Interview: Professor Alessandro Palermo Discusses GFRP Rebar Research

Alessandro Palermo (pictured above) serves as a Professor at the Civil and Natural Resources Engineering Department at the University of Canterbury (UC). His interests include structural bridge engineering, in particular, seismic low-damage technologies for precast concrete.

Later this year, Alessandro will be taking on the role of Professor at the University of California in San Diego (UCSD). We talk to Alessandro about his research and experience with GFRP composite rebar technology.

What inspired you to focus on GFRP composite rebar in your research?

Since early 2000, I was one of the first international researchers to investigate the effects of corrosion on reinforced concrete structures designed for seismic loads. The results were clearly showing that material ageing can drastically reduce the local and global seismic response of bridges, ports or any infrastructure exposed to harsh environments.

I started thinking of alternatives including corrosion-resistant materials. When Pultron approached me and wanted to be involved in collaborative research projects, I felt it would be an amazing win-win situation. I could test my research questions and Pultron could use our findings to optimise their design but more importantly, to share knowledge and improve the confidence in GFRP within the engineering community.

In your tenure at UC, what were some of the most surprising findings in your GFRP research?

The last phase of the project led by my PhD Student Cain Stratford “cyclic testing of GFRP reinforced columns” was the most surprising. The idea of creating a “plastic hinge” which has a lower dissipating capacity but higher “post-yielding” stiffness and no residual strains in the material is something I wasn’t expecting and provides a solid basis for the future of this material in seismic areas.

Have you encountered any unexpected challenges while working with projects requiring GFRP reinforcement bars? 

Challenges are the seeds of opportunities! And although each experimental campaign had unexpected issues I certainly learnt that I need to have a total mind-shift and realise that GFRP bars are different from steel reinforcement, not only in terms of design but also in terms of constructability. For example, in the first tensile tests, it became instrumental to properly design the grip for those bars and have a proper Health and Safety protocol when the bars failed.

Concrete slabs and the concrete-to-pile connections of the ports will be an interesting application where the clients will save millions of dollars on maintenance.

How do the properties of GFRP rebar compare to steel reinforcement bars?

GFRP bars are durable and don’t corrode. Their elastic modulus is 3-4 times smaller than the steel bars, and I see this as a great advantage if we want to use bars for rocking structures where tendons/high-strength bars need large deformability. Although the GFRP strength is twice the steel reinforcement, the creep becomes a limiting factor since the bars can’t be used at their full capacity under sustained loads. However, this can be overcome if we utilise this extra capacity for short-term events such as earthquakes!

Are there any new developments or advancements related to GFRP rebar that you have been researching recently? 

In the latter, we also learnt that a so-called hybrid solution, i.e. GFRP spirals combined with steel reinforcement can be a good compromise to improve the overall member durability and more importantly a more stable cyclic response due to the better performance of the GFRP stirrups.

How has the use of GFRP-reinforced concrete evolved over time, and what advances are being made in the field currently?

International standards have evolved but more importantly, the seismic design philosophies are changing. We are moving away from the sole concept of ductility and targeting resilience. This evolution opens more opportunities for the use of GFRP, which yes is brittle but is elastic, flexible and, if properly designed, can provide a good recentering capability.

In what areas is further research needed when it comes to understanding and utilizing GFRP reinforcing bars effectively? 

I think we need to continue to work on large scale specimens since the mechanical properties of GFRP bars varies within the diameter. Several topics within the mechanics of GFRP structures are not yet well covered, for example, cyclic shear behaviour of bridge piers or large-scale columns under compression loading. 

What is the most exciting research currently in progress using GFRP rebar that you have encountered and would like to undertake?

Although I currently don’t have a project in progress, I want to further develop novel, durable and cost-effective seismic low-damage bridge piers that combine effectively steel and GFRP. New Zealand engineers are confident in the low-damage design and if we could develop a solution that is also durable it will become the new, next generation of design.

What projects of late do you consider good examples of replacing steel with GFRP rebar?

I think that any infrastructure exposed to marine environments is an excellent example to justify the use of GFRP. For example, the concrete slabs and the concrete-to-pile connections of ports will be an interesting application where the clients will save millions of dollars on maintenance.

What are you hoping to research at UCSD?

When I will be moving to the University of California, San Diego, in the fall of 2023. My intention is to use their shake table facilities and test the dynamic behaviour of GFRP and/or hybrid bridge piers. I also hope to continue to work on a few other topics related to the cyclic mechanics of GFRP concrete structures.

What lies ahead for the next generation of engineers?

The next generation of engineers need to design by providing resilience to earthquakes and natural hazards and, at the same time guaranteeing low maintenance (i.e. more sustainable structures). The use of GFRP reinforcement alone or combined with other materials can become a viable alternative to current and most popular structural materials.