TR 331 – HIGHWAY MATERIALS

Students from:TGE – Transportation & Geotech. Eng. (CTE)SCE – Stuctural & Constr. Engineering (CSE)WRE – Water Resources Engineering (CWR)EGY – Engineering Geology (BSc.GY?)PGD – Postgraduate Diploma in Civil Eng.

DR. P. BUJULUMr. F. Mutabazi

TGE Dept.

SUBGRADES• The native material underneath a constucted

pavement• Can also be selected borrow materials for fill

section

• Foundation of pavement structure (major influence on the stability and durability of pavement)

SUBGRADES cont...

Preparation involves clearing & scarifying, levelling and light grading, compaction to specifications

• Strength commonly measured by CBR method (force required for a standard plunger to penetrate 0.25 mm, as a percentage of the force for the same penetration in standard crushed aggregates)

SOIL CLASSIFICATION

• Two systems:- Unified Soil Classification System (USCS)- AASHTO System (American Association of State

Highway and Transportation Officials)

• USCS SystemBased on: - textural characteristics for soils with small omount of

fines that do not substantially affect its behaviour (granular)- plasticity-compressibility characteristics for

plasic soils

USCS System cont....

Classification based on:- Percentage of gravel (G), sand (S) and fines (silt, M and clay, C)- Shape of grain-size-distribution curve (Cu =d60/d10; Cc = d30

2/d60d10)- Plasticity and compressibility characteristics (position on plasticty

chart)

Different Soil Classification Systems

Soil Plasticity Chart

Note generally that:

Ip ≥ 0.73(WL-20%)→ Clay

Ip < 0.73(WL-20%)→ Silt

WL < 50% → High pl

WL ≥ 50% → Low pl

The AASHTO SYSTEM• Based on the observed field performance of

subgrade soils under highway pavements..., i.e. on the desirability of the soil as a subgrade material for highway construction

• Criteria for classification - PSD and Plasticity

• Divided into two major groups:- Granular materials – with 35% or less passing 0.075

mm (75 μm or No. 200) sieve

- Silt-clay materials (fines) – with more than 35%passing No. 200 sieve

NB: According to the AASHTO system, soils having approx. the same general load-carrying capacity and service characteristics are grouped together to form 7 basic groups, designated as A-1, A-2, A-3, A-4, A-5, A-6 and A-7, where:- The best soils for HW subgrades are classified under A-1- Poorer soils are rated in numerical order, with A-7 group being the poorest- The exception is the A-3 group. Soils classified as A-3 are better subgrade

soils than the A-2 soils (why?).- The 7 basic groups have been subdivided into 12 subgroups

AASHTO GROUPS & SUBGROUPS

A. Granular Materials (fines ≤ 35%):1. Group A-1

Well-graded mixture of stone fragments or gravel, ranging from coarse to fine, with a non-plastic or slightly plastic soil binder. Also, this group includes coarse materials without soil binder.

1.1 Subgroup A-1-a: Materials consisting of predominantly of stone fragments or gravel, either with or without a well-graded soil binder

1.2 Subgroup A-1-b:Materials consisting predominantly of course sand, with or without a well-graded soil binder.

2. Group A-3Materials consisting of sands deficient in coarse material and soil binder.

Typical is fine beach sand or desert wind-blown sand without silt or clay fines, or with a very small amaount of non-plastic silt.

AASHTO Groups & Subgroups cont....3. Group A-2

Includes a wide variety of ’granular’ materials that are borderline between the granular materials of groups A-1 and A-3 and the silt-clay materials of groups A-4, A-5, A-6 and A-7. It includes materials with ≤ 35% passing the 0.075 mm (No. 200) sieve, but cannot be classified as A-1 or A-3 due to fines content or plasticity or both in excess of the limitations of those groups.

3.1 Subgroups A-2-4 and A-2-5These fulfill the requirements for group A-2, but with materials passing the 0.425 mm (No. 40) sieve having the characteristics of the A-4 and A-5 groups, respectively.

3.2 Subgroups A-2-6 and A-2-7Same as for Subgroups A-2-4 and A-2-5, except that the fines portion

contains plastic clay with the characteristics of the A-6 and A-7 groups, resp.

NB: A-2 soils are given a poorer rating than A-1 soils because of inferior binder,

poor grading or a combination of the two. A-2 soils are usually used as a

cover material for very plastic subgrades

B. Silt-Clay Materials (fines > 35%)1. Group A-4

The typical material of this group is a non-plastic or moderately plastic silty soil, usually having ≥ 75% passing 0.075 mm (No. 200) sieve. It includes also mixtures of fine silty soil and up to 64% of sand and gravel retained on the 0.075 mm (No. 200) sieve. They are predominantly silty soils (which are difficult to compact).

2. Group A-5The typical material of this group is similar to the A-4 material, except that it is usually of diatomaceous or micaceous character and may be highly elastic as indicated by the high liquid limits. They are normally elastic or resilient in both the dump and semi-dry conditions. They are subject to frost heave, erosion and loss of stability if not properly drained.

3. Group A-6The typical material of this group is a plastic clay soil, usually having ≥ 75% passing 0.075 mm (No. 200) sieve. It includes also mixtures of fine clayey soil and up to 64% of sand and gravel retained on the 0.075 mm sieve. They have high volume changes when moisture content changes and they lose strength when soaked. They do not drain readily.

Silt-Clay Materials cont.....4. Group A-7

The typical materials and problems of this group are similar to those of Group A-6, except that they have the high liquid limits of characteristic of the A-5 group and may be elastic and subject to high volume changes.

4.1 Subgroup A-7-5:Includes materials with moderate plasticity indexes in relation to liquid limit and are subject to considerable volume changes. NB: PI ≤ (LL-30)

4.2 Subgroup A-7-6:Includes materials with high plasticity indexes in relation to liquid limit and are subject to extremely high volume changes. NB: PI > (LL-30)

Refer to THE AASHTO SOIL CLASSIFICATION TABLE

Classification Procedure (with the required data available):- Proceed from left to right on the AASHTO Classification Table-The correct group found by the elimination method-The first group from the left which the test data will fit is the correct classNB: All limiting values must be in whole numbers. Fractional numbers should be converted to the nearest whole numbers for the purpose of classification

ExampleWith the following soil test results, classify the soil according to

the AASHTO system:- Percentage passing 38 mm (1½ in.) sieve = 100%- Percentage passing 2.00 mm (No. 10) sieve = 65%- Percentage passing 0.425 mm (No. 40) sieve = 45%- Percentage passing 0.075 mm (No. 200) sieve = 30%- Liquid limit, LL = 35 - Plasticity index, PI = 21

SOLUTION:Proceeding from left to right on the AASHTO classification table:- It is NOT Group A-1-a, as over 50% (i.e. 65%) passes 2.00 mm sieve- It is NOT Group A-1-b, as over 25% (i.e. 30%) passes 0.075 mm sieve- It is NOT Group A-3, as less than 51% (i.e. 30%) passes 0.425 mm sieve (##)- It is NOT Group A-2-4, as PI is greater than 10 (i.e. PI = 21)- It is NOT Group A-2-5, as LL is less than 41 (i.e. LL = 35)- The soil meets all requirements of Group A-2-6

The soil sample is therefore classified as Group A-2-6

GROUP INDEX of Soils

• Is a function of liquid limit, plasticity index and amount of fines• Used as a general guide to the load bearing capacity of soil• Supporting value of subgrade ~ inverse ratio of its GI• E.g., GI of 0 → excellent SG; GI of ≥ 20→ poor SG material• According to AASHTO, GI can be calculated from:

GI = (F-35)[0.2 + 0.005(LL-40)] + 0.01(F-15)(PI-10)Where: F = Percent passing 0.075 mm sieve (fines) expressed as a whole #

(NB: This %ge is based on materials passing the 75 mm sieve)LL = Liquid limit, PI = Plasticity index

NB: GI should be reported to the nearest whole number- If the calculated GI ≤ 0, it is should be reported as 0- For GI of A-2-6 and A-2-7, only the PI portion is used (why??)- GI values should always be shown in parantheses after the classification group symbol, e.g. A-2-6(3), A-4(12), A-7-5(17) - GI can be estimated using a Nomograph with sufficient accuracy

3. SOIL COMPACTIONDefinition• Mechanical densification of soils• By pressing soil particles (to park more closely together)• Through reduction of air voids (expulsion of air)• Achieved by mechanical means

- Rollers (e.g. for road or dam construction)- Dynamic compaction (densification) by falling mass

Advantages of Soil Compaction

• Generally, compaction high strength and resistance to deformation

• Shear strength increases bearing capacity• Reduces settlements• Decreases volume changes (swell & shrinkage)• Reduces water permeability & capillarity

(number and size of voids)

NB: Extent of improvement depends on type of soil, moisture content, type of equipment, compaction energy (effort) applied (e.g. weight and power of roller, number of repetitions/passes, etc)

PROCTOR (COMPACTION) TESTObjective is to determine the relationship between

compacted dry density and soil moisture content.The test is used to provide a guide for specifications

on field compaction

Density-Moisture Relationship

• Degree of compaction ~ Dry density (kg/m3) at a given moisture content (%)

• NB: ρd = ρ/(1+w)• Dry density ~ compactive effort + moisture

content• OMC = moisture content which gives the

highest dry density (depends on type of compaction)

• Hint: OMC is smaller than the Plastic limit (wp, PL)

Density-Moisture Relationship cont...

