Understanding Macrosynthetic Fibers
October 17, 2010
ABC Polymer Industries has assembled a number of papers authored by Bobby Zellers, Director, Engineering Services to help the Ready Mix Producer understand what exactly is a macrosynthetic fiber and how to evaluate the applicability of and benefits of macrosynthetic fibers using the specific requirements (specifications) of a given project. Several these documents will help in educating engineers and contractors in the use of macrosynthetic fibers.
Macrosynthetic Fibers are the new generation of synthetic fibers. Macrosynthetic fibers have a unique set of chemical and physical properties not provided by microsynthetic fibers which represent the first generation of the family of 3-dimensional fiber reinforcement for concrete and shotcrete. For example, the minimum length of a macrosynthetic fiber is 1.5 inches (38 mm) long, whereas a microsynthetic fiber is typically 3/4 inch (19 mm) long. This additional ‘bond length’ provides the macrosynthetic fibers and opportunity to provide post-first crack engineering properties not available from the microsynthetic fibers.
Before moving forward, it is mandatory to understand that neither microsynthetic fibers or macrosynthetic fibers will replace primary or structural reinforcement. The principle use of synthetic fibers as reinforcement in concrete and shotcrete is to replace the WWF (Welded Wire Fabric aka wire mesh) or #3 or #4 rebar when used as secondary/temperature-shrinkage (non-structural) reinforcement. Temperature-shrinkage reinforcement is defined/delineated within ACI 302, 318 and 360 as well as other committee reports within ACI as well as other organizations. Temperature-shrinkage reinforcement’s sole responsibility is to control cracks created in the concrete because of internal stresses which produce volume change resulting from moisture and/or temperature changes within the concrete.
Brief Description of Macrosynthetic Fiber Papers Available
The first document is simply titled “Definitions-Source of Cracking”. This single page document talks solely about cracking but it begins to tell the story of why synthetic fibers provide more benefits to the concrete matrix than the single plane of WWF. The ability of the 3-dimensionally distributed synthetic fibers to enhance the overall durability of the concrete is first mentioned in this document.
The second document comes from our Frequently Ask Questions series. This document is used to put the correct type of synthetic fibers with the application along with delineating the appropriate fiber dosage range. Zellers has always believed that the application is a critical component in the process of selecting the appropriate synthetic fiber along with dosage level and fiber length.
When we are determining the value of using macrosynthetic fibers on a specific project, there are several physical properties the fibers may enhance.
One of the factors in the selection process of macrosynthetic fibers on industrial and warehouse projects as well as external slabs is axle loading on the concrete. We know from research conducted by Dr. Ramakrishnan and Mr. Zellers that the Fatigue Strength of the concrete is a component positively affected by the synthetic fibers. This work showed that fiber type, length, and dosage reflected in the longevity or service life of the concrete.
Thus, it is easy to understand that in applications where there is multiple axle load traffic like truck terminals the correct synthetic fibers can extend the life of the slabs. Fiber length and configuration (mechanical bonding) are major contributors and therefore point favorably to the selection of macrosynthetic fibers.
With the third document, we take a step back and use another Frequently Asked Question document to define the difference between a structural concrete slab and a plain concrete structural slab. In short, the structural slab uses the rebars to determine the load carrying capacity of the slab whereas in a plain concrete structural slab the thickness of the concrete and the physical properties of the concrete determine the load carrying capacity. We are using this document to stress that macrosynthetic fibers are not structural synthetic fibers as some marketers have labeled them. The macrosynthetic fibers cannot be used to replace structural steel.
Our fourth document comes from our Fundamentals of FRC Series and is titled “Common Sense Rules to Quality Fiber Reinforced Concrete (and Shotcrete). We have found that when using microsynthetic fibers at 0.5 to 1.5 pcy the proportions of a conventional concrete mix are sufficient to ingest the fibers so that both the coarse aggregate and the fibers are coated with mortar. At around 3.0 pcy of synthetic fiber, we find a need to adjust the conventional ingredients so that there is sufficient mortar to coat the coarse aggregate and synthetic fiber surface area. Here the ready mixed concrete laboratory or commercial laboratory enters the picture. In essence, the coarse aggregate component is reduced and the mortar fraction is increased. The dosage level of the macrosynthetic fiber will dictate the quantity adjustment of the two components is required. It is extremely important that the balancing of the conventional components yield a workable mix that can be consolidated and finished to comply with standard practices.
