Bituminous Mix Design & Superpave Mixes

BITUMINOUS MIX DESIGN AND

SUPERPAVE MIXES

BYCHANDRA SEKHAR PASUPULETIB.Tech(CIVIL)

Objective

To understand What are the mix design methods. Marshall method of mix design. Limitations of Marshall method Superpave mixes Importance of other methods

Mix design

Objective: To determine an economical blend of aggregates (gradation within the limits of project specifications), and asphalt that yields a mix of having? Sufficient asphalt to ensure a durable pavement Sufficient stability to satisfy the demands of traffic

without distortion or displacement Sufficient voids in the total compacted mix to allow

secondary compaction and temperature variations. Sufficient workability for efficient placement without

segregation.

Various methods of mix designMarshall MethodHveem MethodRefusal Density MethodSuperpave methodFilm Thickness MethodEtc.

Mix design contd…

Definitions:Bulk Specific Gravity (Gsb)Apparant Specific Gravity (Gsa)Effective Specific Gravity (Gse)

Marshall Method

Specific gravity : Voids absorbed bitumen

Voids not absorbed bitumen

Solid Rock

Marshall Method contd…

Solid rock Vr

Water permeable porosity but not filled by

bitumenVw

Pores filled by bitumen Vb

Bulk SG = W/(Vr+Vw+Vb)

Effective SG = W/(Vr+Vw)

Apparent SG = W/VrPhase Diagram

Definitions:Stability – (60Oc, 30 min, 50.8 mm/min)FlowAir VoidsVoids Filled with BitumenVoids in Mineral AggregatesPercentage of absorbed asphalt

Mineral Aggregate

AsphaltAir voids

Vma Vfa

Vba Vb

VmmVmb

Phase Diagram :

BC-ID 9 for presentation.xls

1. PROPERTIES OF INGREDIENTS Individual gradation of aggregate Other properties of aggregate Properties of bitumen

See sheet “properties of aggr. bit” in BC-ID 9 for presentation.zip

2. BLENDING (HOT & COLD)

See sheet “blend cold” & “blend hot” in

BC-ID 9 for presentation.zip

3. MARSHALL MOULD PREPARATIONGet all the sizes ready for trialDetermining the total required weightProportioning and mould preparationmould preparation.xls

4. MARSHALL PROPERTIES

..\BC-ID 9 for presentation.zip

5. STUDY THE TREND OF PROPERTY CURVES

6. OBC SELECTION AND CONFIRMATION7. PLANT CONTROL

Cold bin calibrationIt ensures correct hot bin proportioningIt helps to ensure nil balance between

production at quarry and consumption at site Reduces the overflow in hot binReduces the re-handling operationsReduces the segregation in the final mixIncreases the production capacity

How to calibrate?

Hot bin calibrationTo ensure the correct proportions in the mix To ensure the weighing balances being used

are correct8. SITE TRIAL

To check the workabilityTo establish the rolling pattern

JMF : Job Mix Formula It defines the tolerance limits for grading of

aggregate as well as binder content.Tolerances for gradation as well as binder

content is given in MOST, but apart from this still mix should be produced as per the limits specified in design criteria.

see sheet ‘JMF graph” in the following slideJMF graph.xls

Sieve Limits Size

37.5 +826.5 +813.2 +84.75 +72.36 +60.300 +50.075 +2Binder +3

JMF Limits as per MOST :

Grading chart with JMF

Grading chart for BC

0.01 0.1 1 10 100

Sieve size in mm

UL LL Designed JMF LL JMF UL

What is most commonly used design method and Why?Marshall Method, BecauseSimple techniqueSimple, inexpensive, and portable

equipmentLess time consumable

Characteristics of Marshall method:Unconfined test and maximum failure load in

the test is recorded as stability.Shortfalls in Mrashall method: It measures merely the adhesive strength of

bitumen-filler mortar. It can not predict the fatigue behavior of the

bitumen. Irrespective of traffic its design blows are 75

Shortfalls in Mrashall method: It is unconfined but at field it is not soEmpirical and parameters are not directly

related to field performance (Deformation, Fatigue resistance etc.)

Wide range of grading limits It doesn't explain about easily compactable

mixesCompaction (Impact method) It doesn’t guarantee the minimum air voids

Due to above said limitations and shortfalls there has been a growing feeling among the Highway engineers, Which led them to other methods like

“ Superpave Mix”“ Refusal Density Method”“ Film Thickness Method”

SUPERPAVE MIXThis method can measure the fundamental properties like fatigue , rutting and low temperature resistance.Developed by SHRP , USAThis is also recommended by (FHWA).This method consists of 1. Selection of material2. Selection of design aggregate structure3. Selection of design asphalt binder content, and4. Evaluation of moisture susceptibility

Notes for Design :Filler to binder ratio : 0.6 to 1.2Air voids : 3 to 5 %Min. VMA w.r.t. nominal maximum sizeVFB w.r.t. traffic volumeAsphalt film thickness : 6 to 8 micro meter.

Superpave Mix Design Criteria.zip

SUPERPAVE MIX contd…

1. Selection of materials: Binder : PG64-22 Aggregate: Restrictions on angularity, flaky and elongated

particles of CA and FA Restrictions on clay content Aggregate Requirements.doc Maximum density line 0.45 power chart Gradation control mechanism. Nominal maximum size and maximum size

Maximum density line :

Maximum density(P) = 100X(d/D)0.45

where :P = Total % passing given sieved = Size of sieve openingD =Max. size of aggregate

(mentioned in sieve size)

0.45 power chartNijboer, a person working for Bureau of Public Roads in Netherlands was done lots of investigation and found that the densest configuration occurs for a straight line gradation plotted on a 0.45 power chart.This is also recommended by Federal Highway Administration(F HWA).

