CE 196H Notes 1 to 12
Alite Hydration (alite is highly soluble in water) STAGE 3 - Acceleration Period
- C-S-H "pulls in" Ca2+ ions -Rapid nucleation of CH and C-S-H -Calcium concentration drops -Heat produced rapidly -Final Set Occurs -Hardening begins
Alite Hydration (alite is highly soluble in water) STAGE 4 - Second deceleration period
- C-S-H layer thickens and acts as a barrier around C3S grain - Mass transport through C-S-H determines reaction rate -THICK BARRIER CSH -Reaction limited by SPACE
C3A w/o Gypsum (Billy Bob Question)
- C3A + H (Calcium aluminate hydrates) Calcium aluminate cements - typically used for repair applications (300 psi in 3 hours) - DONT want FLASH SET in portland cement. Thus, GYPSUM is added to force C3A to form ettringite and control(SLOW DOWN) rate of reaction
Pore Solution Composition
- Cations in pore solution must be matched by anions - The higher the alkali content, the higher the OH- concentration - The higher the OH- concentration, the higher the PH
Hydration (exothermic reaction)
- Chemical reaction between cement phases and water - water becomes "chemically bond" with cement phases - Easier to study hydration by studying cement paste -releases heat
Alite Hydration (alite is highly soluble in water) STAGE 0 - Heat of Dissolution
- First Contact with WATER - Ca2+ and OH- into solution -Occurs almost INSTANTLY -Rapid evolution of heat -pH > 12
Concrete Advantages
- Formable - Durable -Inexpensive -Local materials -High Compressive Strength - eco-friendly - fire-proof
C3A Hydration w Gypsum Stage 3
- Gypsum has been used up = SULFATE DEPLETION PEAK - can think of gypsum as "retardant" - C3A can dissolve rapidly once gypsum is depleted - Conversion of ettringite to AFm
Low permeability
- Less porosity - Smaller pore sizes - Disconnected pore structure -"Depercolated" - water/ions must travel through C-S-H
Lime Concrete Facts
- Lime Concrete is water resistant - good strength - durability issues, especially susceptible to acid attack and leaching - non-hydraulic (will not harden under water)
False Set
- Loss of plasticity without heat evolution - Can be reversed by continuing mixing
high permeability
- More Porosity - Larger pore sizes - Connected pore structure - More drying shrinkage
Flash set (quick set)
- Rapid, early loss of workability - High heat evolution - cannot be reversed without adding water
Cement and water are combined to make cement paste. State the approximate range of paste volume, in terms of percent, that is present in concrete.
25-40%
Reactions in Kiln (700-900C or 1290-1650F)
"Calcination" - free lime increases and reactive silica combines with CaO to begin forming C2S
Concrete Latin Word
"Concretus" - means to grow together or compound
List the four basic ingredients required to produce cement
"LISA" - Lime (60-70%), Iron (2-4%), Silica (20-25%), Alumina (4-6%)
Dissolution
(Occurs first during cement hydration) -solid comes in contact with water and ions go into solution
Cement and Concrete History (c. 7000 BC)
- 1985, oldest concrete to date was a road found in Yiftah El in Galilee, Israel -Lime concrete was used to make the road
What is hydraulic cement?
- a binding material that sets and hardens by chemical reaction with water and is capable of doing so underwater
Five Component of Basic plain Concrete
-Air -cement -fine aggregate or sand -coarse aggregate or rock or gravel, -water
Reactions in Kiln (~1350-1450C)
-Alite crystals form and grow at the expense of Belite crystals -C3S and C2S precipitate at this high temperature
C3A Hydration w Gypsum Stage 1 and 2
-C3A and gypsum dissolution - Forming AFt and AFm = not enough to cause SETTING
Alite Hydration (alite is highly soluble in water) STAGE 2 - Induction Period
-Early C-S-H acts as a barrier -Ions continue to go into solution at a slow rate -Reaction continues slowly -Paste remains fluid -Initial set occurs in 2-4 hours
Portland Cement Type 5 Higher Sulfate resistance
-Exposure to severe sulfate concentrations -C3A content 5% max
Properties of C3A
-Fast Reacting -Large amount of heat released -Rapid strength gain, but not very strong -Susceptible to sulfate attack
Properties of C3S (Alite)
-Fast Reacting (RAPID) -Fast strength gain -Contributes to EARLY strength -Major Phase in portland cement
Portland Cement Type 3 High Early Strength
-Fast Reacting-Higher early strength -Precast and/or prestressed applications -Cold Weather-Repair -Fineness: 550 m^2/kg
Properties of C4AF
-Fast reacting -Small effect on strength -Reduce clinkering temperature (THATS WHY ALUMINA and IRON (FERRITE) is added to kiln to produce clinker) -color of cement due to iron present
Alite Hydration (alite is highly soluble in water) STAGE 1 - First Deceleration