Compaction Mechanism• At low moisture content – particles not lubricated

(friction prevents densification)• Increase of moisture content film of water

develops, reduces friction, increases compactability• At OMC closest packing at that compaction effort• Further increase of moisture creates excess pore

water pressure on compacting; gives lower ρd

• Zero-air voids curve ~ 100% saturation (sat. line)• It is practically not attainable (removing all the air?!)• Points on the zero-air void curve:ρdz= ρwGs/(1+wGs); Gs = spec. Gravity; ’w’ in fraction!

• Points on lines of different saturation levels:ρd = (1-Va)/(1/ ρs – w/ρw)

= ρwGs(1-Va)/(1+wGs)

Standard v. Modified Proctor tests:

• Standard PT used mostly for road pavements• Modified PT used mostly for airfields & heavily loaded

highways. But preferred by PMDM (1999)Standard PT: 3 layers, 2.5 kg hammer, 30.5 cm dropModified PT: 5 layers, 4.5 kg hammer, 45.8 cm drop

NB: Standard PT (AASHTO, ASTM) ≡ BS Standard PTModified PT ≡ BS Heavy compaction test

In CML (2000): 1 litre mould is specified, 27 blows/layer: Drop height = 300 mm (Standard PT)

and 450 mm (Modified PT)

Typical Compaction Curves

MOD. PROCTOR COMPACTION CURVES

1400

1500

1600

1700

1800

1900

2000

2100

2200

2300

5 10 15 20 25 30 35

Moisture content (%)

Dry

den

sity

(Kg/

m3)

Mzumbe

Msamvu

Ngunja

Jaribu

Katoke

Muhutwe

Saturation (ZAV)line for Gs=3.0

Field Compaction MethodsFollowing compaction techniques:1. Kneading – variable comp effort applied thru protrusions

on a padded drum wheel Sheep’s (tamping) foot roller- May also be equiped to vibrate- Used mainly for cohesive soils (clays & silts)- Exerted pressures 1000-1500 kPa (dep. roller size)- Suitable for soil layers 150-300 mm thickness- 3 to 5 passes (repetitions)

Compaction methods cont...2. Static compaction – non-vibratory smooth steel

wheeled and pneumatic rubber-tired rollers- Used mainly for granular materials- Also to finish the upper surface of compacted layers

(subgrade, base course and asphalt surface)- Compaction layer thickness: 100-200 mm- Smooth steel wheeled: recom. max speed 15 km/h- Pneumatic rubber-tired: efficiency dep. on pressure

(NB: too high pressure may cause bearing capacity failure or rutting of soil layer)

Compaction methods cont...3. Vibratory compaction – vibratory smooth-drum

rollers (1 drum + rubber-tired drive or 2 smooth drums, one of which saves as the drive wheel)- Used for gravel, sand & silt soils; granular base courses and asphalt mixtures - Mechanism: either a rotating or reciprocating mass(actuated by a hydraulic motor)- Operating mass varies, 2-15 tons- Layer thicknesses up to 1 m:- Requires 3-5 passes

Compaction methods cont...4. Impact compaction – tamping compactors

- Used for small & inclined areas (patch or trenches)- Can be hand-operated or tractor-mounted- 30-1000 kg tampers manufactured- 5-6 coverages (e.g. by half-ton compactor)- Layer thickness 200-250 mm possible

Field Compaction Procedure• Selection of suitable procedure and equipment [soil

type, specifications (target ρd, normally ±5%), available time, available equipment, economy (cost implication)]

• Embankment formation (spreading thin layers of uniform thickness and compacting each layer to slopes and cambers. This results in uniform strength and moisture contents. Lack of this may result in differential settlements and potholing)

• Moisture control (should be close to OMC, normally ±2%)- If too dry, add water by spraying and mixing thoroughly- If too wet, spread the soil out in thin layers and turn it overto facilitate water evaporation before compaction.

NB: Specification of Soil Compaction (% compaction, related to laboratory Proctor test results on same material)

i.e. Percent compaction = [ρd(field)/ ρd(Proctor,lab)] (x 100%)

Example:

• Minimum percent compaction recommended in RN31

Upper 500 mm of soil (subgrade): 93-95%*

Roadbases and Subbases: 98%*

Lower layers of an embankment: 90-93%*: 95-100%+

NB: * Based on BS Heavy (Modified Proctor) Compaction (4.5 kg rammer)+ Based on BS Light (Standard Proctor) Compaction (2.5 kg rammer)

In Tanzania [PMDM (1999)], we adopt:

Acceptable variation of field MDD = ±5% of lab (specified) MDD

Acceptable variation of field OMC = ±2% of lab (specified) OMC

Field Compaction Controls• Involves determination of field dry density and in-situ

moisture content (then compare with specifications, from PT)

• Two major control methods:- Destructive & Non-destructive methods

Non-destructive method Nuclear method• Nuclear densometer – determination of ρd and w• For ρd , gamma rays emitted into soil from source in

the base of equipment, transmitted through soil (some absorbed) and (the rest) measured by detector infront of equipm. Density of soil determined from calibration.

• For w, neutron radiation emitted into soil, lose energy due to collision with hydrogen atoms and are measured by a detector to give soil moisture content.

Nuclear method – Density & Misture

Nuclear method cont....

Advantages:• Test is very fast → immediate results (corr. measures possible)• Many tests possible → statistical methods in the control process• Soil or pavement layer not disturbed• Can be used over a wide range of materials

Disadvantages:• High capital required to procure the equipment• Field personnel exposed to dangerous radioactive emissions

(protection required and safety standards to be enforced)

Destructive methods ( sampling)• Sample of compacted material dug out → test hole (~100mm Ø)• Total mass (weight) of excavated material determined• Moisture content determined• Vol. of excavated material determined from vol. of test hole• Dry density from bulk density and moisture content

Volume of test hole (sample), two common methods:1. Baloon method2. Sand replacement method (sand-cone apparatus)

The baloon method: by forcing a liquid-filled baloon in the test hole. The rubber membrane allows the fluid to fill all the cavities in the test hole. The volume of the liquid required to fill the hole is read on the apparatus. It gives the volume of the excavated material.

Volume of excavated material cont....

The Sand Replacement method• Vol. of test hole determined from mass of loose standard sand

(known ρo) required to fill the test hole.• Uniform med. sand of essentially constant loose density used.• Sand (density) and pouring funnel (vol.) calibrated in laboratory• Mass of sand that fills the test hole determined (hence, volume)• Mass (weight) of excavated material determined• Bulk density of excavated material computed• Moisture content determined by oven-drying• Dry density of excavated material (field dry density) determined• Compared with specified dry density Relative compaction

- Undercompaction corrective measures (e.g.compactive effort, type of roller, number of passes, layer thickness, etc.)- Overcompaction OK if CBR requirements met, otherwise scarify and recompact

CALIFORNIA BEARING RATIO (CBR)• Performed on subgrade to determine bearing capacity for

pavement design purposes• Subgrade strength for determining required thickness of

pavement for roads & airfields• CBR value = Resistance to penetration of 2.5 mm (or 5.0 mm)

of a standard cylindrical plunger of 50 mm ø, expressed as a %ge of the known resistance for the same penetration in standard crushed aggregate (calibrated as 13.2 kN or 20 kN, respectively).

• Soil sample compacted to anticipated ρd and w (normally OMC)• Surcharge weight (annular discs) placed to simulate pavement

layers; 2 kg disc simulates approx. 70 mm pavement layer. • Normally soaked for 96 hrs (4 days) to simulate the field

soaking (inundation), common in the tropics.

CBR - Lab Test Set Up

CBR continues....• The piston plunger penetrates the compacted sample at a rate

of 1.0 mm/min.• The plunger load recorded for each 0.25 mm penetration to a

max of 7.5 mm• Load-penetration curve is plotted and loads corresponding to

2.5 and 5 mm penetration are recorded• Plunger resistance at 2.5 mm expressed as a %ge of 13.2 kN• Plunger resistance at 5 mm expressed as a %ge of 20 kN• The higher of these two is reported as the CBR of the sample• Load-penetration curves sometimes need corrections

(corrected zero).• Two test methods devised:

- CBR test – One Point Method (explained above & Illustration)- CBR test – Three Point Method (recommended by MoI/TZ)

CBR Test Curves (need no correction)

CBR continues....• The piston plunger penetrates the compacted sample at a rate

of 1.0 mm/min.• The plunger load recorded for each 0.25 mm penetration to a

max of 7.5 mm• Load-penetration curve is plotted and loads corresponding to

2.5 and 5 mm penetration are recorded• Plunger resistance at 2.5 mm expressed as a %ge of 13.2 kN• Plunger resistance at 5 mm expressed as a %ge of 20 kN• The higher of these two is reported as the CBR of the sample• Load-penetration curves sometimes need corrections

(corrected zero).• Two test methods devised:

- CBR test – One Point Method (explained above & Illustration)- CBR test – Three Point Method (recommended by MoI/TZ)

CBR test – Three Point Method• Recommended by Min. of Infrastructure (T)• Test principle similar to the Single Point

Method, but three specimens for each sample.• Specimens compacted at diff. compactive effort

(varying wt of rammer, # of layers or # of blows)• Dry density and corresp. CBR determined for

each specimen• Graph of (soaked) CBR v. Dry density plotted

(see next slide)• CBR value of soil for any degree of compaction

can be determined in field.

