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Tuesday, December 6, 2016

HOW TO MAKE (ASPHALT) SUPER PAVE MIX DESIGN COMPLETE PROCEDURE



WHAT IS SUPERPAVE?

The  Superpave mix design system is a comprehensive method of designing paving mixes tolerated to unique performance requirements dedicated by traffic, environment(climate), and structural section at particular environment site. It facilitates selecting and combing Asphalt binder, Aggregate and any necessary modifier to achieve the required level of pavement performance.

   Superpave History  


Under the strategic highway research program (SHRP) an initiative was undertaken to improve material selection and mixture design by developing:1.     A mix design method that accounts for traffic loading and environmental conditions.
2.     A new method of Asphalt Binder evaluation.
3.     New method of Mixture Analysis
The objective of Superpave mix design system is to define an economical blend of Asphalt binder and aggregate that yields a paving mix having

1. Sufficient Asphalt binder
2. Sufficient Voids in Mineral Aggregate (VMA) and Air voids.
3. Sufficent Workability and
4. Satisfactory performance characteristics over the service life of pavementSuperpave Mix 

The Important Features of Mix Design.
1.     Performance based
2.     It is specification based i.e every part of this is in under control points.
3.     The use of formal aggregate depends on consensus requirement
4.     The use of P G Asphalt binder grading system and its associated asphalt binder selection system.5. The use of Gyractory compactor to know field compaction. So we easily know what will be the field compaction


6.     Its all depend on traffic and environment of project
7.     Full volumetric approach to mix design



    MIX DESIGN STEPS
 

1


SELECTION OF MATERIAL
                      2


SELECTION OIF DESIGN AGREGATE STRUCTURE
                 (DAS)
                        3


SELECTION OIF DESIGN ASPHALT CONENT
                 (DAC)
                      4


MOISTURE EVALUATION

 STEP 1.SELECTION OF MATERIAL 

1A.   ASPHALT BINDER 

1B.      AGGREGATE      

STEP 1 A SELECTION OF MATERIAL (BINDER)ASPHALT BINDER                                                                                  
          Asphalt is a principle constituent of HMA. It work as a inexpensive, water proof, thermoplastic, viscoelastic adhesive its define as "A dark brown or black cementitious material in which the predominating constituents are bitumen, which occur in nature re obtained in petroleum processing".      


SELECTION OF ASPHALT BINDER GRADE

  For Asphalt binder grade selection the following information’s are required.
1.     Determine project  weather data for 30 years in past

2.     Determine design temperature
3.     Determine the performance grade In country
     Selection of Asphalt Binder Grade is based on
1. Country temperature zoning map.
2. Verify Asphalt PG3.     
3. Determine temperature viscosity relationship



 The grading system is based on climate. 

Example     PG =         70  - 10           
   PG= Performance grade    70  = Average 7 day pavement Design Temperature 10= minimum pavement design Temperature



This selection of Asphalt Binder is based on Country temperature Zoning map.GRADE SELECTION (2) BUMPING.Grade Bumping for speed and loading of traffic: increase the selected PG based on the map by the grade equivalent as shown below    



 TRAFFIC CLASS DESIGNATION



ASPHALT BINDER MIXING &  COMPACTION

We can determine Laboratory mixing and Compaction temperature using rotational viscometer  

The method which will we use for this      

ASTM D4402

&AASHTO T316       


 Mixing Temperature at 0.17 Pa.s(±)  


Compaction Temperature at 0.28   Pa.s(±)            











we need to check the consensus requirements and source requirement of aggregate which will we use for superpave design  
Consensus Requirements are

1.    Course Aggregate Angularity(CAA)    
       AASHTO T 335
2.    Fine Aggregate angularity.(FAA)          

       AASHTO T304
3.    Flate and elongated particles(F & E)    

       ASTM D 4791
4.    Clay Content,(SE)                                

       AASHTO T176
The Source Requirement


1.    Toughness                                               
       AASHTO T96
2.    Soundness                                                

       AASHTO T104
3.    Clay lumps and Friable particles              

      AASHTO T112STEP 

1 B. AGGREGATE SELECTION SUPERPAVE AGGREGATE REQUIREMENT

Second we need to see the superpave aggregate requirement .which depends upon traffic and depth of layer





AGGREGATE GRADATION 


It is the relative distribution of the weight of different sizes to the total weight of sample.It is determined by sieve analysis of sample.

Gradation Types         

 Gradation which we obtain it has three

Dense Gradation  
The type of gradation that is near the FHWA’s 0.45 power curve for maximum density
Gap Graded 
The gradation that contains only a small percentage of aggregate particles in the mid size rang. The curve is flate in the mid size range. 
Open Graded
The gradation that only contains small percentage of aggregate particles in the small range. This result in more air voids because there are not enough small particles to fill in voids between the larger particles. The curve obtained in this case is near vertical in the mid size range and flat and near zero in small size range.
Uniform Graded
A gradation that contains most of particle in a very narrow size rang. In essence all particle in the same size. The curve is steep and only occupies the narrow size range specified.
Fine Gradation
A gradation that when plotted on 0.45 power gradation graph fall mostly above the 0.45 maximum density line.
Coarse Gradation
A gradation that when plotted on the 0.45 power gradation graph fall mostly below the 0.45 maximum line Graph shows all types

