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CE 60Instructor: Paulo Monteiro
Portland Cement
PortlandPortland CementCement
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
CE 60Instructor: Paulo Monteiro
Raw Material
CE 60Instructor: Paulo Monteiro
Crushing
CE 60Instructor: Paulo Monteiro
Blending
CE 60Instructor: Paulo Monteiro
Old Method
CE 60Instructor: Paulo Monteiro
Kiln
CE 60Instructor: Paulo Monteiro
Grinding
CE 60Instructor: Paulo Monteiro
Production Process
Production of cementIs responsible for 7%CO2 production in theworld
Problem
Mehta and Monteiro: Concrete
Cement grains
Courtesy from Prof. Karen Scrivener, EPFL
Based on the following notation:Based on the following notation:C CaO
S SiO2
A Al2O3
F Fe2O3
H H2O
Cement MineralsCement Minerals
C3S : 3CaOSiO2C2S : 2CaOSiO2
C3A : 3CaOAl2O3C4AF : 4CaOAl2O3Fe3O4
CE 60Instructor: Paulo Monteiro
Hydrationcement
+water
dissolution precipitation
Courtesy: Prof. Karen Scivener, EPFL
CHEMICAL REACTIONSCHEMICAL REACTIONS
2C3S + 6H --> C3S2H3 + 3CH + 120 cal / g2C2S + 4H --> C3S2H3 + CH + 62 cal / gC3A + CSH2 --> Ettringite + 300 cal / g
CE 60Instructor: Paulo Monteiro
Hydrated Paste
CE 60Instructor: Paulo Monteiro
Early Hydration
3 hours 10 hours
Courtesy: Prof. Karen Scrivener
CE 60Instructor: Paulo Monteiro
Hydration Products
Hadley Grain
SOLIDS IN CEMENT PASTESOLIDS IN CEMENT PASTE
-Calcium Silicate Hydrate
Notation: C-S-HC/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
CE 60Instructor: Paulo Monteiro
C-S-H
SOLIDS IN CEMENT PASTESOLIDS IN CEMENT PASTE
-Calcium Hydroxide ( portlandite)
Ca(OH)2Volume % : 20 to 25
low Van der Walls forceproblems with durability and strength
CE 60Instructor: Paulo Monteiro
Calcium Hydroxide
SOLIDS IN CEMENT PASTESOLIDS IN CEMENT PASTE
-Calcium Sulfoaluminate HydratesVolume % : 15 to 20
first : ettringiteafter : monosulfate hydrated.
CE 60Instructor: Paulo Monteiro
Ettringite
Mehta and Monteiro: Concrete
Review – Identify the crystal
Mehta and Monteiro: Concrete
Review 2 -- Identify the crystal
Mehta and Monteiro: Concrete
Review 3 -- Identify the crystal
CE 60Instructor: Paulo Monteiro
Concrete has a complex microstructure
Cement grain
C-S-H
Sand Particle
Calcium hydroxide
pores
Courtesy Prof. K. Scrivener
CE 60Instructor: Paulo Monteiro
Hydration process – Initial Condition
Let’s study a cement paste with w/c= 0.63Start with 100 cm3 of cement.
Compute the mass of cement: Mc = 3.14* 100 = 314 gCompute the mass of water: Mw = 0.63 * 314 = 200 g
Vc= 100 cm3
Vw= 200 cm3
CE 60Instructor: Paulo Monteiro
Hydration Process
Miracle of hydration: Vp = 2 Vc
50%
Vc= 100 cm3
Vw= 200 cm3
Vc=50 cm3Vp = 100 cm3
Vw= 150 cm3
CE 60Instructor: Paulo Monteiro
Once More…
75%
Vc= 100 cm3
Vw= 200 cm3
Vc=25 cm3Vp = 150 cm3
Vw= 125 cm3
CE 60Instructor: Paulo Monteiro
Finally
100%
Vc= 100 cm3
Vw= 200 cm3
Vp = 200 cm3
Vw= 100 cm3
CE 60Instructor: Paulo Monteiro
Exam question
• Calculate the water/cement ratio needed to obtain zero porosity in a fully hydrated cement paste.
100%
100 cm3
200 cm3100 cm3
W/c = 100/100*3.14
W/c= 0.32
Voids in the Hydrated Cement Paste (HCP)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
CE 60Instructor: Paulo Monteiro
Water inside the pores
CE 60Instructor: Paulo Monteiro
Orders of magnitude
CE 60Instructor: Paulo Monteiro
Orders of Magnitude
Setting and HardeningSetting and HardeningStiffening 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 CementsASTM 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.