Midterm Prep Flashcards
Void Ratio (Formula)
e
e=Vv / Vs
Relationship between void ratio and:
1. Density
2. Strength
3. Permeability
- As e decreases density increases
- As e decreases strength increases
- As e decreases permeability decreases
Porosity (Formula)
n
n = Vv / Vt
Degree of Saturation (Define and Formula)
Sr
Degree of Saturation tells us the percentage of the total volume of voids that contain water
Sr = Vw / Vv x 100%
Density (Formula and Units)
g/cm^3, kg/m^3 or Mg/m^3
Density of Solids, ps = Ms / Vs
Density of Water, pw = Mw / Vw = 1.0g/cm^3
Bulk Density, p = Mt / Vt
Saturated Density, psat = Mt / Vt
Dry Density, pd = Md/Vd = Ms / Vt
Buoyant (Submerged) Density, p’ = psat - pw
Unit Weight (Formula and Units)
γ = pg
kN/m^3
Moisture Content (Define and Formula)
Moisture Content is the amount of water present in a soil in terms of the mass in dry soil.
w = Mw / Ms x 100%
Specific Gravity (Formula)
Gs = γs / γw = ps / pw
Relative Density (Formula)
Dr = (emax - e) / (emax - emin) x 100%
Dr = 100% -> Very Dense
Dr = 0% -> Very Loose
* Can also be expressed in terms of unit weight or density, but you must multiply the fraction by (γdmax / γd) or (pdmax / pd)
List the main differences between Cohesive Soil and Cohesionless Soil
Cohesive:
- Fine Grained
- Grain to grain attraction (force is required to pull the material apart)
- Significantly compressible
- Moisture Content
Cohesionless:
- Course Grained
- No grain to grain attraction
- Very slightly compressible
- No moisture content
Atterberg Limits
Atterberg Limits are really moisture contents of the soil which define the change in behavior from:
Liquid to Plastic - Liquid Limit wL
Plastic to Semi-Solid - Plastic Limit wP
Semi-Solid to Solid - Shrinkage Limit Ws
Plasticity Index, PI
The plasticity index defines the range of water contents over which the soil behaviour is plastic.
PI = wL - wP
High PI indicates considerable clay minerals present.
Low PI indicates a silty material.
Liquidity Index, LI
The liquidity index provides an index to whether the soil will behave in a brittle, plastic, or sensitive manner.
LI = (wN - wP) / PI
LI = 0 -> Plastic Limit
LI < 0 -> Semi-Solid Behaviour
LI = 1 -> Liquid Limit
LI > 1 -> Sensitive (quick) Clay
Sensitivity of Soil
Sensitivity relates the undisturbed strength of the soil to its remolded strength.
When the Liquidity Index is higher than unity, the soil is said to be sensitive.
Sensitivity = (undisturbed undrained strength) / (remolded undrained strength)
Activity, A
Activity is an index that isolates the effect of the clay mineral type.
A = PI / Clay Fraction
Well Graded Soil (Define and Describe the Curve)
A good representation of particle sizes over a wide range.
Gradation Curve is usually smooth, least steep slope.
Poorly Graded Soil (Define and Describe the Curve)
Either excess or a deficiency of certain sizes, or most of the particles are about the same size. (Uniform Soil)
Gradation Curve is very vertical
Gap Graded Soil (Define and Describe the Curve)
A proportion of grain sizes within a specific range is low.
Also poorly graded.
Gradation curve is a bumpy version of a well graded soil.
Coefficient of Uniformity (Formula)
Cu = D60 / D10
1 < Cu < 5 - Uniform Soil (Narrow Range)
Cu > 15 - Well Graded Soil (Wide Range)
Coefficient of Curvature (Formula)
Cc = D30^2 / (D10)(D60)
1 < Cc < 3 is a well graded soil as long as Cu is also greater than 4 for gravels and 6 for sands
Stoke’s Law
v = CD^2 = z / t = D^2(γs - γw)/18n
v = particle velocity
C = f(γs, γw, fluid viscosity)
D = sphere diameter
Z = depth measured from top of fluid
t = time
n = fluid viscosity
Common uses of the Hydrometer Test
- To define the boundary between silts and clays
- To get the distribution of silt sizes
Soil Classification via a 2 letter system
G S M C O Pt
W P M C H L
The first letter describes the major component of soil:
G - Gravel
S - Sand
M - Silt
C - Clay
O - Organic
Pt - Peat
The second letter describes the soil:
- For course grained:
W - Well Graded
P - Poorly Graded
M - Contains appreciable silt
C - Contains appreciable clay
- For fine grained
H - High Plasticity
L - Low Plasticity
What are the three conditions a dual symbol is used under?
