1. Pavement design and construction technique using high strength stone interlocked cemented aggregate low fines matrix.
Gerhard van Blerk
June 2014
In the light of global financial constraints, the last 5 year sow NZTA embarking on a new design and construction technique in persuade of an more cost effective alternative to traditional construction techniques.

2. Introduction: “More for Less”
Global financial constraints and a steep increase in bitumen prices
RCA’s are seeking alternative construction techniques (Hi-Lab)
Embrace the origin of road construction (John Loudon McAdam, 1820) through modern pavement construction techniques
“Can we get more for less” ????
As a result of global financial constraints and a steep increase in bitumen prices over the last decade, road controlling authorities are constantly seeking alternative design and construction techniques.
Thus, we explored a theory based on the origin of road construction as implemented in the early 1800’s by John Loudon McAdam and more important the delivery of this methodology through modern construction techniques.

3. Macadam Pavement Design: “Back to Basics”
The method involved onsite hand crushing of a single size stone (less than 75mm diameter). As depicted by the picture supervisors used a scale to check stone size. A workman can check the stone size himself by seeing if it would fit into his mouth. Final wearing layer consisting of 20mm diameter stone which had to be smaller than the 100mm iron carriage tires.
In 1822 the first Macadam road was build in the United States in Maryland.
As traffic speeds increased with the introduction of the automobile tar was poured onto the surface as shown in the 1926 picture of a road in Kentucky.

4. Design Intent: High degree of aggregate interlock
Maximize stone packing, forcing “full” stone on stone interlock through a controlled process of:
grading (percentage of large aggregate fraction)
aggregate quality (crushing resistance)
small amount of cement (3%)
construction technique
Critical to the design intent is the ability to maximize large stone interlock and packing through a process of controlling the:
Grading,
aggregate quality,
small amount of cement,
and construction technique.
In the presentation this technique will be referred to as Hi-Lab (high strength low fines aggregate base layers).

5. Material Selection and Properties: Aggregate Grading
The Hi-Lab aggregate grading is crucial to maximizing large stone interlock and ensuring sufficient fines to fill air voids.
The plot shows the Hi-Lab 40 grading envelopes used for a base layer construction compared to a typical 37mm aggregate grading and more common US roller concrete.
Note: between 70% and 60% of the stone size within the Hi-Lab 40 grading are greater than the 19mm size.

6. Hi-Lab Construction Technique: Aggregate Placing
The presentation will make use of short video clips to better illustrate the construction technique.
This video clip shows the aggregate placing of a Hi-Lab65 subbase layer consisting of a maximum 63mm stone size.
As shown by the video the aggregate is placed wet to limit segregation during transportation and placing. Limited fines will stick to larger stone.

7. Hi-Lab Construction Technique: Placing and Grading
This clip shows the placing and grading.
Critical is the ability to maintain the grading integrity by limiting segregation. Moving material around is restricted to a limited amount of passes with the grader followed by a steel drum roller.

8. Hi-Lab Construction Technique: Cement Spreading
The following pictures shows a limited amount of normal Portland cement consisting of 3% being placed prior to stabilization.

9. Hi-Lab Construction Technique: Subbase Stabilization (mixing process)
The following video clips shows the stabilization process for a Hi-Lab65 subbase layer.
Sufficient water is injected during the stabilization process to form a cemented paste trapping the limited amount of fines and to ensure workability is increased.

10. Hi-Lab Construction Technique: Base Stabilization (mixing process)
Again this video clip shows the stabilization of the Hi-Lab 40 stone size used for a base layer construction. Sufficient water is added during the mixing process to form a paste, the cement will trap the limited amount of fines.
The paste will improve workability and form a mortar to fill air voids between the interlocked larger stone.

11. Material Selection and Properties: Aggregate Grading
This clip shows a grading sample being taken and emphasis is put on the limited fines, as the ultimate goal is to achieve full stone on stone interlock.
Maximizing load transfer.

12. Hi-Lab Construction Technique: Compaction and Final Surface
This video clip shows the padfoot roller on vibe providing deep compaction and rotating the stones into a position of interlock.
The padfoot roller is followed by the grader blade tilted forward and completing a final sweeping movement to limit possible segregation.
The blade is tilted forward to increase visibility for the operator and limit material being moved around.
The steel smooth drum roller on vibe will follow the grader completing primary compaction. Total of 7 passes is specified, followed by three pin rollers.

13. Hi-Lab Construction Technique: Compaction and Final Surface
This picture shows the final surface after primary compaction, 7mm crusher dust is applied to “shock” the surface within a few hours of stabilizing.
This picture shows the final surface with exposed stone mosaic and surplus crusher dust.

14. Hi-Lab Construction Technique: Engineering Properties (Strength)
Indirect Tensile Strength (ITS)
200mm diameter cores were taken and tested in indirect tensile strength.
When constructed correctly the sample shows excellent packing of the larger stone, forcing load transfer from stone to stone. In this example the stone were sheared during the ITS testing at the point of loading.

15. Hi-Lab Construction Technique: Engineering Properties (Strength)
Beam Fatigue Tensile Strain
Beam samples were cut from the pavement in the field. As it is to difficult to compact samples in the laboratory.
Again we can see the stone sheared in the compression zone during a flexural beam test.

16. Hi-Lab Construction Technique: Engineering Properties (Strength)

17. Hi-Lab Construction Technique: Engineering Properties (Strength)

18. Hi-Lab Construction Technique: Engineering Properties (Strength)

19. Hi-Lab Construction Technique: Observed Performance
These graphs shows the reduction in average maximum deflection (D0) as measured by a Benkelman Beam.
Subgrade max deflection are in the order of 1.7mm.
After placing 230mm Hi-Lab65 the deflections reduced to 0.5mm and finally placing a 180mm Hi-lab40 base layer the deflections were in the order of 0.25mm
FWD data was used to back-calculate layer stiffness using a layered elastic model. The stiffness for the subgrade were approximately 100MPa, subbase layer between MPa and finally the base layer around 5000MPa.
In addition, the subbase and base layers were combined for the back-calculation analysis and stiffness values ranging from MPa were achieved.

20. Case Studies: Cost Saving
Substantial cost savings without sacrificing performance.
Pavement construction cost savings between 30% to 40%.
Base layer construction cost savings between 100% to 400% e.g. SAC ($100/m^2) – Hi-Lab ($25/m^2).
The construction techniques shows a lot of promise, as the case studies showed substantial cost savings without sacrificing performance.
Between 30% and 40% cost savings compared to equivalent pavements structures of similar design traffic loading.
Savings in the order of 100% to 400% compared to bituminous base layers for example structural asphalt of foam bitumen. 20 20

21. Conclusion/Summary:
Realizing the proven performance associated with the Macadam design theory through modern stabilization equipment.
Observed engineering properties are very promising.
Case studies shows this technique to be a viable alternative to more costly options.
We were able to duplicate the Macadam design theory through the use of modern construction equipment making this technique a cost effective and viable alternative. 21 21

22. This is our latest automated high speed data machine collecting road surface data.