7. Materials

Question 1

What is the shear strength of a soil?

Answer 1

Its resistance to shearing stresses.

Question 2

What is shear strength a function of?

Answer 2

cohesion, angle of internal friction, and normal stress on the failure plan.

Question 3

How are the parameters, “c” and “phi” determined?

Answer 3

Directly from standard field vane shear test or indirectly through lab test ( direct shear test, triaxial test).

Question 4

What are three ways soils are compressed?

Answer 4

• Compression of solid particles and water in the voids
• Compression and expulsion of air in the voids
• Expulsion of water in the voids

Question 5

What is the compressibility of a soil mass dependent upon?

Answer 5

The rigidity of the soil skeleton which in turn is dependent on the structural arrangement of the particles (e.g., loose, dense, honeycombed).

Question 6

What does compaction do to a soil?

Answer 6

improves strength and reduces compressibility.

Question 7

What is the coefficient of permeability, k depended upon?

Answer 7

soil particle size, shape, structure, void ratio, degree of saturation, and void connectivity.

Question 8

What is specific discharge (v)?

Answer 8

the discharge per unit x-sectional area, AKA Darcy velocity or discharge velocity (average velocity over an area)

Question 9

What is seepage velocity (Vv)?

Answer 9

velocity through the pore space only.

Question 10

How is hydraulic conductivity determined?

Answer 10

Constant head test or Falling head test.

Question 11

What is frost heave?

Answer 11

When temperature in the a soil mass drops below water’s freezing point, water in the void freezes and therefore expands, causing the soil mass to move upward.

Question 12

What is compaction?

Answer 12

the process of increasing the bulk density of a soil or aggregate by removing air.

Question 13

What is achieve with optimum water content exists?

Answer 13

Maximum dry density.

Question 14

What are the factors affecting field compaction?

Answer 14

besides soil type and moisture content,

• thickness of the lift
• intensity of pressure applied by the compacting equp.
• area over which the pressure is applied.

Question 15

What is the Liquid Limit?

Answer 15

the moisture content at which the cohesive soil passes from liquid state to plastic state.

Question 16

What is Plastic Limit?

Answer 16

the moisture content at which the cohesive soil passes from plastic state to semisolid state.

Question 17

What does the area under a stress-strain diagram represent?

Answer 17

the amount of the strain energy per unit volume absorbed by the material.

Question 18

What is the Modulus of Resilience?

Answer 18

the strain energy absorbed up to the yield point .

Question 19

What is the Modulus of Toughness?

Answer 19

the total area under the diagram up to fracture.

Question 20

What is ductility?

Answer 20

it corresponds to the amount of energy absorbed at failure. Thus toughness can be representative of ductility.

Question 21

How does the increase of Carbon affect steel?

Answer 21

• Increases yield strength
• Reduces fracture strain and toughness
• Does not affect modulus of elasticity

Question 22

What is the purpose of the Torsion Test (Shear Test)?

Answer 22

to calculate the Shear Modulus (G) and thus obtain the Poisson’s Ratio.

Question 23

What is the purpose of the Charpy V-Notch Test?

Answer 23

to measure toughness.

Question 24

How to protect steel material from corrosion?

Answer 24

• Barrier coating using zinc (galvanization) or epoxy (rebar).
• Cathodic protection

Question 25

What is fatigue in steel?

Answer 25

the weakening of a material caused b repeatedly changing the intensity or direction of the loads.

Question 26

What is creep?

Answer 26

the time-dependent deformation under sustained loads.

Question 27

How does the water-cement (w/c) ratio influence the qualities of concrete?

Answer 27

• Reducing w/c, increases strength and impermeability
• Increasing w/c, will improve the workability of the concrete
• Increase in w/c, reduces resistance to weathering

Question 28

Effects of Air Entrainer?

Answer 28

produce air bubbles in the hardened concrete that provide some extra space for expansion of water due to freezing.

Question 29

Effects of Water Reducers?

Answer 29

• Workability is increased
• Workability is achieved at a lower w/c, therefore strength is increased
• Does not affect total cost of concrete.

Question 30

Effects of Superplasticizers?

Answer 30

greatly increases flowability of the concrete and reduces the amount of water required. Thus, increasing the strength and durability of the hardened concrete. E.g., high strength concrete.

Question 31

Effects of Retarders?

Answer 31

increases the time between mixing and finishing the concrete.

Question 32

Effects of Accelerators?

Answer 32

• reduces the time needed to start finishing operation
• reduces curing time
• increases the rate of gaining strength
• plugs leaks under hydrostatic pressure.
• Typically used for work in cold environments

Question 33

Effects of Fine Minerals?

Answer 33

• improve properties of concrete (by replacing cement and reducing shrinkage). E.g. Fly Ash

Question 34

What is the most important mechanical property of concrete?

Answer 34

f’c which is directly used in calculations of structural capacity of reinforced concrete components.

Question 35

What does the Split Tension Test measure?

Answer 35

Tensile strength of concrete.

Question 36

What does the Flexural Strength Test measure?

Answer 36

Flexural strength

Question 37

Name the five types of cement and their respective uses.

Answer 37

Type I - Normal; general applications
Type II - Moderate Sulfate Resistance; warm weather
Type III - High Early Strength; fast track construction, in cold weather
Type IV - Low Heat of Hydration; mass concrete (e.g., large dams)
Type V - High Sulfate Resistance; exposed soil with high sulfate concentrations