Innovations in HMA

RPF May 2006

Content

• Proposed HMA trials

• High Modulus Asphalt

• Bailey method of design

HMA Trials

A GPTRW/Sabita – joint venture

Content

• Background

• Meeting on 23 March 2006

• Forensic study

• Issues

• Way forward

Background

• Negative perceptions on hma wc performance– based on wide range of causative factors– adversely influence the use of a key road

building material

• Ensure that technology is sound and up-to-date to render the product cost-effective

• Welcome the opportunity to cooperate with GPTRW to respond to the challenge

Meeting on 23 March 2006

• Attendance– Senior staff of 4 Sabita members active in Gauteng

(and consultant)– GPTRW– CSIR BE– L Sampson– P Myburgh

• Agenda– Forensic study– Defining issues– Way forward

Forensic study

• In preliminary phase

• Identified three key issues:– Performance widely scattered - distress in a

notable proportion of roads sampled– Prevalence of permanent deformation at

intersections– Lack of correspondence of approved job-

mixes and site materials in several instances

Issues defined

• The trials project should cover two main areas:– Mix designs for adequate performance– Quality management systems

• Job-mix proposals• Aggregate uniformity and relevance

Mix designs

• Aggregate shape, grading and binder content

• Dogged adherence to COLTO grading envelopes to current aggregate shape

• Resultant low binder content/low VIM– Premature brittleness– Lack of resistance to permanent deformation

• Need to differentiate between intersections and open road conditions

Mix designs/cont…

• High crusher sand content vis-à-vis availability (60+% -4.75mm)

• Layer thickness/NMAS ratios (NCHRP: 3 – 4)

• Need to understand and incorporate methods to assess aggregate packing (e.g. “Bailey method” published by TRB)

Mix design/cont…

• Possibly move to stone skeleton mixes (as opposed to sand skeleton ones)

• Ultimately strive for balance:– Durability– Fatigue strength– Resistance to permanent deformation

Way ahead

• Joint enthusiasm to proceed with trial sections

• Mixes would be evaluated by laboratory and APT methods

• Process - joint venture of road authority consultants and suppliers/contractors– Enhanced expertise base– Advance implementation of findings

Way ahead/cont…

• The four contractor/suppliers would partner with specialist HMA design consultants

• Designs based on commercially available binders to be submitted by end June for use on:– Intersections– Open highway

• Each trial would constitute:– 60 tons (160m x 3.7m x 40mm)

• COLTO gradings would NOT be a point of departure

Way ahead/cont…

• Job-mix relevance and aggregate consistency will be key

• Completion of forensic study

• MMLS and laboratory testing of mats

• HVS testing to commence in Oct/Nov

• Formation of broader industry advisory group to monitor and evaluate

Conclusion

• Joint venture presents a model for future cooperation between road authorities, suppliers/contractors and consulting engineers to mobilise experience and expertise to respond to technical challenges

• Springboard for future initiatives

High modulus asphalt

• French initiative Enrobé à Module Élevé (EME) – locally called HiMa

• Tested in the UK (TRL)

• Introduction to SA being investigated (both roads and airports)

What is EME/HiMa?

• Base course - high content of hard bitumen• Low air voids• High elastic stiffness• High deformation resistance• Good fatigue resistance• Impermeable and durable• Aggregate angularity and cleanliness defined• Hard grades of bitumen (15/25pen)• Use in France for 20 years• Tested and reported on by TRL (UK) 2005

TRL report TRL 636)

• EME designed and tested and compared with HDM

• Aggregate size – 20mm• Binder richness modulus 3.65 (b.c. 6%)• Air voids (120 gyrations) 1.8%• Complex modulus (15°C, 10Hz) 14 GPa• Binder penetration (25 °C) 18• R&B SP 66

TRL conclusions

• EME superior to HDM in many respects:– More deformation resistant– Superior load spreading capability– More durable and impermeable– Reduced layer thickness – 25mm for 80 m – esa’s– Trials based on French method – needs to be

verified for other methods and conditions

HiMa in SA?

• Bitumen meeting HiMa requirements can be made available

• Prospect of incorporating trial sections into the GPTRW joint venture on asphalt

• Ultimately present another option to consider in the heavy duty pavement sphere.

