Written By:
Tarun Jami
7 min
How Agrocrete® Stores Carbon: The Science Explained
Buildings and construction account for about 34% of global CO₂ emissions, according to the UN Environment Programme's Global Status Report 2024/2025. Cutting those emissions is essential. But the IPCC's special report on 1.5°C found that every pathway to 1.5°C with limited or no overshoot also relies on removing carbon dioxide from the air.
Agrocrete® is a building block designed to do a small part of that removal while it replaces high-carbon bricks and blocks. This explainer covers how crop residue stores carbon, why the product is carbon-negative within the boundaries its EPD declares, what the verified figures say, what they mean for a wall or a home, and where the limits lie.
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How crop residue stores biogenic carbon
The answer is simple: photosynthesis. A growing rice or wheat plant takes carbon dioxide from the air and, using the energy of sunlight, turns it into long-chain compounds such as cellulose. Every kilogram of carbon fixed this way comes from about 3.67 kg of CO₂, because a carbon atom weighs 12 units and a CO₂ molecule weighs 44. Carbon captured by plants in this way is called biogenic carbon.
After harvest, the grain is eaten, but the straw and stalks remain in the field. That residue is, in effect, a carbon stock, and its fate decides whether the carbon stays out of the atmosphere. If the straw rots, microbes slowly return its carbon as CO₂. If it is burned to clear the field for the next crop, as often happens in north India, the carbon goes back in minutes, along with the smoke.
So there are two problems: a construction sector that emits too much carbon, and farm residue that releases its carbon too quickly. Looked at together, they point to one answer. If the residue is bound into a durable building material before it decays or burns, its carbon stays locked inside the wall for the life of the building. That is the idea behind Agrocrete®.
Why Agrocrete® is carbon-negative within its declared boundaries
Agrocrete® belongs to a family of materials called vegetal, or bio-based, concretes. They have two parts: plant matter and a mineral binder. The binder coats and bonds the plant matter before it can decompose, so the carbon it holds is locked in a mineral matrix instead of being released. That is why vegetal concretes are often carbon-negative, but the result depends heavily on the binder.
Traditional binders for vegetal concrete, such as hydrated lime, hydraulic lime and cement, carry a large carbon footprint of their own. GreenJams therefore developed BINDR™, a cement-free, alkali-activated binder made mostly from industrial by-products such as steel-plant slag. The GreenJams product catalogue declares its embodied carbon at 0.18 kgCO₂/kg, against 0.80–0.90 kgCO₂/kg for ordinary Portland cement, about 80% lower.
How the blocks are made
According to the product's Environmental Product Declaration (EPD), paddy straw is bought from farmers near the plant in Visakhapatnam and processed with water to an even moisture content. A slag-based binder is made in parallel using alkali salts. The straw and fly ash are then mixed with the binder and moulded into solid and hollow blocks, which are cured without kiln firing.
The EPD also records that about 18% of the process water is collected and reused to irrigate adjacent farmland, a benefit it did not credit. The output is a range of Agrocrete® bricks and blocks that store more biogenic carbon than the fossil emissions released in making them, within the life-cycle stages the EPD covers.
What "declared boundaries" means
An EPD states which life-cycle stages it measures. Agrocrete®'s covers raw materials, transport to the plant and manufacturing (modules A1–A3), plus demolition, transport, waste processing and disposal at the end of the building's life (C1–C4). It reports the avoided stubble burning separately, as module D. Transport to site, construction and the use stage were not assessed.
The verified EPD figures
Agrocrete®'s EPD is registered with the International EPD® System as S-P-06876 (registry entry, full EPD as PDF). It was prepared by Monk Spaces, verified independently by Chakra4 Sustainability Consulting Services, and follows ISO 14025 and EN 15804+A2 under PCR 2019:14. It was published on 21 October 2022, is valid until 20 October 2027, and reports results per 1 kg of moulded Agrocrete® mix.
