Portland Cement (Detailed Study)
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Transcript of Portland Cement (Detailed Study)
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A hydraulic cement capable of setting, hardening and
remaining stable under water. It consists essentially ofhydraulic calcium silicates, usually containing calcium
sulfate.
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Raw Materials:2/3 calcareous materials (lime bearing) - limestone
1/3 ar illaceous materials (silica alumina iron)- cla
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Raw Material
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Crushing
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Blending
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Old Method
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Kilniln
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Grinding
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Production ProcessOooops, Problem
Production of cement
CO2 production in theworld
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Cement grains
Courtesy from Prof. Karen Scrivener, EPFL
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Early Hydration
3 hours 10 hours
our esy: ro . aren cr vener
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Hydration Products
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n er
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a
S SiO2A Al2O3
F Fe3O4
H H2O
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C3S : 3CaOSiO2
:C3A : 3CaOAl2O3
C4AF : 4CaOAl2O3Fe3O4
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See video 1
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+ -- + +2C2S + 4H --> C3S2H3 + CH + 62 cal / gC3A + CSH2 --> Ettringite + 300 cal / g
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See video 2
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Hydration Products
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y ra e as e
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-Calcium Silicate Hydrate
Notation: C-S-HC S Ratio: 1.5 to 2.0Main Characteristics: High Surface (100 to 700 m2/ g) ---->
g an er a s orce ----- reng .
Volume % : 50 a 60
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- a c um y rox e port an te
Volume % : 20 to 25low Van der Walls force
problems with durability and strength
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Calcium Hydroxide
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-Calcium Sulfoaluminate Hydrates
first : ettringite
after : monosulfate hydrated.
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Ettringite
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Review
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Review 2
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Review 3
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Type I- General Purpose
Type II- moderate heat of hydration and sulfate resistance8%) : general construction, sea water, mass concrete
ype - g ear y strengt : emergency reprecast, winter construction.
ype - ow ea , , :
concrete
ype - su a e res s an su a e n so , s
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Advanced Light Source at Berkeley
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Imaging at High Spatial Resolution:Soft X-Ray Microscopy to 15 nm
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Two Common Soft X-Ray Microscopes
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Early hydrates forming during the pre-
(Sheaf ofwheat)
Cement
rain
C3S hydrated for 34min. in saturated limeand calcium sulfate atw/c=5, 1s exposuretime, 516eV, scale bar
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(Sheaf ofwheat)
Cement
rain
C3S hydrated for 56min. in saturated limeand calcium sulfate atw/c=5, 1s exposuretime, 516eV, scale bar
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In-situ Massive precipitation
8h 30min.
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In-situ Massive precipitation
8h 36min.
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9h 16min.
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Spot
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Summary
Sheaf of wheat hydrates are forming on thecement rains durin the first minutes
precipitation of C-S-H (needles)
The early hydrate layer covering the cement grains
trans orms ur ng t e acce erat on per o
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Admixtures: Accelerators (CaCl2)
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Summary
CaCl2 increases the rate of formation of- - .
This C-S-H is less dense than in a control
sam le.
e acce erat ve power o a may come
from its ability to flocculate hydrophilic
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Retarders: Sucrose
31 minutes 68 minutes 100 minutes
Sucrose has delayed the early formation of C-S-H. ,
Once the retardation is over, hydration proceeds very rapidly
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Condition
Lets study a cement paste with w/c= 0.63Start 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
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Hydration Process
Miracle of hydration: Vp = 2 Vc
50%Vw= 200 cm3 Vw= 150 cm3
Vc= 100 cm3 Vc=50 cm3
Vp = 100 cm3
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Once More
75%Vw= 200 cm3 Vw= 125 cm3
Vc= 100 cm3 Vc=25 cm3
Vp = 150 cm3
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Finally
100%Vw= 200 cm3Vw= 100 cm3
Vc= 100 cm3
Vp = 200 cm3
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Exam question
Calculate the water/cement ratio needed to
cement paste.
*
100%100 cm3
.
W/c= 0.32
100 cm3
cm
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o s n e y ra e emeno s n e y ra e emen- n er ayer space n
* size = 5 to 25
* some effect on drying shrinkage and creep
-> 50 nm : detrimental to strength and impermeability< 5 nm: im ortant to dr in hrinka e and cree
-Air Voids~
* entrained air: 50 to 200 mm
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Water inside the pores
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Orders of magnitude
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Orders of Magnitude
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