Will fiber keep concrete from cracking?

Do synthetic fibers reduce cracking in concrete? YES. The use of synthetic fibers at the manufacturer's recommended dosage rate per cubic yard can reduce plastic shrinkage cracking in concrete.

jarcosupply.com - FAQ's of Fiber Reinforced Concrete | Jarco Supply | Youngsville, NC

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FAQ’s of Fiber Reinforced Concrete

WHY USE WWM?

Secondary non-structural reinforcement such as wire matts does not keep cracks from occurring, but has traditionally been used to hold the concrete together after it cracks. Synthetic fibers have proven the ability to discourage early plastic shrinkage cracks from occurring in the first place, and the correct macro fiber can also affect post-crack behavior.

Should Monofilament fibers be able to replace Rolled Welded Wire Fabric (WWF) in concrete?

NO. Except for Jarcomesh Type 2. Some fiber manufacturers recommend a single strand, monofilament fiber to replace the rolled wire mesh as secondary reinforcement. Research has shown that while monofilament fibers do reduce plastic shrinkage during the early life of the concrete, they have limited benefit once the concrete cracks. Jarcomesh Type 2 has passed both criteria for the ICC ES AC 32 testing to replace WWF.

Can fibrillated fibers replace wire mesh in concrete?

YES. If the wire mesh is non-structural in nature, then a fibrillated (net-shaped) polypropylene fiber at a minimum dosage of 1.5 lbs. per cubic yard (0.9 kg per cubic meter) can adequately replace the wire mesh as the secondary reinforcement as long as they meet the ICC requirements of a min of 50 psi. Jarcomesh Type 2 at 2/3 lb. per yard can also replace wire mesh with a 60 psi and passes the impact test.

Do synthetic fibers reduce cracking in concrete?

YES. The use of synthetic fibers at the manufacturer's recommended dosage rate per cubic yard can reduce plastic shrinkage cracking in concrete. It is recommended to check with the supplier of the fiber and ask for test results and you will find Jarcomesh Type 2 outperforms all other fibers.

Does the use of fiber affect compressive strength of concrete?

The use of low or high-volume synthetic fibers is not intended as a method to increase the raw strength of the concrete. The use of fibers does not appreciably increase or decrease compressive strength. However, high dosages or macro/structural synthetic fibers have been shown to dramatically change how concrete cracks and fails, encouraging a very ductile mode of failure.

Does the use of fiber require mix design changes?

YES AND NO. When fibers are used at standard dosage and application rates, no mix design changes are necessary. However, when fiber volume rates are dramatically increased, some alterations in the mix design may be required. Please contact us for assistance regarding mix design and fiber dosage rates.

Does the use of fiber eliminate the need for good concrete practices?

NO. The use of any synthetic fiber does not replace the need for good concrete practices. As with any concrete, it is important to follow proper industry-recommended practices in regard to mixing, placing, jointing and curing the concrete.

Why does Jarco Supply offer different types of fiber reinforcement?

Research and development has garnered several grades of fiber reinforcement for various applications and performance level values. Each grade of fiber offers outstanding performance value when matched with the appropriate application.

What is the difference between monofilament and fibrillated fibers?

As the name suggests, monofilament fibers are single strand fibers, similar in shape to fishing line. Fibrillated fibers are deformed or irregular in shape, and expand out in a net like fashion, similar to fishing net.

What type of fiber and dosage rate does Jarco Supply recommend?

Jarco Supply offers a range of synthetic fibers used at various dosages to meet the performance requirements of a project or owner. Jarco Supply recommends the following performance-based characteristics: 1. For plastic shrinkage crack-control during the early life of the concrete: 1 bag per yard of Jarcomesh Type 1 2. For shrinkage and temperature-related crack-control as an alternate to light non-structural wire mesh in most applications: 1 bag per yard of Jarcomesh Type 2 3. For shrinkage and temperature crack-control and enhanced post-crack properties to allow for a welded wire matt reinforcement: 3 or more lbs. per yard of Jarcomesh Type 3:

See your Jarco Supply representative for engineered dose per application.

