Flexural behavior of layered CTRC-ECC reinforced cementitious composite plates

https://doi.org/10.1016/j.jobe.2022.105283Get rights and content

Highlights

  • The production process of layered composite plates combines the advantages of ECC and CTRC to improve the toughness.

  • When the layer thickness ratio of CTRC to ECC is two, a layered composite plate with higher bending property can be obtained.

  • Calculated and experimental results of flexural strength agree well.

Abstract

In this paper, three-point flexural testing was used to study the flexural properties of polyvinyl alcohol fiber-reinforced engineered cementitious composites (PVA-ECC) and carbon textile-reinforced concrete (CTRC)-layered composite plates. Taking the layer thickness of the two materials and the material type of the tensile plate surface as factors, eight research conditions were established. The effects of these factors on the cracking mode, cracking load, ultimate load, deflection, and toughness of CTRC-ECC plates were discussed. The test results show that the ultimate load and toughness of the specimen with CTRC as the tensile face are significantly larger than those of the specimen with ECC as the tensile face. C–P12–C1 has an ultimate load of 2.04 times that of P–P12–C1, C–P9–C2 has an ultimate load of 1.19 times that of P–P9–C2, and C–P6–C3 has an ultimate load of 1.30 times that of P–P6–C3. The greater the thickness of the CTRC layer is, the greater the ultimate load and toughness of the CTRC-ECC layered composite plate are. The ultimate loads of P–P12–C1, P–P9–C2, and P–P6–C3 are 39%, 157%, and 369% higher than that of P–P18–C0, respectively. When the thickness ratio of the CTRC layer to the ECC layer is two, the composite plate shows much higher toughness. The formulas were derived to calculate the flexural strength of the layered composite plate with CTRC as the tensile face, which can be used to guide the design of flexural members of layered composites.

Introduction

Adding fibers is an effective way to enhance the performance of concrete. Metal fibers, synthetic fibers, and natural fibers have been widely used in concrete engineering to improve the ductility, flexural and tensile strength, toughness, and crack propagation of concrete [[1], [2], [3], [4]]. Different fiber types will improve different properties of concrete. Generally, high modulus fibers can significantly improve the ultimate strength, but the strain capacity is relatively unaffected, while the performance of low modulus fiber shows the opposite trend [5].

The reinforcing effects of short-cut fibers and fibrous textiles on concrete are also different. Incorporating short-cut fibers into concrete can effectively improve the brittleness and poor crack resistance of concrete [6]. Randomly distributed short-cut fibers can control the initiation, development, and merging of concrete cracks [7]. Short-cut polyvinyl alcohol (PVA) fiber is a common fiber used to make engineered cementitious composites (ECC). They have been shown to effectively improve the strain hardening performance, toughness, and ductility of concrete [8,9]. Suthiwarapirak et al. [10] found that PVA fiber showed good interfacial bonding strength with concrete, and the PVA-ECC reinforced beam showed obvious multi-slit cracking performance. However, many studies have pointed out that PVA fiber shows no obvious strength improvement for concrete [[11], [12], [13]]. Fibrous textiles is commonly used in textile-reinforced concrete (TRC). Carbon fiber, as a high modulus fiber, is widely used in TRC, which has advantages of high strength, high ratio of strength to mass, and high corrosion resistance, and has generally been used in the field of structural reinforcement [[14], [15], [16]]. Different from the random distribution of short-cut fibers in the matrix, a carbon textile can continuously embed high-performance fibers in the cement matrix according to the expected principal stress direction, which greatly increases the utilization rate of fibers, thereby improving the ultimate strength of cement-based materials [17]. Therefore, short-cut PVA fiber and carbon textile can provide synergistic benefits by simultaneously increasing ductility and ultimate strength, respectively.

If it is necessary to improve the strength, strain hardening performance, and toughness of concrete at the same time, two types of fibers can be used in conjunction to enhance the performance of concrete. Several studies have shown that the addition of short fibers to TRC can improve the interfacial properties between the fiber fabric and matrix [18,19]. Pakrava et al. [20] studied the flexural properties of CTRC containing PVA fiber by three-point flexural testing. Short PVA fiber can improve the bearing capacity of the specimen and increase the number of cracks in the specimen. Du et al. [21] carried out four-point flexural tests on basalt textile-reinforced concrete with steel fibers, and found that the addition of chopped steel fibers in the matrix reduced crack width and increased crack numbers. Du et al. [22] studied the flexural behaviors of carbon textile-reinforced concrete plates by four-point bending tests and found that the prestressed TRC specimens with 1% volume content of steel fibres effectively avoided debonding. Thus, the utilization of the textiles could be improved. Although fiber hybridization can combine the advantages of various fibers, there are still some problems that have not been overcome. The interactions between various fibers may affect fiber performance, and excessive fiber volume fraction may lead to decreased interfacial bonding and matrix performance [23]. Another important issue is that short-cut fibers and textiles have different requirements related to the composition and concentrations of components in the cement matrix. Adding short-cut PVA fibers directly into the CTRC matrix may affect the performance of the reinforcing fibers. For example, thickeners are commonly used to increase the viscosity of PVA-ECC, but the micro-pores they introduce in the matrix reduce the strength of the material [24]. In addition, while producing the TRC matrix, a proper quantity of silica fume is typically added to increase the matrix's early strength and improve the interfacial bonding performance between the fiber fabric and matrix. The strain hardening property of PVA fiber-reinforced composites is achieved when the cracking strength of the matrix is less than the fiber bridging capacity and the maximum complimentary energy is no less than the matrix toughness [25]. To ensure that the short-cut fibers in the ECC matrix are pulled out instead of broken, and to give full play to the deformation capacity of the ECC, silica fume should not be added to the ECC matrix. Normally, it is necessary to apply oil on the PVA fibers to reduce the friction between the fibers and matrix [26]. To solve these problems of different matrix types and fiber-fiber interaction, this paper adopts the layered method to produce composite materials. Two kinds of fibers are added into different matrices, respectively, and then two kinds of cement-based materials are combined in layers to form a layered composite material. At present, the research on layered cement base materials mostly focuses on improving durability, reducing costs, and reducing component weight [27]. Since there is hardly any research on layered composite materials created by the combination of CTRC and ECC, this paper designed a test to evaluate the flexural behavior of the CTRC-ECC layered composite plate.

