Although Wirand concrete was labeled as a new material, the idea of using short fibers has been around for a long time but never appeared economically feasible. It would be of interest to have some cost comparison figures presented. Obviously, the random orientation of the fibers in the material means that the reinforcement is not used as efficiently as in reinforced concrete. The principal effect of random type of reinforcement is an increase in toughness. Also, what about the corrosion of exposed metal in Wirand concrete?
Battelle Development Corporation, developer of Wirand concrete, supplied the following answer.
In regard to the random orientation of fibers, the Battelle Development Corporation states that Wirand concrete cannot be compared to reinforced concrete in respect to steel placement and contribution of the steel. In the simplest form, normal or conventional reinforced concrete is designed as two materials, steel and tensile and concrete in comparison. This being the case, the steel must take the tensile load that exists; therefore, the strength of the steel reinforcement is important to the performance of the reinforced concrete.In the case of Wirand concrete the steel performs an entirely different function. In this case, the steel fibers serve as crack arrestors and their tensile strength is not directly related to the performance of Wirand concrete. It is important, therefore, that the fibers be randomly oriented so that they can efficiently perform their function of arresting cracks. As one would imagine with this type of structure, Wirand concrete is designed as a homogeneous material and not as steel and concrete.We agree that the performance of these steel fibers in Wirand concrete does increase the toughness of concrete; however, the interesting and important point is that these fibers, properly placed, also provide concrete with a meaningful flexural strength, impact resistance, and fatigue resistance.Cost figures are difficult to provide specifically, as people who work with concrete realize. On a cubic yard for cubic yard basis, there is no doubt that Wirand concrete is much more expensive than normal material; however, on an in-place cost comparison this situation does not really exist. In the first place, for most applications about one-half the quantity of Wirand concrete is needed when compared to conventional concrete. In addition, if the conventionally reinforced material requires considerable labor for the installation of the reinforcement, then Wirand concrete, which in many applications can be used without conventional reinforcement, begins to provide economic advantages.It is realized that the basic mix used for Wirand concrete is more expensive in that we use a high-cement content (about an eight-bag mix). In addition, the fibers which are mixed with the concrete can cost up to 30 cents a pound and one uses about 200 pounds per cubic yard for most applications. These material costs are obviously high, but it is necessary to examine the in-place cost before coming to a decision concerning the economics of Wirand concrete.
Englagement of the broken end of a test beam of Wirand concrete.
On the question of corrosion, it is true that fibers on the surface will corrode providing they are exposed to the atmosphere or corrosive media. However, once these fibers corrode there is no continued action and the concrete itself is not weakened. It is fortunate that the cement within the concrete serves as a rust inhibitor to these fibers and, consequently, internal fibers are not affected by corrosion.