Category Archives: Engineering

Researchers Discover New Strategy For Developing Human-integrated Electronics (Engineering)

Polymer semiconductors — materials that have been made soft and stretchy but still able to conduct electricity — hold promise for future electronics that can be integrated within the body, including disease detectors and health monitors.

Yet until now, scientists and engineers have been unable to give these polymers certain advanced features, like the ability to sense biochemicals, without disrupting their functionality altogether.

Researchers at the Pritzker School of Molecular Engineering (PME) have developed a new strategy to overcome that limitation. Called “click-to-polymer” or CLIP, this approach uses a chemical reaction to attach new functional units onto polymer semiconductors.

Sihong Wang researches advanced polymers and skin-like electronics
Asst. Prof. Sihong Wang © University of Chicago

Using the new technique, researchers developed a polymer glucose monitoring device, demonstrating the possible applications of CLIP in human-integrated electronics. The results were published August 4 in the journal Matter.

“Semiconducting polymers are one of the most promising materials systems for wearable and implantable electronics,” said Asst. Prof. Sihong Wang, who led the research. “But we still need to add more functionality to be able to collect signals and administer therapies. Our method can work broadly to incorporate different types of functional groups, which we hope will lead to far-reaching leaps in the field.”

Functionalizing polymers without decreasing their efficacy

To achieve new functionalities of these semiconducting polymers — also referred to as conjugated polymers — many researchers have previously tried to build them from scratch by incorporating advanced features into the molecular designs directly. But conventional procedures for doing this have failed, either because the molecules have been unable to withstand the conditions needed to attach them to the polymer chains, or because the synthesis process decreased their efficacy.

To overcome this, Wang, with graduate student Nan Li, developed the CLIP method, which uses a copper-catalyzed azide-alkyne cycloaddition to add functional units to a polymer. Because this “click reaction” happens after the polymer is created, it does not affect its initial properties much.

Not only that, the reaction could be used in bulk functionalization of the polymer and in surface functionalization — both essential for creating functional electronics.

A potentially game-changing system

To demonstrate the effectiveness of CLIP, the researchers attached units that could photo-pattern the polymer, important for designing circuits within the material. They also added functionality to directly sense biomolecules. Their biomolecule sensor used a glucose oxidase enzyme to detect glucose, which then causes changes to the polymer’s electrical conductance and amplifies the signal.

A diagram of the CLIP method, which uses a copper-catalyzed azide-alkyne cycloaddition to add functional units to a polymer. (Illustration courtesy of Wang Research Group)

Now the group is building upon their success by adding other bio-active and biocompatible functionalities to these polymers, which Li says “has the potential of becoming a game-changing technology.”

“We hope researchers across the field will use our method to endow even more functionality into this material system and use them to develop the next generation of human-integrated electronics as a key tool in healthcare,” Wang said.

Other authors on the paper include Yahao Dai, Yang Li, Shilei Dai, Joseph Strzalka, Qi Su, Nickolas De Oliveira, Qingteng Zhang, P. Blake J. St. Onge, Simon Rondeau-Gagné, Yunfei Wang, Xiaodan Gu, and Jie Xu.

Citation: “A universal and facile approach for building multifunctional conjugated polymers for human-integrated electronics,” Li et. al, MATTER, August 4, 2021, DOI:

Funding: University of Chicago, Office of Naval Research, Department of Energy

Featured image: Asst. Prof. Sihong Wang and his team at the Pritzker School of Molecular Engineering use their new “CLIP” technique to add broader functionality to semiconducting polymers, like the ability to sense biochemicals (copyright

Provided by University of Chicago

Scientists Found the Cause of a Fatal Problem in Rocket Engine Combustors (Engineering)

Via advanced analyses, scientists shed light on the mechanism of a deadly problem plaguing combustion chambers in rocket engines

A vital piece of gas engines, combustors―the chambers in which the combustion powering the engine occurs―have the problem of breaking down due to fatal high-frequency oscillations during the combustion process. Now, through advanced time-series analyses based on complex systems, researchers from Tokyo University of Science and Japan Aerospace Exploration Agency have found what causes them, opening up novel paths to solving the problem.

