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cement - University of California, Berkeley Flipbook PDF
Portland Cement A hydraulic cement capable of setting, hardening and remaining stable under water. It consists essential
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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 This image cannot currently be display ed.
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
Important
Cement Minerals C3S : 3CaOSiO2 C2S : 2CaOSiO2 C3A : 3CaOAl2O3 C4AF : 4CaOAl2O3Fe2O3
Hydration cement
+
dissolution
precipitation
water CE 60 Courtesy: Prof. Karen Scivener, EPFL Instructor: Paulo Monteiro
CHEMICAL REACTIONS Extremelly important!!!
2C3S + 6H --> C3S2H3 + 3CH + 120 cal / g 2C2S + 4H --> C3S2H3 + CH + 62 cal / g C3A +CSH 2--> 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
CE 60 Instructor: Paulo Monteiro
SOLIDS IN CEMENT PASTE -Calcium Silicate Hydrate Notation: C-S-H 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
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.
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