Our next document, number five, talks about the successful use of macrosynthetic fibers, steel fibers, and blends. To some degree, it stresses the important factors found in “Common Sense”. This document as others emphasizes the importance of using a vibrating screed, a laser screed or a roller screed to ensure proper consolidation of the macrosynthetic fibers, steel fibers, and blends. Using this equipment helps to encapsulate the fibers at the surface of the slab within the mortar.
The fifth document is part of an engineering guidelines series wherein we compare the benefits of the synthetic fibers to the old-school WWF. We detail the process used to select the WWF to be used as the secondary reinforcement. All the equations available for use in this process are empirical formulae. This means the formulae or equations are based on observation not testing. We present the 5 empirical formulae recognized by the Wire Reinforcing Institute (See Robert Anderson paper written for WRI). It is very interesting that the drag coefficient formulae selected by ACI 318 (See Chapter 7) yield the smallest steel cross-section required. We feel this selection was pre-meditated to reduce the cost to the contractor and owner and not based on engineering judgment. Check out the table in this document.
The next document is more oriented to marketing and sales. This document explores the “How To’s” when flipping WWF projects to synthetic fiber reinforcement and/or more specifically the ABC Polymer Industries’ family of synthetic fibers. Selecting the proper ABC product is a very important step…
Our final document addresses the adjustments to the mix design that will be required when the elevated dosage levels of macrosynthetic fibers are used. This document is more of a discussion of how to make the adjustments versus a step by step ‘how to’. This is an important step when moving up to the higher dosage levels of macrosynthetic fibers.
ABC Polymer Industries has developed two macrosynthetic fibers; Performance PlusTM and Macro-ProTM. The data sheets for both products are included on our website. Both products have been tested extensively at both commercial and university laboratories. Testing has included conventional ASTM plastic and hardened concrete tests. To evaluate the performance of these products as macrosynthetic fiber reinforcement systems either or both ASTM standard consensus test methods have been used; C1399 and C1609. Data from our test programs are available on request from Mr. Zellers.
ABC Polymer has also developed macrosynthetic fiber and microsynthetic fiber blends as well as steel fiber and microsynthetic fiber blends. Pro Blend is one of these products.
Our Macrosynthetic Fibers have been approved by FL DOH for use in residential septic tanks. We have available the FL DOH document, which provides a comparison of C1399 test results for both Performance Plus and Macro-Pro with other macrosynthetic fibers available on the market.
We have either obtained or are in the process of obtaining approvals from various states Departments of Transportation and Departments of Health for our Macrosynthetic Fiber products and Blends. Please contact Zellers if there is a specific need to acquire approval for these products in a specific state or states.
Important Engineering observation
When first accepted by ASTM as consensus test methods both C1399 and C1609 (previously C1018) were known to have larger than normal standard deviations and coefficients of variation. Over the years, modifications have been made to enhance the precision of these tests. In January of 2010, the Fiber Reinforced Concrete Association voted to fund a research program that would positively identify specific equipment and performance areas within C1609 and later C1399 that needed to be addressed by ASTM Subcommittee C09.42. This program is ongoing and to date the testing laboratory, TEC Services has completed one phase of the program and submitted the data in June to the Subcommittee. The laboratory is now proceeding with the second phase of the program, which is to evaluate the influence of the energy stored in the test frame on the data generated.
This work is extremely important. We need to be confident that the data generated by these test methods are accurate since they are being used in calculations that affect the performance of the concrete composite that would utilize these macrosynthetic fiber and steel fiber products.
-R.C. Zellers, PE/PLS, Director, Engineering Services