AU2019240725B1 - Fiber-reinforced concrete – guided distribution methods for fibers in conventional construction - Google Patents

Abstract

ers or fibres are normally added and are dispersed into wet concrete mixture in a random (or, ideally, 'orm) manner. Each tiny fiber functions as a micro reinforcing element which helps concrete improve not /its structural ductility and post-crack behaviors but also the capacity to resist secondary effects such as nkages and thermal deformation. However, when it comes to large-scale applications of fibers, random or orm distribution does not reflect the actual demand at different locations in structural concrete. This, in s, leads to an unnecessary impact on project budget. Equally, inevitable re-distribution and re-alignment of rs as a result of numerous production activities also strongly influence the consistency of the final concrete lity. address these important shortcomings, this invention introduces a concept of intentional guide, from which ous fiber densities can be achieved to reflect better specific fiber demands at different locations. This bles higher contribution of fibers into structural performance of concrete. Beside the control of fiber density, concept also promotes a random, 3-dimensional orientation/alignment of fibers. For conventional struction techniques, it is interpreted into 2 methods, namely LOCAL INJECTION and MESHING. The l injection method is suitable for local areas carrying intense, concentrated and complicated stresses; while r meshing is proposed for protection or treatment of large surface areas. Both methods can be conducted er automatically or manually, and are more independent of other dynamic production activities, which help te the final concrete with more consistent quality.

Description

ers or fibres are normally added and are dispersed into wet concrete mixture in a random (or, ideally, 'orm) manner. Each tiny fiber functions as a micro reinforcing element which helps concrete improve not /its structural ductility and post-crack behaviors but also the capacity to resist secondary effects such as nkages and thermal deformation. However, when it comes to large-scale applications of fibers, random or orm distribution does not reflect the actual demand at different locations in structural concrete. This, in s, leads to an unnecessary impact on project budget. Equally, inevitable re-distribution and re-alignment of rs as a result of numerous production activities also strongly influence the consistency of the final concrete lity.

address these important shortcomings, this invention introduces a concept of intentional guide, from which ous fiber densities can be achieved to reflect better specific fiber demands at different locations. This bles higher contribution of fibers into structural performance of concrete. Beside the control of fiber density, concept also promotes a random, 3-dimensional orientation/alignment of fibers. For conventional struction techniques, it is interpreted into 2 methods, namely LOCAL INJECTION and MESHING. The l injection method is suitable for local areas carrying intense, concentrated and complicated stresses; while r meshing is proposed for protection or treatment of large surface areas. Both methods can be conducted er automatically or manually, and are more independent of other dynamic production activities, which help te the final concrete with more consistent quality.

AUSTRALIA Patents Act 1990

COMPLETE SPECIFICATION STANDARD PATENT FIBER-REINFORCED CONCRETE - GUIDED DISTRIBUTION METHODS FOR FIBERS IN CONVENTIONAL CONSTRUCTION

The following statement is a full description of this invention, including the best method of performing it known to us.

FIBER-REINFORCED CONCRETE - GUIDED DISTRIBUTION METHODS FOR FIBERS IN CONVENTIONAL CONSTRUCTION

1. TECHNICAL FIELD

The present specification relates directly to the field of civil engineering.

NOTE 1: In this document, the term "fibers" or "fibres" refers to short, thin and discrete elements which can be easily added and dispersed into wet concrete mixture. From this definition, fibers may include, but not limited to, metal wires (e.g. steel, titanium, copper etc.), natural strands (e.g. bamboo, rice husk, banana, oil palm, sugarcane bagasse etc.) and manmade fibrils (e.g. polypropylene, nylon, polyethylene, carbon nanotube, graphene etc.).

NOTE 2: In this document, the term "conventional construction" refers to a sequential concrete production process (i.e. mixing, transporting, pumping, placing, compacting, finishing, curing etc.) with considerable contribution of human factors. This is to differentiate with automatic process (e.g. 3D printing), where machines replace human inputs in most of the major stages.

2. BACKGROUND

Fibers are normally added and are dispersed into concrete mixture in a random (or, ideally, uniform) manner. In general, each tiny fiber exists as a micro reinforcing element which helps concrete improve not only its structural ductility, post-crack behaviors but also load-bearing capacity. Fibers are also known as an important mean in controlling secondary effects, such as shrinkages and thermal deformation.

