Hydration of cement Institut de Minéralogie et Pétrographie

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Hydration of cement
Definition
- w/c, w/s
water to cement / solid ratio by mass
- paste
cement-water mix allowing setting and hardening to occur
w/c: 0.3-0.6
- setting
stiffening without significant increase in strength
- hardening
development of strength
- curing
storage under conditions allowing hydration: under water for
the first 24h, than under 100% humidity or air
Institut de Minéralogie et Pétrographie
Université de Fribourg
Technische Mineralogie
ETHZ IMP 2008
Hydration of cement
Heat evolution during Portland cement hydration
preinduction period
heat evolution rate W/kg
I
II
acceleration period
III
Induction (dormant) period
0
10
20
Institut de Minéralogie et Pétrographie
Université de Fribourg
30
time (hours)
Technische Mineralogie
ETHZ IMP 2008
Hydration of cement
Hydration reaction of the silicates
All clinker minerals undergo hydration reactions:
Alite
C3S + (y+z)H2O = CxS Hy + zCH x+z = 3 x,y,z are not integers
CxS Hy : poorly crystallized phase, structurally similar to tobermorite
C/S ratio of C-S-H 1.7 - 1.8, max range 1.2 - 2.1
CH: portlandite
H=-500J/g
Belite
Reaction stoichiometry similar to alite, but the hydration is much slower and
produces less portlandite than the hydraton of alite C/S ratio of the C-S-H
phase vary between 1.6 and 2.0.
H=-250J/g
Institut de Minéralogie et Pétrographie
Université de Fribourg
Technische Mineralogie
ETHZ IMP 2008
Hydration of cement
Hydration reaction of the aluminates
Aluminate react rapidly to aluminate hydrates
2C3A + 21H = C4AH13 + C2AH8
above 30°C both hydrate convert to a
hydrogarnet C3AH6
In the presence of sulfate the reaction product is ettringite
2C3A + 3CSH2 + 6H = C3A• 3CSH32
when a surplus in C3A is present (almost always the case) ettringite
reacts to monosulfate:
C3A• 3CSH32 + 2C3A + 4H = 3C3A• CSH12
Institut de Minéralogie et Pétrographie
Université de Fribourg
Technische Mineralogie
ETHZ IMP 2008
Hydration of cement
AFm and AFt phases
Hydrated aluminate and ferrite phases are classified according
to their stoichometry into AFm and AFt phases:
C3(A,F)CXn yH = AFm for Al2O3 and,or Fe2O3 plus mono CXn
C3(A,F)(CXn)3 yH = AFt for Al2O3 and,or Fe2O3 plus tri CXn
C4AH13 = C3(A)CH2 11H AFm phase
C3A• 3CSH32= C3A• 3CS•32H32= C3(A)(CS)3 •32H AFt phase
Institut de Minéralogie et Pétrographie
Université de Fribourg
Technische Mineralogie
ETHZ IMP 2008
Hydration of cement
Temporal evolution of the reactants
Temporal evolution of the hydration of clinker phases (Copeland + Kantro, 1964)
Institut de Minéralogie et Pétrographie
Université de Fribourg
Technische Mineralogie
ETHZ IMP 2008
Hydration of cement
Temporal evolution of the products
Temporal evolution of the hydration hydration products (Kurtis, )
Institut de Minéralogie et Pétrographie
Université de Fribourg
Technische Mineralogie
ETHZ IMP 2008
Hydration of cement
Heat evolution and hydration reactions I
Ettringite to monosulfate
transformation and further
aluminate hydration
C3A hydration
Formation of ettringite
Ettringite coating
retards further
aluminate hydration
Relationship between reactions and heat evolution
Institut de Minéralogie et Pétrographie
Université de Fribourg
Technische Mineralogie
ETHZ IMP 2008
Hydration of cement
Stages of Portland cement hydration
•
•
•
•
•
Stage 1: Initial hydrolysis characterized by dissolution of ions
– Coatings form on cement particles that slow dissolution
Stage 2: Dormant period characterized by continued dissolution of ions
with nucleation control
– Determines initial set
Stage 3: Acceleration is characterized by the accelerated formation of
hydration products. CH forms in solution and C-S-H forms around
calcium silicate particles.
– Determines final set and rate of initial hardening.
– Ettringite converts to monosulfate when sulfates in solution are
used up (peak is slightly after C3S peak)
Stage 4: Deceleration is characterized by continued formation of
hydration products with diffusion control
– Determines rate of early strength gain
Stage 5: Steady state is characterized by the slow formation of
hydration products
– Determines rate of later strength gain
Institut de Minéralogie et Pétrographie
Université de Fribourg
Technische Mineralogie
ETHZ IMP 2008
Hydration of cement
Heat evolution as function of grain size
Heat evolution rate
during hydration of alite
as function of grain size
e.g. specific surface
area.
Institut de Minéralogie et Pétrographie
Université de Fribourg
Technische Mineralogie
ETHZ IMP 2008
Hydration of cement
Heat evolution during the hydration of aluminates
Heat evolution during the hydration of an aluminate paste as function
of gypsum concentration. In the presence of sulfate, the aluminates
transform to ettringite, which coat the grains and block further
hydration.
