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)