Can Jarcomesh fibers be pumped?

Yes. Fiber reinforcement has become a desirable construction practice for a wide range of concrete project applications. The ease of addition and the uniform distribution have given fibers distinct job site advantages over non-structural wire mesh. These advantages are even more valuable on projects where the concrete is delivered by a pumping process. The use of integral fiber reinforcement eliminates the wire mesh hassle encountered by the pump-line labor force, and allows the nozzle-man an unencumbered field in which to operate. In lieu of hoisting rolls of mesh onto upper-level deck projects, Jarcomesh-reinforced concrete can simply be pumped into place, offering significant time and labor savings to the project. Though fibers tend to change the "visual appearance" of the concrete, the pump operators typically notice more consistent and slightly lower pump pressures are required for fiber concrete.

Can Jarcomesh fibers be used in precast products?

Yes. The definition of a precast concrete member is simply an item that is "cast before" — one that is cast and cured in a form other than its final position. This concrete product application might include a wide variety of items: patio stones, splash blocks, step units, septic tanks, architectural facade panels, median barriers, railroad ties, burial vaults, utility boxes, bridge beams, grade rings, pipes, hollow-core slabs, manholes, and fence posts, as well as hundreds of different decorative ornamental items. It is very important for the precast producer to find methods to increase the toughness and early strength of his concrete products to reduce waste, minimize callbacks and returns, and aid in the item's long-term durability. If precasters are able to strip the forms and move "green" products to acuring area without breakage, the fiber reinforcement is obviously fulfilling its initial performance obligation. In addition, precasters notice less breakage, chipping, and spalling during handling, delivery, and placement of their products due to the unique three-dimensional Jarcomesh fiber coverage. The use of higher dosages of macro fibers allows the precaster to replace a higher level of conventional steel — contact Jarco Supply for engineering assistance.

Can Jarcomesh be used in shotcrete applications?

Yes. The term 'shotcrete' is generally used to describe concrete or mortar that is placed or shot at a high velocity onto a given surface by means of compressed air. The reinforcement used in typical shotcrete applications is expected to provide resistance to shear, flexure, and bending loading that may result from soil or rock movement, or from local hydrostatic pressures. The placement of wire mesh on typical irregular shotcrete surfaces is both cumbersome and costly with regards to labor. Synthetic fibers may be used as alternate materials that offer the necessary toughness-index and residual strength levels required, without the hassle and labor costs associated with mesh.

Can Jarcomesh fibers be used for elevated slabs?

Yes. There are a number of terms used to describe elevated slab systems, such as slab-on-metal deck and composite deck. The elements of this system are the metal deck, Portland cement concrete, and in most cases, some form of reinforcement. The metal deck can be classified in three categories – structural (composite), form, and roof deck. The first step is to select the proper metal deck for the application. Typically, in most multi-story structures, the composite (structural) floor deck is used, wherein the deck acts as the primary or positive reinforcement. Conversely, in a non-composite deck system, the metal deck is only used as the form the primary or positive reinforcement will be incorporated within the concrete slab. In the composite steel deck system, welded wire fabric is sometimes used as a temperature or secondary reinforcement. The Welded Wire Fabric calculation for temperature and shrinkage reinforcement per the Steel Deck Institute is 0.00075 times the area of concrete above the deck, however, SDI goes on to state that, "if welded wire fabric is used with a steel area given by the above formula, it will generally not be sufficient to be the total negative reinforcement". This consideration allows that Jarcomesh Macro fibers be used as a replacement for welded wire fabric as the secondary reinforcement. These fibers provide uniform, three-dimensional secondary reinforcement that is superior to any other form of temperature/secondary reinforcement, and are safer and more economical to use. In any above grade applications Jarco Supply should be consulted for reinforcement calculation assistance.

Can Jarcomesh fibers be used in toppings or overlays?

