- Publication no: AP-T218-13
- ISBN: 978-1-921991-67-7
- Published: 16 January 2013
Stone mastic asphalt (SMA) is a superior asphalt mix with proven performance. As a consequence of the aggregate skeleton, SMA has an open surface. The experience of some road agency and industry members indicates that the open surface of the SMA leads to incorrect bulk density results and consequently to incorrect air void content determination. The scope of this research work was to investigate which bulk density test method is the most suitable for the air void measurement of laboratory prepared SMA test specimens.
The bulk density measurement practice in the US and in Europe was investigated. Samples for three different SMA 10 mixes were compacted in the laboratory at five different compaction levels and the air void content was determined using the vacuum sealing method, the saturated surface dry (SSD) method, the silicone sealing method and the wax sealing method.
The analysis of the laboratory testing revealed that the SSD method is generally applicable to SMA up to approximately 7% air void content; a water absorption limit of 1.0% may be applicable for SMA mixes. The vacuum sealing method is considered less reliable for laboratory prepared test specimens of SMA.
At an air void content higher than 7%, the SSD method will provide results that are less reliable and the silicone sealing method should be used. This study found that the air voids were approximately 1.5% higher for the silicone sealing method compared to the SSD method.
The design and in situ air void content of the compacted layers according to the German practice was also discussed in this study. This suggested that compacted SMA layers should ideally have an air void content lower than 6%.
- 1. INTRODUCTION
- 2. Bulk density measurement
- 2.1. Bulk Density Measurement Practice in the United States
- 2.2. Bulk Density Measurement According to the European Standards
- 2.3. SMA Volumetric Requirements According to the German, Austrian and Swiss Specifications
- 2.4. SMA Volumetric Requirement and Measurement in Australia
- 3. Laboratory program on Bulk density measurement
- 3.1. Test Methods Selected in the Program
- 3.2. Sample Preparation and Sample Testing
- 3.2.1. Preliminary Work on Silicone Sealing
- 3.2.2. Efficiency of Wax Coating
- 3.3. Bulk Density and Air Void Content Results
- 3.3.1. Bulk Density Testing on Specimens Compacted to 2% Air Void Content
- 4. Data analysis
- Vacuum sealing method
- Wax sealing method
- Silicone sealing method
- SSD method
- 5. Summary
- 5.1. Discussion
- 5.2. Considerations and Conclusions
- Appendix A Surface texture, SMAN-VIC
- Appendix B Surface texture, SMA10-WA
- Appendix C SMA10-QLD