Cement Flashcards
How much of the C02 produced in the production of concrete comes from cement?
> 60% from modern concrete mixes
~25% comes from clinker substitution
80% for ordinary portland cement concrete
What reaction takes place in the production of early forms of cement?
Lime reactions:
Calcinning calcium carbonate at ~700-900 C
(there is more info on slide 10 lecure 6)
What are the 3 main stages of lime reactions
- Calcium carbonate -> Lime
- Quicklime + water –> portlandite
- Portlandite hardens with CO2
Name the main types of Hydraulic Inorganic Calcareous cements
Portland, Calcium aluminate, Pozzolaic, hydrophobic, Natural, expanding
Name the main types of non-hydraulic inorganic calcareous cements
Limes, Gypsum cements and plasters
What is the process for the production of odinary Portaland cement (OPC, ‘CEM 1’)
~75% limestone or chalk + ~25% clay or shale --> Heat to 1450 C --> Forms clinker --> Grind to powder --> add ~4% gypsum
What are the 3 main types of cement for packaging and transport?
- Ready-mix 47% of the market (6.2Mt)
- Precast 22% (2.8Mt)
- Retail 13% (2.4Mt)
How is ready-mix concrete used?
Concrete is mixed and poured on site
How is precast concrete used?
Product is manufactured off-site and tranported to site
How is retail cement used?
must be mixed and poured on site, comes in a dry bag, small scale uses
What is a Supplementary cementitous material (SCM)
Any reactive non-clinkered solid material used in cement (not including admixtures with special functions such as gypsum)
What is cement clinker blended with?
A source of calcium sulphate (e.g. gypsum) and SCMs
Give a few examples of SCMs
- finely ground limestone
- coal fly ash
- granulated blast furnace slag
- calcined clay
(pictures on slide 25 lecture 6)
When are SCMs added?
Either at the cement plant when limestone is added or at the concrete batching plant, this is dependent on cost
What is capillary porosity?
- The space not filled by hydration pores
- 0.05 - 10 um in diammeter
- Influence strength and durability
- Determine transport properties in cement paste