- Coarse Grained soils with 5-12% fines
- The first symbol indicates Well/Poorly graded, the
second symbol defines the fines
- The first symbol indicates Well/Poorly graded, the
- Fine-Grained soils with limits within the shaded zone of the plasticity chart.
- Soil containing similar fines and course-grained fractions.
Asphalt vs Tar
Asphalt:
- Soluble in petroleum products
- A by-product of petroleum distillation process
Tar:
- Resistant to petroleum products
- A by-product of coal
What makes up asphalt cement and what is their role?
Asphaltenes - Strength and Stiffness
Resins - Adhesion and Ductility
Oils - Viscosity and Fluidity
Resin + Oils = Maltenes
Describe Rutting
- Surface depression in wheel path
- Pavement uplift (shearing) may occur along the sides of the rut.
- Occurs due to the binder being too soft
Describe Thermal Cracking
- Cracks perpendicular to the pavement’s centerline or laydown direction.
- Binder may be too hard, especially at low temperatures
Ductility Test
A ductility test measures the amount of elongation before breakage in a standard length of a given binder.
Thin-Film Oven Test
Asphalt binders undergo aging and hence deteriorates over time, due to high temperatures and exposure to the elements.
- Simulates the effect from short-term aging of the binder
Flash Point Test
A minimum temperature is ensured below which the binder is deemed safe.
Solubility Test
In order for the binder to retain a high level of purity, the solubility test is conducted and a maximum is set for the impurities
Internal Structures of Asphalt
- Sol Type - asphaltenes are freely separated and widely dispersed in the oil phase (Newtonian fluid)
- Gel Type - asphaltenes are strongly bound through intermolecular attraction in a complex 3-dimesional network. (Non-Newtonian fluid)
- Sol-Gel Type - Intermediate stage (Non-Newtonian fluid)
Effects of Temperature on Asphalt Cement
- As temperature increases, the asphaltenes become more dissolved in the resin, which in turn becomes more dissolved in the oil.
- Temp. Increase = Less Viscous
- As temperature decreases, the asphaltenes become less soluble, and become increasingly bonded in an ordered structure.
- Temp. Decrease = More Viscous
Glass Transition Temperature
The glass transition temperature is the temperature below which the physical properties of amorphous materials vary in a manner similar to those of a solid phase, and above which amorphous materials behave like liquids.
Why do asphalt pavements fail or crack? (3)
- Pavement deformation or rutting occurring at high temperatures as the asphalt softens and the mix loses elasticity.
- Low temperature cracking as asphalt becomes brittle and the pavement shrinks in cold weather.
- Fatigue cracking due to high temperatures due to high volume of load application combines with aging of the asphalt.
What is the result of higher air voids in Hot Mix Asphalt?
Higher air voids means lower strength and higher permeability
Gmb
Bulk Specific Gravity of compacted HMA
Gmb = Ms / (Mssd - Msubmerged)
(mass of dry sample divided by the mass of SSD sample minus the mass of the sample under water)
Gmm
Maximum Specific Gravity
Gmm = Mass aggregates and AC / Volume of aggregates and AC
Gse
Effective Specific Gravity
Gse = (Dry Mass) / (Effective Volume) = (100 - Pb) / (100/Gmm - Pb/Gb)
VMA (Define and Formula)
Voids in Mineral Aggregate
VMA = (Vbe + Va) / Vt x 100%
VFA (Define and Formula)
Voids filled with Asphalt
VFA = 100 - (VMA - AV) / (VMA)
Air Voids in HMA (Formula)
VA = (1 - Gmb / Gmm) x 100%
Mass of binder (Formula)
Mb = Pb Mt
Mass of solids (Formula)
Ms = Ps Mt = (1-Pb) Mt
Percent Binder Absorbed (Formula)
Pba = 100 x Gb x (Gse-Gsb) / (GsbGse)
Effective Asphalt Content (Formula)
Pbe = Pb - Pba / 100 x Ps
VTM (Formula)
Va / Vt x 100%
