Concrete Production Flashcards
What is concrete made of?
Cement, admixtures, water(all make cement paste), fine aggregates(add to cement paste for mortar), and coarse aggregates
How is lime made from calcium carbonate?
Lime produced by calcining (heating) natural calcium carbonate (limestone, chalk, marble, etc) at approx. 900 - 1200°C to decomposition
CaCO3 -> CaO + CO2
What’s the reaction between quicklime and water?
Quicklime mixed with water
CaO + H2O -> Ca(OH)2
How does slaked lime produce calcium carbonate again?
Slaked lime hardens slowly by reacting with absorbed CO2 from atmosphere
Ca(OH)2 + CO2 CaCO3 + H2O
How was Hydraulic lime made?
1756 Eddystone Lighthouse, Plymouth, UK built by John Smeaton using hydraulic lime (burnt limestone + volcanic ash from Italy), superior cementing properties.
What is Portland cement made of ?
1824 Joseph Aspdin patented ‘Portland cement’ made from limestone + fine clay heated to 1200°C (to produce mainly C2S and CO2).
What sort of cement is Portland?
Inorganic hydraulic calcareous cement
How is Portland cement manufactured?
~75% limestone + 25% clay or slate
or chalk from quarry
Heat to 1400-1500 degrees C in rotary kiln.
Form clinker from silicates and aluminates, put in grinder and add 4% gypsum
What is cement clinker made from?
C3S, C2S, C3A, C4AF, and CŜH2
What do C, S, A, F, H, and Ŝ consist of for cement clinker?
C=CaO S=SiO2 A=Al2O3 F=Fe2O3 H=H2O Ŝ=SO3
What is a hydration product of C3S?
When C3S is hydrated it makes C-S-H gel
What is a hydration product of C2S?
When C2S is hydrated it makes calcium hydroxide
What is a hydration product of C3A?
When C3A hydrated, ettringite is made in middle (this can make concrete explode when concrete rehydrated)
Which constituent of concrete hydrates fastest? what’s it followed by?
Almost all of C4AF hydrates, followed by c3A, then C3S then C2S
1 volume of cement 2.2 volumes of hydration products
Hydration continues if relative vapour pressure (relative humidity) in pores > 0.8 (80%)
How does hydration and hardening work in concrete?
Setting : Portland cement and water, makes workable paste and has initial set. Becomes stiff unworkable paste and has final set. Hardening: strength rises over time.
What happens when cement is hydrated?
Fluidity of cement falls while hydration and strength rise
Which concrete constituents have greatest compressive strength?
C3S has greatest compressive strength as concrete ages, followed by C2S
what can you see in a concrete microstructure?
In microstructure you can see CH which looks like plates, ettringite which looks like needles, capillary pores which look like coral reefs, sand, unhydrated cement, and C-S-H gel
What are capillary pores?
Capillary pores:
Space not filled by hydration products
Typically 0.05 - 10μm in “diameter”
Influence most properties including strength and durability
What is C-S-H known for?
C-S-H has sheets with interlayer water and gel pores contained. Has enormous specific index, porosity, and low permeability.
What are the sizes of CSH gel pores, capillary pores, entrained air voids and entrapped air voids?
CSH gel pores have size of 1nm and capillary pores have 100nm to 10 micrometres. Entrained air voids 100 micrometres in size and entrapped airvoids 100 micrometres to 10mm in size
What water cement ratio is used for structural forms?
w/c ratio of 0.45 used for structural forms. Lower w/c associated with greater performance
Degree of hydration: how does a lower water cement ratio affect this?
For lower water cement ratios, water runs out faster meaning not all cement is used up and not all CH and CSH gel is made.
