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Engineering cementitious composites (ECC) is an innovative high performance engineering structural material with high ductility, high toughness, and unique multiple cracking characteristics. Currently, most of the fibers used in ECC are expensive Kuraray PVA fibers produced in Japan. More and more researchers are using Polyethylene (PE) fibers made in China with low cost, high strength and high elastic modulus to replace Kuraray PVA fibers. However, the finer diameter and hydrophobicity make it difficult for the PE fibers to be distributed in the matrix evenly. In addition, most research currently focuses on the static performance of PE-ECC, with limited research on its dynamic performance. In this study, PE-ECC with different fiber contents was prepared with a high-power, high-speed mixer. Compressive tests, tensile tests and split Hopkinson pressure bar (SHPB) impact compression tests on the specimens were conducted to study their static and dynamic performance. The results indicated that increasing the fiber content can improve the mechanical properties of PE-ECC when the fiber volume fraction is low. Further increasing the volume fraction of fibers will affect the uniform distribution of fibers, leading to a decrease in the mechanical properties of PE-ECC and an increase in the discreteness of test results. Considering the difficulty of fiber dispersion and mechanical properties, it is recommended that the content of PE fibers should not exceed 2.25%. The research results of this paper may provide a reference for the promotion and application of PE-ECC, especially in the field of collision protection.

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The confinement mechanism of ultra-high performance concrete (UHPC) has not been fully explored yet, and there is no analysis-oriented model available for FRP-confined UHPC. This study aims to fill this research gap by implementing new constitutive models of tri-axial compression behavior of UHPC in an existing analysis-oriented FRP-confined concrete model. In the first part, the test findings of tri-axial compression tests on 22 UHPC cubes with different fiber lengths and confining stresses were briefly summarized. In the second part, assessments were performed for four relevant axial stress-strain models using the test results. Generally, the four models yielded overestimations for the axial strains at the peak stresses by at least 30%, and the predicted post-peak decline curves misaligned with the test curves. Inspired by the assessment findings, a new axial stress-strain model was proposed using Liao et al.'s model as the basic form, and replacing the post-peak decline curve with a power-law function to capture the steep descending trend. The new axial stress-strain model showed excellent performance in predicting the peak axial stresses and corresponding strains (average error at around 5% and 9%, respectively), and depicting the tri-axial compressive stress-strain curves. With a newly calibrated dilation equation, the proposed axial stress-strain model was applied for the development of an analysis-oriented model for FRP-confined UHPC, which showed corroborated results with the verification tests in axial stress-strain curves, as well as the ultimate axial strengths and corresponding axial strains (average error at 6.5% and 13.3%, respectively). • Test findings of tri-axial compression tests on UHPC cubes were briefly summarized. • Assessments were performed for four relevant axial stress-strain models. • A new axial stress-strain model for UHPC was proposed with excellent performance. • The proposed constitutive models were applied to develop an analysis-oriented model for FRP-confined UHPC. • The analysis-oriented model for FRP-confined UHPC was demonstrated to have satisfactory performance. [ABSTRACT FROM AUTHOR]

Confinements have been adopted to alleviate the brittleness of ultra-high performance concrete (UHPC). However, as the foundation of confinement mechanism, the research on behavior of UHPC under tri-axial compression is rather limited. Furthermore, the confinement mechanism of PE fiber-strengthened UHPC (PE-UHPC) has not been reported yet. To this end, conventional and true tri-axial compression tests were performed for 22 UHPC cubes with different PE fiber lengths and various lateral confining stresses. The typical axial stress-strain curve has a long elastic ascending stage, a relatively short plastic ascending stage and a steep post-peak decline stage. Increasing the lateral confining stresses could extend the elastic ascending stage, and make the plastic ascending stage longer and clearer. Furthermore, the reinforcement effect of longer PE fibers became more pronounced with increasing lateral confining stresses. However, only increasing intermediate principal stresses with minor principal stresses unchanged had minor effect on the axial strain-volumetric strain behavior. • Confinement mechanism of UHPC further explored. • True tri-axial compression tests on PE fiber-reinforced UHPC. • Increasing confining stresses extended ascending stages of axial stress-strain curves. • Longer PE fibers had better reinforcement effect with increasing confining stresses. • True axial compression had minor effect on dilation behaviour. [ABSTRACT FROM AUTHOR]