Rocket engines contain confined combustion systems, which are, essentially, combustion chambers. In these chambers, nonlinear interactions among turbulent fuel and oxidizer flows, sound waves, and heat produced from chemical reactions, cause an unstable phenomenon called ‘combustion oscillations.’ The force of these oscillations on the body of the combustion chamber―the mechanical stress on the chamber― is high enough to threaten catastrophic failure of the engine. What causes these oscillations? The answer remains to be found.

Now, in a breakthrough, published in Physics of Fluids, a team including Prof. Hiroshi Gotoda, Ms. Satomi Shima, and Mr. Kosuke Nakamura from Tokyo University of Science (TUS), in collaboration with Dr. Shingo Matsuyama and Dr. Yuya Ohmichi from the Japan Aerospace Exploration Agency (JAXA), have used advanced time-series analyses based on complex systems to find out.

Explaining their work, Prof. Gotoda says, “Our main purpose was to reveal the physical mechanism behind the formation and sustenance of high-frequency combustion oscillations in a cylindrical combustor using sophisticated analytical methods inspired by symbolic dynamics and complex networks.” These findings have also been covered by the American Society of Physics in their news section, and by the Institute of Physics on their news platform Physics World.

The combustor the scientists picked to simulate is one of model rocket engines. They were able to pinpoint the moment of transition from the stable combustion state to combustion oscillations and visualize it. They found that significant periodic flow velocity fluctuations in fuel injector affect the ignition process, resulting in changes to the heat release rate. The heat release rate fluctuations synchronize with the pressure fluctuations inside the combustor, and the whole cycle continues in a series of feedback loops that sustain combustion oscillations.

Additionally, by considering a spatial network of pressure and heat release rate fluctuations, the researchers found that clusters of acoustic power sources periodically form and collapse in the shear layer of the combustor near the injection pipe’s rim, further helping drive the combustion oscillations.

These findings provide reasonable answers for why combustion oscillations occur, albeit specific to liquid rocket engines. Prof. Gotoda explains, “Combustion oscillations can cause fatal damage to combustors in rocket engines, aero engines, and gas turbines for power generation. Therefore, understanding the formation mechanism of combustion oscillations is an important research subject. Our results will greatly contribute to our understanding of the mechanism of combustion oscillations generated in liquid rocket engines.”

Indeed, these findings are significant and can be expected to open doors to novel routes of exploration to prevent combustion oscillations in critical engines.

Featured image: Representation of instantaneous flow velocity field during combustion oscillations in the combustion chamber of a model rocket engine: This figure shows that large-scale vortex rings are produced from the injector rim during combustion oscillations. Photo courtesy: Satomi Shima, Kosuke Nakamura, Hiroshi Gotoda, Yuya Ohmichi, and Shingo Matsuyama


  • Title of original paper: Formation mechanism of high-frequency combustion oscillations in a model rocket engine combustor
  • Journal: Physics of Fluids
  • DOI:10.1063/5.0048785

Provided by Tokyo University of Science

Researchers Invented New Isotope-separating Device That Can Withstand Extreme Environments (Engineering)

An Oak Ridge National Laboratory researcher has invented a version of an isotope-separating device that can withstand extreme environments, including radiation and chemical solvents.

ORNL’s Kevin Gaddis designed the automated high pressure ion chromatography, or HPIC, system to improve purification of actinium-225, an isotope used in cancer treatments, from thorium targets that have been irradiated in a particle accelerator.

Previously, technicians relied on gravity to perform separations in hot cells, since high radiation levels would destroy an HPIC’s electronic components. Gaddis used radiation-tolerant materials to build a HPIC that uses air pressure, not electricity, to control the flow of the sample and chemicals that separate Ac-225 from byproducts. In tests, the HPIC cut separations time by 75%.

That’s important because demand is high for Ac-225, which has a short half-life. “Hours matter,” Gaddis said. “If we can reduce the time for the separation, we can get more product out.”

This science news has been confirmed by us from ORNL

Provided by ORNL

Using Heating To Cool Rooms (Engineering)

Climate change is causing a persistent increase in the number of hot summer days. Offices and homes are getting hotter, and the nights bring little respite from the heat. Against this backdrop, a significant increase in new cooling systems installations is anticipated, which in turn will give rise to increased energy consumption. One potential cost-effective alternative is to use existing heating systems. According to an analysis by the Fraunhofer Institute for Building Physics IBP, the heat pumps in these systems can be reverse operated to provide effective cooling.

