Abstract
This paper evaluates and compares the differences in the rheological characteristics of the fine aggregate matrix (FAM) portion of plant produced Foamed Bitumen Mixtures (FBMs) by means of a mechanical foaming process, and by the incorporation of zeolites in combination with Reclaimed Asphalt Pavement (RAP) material. This evaluation explores, for the first time, the impact of plant production variations for half-warm, warm and hot processes (i.e. mixing temperatures around 90°C, 120°C and 160°C, respectively) on their rheological response. A fine Virgin-HMA, a fine HMA-RAP – no foaming technique -, and a 100% fine RAP mixture were also produced for comparison purposes. Dynamic Mechanical Analysis (DMA) tests were conducted on all evaluated FAM mixtures to determine their linear viscoelastic properties. Results indicate that the rheological response of the fine RAP-FBMs is influenced primarily by the contribution of the RAP binder in the total bitumen blend, and ageing of the fine RAP material, which were a function of the foaming technology and the production temperature of the materials.
Highlights
The use of foamed bitumen and its potential applications in road infrastructure projects dates back to the mid-1950s
For the Mechanical foamed-Reclaimed Asphalt Pavement (RAP) fine mixtures, the bitumen was heated at 160oC in all cases for foaming purposes, while the fine virgin aggregates and fine RAP
The former foaming technique has intended to be used mainly for warm mix processes or cold recycling, mainly on in-situ projects and the latter is commonly used for warm mix asphalt production, the study included the evaluation of plant production variations in both foaming techniques for half-warm, warm and hot processes
Summary
The use of foamed bitumen and its potential applications in road infrastructure projects dates back to the mid-1950s. The initial process developed by Csanyi (1957) was mainly used for soil and base stabilization processes and it consisted of foaming hot liquid bitumen with steam. Following the lapse in these patent rights, the use of foamed bitumen gained more acceptance by road authorities across the world, which helped spread its application (Jenkins et al, 2000). This technique has been used in the stabilization of a variety of materials (e.g. sand, gravel and crushed stone aggregates) which include Reclaimed Asphalt Pavement (RAP) material (i.e. cold recycling), and can be applied in the construction of surface and base courses for low and heavily trafficked roads. The use of foamed bitumen in road construction using this technique can be applied in-place or can be accomplished in a central plant
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