In this paper, the flexural properties of polyvinyl alcohol fiber-reinforced engineered cementitious composite (PVA-ECC) and carbon textile-reinforced concrete (CTRC)-layered composite plates were studied. The variables were the composition of the material of the composite plate and the layer thickness of each material in the composite plate. The load-deflection relationship, stiffness, crack morphology, failure mode, ultimate load and ultimate deflection of specimens under various research conditions were studied by three-point flexural testing, and the toughness of the layered composite plates were evaluated.

Section snippets

Materials

The ECC and CTRC matrices are made of fine aggregate concrete and the maximum particle size of the aggregate is 1.2 mm. Thickener was added to the ECC matrix to improve its ductility, and silica fume was added to the CTRC matrix to improve its early strength. The materials used in the matrix include ordinary Portland cement, fly ash (I grade ultra-fine fly ash), silica fume, fine sand (particle size range 0.25–0.5 mm, density 1.529 g/cm3), water reducing agent (HSC polycarboxylate

Uniaxial tensile and compressive properties of CTRC and ECC

Fig. 6 shows a comparison of the cracking morphology of ECC and CTRC specimens under tensile load. ECC shows steady multi-fracture cracking with crack spacing and crack widths significantly smaller than those of CTRC. Since short-cut PVA fibers are randomly incorporated into the ECC, bridging of PVA fibers at the cracks will form more and finer cracks in the matrix, so that the material maintains steady multi-fracture cracking. Steel fibers are generally inserted vertically into the CTRC

Basic assumptions

The C-Px-Cx specimens subjected to three-point flexural tests satisfy the following assumptions:

  • (1)

    Section deformation follows the plane section assumption [33,34];

  • (2)

    The stress and strain of the matrix–textile interface are continuous without bond-slip;

  • (3)

    The stress-strain relationship of the carbon textile is linear, and only the weft fiber bundles carry the load;

  • (4)

    Ignore the shear force carried by the composite plate;

  • (5)

    The fibers only bear tension force.

Models of concrete matrix

The concrete in the compressive zone adopts the

Conclusions

The flexural properties of eight layered composite plate specimens were investigated using the three-point flexural test in this paper, and the following conclusions were drawn:

  • 1.

    The material type of the tensile face has a decisive influence on the cracking mode and stiffness after cracking of the CTRC-ECC layered composite plate. When the tensile face material is ECC, the cracking mode of the composite plate is multi-slit steady-state cracking. The stiffness greatly decreases after cracking. The

Credit author statement

Fen Zhou: Resources, Methodology, Data curation, Formal analysis, Writing-Original draft preparation and Reviewing.Rui Zhou: Conceptualization, Experiment, Writing-Reviewing and Editing.Yunxing Du: Investigation, Supervision, Project administration, Validation.Ying Wang: Experiment, Visualization.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This work was supported by the fund from the National Natural Science Foundation of China (Grant 52178206).

References (35)

  • Y. Du et al.

    Flexural behavior of basalt textile-reinforced concrete

    Construct. Build. Mater.

    (2018)
  • J.-X. Lin et al.

    Static and dynamic mechanical behavior of engineered cementitious composites with PP and PVA fibers

    J. Build. Eng.

    (2020)
  • G. Torelli et al.

    Functionally graded concrete: design objectives, production techniques and analysis methods for layered and continuously graded elements

    Construct. Build. Mater.

    (2020)
  • S. De Santis et al.

    Test methods for textile reinforced mortar systems

    Compos. B Eng.

    (2017)
  • F. Schladitz et al.

    Bending load capacity of reinforced concrete slabs strengthened with textile reinforced concrete

    Eng. Struct.

    (2012)
  • D. Niu et al.

    Experimental study on mechanical properties and fractal dimension of pore structure of basalt–polypropylene fiber-reinforced concrete

    Appl. Sci.

    (2019)
  • M. Maalej et al.

    Behavior of hybrid-fiber engineered cementitious composites subjected to dynamic tensile loading and projectile impact

    J. Mater. Civ. Eng.

    (2005)
  • 1

    The authors Fen Zhou and Rui Zhou contributed equally to this work.

    View full text