# How much CO2 does a hot mix asphalt plant emit per tonne, and does warm mix cut it?

Canonical: https://senseible.earth/answers/hot-mix-asphalt-plant-co2-per-tonne

Work it out as burner fuel per tonne x its factor, plus plant electricity or DG diesel per tonne, from a month of fuel bills and tonnes produced. Warm mix usually cuts it, because mixing runs at lower temperature and the dryer burns less fuel, but only a like for like comparison at the same aggregate moisture proves it.

## Where a hot mix plant's emissions come from

- The dryer drum burner, fired on furnace oil, LDO, diesel or gas, heating and drying the aggregate. This is usually the largest part.
- Heating bitumen tanks, by thermic fluid heater or burner.
- Electricity or DG diesel for motors, fans, conveyors and the baghouse.
- Upstream, outside the plant: bitumen, aggregate and transport, which belong in a product footprint or EPD.

## Why moisture matters more than anything

Every percent of water in the aggregate has to be boiled off in the drum. Wet stockpiles after rain can raise fuel per tonne a lot. Covering stockpiles, sloping them to drain and drawing from the dry face are often the cheapest fuel savings at a plant.

## What warm mix changes

Warm mix asphalt uses additives or foaming to mix and lay at a lower temperature than hot mix. In India the reference is IRC:SP:101-2014, the Indian Roads Congress's interim guidelines for warm mix asphalt. The fuel saving depends on how far the temperature drops and on moisture, so measure fuel per tonne on warm mix and hot mix runs with similar aggregate, and add the additive's own footprint if you report a product figure.

## How to report it

- Plant Scope 1: burner and heater fuel, DG diesel.
- Scope 2: grid electricity at 0.710 kg CO2 per kWh.
- Per tonne: total CO2 / tonnes of mix sent out in the same month.
- For a tender or EPD, add bitumen and aggregate upstream and follow ISO 21930 or EN 15804, the rules construction product EPDs use.

## Illustrative example: one month, 20,000 t of mix

- Burner furnace oil: 150,000 litres x 2.97 = 445,500 kg CO2
- Grid electricity: 60,000 kWh x 0.710 = 42,600 kg CO2
- DG diesel: 10,000 litres x 2.68 = 26,800 kg CO2
- Total: 514,900 kg; per tonne: 514,900 / 20,000 = 25.7 kg CO2
- Warm mix month at 6.6 litres per tonne instead of 7.5 (assumed): 132,000 litres x 2.97 = 392,040 kg, saving 53,460 kg, about 2.7 kg CO2 per tonne

All inputs are illustrative; use your own bills, tonnes and moisture records.

## What Senseible does here

Senseible reads burner fuel, diesel and electricity invoices into a monthly record with factors shown, so CO2 per tonne follows once you add tonnes produced.

- [Construction industry](https://senseible.earth/industries/construction)
- [Diesel emission factor](https://senseible.earth/emission-factors/diesel)
- [Furnace oil emission factor](https://senseible.earth/emission-factors/furnace-oil)
- [How to get an EPD](https://senseible.earth/answers/how-to-get-an-epd-for-indian-exports)

Sources: [ISO 21930:2017, core rules for environmental product declarations of construction products](https://www.iso.org), [2006 IPCC Guidelines, Volume 2 Energy (fuel CO2 defaults)](https://www.ipcc-nggip.iges.or.jp/public/2006gl/vol2.html), [CEA CO2 Baseline Database, version 21.0](https://cea.nic.in/cdm-co2-baseline-database/?lang=en)

Last reviewed 2026-10-18.