Portlandite
Definition
Calcium hydroxide (Ca(OH)2) crystallised during cement hydration; a bright birefringent phase visible in thin section that dissolves progressively as concrete carbonates, providing a rough age indicator.
- Chemical formula
- Ca(OH)2
- Formation process
- Crystalline hydration by-product of Portland cement
- TGA dehydration temperature
- Approximately 450°C
- Carbonation product
- Converts to calcite (CaCO3) via atmospheric exposure
Common questions
What is portlandite and where does it come from?+
Portlandite is calcium hydroxide (Ca(OH)2) formed when Portland cement hydrates. It is a crystalline phase that appears bright and birefringent when viewed in thin section under a microscope.
How can portlandite help date concrete or cement?+
Portlandite converts to calcite (CaCO3) when exposed to atmospheric carbon dioxide through carbonation. As concrete ages and weathers, portlandite dissolves progressively, making its presence and degree of conversion a rough indicator of age.
How is portlandite detected in forensic analysis?+
Petrographers examine thin sections under polarized light microscopy to spot portlandite's characteristic bright, birefringent crystals. Chemists can also use thermogravimetric analysis (TGA), where portlandite dehydrates at about 450°C, creating a measurable thermal signature.
Related terms
- Ettringite
- A calcium sulfoaluminate hydrate that forms early in cement hydration and can re-form later from delayed sulfate attack; its presence or alteration...
- Clinker
- The nodular intermediate product of Portland-cement manufacture, consisting of C3S, C2S, C3A and C4AF mineral phases before grinding.
- Portland Cement
- A hydraulic binder produced by firing calcium and silica sources at 1450°C; the four clinker phases (C3S, C2S, C3A, C4AF) hydrate on...
- Aggregate
- The granular filler (sand, gravel, crushed rock) that occupies 60-80% of a concrete volume; its mineralogy, grain shape, and size distribution are...
- Alite (C3S)
- Tricalcium silicate, 3CaO.SiO2. Dominant clinker phase (50 to 70 percent). Hydrates fast, gives early strength up to 28 days.
- Aluminate (C3A)
- Tricalcium aluminate, 5 to 10 percent. Reacts violently with water, attacked by sulphate. SRC cement is low in C3A.
- ASTM C150
- US standard specifying Portland-cement composition limits and performance requirements by type (I through V); referenced in forensic mineral-phase characterisation.
- Belite (C2S)
- Dicalcium silicate, 2CaO.SiO2. 15 to 30 percent. Hydrates slow, gives long-term strength beyond 28 days.
- C-S-H Gel
- Calcium silicate hydrate, the main hydration binder. Amorphous, broad hump on XRD.
- Calcium Silicate Hydrate (C-S-H)
- The principal binding phase produced when Portland cement reacts with water; a gel-like material that gives concrete most of its strength and...
- Calcium Sulphate Hemihydrate
- CaSO4 . 1/2 H2O; produced by heating gypsum, rehydrates to gypsum on setting; the basis of plaster of Paris and most interior...
- Carbonation Front
- The boundary in concrete where atmospheric CO2 has converted portlandite to calcite; the depth of this front (measured in millimetres) is used...
Explained in these topics
- Cement, Mortar and Concrete: Composition and Forensic AnalysisCalcium hydroxide Ca(OH)2, crystalline hydration by-product. Dehydrates at about 450°C on TGA.
- Cement, Plaster and Building-Material EvidenceCa(OH)2; a product of Portland-cement hydration. In aged cement it converts to calcite (CaCO3) by atmospheric carbonation, providing a rough age indicator.
- Concrete, Mortar, and Cement as EvidenceCalcium hydroxide (Ca(OH)2) crystallised during cement hydration; a bright birefringent phase visible in thin section that dissolves progressively as concrete...