As part of the trial, the researchers collected a large amount of indoor climate data, which they then used to validate the digital twin.
Infographic: Cooling in summer with heating systems.
Above: As part of the trial, the researchers collected a large amount of indoor climate data, which they then used to validate the digital twin. Below Infographic: Cooling in summer with heating systems. © Fraunhofer IBP

Global energy consumption from air conditioning systems continues to rise. According to information from the International Energy Agency (IEA), the total energy used to cool residential and office buildings in 2016 was around 2000 terawatt hours. That is an estimated 10 percent of the world’s total power consumption. This amount could triple by 2050: By then, ten air conditioning systems will be sold every second. In Germany, experts expect energy consumption for cooling residential buildings to double over the next 20 years. For non-residential buildings, the German Environment Agency expects an increase of 25 percent.

How can this expected surge in new cooling system installations be prevented? This is the issue being addressed by a team of researchers at Fraunhofer IBP. “In existing buildings, if a heat pump – i.e. the heat generator – that is already installed can be reverse operated to provide air conditioning, the same system that is already being used for heating could be used for cooling as well,” says Sabine Giglmeier, a scientist at Fraunhofer IBP. This would remove the need to purchase new cooling systems and save energy.

Assessment of the potential of radiators and underfloor heating systems

To assess the extent to which this technology can be used to avoid overheating in summer, the engineer and her team assessed the potential of two heating systems: They investigated whether radiators and underfloor heating systems – heat distributors – could replace the air conditioning units that are often used in existing buildings. These units dissipate their waste heat via a tube through the window or an opening in the wall.

“Not only do these air conditioning systems use a lot of power, they are also loud and create drafts. They can also cause hygiene problems if they are not properly maintained,” explains the researcher.

Simulations with WUFI® Plus

To determine whether heat pumps can be combined with radiators or underfloor heating systems for use as a cooling system, the researcher and her team conducted initial tests under laboratory conditions in the climate chamber with radiators and underfloor heating systems. Digital twins of the heating systems were then tested using the building simulation software WUFI® Plus to determine whether the laboratory measurements matched the software calculations. “We can use the digital twins to produce a valid representation of reality and calculate the effect of the overall system in a wide range of application scenarios. This allows us to identify the specific areas where heat pumps plus radiators or underfloor heaters are most effective.” The simulation software creates a (hygric) link between heat and humidity in the calculation. The simulations can be scaled to any type of building, taking into account a range of parameters such as room and window size, the size of the heating elements, the external temperature and the design and number of windows. The researchers can examine other parameters, such as energy requirements and comfort. This allows for a comprehensive evaluation of heating and cooling systems.

The tests found that both radiators and underfloor heating systems have the potential to reduce the ambient air temperature in the summer significantly and to produce a pleasant cooling effect in office spaces with a standard size of 16 m2, windows of up to 3 m2 and two workers, without unwanted condensation forming on cold surfaces. The inflow temperature of the system must be regulated depending on the dew point of the ambient temperature in order to avoid structural damage from condensation. “The dew point temperature is a critical figure that we need to take into account in our calculations. This is because moisture condenses on a surface when the surface is colder than the dew point temperature of the air. This is why it is important to consider the dew point temperature when cooling. In other words, if the dew point temperature is 13 degrees Celsius, the water we feed through the heating system cannot be any colder than that, otherwise the water from the air will condense on the heating element and supply lines, causing damp.”

Up to 65 percent reduction in over temperature degree hours

Another important criterion for the calculations is over temperature degree hours. This unit of measurement refers to the number of hours and kelvins above the limit temperature of the room, which is 26 degrees Celsius, in the year. A maximum of 1200 over temperature degree hours per year are permitted in residential buildings, and just 500 in offices. The researchers’ calculations showed a reduction of over 40 percent in over temperature degree hours for radiators measuring 70 cm by 1 m. For radiators twice that size, a 65 percent reduction can be achieved compared to an uncooled room.

“All in all, we demonstrated that the cooling performance achieved using radiators is sufficient with a moderate window surface area share. However, a higher window surface area share requires a larger cooling area to achieve comfortable indoor climate conditions. This area can be provided using underfloor heating systems, which also produce a significantly greater cooling effect, as our tests have shown,” says Giglmeier in summary. Heat pumps with cooling functions could be an alternative to expensive cooling systems in existing buildings.

The extent to which the overall system affects the user’s comfort – for example, whether floors become too cold or temperature changes affect floor coverings and other materials in the room – remains to be investigated.

