Application Guide
How mercury intrusion and gas adsorption are used to study the pore structure of cement paste, mortar, and concrete — and why sample drying and the ink-bottle effect dominate the uncertainty.
Most durability problems in concrete — chloride-induced corrosion, carbonation, sulfate attack, freeze–thaw damage — depend on how easily water and dissolved ions move through the hardened cement paste. That transport is controlled mainly by the connected capillary pores, which shrink and become less connected as hydration proceeds, as the water-to-cement ratio is lowered, and as supplementary cementitious materials (fly ash, slag, silica fume) react.
| Pore class | Approximate size | Notes |
|---|---|---|
| Gel pores (interlayer and small gel pores in C-S-H) | below ~10 nm | Part of the C-S-H structure; little effect on permeability; sensitive to drying. |
| Capillary pores | ~10 nm to ~10 µm | Remnants of the original water-filled space; govern permeability and diffusivity. |
| Entrained air voids | roughly 10 µm to 1 mm | Deliberately introduced for freeze–thaw resistance; characterized by microscopy (ASTM C457), not MIP. |
| Entrapped air, compaction voids, cracks | > 1 mm | Defects; best assessed by imaging. |
Mercury intrusion is the most widely used laboratory technique for cement-based materials because it covers most of the capillary pore range in a single test. The most useful outputs are the total intruded porosity and the threshold (critical) pore diameter — the size at which mercury first percolates through the sample, seen as the steep rise in the cumulative curve. Lower w/c ratios, longer curing, and pozzolanic additions all shift the threshold diameter to smaller sizes.
| Test | Standard | What it measures |
|---|---|---|
| Mercury intrusion porosimetry | ISO 15901-1:2016 (general MIP procedure); ASTM D4404 for soil and rock | Pore-entry size distribution, intruded porosity |
| Density, absorption and voids | ASTM C642 | Bulk density and permeable void volume by boiling-water saturation |
| Air-void system | ASTM C457 | Air content, spacing factor, specific surface of air voids (microscopy) |
| Chloride ion penetrability | ASTM C1202 | Charge passed in a 6-hour electrical test (an indirect indicator; not a pore-size test) |
| Freeze–thaw resistance | ASTM C666 | Durability factor after rapid freezing and thawing cycles |
There is no ASTM standard specific to MIP of concrete; laboratories adapt ISO 15901-1 and report contact angle, surface tension, drying method, and sample size alongside the results.
Use the calculators to convert test pressures to pore sizes, or email a short description of your sample and what you need to measure.