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A study into the mechanical properties of foamed bituminous stabilised materials
Weston, Carl Thomas
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Of the most essential objectives of a good mix design procedure is to be able to assess the compactibility of a mix in the laboratory, i.e. to relate laboratory compaction to compaction on site and to give insight into the prediction of the expected performance of the mix. Foamed bitumen treated material has been used with success in many countries around the world. Regardless of the success story, it is also true that there is a dearth of knowledge concerning the understanding of the effect of the current used compaction methods on the mechanical and volumetric properties of foamed bitumen treated material. The use of a variety of mix design and evaluation procedures around the world has led to difficulties in correlating and assessing results obtained in different environments. Experience and research have also revealed the tendency of current mix design methods to underrate the engineering properties of foamed bitumen treated material. This project entails an investigation into the volumetric and mechanical properties of mixes with three types of granular materials. Test specimens were prepared using four of the most commonly used laboratory compaction methods and one field simulating compaction method. The main objectives of the project were to: • Determine and compare the influence of the different compaction methods on the volumetric and mechanical properties of foam bitumen mixes • To make recommendations regarding the suitability of the different compaction methods for use in the mix design of foamed bitumen mixes. Marshall, Hugo, Gyratory and Refusal Density with Kango Hammer compaction were employed as laboratory compaction methods. A Hydrostatic double-drum vibrating roller was used to simulate field compaction. Graded crushed stone and gravel material were used as the granular materials. Indirect tensile (strength and stiffness) and Semi-circular bending (strength) testing was used to assess the mechanical properties. Use was made of 80/100 and 150/200 penetration grade bitumen. The study revealed that binder type has no influence on the mechanical properties of foamed mixes, whilst compaction method influences mechanical properties significantly. The SCB test was found to be inappropriate for foam mixes with low binder contents. All the laboratory compaction methods were found to be suitable for the design of foam Mixes. The results reported in this thesis needs to be validated by more extensive as testing was limited to only two types of granular materials.