Manufacturing Flashcards
Type GU
general purpose cement, pavements, floors, reinforced concrete buildings, bridges, pipe. More alite
Rate of Hydration
mostly affected by aluminate and then belite
Rate of Strength Gain
mostly affected by alite and then belite
Type HE
provides early strength, more economic, permits a shorter curing time in cold weather, high heat of hydration
sulphate attack
in moist soil or water, react with hydrate aluminate, CSH is chief product of reaction
Type MS
moderate sulfate attack resistance, normal structures, for elements exposed to soil or ground water, <8% C3A
Type LH
heat of hydration must be low, slowest strength gain, massive concrete structures, dams, more C2S, less C3S
Type HS
severe sulfate attack, soils or groundwaters have very high concentrates, slower strength gain than Type GU, <5% C3A
Heath of Hydration
highest for C3S and C3A, Mh and LH are low heat types
hydration of C3A
C3A +6H -> C3AH6
flash set
occurs due to rapid hydration of C3A, rapid rigidity and considerable heat. Plasticity is regained only with addition of water
initial set
vicat needle penetrates 25mm, typically takes 2-4 hours
final set
paste is rigid enough to sustain load, vicat needle penetrates 0mm, take 5-8 hours
false set
occurs due to crystallization of gypsum, rapid stiffening shortly before mixing, not much heat. fluidity can be restored by remixing without water
WRA
water reducing admixture, compound is adsorbed at solid-water interface. molecules of WRA neutralizes surface charges or give all surfaces the same charge. no attractive force and causes deflocculation, allows better flowability
AEA
air entraining admixture, volume of air required to provide freeze thaw resistance is 4-9%. foaming agent will create fine network of sphere bubbles, lower surface tension so bubbles form more easily. A hydrophilic and hydrophobic end
long term requirements
strength, durability, volume stability
short term requirements
transport ability, handling, placing, finishing
workability
property of concrete that determines the ease and homogeneity with which it can be mixed, placed, consolidated, and finished
thixotropy
time-dependent fluid, can begin to stiffen but will become less viscous when sheared, then stiffen when allowed to sit. Consistency depends upon both rate of shear and duration of shear
segregation
coming apart of components in the fresh mix resulting in a non-uniform mix
bleeding
appearance of water on the surface of the concrete after it has been consolidated but before it has set
