Curso introductorio sobre cemento y el concreto

1. 1
CONCRETE AND CEMENT
MODULE 417

2. 2
CONCRETE
Per year 5 to 6 billion m³ will be produced
which represent roughly 1 m³ per year and
per person in the world!
Concrete is part of our environment like
water and air and is nevertheless not very
well-known, what a pity! After all it is such
a clever development!

3. 3
CONCRETE -
AN ARTIFICIAL STONE
What is the nearest thing to natural stone?
It is artificial stone made of reagglomerated
stone!
The artificial stone
 has to be as dense as stone
 has to flow in order to be placed
 has to have its components strongly bonded
together

4. 4
CONCRETE -
AN ARTIFICIAL STONE
 ... as dense as stone
This will be achieved by a proper piling of
the aggregates from coarse to fine
higher compacity
lower porosity
= better durability
= better strength
= better flow

5. 5
CONCRETE -
AN ARTIFICIAL STONE
 has to flow in order to be placed
It is a mix of stones with water so that it
flows
thus it can take on the form desired.

6. 6
CONCRETE -
AN ARTIFICIAL STONE
 has to have its components strongly bonded
together
Cement will ensure strong bonds between the
aggregates and will furthermore fill the finest
gaps with the right shape leading to even
higher density

7. 7
CONCRETE -
AN ARTIFICIAL STONE
Concrete is not just any mixture of stone
and cement but must be carefully designed:
1 m³
aggregates 70 %
water 18 %
cement 9 %
air 2 %
25% 0-1 mm
20% 1-4 mm
15% 4-8 mm
20% 8-16 mm
20% 16-32 mm

8. 8
CONCRETE -
A TYPICAL RECEIPE
CONCRETE
density
volume
l/m³
weight
kg/m³
aggregates 2,625 718 1885
water 1 175 175
cement 3,1 87 270
air 20 0
TOTAL 1000 l 2330 kg

9. 9
AGGREGATES
There are a lot of “stones” one can use as aggregates
 Natural aggregates
limestone, quartz, sandstone, granit, basalt, ...
 rolled, when removed from rivers
 crushed, when removed from a quarry
 Synthetic aggregates
 recycled aggregates (old concrete)
 light weight aggregates (wood, polystyrene,
perlit, expanded clay, fly ash, pozzolans ...)

10. 10
QUALITY CONTROL OF
AGGREGATES
The cleanliness, the size gradation, the
strength of the aggregates will all have an
impact on the performance of the concrete.
In addition, certain aggregates will work well
with some cements and not with others.
Quality control testing of the concrete with
the cement, is essential.

11. 11
WATER
Water is used to enable the mix of aggregates
and cement to flow. It also allows the cement to
react to form the insoluble hydrates which will
plug the small gaps between the aggregates
ensuring lower porosity and strong bonds
between the aggregates.
With WATER a concrete mix flows easily
and through its chemical reaction with the water
leads to a structure AS STRONG AS A ROCK!

12. 12
WATER - HOW MUCH TO MAKE
A GOOD CONCRETE?
 X liters are required
to have a concrete
which flows properly
avoiding placing
problems
 Y liters are required
for the chemical
reaction with the
cement
Ykg = 0,4 x cement weight kg
X Y
But X > Y

13. 13
WATER IS THE CHEAPEST
FLUIDIFIER BUT ...
Water / Cement ratio
0,20
0,40
0,6
HYDRATION
HYDRATION
HYDRATION
cement grain
pore
not enough water, some
of the cement is
not hydrated
all cement grains have
reacted with the water
there is excess water
which leads to water
filled pores

14. 14
LOW STRENGTH
POOR DURABILITY
TOO MUCH WATER
0
10
20
30
40
50
60
70
80
90
100
0,4 0,5 0,6 0,7 0,8 0,9 1 1,1 1,2
capillary pores
concrete strength
bleeding and
segregation
percentage
of
strength
according to BolomeyStrength28 = K x G (c/w - 0,5)
K constant for a cement type
G constant for an aggregate type
W/C

15. 15
CEMENT - WHAT FOR?
Cement
 glues on the aggregates
and bonds them together
when it hydrates
 fills the smallest gaps
with the appropriate
shape leading to an even
denser structure
improving strength
without cement
just like a “sand castle”
with cement
as strong as a rock

16. 16
Steel in Concrete
 In order to benefit from the reinforcements
 One has to remove the rust from the steel bars before
using them
 Steel reinforcements have to be sufficiently covered by
the concrete to avoid corrosion.The steel will be
protected by Fe2O3 and Fe3O4 which forms at the pH of
the concrete

17. 17
Steel in Concrete
 In some cases corrosion can nevertheless occur
 Through carbonation pH will decrease
Ca(OH)2+CO2 CaCO3+H2O
the iron oxydes will no longer be stable.
Carbonation proceeds very slowly and the deeper the
slower
 Chloride because of accelerators or deicing salt also leads
to corrosion of the reinforcements
 In case of cracks or insufficient covering of the
reinforcements corrosion will proceed

18. 18
USES OF CONCRETE
GUESS WHERE?