The assessment of potential conducted by the IBP researchers was sponsored by the Fraunhofer High-Performance Center Mass Personalization.

Featured image: View of the corner of the test room with radiator.© Fraunhofer IBP

This science news has been confirmed by us from Fraunhofer

Provided by Fraunhofer

WVU Engineers Develop New Geothermal Energy Technology (Engineering)

As alternative energy sources have become necessary to decrease global carbon emissions and meet growing energy demands, researchers at West Virginia University had ideas that came bubbling to the top—literally.

 As part of the American-Made Geothermal Manufacturing Prize competition, a challenge designed to spur innovation and address manufacturing challenges in geothermal environments, associate professor Terence Musho and Berry Chair Emeritus Nigel Clark in the Statler College of Engineering and Mineral Resources, have developed a new airlift approach to optimize current geothermal pump technologies.

 The two most common methods of bringing geothermal fluids to the surface are by using a line shaft pump or a submersible pump, although both methods have limitations. The method proposed by the engineers employs a 3D-printed device—a sparger head— to generate bubbles and lift water to the surface.

 “Improved design of the sparger head for airlifts will revolutionize what the industry has been doing and eliminate the line shaft pump,” Musho said. “We can access much deeper geothermal wells, which typically have higher temperatures, which is better for direct usage and energy generation type applications.”

 By injecting air deep into a geothermal well, it then rises to interact with geothermal fluids. As the air bubbles rise to the top of the well, an exchange in momentum causes the geothermal fluids to rise.

 According to Musho, the technology works in a similar way to an automatic drip coffee maker. Typically, the water boils and travels up a tube to the top; instead of boiling the water, this method injects air into the water relying on the same buoyancy force to bring fluids up to the surface. 

 “The focus of this project relies on the efficient creation of bubbles,” Musho said. 

“The software-based optimization will provide a more efficient operating environment by tailoring bubble generation for a given well condition.”

 The advantages of geothermal energy production are many: unlike wind and solar, geothermal power plants produce electricity around the clock, modern plants emit no greenhouse gases and have a smaller physical footprint than other energy-generating plants, according to the DOE.

 Musho and Clark teamed up with industry collaborators Dan Hand, a professional engineer from Sustainable Engineering LLC, and Roy Mink from Mink GeoHydro Inc, for the competition. The researchers are working within the Oak Ridge National Laboratory’s Manufacturing Demonstration Facility to utilize their state-of-the-art 3D metal printers.

 As semifinalists of the competition, the team will make their submission for the Make Phase of the competition in November, if their technology is selected, it will be tested on working geothermal wells and the Statler College team will be eligible for up to $250,000 in cash prizes and up to $50,000 in vouchers.

Featured image: Ansan Pokharel, mechanical and aerospace engineering graduate student, tests the improved sparger design created by West Virginia University engineers. (WVU Photo/Paige Nesbit)

Provided by WVU Today

Vanderbilt Engineer the First To Introduce Low-power Dynamic Manipulation of Single Nanoscale Quantum Objects (Engineering)


Led by Justus Ndukaife, assistant professor of electrical engineering, Vanderbilt researchers are the first to introduce an approach for trapping and moving a nanomaterial known as a single colloidal nanodiamond with nitrogen-vacancy center using low power laser beam. The width of a single human hair is approximately 90,000 nanometers; nanodiamonds are less than 100 nanometers. These carbon-based materials are one of the few that can release the basic unit of all light—a single photon—a building block for future quantum photonics applications, Ndukaife explains.

Assistant Professor of Electrical Engineering Justus Ndukaife (Steve Green/Vanderbilt University)
Justus Ndukaife (Steve Green/Vanderbilt University)

Currently it is possible to trap nanodiamonds using light fields focused near nano-sized metallic surfaces, but it is not possible to move them that way because laser beam spots are simply too big. Using an atomic force microscope, it takes scientists hours to push nanodiamonds into place one at a time near an emission enhancing environment to form a useful structure. Further, to create entangled sources and qubits—key elements that improve the processing speeds of quantum computers—several nanodiamond emitters are needed close together so that they can interact to make qubits, Ndukaife said.

