Combining multi-disciplinary talents from two laboratories at the U.S. Army Engineer Research and Development Center (ERDC), a three-person team earned a U.S. patent in July 2020 for the inventive Electro-active Vitreous Enamel Coated Dowel Bar, which stabilizes concrete segments and reduces repair costs.
Dr. Charles A. Weiss Jr. and the late Dr. Phillip G. Malone, both of the Geotechnical and Structures Laboratory (GSL), and Sean W. Morefield of the Construction Engineering and Research Laboratory (CERL) used their material engineering skills to create the two-tier product.
Used in the construction, manufacturing and placement of enamel-coated steel dowel bar assemblies, the device joins and stabilizes concrete slabs and other segments, preventing major high-cost reconstructions.
The invention is an improvement of an earlier patent granted in October 2014 for Configuration for Improving Bonding and Corrosion Resistance of Reinforcement Material, which was awarded to the same researchers, who have shared their expertise over nearly 20 years on a variety of technologies in support of the Army and nation.
How dowel bars are used
According to Morefield, steel dowel bars have generally been used to join together and restrict concrete slabs and segments during construction and formation of highways, airport runways and other concrete structures. During such construction, these concrete slabs are formed in 30 connected sections. Adjacent concrete sections are kept in place using steel-restraining dowel bars. These dowels bars, typically made of high-strength steel, are generally comprised of elongated, cylindrical, high-shear rods.
As an example, Morefield explained that during concrete roadway construction, multiple concrete dowel bars may be embedded between adjacent concrete slabs and spaced intermittently within the sections as joints between slabs.
“These dowel bars need to be as slippery as possible, so that when they are placed within the concrete surrounding the dowel bars, they allow the concrete slabs to move horizontally in relation to each other,” Morefield said. “If the dowel bars do not easily slide or slip within the concrete cavity, contractive and expansive forces caused by thermal heating and cooling will cause the concrete slabs to crack, break or corrode the reinforcing steel, due to exposure to water and/or chemicals.”
Weiss pointed out that concrete is strong against forces of compression, but has low tensile strength and ductility. Reinforcement materials, such as steel, are needed to withstand shear and tensile forces on the concrete.
Weiss also noted that previous research on adding the enamel coating to the steel in cement-based composites improved the bonding between the cement paste and the steel up to a factor of six times.
“The inclusion of this coated dowel bar should mean that that less steel is needed for concrete pavements, based on determination of the development length,” Weiss said. “The development length can be defined as the amount of reinforcement (bar) length needed to be embedded or projected into the column to establish the desired bond strength between the concrete and steel (or any other two types of material).”
Detrimental effects of salt
Steel dowel bars may corrode more quickly and significantly in areas where salt is applied to concrete roadways to reduce icy conditions or where salt may be present from ocean spray/mist. In those cases, the nearby concrete segments may fail, according to the patent application summary.
Rust build-up on the steel dowel bars prevents them from sliding back and forth within the surrounding concrete cavities and causes steel bars to corrode and expand, which results in rust layers up to six times the original volume.
As the steel bars expand due to corrosion, friction within the concrete cavities is increased, thereby failing to allow the concrete slabs to slip and move horizontally in relation to each other, Morefield explained.
“Where salt is applied to the surface of a concrete roadway to reduce the buildup of ice, or may be present in salt spray or mist from oceans, the concrete segments tend to fail quicker over time, as the salt increases corrosion of the steel dowel bars that align the segments,” Morefield said.
As past occurrences revealed, damage to even one steel dowel bar can cause significant harmful effects to adjacent and nearby concrete slabs, requiring expensive and extensive repairs.
Coated dowel benefits
The dowel bar’s protective coating is composed of two parts, a silicon layer, which is fired to create an adhesive layer, and a glassy vitreous enamel coating, which is applied over the silicon layer. Both layers are fired together in a two-coat, one-fire step.
With this patented steel coating, the dowel bars will keep concrete slabs in relative uniformity against one another and restrict unwanted movement.
“The dowel bars prevent vertical displacement, twisting and turning, movement to the left or to the right, and rotation, between the concrete slabs, which can prevent the unevenness or cracking in the pavement surface,” Morefield said. “Such dowel bars assist in maintaining a smooth top surface of the pavement, while simultaneously increasing the strength of the concrete in the region of the joint.”
Prior to his retirement as a research geologist in 2013, Malone worked with numerous interdisciplinary teams, amassing a total of 55 patents throughout his career. He died on Nov. 18, 2020.
“Dr. Malone was the consummate scientist,” said Weiss of his former colleague. “He was proficient in an astonishing array of scientific disciplines in materials science, an amazing intellectual curiosity, and the ability to create new ideas, and areas of research across disciplines. He was a mentor to me and to many others, and had a real hunger to make a difference to support the Army, nation and world though his technical innovations.”
Weiss, an ERDC research geologist since 1991 who has collaborated on 23 U.S. patents, still works at GSL, where he is a member of the Engineering Systems of Materials Division research group.
Morefield is a materials engineer employed in the Facilities Division of the Material and Structures Branch at CERL.
Malone, Weiss and Morefield will be recognized next year at a patent plaque
presentation ceremony, hosted by leaders from ERDC’s Office of Research and Technology Transfer, which processes patent applications for the ERDC.