A MORE SUSTAINABLE MATERIAL TO REINFORCE CONCRETE STRUCTURES

The next generation of ultra high-performance fibre-reinforced concrete
(UHPFRC) has just been created at EPFL. The new material will be used to
strengthen and to extend the life span of bridges and other structures – both
new and old. What’s more, manufacturing this material releases 60–70% less CO₂ than
the previous generation of fibre-reinforced concrete.

The construction
industry accounts for around 40% of global CO₂ emissions,
much of which can be attributed to the manufacture of concrete. And countries
like Switzerland, where concrete
structures have flourished since the 1960s, now face the task of maintaining
these structures to ensure they remain safe far into the future. This is a
daunting challenge with both environmental and technical considerations.

EPFL’s Structural Maintenance and Safety Laboratory (MCS), headed by
Eugen Brühwiler, has built up cutting-edge expertise in this field over the
past 25 years. The MCS specialises in developing more eco-friendly concrete,
and carrying out increasingly sophisticated, largely monitoring-based,
assessments of existing structures, such as road and rail bridges in
Switzerland and around the world.

For his Ph.D. thesis, MCS researcher Amir Hajiesmaeili sought to develop
the next generation of ultra high-performance fibre-reinforced concrete
(UHPFRC). His aim was to develop a material that retains the mechanical
properties found in today’s concrete, but without the steel fibres. The UHPFRC
that Hajiesmaeili came up with is 10% lighter than other fibre-reinforced
concrete, and its environmental impact is 60–70% lower. This new material is so
effective that the first tech transfer will take place in 2020, when it will be
used to reinforce a bridge.

After completing a Master’s degree in civil engineering at the University of Tehran, he
came to EPFL to do his Ph.D. as part of the Swiss National Science Foundation’s
NRP “Energy Turnaround” (NRP 70) project. He spent nearly four years
“cooking” at EPFL. Each week he would prepare various combinations of
powders in a scientific way, according to a novel comprehensive packing model
that they developed in MCS and stir them up in a mixer. He would then run his
samples through various strength and tensile tests and refine his calculations.
His aim was to produce a new UHPFRC that is just as strong as the one currently
used in the construction industry but that produces less CO₂.

“After three years of trial-and-error, we finally found the right
recipe – one that also meets stringent building standards,” says
Hajiesmaeili. How did he do it? Instead of steel fibre, he used a very stiff
synthetic polyethylene fibre that adheres well to the cement matrix. He also
replaced half the cement with limestone, a material widely available around the
world. “The trick was to find a material that’s very strong and produces
the right consistency.”

For the past 15 years, first-generation UHPFRC has been used to
reinforce bridges to make them more sustainable, thanks to a technology
developed in Switzerland and exported abroad. Its carbon footprint is already
lower than that of conventional reinforced concrete.

“With this material, we can add value to age-old structures by ensuring they will last for a long, long time,” says Brühwiler, whose lab has already overseen the structural reinforcement of over 100 bridges and buildings in Switzerland. “This solution is also much more financially and environmentally sound than razing and rebuilding existing structures like bridges and historical monuments.”https://phys.org/news/2019-11-sustainable-material-concrete.html