“We set out to make trapping and manipulating nanodiamonds simpler by using an interdisciplinary approach,” Ndukaife said. “Our tweezer, a low frequency electrothermoplasmonic tweezer (LFET), combines a fraction of a laser beam with a low-frequency alternating current electric field. This is an entirely new mechanism to trap and move nanodiamonds.” A tedious, hours-long process has been cut down to seconds, and LFET is the first scalable transport and on-demand assembly technology of its kind.


Ndukaife’s work is a key ingredient for quantum computing, a technology that will soon enable a huge number of applications from high resolution imaging to the creation of unhackable systems and ever smaller devices and computer chips. In 2019, the Department of Energy invested $60.7 million in funding to advance the development of quantum computing and networking.

“Controlling nanodiamonds to make efficient single photon sources that can be used for these kinds of technologies will shape the future,” Ndukaife said. “To enhance quantum properties, it is essential to couple quantum emitters such as nanodiamonds with nitrogen-vacancy centers to nanophotonic structures.”


Ndukaife intends to further explore nanodiamonds, arranging them onto nanophotonic structures designed to enhance their emission performance. With them in place, his lab will explore the possibilities for ultrabright single photon sources and entanglement in an on-chip platform for information processing and imaging.

“There are so many things we can use this research to build upon,” Ndukaife said. “This is the first technique that allows us to dynamically manipulate single nanoscale objects in two dimensions using a low power laser beam.”


The research was supported by the National Science Foundation grant ECCS-1933109.


The article, “Electrothermoplasmonic Trapping and Dynamic Manipulation of Single Colloidal Nanodiamond”  was published in the journal Nano Letters on June 7 and was coauthored by graduate students in Ndukaife’s lab, Chuchuan Hong and Sen Yang, as well as their collaborator, Ivan Kravchenko at Oak Ridge National Laboratory.

Featured image: Low frequency electrothermoplasmonic tweezer device rendering (Ndukaife)

Provided by Vanderbilt University

Scientists Invent a New Information Storage and Processing Device (Engineering)

Scientists have developed a means to create a new type of memory, marking a notable breakthrough in the increasingly sophisticated field of artificial intelligence.

Advance Holds Promise for Artificial Intelligence

A team of scientists has developed a means to create a new type of memory, marking a notable breakthrough in the increasingly sophisticated field of artificial intelligence. 

“Quantum materials hold great promise for improving the capacities of today’s computers,” explains Andrew Kent, a New York University physicist and one of the senior investigators. “The work draws upon their properties in establishing a new structure for computation.”

The creation, designed in partnership with researchers from the University of California, San Diego (UC San Diego) and the University of Paris-Saclay, is reported in the Nature journal Scientific Reports

“Since conventional computing has reached its limits, new computational methods and devices are being developed,” adds Ivan Schuller, a UC San Diego physicist and one of the paper’s authors. “These have the potential of revolutionizing computing and in ways that may one day rival the human brain.”

In recent years, scientists have sought to make advances in what is known as “neuromorphic computing”–a process that seeks to mimic the functionality of the human brain. Because of its human-like characteristics, it may offer more efficient and innovative ways to process data using approaches not achievable using existing computational methods. 

In the Scientific Reports work, the researchers created a new device that marks major progress already made in this area.

To do so, they built a nanoconstriction spintronic resonator to manipulate known physical properties in innovative ways. 

A schematic of a nanoconstriction spintronic resonator (a), which depicts signal (S) and ground (G) electrical contacts, along with the current flow (b), measured at 200 nanometers. Image courtesy of NYU’s Department of Physics

Resonators are capable of generating and storing waves of well-defined frequencies–akin to the box of a string instrument. Here, the scientists constructed a new type of resonator–capable of storing and processing information similar to synapses and neurons in the brain. The one described in Scientific Reports combines the unique properties of quantum materials together with that of spintronic magnetic devices.

Spintronic devices are electronics that use an electron’s spin in addition to its electrical charge to process information in ways that reduce energy while increasing storage and processing capacity relative to more traditional approaches. A broadly used such device, a “spin torque oscillator,” operates at a specific frequency. Combining it with a quantum material allows tuning this frequency and thus broadening its applicability considerably. 

“This is a fundamental advance that has applications in computing, particularly in neuromorphic computing, where such resonators can serve as connections among computing components,” observes Kent. 

This research was supported by the Quantum Materials for Energy Efficient Neuromorphic Computing, an Energy Frontier Research Center funded by the U.S. Department of Energy’s Office of Science Basic Energy Sciences (BES) under award DE-SC0019273. 

