Materials II

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How can concrete be prepared?
Concrete is made at a concrete batch factory. Components can be allowed to precast and harden in factory or in-situ concrete is cast on site.
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What are concrete compaction methods?
Compaction methods: poker ********, vibrating beam/formwork ********s.
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What are components of concrete?
Mortar: cement and additions, admixtures, water (cement paste), and fine aggregate. Also coarse aggregate.
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What are the lime reactions?
CaCO3 -> CaO |(quicklime)+CO2. CaO+H20-> Ca(OH)2 (slaked lime) ( Ca(OH)2+CO2-> CaCO3 + H20
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What is the history of concrete?
John Smeaton mixed volcanic ash and limestone to make lighthouse. 1824 - Portland Cement made heating limestone and fine clay
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What are qualities of Portland Cement?
Portland cement - inorganic, calcareous (mostly made from calcium carbonate), hydraulic element
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How is PC made?
75% limestone/chalk + 25% clay/shale -> heat 1400 degrees then rotary kiln -> form clinker of aluminates and silicates, grind to powder, add 4% gypsum -> grinder mill
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What are the main components of cement clinker? (basics)
C=CaO, S-Sio2, A= Al2O3, F=Fe2O3, H= H2o, S (with hat)= SO3
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What are PC clinker components?
C3S and C3A make most of cement, and C2S and C4AF make less. Gypsum is CS^H2
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What are basic hydration products?
CS3 hydration product - C3S2H3 (C-S-H gel) C2S- CH (calcium hydroxide), C3A - produces ettringite in process.
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What vapour pressure needed for hydration?
Hydration continues if relative vapour pressure in pores >80%
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Which components of PC clinker hydrate fastest?
C4AF hydrates most, close to 100%, then C3A, then C3S, then C2S has about half of it hydrated
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What are setting and hardening?
Setting - from plastic and workable paste to stiff and unworkable. Hardening - Rigid solid gaining strength with time.
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What are initial and final set times?
Initial set time - getting Portland cement to stiff unworkable paste. Final set time - turning to solid.
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How do fluidity, hydration, and strength of concrete change with time?
Fluidity of concrete drops with time while hydration and strength slowly increase
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Which compound of PC clinker is strongest? Order them
C3S strongest, then C2S, then C4A, then C4AF
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What are the hydration products of concrete?
CSH |(amorphous), capillary pores, CH plates, ettringite needles,
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What is the model of CSH?
CSH consists of C-S-H sheets with interlayer water and gel pores. Have high specific surface and porosity, low permeability
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What do capillary pores influence?
Pores affect ductility and strength
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What is w/c? What's ideal w/c for structural models?
w/c is water/cement ratio. For structural models it's 0.45
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What is curing? What condition is needed for hydration?
Curing : maintaining water content and temperature. No significant hydration if pore relative humidity below 80%
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What are wet and dry curing methods?
Wet curing: Spraying, flooding/ponding, covering with wet material. Dry curing - maintaining surface formwork, covering with impermeable material/liquid curing membrane.
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For British standards, what do CEM 11 A, S, 42.5, AND N mean for BS EN 197-1 CEM II|AS 42.5 N
CEM II - main cement type, A - proportion of PC clinker, A=high, B=med, C=low, S - 2nd main component, 42.5 - standard strength class, N - early strength, N-normal, R-rapid
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What are admixtures?
Admixtures - added to concrete before or after mixing to modify fresh/hardened properties. Usually water-based, blends of proprietary chemicals, dosed by <5% by weight of cement
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What are superplasticisers?
Cement deflocculated to increase workability, easier to compact without affecting strength and better hydration as more particles exposed. w/c can be reduced.
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What are retarders and accelerators?
Retarders extend setting time for elimination of cold joints in large pours, hot weather concrete, delays etc. Accelerators speed up setting. strength hardening accelerators give higher early strength. For urgent repair and cold weather concreting.
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What is the problem with C Cl as an accelerator?
Calcium chloride efficient accelerator but corrosive.
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What are air entraining agents?
Entrain air in uniformly dispersed cavities - increase freeze thaw resistance but reduce strength
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What are some special purpose admixtures?
Foaming agents (trench fill), permeability reducers, pumping aids, admixtures for sprayed/underwater concretes, corrosion inhibitors
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What are aggregate advantages?
Cheaper than cement, less energy in production, can replace cement paste and make 75% of concrete, more durable than cement paste
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What are aggregate origins?
Older semimentary formations (limestone/sandstone), igneous/metamorphic rocks, recent deposits - sand and gravel beds
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Outline sand and gravel production
Remove overburden, dry/wet working and extraction, processing, screening/washing, quality control testing, and restoration of site
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Outline crushed rock production
Remove overburden, blast/drill/break, load and transport, stockpile, process, crush, screen, wash, blend and stockpile, quality control test, restore site.
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Other cards in this set

Card 2

Front

What are concrete compaction methods?

Back

Compaction methods: poker ********, vibrating beam/formwork ********s.

Card 3

Front

What are components of concrete?

Back

Preview of the front of card 3

Card 4

Front

What are the lime reactions?

Back

Preview of the front of card 4

Card 5

Front

What is the history of concrete?

Back

Preview of the front of card 5
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