AGGREGATES FOR H/W CONSTRUCTION

• Refers to granular mineral particles used either alone as road bases, subbases, backfill, etc, or in combination with cementingmaterials, such as cement or bitumen to form concretes for bases, wearing surfaces or drainage structures

• Should be capable of transmitting the stresses induced by traffic loads and resisting wear due to abrasive forces from moving traffic and natural elements (weathering).

• Aggregate specifications tend to seek characteristics that will ensure the required gradation, strength, toughness, durability, cleanliness, and workability

• Can broadly be classified as either natural or artificial aggreg.Natural Aggreg.: Rock fragments, used in natural state except for

crushing, sizing and washing (e.g. crushed rock, gravel, sand)Artificial Aggreg.: Result from physical and chemical modifications

of materials or byproducts (e.g. Blast furnace slag, light wt aggr., fly-ash pellets, recycled concrete and asphalt pavement, etc.

Production of Crushed Rock Aggregates

10mm graded crushed rock aggregate 20mm graded aggregate

Aggregate Properties & TestsThe most important properties:- Gradation (PSD)- Shape and surface texture- Relative density (SG) and absorption- Hardness (resistance to wear)- Crushing strength and toughness (resistance to impact/shock)- Durability (resistance to weathering)- Being free from deleterious substances (cleanliness)

PSD and Gradation- Affects density, strength, and economy of pvmt structure- Usually plotted on aggregate grading chart and judged according to the given specification limits (envelope) for a particular project- Strength (resistance to shear failure) increases if mixture is densely graded- Densely graded mixes are also more economic (less binder needed)

Particle Shape and Surface Texture• They affect aggreg. strength, bond with binder

materials and resistance to skidding and sliding between particles.

• Flat particles, thin particles, or long, needle-shaped particles break more easily than cubical particles

• Particles with rough, fractured faces allow better bond with binder than do rounded, smooth gravel particles.

• The particle shape is expressed in terms of its Flakiness Index and Elongation Index

• Surface texture is expressed in terms of aggregate type, e.g. crushed rock/stone aggregate, crushed gravel (at least with one face broken), natural gravel, etc.

Particle Shape

C ub ica l A gg re ga te

R ounded A gg rega te

Flakiness Index Test

• Aggregates are classified as flaky when they have a thickness of less than 60% of their mean size

• Flakiness Index is found by separating the flaky particles using a standard Metal Thickness Gauge and expressing their mass as a percentage of the sample mass

• The test is applicable to the material passing a 63 mm sieve and retained on a 6.3 mm sieve

NB: For base course and wearing course aggregates, the presence of flaky particles is undesirable as they cause inherent weakness due to the likelyhood of breaking down under heavy traffic loads.

Elongation Index• Aggregates are classified as elongated when they

have a length (greatest dimension) of more than 1.8 of their mean sieve size

• The Elongation Index is found by separating the elongated particles using a standard Metal Length Gauge and expressing their mass as a percentage of the sample mass.

• Applicable to material passing a 50 mm sieve, retained on the 6.3 mm sieve

NB: As for the flakiness, the presence of elongated particles is undesirable for base course and wearing course aggregates, as they cause inherent weaknessdue to the likelyhood of breaking down under heavy traffic loads.

1:5 pivot point

swinging armfixed post (A)

fixed post (B)Determination of Flat and Elongated Aggregate Particles

S.G. OF AGGREGATES• Mineral aggregate is porous; can absorb water and asphalt to a var. degree. • Ratio of water to asphalt absorption varies with each aggregate. Hence,• Three methods of measuring aggregate specific gravity:• Bulk SG, Apparent SG, and Effective SG

Bulk Specific Gravity, Gsb• This includes the volume of the water permeable voids in the aggregate

(often termed the “”saturated surface dry” or SSD volume of the aggregate.

Bulk Volume = solid volume +water permeable voids

Aggregate

Gsb = Dry MassBulk Vol

water permeable voids

“SSD” Level

1.000 g/cm3

S.G. OF AGGREGATES cont…

Apparent Specific Gravity, Gsa

• This does not include the volume of the water permeable voids in the aggregate

Apparent Volume = volume of solid aggr particle

Aggregate

Apparent volume does not includevolume of surface pores

Gsa = Dry MassApp Vol

1.000 g/cm3

S.G. OF AGGREGATES cont…

Effective Specific Gravity, Gse

• This includes the volume of the water permeable voids in the aggregate that cannot be reached by the asphalt.

Effective Volume = volume of solid aggr particle + volume of water permeable pores not filled with asphalt

volume of water permeable pores notfilled with asphalt

Solid AggrParticle

effective asphalt binder

Gse = Dry MassEff Vol

1.000 g/cm3

Specific Gravity and Absorption

• Important in the mix design of concrete and asphalt mixtures

• Apparent Specific Gravity GsA, related to net volume(excluding volume of absorbed water)

GsA = MD/(VN*ρW); MD = dry mass of aggreg., VN = net vol. (=Vs+Vpp-Vpa)

• Bulk Specific Gravity GsB, related to the total volume of aggregate (including the volume of absorbed water)

GsB = MD/(VB* ρW); MD = dry mass of aggreg., VB = bulk vol. (= Vs+Vpp)

• Sat. surface-dry SG (Eff. Spec. Gravity): GsSSD = MSSD/(VB* ρW)

MSSD = Mass of saturated surface dry aggregate

Absorption (%): Abs.= MWA*100(%)/MD; MWA = mass of absorbed water

= MSSD – MD

HARDNESS (→ Los Angeles Abrasion Value, LAAV)

• Expresses the aggregate resistance to wear• Wear due to polishing effect of traffic and internal

abrasion and grinding of the aggregates• Should not be rounded or polished (skid resistance)• Determined by the Los Angeles Abrasion test – LAAT• Degradation of aggregates due to abrasion, impact and grinding

in a rotating drum containing steel spheres• Place a clean sample (mass, m1) in the LAA cylinder + abrasive

charge (standard weight of steel spheres)• Rotate the drum at speed of 30 to 33 rpm for 500 revolutions• Discharge the material and sieve it on the 1.75mm (No.12) sieve• Wash the retained material, oven-dry and weigh (m2)• LAAV (%) = [(m1- m2) /m1] *100; LAAV < 50% is normally required

Resistance to crushing (Aggreg. Crushing Value, ACV)

• ACV gives resistance to crushing under gradually applied compressive load.

• Measures resistance to crushing of traffic wheel loads• ACV determined by measuring material passing 2.36

mm sieve after crushing under a compr. load of 400kN• Applicable to aggr. passing 14 mm, retained on 10 mm• Sieve dry aggr. sample on 14mm and 10mm to remove oversize & undersize• Oven-dry at 105 ± 5°C for about four hours and cool• Place in test cylinder in 3 layers, to each layer apply 25 blows of

tamping rod dropped from h = 50 mm above aggregate surface; level Apply crushing force @ uniform rate so as to reach 400kN in 10 min ± 30sec

• Release the force, remove all crushed material using brush and weigh (m1)• Sieve on the 2.36mm sieve and determine %ge passing (m2)• Calculate the ACV: ACV(%) = (m2/m1)*100• Repeat the test and report the mean ACV to the nearest whole number

Toughness (Aggregate Impact Value, AIV)

• Resistance to sudden shock or impact• Tested on fraction passing 14 mm, retained on 10 mm sieve• Preparation similar to ACV test. Test on dry or soaked condition• Sample in AIV cylinder subjected to 15 blows of hammer (13.5-

14 kg) falling thru h = 380 ± 5 mm, time-interval 1 sec.• Crushed sample is weighed (m1), fraction passing 2.36 mm

sieve determined (m2)• For dry-condition test: AIV(%) = (m2/ m1)* 100• For soaked condition, number of blows adopted is that which

yields between 5% and 20% fines, and we define m, thusm = (m2/ m1)* 100; and AIV = (15m)/n

where m = %ge of materials finer than 2.36 mm sieven = number of hammer blows that produced m% fines

Ten Percent Fines Value (TFV)• Measure of strength of road aggregates (alternative to ACV)• Measures resistance to crushing under gradually applied load• Determined by measuring the load required to produce 10%

material that passes 2.36 mm sieve (for sample 14mm – 10mm)• Applicable to both weak and strong aggr., dry and soaked cond.• Particularly prescr. for relatively weak aggregates (ACV > 30%)• Follows same principles as ACV test, but applied force not fixed• Load varied i.o.t. determine load that will crush the sample to

produce 10% fines (passing 2.36 mm sieve)• Two test methods used:

- The Calculation Method- The Graph Method

NB: The Calculation Method is normally used in our HW Lab.

