Portland Cement
CE 60
Instructor: Paulo Monteiro
Portland Cement
A hydraulic cement capable of setting, hardening and
remaining stable under water. It consists essentially of
hydraulic calcium silicates, usually containing calcium
sulfate.
Manufacture
Raw Materials:
2/3 calcareous materials (lime bearing) - limestone
1/3 argillaceous materials (silica, alumina, iron)- clay
Raw Material
CE 60
Instructor: Paulo Monteiro
Crushing
CE 60
Instructor: Paulo Monteiro
Blending
CE 60
Instructor: Paulo Monteiro
Old Method
CE 60
Instructor: Paulo Monteiro
Kiln
CE 60
Instructor: Paulo Monteiro
Grinding
CE 60
Instructor: Paulo Monteiro
Production Process
Problem
Production of cement
Is responsible for 7%
CO2 production in the
world
CE 60
Instructor: Paulo Monteiro
Cement grains
Courtesy from Prof. Karen Scrivener, EPFL
Mehta and Monteiro: Concrete
Based on the following notation:
C
CaO
S
SiO2
A
Al2O3
F
Fe2O3
H
H2O
Cement Minerals
C3S : 3CaOSiO2
C2S : 2CaOSiO2
C3A : 3CaOAl2O3
C4AF : 4CaOAl2O3Fe3O4
Hydration
cement
+
dissolution
precipitation
water
CE 60
Courtesy: Prof. Karen Scivener, EPFL
Instructor: Paulo Monteiro
CHEMICAL REACTIONS
2C3S + 6H --> C3S2H3 + 3CH + 120 cal / g
2C2S + 4H --> C3S2H3 + CH + 62 cal / g
C3A + CSH2 --> Ettringite + 300 cal / g
Hydrated Paste
CE 60
Instructor: Paulo Monteiro
Early Hydration
10 hours
3 hours
CE 60
Instructor: Paulo Monteiro
Courtesy: Prof. Karen Scrivener
Hydration Products
Hadley Grain
CE 60
Instructor: Paulo Monteiro
SOLIDS IN CEMENT PASTE
-Calcium Silicate Hydrate
Notation: C-S-H
C/S Ratio: 1.5 to 2.0
Main Characteristics: High Surface (100 to 700 m2/ g) ----> High Van
der Walls Force -----> Strength.
Volume % : 50 a 60
C-S-H
CE 60
Instructor: Paulo Monteiro
SOLIDS IN CEMENT PASTE
-Calcium Hydroxide ( portlandite)
Ca(OH)2
Volume % : 20 to 25
low Van der Walls force
problems with durability and strength
Calcium Hydroxide
CE 60
Instructor: Paulo Monteiro
SOLIDS IN CEMENT PASTE
-Calcium Sulfoaluminate Hydrates
Volume % : 15 to 20
first : ettringite
after : monosulfate hydrated.
Ettringite
CE 60
Instructor: Paulo Monteiro
Review – Identify the crystal
Mehta and Monteiro: Concrete
Review 2 -- Identify the crystal
Mehta and Monteiro: Concrete
Review 3 -- Identify the crystal
Mehta and Monteiro: Concrete
Concrete has a complex microstructure
pores
Sand Particle
C-S-H
Cement grain
Calcium hydroxide
CE 60
Instructor: Paulo Monteiro
Courtesy Prof. K. Scrivener
Hydration process – Initial Condition
Let’s study a cement paste with w/c= 0.63
Start with 100 cm3 of cement.
Compute the mass of cement: Mc = 3.14* 100 = 314 g
Compute the mass of water: Mw = 0.63 * 314 = 200 g
Vw= 200 cm3
Vc= 100 cm3
CE 60
Instructor: Paulo Monteiro
Hydration Process
Miracle of hydration: Vp = 2 Vc
Vw= 200 cm3
50%
Vw= 150 cm3
Vp = 100 cm3
Vc=50 cm3
Vc= 100 cm3
CE 60
Instructor: Paulo Monteiro
Once More…
Vw= 200 cm3
75%
Vw= 125 cm3
Vp = 150 cm3
Vc=25 cm3
Vc= 100 cm3
CE 60
Instructor: Paulo Monteiro
Finally
Vw= 200 cm3
100%
Vw= 100 cm3
Vp = 200 cm3
Vc= 100 cm3
CE 60
Instructor: Paulo Monteiro
Exam question
• Calculate the water/cement ratio needed to
obtain zero porosity in a fully hydrated
cement paste.
W/c = 100/100*3.14
100 cm3
100%
W/c= 0.32
200 cm3
100 cm3
CE 60
Instructor: Paulo Monteiro
Voids in the Hydrated Cement Paste (HCP)
-Interlayer space in CSH
* size = 5 to 25 Å
* no adverse effect on strength and permeability
* some effect on drying shrinkage and creep
-Capillary Voids
> 50 nm : detrimental to strength and impermeability
< 50 nm: important to drying shrinkage and creep.
-Air Voids
* entrapped air: ~ 3 mm
* entrained air: 50 to 200 mm
Water inside the pores
CE 60
Instructor: Paulo Monteiro
Orders of magnitude
CE 60
Instructor: Paulo Monteiro
Orders of Magnitude
CE 60
Instructor: Paulo Monteiro
Setting and Hardening
Stiffening is the loss of consistency by the plastic cement paste and it
is associated with the slump loss phenomena in concrete.
Setting : Solidification of the plastic cement paste
Initial Set : Beginning of solidification (point in time when the paste
has become unworkable) (>45 min.)
Final Set : Final solidification (< 375 min.)
ASTM Portland Cements
Type I-
General Purpose
Type II- moderate heat of hydration and sulfate resistance (C3A <
8%) : general construction, sea water, mass concrete
Type III- high early strength (C3A < 15%) : emergency repairs,
precast, winter construction.
Type IV- low heat ( C3S < 35%, C3A < 7%, C2S > 40%) : mass
concrete
Type V-
sulfate resistant ( C3A < 5%) : sulfate in soil, sewers.