A Fiber-reinforced Concrete Testing Primer for Ready Mix Concrete Producers (Part 2)
June 3, 2015
Our first article (Ready Mixer News Memo Feb./Mar. 2015 issue) in this important series explained the Fiber-reinforced Concrete (FRC) sampling procedure, including some of the most critical points of test specimen fabrication. This issue’s article continues the series with details of the proper testing process, along with a review of approved fibers from the ABC Polymer stable of products.
It is our hope that this primer for ready mix concrete producers, as well as engineers, contractors and commercial laboratory personnel, will help ensure that the product delivered to each and every project is sampled properly and specimens are fabricated and tested properly. It is essential that ready mix producers fully understand the importance of these three critical areas, including making sure that the FRC’s performance tests meet with local DOT or other codes/specifications or with ASTM or other national or international consensus procedures.
Without the Quality Control (QC) Manager of a ready mix company monitoring and policing project inspectors and commercial laboratory technicians, the potential exists for the concrete test data generated for a given project to be rejected, ultimately resulting in non-payment of the concrete.
It is impossible to overemphasize the importance of correctly sampling and testing the FRC/FRS. If the FRC sample-gathering process, test specimen fabrication and testing are not conducted per standard consensus practice the test results may not accurately reflect the parent FRC. If the finished product is not approved, this could result in significant penalties for the contractor, ready mix producer and vendor.
Part 2 — Standard Test Methods & Specifications
Required Testing Equipment
- Selection of the equipment to measure the air content of fiber-reinforced concrete/shotcrete when low dosage levels of fibers are used is not critical (0.5 to 2.0 pcy). Here the pressure meter (ASTM Test Method C231) can be used without concern.
Equipment setup for the ASTM Pressure Meter Air Test for Concrete. This test can be used with all types of FRC.
When higher dosage levels of fibers (typically macrosynthetic fibers at 3.0 pcy or higher) are specified some potential exists for the fibers to bridge in the cylindrical pressure vessel and create entrapped air voids, even when the proper consolidation method is followed.
DO externally vibrate the vessel.
DO NOT internally rod the vessel.
To determine true air content values at the higher fiber dosage level a roll-o-meter test (ASTM Test Method C173) should be considered to run as a companion with the C231 method. This practice is recommended for synthetic fiber dosage levels at or above 3.0 pounds per cubic yard and steel fiber dosage levels at or above 65.0 pounds per cubic yard.
Standard Test Methods and Specifications
- ASTM Subcommittee C09.42 Specifications and Consensus Test Methods
ASTM FRC/FRS specifications and test methods are under the purview of Subcommittee C09.42. The specification for Fiber Reinforced Concrete and Shotcrete is C1116. The value of this specification is very limited. Basically, it addresses the chemical compatibility of the various fiber groups with cement concrete. Additionally, it covers the approach to use when specifying FRC.
Four test methods fall within the control of Subcommittee C09.42.
- C1579 —Evaluating Plastic Shrinkage Cracking of Restrained Fiber Reinforced Concrete (using a Steel Form Insert). This is a relatively new test method and has been in the development stage since the early ‘90s when originally conceived by Dr. Paul Kraii. Some limits still remain to this test method in terms of the variability of the data generated. It is a good indicator of the FRC’s ability to reduce the number and size of plastic shrinkage cracks. This test method, as well as the others cited below, can be found in ASTM Standards Volume 04.02.
Three post-first crack test methods basically look at the same engineering properties, but each in a different way.
- C1609 —Flexural Toughness and First-Crack Strength of FRC. This test replaces the C1018 test method, which has been abandoned by ASTM International.
- C1399 —Average Residual Strength of FRC. This test is unique in that a steel plate is inserted beneath the test beam up to and including first crack at which time it is removed and the test is continued. This test was originally conceived solely for use with synthetic fibers.
- C1550 —Average Residual Strength using a Round Panel Test of FRC. This is the newest of the three post-first crack test methods. The equipment required to conduct this test is supersized based on the dimensions of the round panel. To date, the test has not gained traction in the U.S.
The selection of one procedure over the other seems to be more political than technical. Today C1609 is becoming the preferred test method in the U.S. Reasons for selecting this test method over C1399 include the fact it is a continuous test and the loading is by closed loop. Closed loop is defined as loading of the test specimen based on the deflection of the specimen. The loading is not uniform based on pounds per time increment.
