Recycled Aggregate Concrete Lab (2D)

Mix Design

Recycled aggregate (RCA) 30%

Water / cement ratio 0.45

Curing time 28 d

Ready — press Run Compression Test

Live Readouts

Predicted f'c

— MPa

Applied stress

0.0 MPa

Water absorption

— %

CO₂ saved / m³

— kg

Virgin aggregate RCA (old mortar) Cracked

How it works

Replacing virgin quarried stone with crushed, screened old concrete (RCA) diverts demolition waste from landfill and cuts quarrying, but each RCA particle carries a shell of old, porous cement mortar attached to it — that shell is the whole story of this simulator.

Baseline strength (Abrams' law):
  f'c0 = 96.5 / 8.5^(w/c)         [MPa]

RCA strength reduction (empirical, ~literature trend):
  f'c(r) = f'c0 · (1 − 0.0022·r)   r = % RCA replacement

Curing gain (ACI 209 form, relative to 28-day):
  gain(t) = t / (4 + 0.85·t)       t = days

Predicted strength:
  f'c(r,t) = f'c(r) · gain(t)

Water absorption (porosity proxy):
  WA(r) = 1.0% + 0.045·r

RCA % — old adhered mortar is more porous and weaker than the parent rock, so strength falls and water absorption rises roughly linearly with replacement ratio.
Water/cement ratio — the classic Abrams' law driver: less water per unit cement gives a denser, stronger paste.
Curing time — cement hydration keeps adding strength for months; the ACI 209 curve captures the fast early gain and the slow long tail (gain(28d) ≈ 1.0, confirmed by direct calculation, so "predicted strength" reads as the familiar 28-day-equivalent number).
Run Compression Test — a virtual press ramps load on the specimen cross-section; when applied stress reaches the predicted f'c the specimen cracks and the stress-strain curve on the right rolls over, exactly like a real cylinder test.

Real building codes (EN 206, ACI 555) cap structural RCA replacement around 20–30% for exactly this reason — beyond that, either the mix has to be over-designed (lower w/c) or the material is limited to non-structural fill and pavement base.

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