Currently, there exists no universally accepted Cold Bituminous Emulsion Mixtures (CBEMs) design procedure. Three of the most popular design procedures, which in essence were based on AASHTO and the Asphalt Institute design guidelines were studied and tested in detail during the course of this investigation. In general, the design procedures investigated were found to be not user-friendly or simple to implement. The main obstacles that restrict the
adoption of CBEMs as the first choice material as opposed to conventional hot asphalts, for all bound pavement layers are: the high compacted mixture porosity, low early life strength and long curing times. CBEMs are more widely accepted in low to medium trafficked pavements.
The key aims of this investigation were to improve and simplify the design procedure of CBEMs, and to investigate ways of improving CBEMs volumetric and mechanical properties.
The main aggregate materials used in this investigation were carboniferous limestone and quartzitic asphalt sand. But in response to environmental conservation campaigns, a range of selected waste materials were also tested as partial and full replacement to the virgin mineral
aggregates, including: pulverized fuel ash (PFA), red porphyry sand, synthetic aggregates, steel slag, crumb rubber, and crushed glass. The aggregate gradations were designed using a modified Fuller's curve. The emulsion used in this investigation was a cationic bitumen emulsion with
60% and 62% binder content composed of 100 pen base bitumen.
The mix design procedure initially developed in this investigation was found to be complicated from a practical application point of view, in particular the steps required to determine the optimum total liquid content at compaction, which were unlikely to be practicable
for site applications.
A more simplified CBEMs design procedure was therefore introduced in this thesis, where the coating test was found to play a very essential role. Improvements in all mixture properties were readily accomplished by increasing the compaction effort to reduce porosity and by incorporating cement. The porosity target of 5-10% and minimum indirect tensile strength (ITSM) value of 2000 MPa at a fully cured condition were more easily achievable. The main emphasis of this modified design procedure was on simplicity and practicality whilst maintaining the key volumetric and mechanical properties of the mixtures. In this investigation, the mechanical Performances of the CBEMs at full curing condition were more comprehensively evaluated in terms of fatigue and creep tests.
Attempts to accelerate the curing times of cold asphalt mixtures were made by compacting the CBEM specimens in two layers (two lifts) thus allowing the moisture to escape
faster from each layer and hence reducing the overall curing time. The results from these laboratory trials were very encouraging. Additionally, the incorporation of plastic cells was found to significantly reduce shear deformations of CBEMs under loading during their early
lives. The inclusion of plastic grids in the upper layer of a two layered cold mixture system appeared to be very promising.
It was concluded that the CBEMs design procedure proposed in this investigation was simpler than the initially adopted procedure. The main advantages of this modified design procedure were that whilst it maintained all the key volumetric and mechanical properties of the mixtures it was simpler and more practical than other existing procedures. Heavier compaction effort and the incorporation of I to 2% cementitious materials were found to be essential for
improving the performance of CBEMs, and as is well known, CBEMs are most suitable in dry warmer climates. When CBEMs are carefully designed and are allowed to achieve a full curing condition, the performance of CBEMs can be comparable to hot asphalt mixtures with the same penetration grade binder.