The Calculation Method• A static force is applied thru plunger at uniform rate so that in 10

min ± 5 sec a penetration of 20 mm (crushed aggr.), 15 mm (rounded/partially rounded aggr., e.g. uncrushed gravel) or 24 mm (honeycombed aggr., e.g. slags) is attained.

• The force (f) required for this penetration is recorded• The specimen is weighed (m1) and sieved on 2.36 mm sieve.• Fraction passing 2.36 mm sieve is weighed (m2) • Its percentage is calculated: m (%) = (m2/m1)* 100• m should fall between 7.5% and 12.5%• Do second test using specimen of same size, applying same

force f, to obtain second value of m• Determine force F (whole #) to produce 10% fines for each test

F = 14f /(m+4)• Report the mean of the two F values as the TFV of aggregate.

The Graphical Method

• Four test specimens are prepared and subjected to 50 kN, 100 kN, 150 kN and 400 kN.

• Four values of m are determined and plotted (ordinates)against corresponding loads (abscissas); curve is drawn

•

• The force F corresp. to 10% fines is reported as TFV

• This method combines TFV test with ACV test (why?)

Durability of Aggregates (Soundness Test)• Shows the resistance of aggregate to disintegration due to

cycles of wetting and drying, heating and cooling, freezing and thawing (should be sound)

• Used to measure the aggregates susceptibility to weathering.• The weakening effect is more remarkable for sedimentary rocks

due to existence of planes of weakness between layers• Commonly measured by the Soundness Test (AASHTO

designation T104, or ASTM C88-90)• In lab, the test measures the resistance of aggregates to

disintegration in a saturated solution of Na2So4 (or MgSo4)• Immerse the aggregate in Na2SO4 soln for 16-18 hrs, remove

and allow to drain for 15 ± 5 min. oven-dry the sample at 110 ± 5 °C and allow it to cool. Repeat the process 4 more times. Wash the aggregates, dry and sieve them.

• Express the %ge passing (lost or broken) related to the initial

In lab, the test measures the resistance of aggregates to disintegration in a saturated solution of Na2SO4 (or MgSO4)Immerse the aggregate in Na2SO4 soln for 16-18 hrs, remove and allow to drain for 15 ± 5 min. oven-dry the sample at 110 ± 5 °C and allow it to cool. Repeat the process 4 more times. Wash the aggregates, dry and sieve them.Express the %ge passing (lost or broken) related to the initial sample massGuide: Loss not to exceed 12% if Na2SO4 is used or 18% if MgSO4 is used

Aggregate Blending• Aim is to obtain aggregate of required (specified)

gradation (within grading envelope)• Gradation affects density and strength of pavement• During production, aggregates are sorted in closely-

graded ’single-sizes’• These can be remixed in desired proportions (i.e.

combined or blended) in order to meet the gradation specified for use

• Descriptive terms include dense-(or well-) graded, open- (or uniformly-) graded, and gap-graded (ref. Next slide)

Design of Aggregate Gradation

• Refers to blending of crushed aggregates, starting with ’single sized’ aggregates (by nominal sizes)

• A trial-and-error procedure is generally used, but two methods used to decide on ’where to start’:- The Mathematical Method - The Graphical Method

The Mathematical Method of aggr. blending• The general formular expressing the combination (blending) is:

P = aA + bB + cC + ......where P = %ge passing a given sieve for the blended aggr.

A, B, C, ... = %ge of ’single-sized’ materials passing the given sievea, b, c, ... = Proportions of aggregates A, B, C, ..., used in combination

NB: a + b + c + ... = 1.00

Case 1: Combining two aggregates.

P = aA + bB; a + b = 1 a = 1 – b; Substituting in first eqn:b = (P –A)/(B –A) and a = (P – B)/(A –B)

Example: Required to blend aggregates A and B in the Table (next slide) to meet the specification (envelope) given in the same table.

Example cont.

By examining the gradations we note that most of the materials passing 2.36mm will be provided by aggregate B

Proportions are determined to meet the mid-point of the specification envelope

Thus: b = (42.5 – 3.2)/(82 – 3.2) = 0.5; Hence, a = 1.0 – 0.5 = 0.5

Then, the blended gradation is shown in the Table (next page)

Example cont.

Example cont.

Graphical Method (Two aggrates, same example)Graphical solution for proportioning of two aggregates

General equation for blending: P = aA + bB + cC + ... (%Passing)Can also be expressed in terms of ”% Retained”, thus:

(100-P) = a(100-A) + b(100-B) + c(100-C) + .....E.g: Passing sieve 4.76 mm: 100a + 100b + 54c = 67.5 (Remember: a+b+c = 1)Is equivalent to: 0a + 0b + 46c = 32.5 (% Retained)Then: Apply the simultaneous equations variable elimination method, or graph

COMBINING MORE THAN TWO AGGREGATE FRACTIONS

HW-Solution• E.g. changing spec. for 1.18 mm to 44% and 0.30 to 28.5%• Specification (passing): 4.76 mm→ 70%, 1.18 mm→ 44%, 0.30 mm→ 28.5%

• Sieve 4.76 mm retained: 0a + 0b + 46c = 30 c = 0.65• Subtraction of 0.300 mm sieve from 1.18 mm sieve (passing):

0a + 40.4b + 8.5c = 15.5 40.4b + 8.5(0.65) = 15.5 b = 0.25a = 1 – b – c = 1.00 – 0.65 – 0.25 a = 0.1

• a = 10%; b = 25%; c = 65%

BS sieve size (mm)

Aggreg. A x 10% Aggreg. B x 25% Aggreg. C x 65% Combined

25.412.74.761.180.3000.1500.075

100 x 0.1 = 10.0100 x 0.1 = 10.0100 x 0.1 = 10.0100 x 0.1 = 10.0100 x 0.1 = 10.073.6 x 0.1 = 7.3640.1 x 0.1 = 4.01

100 x 0.25 = 25100 x 0.25 = 25100 x 0.25 = 2566.4 x 0.25 = 16.626.0 x 0.25 = 6.517.6 x 0.25 = 4.45.0 x 0.25 = 1.25

100 x 0.65 = 6594 x 0.65 = 6154 x 0.65 = 35.131.3 x 0.65 = 20.422.8 x 0.65 = 14.89 x 0.65 = 5.93.1 x 0.65 = 2.0

100.0 (100)96.0 (90-100)70.1 (60-75)47.0 (40-55)31.3 (20-35)17.7 (12-22)7.3 (5-10)

Natural Gravel Bases

• Suitable are lateritic or quartzitic gravels, river gravel or decomposed rock gravel, etc. Others are calcrete & silcrete gravels, especially in the southern Africa region.

• Must be well graded (fall within relevant grading envelope) and must contain sufficient fines to provide a high density on compaction.

• The fines should preferably be non-plastic or meet the specified (prescribed) range of Atterberg Limits, thus:

LL < 25%PI < 12% (dry areas) or PI < 6% (wet areas)Shrinkage limit < 4%

• Must have a minimum 4-day soaked CBR of 80%

SOIL STABILIZATION• A technique used to improve engineering properties of

weak or problem in-situ (local) soils (→ in-situ soils that do not meet the specified engineering requirements)

• Properties that may be improved include- Strength → increase strength, stability & bearing capacity

- Plasticity & workability → reduces plasticity, incr. workability

- Volume stability→reduces swell + shrinkage potential, pressure- Durability → increases resistance to erosion, weathering and

breakdown caused by traffic. Reduce dust.- Permeability → reduces permeability, prevents water from

entering pavement structure

Stabilization cont....• Functional advantages:

- Stabilized soil provide firm support for wearing course (low vol.) or may function as a base course for pavement (heavy traffic).

