Is site-mixed concrete higher or lower carbon than ready-mix concrete?
Start with the cement per cubic metre in each mix, times the supplier's factor. Then add mixing energy: site mixer diesel at 2.68 kg CO2 per litre, and for ready mix the plant electricity and truck mixer diesel.
What decides it
- Cement content per cubic metre, from the mix design or batch sheets.
- Use of fly ash or slag in place of some cement.
- Mixing energy at site or plant.
- Delivery distance for ready mix.
Evidence for each
Ready mix suppliers can give batch tickets with cement and blend per load. For site mixing, divide cement bags used by cubic metres poured over the same period.
Which scope
A site mixer the contractor runs is Scope 1. Bought ready mix, including its plant and delivery, is Scope 3 purchased goods.
Worked example: per cubic metre (illustrative inputs)
- Site mixer: 0.5 litre diesel per m3 x 2.68 = 1.34 kg CO2 per m3
- Ready mix: plant 2 kWh x 0.710 = 1.42 kg, plus truck mixer 1 litre x 2.68 = 2.68 kg, so 4.10 kg CO2 per m3
- Mixing difference: 4.10 minus 1.34 = 2.76 kg CO2 per m3
- Cement: site mix 340 kg vs ready mix design 320 kg per m3, a 20 kg difference
- Cement difference: 20 kg x the cement factor per kg from the supplier
Values are illustrative; use batch tickets, cement issue records and the cement supplier's factor.
What Senseible does here
Senseible reads diesel invoices, fuel slips and site electricity bills into a dated, fingerprinted record per project, so a contractor can hand a client Scope 1 and 2 figures with the document behind each line. Estimates from hours or distance are labelled as estimates.
Sources: GHG Protocol Corporate Value Chain (Scope 3) Standard, IPCC 2006 Guidelines, Volume 2 Energy (fuel defaults), CEA CO2 Baseline Database, version 21.0
Last reviewed 2026-10-21.