A nanomaterials-engineered penetrating sealer developed by Washington State University researchers is able to better protect concrete from moisture and salt – the two most damaging factors in crumbling concrete infrastructure in northern states.

The novel sealer showed a 75% improvement in repelling water and a 44% improvement in reducing salt damage in laboratory studies compared to a commercial sealer. The work could provide an additional way to address the challenge of aging bridges and pavements in the U.S.

“We focused on one of the main culprits that compromises the integrity and durability of concrete, which is moisture,” said Xianming Shi, professor in the Department of Civil and Environmental Engineering who led the work. “If you can keep concrete dry, the vast majority of durability problems would go away.”

Shi and graduate student Zhipeng Li recently published their work in the Journal of Materials in Civil Engineering and have applied for a provisional patent.

Much of the nation’s critical infrastructure, such as the U.S. highway system, was built from the 1950s to the 1970s and is now reaching the end of the lifetime for which it was designed. Every four years since the late 1990s, the American Society of Civil Engineers has provided a report card of U.S. infrastructure that shows consistently poor or failing grades. About 8% of approximately 600,000 bridges in the U.S. are considered structurally deficient, and one out of every five miles of highway pavement is in poor condition. The problem is exacerbated in cold climates by multiple freeze and thaw cycles and by the increased use of deicer salts in recent decades, which can degrade the concrete.

“Concrete, even though it seems like solid rock, is basically a sponge when you look at it under a microscope,” Shi said. “It’s a highly porous, non-homogenous composite material.”

Topical sealers have emerged as one tool to protect concrete, and many state departments of transportation use them to protect bridge decks in particular, which seem to suffer the worst from salt damage. The sealers on the market provide some level of protection, but moisture is often able to make its way into the concrete, Shi said.

In their study, the researchers added two nanomaterials, graphene oxide and montmorillonite nanoclay, to a commercial siliconate-based sealer. The nanomaterials densified the microstructure of the concrete, making it more difficult for liquid water to penetrate. They also formed a barrier against the intrusion of water vapor and other gasses that tend to make their way into the concrete. The nanomaterial also protected the concrete from the physical and chemical attacks of deicing salts. The penetrating sealer is designed to be multi-functional, as it can also serve as a curing aid for fresh concrete.

The WSU sealer is water-based instead of using any organic solvent, which means it’s more environmentally friendly and safer for workers, Shi added

“Traditionally, when you switch from an organic solvent to water, you sacrifice the sealer’s performance,” he said. “We demonstrated that the use of nanomaterials mitigates that reduction in performance.”

The researchers have done preliminary market analysis with industry stakeholders and are studying ways to further optimize the sealers. They are investigating how the nanomaterials-based sealers might help protect concrete from microbial damage or abrasion, the daily wear and tear that damages the material in high-traffic areas. They plan to conduct pilot-scale demonstrations in the next two years, deploying an experiment of concrete infrastructure on the WSU campus or in the city of Pullman.

Reference: “Effects of Nanomaterials on Engineering Performance of a Potassium Methyl Siliconate–Based Sealer for Cementitious Composite” by Zhipeng Li, S.M.ASCE and Xianming Shi, F.ASCE, 16 February 2022, Journal of Materials in Civil Engineering. DOI: 10.1061/MT.1943-5533.0004148

QUT Centre for Materials Science co-director Professor Dmitri Golberg, who led the research project, said the result was a "very interesting fundamental discovery" which could lead a way for the future development of tiny transistors for future generations of advanced computing devices.

"In this work, we have shown it is possible to control the electronic properties of an individual carbon nanotube," Professor Golberg said.

The researchers created the tiny transistor by simultaneously applying a force and low voltage which heated a carbon nanotube made up of few layers until outer tube shells separate, leaving just a single-layer nanotube.

The heat and strain then changed the "chilarity" of the nanotube, meaning the pattern in which the carbon atoms joined together to form the single-atomic layer of the nanotube wall was rearranged.

The result of the new structure connecting the carbon atoms was that the nanotube was transformed into a transistor.

Professor Golberg's team members from the National University of Science and Technology in Moscow created a theory explaining the changes in the atomic structure and properties observed in the transistor.

Lead author Dr Dai-Ming Tang, from the International Centre for Materials Nanoarchitectonics in Japan, said the research had demonstrated the ability to manipulate the molecular properties of the nanotube to fabricated nanoscale electrical device.

Dr Tang began working on the project five years ago when Professor Golberg headed up the research group at this centre.

"Semiconducting carbon nanotubes are promising for fabricating energy-efficient nanotransistors to build beyond-silicon microprocessors," Dr Tang said. "However, it remains a great challenge to control the chirality of individual carbon nanotubes, which uniquely determines the atomic geometry and electronic structure. "In this work, we designed and fabricated carbon nanotube intramolecular transistors by altering the local chirality of a metallic nanotube segment by heating and mechanical strain." Professor Golberg said the research in demonstrating the fundamental science in creating the tiny transistor was a promising step towards building beyond-silicon microprocessors.

Transistors, which are used to switch and amplify electronic signals, are often called the "building blocks" of all electronic devices, including computers. For example, Apple says the chip which powers the future iPhones contains 15 billion transistors.

The computer industry has been focussed on developing smaller and smaller transistors for decades, but faces the limitations of silicon.

In recent years, researchers have made significant steps in developing nanotransistors, which are so small that millions of them could fit onto the head of a pin.

"Miniaturization of transistors down to nanometer scale is a great challenge of the modern semiconducting industry and nanotechnology," Professor Golberg said.

"The present discovery, although not practical for a mass-production of tiny transistors, shows a novel fabrication principle and opens up a new horizon of using thermomechanical treatments of nanotubes for obtaining the smallest transistors with desired characteristics."