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  Polymer Binder, Impact on the Pull-Out Force of Macro Fibers in Sprayed Concrete

  Macro-fibers have been used in sprayed concrete for many years now, particularly to prevent cracks from developing in the concrete due to deformation energy. These fibers can be made of steel or plastics and are provided to the customer. The type of fiber to be used is selected based on the building project’s requirements. Usually, the fibers are added to the sprayed concrete in the standard application’s mixture, regardless of whether the concrete is wet or dry (fiber-reinforced concrete or FRC). FRC’s functional principle is to mechanically anchor the steel or polymer fibers in the dense matrix of the binder or concrete. Steel fibers are available to customers in various forms, depending on the manner in which they are bent. The shaping process aims to impede or prevent them from sliding out of the concrete. Macrosynthetic fibers also have different structures with the aim of achieving high pull-out resistance via mechanical anchorage. Based on the typical material properties, suppliers of macro-fiber technologies (whether steel- or plastic-based) develop the optimum geometry to achieve the best composite structure.The use of Macro fibers in construction materials is current practice, particularly when it comes to short-cut fibers. Short-cut polymer fibers are normally used to protect the concrete shell in the event of a fire. Polymer binders are used to improve adhesion to the substrate and to lower the modulus of elasticity. This test method was used to study the interaction of the polymer binder with the fiber (the interface of the distinct materials, concrete and fiber) and to determine whether polymer-containing concrete demonstrates better adhesion to the fiber, thus increasing the pull-out force. The study showed that there was very strong interaction between the polymer fibers and the VAE polymer used. It was possible to increase the relative pull-out force from 1 for the reference concrete to 1.48 (+50%) for the polymer concrete. The polymer binder has a high affinity for the fiber material, thereby enabling the production of a composite material that clearly surpasses the mechanical anchorage to, or embedding in, the concrete. If composites are generated by adding 10% polymer binder, the system can be considered to be more robust. Systems that are more robust are user friendly and facilitate better structures.

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