CIVE 285 Midterm 2

What was the biggest truck load?

200 wheels in Alberta in 2009

What is important when analyzing road loads

Commercial vehicles ( busses and semis)

What are the types of axles for traffic loading

single axles, single tire to tridem axels and double tires

(Mostly) What does tire pressure equal

Contact pressure

What does traffic mean

number of repetitions, can be included in design using computers, for flexible pavements the design is empirical. Empirical factors are used to conver load groups as in ESAL of 80 KN

What are other factors to consider for road analysis

Vehicle speed- determines the duration of loading

Environmental effects- asphalt, concrete, frost penetration, freezing index, precipitation (water must be drained quickly)

What are the properties of asphalt cement

At room temp- viscous and semi solid. Behaves as a viscous liquids at high temperature and elastic solid at low temperatures. Chemistry is carbon and hyrdocarbons and their derivatives. Primarly used in HMAs since asphalt is liquid at higher tems

What are the engineering characteristics of AC

Consistency, Viscosity, like plastic when heated

How to find the purity of asphalt cemment

Binders are generally bitumus so they are soluable in carbon di sulphide. generally

What do they results of a flash point represent

It shows the safe working temperature of the binder

What are the different tests for AC

Specific gravity, solubility, viscosity, penetration, flash point, ductility, aging

What does heat during the day do to rigid pavement

expansion at the top curling downward, compressive stress develops on the top

What does the cooling during the night do to rigid pavement

causes curling upward

What methods are used to analyze stress due to loading in rigid pavements

Formulae (westergaard), influence charts, and FEM programs

What does FEM stand for

Finite Element Method

What assumptions are made when analyzing stress due to loading in rigid pavements

Slabs are large and rest on a liquid foundation, and the foundation deflects with the pavement

What is the aim when analyzing the stress due to loadings in rigid pavements

TO determine the max stress and deflection due to loading

What are the design methods for flexible pavements

Empirical - CBR ( California Bearing Ratio), Limiting shear failure, limiting deflection, Regression method, Mechanistic (empirical)

What is the design principle for the empirical method

Determine penetration resistance

What is the design principle for the limiting shear failure method

Thickness to resist shear

What is the design principle for the limiting deflection method

Limit vertical deflection

What is the design principle for the regression method

pavement performance

What is the design principle for the mechanistic method

based on mechanics of materials

Initially how were flexible pavements analzed?

As A homogeneous half space

How would you interpret this image

As a homogeneous half space (with modulus E) with circular load with radius “a” and uniform pressure “q”. Possions ration is V. A cycldinrical element has a depth “z” and a radius “r”

What is the Homogeneous Half Space Theory

The pavement had indefinite area and depth, the load is applied on top of the plane

What types of stresses are on an element in half space

Due to the axisymmetric conditions, there 3 normal (z,r,t) and 1 shear stress.

These can be found using the Foster and Ahlvin charts

What is Burmister’s Method for flexible pavement?

Flexible pavements are layered systems and can’t be properly represented by the homogeneous mass theory

What are the 2 types of mix design we looked at

Marshall and SUPERPAVE

What are 2 the analysis of layers looked at?

bous, and burm

What is HMA?

Hot Mix Asphalt- combination of aggregates mixed and hot mix asphalt binder

Why is heat used in HMA

Workability, Uniform mix (coating), removes moisture, compaction and fluidity of AC for proper mixing

What are the main requirements for mix design

-Type and gradation of mineral aggregate -Type and grade of AC -Amount of diner to meet specs

What are Marshall and SUPERPAVE samples called?

Briquettes

What are the classifications of HMA

Dense graded HMA, Open graded HMA, Stone matrix Asphalt (SMA),

What is dense graded HMA

Asphalt concrete that has well graded aggregates that are compacted

What is open graded HMA

large volume of air voids either for skid resistance or for drainage. (also called no-fines mix)

What is stone matrix asphalt

High content of CA (70-80), AC (>6%) and filler content around 10%. HIgh stone on stone contact ( resistant to rutting but not flexible anymore)

What are the goals of mix design?

Resistance to permanent deformnation, fatigue resistance, low temperature cracking, moisture resistance, durability, skid resistance, and workability

What is stripping in terms of moisture resistance

When moisture enters between the asphalt film and the aggregate and affects the bond

What are the components of a HMA anaylsis

Mix density, air-voids, voids in mineral aggregates (VMA), asphalt content,

Resilient Modulus

Paving materials are not elastic but undergo permanent deformation after each loading cycle. Elastic modulus is based on the recoverable strain under repated loads this is used in elastic theory.

Who developed the Marshall Method

Bruce Marshall

Where can the Marshall method be applied?

Dense graded HMA, performance grade (PG) asphalt, max size of aggeragte linch, lab design or quality control

Asphalt Pavement history

Natural asphalts: early asphalts were naturally occurring in the earths surface

Use of vehicles created the demand for better roads, design and testing

Mid 1920’s

SUPERPAVE History

In 1987 the US congress allocated 150 million $ to a research program SHRP.

to relate lab analysis to field for asphalt specifications 50 million $ was spent. Canada spent 15 million$ to their own reasearch ( C-SHRP).

