Portland cement Flashcards
Describe three properties of cement.
-Binds solid aggregates together by hardening from a plastic state
-Has both adhesive and cohesive properties
-Functions by forming a plastic paste when mixed with water, which develops rigidity and then steadily increases in compressive strength by chemical reactions with water
What is Portland cement?
A hydraulic cement produced by pulverising clinker, consisting of crystalline hydraulic calcium silicates, usually containing one or more of the following: water, calcium sulphate, up to 5% limestone, processing additions
How much of the worlds concrete uses Portland cement?
> 95%
Give the following compounds abbreviations: Calcium oxide (CaO), Silicon Dioxide (SiO2), Aluminium Oxide (Al2O3), Iron Oxide (Fe2O3), Water (H2O), Sulphur Trioxide (SO3), Carbon Dioxide (CO2), Sodium Oxide (Na2O), Potassium Oxide (K2O)
CaO - C
SiO2 - S
Al2O3 - A
Fe2O3 - F
H2O - H
SO3 - S(bar)
CO2 - c
Na2O - N
K2O - K
Describe Alite clinker.
(C3S) Hardens rapidly, develops high strength
Describe Belite clinker.
(Beta-C2S) Hardens slowly, develops high strength
Describe Aluminate clinker.
(C3A) Reacts with gypsum, products are of low solubility
Describe Ferrite clinker.
(C4AF) Similar of C3A Aluminate but not as rapid
Describe Calcium Silicate Hydrate (C-S-H).
-Formed by the hydration of Alite and Belite
-Makes up to 70 wt% of fully hydrated phase
-The major strength contributing phase
Describe Calcium Hydroxide/Portlandite (C-H).
-By product of Alite and Belite hydration (they have more Ca than can be accommodated for in C-S-H)
-Makes up to 20 wt% of fully hydrated phase
-Does not contribute to strength
Describe Ettringite.
-Direct reaction of Aluminate with water leads to flash set (stiffening without strength development) forming aluminate hydrates
-By adding gypsum, aluminate reacts moderately an forms ettringite (Alumina ferric oxide tri-sulphate)
Why is mineral component tat added to cement?
To improve performance and reduce cost
What are supplementary cementitious materials (SCMs)?
Mineral component tat (NOT AGGREGATES)
What is a Pozzolanic reaction?
Silica and alumina component reacts with portlandite to produce more C-S-H
What is the point of carrying out pozzolanic reactions?
C-S-H fills pore spaces at longer age, improving strength and durability
How fast is a pozzolanic reaction?
Generally slower than cement hydration
What happens when cement is substituted for pozzolans?
Early strength is reduced
What physical properties change when the cement is blended?
-Extra C-S-H fills in space, which gives extra strength
-Chemical durability improves
Give some examples of Pozzolanic SCMs.
-Fly ash
-Volcanic earth
-Calcines clays
-Silica fumes
-Rice husk ash
-Waste silicate glass
Give two examples of non-pozzolanic SCMs.
-Limestone
-Blast furnace slag
