Water's Hidden Dance: Neutron Imaging Unlocks Key to Greener Concrete

Scientists have cracked a crucial puzzle in the quest for eco-friendly construction, using advanced neutron imaging to reveal precisely how water sabotages efforts to store CO2 in recycled concrete. Researchers at the Institut Laue-Langevin (ILL) recently uncovered that water, both essential for the carbonation process and then surprisingly released by it, ends up blocking the very pores needed for CO2 to get trapped. This groundbreaking discovery, published on July 9, 2026, means we now understand a key bottleneck in turning mountains of concrete waste into climate solutions. The construction sector is currently facing a double whammy: it's a huge emitter of carbon dioxide – accounting for 5-8% of global CO2 emissions – and generates billions of tonnes of concrete waste annually, making it the largest contributor to global waste. Accelerated carbonation offers a promising way to tackle both problems by treating crushed concrete waste with CO2-rich gas, turning it into a stable mineral like calcium carbonate. However, until now, the exact role of water in this process was a mystery, with too little water slowing the reaction and too much blocking CO2 pathways. The ILL combined neutron and X-ray tomography provided a real-time, 3D view, showing that as CO2 reacts, it frees up water previously bound in the cement, which then clogs the pores and stops further CO2 uptake, a dynamic far more complex than previously thought. This fresh understanding is set to revolutionize how we design accelerated carbonation treatments for recycled concrete, making them far more effective. Researchers can now optimize conditions to manage water movement better, potentially leading to more efficient CO2 sequestration and stronger, more sustainable building materials. The goal is to move beyond simply exposing concrete to CO2 and instead precisely control the internal conditions to maximize carbon storage, pushing us closer to a truly circular economy in construction and turning waste into a valuable carbon sink.