A self-healing cement recently developed at the U.S. Pacific Northwest National Laboratory (PNNL) (Richland, Washington, USA) can outperform conventional concrete, according to the researchers, who believe it offers a potentially pollution-preventing technology for industries, such as geothermal.
The work by PNNL staffers was performed at Brookhaven National Laboratory (BNL) (Upton, New York, USA) and at the Environmental Molecular Sciences Laboratory, a U.S. Department of Energy (DoE) Office of Science user facility located at PNNL.
Funding was provided by the DoE’s Geothermal Technologies Office (Washington, DC, USA).
Flexible Polymer Ingredient
Cement is the second largest consumable in the world behind water, the researchers note. Thus, finding a way to make cement even more effective could be a game changer, not only for the geothermal industry, but even for the broader construction industry.
“The idea in a few years would be to extend it to everything,” says Carlos Fernandez, a PNNL chemist and leader of the research team. “The sky’s the limit.”
In their study, the new cement uses a flexible polymer ingredient to repair fractured surfaces and fill cracks. In turn, this minimizes mechanical failure risks and provides a sustainable energy source, PNNL explains.
Cement used in geothermal wells is known to crack under pressure and in high-temperature environments associated with drilling for geothermal energy. As such, the objective of PNNL’s study was to see how its self-healing cement would hold up when tested against conventional cement in these extreme heat conditions.
Through a variety of tests, performed at PNNL and at BNL’s National Synchrotron Light Source II, the team found that the self-healing cement technology could eliminate the need to remove, repair, and replace cracked cement wells.1
Initial Testing Results
Researchers tested their self-healing cement’s strength and reactions to mechanical stress and conducted analyses of surface area, chemical composition, and surface topography. The tests confirmed that the self-healing cement is a significant alternative to conventional cement because it is flexible and autonomously heals cracks.
The flexibility is attributed to chemically “soft,” or flexible, bonding between the atoms in the polymer and cement. This soft bonding allows large deformations that can be contained within the cement without breaking the bonds.
This was predicted through computational modeling done by PNNL’s Vanda Glezakou. According to the researchers, the polymer adds 60 to 70% more elasticity to the cement when it is added, reducing fractures in the cement.
On their own, polymers are large, chain-like molecules that work to hold substances together and are naturally found in the human body, the PNNL team explains. When added to cement, polymers add flexibility to brittle material and keep cracks from spreading quickly. The polymer detaches, migrates to the crack, and reattaches to fill the crack. In all, there was an 87% reduction in crack size when the polymer was added to the concrete.
Potential End Applications
Citing prior studies, infrastructure repairs due to the cracking of conventional cement cost $12 billion per year globally, according to Fernandez, who says the polymer-cement mix could realize $3.4 billion in annual savings for infrastructure, such as dams, nuclear waste facilities, and skyscrapers.
Fernandez says the average cost of conventional cement is 5 cents/lb, as compared to 30 to 35 cents/lb for the polymer cement. However, he believes the polymer cement could potentially extend the life of concrete-based structures by 30 to 50 years, which could make up for the cost gap. The extended lifecycle of the polymer cement could also reduce the volume of cement that goes to landfills.
Fernandez points to the oil industry as one potential beneficiary of the self-healing cement technology, since high temperatures are constant and removing and replacing cracked concrete is both time consuming and expensive.
The cement also could be used at nuclear waste facilities and hydropower dams, he says, where cracks in the structures and mechanical failure could result in flooding or contamination. With the cement, Fernandez believes the amount of inspections and repairs would decrease. The flexible nature of the cement also allows it to withstand greater mechanical stresses from natural disasters and extreme weather conditions, he adds, such as earthquake tremors or high winds.
The self-healing cement could further resolve major concerns about the sealing of wellbores for oil, gas, and geothermal heat production, according to the researchers. Leaks in wellbores often lead to the contamination of aquifers and surface waters and limit the ability to provide clean energy alternatives.
Large geothermal energy reserves across the United States and around the world are not in use because wellbore cement fails in high temperature conditions and in chemically corrosive environments, Fernandez says. However, the researchers believe the self-healing cement can deliver significant energy with minimal carbon release into the atmosphere.
Source: PNNL, www.pnnl.gov.
1 “PNNL’s Self-Healing Cement Could Transform Geothermal Industry,” Pacific Northwest National Laboratory News & Media, May 3, 2019, https://www.pnnl.gov/news-media/pnnls-self-healing-cement-could-transform-geothermal-industry (July 15, 2019).