By incorporating recycled waste plastic and other byproducts from the iron and steel industry, researchers have created a more sustainable version of concrete that shields nuclear radiation better than standard concrete.
Their study, published March 10 in Progress in Nuclear Energy, opens up new possibilities for recycling plastic waste. It also demonstrates how waste polymers, in the form of ground-up powder, can be applied toward the existing industrial need for dense but lightweight materials that can effectively shield gamma and neutron radiation.
"With the ever-increasing plastic waste and the numerous environmental problems [it] creates, we wanted to explore whether the waste plastic could be used for neutron radiation shielding," said first author Santhosh Malkapur, a civil engineer at Basaveshwar Engineering College, in India. "Concrete is known to be a good radiation shield material and has been used conventionally all these years in making shielding walls."
There are four main types of nuclear radiation: alpha, beta, gamma and neutron. Nuclear radiation is dangerous to humans, so it must be shielded in power plants, research sites and other areas with active nuclear radiation.
Alpha and beta radiation are easy to filter with thin shielding layers, but gamma and neutron radiation are extremely high-energy and not as easy to block, requiring a mix of dense and light materials.
"It is a well-known fact that for gamma radiation, shielding density is the key, and increasing the density of the material by using high-density ingredients can make a good gamma radiation shield," Malkapur said. "On the other hand, neutron radiation shielding is complex and requires good amounts of hydrogen and other lighter nuclei."
Historically, concrete has proved to be up to the task.
"Concrete is naturally a good material, as it contains both light and heavy ingredients required for a radiation shield, and also, it offers a possibility to try and use newer materials in it," Malkapur said. "No specialized materials are required [to produce concrete], and shields can be made using locally available ingredient materials. Concrete offers a lot of flexibility in terms of molding, customized strength and durability, which makes it unique."
For their study, Malkapur and his colleagues sought to incorporate waste plastics into a concrete formulation specifically designed to shield nuclear radiation. While a 2016 study did evaluate the radioactivity of concrete made with e-waste plastic, those researchers were interested in testing the safety of plastic-based concrete for general construction, not using it for nuclear shielding.
According to Malkapur, there have to date been "no works studying the shielding aspects of concrete mixes with plastics."
To make their concrete, Malkapur and the team used a fine powder of waste plastic, sourced from a local steel manufacturer, as a replacement for the sand usually found in concrete. They also incorporated industry byproducts such as iron ore tailings, fly ash and ground-granulated blast-furnace slag.
They then tested their concrete by bombarding it with neutron and gamma radiation and measuring how much penetrated the material.
Not only did their material shield both types of radiation, but the researchers also were able to improve upon the performance of regular concrete. The study reported "significant improvements in the neutron-shielding properties" of the plastic-infused concrete, reducing transmission by 15.7% to 20.5%, depending on the specific formula.
The team has now turned its interest to incorporating waste plastics into building materials to improve insulation. However, Malkapur maintains he still has "further research plans in this particular area," and he hopes that others continue to work on this topic as well.
"There are many solutions to recycle and reuse waste and discarded plastics. We have worked with one such application, and we have proved that we can successfully utilize waste plastics for making concrete radiation shields," he said. "Similar attempts can be made elsewhere to use and make sustainable radiation shields using locally available materials."
The study, "Waste-polymer incorporated concrete mixes for neutron and gamma radiation shielding," published March 10 in Progress in Nuclear Energy, was authored by Santhosh M. Malkapur, Basaveshwar Engineering College; Shobha S. Ghodke, P.N. Sujatha, Yashoda Singh and Meghanath Sen, Bhabha Atomic Research Centre; K. S. Shivakumar, Global Academy of Technology; Mattur C. Narasimhan, NITK Surathkal; and Abhishek V. Pulgur, Ramaiah University of Applied Sciences.