1) Cement is a substance used to bind together sand and aggregates like stone. Hydraulic cement forms water resistant products when mixed with water. 2) The main chemical compounds in Portland cement are tri-calcium silicate (C3S), di-calcium silicate (C2S), tri-calcium aluminate (C3A), and tetra-calcium aluminoferrite (C4AF). 3) When mixed with water, cement undergoes hydration reactions where the compounds react to form products like calcium silicate hydrates and calcium hydroxide that harden and bind the materials together.

1. CHEMISTRY of CEMENT
for THIRD YEAR STUDENTS
MAJOR CHEMISTRY
Dr. Safaa El-gamal

2. introduction
 Cement: given to a substances which can be used to
bind together sand and any form of aggregate. (eg.
broken stone).
 Primitive cement is Ca(OH)2 (hydrated lime).
 Hydraulic cement: is the cement that not only react
with water ,it also form water resistant products.

3. Cement can be
used as
Paste Mortar Concrete
Some important Terms:
1-Setting 2-Hardening
3-Hydration reaction. 4-Curing condition.

4. Oxide Abbreviation Compound Abbreviation
CaO C 3 CaO.SiO2 C3S
SiO2 S 2 CaO.SiO2 C2S
Al2O3 A 3 CaO.Al2O3 C3A
Fe2O3 F 4 CaO.Al2O3.Fe2O3 C4AF
MgO M 4 CaO.2Al2O3.SO3 C4A2S
SO3 S 3 CaO.2 SiO2.3 H2O C3S2H3
H2O H CaSO4.2 H2O CSH2
C3S = Tri Calcium Silicate, C2S = Di Calcium Silicate
Cement chemical nomenclature

5. Manufacture of Portland Cement
 Lime stone (CaCO3) +Clay (or other compounds
with similar bulk composition)heating to about
1450 oC → partial fusion →clinker(67%C, 22%S,
5%A, 3% F+ 3% other component) → grinding and
mixed with few %gypsum (Ca SO4.2 H2O) →
Portland cement
 Main phases of PC clinker:
1) C3S 2) C2S 3)C3A 4) C4AF

6. Rule of each phase in the Hydration
characteristics of Portland Cement
Percentage and the rule of each phase in PCC
I) Compressive strength:
C3A,C4AF give little strength compared to C3 S, β-C2S.
II)Evolution of heat:hydration of PC is an exothermic
process(C3S and C3A) make large contribution to heat
of hydration.
III) Sulphate resistant: some ground water and sea
water contains enough sulphate to attack PC and
causes its expansion and disintegration.
Sulphate attack depends on C3A content, and formation
of ettringite (C3A.3 CaSO4.32H2O).

7. Types of Portland Cement according to ASTM Classification
ASTM type
and name
Composition ( % ) Characteristic
s
C3S C2S C3A C4AF
I (Ordinary
Portland
cement)
42-
65
10-
30
0-17 6-18 no special
requirements.
II (
Modified
Portland
cement)
35-
60
15-
35
0-8 6-18 moderate sulfate
resistance,
moderate heat
of hydration.

8. III ( High - early
strength
Portland
cement)
45-70 10-
30
0-15 6-18 higher
strength
soon after
pouring.
IV ( Low - heat
Portland
cement)
20-30 50-
55
3-6 8-15 low heat of
hydration.
V ( Sulfate -
resistant
Portland
cement)
40-60 15-
40
0-5 10-
18
high sulfate
resistance.

9. Specification of PC is based on
1)Test on unhydrated cement.
2)Test on behaviour of cement
during hydration.
3)Test on the hardened pastes.
White cement (other Type of Portland Cement):
made from iron free materials (e.g lime stone and
china clay), they contain C3A,C3S and C2S.
non Portland cement:
I) Aluminous cement:
Lime stone +bauxite (heating) →complete fusion →
aluminous cement.

10. Properties of Aluminous cement
1)set and harden quickly compared to PC
2)High early strength.
3)High resistant to sulphate attack.
II) Slag cement:
a) blastfurnace slag b)supersulphated cement.
III- Pozzolanic Cement:
Pozzalanas: are substances which are not in
themselves cementitious, but reacts with Ca(OH)2 in
presence of water and act as cement.
Expansive cement: cement that give paste which
expand slightly on hydration.

11. Mechanism of cementing action
1)Reactivity of anhydrous compounds
1)C3S ,CA react rapidly with water and strongly
hydraulic.
2)β-C2S reacts slowly with water and strongly
hydraulic, but γ-C2S is inert.
3)C3A,C4AF reacts rapidly with water, but they are
weakly hydraulic.
b)β-C2S reacts slowly with water and strongly
hydraulic, but γ-C2S is inert.
c)C3A,C4AF reacts rapidly with water, but they are
weakly hydraulic.

12. Explanation
i) many compounds are stable at room temperature
when (Ca) atoms coordinated to six oxygen. In
compounds formed at high temperature the
coordination number of (Ca) is less than (6) and
the reactivity is attributed to tendency of (Ca) to
attain (6) CO.NO.
ii) Also irregularity in arrangement of coordinated
oxygen was an important factor
iii) Finally presence of minor impurities may be a
reason for reactivity.