0.45 power chartIt is a graphical representation of sieve sizes raised to power 0.45 in x-axis and % passing in y-axis.This curves are helpful in making necessary adjustments in mix designs. The grading line matching with this line gives the mix, which is having maximum density and min. VMA. The air voids of the mix shall become very low that is why this type of mix can not be used.

0.45 power chartThe line deviates from this either finer side or coarser side shall make a mix having more air voids and adjustment can be done based on the requirements.To determine the line easily just draw a line from % passing the 0.075mm sieve to the sieve first passing 100%It is always advisable to avoid the design grading which matches the maximum density grading line.

Gradation control mechanism:It specifies the detailed grading limits which gives better quality mixes. Restricted zones of gradation is specified based on the maximum nominal size of the aggregate in the mix. The mix design which by-pass this restricted zone shall always gives better results with respect to workability stability and surface texture etc. restricted zone as per superpave.htm

Sieve size in mm

For 37.5 mm nomi. Size(% passing)

For 25.0 mm nomi. size(% passing)

For 19.0 mm nomi. size(% passing)

4.75 34.7 34.7 39.5 39.5

2.36 23.3 27.3 26.8 30.8 34.6 34.6

1.18 15.5 21.5 18.1 24.1 22.3 28.3

0.600 11.7 15.7 13.6 17.6 16.7 20.7

0.300 10.0 10.0 11.4 11.4 13.7 13.7

Restricted zones for diff. sizes

Importance of restricted zone:The restricted zone has been specified to ensure adequate aggregate structure is developed in the mixture.Gradation requirements specify that mixes must plot either above the restricted zone or below the restricted zone.Gradation control points on the 2.36 mm sieve control the amount of sand sized particles in the mixture.

Importance of restricted zone:The upper control point limits the sand, in the mixture to exclude sand-asphalt mixes which are quite difficult to compact.The lower control point ensures adequate sand in contained in the mix to ensure a dense graded mixture. Mixes which passes above the restricted zone will tend to be sandier and have a weaker aggregate structure than mixes which pass below the restricted zone.

Importance of restricted zone:Mixes which pass below the restricted zone are gap graded.They develop an aggregate structure with the load carrying capacity provided by the large aggregate particles.Sand size particles play more passive role. If additional sand is added, then the gradation will enter into the restricted zone, and sand particle would begin to separate the coarse aggregate particles reducing the load carrying capability of the mixture.

Importance of restricted zone:Which structure can bear more load?

Below the restricted zone

Through & abovethe restricted zone

Gap graded Dense graded

Various types of gradations:Maximum density graded: This is the gradation, which will give the maximum density for the specified maximum size of aggregate.Dense graded: Refers to a gradation that is near maximum density grading line. Gap graded: Refers to a gradation that contains only a small percentage of aggregate particles in the mid-size range. The curve is flat in mid-size range. These mixes can be prone to segregation during placement.

Various types of gradations:Open graded: Refers to a gradation that contains only a small percentage of aggregate particles in the small-rang. This results in more air voids, because there are not enough small particles to fill in the voids between larger particles. The curve is flat and near zero in the small-size range.

Uniform graded: Refers to a gradation that contains most of the particles in a very narrow size range. In essence, all the particles are the same size. The curve is steep and only occupies the narrow size range specified.

Grading chart with all details

0.01 2.01 4.01Sieve sizes raised to 0.45 power

spec LLspec ULmax densityrestric LLrestric ULBC9BC 7

Nominal Max. & Max size:Nominal maximum size = one size larger than the first sieve to retain more than 10%Maximum size = one size larger than nominal maximum sizeEx: 12.5 nominal maximum size aggregate

Sieve size in mm

%age passing

Remarks

19 100 Max. size12.5 90 - 100 Nom. Max. size10.0 <90 One size smaller than

nom.mx.size

Bitumen content:which project consumes more bitumen per cu.m.?

PROJECT A% bitumen in DBM 4.2%

PROJECT B% bitumen in DBM 4.0%

Density : 2.450 g/cc Density : 2.680 g/cc

102.9 kg/ cu.m 107.2 kg/ cu.m

OTHER METHODS

Right or wrong??? Binder content in DBM:

Min. 4.0% by wt. Of total mix.

Rock B

Volume : 1 cu.m. Volume : 1 cu.m.Specific gravity : 2.45 Specific gravity : 2.95Bitumen required =

2.45X4/100 = 98 kg/cu.mBitumen required =

2.95X4/100 = 118 kg/cu.m

OTHER METHODS CONTD…

Coating thickness??

Bitumen is not to increase the volumeIt may require to give adequate coat to the aggregate.

Rock B

Coating thick nessCoating

thick ness

Conclusions:

It may be wrong perception to express the bitumen content based on the total weight of mix.

Another method to arrive at optimum bitumen content “Asphalt film coating thickness”

OBC based on Asphalt film thickness:

b = (100-b) x A x t x rb

where,b = % binder contentA = surface area of the aggregate, m2/kgt = Asphalt film coating thickness, mrb = Unit weight of asphalt, kg/m3

OBC based on Asphalt film thickness:Example:

A = 4.620 m2/kgb = 4.8%rb =1050 kg/m3Film thickness, t = =

T = 10.4 microns

6 – 8 mic. asphalt film thickness is advisable

Refusal Density Method:Keeping the bitumen content same

establish number of blows required to achieve maximum density/minimum air voids for the given mix.

Use that number of blows for mix design

All the remaining steps would be same.

ANY QUESTIONS ??

**********

THANK YOU

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