Effect of rubber size and shape on Proctor elements of CBC mixtures

Abstract

The application of recycled rubber in cement bound base courses (CBC) has recently become a subject of research. There are several advantages of the application of rubber in CBC. One is the environmental benefit considering the major problem of disposing of end-of-life tires (ELT), whose number is rapidly increasing in the modern world. On the other hand, CBC is known as the most rigid course of pavement, and is very prone to cracking. Rubber has the potential to reduce the cracking, which is another benefit of its use in those courses. This paper presents laboratory research on a reference mixture and five rubberized mixtures with different fractions of recycled rubber. The mixtures are modified with 20 % of rubber as a replacement for sand. Three fractions of granulated rubber and two fractions of rubber threads are used. The research encompasses the impact of rubber of different sizes and shapes on the Proctor elements of the CBC mixture. Furthermore, specific surface area (SSA) and SEM analysis is presented. The SSA value was found to be the most influential factor on the optimal moisture content (OMC) values, which is confirmed by SEM images. SEM analysis showed that larger particles have a flatter surface and demand higher water content. Furthermore, the rubber particle shape has a greater impact on the mixture MDD compared to the particle size, while the rubber particle size has a greater effect on the OMC compared to the rubber particle shape. Finally, the effect of the rubber particle size and shape on the OMC and MDD can be neglected and the production of cement bound aggregate incorporating waste rubber can be designed and built using reference values of the OMC and MDD.