Portland cement Flashcards
glue that bonds aggregate together to make concrete
cement paste (cement + water)
cement paste and sand
mortar
cement + water + sand + gravel
concrete
process to make portland cement
crushing and grinding of raw materials, heat and melt in kiln that forms cement clinker, add gypsum to clinker and pulverize to fine powder
chemical composition of PC
tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracalcium aluminoferrite
How is fineness important when making PC
smaller particles have more surface area to react with water, fineness controls the rate of hydration (heat and strength game)
measures air permeability against known standard material
Blaine test
measures sedimentation rate suspended in kerosene
Wagner Turbidimeter
specific gravity of cement (w/o air voids)
3.15
chemical reaction of cement w water
hydration
dominates early stage of hydration
through-solution
solid state reaction at cement surface
topochemical
Hydration rate: aluminates > silicates
needs balance
Hydration of C3S & C2S
makes paste strong
Primary Chemical Reaction Chemical reactions that harden cement paste
Fast in the beginning but is long term (decades in dams), Causes heat, which can be a problem if there’s too much
Voids in hydration space
interlayer hydration space, capillary voids, trapped voids, entrained air
space between atomic layers, shrinkage if humidity is less than 11%
interlayer hydration space
w/c too high, decrease strength and increased permeability
capillary voids
large pockets caused by handling, decrease strength and increase permeability
trapped voids
microscopic bubbles caused by admixtures, increased durability
entrained air
change from plastic state to solid state
stiffening
premature stiffening within a few minutes
False Set
sets that cannot be fixed
quick and flash sets
Ability for concrete to retain volume after setting
Soundness
Most important property of hydrating cement
water-cement ratio
w/c need for hydration
0.4
Pros and cons of adding extra water to cement?
improves workability but also causes voids
types of PC
I. Normal II. Moderate Sulfate Resistance III. High Early Strength IV Low Heat of Hydration V. High Sulfate Resistance
produce tiny, dispersed air bubbles into the concrete, causes cracking and internal stress, this prevents this from happening
Air Entrainers
Air Entrainers decrease strength by 20% but can be compensated with lower w/c ratio
true
Three ways to use water reducers
- ) improve workability using same w/c ratio
- ) increase strength using lower w/c ratio
- ) reduce cost at same w/c ratio by reducing both water and cement
delay or retard initial set (increase set time), may reduce early strength, usually doesn’t reduce final set time, long haul time
Retarders
have the ability to stop and reactivate the hydration process of concrete
Hydration Controllers
2 parts to hydration controllers
stabilizer and activator
speed up initial and final set times
Accelerators
What are accelerators used for?
increase rate of strength gain, reduce the amount of time before finishing operations begin, reduce curing time, plug leaks under hydraulic pressure efficiently
Most common accelerator
calcium chloride
most common supplementary cementitious Materials
Fly Ash
Classes of Fly Ash
N, F, and C