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Yes. An overlay is defined as a layer of concrete or mortar, seldom thinner than 1 inch (25 mm.), placed on, and usually bonded onto, the worn or cracked surface of a concrete slab. The overlay is usually designed to either restore or improve the function of the previous surface. Similarly, a topping is also defined as a layer of concrete or mortar placed to form a floor surface on a concrete base, yet is not necessarily bonded to the existing slab. Although deterioration of the old surface or severe cracking of the old slab is most often the reason for a topping course, other reasons might include a lack of floor levelness, improper elevation or plane, inadequate skid or slip resistance, or a lack of wear resistance. Regardless of the reasons, slab toppings and overlays can provide a cost-effective method of restoring an existing slab into serviceable condition, without the expense of removal and replacement. In addition to the normal difficulties of placing mesh in flatwork applications, there are additional related complications when toppings and overlays are placed. Naturally, the steel wire mesh requires sufficient cover within the concrete (usually a minimum of 2" or 5 cm.) to prevent corrosion-related spalling and unsightly mesh lines. Obviously, this cover becomes impossible in thin concrete toppings. In unbonded overlay applications, the placement of wire mesh becomes equally difficult without disrupting or damaging the bond-breaking layer or sheeting. One of the most important negatives with regards to mesh is the lack of uniform reinforcement coverage. The mesh is obviously located in one plane only in these thin applications that demand reinforcement to counter problems caused by one-directional bleeding, differential shrinkage, and curling.

When is the best time to add Jarcomesh fibers to concrete?

Jarcomesh products should be added to the concrete mixing system at the batch plant for best distribution. Follow the normal mixer manufacturers' standard recommendations and ASTM C-94. Mixing time should be a minimum of four to five minutes per load at a normal mixing speed. The batch plant will be the most economical and safest place for addition of the fibers. Typically it is not recommended that fibers be introduced to the mixer as a first ingredient, but added with other ingredients or at the end of the addition sequence.

Will adding Jarcomesh fibers at the job site cause any problems?

Fibers can be added to ready-mix trucks at the job site, though it is recommended they be added at the batch plant for optimum mixing and distribution. If fibers are added at the site, extra caution should be exercised to ensure sufficient mixing time. Allow at least 4 to 5 minutes of mixing time at drum mixing speed after the last product bag has been added.

Are Jarcomesh fibers compatible with liquid admixtures?

Synthetic fibers have no effect on air entrainment, super plasticizers, or water reducers. If possible, synthetic fibers should be added prior to any liquid admixtures to take full advantage of the mixing shear and friction of the mix to optimize the distribution.

Will Jarcomesh fibers interfere with a laser screed or power trowel finish?

NO, the vibration of the laser guided screed brings cement paste to the surface and covers almost all exposed fibers. Those not covered will be burned off with any power trowel finish. The possibility of replacing conventional steel mats with High Volume Synthetic Fibers allows for a much easier laser screed placement and finishing process.

What process should you use when applying a broom finish?

The use of a stiff bristled broom used in only one direction will help align surface fibers with the texture ridges, making them considerably less noticeable.

Do fibers hinder the adhesion of sealers or floor coverings?

Surface fibers will not react with sealers and/or interfere with carpeting, tile, etc. A heat torch could be used if necessary to remove any fibers that might be of concern.

What effect does fiber in concrete have on slump?

Because of its three-dimensional cohesive nature, fiber-reinforced concrete has the appearance of being less workable than plain concrete. In actuality, the visual slump may be reduced slightly but the flowability remains nearly same. Caution; never allow water to be added at the job site to bring back slump loss. The use of a super plasiticizer is recommended to increase slump if needed.

Are Jarcomesh fibers recognized by U.S. national code bodies?

Yes. Jarcomesh has had all of its fibers tested to comply with all codes and standards used by the ICC. All of the national building codes, such as the Uniform Building Code (I.C.B.O. - International Conference of Building Codes), the Standard Building Code (S.B.C.C.I. - Southern Building Code Congress International), the Basic Building Code (B.O.C.A. - Building Officials Code Administrators), and the One and Two Family Dwelling Code (C.A.B.O. - Council of American Building Officials.) These three codes have now been combined into the I.C.C. International Code Council) code, by which all Jarcomesh products are tested.