The test equipment and the assembly of this equipment are paramount to the success of producing valuable, reliable test data. Unfortunately, some laboratories misinterpret the equipment requirements, do not have the proper equipment to conduct the tests, or fail to understand the need for precise assembly of the required equipment.
Accurate beam test assembly as prescribed by ASTM C1609 for Macrosynthetic Fibers.
To address this critical issue, the Fiber Reinforced Concrete Association has contracted with TEC Services in Lawrenceville, Ga. to conduct testing intended to: first, establish the contribution of various equipment components to the test results and, second, offer solutions to improve the equipment or assembly to ASTM Subcommittee C09.42. The goal is to reduce the Standard Deviation and Coefficient of Variation issues that have plagued these test methods.
- FRC Impact Tests
One additional test method has yet to be adopted by ASTM Subcommittee C09.42, but is used by the industry for compliance testing and/or research.
Impact Test — How the fibers affect the energy required to initiate cracking and to what degree the fibers hold the concrete together after it has cracked. A modified Proctor or Marshall test-assembly (a 10-pound hammer is dropped 18 inches onto a steel ball that imparts a point impact load to a concrete disk measuring 6” in diameter that is 2.5” high). This test method can be found in ACI Committee Report 544.2R.
- ICC ES AC32
ICC ES (Engineering Services) adopted an Acceptance Criteria (AC32) for synthetic fiber reinforced concrete originally created by the International Conference of Building Officials (ICBO).
This is the most detailed specification/testing criteria available in the world today for use in evaluating microsynthetic fiber-reinforced concrete. AC32 details specific test methods and numerical limitations for the use of microsynthetic fiber as plastic shrinkage reinforcement (see Section 3.1.1) and as secondary/temperature-shrinkage reinforcement (see Section 3.1.2).
Caution: This Acceptance Criteria (AC32) was written for microsynthetic fibers and is not appropriate for macrosynthetic fibers.
The notes and cautions throughout this and our previous article on this topic reinforce the critical need for absolute consistency throughout the testing program. It is very easy to introduce erroneous data when details are ignored.
We in the Fiber Reinforced Concrete industry believe that all parties are responsible in the process of securing accurate test results. Therefore all parties should be educated as to the proper procedures related to the process.
Tested and Approved Fibers
ABC Polymer has tested our principal microsynthetics against the ICC ES AC32 requirements, and in all cases each of the products meets the appropriate requirements for plastic and/or secondary reinforcement at the standard dosage levels or modified dosage levels as noted.
ABC Polymer’s FiberForce 150™ (Mono-Tuf™), FiberForce 100™ (Mono-Pro™) and FiberForce 300™ (Fibril-Tuf™) all have gone through the ICC ES product evaluation program and are listed by ICC in ESR-1699.
FiberForce 500™ (Fibril-Pro™) has also been subjected to the ICC ES AC32 evaluation and complies with the requirements for both plastic shrinkage crack reinforcement and temperature-shrinkage crack reinforcement. Fibril-Pro will be listed in ESR-1699 in the fall of 2015.
ABC Polymer’s Ny-Tuf™, our monofilament nylon fiber, has been tested for compliance with ICC ES AC32 at .75 pcy as plastic shrinkage crack reinforcement and at 1.0 pcy as temperature-shrinkage reinforcement. In both cases the product met the applicable AC32 requirements.
FiberForce 650™ (Tuf-Max DOT™), our embossed tape fiber, meets the criteria for macrosynthetic fiber and, as the name implies, has been successfully tested for compliance with various state DOT specifications.
Macro-Pro™ is a highly modified fibrillated fiber meeting the criteria for macrosynthetic fibers that typically is specified in precast and specialty application concrete products.
Performance Plus DOT™ is a blend of FiberForce 650 (Tuf-Max DOT) and Macro-Pro that meets the criteria for macrosynthetic fibers and has also been successfully tested for compliance with various state DOT specifications.
FiberForce 650™ (Tuf-MAX DOT™)
Performance PLUS DOT™
Need help to ensure that your FRC sampling and specimen fabrication are being performed properly?