However, considering the efficiency of fiber addition in light of its budget friendliness and structural necessity, several issues remain, as below:

• First, random or uniform distribution does not reflect the actualfiber demand in structuralconcrete. In fact, depending on dimensional attributes and practical purposes of a certain structural member, it is a common situation that some locations in the member require denser fibers than the others. To illustrate this point, Figure 1 presents a typical system of a residential building comprising slabs, columns and beams. In this system, it can be seen that fibers of high density are required (i) under concentrated/intense loads, (ii) at connection points or sharp changes in shape and (iii) close to the surfaces to protect them against spalling due to extreme events (e.g. fire) or early-age cracking (i.e. due to shrinkages and thermal deformation);

• Second, the effects of fibers are strongly influenced by their density and alignment inside concrete. For conventional construction techniques, dispersed fibers may create the final concrete with inconsistent properties due to inevitable re-distribution and re-alignment as a result of numerous production activities (e.g. transporting, pumping, placing, compacting, finishing etc.).

- To make the issue even more serious, for specialty mix designs such as highly workable concrete or self-compacting concrete, fibers will move along with the "flow" of concrete mixture into place. Such a rapid flow inevitably causes a universal re-alignment and re-distribution of fibers, which in turns exert larger impacts on hardened concrete. • Third, there are situations where fiber addition is the most/only convenient measure to reinforce concrete. For instance, in automatic concrete production such as 3D printing, fibers may be used to partly or completely replace conventional reinforcing bars. In these cases, the increase of fiber consumption due to r,6 2 cQ unreasonable distribution methods may become more substantial, causing heavier pressures on project budget.

Accordingly, there exists a need to address all the issues above by providing methods to purposely "guide" fiber distribution so that varying density can be achieved as desired. For convenience, the document only focuses on concrete produced by conventional construction techniques.

3. SUMMARY OF INVENTION

An aspect of the present disclosure provides a method for concrete preparation, the method comprising the steps of: preparing fibre meshing by: applying an adhesive to at least a portion of a base mesh; attaching reinforcing fibres to the at least a portion of the base mesh such that at least some of the reinforcing fibres are oriented at an angle relative to a plane of the base mesh; allowing the adhesive to dry; and shaping the base mesh with the reinforcing fibres attached in accordance with a shape of an intended concrete structure; installing the prepared fibre meshing for concrete placement at a desired location in the intended concrete structure; placing concrete around the installed fibre meshing; and compacting the concrete, wherein the installed fibre meshing is restrained in place during the concrete placement and the compacting.

There is also disclosed a fibre injection device for injecting reinforcement fibres into concrete, the device comprising: an outer tube; and a rod located inside the outer tube, the rod being slidable along a longitudinal axis of the outer tube between a retracted position and an extended position, wherein the rod includes: a hollow main body having a proximal opening and a distal opening; a gripping means disposed at the distal opening of the main body and adapted to be inserted into concrete when the rod is in the extended position, wherein the main body is adapted to receive fibres through a proximal opening and to release the fibres through a distal opening into the gripping means; and the gripping means is adapted to be closed, when the rod is in the retracted position, to hold the fibres and to be open, when the rod is in the extended position, to release the fibres to inject the fibres into the concrete.

There is also disclosed a method for injecting reinforcement fibres into concrete using the fibre injection device described above, the method comprising the steps of: while the rod is in the retracted position, inserting fibres into the proximal opening of the main body of the rod; inserting a distal end of the fibre injection device into a desired location of fresh concrete to position; sliding the rod from the retracted position to the extended position, causing the gripping means to open and release the fibres; and applying rotation and vibration, through the distal end of the fibre injection device, to the desired location of the concrete to disperse the released fibres.

The core and unique concept of the methods and devices disclosed in the present application is as follows:

• First, the conventional distribution technique for fibers in concrete (i.e. random or uniform dispersion from mixing) is supplemented by new methods to intentionally control fiber density. Denser fibers are achieved at critical locations (as in Figure 1) while those of lower demand may contain either less or no fibers. With such a combination, fiber distribution reflects better the actual structural and loading characteristics. The fibers then can participate into the load carrying process in their most reasonable manner;

• Second, the new methods to be introduced are more independent of major on-site construction activities, thereby helping reduce their undesired effects on fiber distribution and orientation. This helps create the final concrete with more consistent quality;

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• Third, with more reasonable fiber distribution, this concept allows fibers to replace conventional reinforcing bars in situations where the bar arrangement is either difficult or expensive. Importantly, it assists automatic production technology such as 3D printing, enabling more flexible production of concrete structures in terms of shape, size, connection, composition and loading characteristics;

• Finally, this concept promotes more budget-friendly applications of fibers in practice, as dense fibers are only supplied where needed.

NOTE 3: Structural concrete rarely carries a monotonic load but a complex combination of more than one load cases, either as designed or unexpectedly. At any location inside concrete, intense stresses may exist in any direction which, as a result, requires reinforcing. On this basis, the intention of the methods described in this application is not only to control fiber density but, importantly, also to promote their random, 3D orientation. It is thought to be the most effective reinforcing strategy for concrete structures using fibers.

Two methods are introduced in this application, namely local injection and meshing. Descriptions are provided in the following sections.

