Calcium silicate hydrate(C-S-H)

Insights into the Very Early Nucleation and Crystallization

C-S-H or calcium silicate hydrate presents the main hydration product of ordinary Portland cement (OPC). C-S-H is generated from the hydration of the dicalcium silicate (C2S) and tricalcium silicate (C3S) phases via a dissolution-precipitation mechanism and presents the binding phase which is responsible for the strength and durability properties in hardened cement.

Generally, C-S-H exhibits a low crystallinity and typically a Ca/Si molar ratio of ~ 1.6 - 1.8 in hardened cement. The layered structure of C-S-H consists of linear silicate chains which are aligned in “dreierketten” sequences and share oxygen atoms with calcium ions in the same plane.

In order to be able to observe its very early nucleation, C-S-H was synthesized from Ca(NO3)2 and Na2SiO3 via the co-precipitation method. The early nucleation and crystallization of the synthesized C-S-H were observed via TEM imaging

After 5 minutes of reaction, pure C-S-H particles exhibit a globular morphology, with diameters in the range of ~ 40 - 60 nm. For the synthesized C-S-H, the transformation from a globular to a foil-like morphology had already started 15 minutes after the Ca(NO3)2 and Na2SiO3 solutions had been combined. After 1 hour, the C-S-H globules had completely disappeared while a network of C-S-H nanofoils with lengths of ~ 150 nm and a thickness of ~ 5 nm was found.

The globular precursor of C-S-H exhibits a highly disordered structure containing branched silicate chains. Whereas the C-S-H foils formed after the conversion show a layered structure of semi-crystalline C-S-H containing non-branched silicate chains.

This shows that synthetic C-S-H follows a non-classical nucleation mechanism where the morphology of the precursor significantly differs from that of the final bulk material.

Related articles:

Issue 02/2019 Concrete without cement

Geopolymer Concrete for the Precast Construction

The use of alkali activated binder systems becomes increasingly important in concrete technology. Besides the ecological aspects, especially the reduction of the CO2 emissions when producing the...

more
Issue 02/2016 What can we learn from this?

Cement hydration in a zero-gravity environment

The reaction of Portland cement with water (the hydration of cement) presents an extremely complex process involving dissolution, crystallization, recrystallization and precipitation steps as well as...

more
Issue 02/2015 BASF SE

Rapid hardening, also in wintry temperatures

Cold, snow and ice are special challenges that building contractors face in winter. Special concrete admixtures from Master Builders Solutions makes casting possible, also in wintry temperatures. At...

more
Issue 01/2013

C-S-H: A state-of-the-art concept to accelerate concrete hardening; Part I

Mixing the concrete, transporting it to the job site, pouring it into the formwork, flicking a switch, stripping the formwork – and that’s it: Generations of researchers and concrete technologists...

more
Issue 02/2016 Influence of processes, raw materials, additives, curing conditions, securing of product layers, and weather protection

Protection of concrete products to prevent efflorescence

Efflorescence that occurs on products made from low-slump concrete is not only an unsightly phenomenon for the client but also a significant cost driver for the producer when it comes to complaints...

more