Buildings & infrastructure · START WITH SOMETHING FAMILIAR
What can move through a seemingly solid material?
The wall joins aggregate with a hydrated binder. Water in connected pores can transport dissolved species even though the material looks solid. A selected diffusion coefficient explores one transport consequence; it cannot establish the wall’s composition, curing quality or damage. A real inspection would connect observations to a named mixture and location.
For the named chemistry example, tricalcium silicate, Ca₃SiO₅, reacts with water and forms calcium silicate hydrate and calcium hydroxide. Calcium and silicon belong to compounds; there are no droplets of elemental calcium or silicon inside the binder.
Explore the model (optional)
EXPLORE THE MODEL
Inspect the structure; select a site or component for its label.
Assumed transport coefficient and fixed surface concentration; initially zero interior concentration. No reactions, binding, convection, finite back face or aging. This does not predict a concrete structure’s service life.
C / Csurface = erfc[x / (2√Dt)]
| Depth below exposed face (mm) | Normalized concentration |
|---|---|
| 0 | 1 |
| 3 | 0.388 |
| 6 | 0.085 |
| 9 | 0.01 |
| 12 | 5.600e-4 |
| 15 | 1.612e-5 |
| 18 | 2.277e-7 |
| 21 | 1.565e-9 |
| 24 | 5.208e-12 |
| 27 | 8.356e-15 |
| 30 | 6.446e-18 |
The concentration is prescribed at the exposed surface and falls with depth. Increasing elapsed time or D spreads this ideal profile farther into the material. A diffusion length is not a crack depth or a failure boundary.
Assumed transport coefficient and fixed surface concentration; initially zero interior concentration. No reactions, binding, convection, finite back face or aging. This does not predict a concrete structure’s service life.
MAKE THE CONNECTION
What does the calcium in this binder represent?
HISTORY THROUGH EVIDENCE
The history of concrete includes deliberate ways to keep water available inside the material.
Explore how the evidence changed the explanation →MAKE A MATERIAL DECISION
Authored design scenario: A trial low-water concrete wall mixture is prone to early shrinkage cracking. The team can redesign the aggregate blend before casting.
Choose a candidate that addresses internal water availability.
Why could a nominally dense concrete still transport salts quickly after cracking?
NIST’s bridge work connects internal curing with reduced early cracking and pathways by which deicing salts reach reinforcing steel.
Explore this connection →ANOTHER HISTORICAL INVESTIGATION
1756–1759 · Reveal observations and weigh an interpretation.
Open the evidence desk →Mineral phases and pore pathways together matter in a cement-based material.
Compare material behaviorTransport in concrete and slip in metals are distinct mechanisms behind large-scale behavior.
