Macrosynthetic Fibers Save Owners Money Over Conventional Temperature-Shrinkage Steel Reinforcement
July 21, 2014
When using conventional temperature-shrinkage steel reinforcement the Structural Engineer tends to use a one-size-fits-all approach on projects to offset the potential for the field crew to place the wrong reinforcement system in a cross-section. Too often the Structural Engineer determines what temperature-shrinkage reinforcement is needed for the most demanding concrete application and then specifies that reinforcement throughout the construction.
For example, if a project includes a maintenance garage and an office, then most often the office is specified the same temperature-shrinkage reinforcement as the maintenance garage — resulting in a costly dollars and cents penalty to the owner. However, when macrosynthetic fibers are added to the concrete mix at the plant the dosage rate from truck to truck can be adjusted to meet the exact needs of the project. This means the office floor slab can be specified with the precise quantity of macrosynthetic fibers needed versus the overkill created when the maintenance garage floor slab reinforcement is used.
Conventional Steel Costs the Owner Macro Bucks
This over-specification of steel reinforcement is not the first hit to the owner’s pocket. The use of conventional temperature-shrinkage steel reinforcement creates additional costs related to labor, equipment, and material that are not present when using macrosynthetic fibers. For example, when placing a slab with welded wire fabric (WWF) or #3 or #4 rebar as the temperature-shrinkage reinforcement the concrete trucks must stay off of the slab area, thus requiring the need for a concrete pump and a $2,500-plus-per-day added cost. Furthermore, the codes are now requiring that the steel is placed on permanent supports, producing yet more of a cost burden for the owner. All of this is eliminated when using macrosynthetic fibers.
Value Engineering Solution for Structural Engineers
For the Structural Engineer macrosynthetic fibers provide a Value Engineering solution for replacing conventional temperature-shrinkage (non-structural) reinforcement used in Plain Structural Concrete. Plain Structural Concrete slabs utilize the thickness of the slab and the engineering properties of the concrete to determine the load-carrying capacity of the slab.
Macrosynthetic Fibers Deliver:
- Macro Benefits
The first generation of synthetic fibers provided both plastic shrinkage crack reinforcement and temperature-shrinkage crack reinforcement.
The new generation of synthetic fibers (macrosynthetic fibers) affords the opportunity to expand on these contributions, thus enhancing further the durability of the concrete.
The difference in these two generations of synthetic fibers is considerable. For example, the macrosynthetic fibers are more robust with an increased cross-section and a minimum 1.5″ fiber length versus the 0.75″ standard length of microsynthetic fibers.
The added length provides a better mechanical bond that contributes to increased post-first crack toughness/residual strength — the greatest enhancement and one that can be quantified. The minimum dosage rate of 3.0 pcy compared to 0.5 to 1.5 pcy for the microsynthetic fibers also contributes to enhanced engineering properties including fatigue strength and impact and surface abrasion resistance. Fatigue strength is key when designing an industrial or warehouse floor slab or pavement area where there is a high concentration of 18 kip loads.
Three ASTM International test methods are available to evaluate the performance characteristics of the macrosynthetic fibers: C1399, C1550 and C1609. Each test method approaches the evaluation of the 3-dimensionally reinforced concrete from a different direction. ASTM C1609 would be the most-called-for test method. This test uses a closed loop approach in loading the test beam.
ASTM C1399 ranks second and requires the use of a steel plate up to the first crack. After it is removed, the standard ASTM C78 flexural beam testing method is utilized. State DOTs will specify one or the other of these two methods to achieve their approval. ASTM C1550 requires equipment that a vast majority of the commercial laboratories do not have available, so it is rarely used.
- Unique Benefits
The three-dimensional reinforcement system provided by macrosynthetic fibers yields a number of benefits not remotely possible when using conventional steel reinforcement.
One of the principal benefits is a reduction in water migration/bleeding that produces a more homogeneous concrete with a much smaller water/cement ratio range. Thus the actual strength of the concrete in the slab surface will be increased.
A further benefit of extreme value in industrial and warehouse floor slabs is the measurable increase in fatigue strength, which translates into longer service life. Here we are talking about increasing the number of axle loads by some measurable number over the life of the concrete.
Also, note that there will be less settlement of the plastic concrete due to the modification to the thixotropic properties of the concrete.
