Prior to carrying out a stabilisation design, all materials are prepared and subjected to basic soils tests to determine:
Results from the basic soils test are first used to check that the material to be stabilised with bitumen meets the minimum classification requirements (e.g. G6 or better). If this requirement is not met, blending with fresh material (e.g. crusher dust) is an option that can be considered.
Stabilisation designs are undertaken using both bitumen emulsion (supplied by the manufacturer) and foamed bitumen (where the foaming characteristics are determined prior to commencing with the design).
The procedure described in Appendix B of TG2 (2020) is then followed in three sequential steps:
▶ Step 1. Determination of the effect of active filler. Three material samples are mixed with the same application rate of the selected bitumen stabilising agent, but with different active fillers. Usually, the first mix includes no active filler, the second 1% cement and the third 1% lime. Specimens 152mm in diameter x 95mm high are manufactured and cured to constant mass before testing to determine the ITSDRY and ITSWET values. The results are then used to indicate any preference for a particular active filler, or if there is a need for any active filler.
▶ Step 2. Optimum bitumen application rate. Material samples are mixed with the selected bitumen stabilising agent at four increments (as well as the active filler determined from the Step 1 test results). Specimens 152mm in diameter x 95mm high are manufactured and cured to constant mass before testing to determine the key ITS values (ITS DRY and ITS WET). These results are then interrogated to determine the optimal application rate for the bitumen stabilising agent.
▶ Step 3. Determination of the shear properties by carrying out triaxial tests on large specimens (150mm diameter x 300mm high) mixed with the selected application rates for bitumen and active filler and cured at the equilibrium moisture content. Four confining pressures are applied and two specimens tested at each confining pressure in order to determine the Mohr-Coulomb circles that provide the shear properties. Finally, the Retained Cohesion (RetC) is determined by testing two specimens at one selected confining pressure after soaking for 24 hours.
Field samples of treated material are brought to the laboratory, prepared and used to manufacture specimens that are then cured and tested to determine the ITS strength. The results are used to determine the BSM classification.
Once the BSM has cured sufficiently (weather dependent, but normally 2 weeks for foamed bitumen treatment and 4 weeks for bitumen emulsion), core specimens can also be extracted from a BSM layer and tested to determine the BSM classification.
In the interests of promoting the technology, BSM Laboratories helps others in need of assistance, be it for in-house training or helping to solve problems experienced on a construction site.
In addition, experienced technicians often undertake visits to construction sites to assist resolving problems experienced with BSMs. Assistance is also provided in establishing site laboratory facilities and training site personnel. In addition, non-standard equipment (e.g. vibrating hammer) can be either purchased or rented from BSM Laboratories.
BSM Laboratories is part of the “Global BSM Network” that is concerned with the promotion and application of BSM technology. Valuable experience acquired from
involvement in projects on all continents (except Antarctica) is available to anyone who is serious about using the technology for the first time or those who are experiencing problems with an application. It is of paramount importance to understand that BSM is totally different from other bitumen-treated materials (especially
hot mix asphalt) and we appreciate the challenges that are faced by many and empathise with them. If you are one of them, please use the “Contact Us” menu to let us
know who you are, where you are from, what help is required and we’ll get straight back to you. Remember, you are not alone!
BSM Laboratories offer testing, training and even set up of mini satellite laboratories on projects around Southern Africa. We are continuously striving to improve testing and knowledge in Bitumen Stabilised Materials.
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