A nanomaterial-containing penetrating sealer developed by researchers at Washington State University (WSU) is better able to protect concrete from moisture and salt – the two most damaging factors in crumbling concrete infrastructure in northern US states.
Compared to a commercial sealer, the novel sealer showed a 75% improvement in repelling water and a 44% improvement in reducing salt damage in laboratory studies. This work could provide an additional way to address the challenge of aging bridges and pavements in the US.
“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 report their work in a paper in the Journal of Materials in Civil Engineering and have applied for a provisional patent on the sealer.
Much of the critical infrastructure in the US, such as its 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 US infrastructure that shows consistently poor or failing grades.
About 8% of approximately 600,000 bridges in the US 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 for protecting concrete, and many state departments of transportation use them to protect bridge decks in particular, which seem to suffer the worst from salt damage. But according to Shi, although current sealers on the market provide some level of protection, moisture is often still able to make its way into the concrete.
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, and formed a barrier against the intrusion of water vapor and other gasses that tend to make their way into concrete. They also protected the concrete from the physical and chemical attacks of deicing salts.
The WSU sealer is designed to be multi-functional, as it can also serve as a curing aid for fresh concrete. In addition, it is water-based, rather than using organic solvents, which means it’s more environmentally friendly and safer for workers.
“Traditionally, when you switch from an organic solvent to water, you sacrifice the sealer’s performance,” Shi 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 nanomaterial-containing sealer. They are currently investigating how the sealer might help protect concrete from microbial damage or abrasion, the daily wear and tear that damages concrete in high-traffic areas. They also plan to conduct pilot-scale demonstrations in the next two years, deploying an experimental piece of concrete infrastructure on the WSU campus or in the city of Pullman.
This story is adapted from material from Washington State University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.
Comparison of a concrete sample coated with the new nanomaterial-containing penetrating sealer (left) versus untreated concrete (right). Photo: WSU.