EPD result (per kg of mix) | Value | What it means |
|---|---|---|
GWP-total, A1–A3 | −0.143 kgCO₂e | Cradle-to-gate result, including the biogenic carbon stored in the straw |
GWP-GHG, A1–A3 | +0.307 kgCO₂e | The same stages with biogenic carbon left out: the fossil footprint of making the block |
GWP-total, C1–C4 | About +0.010 kgCO₂e | Demolition, transport, waste processing and landfill at end of life |
GWP-total, D | −0.018 kgCO₂e | Stubble-burning emissions avoided, reported separately and not netted off |
Reading the results
Two readings follow. Cradle to gate, each tonne of Agrocrete® mix stores about 143 kg more CO₂e than its manufacture emits, which GreenJams rounds to −0.14 kgCO₂e/kg. Adding the end-of-life stages gives about −0.13 kgCO₂e/kg, so the product stays carbon-negative across every stage the EPD declares. The avoided burning in module D is a further benefit, but EN 15804 keeps it out of the headline figure.
By mass, the mix is 9% straw, 35% fly ash, 17% ground slag, 2% alkali salts and 37% water, so just over half of it (52%) is recycled industrial by-product. The EPD notes that fly ash alone accounts for about 85% of the fossil emissions. For the story of how the EPD was prepared and verified, read World's First Verified Carbon-Negative Construction Block.
What it means for a wall or a home
The EPD gives a figure per kilogram, so the carbon a wall stores depends on how much Agrocrete® it contains. The Agrocrete® catalogue declares a dry density of 800–1,000 kg/m³. Multiplying that by the EPD's −0.143 kgCO₂e/kg gives roughly 115–145 kg of CO₂e stored per cubic metre of block, cradle to gate.
Worked example: one square metre of wall
A 200 mm thick wall contains 0.2 m³ of blockwork per square metre of face. If that were all solid block, it would hold 160–200 kg of Agrocrete® and store roughly 23–29 kg of CO₂e per square metre. Mortar joints, plaster and the cores of hollow blocks all change the figure, so treat this as an upper estimate for solid blockwork, not a design value.
For comparison, a 2023 study of a brick plant in Varanasi by Dr Sameer Maithel measured about 199 kg of CO₂ per cubic metre of solid burnt clay brick, cradle to gate (reported in TheAPN). On the same basis, a 200 mm solid brick wall would emit around 40 kg of CO₂ per square metre instead of storing it.
Case study: a family home in Gudivada
Real projects make the numbers concrete. In Gudivada, Andhra Pradesh, a 2,000 sq ft family home was built with 1,100 Agrocrete® blocks. Its walls store 2.1 tonnes of CO₂, about 1.9 kg per block. The family lives there without air conditioning, and the builders used their usual mortar, plaster and tools. Storage is a side benefit of a working wall: GreenJams declares 3.5× better thermal insulation than conventional walls and 4 hr+ fire resistance.
At industrial scale, ITC's 1.8 km perimeter wall in Kapurthala, Punjab used 28,000 Agrocrete® Solid Blocks. It stores 38.5 tonnes of CO₂, and using crop residue while replacing conventional masonry avoided a further 130.76 tonnes. For a thought experiment at skyscraper scale, see how the Empire State Building could have stored carbon had it been built with Agrocrete®.
Limits and caveats
A carbon-negative label is only useful if you know what sits behind it. The EPD is a strong foundation, but it answers a narrow question about one kilogram of material. These are the points we think every architect and specifier should weigh before relying on the figures above.
The negative figure depends on biogenic carbon. Leaving out the carbon stored in the straw, making Agrocrete® emits about 0.30 kgCO₂e/kg. The block is carbon-negative because the stored carbon outweighs that, not because its manufacture is emission-free.
Storage lasts as long as the material does. The EPD assumes 85% of demolished blocks are recycled into aggregate or pavers and 10% are landfilled. If the residue were later burned or left to decay, its carbon would return to the air.
It covers the block, not the building. Transport to site, construction, mortar, plaster and the use stage were not assessed. A whole-building assessment still needs those numbers: see our guide to embodied carbon in buildings.
The storage per kilogram is modest. At about 0.14 kg of CO₂e per kg, Agrocrete® is not a substitute for cutting emissions elsewhere. Much of its benefit comes from replacing high-carbon masonry while storing some carbon as well.
Compare like with like. EPDs are only comparable when they follow the same rules, here EN 15804+A2. This EPD runs until 20 October 2027 and will need renewing.
The bottom line
Within those limits, the evidence is clear: a wall made with crop residue can hold carbon that would otherwise return to the air within a season. Compare Agrocrete® Solid Blocks and Agrocrete® Hollow Blocks, see how they stack up in AAC Blocks vs Red Bricks vs Agrocrete®, or get a sample.
Agrocrete® Blocks