19. 19
LIST OF APPLICATIONS
 Transport
 foundations for road
 suface concrete
 paving slabs
 curb stones
 central barriers
 bridges
 tunnels
 runways
 lamp posts
 Houses
 foundations and walls
(precast or not)
 beams and lintels
 drains / sewers
 pools and tanks
 decorative panels
 safes
 floors
 fencing posts
and also: ships
containment for radioactive waste
power plants
dams ...

20. 20
TYPES OF CONCRETE
 Reinforced or not
 Pre- or post-stressed
concrete
 High performance
100 MPa
 Light weight
 Heavy concrete for
radioactive wastes
 Fibers
 Washed and
decorative
 Large structures
 Insulating
 Selflevelling
 Precast
 Corrosion resistant
 Frost resistant
 Lean concrete
 In-filling concrete

21. 21
CEMENT
 We said cement reacts with water to form
hydrates which plug the tiniest gaps
between the sand grains gluing the
aggregates together.
 What is this wonder, what is this reaction
with water?

22. 22
HOW IS THE CEMENT MARKET
DISTRIBUTED?
Prefab
14%
slabs, pavestones,
concrete blocks
11%
Big projects
8% Bags
5%
Miscellaneaous
5%
Ready mix concrete
41%
concrete made
on site
16%
In Germany for example:

23. 23
CEMENT
HYDRATES

24. 24
HOW IS CEMENT PRODUCED
Raw
Material
Kiln Mill Mixer
Clinker Cement
Concrete
Aggregates/Sand
Water
The finely ground
minerals react together
when heated, new
chemical bonds are
formed. The reaction
requires heat.
Clinker is ground to
increase its reactivity
when mixed with
water. Cement is not a
stable material, it ages.
Cement reacts
chemically with water
to form stable
hydrates. The reaction
with water releases
heat.

25. 25
CHEMISTRY OF PORTLAND
CEMENT
It is usual for people working in cement not to use
the official chemistry but to use a jargon.
Lime CaO C Magnesia MgO M
Silica SiO2 S Sulfur oxyde SO3 S
Alumina Al2O3 A Potassiumoxyde K2O K
Iron oxyde 3 Fe2O3 F Sodiumoxyde Na2O N
Iron oxyde 2 FeO f Water H2O H

26. 26
CAC
OPC
Slag
Lime
1
2
3
4
4
SiO2
CaO
C3S
C2S
C3S2
CS
CAS
C2 AS
1
3
2
Al2O3
C3A C12A7 CA CA2 CA6
MINERAL BINDERS

27. 27
THE CEMENT PRODUCTION
LINE
Stone
Raw Materials
Raw meal
Clinker
Cement
Retrieved from the quarry
and crushed
Preblended + Ground + Homogenised
(Exchanger)
Kiln + Cooler
Milling
Stored or Delivered
Gypsum
Other
Minerals

28. 28
HOW THE CLINKER MINERALS
FORM

29. 29
CLINKER AND CALCIUM
SULPHATE
The Clinker
- Silicates "alite" C3S 50 to 70%
"bélite" C2S 10 to 20%
- Tricalcium aluminate C3A 1 to 15%
- Aluminoferrite C4AF 1 to 15%
- Free - lime CaO 0.5 to 1%
For Setting and Placing
- Calcium sulphate 3 to 8%

30. 30
alite
alite
Interstitial phase

31. 31
alite
bélite
alumino-ferrite

32. 32
0
100
200
300
400
500
600
700
800
0 50 100 150 200 250 300 350 400
C3S
C2S
C3A
C4AF
Comp.
kg/cm²
days
REACTIVITY OF THE MAIN
MINERALS

33. 33
As an example ....
Clinkers from Karsdorf
Mineralogical comp. LSF 90 LSF 98
C3S % 45 66
C2S % 31 9
C3A % 10 9
C4AF % 8 8
INFLUENCE OF C3S / C2S

34. 34
INFLUENCE OF C3S / C2S
0
10
20
30
40
50
60
70
0 5 10 15 20 25 30
LSF 90
LSF 98
Comp.
(MPa)
days
Fineness 430 m²/kg
SO3 tot. = 3,3%

35. 35
INFLUENCE OF C3A / C4AF
 Tricalcium aluminate C3A reacts very quickly
 Its hydration needs to be controlled
 Calcium iron aluminate C4AF reacts very slowly

36. 36
INFLUENCE OF MINOR
ELEMENTS
 Free lime
 It is the lime which is not combined to other
elements. This CaO in too large amount brings
expansion. A too low content is a sign of an
overburnt clinker which is going to be much less
reactive.
 The optimum is around 1%, its effect is more
important on low C3A cement(<5%)
 Magnesia
 It is also dangerous in too large amount because it
leads to expansion and cracks.

