A weaker building material can be the right answer. That is the counterintuitive read we keep coming back to with a Purdue pilot study that fed dead-battery waste into cement mortar and, on purpose, watched the strength drop.
The interesting part is not that the cubes got weaker. It is that the researchers expected exactly that, and built their argument around it.
A team from Purdue’s chemical engineering and civil engineering schools took the leftovers of spent lithium-ion batteries and swapped them in for part of the sand in mortar. In the pilot study, published in CivilEng in January 2026, they used two different wastes. One was “black mass,” the fine powder scraped off the battery electrodes. The other was a mix of crushed metals like steel, copper and aluminum from the battery casings. Then they cast three sets of cubes.
A tenth of the sand, swapped for battery leftovers
The recipe was simple. One mix was a plain control. In the other two, 10% of the sand was replaced, once with black mass, once with the shredded metals. Everything else stayed the same, including the amount of water and cement in each batch. The only variable was the swapped-in waste.
Then they waited and crushed. They tested 45 cubes for strength over 28 days, and the pattern was clear by the end. The black-mass mix came out 35% weaker than the control. The metal mix came in 55% weaker.
We are not materials scientists or structural engineers, so read this as a walk through one pilot study, not guidance for anyone’s building project. The findings come from a small controlled experiment, and a result from a batch of lab cubes is a long way from a rule about what belongs in a real slab.
Why the cubes got weaker, not stronger
Sand is not just filler. In mortar, the sand grains carry the load, and the cement paste is the glue that binds them and hardens over time. Swap a tenth of that sand for a material that does not lock into the paste the same way, and you weaken the frame the strength was built on. That is roughly what seems to be happening in both mixes, though the two wastes behave differently.
The black mass is a fine powder. The shredded metals are irregular, harder pieces that probably bond poorly with the cement and leave gaps where the paste cannot grip. The metal mix lost more strength; the powder mix held up better. For a sense of how normal mortar hardens, the control gained about 60% of its 28-day strength in the first 7 days. Most of the hardening happens early, and the waste mixes were being measured against a well-set benchmark.
If it’s weaker, why bother?
This is the obvious question, and the Purdue team’s answer is what makes the study more than a failed experiment. Not all concrete has to hold up a building. A lot of it goes into things that mostly just have to sit there, take foot traffic and not crack, like sidewalks, curbs and paving. For those jobs, you do not need maximum strength. You need enough strength at a lower cost, ideally a lower environmental cost.
So the researchers changed the question. Instead of asking how strong the mix is, they weighed strength against the carbon saved by keeping battery waste out of landfill. On that measure, the black-mass mix scored four times higher than the control. The cube is weaker, but for each unit of strength, it carries far less carbon once the avoided emissions are counted.
Behind all this is a waste problem growing fast. As electric vehicles have gone from 4% of the global market in 2020 to 18% in 2023, the pile of spent batteries has grown with them. Purdue’s release points to projections of 1.2 million units of battery waste per year by 2030, with recycling rates still below 10%. That is the appeal of pointing this waste at concrete, an industry that uses enormous amounts of material and carries a heavy carbon footprint of its own. Vilas Pol, a chemical engineering professor on the team, frames the aim as tackling both at once: “What we’re really doing here is solving two problems that are usually treated separately — battery waste management and the carbon footprint of construction — and showing they can solve each other.”
We would treat that as the goal the pilot points toward, not a settled result. What the study shows is narrower and still worth something: one waste stream can be turned into a lower-grade building material without the mortar simply falling apart.
What this pilot settles, and what it doesn’t
This is one small experiment, three mixes and a batch of cubes, run in controlled lab conditions. It measures one thing, strength, at one replacement level, and it does not yet say how these mixes behave over years in the real world, which is where the harder questions live.
How much water the material soaks up, how porous it is, and whether anything leaks out of the battery waste over time are all open questions. For a material made partly from battery scrap, that last one, leaching, is the one we would want answered before anyone poured it anywhere near soil or water. Amit Varma, the civil engineering professor and Bowen Lab director on the project, keeps the framing open: “Sustainable construction materials and methods are an important focus for the Lyles School, and there is a lot of exciting potential here.” Varma adds that “with further research and development, this sustainable concrete mix design could be a tremendous energy and environment saver.”
What strikes us about this study is that the weakness is not the finding being hidden, it is the finding being priced. A 35% or 55% strength drop reads like a failure only if you assume every mortar mix is competing to hold up a high-rise. The Purdue team is doing something more careful: measuring exactly how much strength you give up, then asking whether the carbon you save is worth that trade for jobs that never needed the full strength to begin with.