-Ions continue to go into solution -Rate of dissolution slows down because ionic concentration in solution has increased (approaching EQUILIBRIUM in solution) -Stage 0 and 1 combine occur in about 15 mins -Higher concentration of calcium ions compared to silica
Cement Kiln Facts
-Kiln is made out of steel and lined with refractory bricks -Up to 20 ft in diameter -Up to 600 ft long -Up to 35,000 tons of cement per day -60 to 200 rev/hr -Material stays 1 to 1.5 hours in kiln -24/7/365 operation
Concrete disadvantages
-Low tensile strength - Brittle - Low ductility - low strength-to-weight ratio - durable - volumetric changes (creep and shrinkage)
Portland Cement Type 4 Low Heat of Hydration
-Minimize the amount of heat -Slow reacting -Low C3S/High C2S -Dams -Not used anymore -Coarser than Type 1
Concrete Facts
-Most widely-used material in the world -Second most widely substance in the world -70% + of bridges in US made out of concrete
Portland Cement Type 1 Ordinary all-purposes cement
-Pavement, buildings, bridges -Fineness: 365 m^2/kg
Cement and Concrete History (Second Century BC)
-Pozzolanic cement combine with water results in a strong, durable binder
Alite Hydration (alite is highly soluble in water) STAGE 5 - Steady state
-Reaction continues very slowly and is controlled by DIFFUSION
Properties of C2S (Belite)
-Slow reacting -Slow strength gain -Good for LONG-TERM strength
Transportation and Packaging
-Tens of millions of metric tons shipped per year in US -Most in bulk by rail, truck, barge , or ship -Very small amount packed in water proof sacks
Portland Cement Type 2 Moderate Sulfate-resistance cement
-Used where moderate exposure to sulfate is expected -C3A content 8% max
Precipitation
-When a solution becomes supersaturated with certain ions, ions combine to form solids. -This method follows solubility rules.
The typical percentage of BELITE present in Portland cement
15-30%
The first Portland cement produced in the US occurred in
1871
Belite Hydration vs Alite Hydration
Belite hydration is similar to Alite hydration but it occurs much more SLOWLY and liberates less heat, which can be difficult to measure
What is the most abundant Hydration product @100% hydration?
C-S-H
Of the four primary clinker phases, which contributes the most to long term compressive strength?
C2S
Of the four primary clinker phases, which is LEAST REACTIVE in Portland cement?
C2S (Belite)
Of the four primary clinker phases, which is the most reactive?
C3A (Tricaclium Aluminate)
Reactions in Kiln (COOLING)
C3A and C4AF do not precipitate until the cooling process
Reactions in Kiln (~1250-1300C)
C3A and C4AF melt and particles start to clump (Molten liquid is key, it allows the formation of the most important cement phase)
Cement Compound Composition
C3S (50-70%) C2S (15-30%) C3A (5-10%) C4AF (5-15%) C$H (less than or equal to 5%) Depends on the relative proportions of the chemical compounds and the fineness of the cement
Complete the hydration of alite: 2C3S + 11H --->______
C3S2H8 + 3CH
Complete the hydration of belite: 2C2S + 9H --->______
C3S2H8 + CH
Complete the hydration of C3A (Monosulfate): 2C3A + C6A$3H32 +4H --->______
C4A$3H12 Hint: Look at the numbers of C and H
Why are alumina and ferrite added to the kiln to produce clinker?
C4AF - Alumina and ferrite act as flux agents. They allow the formation of alite to occur at a LOWER TEMPERATURE
Complete the hydration of C3A (Ettringite): C3A + 3C$H2 + 26H --->_____
C6A$3H32 -created with gypsum (3C$H2) Hint: Look at the numbers of C and H
Lime concrete is made by..
Calcinating limestone
During clinker production, once raw materials are ground and blended together they are fed though a preheating tower to:
Calcine the limestone Decrease the length of the cement kiln Reduce the cost of manufacturing cement Reduce the carbon dioxide emissions (ALL OF THE ABOVE)<<<<<-----
Type II and Type V Portland cement are very commonly used in California. Briefly explain why.
California has high sulfate contents present in the soil and groundwater. Type II and Type V cements are used in sulfate environments to prevent sulfate attack.
Manufacturing Process - Step 5
Cement clinker nodules form and are cooled very rapidly
Reactions in Kiln (~1350-1400C)
Chemical Reactions start in the liquid to begin forming Alite crystals (C3S)
Manufacturing Process - Step 6
Clinker is inter ground with gypsum and limestone using a steel ball mill to produce cement. Then, cement is stored in silos and then shipped.
Portland Limestone Cements (PLCs)
Contain ground limestone, including monocarboaluminate and Hemicarboaluminate. Not reacted limestone or calcite is present with higher limestone contents
Hydration Products: Ettringite(AFt)
Crystallinity: Good Morphology: Long slender needles, hexagonal cross section -Most water bound -ONE OF THE FIRST HYDRATION PRODUCTS TO FORM!!!
