Engineers have created a new type of concrete that is stronger than conventional concrete while also capturing carbon dioxide from the atmosphere. The findings, reported in Carbon Research, suggest that adding carefully selected natural materials could give concrete a second role beyond construction by helping remove CO2 from the surrounding air.
Researchers at Mepco Schlenk Engineering College in India developed the mixture as a possible way to make construction materials more sustainable. Their approach targets a major environmental challenge: rising atmospheric CO2 levels driven in large part by fossil fuel use and cement production.
The team, led by Srinivasan Revathi, focused on two natural additives. One was zeolite, a highly porous mineral, and the other was bamboo biochar, a carbon-rich material. Both have large pore volumes and high specific surface areas, properties that make them well suited for trapping gas molecules.
Testing a Stronger Concrete Mix
The researchers tested several versions of M35 grade concrete, which is commonly used in infrastructure designed for moderate traffic. They replaced fine aggregate with zeolite at levels of 25% and 50%. They also substituted bamboo biochar for cement at concentrations of 0.5%, 1%, and 1.5%.
Each formulation was tested for several important properties, including compressive strength, split tensile strength, water absorption, and impact resistance. The researchers were looking for a mix that could absorb more CO2 without weakening the concrete. Ideally, they wanted the material to become stronger at the same time.
One combination stood out from the rest. The mix containing 50% zeolite and 1% bamboo biochar (dubbed ZB5) delivered the best overall performance.
Its compressive strength reached 38.49 MPa, about 7.48% higher than conventional concrete. Its split tensile strength reached 4.39 MPa, representing a 15% improvement over the standard mixture.
The researchers attribute the added strength to the interaction between zeolite's alumina-silicate structure and the hardness of bamboo biochar. Together, these materials appear to produce a denser and more durable cement-based matrix.
Concrete That Captures CO2
Strength was only part of the result. The ZB5 mixture also demonstrated an ability to absorb carbon dioxide.
When the concrete was placed inside a carbonation chamber, it captured 1.2 grams of CO2 per day. Over seven days, the gas penetrated 15 mm into the material.
The researchers linked this carbon uptake to the microporous structure of zeolite and the high carbon content of bamboo biochar. By combining these properties, the concrete can serve both as a structural material and as a medium for capturing atmospheric CO2.
Srinivasan Revathi, the corresponding author from the Department of Civil Engineering, provided her perspective on the findings. "Our work demonstrates a dual-benefit approach. We are not just creating a stronger concrete, but we are transforming a common building material into an active tool for environmental remediation. By integrating zeolite and bamboo biochar, we can build structures that not only stand strong but also actively cleanse the air of excess carbon dioxide, paving the way for truly sustainable infrastructure in high-emission areas like urban roadways and industrial zones."
Potential for Carbon-Neutral Construction
The findings point toward a possible new approach to developing carbon-neutral construction materials. Concrete made with the ZB5 formulation could be especially useful in locations where CO2 concentrations are relatively high.
Potential applications include concrete pavements, highway parapet walls, and sewer pipelines. These structures could continue serving their traditional engineering functions while also capturing some carbon dioxide from their surroundings.
The researchers caution, however, that the work is still a proof of concept and that additional testing will be necessary before the material can be widely adopted.
Next Steps for Carbon-Capturing Concrete
Future studies will examine how the concrete performs over longer periods, including whether it maintains its durability and ability to absorb CO2.
The researchers also plan to test other forms of biochar, evaluate the mixture in different grades of concrete and mortar, and study whether pre-soaked biochar can further improve its performance.
Those experiments will help determine whether the technology can be scaled for broader commercial and industrial use. If successful, the approach could provide the construction industry with a way to produce stronger infrastructure while also reducing some of the environmental impact associated with the built environment.