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Flashcards in Concrete Deck (151)
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1

Manufacture process of cement

-begins w/ decomp of CaCO₃ @ ~900°C
-leaves calcium oxide CaO + libreates gaseous carbon dioxide (calcination)
-clincering process, CaO reacts @ high temp (1400-1500°C) w/ silica, alumina, ferrous oxide to form silicates, aluminates, ferrites of calcium which comprise the clincer
-clincer ground/milled together w/ gypsum + other additives to produce cement

2

decomp of CaCO3

CaCo₃--> CaO + CO₂

3

concrete

construction material composed of crushed rock/gravel + sand bound together w/ a hardened paste of cement and water

4

basic materials of concrete

1. cement
2. aggregates
3. water
4. admixtures
5. voids

5

portland cements

-Ordinary Portland Cement (OPC)
-Rapid Hardening Portland Cement (RHPC)
-Sulphate Resistant Portland Cement (SRPC)
-White Portland Cement (WPC)

6

Portland cement - raw materials in clinker

-limestone
-iron stone
-sand
-shale
-clay
-other

7

unsustainability of cement manufacturing

-manif results in high levels of CO₂ output, third ranking producer of anthropogenic CO₂ in world
-1 tonne of cement prod 780kg of CO₂
-4-5% of total CO₂ emissions worldwide caused by cement prod

-extraction + processing: landscape degradation
-dust + noise pollution
-energy consumption + vehicle pollution of transportation

8

anthropogenic

man-made

9

cement manufacture

-limestone, shale, silica, iron oxides quarried from ground
-rock materials run thru crusher that turns rock into smaller pieces
-crushed limestone + Si + shale + iron oxides mixed together and run thru rotary kiln
-rotary kiln continuously mixes ingredients + "calcines" limestone so that CO₂ is driven off, forming clinker
-clinker ground to fine powder + mixed w/ gypsum (helps moderate how fast cement sets)
-bagged for sale

10

alternative cementitious (cement-like) materials

-blastfurnace slag cement (GGBS)
-pulverised-fuel ash cement (PFA)
-metakaolin
-rice husk ash
-silica fume

11

GGBS

-by-prod of iron smelting, quenched slag forms granules
-generally blended with OPC up to 70%
-reduced early age strength + early heat of hydration
-lower carbon footprint

12

how cements in Europe are classed

-based on perc of portland cement that has ben replaced/substituted

13

classes of cements in Europe

CEM I - OPC/RHPC (100% cement)

CEM II (65% cement)

CEM III (45% cement)

CEM IV (<45%)

CEM II-IV: OPC with limestone, PFA, or GGBS

14

when water is added to cement

-each compound undergoes hydration + contributes to final concrete product
-only calcium silicate contributes to strength
-tricalcium silicate: early strength, reacts more rapidly
-dicalcium silicate: late strenth

15

equation of hydration

Cement + H₂O -> Calcium Silicate Hydrate (C-S-H) + Ca(OH₂) + H₂O

16

cement compounds

Tricalcium Silicate C₃S

Dicalcium Silicate C₂S

Tricalcium aluminate C₃A

Tetracalcium aluminoferrite C₄AF

Gypsum

17

setting of cement and hardening of concrete

-a process of crystallization
-crystals form after certain length of time (initial set time), + interlock w/ each other
-cement + water that has crystallized in this way encloses aggregate particles + produces dense material

18

heat effect on setting and hardening

-speeds up setting + hardening of cement
-cold slows down + can even completely stop process

19

cement hydration

-setting + hardening results from chem reaction between cement + water, not drying process
-reaction exothermic + irreversible
-heat produced: "Heat of Hydration"
-usually workable up to 2 hours before it begins to set, then harden
-strength gain initially rapid, becoming progressively less
-strength gain continues indefinitely, provided moisture present (CURING)

20

cement at start of hydration vs at end

1. hydration not yet occured, pores filled with water

2. hardening cement paste, majority of space filled with C-S-H

21

heat of hydration evolution stages

stage 1
stage 2
stage 3
stage 4
stage 5

22

stage 1

-initial dissolution
-hydrolysis of cement compounds occur rapidly w/ significant temp increase

23

stage 2

-dormant period
-evolution of heat slows down
-conc in a plastic state which allows problem free transportation + placing

24

stage 3 + 4

-concrete starts to harden
-heat evol increases due to hydration of tricalcium silicate

25

stage 5

-slow formation of hydrate products continues as long as water + unhydrated silicates present

26

cement hydration notes

-when you add water to cement, solid content of mixture increasing due to hydration
-cement particles suspended in water
-hydration continues as long as water is present + there are still unhydrated compounds in cement paste

27

concrete strength gain with time graph

check slides 1 pg 25

28

aggregates

-Gravels, crushed rock + sands that are mixed w/ cement + water to produce concrete.

-generally make 50%-80% of concrete mix

29

coarse aggregates

(stone)
do not pass through a 5mm sieve

30

fine aggregates

(sand)
pass through 5mm sieve