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
Aggregate particles coated with dirt, silt or clay cannot be …. (mortar) and it will reduce …….
Well bonded with concrete
Concept strength
Properties of aggregate that affect concrete MIX DESIGN
Shape and texture
Size gradation
Moisture content
Specific gravity, bulk unit weight
What does “shape and texture” affect to concrete MIX DESIGN?
Effect on workability (good: close to sphere, with relatively smooth surface)
Effect on mechanical properties (characteristics of coarse aggregates) (shape affect strength by increasing the surface area for bonding with paste) - rough texture improve mechanical bond
What does “size gradation” affect to concrete MIX DESIGN?
The amount of paste depends on the amount of void space between particles that must be filled.
Variety of sizes is preferred to pack smaller particles between larger ones and decrease voids.
Coarse aggregate retains at
4.75 mm (sieve no 4)
Importance of maximum aggregate size
influences the required paste amounts, and the optimum gradation of the coarse aggregate.
According to ASTM 125, what is the maximum coarse aggregation size?
the smallest sieve opening through which the entire sample passes.
ASTM gradation requirements are based on…
The nominal maximum size
What is the affect of max size change?
Increase will improve concrete durability (because of less paste)
Decrease if aggregate is subject to freeze-thaw damage
Sieve analysis should be done using ……
The gradation curve can be prepared using …………. retained on each successive sieve or cumulative percentage passing each sieve.
ASTM 136
Cumulative Percentage
https://ibb.co/Y8dkK3M
a. Well Graded : concave
b. Poorly Graded : steep shape (most sre 3/8”)
c. Gap Graded n:stepped (missing 3/8”)
Fineness modulus of fine aggregate is used to…
Design mix proportions
…… has large effect on workability
Lower FM leads to …..
Sand gradation
Greater number of small particles
What is the FM range for coarse aggregate and fine aggregate
Fine : 2 to 4
Coarse : 6.75 to 8
How to calculate FM for coarse?
FM = (total of cumulative passing including no 8 (the least) +400]/100
How to calculate FM for fine?
FM = (total of cumulative passing retained on standard sieves (from 3” to sieve no 100))/100
GRADATION LIMITS
There are separate limits for fine aggregate and coarse aggregate, depending on …….
These limits are set to prepare concrete with ……. and resistant to segregation during …….
Nominal max size
Minimum paste
Handling and placing
What is absorption capacity, surface moisture, and moisture content?
Absorption capacity: maximum water aggregates can absorb[ (Wssd-Wod)Wod]
Surface moisture: water on surface of aggregate [(Wwet-Wssd)/Wssd]
Moisture content: water in any states of aggregate [(Wagg-Wod)/Wod]
