ACTIVATED MINERALS AS BINDER STABILIZERS IN SMA PAVING MIXTURES

摘要

Due to problems associated with the addition of cellulose fibers to SMA mixes, a newbinder stabilizer was developed to prevent excessive drainage of the bitumen during hauling andplacement of the mix. This stabilizer is an activated fine-ground raw silica mineral, which is thewaste by-product of the mining for the Phosphate Industries. The activation was aimed forobtaining Thixtropic and Shear-Thinning properties for the bitumen, by which the mastic in themix possesses high viscosity at rest (hauling and after placing) for reducing draindown, and lowviscosity at motion (mixing and placing) for maintaining the proper workability.The objectives of this study were: 1) Practical development of a more efficient and userfriendly binder-stabilizer for preventing the bitumen draindown in SMA mixes, 2) Identifyingsome positive added values of the role of the active bitumen-stabilizer in the compacted SMAalso under service condition, and 3) Verification of these advantages by a comprehensivelaboratory study, as compared to the cellulose fibers.In preliminary laboratory studies it was found that SMA mixes, combined with the newbitumen stabilizer, exhibit low acceptable bitumen draindown values which are comparable tothose with the fibers. As a result of systematic mix designs, European and American SMA mixesalso show comparable and better mechanical properties related to: resistance to water damage,wear resistance, indirect tensile strength, and rutting resistance. These results were obtained with0.5% less binder content and 10°C lower mixing temperature, as compared to the fibers.In addition to the engineering advantages, an analysis of the environmental benefits wasperformed. Generally, the comparison of the environmental indicators analyzed, clearlydemonstrates a quantitative decline in the negative environmental economic cost per ton SMAmix, when using the activated-mineral binder-stabilizer as compared to the cellulose fibers.The present research is continuing to include extensive fatigue, tri-axial shear, anddynamic modulus tests, as well as actual trial controlled field test sections.