Civil Engineering Reference
In-Depth Information
2.1.8
Alkali sulfates
The following alkali sulfates may be present in Portland clinkers:
• K
2
SO
4
(abbreviation K ; arcanite);
• K
2
Ca
2
(SO
4
)
3
(abbreviation KC
23
; calcium langbeinite);
• K
3
Na(SO
4
)
2
(abbreviation K
3
N
4
; aphtitalite).
Upon mixing with water these phases are rapidly dissolved in the liquid phase, and their
SO
4
2−
ions participate in the formation of SO
3
-bearing hydrate phases.
2.1.9
Composition of Portland clinker and Portland cement
In ordinary Portland clinker (corresponding to ASTM type I Portland cement) tricalcium
silicate is the most abundant phase, present in amounts between about 50% and 70%.
Dicalcium silicate usually constitutes 15-30% of the clinker. Typical amounts of
tricalcium aluminate are 5-10%, and of the ferrite phase 5-15%. In special Portland
clinkers the individual clinker phases may be present in increased or reduced amounts, or
may be absent entirely. Free lime, free MgO and alkali sulfates are minor constituents of
Portland clinker that are present only in small amounts or may be absent entirely.
Calcium sulfate is only rarely a constituent of Portland clinker, but is interground in
limited amounts with it, to obtain Portland cement. In Table 2.1 different types of
Portland cement are compared.
The composition of Portland cement raw meals and Portland clinkers can be
characterized by the mutual ratio of the main oxides present. The following ratios are
those most widely employed (all amounts of oxides are given in wt%):
Table 2.1
Types of Portland cement.
Designation
C3S
C2S
C3A
C4AF
Other characteristics
Ordinary PC
High-C
3
S PC
High-C
2
S PC
High-C
3
A PC
Low-C
3
A PC
Low-iron PC
High-iron PC
Ferari cement
A/F=0.64
