As more attention is put on the nation’s aging infrastructure, deeper investigation must be done into the materials chosen to rebuild it. Traditionally, the infrastructure industry has relied on the classics - steel and concrete - for building materials. More recently, however, composites are playing a vital role in this effort.

Composites can be loosely defined as heterogeneous materials consisting of a polymer or metal matrix with reinforcing fillers that provides a lightweight, high-strength, and cost-effective alternative to steel with minimal maintenance requirements. These materials are well understood in terms of their performance characteristics and limitations and have been around for quite some time. But, for composites to find greater use in different infrastructure applications there must be consistency of materials and performance that allows engineers to confidently replace conventional materials with new ones.

During the ‘70s and ‘80s, with the advent of composites as the material of choice for building aircraft structures, the aerospace industry set forth to develop a set of test methods, protocols, and standards that has enabled them to build entire aircraft frames like those of the Airbus 380 and the Boeing 787 from composites.

For similar adoption to occur for the underground infrastructure industry, stakeholders must make a parallel effort to develop testing and design standards by working closely with academia, specifying agencies, and end users.

One area within the infrastructure industry in which composites have made a significant foray is within the area of underground utility enclosures. Over the past several decades, enclosures made of Fiber Reinforced Polymer (FRP or Fiberglass) and Polymer Concrete have largely replaced those made earlier with Portland cement concrete and steel. These composite enclosures are often very durable and lightweight, and present significant cost savings to the utilities in terms of installation, transportation costs, and lower maintenance costs.

However, the main constraint that these materials face is a lack of uniform standards for testing and design of structures that employ their use. Within the utility enclosure arena, there are several competing standards, each with its own definition of minimum loading requirements for the structure. Often, the various standards conflict with each other, leaving the end user confused as to which standard to use. Most of these standards lay emphasis on some type of structural testing that is said to mimic the passage of the wheel of a truck on or near the enclosure, causing it to stress under that load. However, the industry is far from reaching a consensus on what these loads should be, over how much area, and for what duration of time and for how many cycles.

Also, is appears that the current standards do not call for consistency in material properties. Unlike polycrystalline materials, like metals which follow elastic behavior, polymer composites are viscoelastic in nature and the response to load depends on several factors like temperature, duration, and rate of loading. In addition, none of the standards address or try to define the materials themselves. You see, one man's polymer concrete may be radically different from another's.

These inconsistencies beg for a testing program that emphasizes standardized materials testing in addition to the structural tests performed on the final products. This materials testing should take into account various factors including:

• Consistency of material performance.
• Different environmental conditions such as temperature and humidity.
• Exposure to sunlight.
• Exposure to chemicals.
• Time of loading.
• History of area where product is to be installed.

For instance, if an enclosure is designed to withstand a certain load and the structural test requires a certain safety factor, material testing must be done to prove its safety factors. It must also be proven that variances within the material properties and the external influences are accounted for in that safety factor. Finally, a number of these enclosures are used by various utilities to house electrical equipment and yet, few of the existing standards require testing on electrical insulation or arcing resistance.

Simply put, the industry needs a forum for development of these testing methods and standards that will help propel composites as a new class of cost-effective, high-performance materials for the country's infrastructure needs.

About the Author
Ruchir M. Shanbhag is Director of Engineering, NewBasis. For more information, email him at rshanbhag@newbasis.com or visit www.newbasis.com.

What’s your take on this subject?  Leave a comment and get the conversation going.