The Wibau-SL process was developed as a means of producing bituminous materials more economically than by conventional processes; this is achieved because the process does not require elaborate dust-suppression equipment and, as a consequence, operating costs are lower. This report describes mixing and laying trials of bituminous materials produced by the Wibau-SL process. The aggregates used in the trials included limestone, basalts, gravels, slag and natural sands and the binders were petroleum bitumens and pitch-bitumens of penetration grades. The materials successfully produced included rolled-asphalt wearing courses and basecourses, dense roadbase and wearing-course macadams, open-textured macadams and fine cold asphalt. The report indicates that: (i) all of the materials covered by British standard 594 and 4987 that contain penetration-grade petroleum bitumen or pitch-bitumen can be successfully produced. (ii) it was not found possible to produce tarmacadam of an acceptable quality. (iii) very little water remained in the activated materials. (iv) the addition of the adhesion agent, adhistab, only marginally improved the adhesion of the binder to the aggregate. (v) the hardening of the bitumens and pitch-bitumens during activation was similar to that occurring during conventional processing. (vi) dust emission and noise levels were lower than for conventional plants. (vii) the mixed materials behaved normally during laying and compaction. Materials laid on the public highway, for 3 years have, on the whole, performed well. (viii) pre-mixed materials were stored for periods up to one year before activation was attempted; during the storage period the binders hardened slowly and provided the binder was finely dispersed, successful activation was possible. (Author/publisher)
Abstract