4. LOCAL FIBER INJECTION METHOD

4.1. Principles

This method is suitable for local positions suffering intense stress concentration. Denser fibers help carry complicated stresses, especially tensile stresses, and disperse them to a larger area; therefore, either reducing cracking risk or preventing large crack opening. Examples include, but not limited to, under point loads, behind anchorages, at sharp changes in geometry and at connection joints among different structural members (e.g. slab-column, column-beam, pile-cap etc.). In these local areas, intense stresses may exist in all principle directions. As a result, denser and 3D-alignedfibersare preferable.

As the name implies, this method employs a specialized device to "inject" fibers into fresh concrete after placement. Descriptions of the device are given below.

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4.2. Concept of injection device

Concept of the injection device is presented in Figure 2. Although slightly changes of important design parameters (e.g. size, shape, connection, material etc.) may be necessary to suite specific circumstances in practice, the device consists of the following major components:

• One straight rod located at the center of the device. The rod is preferably made of steel, although other materials of suitable strength and durability may also be used.

- One end of the rod is connected to a system of gripping claws. These claws are attached to the rod by spring hinges or other suitable devices with similar functionalities. Depending on relative position of the claws and the outer tube, the spring hinges can automatically control claw movement: close when inside and open when outside. All the gripping claws are preferably made of steel, or other materials with suitable strength and impact resistance; - The other end of the rod is connected to a vibration-rotation mechanical generator. The generator incorporates an ON/OFF switch to allow flexible operation; - A through hole is arranged inside the rod, acting as a fiber input channel; - The rod is protected inside an outer tube and in operation, will slide along the longitudinal axis of the tube.

• One outer tube to protect the main rod inside. The outer tube may be made of aluminum alloys or other suitable materials in terms of lightweight and durability, also allowing a convenient maneuver.

- For protection and navigation purposes, the main rod is supported inside the tube by at least 2 elastic seals made of rubber or other materials of suitable elasticity and durability; - The presence of these elastic seals is also important to absorb impacts from the rotation and vibration of the main rod, enabling a comfortable handling and operation.

4.3. Preparationand applicationprocedures

Procedures are described below:

• First, determine the required amount of fibers to be injected, considering both structural demand and degree of dispersion (i.e. to ensure a specific density within a specific local space/volume). Also, from the fiber amount, degree of dispersion and based on the capacity of available rotation-vibration generator, estimate the optimum operation duration;

• Second, for fiber input, when the rod is in vertical position with the gripping claws at the bottom and all the claws are closed, fibers are inserted from the top end, falling along the hole inside the rod under gravity then are stored within the closed claws;

• Third, locate an appropriate injection point. As a rule of thumb, it should be near the local areas in need and where a safe standing spot for operators is available. Although a perpendicular direction to the concrete surface (i.e. to be injected) is preferable, if necessary, the injection device may also work at an inclined angle as shown in Figure 2;

• Fourth, inject fibers. This is done by gliding the main rod along the longitudinal axis of the outer tube toward and into concrete. Once the claws are outside the tube, they will be triggered by the spring hinges to open, releasing fibers to concrete;

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• Fifth, apply rotation and vibration on the main rod and the claws. Such movements allow fibers to disperse further into the vicinity of the injection point, simultaneously acting as a compaction mean for concrete. The process ceases when the optimal duration is met (i.e. determined from Step 1);

• Sixth, turn off the rotation and vibration generator, pull out the injection device while the claws are still open and if necessary, conduct finishing tasks for the affected concrete surface(s).

The procedures are proposed for newly placed concrete and may be applied before or immediately after compaction.

5. FIBER MESHING METHOD

5.1. Principles

As the name implies, this method employs a 2D base mesh to attach and "guide" fiber so that higher density is achieved on the provided surface of the mesh. After attaching fibers, the mesh may be reshaped to reflect the 3D forms of specific concrete surfaces (i.e. to be protected) and is installed under, yet close to, the expected surfaces before concrete placement. It should be noted that in this case, fibers are still the major surface protection measure; while the base mesh itself may also have a certain/minor contribution.

This method is suitable for protection and/or treatment for large areas of concrete surfaces. The presence of fiber mesh(es) helps reduce/avoid the risk of violent spalling under extreme events such as fire or earthquake. Equally, it also helps concrete resist on-going driving forces such as shrinkages and thermal deformation, which may lead to early damages.

Again, although this is a 2D guide method for fibers, a random/3D fiber orientation is strongly promoted (Figure 3). Techniques to ensure this characteristic are described below.

