Fiber-Reinforced Concrete – A Case for Alternative Reinforcement Strategies for Construction Systems

The main challenges facing our generation are sustainability, climate change, and carbon-footprint reduction. Considering that within the next 30 years, the population of the earth will reach the 10 billion mark, future generations will have to deal with two main problems of curbing consumption and resource management. These topics dominate the central themes of scientific efforts in so many disciplines, and as materials, mechanics, and structural engineers, we are obligated to address them with scientifically viable solutions.  These areas should remain the focal point of our professional contributions. Three distinct areas to address are as follows:

1. The global numbers are astounding.  Every year we use more than 20 billion tons of concrete and 2 billion tons of steel in a variety of applications. Nearly half of all steel is used in the construction sector worldwide. Reinforcement of concrete by steel is necessary due to its low tensile strength and brittle nature, and results in more than 500 million tons of rebar, or 25% of all steel supplied in a single and unique application.
   
2. For the past 100 years, the design principles by all international codes have no option but to ignore the limited and marginal contribution of plain concrete phase in carrying tensile forces. This leads to inefficiency of the material due to tensile forces throughout the service life for almost 70% of the volume of a beam, or slab.  Furthermore, due to the manual nature of many construction projects, the extended time and labor cost for forming and placement of rebars within a 3-D concrete member accounts for almost half of the cost of the finished product.
   
3. Significant resources have focused on finding alternative solutions for supplementary materials to reduce the carbon footprint and volume of Portland cement used in concrete products. However, we have been quite slow in adopting alternative reinforcement strategies. Such efforts should be aimed at increasing the efficiency of a variety of reinforced concrete systems both in terms of structural design and durability while sustainably reducing the carbon footprint.

For more than 60 years, many well-respected engineers and researchers have worked through proper materials and structural design to reinforce concrete at the microstructural level with a variety of fiber forms. This modification at the small scale results in the control of microcracks which would grow and cause loss of stiffness and strength.  An extremely brittle material such as concrete can be made ductile and energy-absorbing by using fibers, even if those fibers are brittle themselves such as carbon, or glass. The additional load-carrying capacity can be integrated into the design equations, therefore reaching a higher efficiency. Through a variety of alternative reinforcing systems, we can now engineer durable structural designs that improve efficiency in carrying tension loads when the bulk volume is considered. This approach can provide us with corrosion-free infrastructure that lasts for more than 100 years as a ductile, durable, and efficient construction material of choice.

We can invest in this opportunity to change our frame of reference and save resources, reduce cost, and extend the service life and durability of our infrastructure. As the applications are being developed at a fast pace, we are witnessing many options in the construction industry to address the conventional design of infrastructure, transportation systems, renewable energy, green buildings, tunneling, and water and wastewater distribution systems. The research and development efforts have given rise to a mature set of ideas for proper structural design of new and repair applications with a variety of choices that encompass Fiber Reinforced Concrete (FRC), Hybrid Reinforcements, Fiber reinforced Plastics (FRP), Ultra-high-Performance Concrete (UHPC), and Textile Reinforced Concrete (TRC and FRCM). Using various classes of strain softening and strain hardening systems many solutions are now available to designers, architects, and owners by playing an important role as a multi-objective solution in reducing the embedded energy and carbon footprint, serviceability-based design, and enhancing durability through ductility.

The theme of this workshop is to present various cases of “Application-Centered Design”, and emphasize solutions that are available today for contributing to environmental sustainability through optimized structural design and validation of performance. These goals are achieved by increasing the specific post-cracking residual strength and stiffness, in addition to reducing the crack width, corrosion, shrinkage, and creep-associated durability problems thus extending the service life. Hopefully, we can expand our forum to a broader community of engineers, practitioners, and owners who can benefit from the ideas and viable solutions presented. We look forward to seeing you at the campus of Arizona State University in Tempe, Arizona in September at FRC 2023.

Barzin Mobasher, August, 2023