and defects

    on the surface of concrete structures to improve interface waterproof ability. Cross

    section dimensions and picture of the rubber strip are shown in Fig. 1.
        Figure 2 displays the lateral confinement loading test device, which is composed of two

    parts: convex shape of the upper part and concave shape of the lower part. The inner and

    outer diameter of the annular groove was 170 mm and 220 mm, respectively. The upper part

    has protrusion that squeezes the strip, and the annular groove is set at the lower part of

    the device with an annular rubber strip installed in it (see Fig. 2c). The length of the

    EPDM foam rubber in the elastic state has 640 mm, and the compression area is 15,315 mm2.

    Quasi-stress control was selected for the tests.
        Experimental results of the putty-based composite strip under lateral confinement for

    compressive stress and displacement are provided in Fig. 7. At the early stage of loading,

    the compressive stress of the composite strip gradually increased with the displacement. It

    was observed that the displacement dramatically increased and at the later stage of the

    loading when the load reached at 112.36 kN primarily maintained at 11 mm. At end of the

    test, the rubber strip was not crushed and the internal EPDM foam rubber after unloading

    almost recovered to its original shape. The maximum displacement of the putty-based

    composite rubber strip under lateral confinement was approximately 11 mm, which was brought

    on by the squeezing of the inner hole of the composite strip raising the internal pore of

    the EPDM rubber. The instantaneous elastic recovery during the unloading process was 85% of

    total deformation. The residual deformation of the composite rubber strip was gradually

    recovered to its original state with time. Eventually, the rubber strip was not damaged.

    The deformation recovery of the inner elastic material to its original shape can partly

    drive unrecoverable external putty material.
        In the loading process, the two end faces of the rubber sealing strip weatherstrip for window were

    partially extruded upon loading, since they were not restrained at the end face (see Fig.

    8). When maximum deformation was reached, the upper and lower parts of the concrete were in

    contact with each other.
        There was an inflection point in the curves of the rubber strip in the two different

    grooves, as presented in Fig. 10. Before the point, the internal pore and middle hole of

    the sealing strip were not tightly compressed signifying that the compression strain

    increased gradually with compressive stress. Moreover, the relationship between compressive

    stress and compression strain for the two different sizes of groove were almost the same

    before the inflection point. At the inflection point, the central hole of sealing strip and

    the pore of foam rubber were completely compressed. The whole strip was so dense that the

    compressive force increased sharply with the compression strain. The compressive stresses

    of the sealing strip in the two different grooves at the inflection points were almost the

    same and their corresponding compression strain differed by roughly 20%.
        In the early stage of compression, the compression moduli of the

    Waterproof Rubber Seal Strip Gasket
    were almost the same under the two groove

    constraints. In the later stage of loading, the compression stress of 6 mm depth of groove

    was greater than that of 4 mm depth under the same compression strain, and the compressive

    strain of the 4 mm depth of groove was greater than that of the 6 mm depth of groove under

    the same stress. This was mainly attributed to the difference in the constraint degree of

    the groove to the strip at the later stage of loading. In the final stage, the two

    compression interfaces of the 6 mm depth specimens were close in contact with each other.

    The remaining space at the joint was rather small, and there was no compression space.

    However, there was still a large space between the two interfaces of the 4 mm deep

    specimens. This was mainly due to the sum of the strip deformation and groove depth limit.

    The bilinear outsourced line was taken as an approximate stress-deformation relation model

    as shown in Eq
        The tests started with two culverts gradually assembled in place. After initial post-

    tensioning, dial gauges were installed inside the culverts to measure joint space

    variations in the process of post-tensioning. Simultaneously, the strains on the post-

    tensioning steel bars were recorded. The water injection pump and water pressure gauges at

    the lower part of the water injection hole of the box culvert were installed. After the

    steel bars were set in the duct, the conductor was run through the perforated sheet. The

    sheet was tightly attached to the concrete surface and bolts fastened. Table 2 provides

    experimental results of the post-tensioning process. The upper and lower prestressed steel

    bars were tensioned at the same time, otherwise the friction resulted in the vertical

    location due to the friction at the bottom so that the two tendons were employed. Upon

    completion of a post-tensioning cycle, the gap change and steel strain were measured. The

    bolts were then fastened. The maximum tension force was 180 kN. During the post-tensioning

    process, strain of steel bars varied linearly, indicating that the post-tensioned steel

    bars were in the elastic state with strain close to the theoretical value.
        In order to investigate the waterproofing performance of the putty-based composite

    rubber, mechanical behavior tests using rubber strip and waterproofing performance tests of

    the interface between the strip and precast concrete were performed. 

    TFP Si

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