This resulted in a new test and mix design method

What is the acronym SHRP

Strategic Highway Research program

What is acronym SUPERPAVE

Superior Performing Asphalt Pavement

What is the use of SUPERPAVE

its is a system for designing HMA based on mechanistic concepts. The intention is the same as the Marshall Method. It accounts for material characteristcs recognizing the traffic loads (ESALs) and climate.

What is the asphalt binder grading system

Performance grade system (PG)

Different from previous: penetration, viscosity, penetration and viscosity, and aged residue (AG)

What is the penetration grade for Marshall

80-100, its a range at 25 degrees c

What are the pros and cons of the existing penetration system

Tests are empirical and before they can be related to field performance, experience is required. Called it evidence based

What does SUPERPAVE account for

cold and hot temperature regimes, traffic, traffic and aging control

How do you interpret PG 64-28

That it is suitable for pavement temperatures no greater than 64 degrees and not less than 28 degrees

What are the stages in SUPERPAVE grading

binders life, storage, handling and transportation

What are the modes of distress are considered in the SUPERPAVE grading system

Rutting, fatigue, cracking and thermal cracking

What does SGC stand for

SUPERPAVE gyrator compactor

What are the 2 principal features of the Marshall method

Density- void analysis, stability-flow test of compacted samples

What are the Marshall Method Steps

Aggregate selection, asphalt binder selection, preparing test samples

What temp and rate are the Marshall samples tested at

60 degrees celsius at a rate of 2” a min

Why is the Marshall sample heated to 60 deg and how

It is heated using a water bath, it is heated to 60 because that is the internal temperature that the pavement would reach on a hot day

How many strikes does the sample get from the Marshall compaction hammer

50-75, 100 for high traffic

What is rehabilitation in pavement

Structural enhancements that extend the service life of an existing pavement and or improve its load carrying capacity

What is reconstuction in pavement

Replacement of the entire existing pavement structure by the placement of an equivalent or improved structure.

What are the typical pavement distresses

Fatigue cracking, rutting, transverse cracking, longitudinal joint cracking, shoving, pothole, pavement edge cracking, longitudinal meandering cracks

What are the requirements for pavement data collection

project level vs network level, pavement surface condition assessment, industry specifications, identifying failure criteria (structural vs climatic)

What are the branches of Pavement Surface Profilers

Distress data, video log, profile, LiDAR

What are the types of destructive testing

Probe holes, asphalt coring, geotechnical drilling

What are the pavement strength testing methods

Benkelman beam (static deflection), Dynaflect (steady state), Falling weight deflectometer ( impulse load)

What is the air void range in HMA? What is the usual design value?

3-8%, design usually 4%

What are air voids?

Small pockets between coated aggregates

What is the impact durability of air voids?

too little→leads to bleeding too high→ leads to free passage of air + water

What is VMA

Voids in Mineral Aggregate / Voids between compacted aggregates

What is included in VMA

Air voids and spaces filled with asphalt

What does VMA represent?

Space available to accommodate the AC

Why is a minimum VMA required

To allow AC films to form on aggregates, increasing their durability

What is VFA

Voids Filled with Asphalt

Why do finer aggregates need more asphalt binder?

The finer aggregates have more surface area to coat

What is the aggregate absorbtion you should consider

3-6% of the dry weight of the aggregates

How do you get VMA

Air voids+ volume of asphalt

How do you get total asphalt content

Effective asphalt content + absorbtion

What is RAP

Recycled Asphalt Product

What is a disadvantage of RAP

You don’t know the properties of the aggregates and the binder. Also moisture

How is HMA produced?

heating aggregate and binder to the appropriate temperature of 150-165 degrees, then mixing thoroughly and finally transporting to site

What are the 2 types of HMA plants

Batch mix and drum mix

For drum mix, what goes into the parallel flow drum mixer

Wet aggregate + process gas enter

What are the difficulties with transporting HMA

Maintaining its temperature and preventing segregation

What can happen to HMA if not handled correctly

The mix can cool down too much, leading to poor compaction and premature pavement failure

What are some thermal protection measures for HMA

Using insulated truck beds, covering with tarps, minimizing waiting time at plant and site, and avoiding excessive rain exposure

What are the steps in HMA placement

Prep of the base or previous layer, delivery of the HMA to the paver, load the paver ( maintain head of material), distributing and levelling by the screed, initial compaction

How does the transfer from truck to paver go

Truck arrives, backs up slowly, lifts bed to carefully dump mix into the paver’s hopper

What does the paver do?

Receives HMA and lays in a uniform layer→ screed (built in) levels the material and partially compacts it→ sensors maintain correct height and slope

What are the 3 important effects of compaction

Asphalt coated aggregates are pressed together, air voids are reduced, mix density increases

What are the advantages of compation?

Locking the aggregate into place, reduces permeability, increased stability

What are the types of compaction equipment

Static wheel roller (2-14 tons), self propelled pneumatic roller (10.5-30 tons), vibratory roller (2.5-18) tons

What are reasons for pavement failure?

Poor material, poor workmanship, excessive loading, severe environmental conditions, poor drainage, failure of subgrade or underlying layers

What are characteristics of a Batch plant?

Productions mode: batch wise, Flexibility: high (easy to change mix), Efficiency: lower, Initial cost: higherbatch-wise

What sre the characteristics of a Drum plant

Production mode: continuous, Flexibility: low (one mix at a time), Efficiency: higher, Initial cost: lower