• Stabilization technique is suitable for ”stage construction” (i.e. may function briefly as wearing course, then apply surface treatment for increased traffic, finally apply AC surface on top(functions as base course) for heavy traffic

Main Categories:- Mechanical stabilization

- Chemical stabilization (use of agents)

Mechanical Stabilization• Technique applied to soil that can not satisfactorily be improved

by compaction (poor gradation, e.g. uniform interm. sand → A3)• Soil, gravel or aggregate of the missing sizes is added and

admixed so as to improve engineering properties of original soil• NB: Admixtured material should be relatively inert so that it

affects only the physical properties of original soil- Includes thermal stabilization (freezing/heating), geosynthetics- To cohesive soils, sufficient granular materials should be added to make sure grains come into contact with each other (?)- Normally more than 10%, sometimes up to 50%

• Technique used for sub-bases of high-quality roads or base and surface courses of lower-quality roads (ADT < 50 veh./day)

- Above 100 veh/day, maint. cost increases rapidly due to loss of materials and formation of dust. 200-300 veh/day require higher-quality surfacing

Mechanical Stabilization cont....• Mechanical requirements for stabilized soil surface (light traffic):

(1) Stability to support weight of traffic (strength, toughness)(2) Resistance to abrasive action of traffic (hardness)(3) Ability to shed rain water as surface run-off(4) Capillary properties to replace the moisture lost thru surface evaporation, thus maintain dumpness to bind materials together

NB: i. Aggregate larger than 25 mm should not be used (dislocation fr. surface)ii. Angular particles provide best interlock (e.g. crushed gravel and sands)iii. High stability can be obtained by a dense mixture of course and fine

materials (which provide good interlock and high shear strength)iv. Dense grading may be approximated by the Fuller’s power grading law:

p = 100(d/D)n

where p = %ge by mass passing a given sieve,d = aperture size of the sieveD = size of the largest particle in the mixture (largest sieve)n = an exponent between 0.3 and 0.5, normally 0.5

CHEMICAL STABILIZATION→ Use of Stabilizing Agents

• Improvement of soil properties by incorporation of reactive substances, known as stabilizing agents (binders, stabilizers)

• Common stabilizers are cement, lime and bitumen• Others include blast furnace slag (normally as GGBFS), fly ash,

pozzolans (mainly ashes) and industrial chemicals (e.g. polymers)

• Usually added in relatively small amounts ~5-15% by weight.

• Stabilization may be due to either- binding soil particles together, i.e. cementation (→ binders,

e.g. cement)- water-proofing soil partcles (e.g. bituminous stabilization), or- both, binding and water-proofing (e.g. in chemical

stabilization)

An intimate mixture of soil (or gravel) and cement

• Cement contents vary: 5-14% by vol., 3-16% by

wt.• Sands & gravels require lower amounts, silts

and clays require higher percentages (why?) • Mixture compacted, normally at OMC, targeting

MDD• Then cured (high moisture/humidity and temp.)

for cement hydration → strength, stiffness, durability

Cement Stabilization

Hydration of cement → Cementation

• Starting with cement clinker compounds:- Tricalcium silicate 3CaO.SiO2 →C3S- Dicalcium silicate 2CaO.SiO2 → C2S- Tricalcium aluminate 3CaO.Al2O3 → C3A- Tetracalcium aluminate ferrite (Ferrit)

4CaO.Al2O3.Fe2O3 → C4AF• C3S / C2S / C3A + H2O → C-S-H / C-A-H

(hydration products)• Effect increases with time (age), continues for

years.

• Min. cement cont. determined in UK and TZ byspecified strength (7 days UCS, 4hrs soaking; ref. CML Test 1.19-1.22). In US by compaction(OMC/MDD) and durability test (wetting/drying, freezing/thawing); then, strength is usually guaranteed

NB: OMC/MDD values for soil-cement differ from those of orig. soil

Tab. 2.1: American Recommendations fot Amount of Cement required for Stabilization

Construction Process• Pulverisation

The soil to be stabilized must be thoroughly pulverised before cement is added (e.g. scarify existing soil to required depth using scarifier attached to grader or spread imported material to required depth, then pulverise using rotary speed mixers or gang ploughs).

• Mixing of soil and cementNormally, cement is spread (e.g. by a spike-toothed harrow) to provide a uniform amount over the pulverised soil. Enough water is added to achieve moisture content 1-2% over OMC (why?). The mixture is then well blended

• Compacting & FinishingThe soil-cement is initially compacted using sheepsfoot rollers. The uppermost 25-50 mm using pneumatic-tired rollers, and the final surface using a smooth-wheel roller

• CuringA bituminous curing membrane (e.g. emulsions & tars, rate: 0.5 l/m2; cutback bitumen RC-250/MC-250, rate: 0.07-0.14 l/m2) or use impermeable sheeting

PLACEMENT, SPREADING AND MIXING

Soil-cement is friable, must be protected→surface treatment,cover

LIME STABILIZATION

• Lime occurs either as QUICKLIME (CaO) or SLAKED(Hydrated) Lime [Ca(OH)2]

• CaCO3 + heat → CaO + CO2 [Production of quick lime]• CaO + H2O → Ca(OH)2 + heat [Hydration of q/l, slaking]• But also: Ca(OH)2 + CO2 → CaCO3 + H2O [Carbonation] !!

• Addition of lime [CaO or Ca(OH)2] to soil/gravel changes the physical-chemical properties of soil → Modification/Stabilization

• Takes place in two stages:- Modification (→ immediate process/effect), and- Cementation (with sufficient lime, long-term process/effect)

Soil Modification / Initial consumption of limeSM Refers to the effects of the initial chemical reactions

between lime and clay minerals (cation exchange)• Reduces plasticity (→ increases workability: e.g. 3% lime

may reduce PI by ⅓ to ⅔; 5% may change soil to non-plastic)• Increases volume stability (reduces swelling & shrinkage)• Also increases CBR (i.e. Subgrade strength)

NB: Addition of lime to soil produces a highly alkaline environment (pH 12.4) which promotes formation of silicates & aluminates that react with Ca2+ to produce cementitious materials. Minimum lime content to produce pH 12.4 is known as the Initial Consumption of Lime (ICL)

Cementation• Reaction of lime with silicates and aluminates

of clay (or from added pozzolanic materials, in the presence of water) produces cementitious compounds similar to hydration of Portland cement → binding of soil particles (cementation)- SiO2 + Ca(OH)2 + xH2O → C-S-H- Al2O3 + Ca(OH)2 + yH2O → C-A-H

- C-S-H & C-A-H → Cementitious, binding properties

• Known as pozzolanic reactions

Lime stabilization cont......

Pozzolanic reaction is relatively very slow (time and temperature dependent), hence CBR,UCS, stiffness & durability

In highly plastic clays, addition of lime may be done first to modify the clay (to reduce plasticity and increase workability) and followed (after a mellowing time) by cement to increase strength by the cementation (hydration) reactions.

This technique is known as “Two Stage Stabilization”

Pozzolanic Stabilization• A pozzolanic material (pozzolana) is a siliceous or siliceous and

aluminous material which in itself possesses little or no cementitious value (binding property), but will, when in a finely divided form and in presence of moisture, chemically react with lime at ordinary temperatures to form compounds possessing cementitious properties.

• Generally have a glassy or non-crystalline structure• Typical are volcanic ash, fly ash/pulverized fuel ash,

ground granulated blast furnace slag (GGBFS), rice husk ash, some clay minerals (e.g. in ground bricks), etc.

• NB: Most artificial pozzolans are industrial waste products (e.g. fly ash & GGBFS). Their utilization has environmental advantages (apart from possible economical & technical advantages)

Bituminous Stabilization• A bituminous material is dispersed throughout the soil

and compacted. Functions through: - Waterproofing the soil, thereby maintaining the already existing strength (main mechanism)- Cementing through binding soil particles together, thus enhancing strength (→ adhesion, surface tension)- A combination of both mechanisms (in many instances)

• Different types of bitumen can be used; e.g. penetration grade (Pengrade 85-100 and 120-150), tars, cutbacks and emulsion bitumen (depending on circumstances → type of soil/gravel, temperature and moisture content, required end product, economy, etc.

• In layers of 50-150 mm, compaction by sheepsfootroller or pneumatic-tired roller, controlled by density.

Selection of a stabilizing agent

• Selection of a stabilizing agent depends on many factors, mainly the type of soil to be stabilized, type of improvement, economy and the environment

• Following figure gives a procedure suggested by FHWA (US) – next slide

• Table 7.8 (PMDM, 1999) gives stabilizer selection criteria adopted in Tanzania

Laboratory Tests on Stabilized Materials• Tests carried out during design and construction are:

- Atterberg limits (plasticity)- Grading analysis (PSD)- Initial consumption of lime (ICL)- Moisture-density relations (Proctor test)- California bearing ratio (CBR)- Unconfined (uniaxial) compressive strength (UCS)- Indirect tensile strength (ITS)- Stabilizer application rate- Durability tests- Tests for deleterious materials (?)

• Notes given for self-reading

Deep Stabilization

PenetratnRetrieval+ Binders

PAVEMENT STRUCTURE• Components usually include the subgrade, subbase,

base and surface• Subbase, base and surface courses Pavement• Two types: Rigid pavement and Flexible pavement• Strength of the subgrade is the main factor controlling

design of flexible pavements• Basic design criterion is the depth of pavement

required to distribute the applied surface load to the subgrade in such a way that the S/g will not be overstressed to cause an unacceptable deformations.

• The base (road base) is designed to bear the burden of distributing the applied surface loads and to ensure the bearing capacity of the subgrade is not exceeded.