ABC Polymer’s Macrosynthetic Fibers: Engineered for Specific Applications
ABC Polymer’s Macrosynthetic Fibers are the solution to a number of issues that confront the Structural Engineer technically and, of equal importance, financially. When one weighs the facts, there is only one answer: specify the ABC Polymer family of macrosynthetic fibers. To assure the Structural Engineer that he/she is selecting the exact product needed for a specific application all that is required is a call to Bobby Zellers, PE, Director, Engineering Services, at (724) 475-1177 or via email to RZellers@ABCFibers.com.
ABC Polymer Industries: Departing from Standard Industry Practice
ABC Polymer Industries believes that a single macrosynthetic fiber does not provide the engineering response required for the broad range of applications available to this newest generation of synthetic fibers.
Looking at cast-in-place concrete, shotcrete and precast concrete as the principal application areas, ABC Polymer’s macrosynthetic fibers were developed to yield specific engineering properties for each application.
In general, FiberForce 650 has been designed to maximize benefits in cast-in-place concrete. Performance Plus DOT works well in cast-in-place concrete as well as shotcrete, and Macro Pro’s contributions to precast products like septic tanks and burial vaults are excellent.
FiberForce 650 is a flexible embossed tape with excellent mechanical bonding properties.
FiberForce 650 is an embossed tape fiber manufactured from a blend of polypropylene and polyethylene resins.
The dimensions of the tape are critical to the performance, which reflects in the C1609 test results. Furthermore, the reduction in crack mouth opening at a given deflection compared to competitors’ macrosynthetic fibers is significant. FiberForce 650 distributes evenly in the concrete matrix and places and finishes extremely well.
Approved by the state DOTs with synthetic fiber concrete specifications, this product is an excellent choice for cast-in-place concrete. When used within the standard dosage range of 3.0 pcy to 7.5 pcy it is recommended that the concrete mix design should be reviewed to ensure there is sufficient mortar to coat the coarse aggregate and the increased fiber surface area. Use of a mid- or high-range water reducer is recommended. A vibrating screed or laser screed will make sure the concrete is consolidated and that there is sufficient mortar on the surface of the slab.
The intricate fibrillation pattern in the Macro-Pro is more robust than that in the polypropylene fibers to provide more strength.
Macro-Pro is a highly modified fibrillated fiber manufactured from a blend of polypropylene and polyethylene resins. The fibrillation pattern in the Macro-Pro is more robust, with the main fibrils being larger than the fibrillation pattern found in the polypropylene fibers, which provides more strength.
This product has been used successfully for years in precast products such as septic tanks, burial vaults and utility vaults. Macro-Pro distributes evenly in the concrete matrix and places and finishes extremely well.
When used within the standard dosage range of 3.0 pcy to 7.5 pcy it is recommended that the concrete mix design should be reviewed to ensure there is sufficient mortar to coat the coarse aggregate and the increased fiber surface area. Use of a mid- or high-range water reducer is recommended.
Performance Plus DOT blends FiberForce 650 and Macro Pro to offer the advantages of both.
Performance Plus DOT is a blend of FiberForce 650 and Macro-Pro, thus benefitting from the outstanding qualities of both these products.
The versatility of this product is obvious. It works equally well in cast-in-place applications as in precast applications.
As the name connotes, Performance Plus DOT is approved by all state DOTs with synthetic fiber concrete specifications. Industrial and warehouse floors where the finish is of paramount importance provide an outstanding showplace for Performance Plus DOT.
When used within the standard dosage range of 3.0 pcy to 7.5 pcy it is recommended that the concrete mix design is reviewed to ensure that sufficient mortar to coat the coarse aggregate and the increased fiber surface area is present. Use of a mid- or high-range water reducer is again recommended. A vibrating screed or laser screed will make sure the concrete is consolidated and that there is sufficient mortar on the surface of the slab.
How to Specify Macrosynthetic Fibers
ABC Polymer’s Three-Part Master Specification: Macrosynthetic-Fiber Reinforced Concrete is a sample approach that Structural Engineers can use to specify macrosynthetic fibers as a Value Engineering alternative to WWF or #3 or #4 rebar for temperature-shrinkage reinforcement.
If you need additional information or have questions about the specification, simply contact Bobby Zellers, PE, Director, Engineering Services, at RZellers@ABCFibers.com.
Don’t over-spec your projects to avoid construction site errors – use ABC Polymer’s macrosynthetic fibers added to the concrete mix to meet the exact needs of each unit of the project while saving your client money.