Are all steel fibers the same?

No – Steel fiber performance is a function of dosage rate, tensile strength, aspect ratio and anchorage. The combined effect of these four factors in concrete are determined through testing in accordance with ASTM C1609 (Standard Test Method for Flexural Performance of Fiber-Reinforced Concrete Using Beam with Third-Point Loading). From the test an average equivalent flexural strength (EFS) of the reinforced concrete can be determined. The EFS is the tested post crack strength of the reinforced concrete.

What do denier and aspect ratio have to do with fibers?

Denier of fiber is a measurement of the mass of a single yarn or filament of fiber over a length of 9000m. This is generally used only in the manufacture of synthetic materials and is used for QA/QC procedures. The aspect ratio of a fiber is the length of a single fiber divided by its equivalent diameter (L/d). This term is generally only used with larger fibers such as steel and macro-synthetics and while a specific value is not important, aspect ratios of greater than 100 can sometimes cause placement and finishing difficulties.

Why do fibers “ball up” in concrete mixes?

All fiber types (steel, micro and macro synthetic) have the potential to “ball up” in concrete. This phenomenon is usually caused by addition of fibers into concrete mixes that are too dry (slump decreases to zero) or into mixtures that do not have enough fine particles (cement, sand, supplemental materials, etc.) to coat the fiber particles, which in turn “paste starves” the system and again causes the slump to decrease to zero. Loose fibers in an empty drum may clump together and fiber types that are too long or have varying geometries may also cause problems. As always, a test trial should be performed to ensure that the mixture will support the fiber type and dosage and that the batching sequence will not cause any problems. If necessary, the use of a water reducing admixture may be warranted to maintain the desired slump for placement.

Can high dosage micro-fibers be used in replacement of low dosage macro-fibers?

Possibly — Again, the key will be the dosage rate and the intended function of the fibers. The primary function of a micro-synthetic fiber is the control of plastic shrinkage cracks and research has shown that these fibers do not have a significant ability to carry load across a crack. While the test data may support the use of a micro-fiber, it may not be the best option. Secondly, high dosages of micro-synthetics will be more difficult to mix as the fiber counts and surface area of the fibers will be extremely high causing possible significant loss in slump.

Are all macro-synthetic fibers the same?

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No — There are several different types of macro-synthetics on the market all with individual benefits and advantages. Remember the old adage; “you get what you pay for”. The key to the successful use of a macro-synthetic fiber for replacement of WWM, rebar or steel fibers is the dosage rate. Stronger fibers or higher bonding fibers will likely require less material than weaker fibers or fibers with less bonding capacity. The manufacturer must support dosage values with testing information. If questions are still present, a trial should be performed to ensure the desired performance is met.

How do you classify steel fiber reinforcing for concrete?

Steel fibers are defined in ASTM A820 as pieces of smooth or deformed fibers that are sufficiently small to be dispersed at random in a concrete mixture. There are currently 5 designations for steel fibers based on the product or process used as a source material:

 Type I - cold-drawn wire

 Type II - cut sheet

 Type III - melt-extracted

 Type IV - mill cut

 Type V - modified cold-drawn wire

The discussion of steel fiber reinforced concrete in ACI 360 states that “steel fibers have a higher elastic modulus and tensile strength than the surrounding concrete. In addition, many types of steel fibers are deformed to optimize anchorage in the concrete. These attributes allow steel fibers to bridge cracks that develop in the hardened state and redistribute the accumulated stress caused by applied loads and shrinkage.”

Can steel fiber reinforced concrete be pumped?

Yes, but expect a 1 to 3 inch slump loss through the hose depending on the steel fiber dose rate, ambient temperatures and hose length. A mid-range water reducing agent (MRWR) is commonly used to enhance workability and ease of flow through pump lines. High-range water reducers (HRWR) may be required in some cases. Typically, a 4 to 6 in. diameter hose is required.