Institut de Minéralogie et Pétrographie
Université de Fribourg
Technische Mineralogie
ETHZ IMP 2008
Hydration of cement
Composition of the solution
Temporal evolution of the Ca2+, SiOx, pH and C/S of products
Institut de Minéralogie et Pétrographie
Université de Fribourg
Technische Mineralogie
ETHZ IMP 2008
Hydration of cement
Theories for the dormant period
Alite hydration
C-S-H
Ca2+
Ca2+
Ca2+
C-S-H I
Ca2+
Alite
poisoned portlandite nuclei
Ca2+
The initial C-S-H product form a surface
layer, which slows down
the transport of water
to the reactant and thus
the hydration rate. The
acceleration is due to a
breaking of the layer
due
to
morphological
changes in the C-S-H
layer
C-S-H II
Ca2+
Supersaturation of the liquid
in Ca(OH)2 due to the
poisoning of the portlandite
nuclei by silica ions slows
down the dissolution of alite.
With
time
the
silica
concentration decreases due
to formation of first CSH
and the calciumhydrox-ide
becomes high enough to
overcome the poisoning = end
of the dormant period.
Institut de Minéralogie et Pétrographie
Université de Fribourg
The formation of the first
C-S-H
I
product
is
slowed down by the supersaturation in Ca(OH)2.
Nucleation of a second CS-H II phase becomes
possible after thermodynamic
barriers
of
nucleation are overcome.
Technische Mineralogie
ETHZ IMP 2008
Hydration of cement
Hydration products II
SEM micrographs of fractured C3S pastes (w/c = 0.4) in pure water at (A) 7
days, (B) 13 days, (C) 1 month of hydration
Institut de Minéralogie et Pétrographie
Université de Fribourg
Technische Mineralogie
ETHZ IMP 2008
Hydration of cement
Hydration products III
Early Porous C-S-H gel (Eternite shingle, 2100x)
Institut de Minéralogie et Pétrographie
Université de Fribourg
Late dense C-S-H gel (Eternite shingle, 800x)
Technische Mineralogie
ETHZ IMP 2008
Hydration of cement
Hydration products IV
Lathshaped AFm (sulfatefree) crystals (3900x)
Ettringite (sulfatefree) crystals (1500x)
All images are from fiber concrete
samples.
Hydrogarnets (1500x)
Institut de Minéralogie et Pétrographie
Université de Fribourg
Technische Mineralogie
ETHZ IMP 2008
Hydration of cement
Structure of C-S-H gel I
Polymerisation degree of silicate anions during the hydration cement
Institut de Minéralogie et Pétrographie
Université de Fribourg
Technische Mineralogie
ETHZ IMP 2008
Hydration of cement
Structure of C-S-H gel II
Structure of 1.4 nm tobermorite, a sheet like silicate composed of
octahedral layers and silicate chains. The silica tetrahedra can be
replaced by hydroxil ions. If part the bridging tetrahedra (B) are
replaced only paired groups remain explaining the dimer signal in
NMR studies.
Institut de Minéralogie et Pétrographie
Université de Fribourg
Technische Mineralogie
ETHZ IMP 2008
Hydration of cement
Structure of C-S-H gel III
x
c
C-S-H gel models
Institut de Minéralogie et Pétrographie
Université de Fribourg
Structural water
Adsorbed water
Capillary pore
C-S-H layer
C-S-H particle
Technische Mineralogie
ETHZ IMP 2008
Hydration of cement
Voids in Hydrated Cement
•
•
•
•
•
Concrete strength, durability, and volume stability is greatly influenced by
voids in the hydrated cement paste
Two types of voids are formed in hydrated cement paste
– interlayer hydration space (gel pores)
– capillary voids
Concrete also commonly contains entrained air and entrapped air
Interlayer Hydration Space
– Space between layers in C-S-H with thickness between 0.5 and 2.5 nm
– Can contribute 28% of paste porosity
– Little impact on strength, permeability, or shrinkage
Capillary Voids
– Depend on initial separation of cement particles, which is controlled by
the ratio of water to cement (w/c)
– On the order of 10 to 50 nm, although larger for higher w/c
– Larger voids effect strength and permeability, whereas smaller voids
impact shrinkage
Institut de Minéralogie et Pétrographie
Université de Fribourg
Technische Mineralogie
ETHZ IMP 2008
Hydration of cement
Volume relationships
w/c is 0.5 for (a)
a is 1.0 for (b)
Institut de Minéralogie et Pétrographie
Université de Fribourg
Technische Mineralogie
ETHZ IMP 2008
Hydration of cement
Hydration mechanisms
in Portland cement I
Institut de Minéralogie et Pétrographie
Université de Fribourg
Technische Mineralogie
ETHZ IMP 2008
Hydration of cement
Hydration mechanisms
in Portland cement II
Institut de Minéralogie et Pétrographie
Université de Fribourg
Technische Mineralogie
ETHZ IMP 2008
Hydration of cement
Hydration products I
X-ray microscopy images of C3S in a solution saturated with portlandite
and gypsum after 14 min (left) and 31 min (right). The fibrous phase is
C-S-H that forms at the surface (scale bar 1micron).
Institut de Minéralogie et Pétrographie
Université de Fribourg
Technische Mineralogie
ETHZ IMP 2008
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