Lec 3 Flashcards
Portland cement composition
Limestone and clay in 1400-1600 C
Results: calcium silicate
Limestone and clay chemical processes
Limestone: CaCo3 -> CaO + CO2
Clay: SiO2 + AlO3(Fe2O3)2H2P -> SiO2 + AlO3 + Fe
…… Limestone and clay are main components. …. And ….. are added as fluxing agents to lower temperatures.
High purity
Aluminum and Iron
Materials entering the kiln should have … and should …. The optimum burning temperature varies with …. To assure complete chemical combination in kiln, ……
Constant composition
Well blended
Mix composition
Particle size shouldn’t be too large
What is clinker
A material that is coming out from the kiln. It will be conveyed to ball then be grounded to powder. ADD GYPSUM AT THE END.
The oxide analysis of the cement components can be done by
X-ray fluorescence spectroscopy
Gypsum’s chemical reaction
CaSO4 + 2H2O -> CaO + SO3 -> C3H2
What is the function of information on compound composition?
To predict properties of the cement.
https://ibb.co/WvwT2r0
Lime
Silica
Alumina
Ferric Oxide
Magnesia
Alkalis
Sulfur Trioxide
Carbon Dioxide
Water
64.67
21.03
2.58
0.34
-
-
…./…./…. + H -> C-S-H gel
C3S, C2S, C3A
https://ibb.co/dkN5FDr
Tricalcium silicate
Dicalcium silocate
Calcium sulfate dihydrate (gypsum)
3CaO+Al2O3
C4AF
The most important is gypsum even though it is the lowest
0.6
https://ibb.co/3Rkxgws
C3S
C2S
Gypsum
C4AF
C3A
Portland cement mixed with water undergoes a series of chemical reactions that are responsible for …………. These reactions with water are called ……, and a new solids formed on hydration are referred to as ….. …..
Hardening of concrete
Hydration
Hydration products
https://ibb.co/FbGf7hr
Moderate
Moderate
Low
Very high
High
Low
Low
Very high
Five types of Portland cements
Type I: Ordinary cement → general use
Type II: When moderate sulfate resistance is desired → Underground structure, seaside
Type III: When high early strength is desired→ Road, Airport Runway
Type IV: Low-heat cement → mass concrete
Type V: When high sulfate resistance needed
What type has the most or least C3S, C2S, C3A, C4AF, CsH2, Fineness, Compressive Strength, Heat of Hydration
IV (least = 42)
IV (most = 32)
I and III (most =10) IV and V (least = 4)
IV (most = 15)
I and III (most = 6) and Iv and V (least = 4)
III (most = 550)
III (most = 24)
IV (least = 235)
Explain Type I to Type V according to chemical composition
Type I – commonly used in general construction.
▪ Type II – Higher C3S content than Type IV and better strength development, but it has a higher heat of hydration. Similar in performance to Type V except has a lower sulfate resistance. It is often used when a lower heat of hydration is required.
▪ Type III – used when rapid rate of strength is required and when concreting in low temperature. The amount of strength gained after 24 hrs. Because of rapid rate of hydration, a lot of heat is generated; this cement is not good for adiabatic conditions.
▪ Type IV – low heat of hydration. Good for mass concrete applications, thermal cracking can be eliminated after proper care.
▪ Type V – satisfactory performance containing high concentration of sulfate. If C3A content by weight is below 5%, concrete exhibits resistance to aggressive environment. This cement has a low rate of strength development.
What is aggregate
Economical fillers, provide dimensional stability and wear resistance
Occupy 70-80% of concrete volume
Types of aggregate
Natural rock - sands, crushed stone
Synthetic materials - slag, expanded clay
General requirements for aggregate
Strong, hard, free of undesirable impurities (silt, clay, dirt)
Chemically stable
Aggregates classifications based by weight
- Ultra-lightweight, can be sawed or nailed, used for its insulating properties (vermiculite, ceramic)
- Lightweight, used for insulating properties (expanded clay, shale or slate, crushed brick)
- Normal weight, used for normal concrete (crushed limestone, sand, river gravel j
- Heavy weight, for high density concrete for shielding against nuclear radiation (steel or iron shot/pellets)
Volumetric stability of aggregates
Large shrinkable (unstable): fine grained sandstones, slate, basalt, clay-containing, ELECTRIC ARC FURNACE REDUCTION SLAG
Low shrinkage: quartz, limestone, granite, feldspar
Which slag is good to use
Iron ore to pig iron: blast furnace
NOT GOOD
pig iron to steel: converter
Scrap iron to steel: arc furnace
….. and …. can limit strength and wear resistance of concrete.
Soft
Porous rock