cement in ternary system

So called ternary systems are being used for several decades by the construction chemistry predominantly in making self-‐leveling screeds , under-‐ and over layments – non shrink grouts , repair mortars etc.

They are based on mixing calcium , alumina and sulphate together to obtain;

ettringite = C4A3Š 3CaAl2O3 � 3CaSO4 � 32H2O

The effect on the binder;

•  rapid set

•  high early strength

•  shrinkage compensation

•  fast drying

•  low alkali

•  no effluoresence

•  improved sulphate resistance

what is needed to form C4A3Š ?

what is needed to form C4A3Š ?

•  aluminium •  sulphate •  calcium

Calumex

Anhydrite, hemi-‐hydrate, gypsum

Portlandcement, calcium-‐oxide/-‐hydroxide

a fibrous needle shaped crystal , holding 32 water molecules

what is to be considered ?

PORTLANDCEMENT Content of •  C3A tri-‐calcium aluminate •  amount of free lime ( fCaO ) •  type and amount of sulphate added

CALCIUM SULPHATE •  hemi-‐hydrate •  micronized gypsum •  anhydrite

choice of type of CALUMEX CALCIUM SULPHO ALUMINATE CEMENT Content of •  CALUMEX CSA – ground clinker ;

•  Al2O3 content ~ 46 % •  SiO2 ~ 3 % •  fCaO 0 •  CaSO4 ~ 7,5 % •  CALUMEX Quick •  Al2O3 content ~ 32 % •  SiO2 ~ 3 % •  fCaO 0 •  CaSO4 ~ 20 %

•  BELICEM •  Al2O3 content ~ 32 % •  SiO2 ~ 10 % •  fCaO 0 •  CaSO4 ~ 10 %

why is sulphate added to OPC ? Portlandcement mainly forms minerals;

•  C3S – alite •  C2S – belite •  C3A – tri-‐calcium aluminate

C3A is the most reactive phase – it forms with water rapidly C4AH crystals at the surface of C3S – causing rapid setting of the cement To retard the quick setting gypsum or anhydrite or a combination of both is added at the grinding stage of the cement clinker. As this generates heat sometimes part of the gypsum is converted to hemi-‐hydrate. The sulphate reacts with the alumina and enrobes a layer of ettringite around the C3A particles. Thus preventing them to go in solution quickly.

binary system CSA+OPC

When CSA cement is used most of the sulphate of the OPC is absorbed immediately by the additional aluminates. It therefor cannot act as a retarder of the C3A phase leading to rapid setting of the matrix. The strength development however is limited because still the amount ettringite is relatively low. Also the long term strength is reduced because C3A is putting a gel around the C3S and C2S phases preventing a regular hydration.


CSA is more soluble than anhydrite but less soluble than gypsum and hemi-‐hydrate. So when Calumex is mixed with an OPC that contains anhydrite – Calumex will dissolute quickly enough to react with the sulphate ions released by anhydrite thus preventing them to retard the C3A phase of the OPC, giving rapid set at relative low dosage. When on the other hand an OPC is used containing hemi-‐hydrate – the dissolution is higher, sulphate ions are released more quickly and react with the C3A. In this case a higher dosage is needed to give the same acceleration.


In any case if an OPC is used with a higher C3A content it will contribute to a rapid set. A higher free lime content of the OPC – and/or an addition of calcium ions (calcium oxide/hydroxide) will accelerate the formation of ettringite. It is essential to choose the right OPC for the intent use of the mortar In any case a stable cement is essential – any variation in free lime content and amount and type of calcium sulphate (di-‐hydrated) asks for re-‐establishing the amount of CSA to be used.

ternary system CSA+OPC+additional CŠ

When additional calcium sulphate is added to a blend of CSA and OPC more ettringite crystals are formed i.e. a higher initial strength is obtained. Ettringite is the first strength found CALUMEX CSA generally releases more quickly its alumina ions compared to other sources of calcium aluminate. Slow soluble anhydrite is by far the preferred source of sulphate in a Calumex system – aluminate phases go in solution first allowing to absorb all of the sulphate (even if the OPC brings hemi-‐hydrate) and converts it into ettringite crystals.


Calumex gives no lime nor reactive silicates which guarantees long storage. The lime needed to form ettringite is taken from the Portlandcement. As lime is taken out of the equation – normally acting as a gel preventing silicate and aluminate phases to go in solution – this further contribute to the increase of the strength. In case more soluble types of calcium sulphate are being used (i.e. hemi-‐hydrate –α or β or gypsum) because of their higher solubility – they will react only with the aluminate phases. It will give acceleration of the set – by early formation of ettringite – but to a lesser extend compared to anhydrite The higher solubility leads to slower reaction because it will prevent the C3A to react.


To overcome this effect a higher dosage of CSA is needed An ideal binder system combining all elements of rapid set, high early strength and shrinkage compensation could be 2 parts of OPC CEM I 42,5R to 1 part of Calumex Quick.

binary system ACA+CŠ

An ideal binder system is a combination of amorphous calcium aluminate and calcium sulphate – without addition of OPC. As the CaO to Al2O3 ratio is to the advantage of calcium and the main phase formed by the alumina phase is C12A7 – the reaction with sulphate is much faster and more C4A3Š is formed without the further addition of lime (i.e. OPC) The reaction in short is ;

C12A7+3CŠ C4A3Š + AH3 When used as an addition to Portlandcement the excess of lime will give an instant setting of the binder , and the high amount of ettringite formed gives an extreme fast strength development. There is no risk on “conversion” of the hydrates in time.

conclusion

CALTRA offers a wide range of calcium aluminate , calcium sulpho aluminate and amorphous calcium aluminates giving formulators the complete freedom to choose the correct type to satisfy their needs. CALTRA continues to develop binders and binder systems for specific applications. Some of the latest ; CALUMEX WHITE – a white CSA for decorative screeds , terrazzo , decorative prefab concrete – GRC panels , tile grouts – natural stone adhesives etc. CEM-‐FLUX – a cement designed for the RMC plants as a ready binder for pumpable screeds ULTRA-‐FLUX – a cement for decorative overlayments

R&D

CALTRA has its own r&d lab – ready to answer any queries you may have. To further improve or optimize existing products or help develop new products. We work closely together with our customers in strict confidentiality – to mutual benefit.

cement in ternary system

Technology