Let's Set the 3D Gold Standard

Mix Design for 35-40°F Mix proportions (per m³): Use a high-cement, low water‐to‐cement (w/c) mixture for rapid strength gain and pumpability. For example, start with ~600 kg Type I/II Portland cement, ~60 kg silica fume (≈10% of cement), and ~1200 kg fine silica sand (0–4 mm). Add ~180 L water (w/c≈0.30) to achieve a thick but extrudable consistency cdn.ymaws.com. Incorporate a polycarboxylate superplasticizer (~0.5–1.0% by cement weight, e.g. BASF MasterGlenium 7500) to maintain flow at low w/c cdn.ymaws.com. The binder-to-sand ratio (~0.5) and low w/c ensure good buildability cdn.ymaws.com.

Cold‐weather measures: Heat the mix water (e.g. to ~70°C) so that the fresh concrete is ≈60–70°F at placement folsomreadymix.com. Use insulating blankets or tents on printed layers until they reach ~500 psi folsomreadymix.com. Employ set accelerators: non-chloride additives (e.g. SikaSet® NC) are safest with steel, but calcium chloride (≤2% by cement) is very effective in cold (it “warms” the mix and speeds hydration) glchloride.comgcpat.com. For example, adding 2% CaCl₂ can halve set time and achieve 3-day strength in 1 day glchloride.com. Proprietary accelerators (like PolarSet®, Daracem®) can also extend workability down to 20°F gcpat.com. Air‐entrainment: Include a small air-entraining admixture (≈0.05–0.10% by cement, e.g. MasterAir AE-200 or Sika Air) to entrain ~4–6% air for freeze–thaw durability mdpi.com. This level of air (as shown by 0.06% AEA yielding ~14% air in tests) protects against F/T damage without excessive strength loss mdpi.com. Optionally add a viscosity modifier (cellulose ether) to prevent segregation. Cure in still, frost-free air; with hot-mix and accelerators, concrete can gain ≥500 psi in ~24 h even near freezing folsomreadymix.com. Final mix (example, by mass): Cement ~600 kg, silica fume ~60 kg, fine sand ~1200 kg, water ~180 L, superplasticizer ~3–6 kg, CaCl₂ solution (30%) ~12 kg (≈2% cement), air-entrainer ~0.3 kg (≈0.05% cement). Use Type I/II cement (or Type III for extra early strength, per ACI 306) gcpat.com. This mix balances pumpability (via SP and fine sand) with cold‐weather cure (via heated water, accelerator and entrained air) cdn.ymaws.comgcpat.com.

Sourcing of Materials
Portland cement SAKRETE 94 lb Portland Cement (Type I) homedepot.com 94 lb (42.6 kg) bag (Home Depot)
Silica fume Trinic Z3-95 Silica Fume trinic.us 55 lb bag (≈25 kg)
Fine sand SAKRETE 60 lb Multi-Purpose Sand homedepot.com 60 lb bag
Superplasticizer BASF MasterGlenium 7500 (full-range water reducer) store.concreteexchange.com 3 gal jug (Concrete Exchange)
Accelerator ChemMasters FreezBan (CaCl₂ accelerator) altrarental.com 5 gal container
Air-entrainer Sika® AIR (air-entraining admixture) usa.sika.com 55 gal drum

Each product above is available through construction suppliers or online distributors (e.g. Home Depot for cement/sand homedepot.comhomedepot.com; specialist chemical suppliers for admixtures store.concreteexchange.comaltrarental.comusa.sika.com). Packaging sizes are chosen for on-site use (e.g. 55 gal drums or 5 gal pails).
‍Sources:  Guidelines and data from cold‐weather concreting (ACI 306) and 3DCP research were used to set proportions folsomreadymix.comcdn.ymaws.com. Details on accelerators and admixtures are from manufacturer literature glchloride.comgcpat.comaltrarental.comusa.sika.com. The table lists concrete products and vendors for Oregon delivery.

Application Tips: Print Layer Protection: Cover each print with thermal blankets immediately to retain heat. Monitor Temperature: Ensure concrete temperature remains above 40°F during the first 24 hours. Curing Time: With proper accelerators, concrete can reach 500 psi within 24 hours, even in near-freezing temperatures.
Compressive Strength Estimates:
‍1 Day (24 hours): ~500–700 psi
‍3 Days: ~1500–1800 psi
‍7 Days: ~3000–3500 psi
‍28 Days: ~5000–6000 psi
6 to 10 minutes layer time