Asphalt

Question 1

What is Asphalt? And describe three properties.

Answer 1

Dark brown black highly viscous hydrocarbon and is a petroleum residue left from the distillation of crude oil.

Highly waterproof, thermoplastic and viscoelastic adhesive.

Question 2

What important properties should Asphalt have and why?

Answer 2

1. Durability
   Measure of how asphalt binder changes with age. As asphalt binder ages it’s viscosity increases and it becomes more stiff and brittle
2. Rheology
   Study of deformation and flow of matter. Pavements that deform a lot may rutt and bleed more but those that are too stiff might be susceptible to fatigue cracking.

Question 3

What is the advantages of hot and cold asphalt?

Answer 3

Hot asphalt binder is fluid and can be spread and compacted easily
Cool and stiff asphalt is able to withstand heavy loading without appreciable deformation

Too cool and stiff can cause cracking
At higher temperatures too fluid can cause deformation

Question 4

What methods can you use to grade asphalt binders?

Answer 4

1. Penetration grading
   Using a standard needle to penetrate binder sample when place under 100g load for 5 seconds. Typical U.S. binders have 65-70 pen and 85-100 pen.
2. Viscosity grading
   Measures penetration and viscosity at different temps. Can be done on virgin or ages asphalt binder. Measurements come out in poises. However doesn’t test low temperatures

3) performance grade (no need to remember)

Question 5

What are Asphalt binder modifiers and why are the needed/ what do they help improve?

Answer 5

They are needed to help asphalts meet specifications. They help improve:
1) Lower stiffness (or viscosity) at higher temperatures in construction (means liquid asphalt binder can be pumped better)
2) Lower stiffness at lower temperatures (reduces thermal cracking)
3) Higher stiffness at high service temperatures (reduces rutting and shoving)
4) increases adhesion between binder and aggregate in presence of moisture (reduces likelihood of stripping) you can do this by adding anti-stripping modifier

viscous means thicker= is opposite to runny
At higher temps, asphalt binder gets LESS viscous. Viscosity= stiffness!= more viscous= more stiff. Less viscous =less stiff

Viscosity and Stiffness Relationship: Viscosity measures a fluid’s resistance to flow, while stiffness (or modulus) measures a material’s resistance to deformation. In asphalt, higher viscosity means the binder is thicker and flows less easily, which translates to greater resistance to deformation under load1.
Temperature Effects: As temperature decreases, asphalt viscosity increases, making the binder stiffer. This increased stiffness helps the asphalt resist deformation and rutting under traffic loads2.
Performance: High-viscosity asphalt binders are often used in applications where enhanced stiffness is needed, such as in high-traffic areas or regions with extreme temperature variations3.

Question 6

What are the 4 types of asphalt used?

Answer 6

1) Asphalt cement
2) Emulsified asphalt- this is a suspension of small asphalt cement droplets in water, and an emulsifying agent (such as soap)- these have lower viscosities than plan asphalt so can be used in low-temp applications. Emulsions are used as prime/ tack coats. After it is applied the water evaporates, leaving the asphalt cement.
3) Cutback asphalt= is combo of asphalt cement and petroleum solvent. They also have low viscosity and can be used in lower temps like emulsified asphalts. After it is applied the solvent evaporates leaving the asphalt cement. used as prime/ tack coats, but not a common use because petroleum is more expensive than water.
4) Foamed asphalt- combo of hot asphalt binder with small amount of cold water. When water touches the hot material it turns into steam, which is trapped in tiny asphalt binder bubbles= resulting in thin high volume asphalt foam. This only lasts a few minutes before it returns to original state. used as a binder in soil or base course stabilisation.

Question 7

1.What’s recycled Asphalt called?

2.What are it’s uses?

3.What are it’s benefits?

4.What are it’s drawbacks?

Answer 7

1.Reclaimed Asphalt Pavement (RAP)

2.RAP can be used for embankment/ fill material, or granular base course, or as an aggregate in cold-mix asphalt or added to regular HMA

3.If it’s added to HMA it is added at 10-30% though additions as high as 80% have been done. It is said that HMA with RAP performs just as well as HMA without RAP.
When added it is used instead of the virgin aggregate so reduces cost/ waste.
Adding RAP makes the mixture more viscous= more stiff

4. When RAP is heated it gives off gassy hydrocarbons- so it’s better to heat RAP indirectly or it’s added after the aggregate is already heated so it heats up from being in direct contact.
   RAP is also usually added cold so requires longer HMA plant heating times. Which halves the plant output. to avoid this RAP can be preheated by this is extra energy/ emissions/ equipment.

Question 8

Explain TSCS and it’s properties

and what clause does it fall under

How does it differ from HRA/ SMA

Answer 8

Thin surface course system
#942

HRA= very stiff and used on heavier trafficked roads
less permeable than SMA/ so doesn’t allow water to infiltrate

lower voids content= so less bubbles to form in it so hard for water to permeate

Useful for bridge deck for this reason

SMA is permeable!= not noisy and available in three stone sizes 14mm/ 10mm, 6mm. the smaller the size the quieter

Question 9

What are the clauses for each material

Answer 9

924= HFS
#942= TSCS
943= HRA
937/ 929= Binder SMA PMB
936= geosynthetic SAMI

Question 10

What is life for TSCS/ HRA?

Answer 10

10-15 years