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As the use of Macrosynthetic Fibers and Macrosynthetic Fiber-Microsynthetic Fiber Blends grows, a more precise understanding of the properties of concrete reinforced with these materials is required. Currently, there are three tests on the books at ASTM that are specific to the testing of fiber reinforced concrete (FRC) post-first crack. These tests methods are C1399, C1550, and C1609. Here in the United States C1399 and C1609 are the test methods of choice. C1399 was originally developed to test microsynthetic fibers but has become the secondary test for macrosynthetic fibers and macro-micro blends. C1609 is an updated test method of the ASTM C1018 test, which has been eliminated. The C1609 test method is the most versatile as it can be used with macros, steel, and blends.

Selecting a commercial laboratory to conduct these tests is critical to the success of the project. The Fiber Reinforced Concrete Association of which ABC Polymer is a member is funding an extensive program to identify those parameters that affect the precision of the test. The program is being conducted at the TEC Services lab in Atlanta. A number of the industry’s engineering community have questioned the values generated in some of the commercial laboratories across the country. One of the engineer’s comments asserted that the numbers could be inflated as much as 66%.

We have learned that laboratories that can properly test concrete beams solely for flexural strength (ASTM C78) may not be candidates for performing C1399 or C1609. Important to this discussion of these tests are three talking points:

Both C1399 and C1609 look at the FRC properties post-first crack. The first crack being the point when C78 ends producing the flexural strength result for the concrete. This means that special equipment is required to amass the data and new software to analyze the data.

C1609 requires that the test is conducted closed loop, whereas the flexural test and C1399 are run open loop. This means that the loading of the beam post-first crack is based on the deflection of the beam versus a constant loading per time increment. We have learned that very few laboratories are capable of conducting truly closed-loop testing. This is a very critical concern as this is the source of some of the elevated data currently appearing in the marketplace.

Finally, elements of the testing system that are not critical to the performance of the C78 testing become very important when we look at the FRC post-first crack. For example, the rollers that support the beam in the test set-up must be free to rotate. If they are not free to rotate they will not permit the two pieces of the fractured beam to move apart. The energy imparted on the test specimen at the point of the first crack from the test frame is yet another issue.

The work being done at TEC Services is being monitored by FRCA and all of the data generated is being turned over to ASTM C09.42, which is the subcommittee responsible for generating FRC specifications and test methods.

All of the information offered above is intended to enlighten more than educating the reader as to the foibles involved in the growth of our industry and to make sure that we always elect to follow the prudent path. That said ABC Polymer has made it a priority to first, find the commercial laboratory that will meet the high-performance standards required for conducting ASTM C1399 and C1609. That commercial laboratory, in our opinion, is TEC Services. Second, ABC Polymer must strive to continually upgrade this new generation of FRC. ABC Polymer now has available to the market three Macrosynthetic Fibers. We are in the process of obtaining approvals from state DOTs for these Macrosynthetic Fibers.

There are a number of major benefits available when a Macrosynthetic Fiber or a Macro-Micro Blend is selected for a project. ABC Polymer has a number of documents that speak to the benefits of these products and of equal importance we have engineering reports that provide the data for the engineers to evaluate.

Please call on us with any questions you may have regarding Macros in general or the ABC Polymer product line in particular or need to talk to Bobby Zellers to relay information so he can talk with an engineer/specifier to ensure that the proper product and dosage level are selected for a given application.

Let us know if you have any specific questions regarding this article.

-R.C. Zellers, PE/PLS, Director, Engineering Services