Hydration Products: Monosulfate(AFm)
Crystallinity: Poor-fair Morphology: Very thin irregular hexagonal plates
Hydration Products: CH
Crystallinity: Very Good (Highest Degree) Morphology: Hexagonal Plates (looks similar to monosulfate) "Poor Binder" Durability issues INCREASE CH = INCREASE Permeability (which is bad)
Hydration Products: C-S-H
Crystallinity: Very Poor Morphology: Unresolved: spines, spongy, very small "Glue" that binds aggregates Amorphous material
Of the four primary clinker phases, which contributes the most to early compressive strength?
Early on C3S
Different types of cement uses
Expansive cement Plastic cement Ultra fine cement Calcium aluminate cement
Reactions in Kiln (1150-1200C or 2100F-2190F)
Formation of BELITE crystals (C2S)
Reactions in Kiln (~1200C)
Formation of C3A and C4AF
How many tons of concrete produced per person per year worldwide?
Four Tons
Cement and Concrete History (c. 500 BC)
Greeks using lime-based mortars as binders between stone and bricks
Manufacturing process - Step 2
Grind raw materials and blend together Modern cement plants grind and blend the materials in DRY CONDITIONS. (Dry Process) and it is more efficient than the "WET PROCESS". Wet process - Water is added during grind and blending and a slurry is created.
Who patented portland cement and in what year was the patent granted?
Joseph Aspdin in 1824
Cement and Concrete History (c. 2500 BC)
Lime mortar or gypsum-based mortar used between stone blocks for the great pyramid of Giza
Lime cycle
Limestone, calcium carbonate, CaCO3 ⬇️ add heat (~1000C) --> CaO + CO2(g) removes CO2 (CALCINATION) Quicklime, calcium oxide, CaO ⬇️ Add water (H20) calcium hydroxide, Ca(OH)2 <==(hydrated lime) ⬇️ Add carbon dioxide(from air), CO2 CaCO3+H20 Back to start.
Manufacturing Process - Step 4
Material is fed into rotating kiln
Calorimetry
Monitor the heat of hydration to evaluate the rate of the reaction
AFm
Monocarboaluminate formed in the presence of carbonate iron (PLCs)
Cement Mill Sheet
Must meet ASTM requirements Must include: -Oxide Composition -Fineness -Insoluble residue -Compound composition - an estimate, not always accurate - X-ray Diffraction (XRD) - exact, more accurate
Reactions in Kiln (700C or 1290F)
Occurs in pre-heating tower (not in kiln)
Capillary Porosity
Original water-filled pores W/CM = 0.32 by mass= 1 W/CM = 0.64 by mass = 2 For any concrete mix, increasing the degree of hydration through moist-curing reduces the porosity.
List two things that a cement manufacturer is required to list in a cement mill sheet.
Oxide composition fineness insoluble residue chemical composition physical properties
Diffusion
Particles swim around until equilibrium is achieved
Manufacturing process - Step 3
Place blend raw material into a preheater/precalciner
Pore Solution Extraction: After Setting
Pore Press
Manufacturing process - Step 1
Quarry raw materials, crush them and store them
Where does cement end up?
Ready Mix (Most common) 68.6% Concrete Roof tile (Least Common) 0.5%
Sulfate Addition
Sulfate is added to control the setting of concrete Sulfate forms: -Gypsum (Most Common) -Anhydrous Calcium Sulfate (Anhydrite) CaSO4 -Calcium Sulfate Hemihydrate - CaO4 *1/2H20
True or False: Total porosity decreases as curing time increases
TRUE bc curing reduces water-to-cement ratio
Describe the main difference between Type I and Type III cement Portland cement.
Type I and Type III have approximately the same chemical composition, however Type III cement is ground much finer to increase its reactivity. (Higher FINENESS)
Pore Solution Extraction: Before Setting
Vacuum or Nitrogen Gas Pressure-Assisted Filtration
Cement Storage
Very reactive with water -Be kept Dry -Be stored in a place with low relative humidity -Be stored on pallets, never on ground -Be stacked together to reduced air circulation -Be covered with a tarp if stored outside temporarily -BE NOT STACKED AGAINST EXTERIOR WALLS
Pozzolanic cement is..
hydraulic (used by Greeks, Indian, Egyptians, and etc)
Heat of Hydration: Semi-Adiabatic
known heat loss (insulated)
Heat of Hydration: Isothermal
measure amount of energy required to keep temperature constant -temperature of the sample remains constant! -Most common for Calorimetry
Most modern cement plants are built..
near a Limestone source
Heat of Hydration: Adiabatic
no heat loss to create mass concrete (perfectly insulated)
Pozzolanic Reaction
xCaO + ySiO2 + zH2O --->> xCaO x ySiO2 x zH2O lime silica calcium-silicate-hydrate calcin. pozzolan (C-S-H)