37. 37
FREE LIME AND SETTING TIME REDUCTION
100
120
140
160
180
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
Free lime clinker
Initial set (mortar)
( min. )
%
St Constant

38. 38
INFLUENCE OF ALKALIES
 Definitions
the alkalies which are in the cement come from
the raw materials. They are Sodium and
Potassium.
 Soluble: it is the fraction which is associated with the
sulphate coming from the raw materials or from the fuels.
 Insoluble: it is the fraction which is not combined with
the sulphates. The alkalies enter into the cristals of
silicates or aluminates
 Total: it is the sum of both Soluble and Insoluble

39. 39
WHERE ARE THE ALKALIES IN CLINKER?
How do the behave?
It depends on the % sulphur in the clinker
S in C2S
S in C3A
C3A
Na2SO4
K2SO4
Na2SO4 Na2SO4
orthorhombic
Na, K C3A
orthorhombic
K2SO4 K2SO4
workability
problem
the early strength increase
when sulphate content increases
clinker is harder
to grind
sulfate content

40. 40
PLANT
% SO3
Clinker
%K2O
Total
%Na2O
Total
SSB
m²/kg
R1d
(MPa)
Ranteil
Reference
+ gypsum
0,2
1,1
1,15
1,15
0,1
0,1
400
375
11,5
18,0
Séte
Reference
+ gypsum
0,1
1,3
0,6
0,6
0,2
0,2
402
413
11,5
17,0
Increasing the soluble alkalies increases the early strength .
INFLUENCE OF ALKALIES

41. 41
CEMENT IS A REAL REAGENT!
What happens when mixing water and cement?
 The anhydrous cement (cement is a cristallised material
without water) first dissolves in the water.
 The dissolved cement then, after the nucleation period
chemically reacts with the H2O molecules to build
hydrates. These new crystals contain water in their
structure. It is now crystallised "solid" water .
 The hardening of the cement is NOT due to some kind of
drying effect. It is indeed a chemical reaction leading to a
new structure with new bonds bringing strength to the
material.

42. 42
water
Dissolution
Solution
undersaturated with
respect to ciment
Solution saturated
with respect to
cement
Precipitation of hydrates
Precipitation
of hydrates
Solution saturated
with respect to
hydrates
Solution sursaturated
with respect to
hydrates
Cement
(anhydrous)
solid
hydrates
Slow nucleation
and precipitation
of hydrates
1
2
3
4
5
6 7
8
9
1st cycle
2nd and following cycles
5 6 7 8 9
1 2 3 4

43. 43
C3A
C2S
C3S
C4AH13
C4AH13
C2S
C3S C4AH13
Water
+
Portland without Gypsum
Instantaneous Stiffening
Gypsum
Portland with Gypsum
C3A
C2S C3S
Water
+
C3A
C2S
C3S
Ettringite
Blockage of C3A
Conserved fluidity

44. 44
HYDRATION OF SILICATE
PHASE
The Michaelis Process
C3S
Primary
hydrates
C2,8SH
C
and further
C3S
C1,5SH1,5 C
C3S + 3 H C1,5SH1,5 + 1,5 Ca(OH)2
C2S + 2 H C1,5SH1,5 + 0,5 Ca(OH)2

45. 45
OTHER COMPONENTS
 Limestone Fillers
 Finely ground limestone (cement fineness) improves
workability. Concretes are easy to place and
sedimentation (bleeding) is less.
 The limestone has to be very pure (avoid dolomite
limestone, clay and organic material)
 Limestone has to be hard, otherwise it is going to
perturb the grinding of the clinker
 During hydration a small amount of carbo-aluminate
is formed with the C3A

46. 46
OTHER COMPONENTS
 Slag * Chemical Analysis
CaO 38 to 46% 63 to 70%
SiO2 30 to 36% 20 to 24%
Al2O3 11 to 21% 3 to 7%
Slag Clinker
* Consequences on properties
- reduces Ca(OH)2 % after hydration
more CSH
pH is lower, less protection of reinforcement
better behaviour in corrosive water
- hydration is slower
setting time is longer
strength at 1 day is weaker but long term can be higher
heat of hydration is lower

47. 47
0
5
10
15
20
25
30
35
40
45
50
0 5 10 15 20 25 30
Comp.
(MPa)
CPA 45
CPA 45 / Slag (65/35)
CPA 45 / limestone (65/35)
days
Slag was ground to 350 m²/kg
INFLUENCE OF SLAG /
LIMESTONE FILLER

48. 48
0
10
20
30
40
50
60
0 5 10 15 20 25 30
Comp.
(MPa)
days
Mixes CPA with 35% Slag
CPA
790 m²/kg
350 m²/kg
280 m²/kg
INFLUENCE OF FINENESS OF
SLAG