Lecture #3 - Concrete Ingredients - Part 3 Flashcards
(32 cards)
Define cement.
a powdery substance made with calcined lime and clay
Define portland cement.
cement that is manufactured from limestone and clay and that hardens underwater
What is calcination? What is the chemical formula for this process?
The decomposition process. CaCO3(s) gives CaO(s) + CO2(g) or limestone gives lime and carbon dioxide
What is the main cement ingredient?
lime (60-66%)
Define calcined.
To heat a material to a high temperature but without fusing to drive off volatile matter or to affect changes (such as oxidation or pulverization)
What is the manufacturing process of portland cement?
Extract, crush and store raw material, then ground and blend it, then chemicals change it to cement clinker, then the clinker is ground with gypsum into Portland cement and shipped
What does GU stand for?
General Use
What does HE stand for?
High early strength
What does MS stand for?
Moderate sulfate resistance
What does HS stand for?
High sulfate resistancce
What does MH stand for?
Moderate heat of hydration
What does LH stand for?
Low heat of hydration
Define the properties and applications of portland cement type I (GU).
most commonly used cement, used when special properties for the other types are not required, has a moderate rate of strength development and heat evolution
Define the properties and applications of portland cement type II (MS and MH).
moderate exposure to sulfate attack and heat of hydration, so good for mass concrete structures, sulfate resistance and heat control, gains strength slower than type I but has same ultimate strength, reduced temperature-related cracking from concrete pouring in warm weather, should have a lower water-to-cement ratio to lower permeability to prevent chemicals from entering and travelling in concrete and to control sulfate attack, used in structures exposed to soil or groundwater
What are some sources of sulfate?
water, cement, aggregate (internal)
Define the properties and applications of portland cement type III (HE).
has high early strength and rate of heat evolution, so not good for mass concrete, takes 7 days to reach 28 day strength of types I and II, finer cement grinding, used for optimizing construction process and early removal of forms, good for cold weather because doesn’t take as long to cure, cheaper than type I to reach high early strength (b/c I w/ high cement contents can reach high early strength)
Define the properties and applications of portland cement type IV (LH).
has a low rate of strength development, same ultimate strength as type I and II, low rate of heat evolution so good for mass concrete, heat of hydratoin is controlled, typically used in massive structures like large gravity dams
Define the properties and applications of portland cement type V (HS).
used when extensive exposure to sulfates exists, low to medium rate of heat evolution and strength development, low water-to-cement ratio and permeability resist against sulfate attack, no resistance to acids and highly corrosive substances
Explain air-entraining portland cements.
Small quantities of air-entraining material grounded with clinker for improved resistance to freezing and thawing and scaling, concrete will contain tiny, well-distributed and seperated air-bubbles, typically achieved with air entraining admixture rather than air entraining cement
What materials are used in blended hydraulic cements?
portland cement clinker, calcium sulfate (gypsum), supplementary cementious materials like fly ash, ground granulated blast-furnace slag, silica fumes, pozzolans
Explain the fineness of cement.
particle size of cement which affects hydration and thus determines the rate of strength gain, finer grinding of cement gives a more cohesive paste which gives increased workability, finer particle size gives more surface area which gives an increased hydration rate which gives early strength gain
Explain the setting time of cement.
time taken by cement paste to change from fluid to solid state, initial setting time is when the paste loses its plasticity and begins to stiffen considerably, final setting time is when the paste becomes a hard mass and can sustain a load, controlled by the amount of mixing water, temperature of atmosphere, cement composition, fineness
Explain hydration of cement.
portland cement and water mixed creates a series of chemical reactions which result in setting, hardening, heat release, and strength development which is called the hydration process
When is the greatest heat release? Up to how many days is there a large amount of heat release?
at 24 h, up to 3 days