Ultra high performance strain hardening cementitious composites (UHP-SHCC) is a special type of cement-based composite material with outstanding mechanical and protective performance at room temperature. But its fire performance is unknown and there is a lack of research in this aspect. This study presents an experimental program to study fire resistance of UHP-SHCC under two aspects, viz. high-temperature explosive spalling resistance and residual mechanical performance after a fire. Both compressive strength and tensile strength of UHP-SHCC were found to deteriorate with increasing exposure temperature. Tensile strain-hardening feature of UHP-SHCC would be lost at 200 °C and above. It was found that PE fibers are found not effective in mitigating explosive spalling, although they start to melt at 144 °C. FE-SEM (Field Emission Scanning Electron Microscopy) and EDX (Energy Dispersive X-ray) techniques were used to study the state of fiber, fiber/matrix interaction, and microcracks development. Microscopic study found that melted PE fibers were still present in the cementitious matrix, and the melting did not introduce more microcracks. Furthermore, it was difficult for melted PE fibers to diffuse through the matrix, thus providing the reason that PE fibers did not mitigate explosive spalling in UHP-SHCC. [ABSTRACT FROM AUTHOR]

The permanent functionalization of synthetic fibers and especially of polyethylene fibers (PE fibers) is usually difficult, because the synthetic fiber surface does not contain many functional groups for fixation of finishing agents. For this, the aim of the now presented paper is to report of a functionalization process for PE fibers using the polyelectrolyte polyvinylamine (commercially also named as Lupamin™). The polyvinylamine is applied in a HT process (HT for high temperature process using process temperatures of 95 to 140 °C) and usable to work as anchor for further applied negatively charged functionalizing agents as demonstrated in the current study with acid dyes. Also demonstrated is excellent antibacterial activity againstE. coliandS. aureusby simple polyvinylamine application onto PE fibers. This reported method has a high potential for the functionalization of PE fibers and could lead in future to appropriate industrial applications using functionalized PE fibers. [ABSTRACT FROM AUTHOR]

• 45 pullout tests for GFRP bars in normal concrete and SSC with PE fiber addition. • Two types of bond-slip curves with different post-peak behaviors were obtained. • Replacing normal concrete by SSC has no distinct effects on short-term bond strength. • Increasing concrete strength and PE fiber content could enhance the bond strength. Fiber reinforced polymer (FRP)-reinforced seawater sea-sand concrete (SSC) structures are prospective substitutions for traditional steel-reinforced concrete structures, especially in maritime environment. To demonstrate the feasibility of the FRP-reinforced SSC structures, an in-depth understanding on the bond strength of glass FRP (GFRP) bars to SSC under pull-out loading is essential. In this regard, pullout tests on 45 specimens with a 10 mm diameter GFRP bar embedded in ultra-high strength concrete (including normal concrete with river-sand and fresh water and SSC) are conducted in this study. Particularly, the experimental tests focus on some key factors that governing the GFRP bars in concrete, such as the bar embedment length, the polyethylene (PE) fiber volume fraction, and the concrete strength (i.e. , 80 MPa and 120 MPa). Three major failure mechanisms and two types of average bond stress-slip curves are obtained from the tests. The results show that substitution of seawater and sea sand for normal concrete has no distinct effect on short-term change in bond strength (less than 9%). In addition, it indicates that the increase in concrete strength and PE fiber content could improve the bond strength, whereas increasing the embedment length (from 2.5 times to 10 times of bar diameter) could result in a decrease in bond strength (by 20–30%). Furthermore, it demonstrates that the CMR model has better performance than the mBPE model in capturing the experimentally observed ascending part of the bond-slip curve. [ABSTRACT FROM AUTHOR]