• The materials used in the base must be of high quality

The SubbaseCan be considered as an extension of the road baseIts essence depends on the intended function; as:• A structural member (layer) of pavement (lower

quality than road base but stronger than subgrade)• A drainage layer and to control the capillary rise

D15 subbase > 4 ; D15 subbase < 4D15 subgrade D85 subgrade

• A service layer, as- a platform for construction traffic- a cut-off blanket to prevent moisture migratingupward from the subgrade- to prevent infiltration of s/g material into the pavnt str.

Specifications for Base and Subbase Materials

Sieve Grading; Percent passing by wt(mm) Gr. A Gr. B Gr. C Gr. D Gr. E Gr. F

50 100 100 - - - -25.0 - 75-95 100 100 100 1009.5 30-65 40-75 50-85 60-100 - -

4.75 25-55 30-60 35-65 50-85 55-100 70-100

2.00 15-40 20-45 25-50 40-70 40-100 55-100

0.425 8-20 15-30 15-30 25-45 20-50 30-700.075 2-8 5-20 5-15 5-20 6-20 8-25

Coarse aggreg. – Not over 50% Los Angeles Abrasion ValueAmount passing 0.075 shall be no more than 2/3 of passing 0.425Fraction passing 0.425mm: Max. LL =26, Max. PI = 6

MACADAM SYSTEM OF PAVENT CONSTR.

• Developed 1783-1826 by John Laudon Mac Adam• The foundation (subgrade) is shaped and compacted

to the intended surface camber, thereby giving:- good side drainage to the foundation- uniform construction thickness

• Can easily be brought to a highly stable state, resulting in minimal deformation in pvmnt under traffic load

• Uses crushed rock/stone, crushed gravel or crushed slag for aggregate materials

• Stability mechanism rely on interlocking and friction• Types: dry- & water-bound, crusher-run, bituminous

coated macadams

3.0 BITUMINOUS MATERIALS3.1 INTRODUCTION• Also known as Asphaltic Materials.• Are materials that contain bitumen (US: asphalt), resemble

bitumen, or constitute a source of bitumen.• They include bitumen (asphalt) and tar binders.

Bitumen (Asphalt)A solid or semi-solid (viscous) material, black or dark-brown in colour, having adhesive properties (cementitious), and consisting essentially of hydrocarbons, derived from petroleum or occurring in natural asphalt deposits, and soluble in carbon disulphide, CS2.

TarA viscous liquid, black in colour, with adhesive properties, obtained by destructive distillation of coal or wood. In H/E we mostly refer to tar derived from bituminous coal.

NB: Tar can also be obtained from petroleum by chemical treatment (cracking), not physical processes such as fractional distillation used for production of bitumen (asphalt)

Bitumen (Asphalt)- Two main categories: Natural asphalt & Petroleum asphalt

Natural AsphaltOccurs naturally in natural deposits (as native asphalt e.g. in Trinidad lake, etc; or rock asphalt in sandstone or limestone)

Petroleum AsphaltAlso known as refinery asphalts. It is produced by industrial (fractional) distillation of crude petroleum (crude oil)It is the heaviest fraction and the one with the highest boilingpoint, boiling at 525 °C (977 °F).

3.3 PHYSICAL PROPERTIES• Those which directly affect the performance of asphalt

in a mixture while being mixed, laid and in service.

• Challenge: To develop physical tests that satisfactorily characterize key asphalt binder parameters and how they change throughout the lifetime of a mix.

• Asphalt is a rheological material→ Its stress-strain characteristics are time-dependent

• Asphalt is a thermoplastic material→ Its stiffness (or consistency) varies with temperature

→ Physical properties of asphalt are time and temperature dependent

3.3.1 RHEOLOGY• Study of deformation and flow of matter• Important in determining physical properties of asphalt• HMA deformation closely related to rheology of asphalt→Rheology determines performance of HMA pavement

• Example:- High HMA deformations and flow → rutting and bleeding- High asphalt stiffness → fatigue cracking

Thus:Comparison of diff binders must be done at some common

reference temperature

Characterizing asphalt binder properties should involve examining rheological properties over the range of temp that may be encountered in its lifetime.

Rheological Properties (Consistency parameters)Measure of hardness or degree of fluidity.1. Penetration Test (AASHTO T49, ASTM D5)

Penetration depth of a standard needle under specified cond. of weight (100g), time (5 sec) and temperature (25°C)- Pen units expressed in 0.1 mm (e.g., 8 mm → 8/0.1 = 80)- Assumption: same penetration deform similarly

NB: Based on field performance, no relation with test parameter

Asphalt Penetration cont…

- It is an empirical parameter used in grading asphalt

- The harder an asphalt cement, the lower will be its penetration & vice versa

- Five stand. penetration grades exist: 40-50, 60-70, 85-100, 120-150, 200-300

- The values represent the min & the max pen for each pen grade

- Two common grades are 60-70 (for hot regions) and 85-100 (for cold regions)

- Asphalt of lower pen grades are used at bus-stops or parking places where traffic stresses are very high.

2. Softening Point• Also known as the “ring and ball” softening point.• Temp. at which asphalt change from solid to liquid• At this temp. asphalt can no longer support the weight

of a 3.5g steel ball.• The ball, enveloped in binder, falls through h = 25 mm

(touches the base plate)

• The harder an asphalt, the higher is its softening point• At the softening temp., many asphalt types have a

penetration of 800 (= 80 mm).

VISCOSITY (KINEMATIC AND ABSOLUTE)• Viscosity measures resistance to flow at a given temp.• It is a fundamental property of fluid (asphalt), whereas

penetration and softening point are empirical tests.• Asphalt viscosity measured at two temp.:60°C &135°C• Viscosity at 60°C is called absolute viscosity [poise]• Corresp. approx. to viscosity of asphalt in HMA pvmnt

during hot summer (most critical state in service)• Visc. at 135°C is called kinematic viscosity [centistokes]

• At this temp. asphalt is sufficiently fluid to flow under gravitational forces alone.

• Corresp. approx. to viscosity of asphalt at mixing and laydown conditions.

3. Absolute Viscosity• Also known as dynamic viscosity• Measured at 60°C, using a vacuum viscometer.

μ = τ/γWhere: μ = viscosity [poise = g/cm-sec]; NB poise = Pa-sec/m2

τ = shear stressγ = rate of shear (= dγ/dt)

4. Kinematic Viscosity

• Kinematic viscosity = absolute viscosity/density• Measured at 135°C to simulate the mixing process• The cross-arm (capillary tube) viscometer is used• A constant head is maintained, flow under gravity• Measures time to flow between two timing marks

5. Ductility Test• Test involves stretching a standard-sized asphalt

briquette (dumbbell) to its breaking point.• The sample under water at 25°C is stretched at

50mm/min until it breaks.

• The distance at rapture, in cm, is reported as ductility.

6. Rotational (brookfield) Viscometer (RV) testWill be discussed in the Superpave Mix Design chapter.

3.3.2 DURABILITY (AGING) TESTS• Short-term aging → During the mixing process

• Long-term aging → After pvmt construction due to environmental exposure and loading

• No direct measure for binder aging (age-hardening)

• Aging effects accounted for by subjecting asphalt binder to simulated aging, then conducting other standard physical tests to evaluate the changes

• Durability tests include:1. Thin-film oven test (TFO) – NEXT SLIDE2. Rolling thin-film oven test (RTFO)→Not covered3. Pressure aging vessel test (PAV)→ Not covered

1) Thin-film Oven (TFO) Test• Determines the effect of heat and air on a thin film of a

bituminous material.• Indicates changes in asphalt properties during

conventional mixing; the residue approximates binder condition in newly constructed pavement

• A thin film of asphalt heated in oven at 163°C for 5 hrs

• Changes in other properties – penetration, viscosity & ductility expressed as a %ge of the original values.- Retained penetration = Penetration of aged sample * 100%

Penetration of original sample

- Aging index = Viscosity of aged sample * 100%Viscosity of original sample

3.3.3 Safety Tests• Measure temperature at which asphalt materials will

burst or flash into flames• Working temperatures must be controlled (kept below

Flash Point by ~ 50°F) for safety purposes.• Recommended safe temp for Pen-grade ~ 245-335°C• Flash Point is the lowest temp at which the vapour

from (heated) asphalt is ignited by an open flame• Fire Point is the lowest temp at which asphalt continues

to burn without further heat supply. • Safety tests include:

- Cleveland Open Cup (Flash and Fire Point test)- Tag Open Cup test and - Pensky Martin Flash Point test

Safety Tests cont…

3.3.4 TEMPERATURE SUSCEPTIBILITY

• Refers to the rate at which consistency of asphalt changes with changes in temperature.

• Consistency is measured by penetration and viscosity

• Two common parameters for temp susceptibility are the Penetration Index (PI) and Penetration-Viscosity number (PVN)

• The Penetration Index (PI) only will be discussed

1. Penetration Index (PI)

• If logarithm of penetration, log(Pen), is plotted against temperature (T), a straight line is obtained; thus:

log(Pen) = A*T + k where A (= slope) shows the temp susceptibility of the asphalt, k is a constant.