13. 2-product formed on hydration
i) Chemical nature of it.
ii) Particle size and particle shape.
iii)Surface structure: hydraulic reactivity is high for
compounds have surfaces in which coordination
of ions or atoms are unsatisfactory.
iv-Condition of formation of hydration products
a) If the hydration product occurs under conditions
which do not causes disruption of the pre-existing
structure it give strength.
b) If the reverse of (a) occurs it will causes low
strength.

14. v-Condition of formation of hydration products
a) If the hydration product occurs under conditions
which do not causes disruption of the pre-existing
structure it give strength.
b) If the reverse of (a) occurs it will causes low
strength.

15. Theories of setting and hardening
1) Crystallization hypothesis (by Lechatelier):
Cement+H2O→solution(supersaturated relative to
hydration products) →precipitation of hydration
products as crystals, interlocked with each other →
hardened mass .
2) Gel hypothesis (by Michael’s):
He attributed the hardening of hydraulic cement
due to formation of gel.
a) Gel is soft and contains much water.
b) Unreacted cement particles which still present
absorbs this water from this gel and use it for
hydration
c) The gel becomes hard and impermeable

16. 3-Modern Views
a) Cement +H2O → dispersion system (cement grains not
close packed)
b) Large amount of hydration products (of colloidal
dimension) were formed on the surface of grains.
c) After few hours amount of hydration increase and
extended to meet each other, so that give gel in the space
between the grains (setting stage).
d)(after few days), the colloidal particles between the
cement grains becomes densely packed, give
hardened materials, also the gel becomes closely
packed in some regions and less dense in other,
which give pores (hardening stage)

17. a) Through solution mechanism:-
Reactants → dissolves gives ions in solution
→ ions combined giving products → precipitate from
solution.
b) Topochemical mechanism:- reaction occurs directly on
surface of solid.
 1)hydration of C3S
2 C3S +6H→ C3S2H3 +3 Ca(OH)2
 2)hydration of C2S
2 C2S +4H→ C3S2H3 + Ca(OH)2
Hydration of Portland Cement

18. 3)Hydration of C3A
a)C3A+excessH2O→(C4AH19+C4AH8 ) these are metastable
hydrates by time→ C3 AH6(more stable and less soluble)
b) C3A+less H2O and room temp.→C3 AH6
3)Hydration of C4AF:
C4AF +CaSO4.2H2O +Ca(OH)2 →3CaO(Al2O3.Fe2
O3).3CaSO4(aq)
Role of gypsum in setting and hardening
It added to cement to delay its setting.

19. Mechanism of hydration
1)pre-induction period (first minutes) (fast hydration).
induction period : the rate is slow down. ’’dormant
period’’ (period of relative inactivity) lasting 1-2 hours.
3)acceleration period: (3-12 hours after mixing) due to
break up CSH coating and continuation of
hydration process).
4)post acceleration: in this period the rate of
hydration is slow down gradually as the amount of
unhydrated materials decreases.

20. Blast-Furnace Slag Cement (BFC)
BFS is by-product obtained in manufacture of pig-
iron in the blast –furnace as molten at 1400-1500 oC.
then cooling may be:
a) Slow cooling which give grey crystalline ,stony
material known as dense slag.
b) Rapid cooling using limited amount of water ,
giving light weight materials called foamed slag
and after cursing and grinding used as light weight
aggregates.
a) very rapid cooling of the slag by pouring into
excess water
b)or by very rapid cooling using jets of water or of air
and water.

21. The product known as granulated slag.
Reaction of blast-furnace slag with water
It react very slowly with water but without
Setting
. But when some Ca(OH)2 is added to it
,setting and hardening reactions occurs,
similar to PC but with slower rate.
The products formed are: CSH (tobermorite),
C4AH13

22. Reaction of blast-furnace slag with
water
It react very slowly with water but without
setting.
But when some Ca(OH)2 is added to it
,setting and hardening reactions occurs,
similar to PC but with slower rate.
The products formed are: CSH (tobermorite),
C4AH13
What is the rule of activator (e.g. Ca(OH)2 , NaOH or
KOH)?

23. Mechanism of hydration of slag in
slag –cement mixture
1)Fast hydration reaction from time of mixing with water(0.5
h) (pre-dormant period).
2)first dormant period, this period( ended at 0.5 day of
hydration). Very slow –stage of hydration (due to initially
formed hydrates with high amorphous character)
3)first acceleration period ends at 3 days of hydration.
4) Second dormant period (after 3-days) the hydration is
slow down.
5)Second acceleration period (after 28-day) . In this
period a marked decrease in free lime and free slag
were observed up to 180 days

24. The beginning and duration of each stage :
depends on
a) Fineness
b) Composition of the original slag –cement mixture.
Super sulphate Cement
 It made from (80-85%)of granulated blast furnace
slag + CaSO4 (as activator)+5% PC

25. Super sulphate Cement
 It made from (80-85%)of granulated blast
furnace slag + CaSO4 (as activator)+5%
PC