Mix design considerations for cold and half-warm bituminous mixes with emphasis of foamed bitumen

[摘要] ENGLISH ABSTRACT:The use of foamed bitumen and bitumen emulsion as binders for use in roadrehabilitation is gaining favour globally. High-level road facilities through to unpavedroads requiring attention are being treated with these binders due to environmental,economic and practical benefits in the use of cold bituminous mixes. In addition,static and mobile plant with the capability of performing stabilisation using bitumenemulsionand foamed bitumen has become commercially available and widelyutilised, as a result of development in recycling technology and lapse in patent rightson foam nozzles.An understanding of the behaviour and failure mechanisms of these cold mixes, aswell as sound guidelines for the mix design procedures of cold mixes, especiallyfoamed bitumen, and design guidelines for pavements structures incorporating thesematerials, are lacking however. Mix designs are carried out primarily on the basis ofexperience and pavement designs are empirically based.The main objective of this dissertation is to address the need for a fundamentalunderstanding of foamed bitumen and foamed bitumen mixes, and in so doing todevelop techniques for adjudicating mixes, optimising their composition andrationalising their design both as mixes and as layers in road pavements. At thesame time the exploration of new applications for foamed bitumen and thepossibilities for progressive related technology, is a priority.To commence, this study includes an appraisal of most of the literature available onfoamed bitumen. This is followed by a fundamental investigation of the colloidal massof foam that is produced when small quantities of cold water are added to hotbitumen. Factors influencing the quality of the foam are identified and a Foam Indexis developed for characterisation and optimisation of the foam.The spatial composition of a cold foamed bitumen mix, including Interaction of thefoam with moist mineral aggregate, is also addressed in this dissertation. Inparticular, the stiffening of the filler mastic using foamed bitumen as binder isanalysed. Techniques of optimising the sand type and content in the mix are alsodeveloped and guidelines for desired aggregate structures for foam treatment areestablished.The temperature of the mineral aggregate has been shown to have a profoundinfluence on the behaviour and performance of a foamed bitumen mix. This has beenselected as a focal area of further investigation and the research has lead to thedevelopment of a new process called The half-warm foamed bitumen treatmentprocess that can produce mixes with almost the quality of hot mix asphalt with up to40% less energy consumption.Other processes developed in this research include the use of cold mix asphalticblocks for construction of road pavements in developing areas. This technologyenhances the use of a high labour component in road construction in aneconomically competitive manner. The dissertation provides details for mix designand construction of the cold mix blocks. Finally, the study includes models for the performance prediction of foamed bitumenmixes. In particular, foamed mixes that exhibit stress-dependent behaviour havebeen investigated and models established on the basis of triaxial testing andaccelerated pavement testing for the prediction of permanent deformation of suchlayers under repeated loading.Practical applications of the research findings are summarised in Appendix F. Thisincludes:• methods for optimisation of the foamed bitumen properties,• guidelines for the selection of the ideal aggregate structure for cold foamedmixes,• procedures for carrying out cold mix design in the laboratory (including mixing,compaction and curing),• procedures for manufacturing half-warm foamed mixes in the laboratory,• methods for manufacturing cold mix blocks, and• pavement design methods for road structures incorporating foamed mix layers.Appendix G outlines statistical techniques that are relevant to the design ofexperiments in pavement engineering including examples of applications of theseprocedures. The techniques are applied selectively in the relevant chapters of thedissertation.

[发布机构] Stellenbosch University