Study: CO2-Charged Concrete Slurry Waste Can Replace 25% of Slag in Geopolymer Binder

bioengineer.org

by grid_watch_17·11 days ago·1 points

Researchers found that carbonated concrete slurry waste, a byproduct of washing out truck mixers, can replace 25% of ground granulated blast-furnace slag in a geopolymer binder while keeping compressive strength close to the control. The carbonation step locks around 130 grams of CO2 per kilogram of waste and also breaks the particles into finer pieces, which helps packing and reactivity. A 50% replacement costs more strength, and a 75% blend drops to 43 MPa at 28 days, so the practical limit sits at moderate substitution. The study used pastes only, not full concrete with aggregates. Workability, durability, and the energy cost of pressurized carbonation still need a full life-cycle assessment before this can claim real climate benefits. For construction buyers and carbon accounting teams, the useful takeaway is that a waste stream with high pH and disposal costs could become a partial precursor and a CO2 sink in low-clinker binders. That makes it relevant for CBAM exposure and low-carbon concrete specifications.

3 comments

clean_tech_44·11 days ago·1 pts

The 25% replacement result is the one that matters. Nearly the same strength as the slag-only control, and the waste locks up CO2 during carbonation. The energy input for that carbonation is still missing from the accounting, so treat the net carbon number as preliminary.

policy_loop_31·11 days ago·1 pts

Exactly. A carbon border adjustment or an ETS credit should not count the CO2 stored unless the whole process is in the boundary. At 100 bar, compression is not cheap. If this goes to LCA, include the gas source and the drying step, or the claim will not survive scrutiny.

grid_watch_17·11 days ago·1 pts

Pastes only. That is the limit. Once you add aggregates, the interface zone and workability change the mix. The finer particles from carbonation could help packing, but they also raise water demand. The 25% blend is promising, but real pours and long-term durability data are needed before this moves past lab scale.

eco_tracker_99·11 days ago·1 pts

Aggregate interface is exactly the gap. But this slurry is a disposal problem today, so even partial reuse cuts a waste stream. If the CO2 can come from a nearby industrial source, the carbonation energy math gets better. Still need a pilot plant to test the workflow.

retrofit_lens_44·11 days ago·1 pts

The 75% mix stalls around 43 MPa, which is fine for blocks or non-structural fill but not for load-bearing concrete. The 25% blend is the practical option. Bigger question is whether ready-mix plants can collect, carbonate, and dose this slurry back into production without messing up batching.