Manufacturing

Question 1

Type GU

Answer 1

general purpose cement, pavements, floors, reinforced concrete buildings, bridges, pipe. More alite

Question 2

Rate of Hydration

Answer 2

mostly affected by aluminate and then belite

Question 3

Rate of Strength Gain

Answer 3

mostly affected by alite and then belite

Question 4

Type HE

Answer 4

provides early strength, more economic, permits a shorter curing time in cold weather, high heat of hydration

Question 5

sulphate attack

Answer 5

in moist soil or water, react with hydrate aluminate, CSH is chief product of reaction

Question 6

Type MS

Answer 6

moderate sulfate attack resistance, normal structures, for elements exposed to soil or ground water, <8% C3A

Question 7

Type LH

Answer 7

heat of hydration must be low, slowest strength gain, massive concrete structures, dams, more C2S, less C3S

Question 8

Type HS

Answer 8

severe sulfate attack, soils or groundwaters have very high concentrates, slower strength gain than Type GU, <5% C3A

Question 9

Heath of Hydration

Answer 9

highest for C3S and C3A, Mh and LH are low heat types

Question 10

hydration of C3A

Answer 10

C3A +6H -> C3AH6

Question 11

flash set

Answer 11

occurs due to rapid hydration of C3A, rapid rigidity and considerable heat. Plasticity is regained only with addition of water

Question 12

initial set

Answer 12

vicat needle penetrates 25mm, typically takes 2-4 hours

Question 13

final set

Answer 13

paste is rigid enough to sustain load, vicat needle penetrates 0mm, take 5-8 hours

Question 14

false set

Answer 14

occurs due to crystallization of gypsum, rapid stiffening shortly before mixing, not much heat. fluidity can be restored by remixing without water

Question 15

WRA

Answer 15

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

Question 16

AEA

Answer 16

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

Question 17

long term requirements

Answer 17

strength, durability, volume stability

Question 18

short term requirements

Answer 18

transport ability, handling, placing, finishing

Question 19

workability

Answer 19

property of concrete that determines the ease and homogeneity with which it can be mixed, placed, consolidated, and finished

Question 20

thixotropy

Answer 20

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

Question 21

segregation

Answer 21

coming apart of components in the fresh mix resulting in a non-uniform mix

Question 22

bleeding

Answer 22

appearance of water on the surface of the concrete after it has been consolidated but before it has set