Featured Photo credit: metamorworks/Getty Images

Reference: Xu, JW., Chen, Y., Vargas, N.M. et al. A quantum material spintronic resonator. Sci Rep 11, 15082 (2021).

Provided by NYU

The Mechanics of Puncture Finally Explained (Engineering)

The feeling of a needle piercing skin is familiar to most people, especially recently as COVID-19 vaccinations gain momentum. But what exactly happens when a needle punctures skin? The answer is revealed in a new paper published recently in the Journal of the Mechanics and Physics of Solids.

Mattia Bacca, assistant professor at the University of British Columbia, often looks to the natural world for answers when he’s faced with a mechanical engineering problem–like the way a gecko can cling to a surface with the pads on its toes, or an ant can cut through a leaf many times its size.

Bioinspired engineering helped Dr. Bacca, along with PhD candidate Stefano Fregonese, to answer the previously unsolved question of how the mechanics of piercing works on soft materials, like skin.

“Cutting is ubiquitous in our survival and daily lives,” Bacca explains. “When we chew food, we cut tissue to make it digestible. Almost every species in the animal kingdom evolved with the ability to cut tissue to feed and defend, hence have acquired remarkable morphological and physical features to allow this process efficiently.”

They created a mechanical theory to determine the critical force required for needle insertion–the pivotal phenomenon of puncture. Their work provides a simple, semi-analytical model to describe the process, from dimensional arguments to finite element analysis.

Mechanisms involved in cutting soft tissue have only gained attention in engineering over the last several decades, initially with investigations into the properties of rubber. Previous approaches determined the force needed to insert a needle in tissue after its initial puncture, using physical experiments that couldn’t fully measure the deformations and complex failure mechanisms involved in breaking through the surface of a soft material.

In contrast, the new model created by Fregonese and Bacca can finally predict the puncture force and validate this with previous experiments. They discovered that the needle insertion force is proportional to the toughness of tissue and scales inversely with the radius of the needle–meaning thinner needles require less force. Albeit both these observations are intuitive, they provided quantitative prediction. What is counterintuitive, however, is the role of material rigidity in this process. Tissue rigidity scales inversely with puncture force, with softer tissue requiring higher force (at same toughness). The UBC team is currently performing additional experiments and model refinements to get “deeper” into the physics of this problem.

So far, their results come from various inquiries into animal solutions. At first, Fregonese joined Dr. Bacca’s Micro & Nano Mechanics Lab for a project related to the mechanics of adhesion in animals like geckos. Exploring overlaps with this area and the problem of cutting, they began to investigate fundamentals of cutting and the link to the morphological evolution of animals, with an international collaboration >studying leafcutter ants with animal biomechanics expert Dr. David Labonte (Imperial College), and muscle physiology expert Dr. Natalie Holt (University of California). They also collaborated with UBC Okanagan’s Dr. Kevin Golovin and mechanical engineering colleague Dr. Gwynn Elfring to research the interaction between ballistics and gels.

Their new theoretical model may help engineers developing various applications such as protective equipment, automation processes involving food and the emerging technology of robotic surgery.

It may also impact how people experience injections in the future, something top of mind for people who’ve recently lined up to receive their COVID-19 vaccination. For example, future technology could provide options like self-administered disposable pads armed with microneedles–like the ones designed by UBC’s Dr. Boris Stoeber–designed to pierce skin at the right depth and with the right force.

“Piercing soft solids: A mechanical theory for needle insertion,” published in Journal of the Mechanics and Physics of Solids is available at

This research was supported by the Department of National Defense of Canada, the Natural Sciences and Engineering Research Council of Canada, and by the Human Frontiers in Science Program.

Provided by UBC

What Are The Effects Of Fiber Addition On The Properties Of High-Performance Concrete? (Civil Engineering)

Szymon Grzesiak and colleagues investigated the influence of fiber addition on the properties of high-performance concrete. They showed that addition of fibers reduced compressive strength and the modulus of elasticity of the concrete. Their study recently appeared in the Journal Materials.