APPLICATIONS

Potential projects suited to the use of fiber reinforced concrete are listed below. Residential: including driveways, sidewalks, pool construction with shotcrete, basements, colored concrete, foundations, drainage, etc.

Warehouse / Industrial: light to heavy duty loaded floors and roadways

Highways / Roadways / Bridges: conventional concrete paving, SCC, white-toppings, barrier rails, curb and gutter work, pervious concrete, sound attenuation barriers, etc. Ports and Airports: runways, taxiways, aprons, seawalls, dock areas, parking and loading ramps.

Waterways: dams, lock structures, channel linings, ditches, storm-water structures, etc.

Mining and Tunneling: Precast segments and schotcrete, which may include tunnel lining, shafts, slope stabilization, sewer work, etc. Elevated Decks: including commercial and industrial composite metal deck construction and elevated formwork at airports, commercial buildings, shopping centers, etc.

Agriculture: farm and animal storage structures, walls, silos, paving, etc.

Precast Concrete and Products: architectural panels, tilt-up construction, walls, fencing, septic tanks, burial vaults, grease trap structures, bank vaults and sculptures

Other Applications: includes any other FRC related applications not specifically described above.

FIBER TYPES

Fiber types for use in FRC Applications come in many sizes, shapes, colors and flavors. Steel Fibers: These fibers are generally used for providing concrete with enhanced toughness and post-crack load carrying capacity. Typically loose or bundled, these fibers are generally made from carbon or stainless steel and are shaped into varying geometries such as crimped, hooked-end or with other mechanical deformations for anchorage in the concrete. Fiber types are classified within ACI 544 as Types I through V and have maximum lengths ranging from 1.5” to 3” (30 – 80 mm) and can be dosed at 10 to 100 lbs/yd (6 to 67 kg/m3). Micro-synthetic fibers: These fibers are generally used for the protection and mitigation of plastic shrinkage cracking in concrete. Most fiber types are manufactured from polypropylene, polyethylene, polyester, nylon and other synthetic materials such as carbon, aramid and other acrylics. These fiber types are generally dosed at low volumes ranging from 0.03 to 0.2% by volume of concrete – 0.5 to 3.0 lbs/yd (0.3 to 0.9 kg/m3). Macro-synthetic fibers: This newer class of fibers has emerged over the past 15 years as a suitable alternate to steel fibers when dosed properly. Typical materials include polypropylene and other polymer blends having the same physical characteristics as steel fibers (length, shape, etc.), These fibers can be dosed from 3 to 20 lbs/yd (1.8 to 12 kg/m3). Glass Fibers: GFRC (Glass Fiber Reinforced Concrete) has been predominantly used in architectural applications and modified cement based panel structures. Cellulose Fibers: manufactured from processed wood pulp products, cellulose fibers are used in a similar manner to micro-synthetic fibers for the control and mitigation of plastic shrinkage cracking. Natural Fibers: Not typically used in commercial applications of fiber reinforced concrete, natural fibers are used to reinforce cement based products in applications around the world and include materials such as coconut, sisal, jute and sugarcane. These materials come in varying lengths, geometries and material characteristics. PVA Fibers: Poly-vinyl alcohol fibers are synthetic made fibers that when used at higher volumes, can alter the flexural and compressive performance of concrete Specialty Fibers: This classification of fibers covers materials not described above and generally pertains to newly manufactured or specified materials not common to the above categories. Steel & Micro / Macro blends: A recent development in the field of fiber reinforced concrete that has emerged in the marketplace has been the combination or blending of steel and / or macro-synthetic fibers with various types of micro-fibers to help control plastic shrinkage cracking (ie: micro-synthetics) while at the same time providing concrete with enhanced toughness and post-crack load carrying capacity achieved only with the use of steel and macro-synthetic fibers. These fibers are typically dosed at the prevailing