Portland Cement (extra)
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what are the three main raw materials of PC cement?
• lime CaO • silica SiO2, alumina Al2O3 • gypsum CaSO4
what do the three main raw materials of PC form? what is it called?
clinker
what does the C notation mean?
CaO
what does the S notation mean?
SiO2
what does the A notation mean?
Al2O3
what does the F notation mean?
Fe2O3
what does the H notation mean?
H2O
what does the Š notation mean?
SO3
what is the reaction for stage 1 (alite phase)?
2C3S + 6H —> C3S2H3 + 3Ca(OH)2
what is the reaction for stage 2 (belite phase)?
2C2S + 4H —> C3S2H3 + Ca(OH)2
what is the reaction for stage 3 (tricalcium alumninate phase)?
C3A + 6H —> C3AH6 C3A + 3CŠ.2H + 26H —> C6AŠ3H32 (ettringite)
what is the reaction for stage 4 (calcium alumino ferrite phase)?
C4AF + calcium hydroxide + gypsum + water —> solid solution of sulfoaluminate & sulfoferrite
which stage is faster, alite or belite?
alite is FAST belite is SLOW
what is the alite phase responsible for?
early, initial strength
what is the belite phase responsible for?
long term strength
why is gypsum added in stage 3?
added to slow the rate of reaction, stage 3
what product of the hydration reactions is the main source of the concrete’s strength?
C-S-H gel
where is most of the C-S-H gel formed, in the alite or belite stage?
the alite stage
what happens in stage 3 (general)?
• produces rapid setting “flash set” • high heat of hydration • ettringite and then monosulfate form • ettringite = rod like crystals • monosulfate usually replaces ettringite
what stage gives concrete its characteristic grey colour?
stage 4
what are the pozzolanic reactions?
S + CH + H —> C-S-H AxSy + mCH + nH —> C-S-H + C-A-H