In this episode, we will explore the importance of active filler and its limitations in Bitumen Stabilised Material (BSM). 

Active filler, such as cement or hydrated lime, is added to BSM to improve its resistance to moisture damage. However, it’s essential to use the right amount, as adding more than 1% (by mass) can change the material’s nature and performance characteristics. 

Once the active filler exceeds 1%, the BSM starts behaving more like a cement-treated material. This alteration can reduce flexibility and increase the risk of block cracking, ultimately affecting the pavement’s performance and durability. 

There are cases where adding more than 1% hydrated lime becomes necessary. For materials with a high plasticity index (more than 6%), the application rate of lime is determined through an ICL test. The lime is then premixed with the material and can be further treated with foamed bitumen or bitumen emulsion, along with an additional 1% of active filler. 

The key to optimal performance in BSM lies in achieving the right balance between strength and flexibility. This is done by limiting the amount of active filler, optimizing the bitumen addition, and selecting the appropriate stabilising agent for the specific material and project requirements. 

Maintaining the granular nature and performance characteristics of BSM relies on limiting the addition of active filler to 1%. However, in cases where modification is necessary due to high plasticity, adding more lime becomes crucial. 

In our next episode, we will compare BSM to thick asphalt, exploring their similarities and differences.