High performance fiber reinforced concrete (HPFRC) is developing quickly to a modern structural material with a high potential. HPFRC is a ductile concrete with high metallic fiber content (1% or more by volume), with uniform or hybrid fibers. Experimental tests showed that fiber dosage improves the energy absorption capacity of concrete and enhances the robustness of concrete elements. However, the addition of fiber does not have always have a positive effect on the mechanical properties. Besides, due to increasing costs of the produced fiber reinforced concrete there is a demand to analyze the necessary fiber dosage in the concrete composition.

Now, Szymon Grzesiak and colleagues investigated the influence of fiber addition on the properties of high-performance concrete.

“It is expected that the surface and length of used fiber in combination with their dosage influence the structure of fresh and hardened concrete.”

— they said

In order to determine the influence of fiber addition, they carried out tests on a mixture with polypropylene (PP) and polyvinyl alcohol (PVA) fiber with dosages of 15, 25, and 35 kg/m³ as well as with control concrete without fiber.

Fig 1. (A) Slump experiment for MasterFiber 401 (PVA). (B) Fresh concrete with MasterFiber 401 (PVA). (C) Fresh concrete with MasterFiber 235 SPA (PP). © Authors

They found that, due to the addition of fibers to the concrete mix, a significant difference was observed in the compressive strength of the concrete. The fiber addition of 15 kg/m³ in the concrete composition reduced the compressive strength from 83.2 MPa to 79.6 MPa. The higher fiber dosage showed a similar trend. Furthermore, it reduced bulk density and the modulus of elasticity of the concrete.

“Due to the higher air content in the fiber-reinforced mixtures compared to normal concrete, the compressive strengths differed from each other.”

— they said.

They also showed that, PP and PVA fibers are effective in increasing the splitting tensile strength of concrete, which allows better utilization of material capacities and has an impact on the production costs of Fiber Reinforced Concrete (FRC) members. The comparison showed that the dosage of fibers increased from 4.0 MPa to 5.0 MPa (for 15 kg/m³), 6.7 MPa (25 kg/m³), and 6.9 MPa (35 kg/m³).

Additionally, the fiber dosage improved the flexural properties of concrete. The flexural strength increased the maximal 31% for a fiber dosage of 25 kg/m³ in comparison to the plain concrete. The bending tensile strength of concrete with added fibers also increased by up to 18% compared to materials without fibers.

© Authors
Figure 2. Bending-tensile strength of concrete with different fiber types (MasterFiber 235 SPA and MasterFiber 401) for a fiber dosage of 35 kg/m³ in accordance with EN12467 © authors

Moreover, it has been shown from stress–deflection curves that long MasterFiber 235 SPA (PP) is better than short MasterFiber 401 (PVA). This is because the stress–deflection curve of fiber type MasterFiber 401 (PVA) revealed a higher increase in deflection compared to fiber type MasterFiber 235 SPA (PP), which may indicate unfavorable adhesion forces between PVA fiber and the matrix. Shorter fibers pull-out of the matrix faster than longer fibers. This is attributed to the bonding forces between the fibers and the concrete matrix.

“The 30 mm long fibers provided a better friction range than the 12 mm long fibers and also provided a better stress transfer in the matrix.”

Finally, the highest PP fiber dosage examined in the concrete composition amounted to 35 kg/m³. However, the addition of more than 25 kg/m³ of fibers to the concrete mix had less influence on the bending tensile strength of the concrete. This concrete mix had an overcritical fiber dosage and was characterized by tensile strain-hardening behavior. A comparison of the stress–deflection curves with the addition of 25 kg/m³ and 35 kg/m³ of fibers also revealed that the cracking behavior of concrete for these two fiber contents did not differ significantly.

Fig 3. Top: Typical failure modes for specimens with MasterFiber 235 SPA (PP). (A) Images of the tensile fracture face of a fiber. (B) Images of the pull-out fracture face of a fiber. Middle: Typical failure modes for specimens with MasterFiber 401 (PVA). (A) Images of the pull-out fracture face of a fiber. Bottom: Typical failure modes for specimens without fiber. © Authors

Funding: Their research was funded by the Master Builders Solutions Deutschland GmbH.

Featured image: (A) Polypropylene fiber MasterFiber 235 SPA (PP). (B) Polyvinyl alcohol fiber MasterFiber 401(PVA) used in the present study. © Authors

Reference: Grzesiak, S.; Pahn, M.; Schultz-Cornelius, M.; Harenberg, S.; Hahn, C. Influence of Fiber Addition on the Properties of High-Performance Concrete. Materials 2021, 14, 3736.

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