TOWARDS LABORATORY REPLICATION OF FIELD COMPACTION ASPHALT SHEAR BOX COMPACTOR TOM GABRAWY PIONEER ROAD SERVICES PTY. LTD. February 2000 INTRODUCTION This Shear Box Compactor (SBC) is a dual-purpose tool for both sample preparation and mix
TOWARDS LABORATORY REPLICATION OF FIELD
“ASPHALT SHEAR BOX COMPACTOR”
PIONEER ROAD SERVICES PTY. LTD.
This Shear Box Compactor (SBC) is a dual-purpose tool for both sample preparation and mix evaluation. The prototype Asphalt Shear Box Compactor was developed by Pioneer Road Services (PRS) R&D Department in 1994.
The compaction principle is based on simulating the action of a field compaction-roller, achieving high accuracy and homogeneity in the targeted compaction density.
The produced sample is of prismatic shape and is large enough to provide specimens for beam fatigue and wheel tracking tests and cylindrical specimens used for other common tests.
The SBC equipment is able to produce the required compacted samples rapidly, repeatedly and cost effectively, while providing valuable data about the mix workability and the strength/stability of the aggregate structure.
PH. 1 : PRS ASPHALT SHEAR BOX COMPACTOR
In 1988, AAPA established the R&D Steering Committee to guide the industry into the new era of asphalt technology. It resulted in the local development and adoption of the new generation sample preparation and characterization techniques such as the Gyropac, the Servopac, the Indirect Tensile Modulus Test and Beam Fatigue Test Apparatus.
One of the proposals under the R&D Committee Ideas Scheme was the “Shear Box Compactor”. The proposal was made by Ian Rickards (AAPA’s Technical Director at the time). This proposal attracted an initial fund allocation of $2,000 to build a manual prototype shear box compactor to demonstrate its feasibility. The basic operating model was developed by the author at the Materials Laboratory of the Sydney City Council.
Evaluation of the first sample produced was carried out at the NSW Roads and Traffic Authority (RTA) Milson’s Point Laboratory in Sydney. They confirmed that the sample was uniform and had even air voids distribution.
However, interest waned because of the perceived complexity of the process and the anticipated excessive cost of the equipment.
WHY DO WE NEED A SHEAR BOX COMPACTOR?
PH. 2 : PRS SAMPLE FEEDING TOOL FOR BLOCKS
SOME OF THE ADVANTAGES OFFERED BY THE SHEAR BOX COMPACTOR
The ability to compact thicker samples (up to 185mm) in one run because of its mode of shearing.
Excellent control of compacted density with improved repeatability.
Produces large samples that can be sawn or cored to provide 4 fatigue beams, 8 modulus/creep cylindrical specimens or a combination of two beams and 4 cylindrical specimens.
Sets of cored specimens are free from surface voids affect and have very similar (if not identical) conditioning (heating time and compaction temperature).Cores can be taken in 3 perpendicular directions (X, Y & Z) thus enabling properties such as “modulus” to be evaluated in various directions relative to compaction and traffic direction.