C-S-H Gel
Definition
Calcium silicate hydrate, the main hydration binder. Amorphous, broad hump on XRD.
- Full name
- Calcium silicate hydrate gel
- Role
- Main hydration binder in cement paste
- Structure
- Amorphous, non-crystalline
- XRD signature
- Broad hump rather than sharp peaks
Common questions
Why does C-S-H gel's amorphous nature matter for XRD analysis?+
X-ray diffraction identifies crystalline phases by their sharp diffraction peaks. Because C-S-H gel lacks long-range crystalline order, it shows only a broad diffuse hump, so examiners rely on other techniques such as SEM imaging or thermal analysis to characterise it directly.
What does the appearance of C-S-H gel reveal about a concrete sample's history?+
Its microstructure and density under SEM reflect the original water-to-cement ratio and curing conditions, which can help a forensic examiner assess whether a concrete pour or repair matches claimed specifications or timelines in a construction failure case.
Related terms
- 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.
- Belite (C2S)
- Dicalcium silicate, 2CaO.SiO2. 15 to 30 percent. Hydrates slow, gives long-term strength beyond 28 days.
- Clinker
- The nodular intermediate product of Portland-cement manufacture, consisting of C3S, C2S, C3A and C4AF mineral phases before grinding.
- Ettringite
- A calcium sulfoaluminate hydrate that forms early in cement hydration and can re-form later from delayed sulfate attack; its presence or alteration...
- 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...
- Portlandite
- Calcium hydroxide (Ca(OH)2) crystallised during cement hydration; a bright birefringent phase visible in thin section that dissolves progressively as concrete carbonates, providing...