Bailey method

Published as TRB Circular E-C044 (2002)

Bailey method for Gradation Selection in Hot-mix Asphalt Mixture Design

It presents:

A systematic approach to blending aggregates that provides aggregate interlock as the backbone of the structure and a balanced continuous gradation to complete the mixture

Basic principles

• Definition of coarse and fine aggregate

• Aggregate packing– Coarse aggregates create voids– Fine aggregates that can fill these voids

• Combination of aggregates (by volume)

• Analysis of blends

Combination process

• Boundary of coarse and fine aggregate (PCS = 0.22 of NMPS)

• Loose and rodded unit weights – voids• Mix type

– Coarse graded – coarse aggregate skeleton– Fine graded – load carried by fine aggregate,

• Meeting aggregate ratios to ensure packing is as intended and not interfered with

Step4: Check PCS size marked in green below in Step 7NMPS = NMPS for the overall blend, which is one sieve larger than the first sieve that retains more than 10%

Results% Passing NMPS for mix 26.5

CA 1 CA 2 CA 3 FA 1 MF16.5% 37.5% 12.5% 33.4% 0.0% Total vol CA 55.9

Combined 100.00% Total vol FA 44.137.5 100.026.5 100.0 Step 6: Enter Guideline limits % Passing 0.075

19 85.1 Calc Selected % Passing Coarse Limit Fine Limit 0.075 5 0.075 0.15

13.2 82.5 Half Sieve 13.25 13.2 82 37.5 100 100 0.15 6 0.15 0.3

9.5 57.6 PCS 5.83 6.7 46 26.5 100 100 0.3 8 0.3 0.6

6.7 45.7 SCS 1.47 1.18 17 19 100 85 0.6 12 0.6 1.18

4.75 36.5 TCS 0.26 0.3 8 13.2 84 71 1.18 17 1.18 2.36

2.36 24.5 9.5 76 62 2.36 24 2.36 4.751.18 16.5 6.7 68 52 4.75 37 4.75 6.70.6 11.7 Desirable 4.75 60 42 6.7 46 6.7 9.50.3 8.3 CA Ratio 0.80 0.7-0.85 2.36 48 30 9.5 58 9.5 13.2

0.15 5.9 FAc Ratio 0.36 0.35-0.5 1.18 38 22 13.2 82 13.2 190.075 4.5 FAf Ratio 0.50 0.35-0.5 0.6 28 16 19 85 19 26.5

0.3 20 12 26.5 100 26.5 37.50.15 15 8 37.5 100 37.5

37.5 26.5 19 13.2 9.5 4.75 0.075 10 4CA Ratio 0.8-0.95 0.7-0.85 0.6-0.75 0.5-0.65 0.4-0.55 0.3-0.45FAc Ratio 0.35-0.5 0.35-0.5 0.35-0.5 0.35-0.5 0.35-0.5 0.35-0.5FAf Ratio 0.35-0.5 0.35-0.5 0.35-0.5 0.35-0.5 0.35-0.5 0.35-0.5

Step 1 Determine chosen unit of weight for each aggregateBulk SG

CA 1 1379.0 kg/m3 2.733CA 2 1393.0 kg/m3 2.708CA 3 1360.0 kg/m3 2.716

Step 2 Determine unit weight contributed by each CA according to blendVol of each agg (Litres)

CA 1 344.8 kg/m3 126.14CA 2 766.2 kg/m3 282.92CA 3 136.0 kg/m3 50.07Sum 1246.9 459.14 540.86Step 3 Determine the voids in each CA according to weight and contribution by volume. Sum the voids.

CA 1 12.4 %CA 2 26.7 %CA 3 5.0 %

Voids in CA 44.1 %

Table to show Desirable ratios

Combined grading to calc NMPSStep5: Select Half S, PCS, SCS & TCS

Step7: Check Ratios and adjust propostion as necessary

Calculations

Grading based on N=0.45

0

10

20

30

40

50

60

70

80

90

100

% P

assi

ng

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1 10 100

Partical Size (mm)

Perc

enta

ge P

assi

ng

Coarse Fine Theoretical