Thus: A = log(PenT1)-log(PenT2)T1 - T2

Then, Penetration Index (PI)PI = (20-500A)/(1+50A)

NB: The lower the PI value, the higher the temp susceptibility. For paving asphalts, PI = +1 to -1

Penetration Index (PI) cont…

• Considering the “Ring-and-Ball” softening point (TR&B, where penetration ≈ 800) and penetration at 25°C:

• A can be determined (and hence PI) from:A = log(800)-log(Pen25°C)

TR&B - 25°COr, at any temperature T: A = log(800)-log(PenT)

TR&B – TFrom equation for PI: A = (20 - PI)/[50(10+PI)]Substituting in equation above:

(20-PI)/(10+PI) = 50* log(800)-log(PenT)TR&B – T

Temperature susceptibility for different asphalts

3.4 LIQUEFIED ASPHALTS

• Normal (Pen-grade) asphalts exist as semi-solids (highly viscous) at room temp.

• May be liquefied so they can be used without necessity of (or with min.) heating

• Two products are common- Asphalt emulsions (bituminous emulsions or emulsified asphalt/bitumen)

- Cutback asphalts (cutback bitumen or cutbacks)

3.4.1 Asphalt Emulsions• Liquefied asphalt obtained by dispersion of asphalt

globules in water (containing emulsifying agent/stabilizer).

• Manufacturing involves passing hot asphalt and water containing emulsifying agent under pressure through a colloid mill to produce extremely small (< 5-10 μm) globules or droplets of asphalt suspended in water

Asphalt Emulsion cont…• Emulsifiers are additives used to promote dispersion

and stability of asphalt-water mixture (w/out segregation)

NB: Asphalt is an organic material → does not mix with H2OEmulsifying agent imparts an electric charge to surface of asphalt globules → globules repel one another (dispersed)

• On the basis of the type of electric charge, asphalt emulsions may be categorized as:

- Cationic emulsion (electro-positively charged), or- Anionic emulsion (electro-negatively charged)

• Most siliceous aggreg. (sandstone, quartz, and siliceous gravel) are negatively charged → compatible with cationic emulsions

• Aggregates of limestones, dolomite, etc. are positively charged and are therefore compatible with anionic emulsions

Classification of Asphalt Emulsions

Setting/breaking of emulsions:• Evaporation of emulsion water leads to formation of a

continuous film of asphalt on the surface of aggregates (coalescing).

• Depending on the rate of setting or breaking, emulsion may be classified as:

- Rapid setting (RS)- Medium setting (MS), or- Slow setting (SS)

• Depends on composition of emulsion; porosity of aggr; rate of evaporation of water (wind, RH, temp); surface chemistry of aggregates.

3.4.2 Cutback Asphalts• Obtained when an asphalt is liquefied by dissolution in

an organic solvent (called cutter)• Curing of cutback-aggregate mixtures occurs by

evaporation of the cutter from the cutback.• Highly-volatile cutter (e.g. naphtha or gasoline) gives a

“Rapid Curing (RC)” cutback• Medium-volatile cutter (e.g. kerosene) gives “Medium

Curing (MC)” cutback• Low-volatile cutter (e.g. diesel or gasoil) gives “Slow

Curing (SC)” cutter• Common cutback grades are MC-30 and (RC, MC,

RC) – 70, 250, 800 and 3000• The number gives the min. viscosity at 60°C (cSt)

3.5 Distillation of Asphalts

• For separation into components:- fugitive petrolenesand residual asphaltic bitumens

• Can be done on liquid asphalt as well as emulsions- Cutbacks (ASTM D-402)- Emulsions (ASTM D-244)

Distillation of Cutbacks

Distillation of Emulsions

4.0 ASPHALT MIX TYPES AND DESIGN• Types of asphalt mixes for pavements include

- Hot Mix Asphalt (HMA) – heated asphalt + heated aggreg.

- Cold Mix Asphalt – cutback or emulsion mixed with aggreg. and laid at ambient temperature.

- Penetration Method – heated asphalt sprayed over and allowed to penetrate compacted crushed aggregates

- Inverted Penetration Method – spreading asphalt binder over the roadway surface and laying selected aggregates to penetrate the asphalt.

• Asphalt mixes so produced include(i) Asphalt concrete (AC); (ii) Rolled asphalt; (iii) Mastic asphalt; (iv) Surface treatment (slurry seals, dressing); (v) Bituminous macadam; (vi) Penetration macadam

Principal Bituminous Mix Types1. Asphalt Concrete: A high quality, thoroughly controlled

mixture of hot asphalt binder and hot mineral aggregates 2. Rolled Asphalt: A high quality mortar type produced using

fine aggregate and penetration grade asphalt. These mixes are more flexible and durable than asphalt concrete

3. Mastic Asphalt: A mortar type of bituminous mix usually cast into blocks, with 14-17% hard asphalt binder (10-25 pen). For crack sealing, to prevent attrition of aggregates, etc.

4. Bitumen Macadams: They contain coarsely graded mineral aggregates coated with asphalt in premix plants. They have higher air voids than AC

5. Penetration Macadams: Produced by spraying heated, dissolved or emulsified asphalt over compacted crushed aggregate in-situ.

6. Surface Treatments: Inc. surface dressing, tack coats etc

5.1 Types of Bituminous Surfacing

OTTA SEAL CONSTR.

Spreading of aggregate over cutback asphalt spray

Rolling with pneumatic Rollers in Otta seal construction

4.1 ASPHALT CONCRETE• Produced by the HMA method• Primarily used for construction of flexible pavements• Very strong paving material, can sustain very heavy

traffic loads (roads & airfields) - structural strength to pvmt

• May be designed as “open-graded” or “dense-graded”• Large-stone open-graded mixtures are more suitable

for supporting heavy truck traffic

• Important (required) properties of AC:(i) Stability; (ii) Durability; (iii) Flexibility; (iv) Fatigue resistance; (v) Skid resistance; (vi) Impermeability; (vii) Workability

Required Properties of AC1) Stability:

- Resistance to deformation due to applied load- Depends on cohesion of binder and internal frictionof mineral aggregate- Associated with low asphalt contents, dense aggreggradation & well compacted impervious mixtures- Insufficient stability leads to rutting and corrugations

2) Durability:- Resistance of AC to disintegration by weathering and traffic. Weather → oxidation (age-hardening)- Controlled by thickness of asphalt film around aggr- Enhanced by high AC contents, dense aggregategradations and well-compacted impervious mixtures

3) Flexibility- Ability of AC to conform to base deformations (e.g. localized/differential settlements) without cracking- Enhanced by high asphalt contents and relatively open-graded aggregates

4) Fatigue resistance- Resistance to pavement failure due to repeatedtraffic loading (failure in form of alligator cracking)- Dense-graded mixtures offer higher fatigue resist.

5) Skid resistance- Controlled by aggregate physical characteristics (texture, shape & resistance to polish)- Also, low asphalt content & open-graded aggregate

6) Impermeability- Resistance to penetration of water and air- Improves pavement durability and stability- Facilitated by high asphalt content, dense gradation and sufficient compaction (→ imperviousness)

7) Workability- Ease of AC placement and compaction (with reasonable effort)- Factors that promote high stability cause workability problems (→ a compromise required)

8) Others include “Resistance to temperature cracking”and “Resistance to stripping”

Bitumen content

Aggregate gradation

Air Voids (in compacted mix)

High Low Dense Open High Low

Stability X X X

Durability X X X

Flexibility X X X

Fatigue resist X X X

Skid resist. X X X

Impermeab. X X X

Workability X X X

MIX PROPERTY

4.2 ASPHALT MIX DESIGN• Two primary properties desirable in design of asphalt

concrete mixtures are stability and durability (i.e. getting a stable AC mix that is durable)

• Additional factors are also economy and workability• Aim is therefore to find an economical gradation and

blend of aggregate and asphalt that will yield a mix having:

1. Sufficient asphalt binder to ensure a durable pavmnt2. Sufficient mix stability to serve without distortion or

displacement at the anticipated traffic load3. Sufficient voids in the compacted mix to avoid bleeding4. Sufficient workability to facilitate proper compactionAddit. requirements: Flexibility, fatigue- & skid resistance

4.2.1 MARSHALL MIX DESIGN• Developed by Bruce Marshall in the US• Aims at obtaining a dense mix of high stability but with

adequate void content to allow sufficient binder content for good durability and flexibility

• Standardized in ASTM D1559 and AASHTO T245• Standard procedure involves:(i)Prep. of test specimens, h ≈ 63.5 mm, Ф ≈ 101.5 mm

- heating, drying, mixing and compacting in mould- both faces of sample receives same number of compaction blows, determined by the traffic levels

Traffic level Number of blows/face

Light (ESAL < 104) 35

Medium (ESAL = 104-106) 50

Heavy (ESAL > 106) 75

Marshal Mix Design cont…(ii) Bulk density test

Determined on compacted cooled specimens by the water displacement method, with a thin coat of paraffin wax on it

(iii) Stability and flow testSpecimens are conditioned for 30-40 min in water bath at 60ºC. They are compressed in the Marshall test machine (rate 51mm/min) for determination of Stability and Flow

NB: Stability is the max load resistance (kN) that the test specimen will develop at 60ºC in the Marshall test.