SELECTION OF DESIGN AGGREGATE STRUCTURE (DAS)

Selection of DAS based on four steps

1.     Develop Trial Blends
2.     Compact blends
3.     Evaluate blends
4.     Select confirming blend
Develop Trial BlendsThis depends on three points


1. For DAS minimum three blends selected
2. Gradation of Samples from hot bin
3.  It must vary three blend so it fulfill Superpave criteria 

Calculate combine propertied 

  Estimate mathematically the combined aggregate properties based on blending percentage and the individual aggregate properties. For the selected blend verify the combined properties by testing

2. COMPACT BLENDS

Select % trial Asphalt binder Pbi one of the following methods             AASHTO R-35
A)Estimate effective specifc gravity of each blend using Gse using
     Gse=Gsb+C*(Gsa-Gsb)


Gsb= Apparent bulk Specific Gravity


Gsa= Apparent specific Gravity


C= Aggregate absorption factor assumed but for absorptive aggregate use 0.6 or 0.5


B)  Estimate the volume of Asphalt binder  (Vba) absorbed into aggregate for each blend


Vba = 
Ps*(1-Va) * (1/Gsb-1/Gse)
            (Pb)/Gb –(Ps/Gse)


Vba = Volume of absorbed binder


Va = Volume of Air Voids


Pb= Percent of binder


Ps= Percent of Aggregate


Gb= Specific Gravity of binder


C) Estimate Volume of effective binder (Vbe for trial Blend)


Vbe= 0.081-0.02931*In(Sn)


Sn= The Nominal Maximum size in inches

 
D)Finally estimate the Initial AB% (Pbi) for each trial blend using
 

Pbi=         Gb*(Vbe+Vba)
            Gb*(Vbe+Vba)+Ws
 Ws =      Ps*(1-Va)    (Pb/Gb+Ps/Gse)


 Compact 2 specimen from each blend to Ndes then for each compacted specimen
Measure Gmb AASHTO T166
3 . Get the specimen height at Nini and Ndes in mm from Gyractory compactor data


 1.   For each blend mesure Gmm method AASHTO t 209
 C. Evaluate Trial Blends
Evaluate trail blend from the following equation
%Gmm =Gmb/Gmm*100


% Gmm at any Nx Gmm Nx=
Gmm Ndes*Hnx                                                                    Hnx
 

% of Air Voids = 100-% Gmm at Ndes

% VMA = 100-(%Gmm@ Ndes*Gmm*Ps)/Gsb


 % Gmm at Nini = % Gmm at Ndesx   * HNdes                                             HNini


 HNdes=  Height of specimen at Ndes


HNini= Height of specimen at Nini

2. Reculculate 4 % air voids(96% Gmm at Ndes)
Asphalt content percent using 

Pb estimated =Pbi-(0.4+(4-Va)

VMA using = % VMAinitial+C(4-Va)

VFa Using

%VFa estimated =100*(%VMA estimated – 4.0)

VMA estimated

%Gmm @ Nini=%Gmm@ Nini-(4.0-Va)

Calculate DP ratio
Compute Pbe using

Pbe=(Ps*Gb)*(Gse-Gsb)/Gse*Gsb+pb estimated

DP Using

DP= P0.0075/Pbe 

Step3
 SELECTION OF DESIGN ASPHALT CONTENT

A.Compact samples 

 Prepare HMA using four Asphalt binder

X
X-0.5
X+0.5
X+1.0

Here X= Estimated binder content from step 2 at 0.40 % air voids for the selected blend·        

 Compact 2 samples at each AB% to Ndes
·         Measure specimen height and gmb @ Ndes
·         Measure 2 Gmm for each mix


 1.     Analyse the Result
Use the same formula in the selection of DAS to compute


% of Gmm at Nini and Ndes

Volumetric properties( Air Voids,VMA,VFA)

DP ratio Generate graph for each property vs AB%

C. SELECT DAC

From the graph at 4.0 % airvoids determine DAC and check

VMA and VFA and % Gmm @ N ini

Compute DP at the effective DAC

Compare with super pave criteria and adjust your design as needed

D. Ndes & Nmax verification

Prepare Hot mix at selected DAC & DAS

Gyractory compactor 2 specimen to Ndes and 2 specimen for Nmax

Compare the result with Superpave criteria and adjust as required 

STEP4 . 
MOISTURE SENSTIVITY
It consists of four parts
1.     Select Nx
2.     Compact samples
3.     Evaluate Strength
4.     Evaluate Moisture sensitivity
 

1.     Select Nx
Use the densification data of  the Nmax verification step to determine the number of gyration to achieve 7 % air voidsi.e % Gmm 93%%

Gmm @ Nx = %Gmm @ N      Hn                                                                                      Hnx
2.COMPACT SAMPLES

Prepare HAM using DAS AND DAC
Gyractory compactor 6 specimen to Nx
Three specimen are control (non conditioning)
The other three is conditioned for 24 hrs at 60 degree centigrade

Test all specimen to determine maximum indirect tensile load and failure 

C. EVALUTATE

Now to Calculate indirect tensile strength (ITS)Maximum allowable Strength.
 ITS loss is 20 %Compare with Superpave criteria and adjust design In case 
Note.ITS is failing use cement dust, lime and Portland cement or anti striping agent as MOT specifications.

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