cement

Question 1

how is cement formed

Answer 1

limestone+shales»clinker (when heater)

|&raquo_space;add gypsum to clinker» cement

Question 2

name the 4 clinker compositions and what the do

Answer 2

C3S- early strength
C2S-long term strength
C3A-initial setting
C4A-controlls melting in kiln

Question 3

describe what happens when cements hydrated

Answer 3

1-particles dissolve and ions rearrange in the solution phase
2-solid hydrate phases solidify and give strength

Question 4

name the 4 hydrate phases

Answer 4

1-C-S-H
2- calcium hydroxide
3-Aft (ettringite )
4-Afm

Question 5

describe C-S-H

Answer 5

• formed from the hydration of C3S and C2s
• fills the space
• non crystaline

Question 6

describe calcium hydroxide

Answer 6

• by product of the hydration of c2s and c3s

- HOLDS INTERNAL PH HIGH helping durability of the steel

Question 7

explain ettringite Aft

Answer 7

• formed from reaction of C3A+water+gypsum
• needle shaped crystals interlocking gives initial setting
• too much gypsum added» false set
• too little» flash set
• forms Afm too quick and has no strength

Question 8

Afm

Answer 8

gives slight strength

can cause durability probs- sulphate attack which causes binder to expand>cracking

Question 9

what a supplementary cementation materials and give an example

Answer 9

-added to alter the properties of binder improving performance
eg limestone
-pozzolans are SCM but contain Si or Al or fly ash

Question 10

how do pozzolans form

Answer 10

cement blended with sources of Si0
-which react with CH»CSH
increasing strength and durability

Question 11

are pozzolanic reactions slower or faster than hydration and whats the effects

Answer 11

slower then hydration»> gives strength at later stages/enhances long term properties