Investigation on the Curing Rate of a Storable Foamed Bitumen Stabilised Mix

Abstract

The technology of Foamed Bitumen (FB) stabilisation has been in use since the 1950s. In-situ and ex-situ stabilisation are techniques to increase stiffness, reduce moisture sensitivity, and add flexibility to an aggregate layer. The addition of bitumen increases the overall cost of this material. To ensure full efficiency on site, engineers are constantly looking for ways to optimise production, construction, and reduce material costs. This study examines the possibility of creating a storable FB mix that allows continuous production until demand on site is met. Construction can then proceed using this storable material until the pavement is complete. To achieve storability, a mix without an active filler, a Slow Visco- Elastic (SVE) mix was used. This method of stabilisation is already practised internationally, however it is not yet used in New Zealand (Highways Agency United Kingdom, 2008). All materials used within this research were locally sourced. The testing regime was split into four phases. Firstly, (the Pilot Phase), the engineering structural performance of a non-stored mix, a short term, and long term stored FB mixes were compared. Tests used to investigate structural performance included Indirect Tensile Strength (ITS) test and Material Testing Apparatus (MATTA) testing to measure resilient modulus. The second phase included field testing, using a Clegg Hammer on an SVE and Quick Visco- Elastic (QVE) test strip. The initial curing rates of the test strip were compared to the third phase (Refined Phase) laboratory samples. Finally, the fourth phase (Refined Phase II) assessed the effects of an unsealed ambient curing technique and its relativity to field results from the second phase test results. From the Pilot Phase results, it appeared that the storable characteristics of the SVE were not a hindrance to performance. The findings also demonstrated that a positive relationship could be obtained from moisture dissipation during curing and stiffness gain. However, from the second phase results, it was apparent that the soaking method, during laboratory testing, was overly conservative. The importance of sufficient fines was confirmed from the Refined Phase II component of the research. From all phases, a model which captured moisture dissipation was developed to predict stiffness gain during initial curing. This model allows opportunities to capture the approximate duration required between compaction and trafficking, through field testing, hence minimising the risk of causing significant damage to the pavement.