5.2. How to "mesh"fibers?

Techniques to prepare a base mesh and attach fibers are as follows:

• First, from the chosen type of fibers and concrete mix design, decide a suitable type of mesh. The mesh should:

- have a suitable shape that allows easy passing of aggregates and other coarse particles in concrete mixture. Although other shapes may also be considered, in this invention, rectangular or hexagonal meshes are preferable; - be sufficiently strong to carry the attached fibers without being deformed or distorted. Mesh material should enable a reshape and should not exert adverse effects on concrete strength and durability. For this reason, steel mesh is preferable in this invention, although other materials with equivalent properties may also be used; - have an open area with the minimum mesh spacing (i.e. mesh size or nominal pitch) greater than or equal to the nominal length of fibers. This is necessary to ensure minimum congestion; - have an open area with the maximum mesh spacing less than or equal to twice the nominal length of fibers. This is important to ensure the bridging effects (i.e. continuous reinforcement); - have an open area with the minimum mesh spacing greater than or equal to twice the maximum size of aggregates used in the concrete.

• Second, determine a required fiber density per unit area of the mesh based on structural design;

• Third, immerse the portion of interest of the mesh (i.e. intended for fiber attachment) into a sink of adhesive liquid. Immediately after removing the mesh from the sink, while the adhesive substance on the mesh is still r,6 5 cQ wet and active, place the mesh horizontally above a clean base. The mesh is supported around its edges and/or at intermediate locations and must not touch the base. Distance between the mesh and the base is around half the nominal length of the chosen fibers;

• Fourth, uniformly distribute fibers from around 1m to 2m above the mesh. The fibers are allowed to fall freely under their own weight to ensure that they touch and adhere to the mesh in their most natural manner. The amount of fibers used for this step should be more than those intended to attach on the mesh (i.e. to compensate for those falling out);

• Fifth, quickly and continuously distribute all fibers while the adhesive substance on the mesh is still wet. Additional adhesive spray should be ready to improve the effectiveness of fiber attachment. This step is considered complete once the fiber density attached to the mesh reaches the desired level (Step 2);

• Sixth, wait until the adhesive substance completely dry and harden, to ensure the fibers are firmly adhered to the mesh, then clean up the base. The mesh with guided fibers attached on it may be bent or reshaped to reflect the actual concrete surfaces it is intended to support.

NOTE 4: The techniques can be conducted either manually or automatically. It should be facilitated in a controlled environment with minimum air flow and optimal temperature for the adhesive liquid/spray to dry and harden. Also, this guided fiber mesh requires careful transport and handling to respect not only the fiber density but alignment as well.

5.3. Applications

The fiber meshes may be flexibly applied in various situations of surface protection and treatment. They may be installed as a single or multiple layer(s) under, yet close to, concrete surfaces. They may also be used in conjunction with reinforcing bars or as a sole/standalone system. Examples are given in Figure 3, where they are employed to supplement existing reinforcing bars of a concrete column and act as a sole reinforcing system of a concrete slab.

The installation of the meshes is similar to conventional methods for reinforcing bars. However, due to their lightweight, the meshes must be firmly restrained in advance to ensure their stability during concrete placement, compaction and finishing.

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Editorial Note

2019240725 Pages are non sequential standard format of IP Australia The claims should be page 7

Claims (7)

LIST OF CLAIMS The claims defining this invention are as follows:

1. A method for concrete preparation, the method comprising: preparing fiber meshing by: applying an adhesive to at least a portion of a base mesh; attaching reinforcing fibres to the at least a portion of the base mesh such that at least some of the reinforcing fibres are oriented at an angle relative to a plane of the base mesh; allowing the adhesive to dry; and shaping the base mesh with the reinforcing fibres attached in accordance with a shape of an intended concrete structure; installing the prepared fibre meshing for concrete placement at a desired location in the intended concrete structure; placing concrete around the installed fibre meshing; and compacting the concrete, wherein the installed fibre meshing is restrained in place during the concrete placement and the compacting.

2. The method of claim 1, wherein the prepared fibre meshing is installed in a position that will be under and close to a surface of the intended concrete structure after concrete placement.

3. The method of any one of claims 1 and 2, wherein the base mesh has mesh spacing that is sized to allow easy passing of aggregates in concrete mixture of an intended concrete structure.

4. The method of any one of claims 1 to 3, wherein the base mesh has spacing that is less than or equal to twice a nominal length of fibres.

5. The method of any one of claims1 to 4, wherein, to attach reinforcing fibres to the base mesh, the base mesh is suspended above a work surface at a height that is approximately half of a nominal length of the fibres, and fibres are allowed to fall onto a surface of the base mesh.

6. The method of any one of claims 1 to 5, wherein the base meshing is made of steel or another shapable material.

7. The method of any one of claims 1 to 6, wherein the base mesh with the reinforcing fibres attached thereto is shaped into a three-dimensional shape in accordance with a three-dimensional surface of the intended concrete structure.

Duy Huu Nguyen By Patent Attorneys for the Applicant

©QCOTTERS Patent & Trade Mark Attorneys

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Editorial Note 2019240725 Pages are non sequential standard format of IP Australia The drawings should be page 8-10

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