:Flow is the total deformation (in 0.25 mm units) of the specimen at failure when subjected to compression in the Marshall stability test

Marshall Mix Design Test Set-up

Marshal Mix Design cont…(iv) Density-voids analysis

- This involves determination of voids using known and computed density (specific gravity) values

- Three types of voids are considered, namely:VMA = Voids in Mineral AggregatesVTM = (Air) Voids in Total MixVFB = Voids Filled with Binder (also VFA - asphalt)

(v) Interpretation of test results The obtained data are used to prepare plots which are used to determine the optimum binder content

(vi) Determination of the optimum binder contentThe content that fulfills the requirements

Density-Voids Analysis• Mineral aggregates are porous; can absorb water and

asphalt to a var. degree. • For Marshall mix design, we consider Bulk SG and

Effective SG

1. Bulk Specific Gravity, Gsb• This includes the volume of the water permeable voids

in the aggregate (often termed the “”saturated surface dry” or SSD volume of the aggregate.

Bulk Volume = solid volume +water permeable voids

Aggregate

Gsb = Dry MassBulk Vol

water permeable voids

“SSD” Level

1.000 g/cm3

2. Effective Specific Gravity, Gse

• Includes the volume of the water permeable voids in the aggregate that cannot be reached by the asphalt.

Effective Volume = volume of solid aggr particle + volume of water permeable pores not filled with asphalt

volume of water permeable pores notfilled with asphalt

Solid AggrParticle

effective asphalt binder

Gse = Dry MassEff Vol

1.000 g/cm3

IMPORTANT DEFINITIONS1. Voids in Total compacted Mix (VTM)

Total volume of the small pockets of air existing between the coated aggregate particles in a compacted asphalt paving mixture, expressed as a percentage of the bulk volume of the compacted mixture

VTM = (Va/Vm)* 100%2. Asphalt binder content (Pb)

Pb = (Mb/Mm)* 100%3. Effective asphalt binder (volume) (Vbe)

The volume of total asphalt (content) minus the portion of asphalt ‘lost’ by absorption into the aggregate particles

Vbe = Vb – Vba

NB: BA Pba = (Mba/Mg)*100%

IMPORTANT DEFINITIONS cont…

4. Voids in Mineral Aggregate (VMA)The volume of inter-granular void space between the aggregate particles of compacted paving mixture that includes the air voids (VTM) and effective asphalt binder content (Pbe), expressed as a percent of total volume of the mixture specimen

VMA = [(Va + Vbe) / Vm] *100%5. Volume Filled with Binder (VFB)

The percentage of the voids in the mineral aggregates (VMA) that is ‘occupied’ by the effective asphalt binder (i.e. voids in mineral aggregate minus voids in the compacted total mix, expressed as a percent of the voids in mineral aggregates)

VFB = (Vbe/VMA)*100%= [(VMA-VTM)/VMA] * 100%

SUMMARY OF RELATIONSHIPS1) Mm = Mb + Mg

= Mbe + Mba + Mg

2) Vm = Vg + Vbe + Va

= Vg + (Vb - Vba) + Va

3) ρmb = Mm/Vm ; (Gm = ρmb/ ρw)

4) Vgb = Mg/ ρgb = Mg/(Ggb*ρw)

5) Mb = Pb * Mm ; Vb = Mb/ρb = Mb/(Gb* ρw)

6) Mba = Pba * Mg ; Vba = Mba/ ρba = Mba/(Gb* ρw)

7) Vbe = Vb - Vba

8) Va = Vm - (Vg + Vbe) = 1 - (Vg + Vbe), cons. unit volume

SUMMARY OF RELATIONSHIPS cont…

9) VTM = (Va/Vm)*100% = (Va/1)*100% if Vm = 1 m3

10) VMA = [(Vbe + Va)/Vm] *100% = (Vbe+Va)*100%

11) VFB = [Vbe/(Vbe+Va)] *100%

= [(VMA-VTM)/VMA] *100%

NB: Theoretical maximum density (spec. gravity, Gmm):Imaginary density that would result if the specimen had been compacted so that there were no voids in the aggregate-binder mixture (i.e. Va = 0; VTM = 0%)Gmm = Mm/(Vbe+Vg) = Mm/[(Mb/Gb) + (Mg/Gge)]

= 100/[(Pb/Gb) + (Pg/Gge)]

Marshall Mix Design - EXAMPLEAn asphalt concrete mix has a bulk density of 2440kg/m3,

a binder content, Pb of 5.8% and aggregate binder absorption of 0.8%. If the specific gravities of aggregates and asphalt binder are 2.67 and 1.03 respectively, find the AV (VTM), VMA and VFB

SOLUTION:Considering 1 m3 of AC mixture: Mm = ρm *1 = 2440 kgMb = Pb * Mm = 0.058 * 2440 = 142 kgMg = Mm - Mb = 2440 - 142 = 2298 kgMba = Pba * Mg = 0.008 * 2298 = 18 kgMbe = Mb - Mba = 142 – 18 = 124 kg

SOLUTION cont…

Vg = Mg/(Ggb * ρw) = 2298/(2.67 * 1000) = 0.861 m3

Vbe = Mbe/(Gb * ρw) = 124/(1.03 * 1000) = 0.120 m3

Va = Vm – (Vgb + Vbe) = 1 – (0.861 – 0.120) = 0.019 m3

Therefore:

VTM = (Va/Vm) * 100% = (0.019/1)*100% = 1.9%

VMA = [(Va+Vbe)/Vm]*100% = [(0.019 + 0.120)/1]*100% = 13.9%

VFB = [Vbe/(Va+Vbe)]*100% = [0.120/(0.019+0.120)]*100%

= 89.5%

ALTERNATIVE USEFUL FORMULAS

b

b

se

b

mmmm

GP

GP

PG

+−

=100

( )⎥⎦

⎤⎢⎣

⎡ −−= mb

sb

b GG

PVMA

100100

1100

⎥⎦⎤

⎢⎣⎡ −=

VMAVTMVFA 1100

⎥⎦

⎤⎢⎣

⎡−=

mm

mb

GG

VTM 1100

3

3

2

2

1

1

321

GP

GP

GP

PPPG++

++=

ALTERNATIVE USEFUL FORMULAS cont..

bsbse

sbseba G

GGGG

P−

= 100

ββ

−−

=100

100 bbe

PP

( )100

100 bba PP −=β

B

b

MM

mm

bmm

GP

GP

PPGse

−

−=

The table below lists data used in obtaining a mix design for anasphaltic concrete paving mixture. If the maximum specific

gravity of the mixture is 2.41 and the bulk specific gravity is2.35, determine:

a) the bulk specific gravity of aggregates in the paving mixture, b) the absorbed asphalt,c) the effective asphalt content of the paving mixture, and d) the percent voids in the mineral aggregate.

Material Specific gravity

Mix composition by weight of total mix

Asphalt cement 1.02 6.40Coarse aggregate 2.51 52.35Fine aggregate 2.74 33.45Mineral filler 2.69 7.80

EXAMPLE 2 (HOMEWORK)

INTERPRETATION OF DATA

From the test results, prepare the following plots:

• Binder content vs. Corrected Marshall Stability

• Binder content vs. Marshall Flow

• Binder content vs. Density

• Binder content vs. VTM

• Binder content vs. VMA

• Binder content vs. VFB

DETERMINATION OF OPTIMUM ASPHALT CONTENT

Two methods available:• The Asphalt Institute’s Method• The NAPA Method (National Asphalt Paving Association)

1. The Asphalt Institute’s Method(a) Determine the asphalt content at:

- maximum stability- maximum density- mid-point of specified air voids range (e.g. 4 for 3-5)Find the average of the three values obtained

(b) In the respective plots and at average asphalt content (from (a)), determineStability, Flow, Air voids (VTM), VMA and VFB

(c) Compare the values of the above parameters obtained from the plots with the specification values or limits (next slide). - If any of the values fails to meet the specifications, the mixture should be redesigned, otherwise the mix formulation is accepted

2. The NAPA MethodEmphasis is placed on the air voids in the total mix, VTM(a) Determine the asphalt content corresponding to the

median of the specifications air voids content (usually 4%). Take this value as the tentative optimum asphalt content, then:

(b) Determine the values of the following parameters (from the plots) at the tentative asphalt content:

Marshall stability, Flow, VMA and VFB(c) Compare the values of each of the above parameters

against the specifications or limits (tables). If all are within the requirements, then the tentative asphalt content is adopted, otherwise redesign the mixture

SELECTION OF THE JOB FORMULA

The Job Mix Formula is the gradation and the asphalt content which satisfy all specification requirements and upon which plant mixtures are to be produced for the construction. This is selected at the final stage of the laboratory design as the mix that was most economical and give the most satisfactory results OPTIMALITY