Abstract
Emulsion stabilisation of base layers surfaced with chip seals often proves problematic, with chips punching into the base and early distress. This can be aggravated by the use of modified binders that restricts the evaporation of moisture from pavement layers. The introduction of new-age (nano)-modified emulsion (NME) stabilisation has the advantage that water is chemically repelled from the stabilised layer, resulting in an accelerated development of strength. A need was identified to evaluate the early-life performance of selected chip and Cape seals, together with identified modified binders on anionic NME-stabilised base layers constructed with materials traditionally classified as unsuitable, using archaic empirically derived tests. Three different chip seal surfacings with unconventional modified binders were constructed and evaluated using accelerated pavement testing (APT) with the Model Mobile Load Simulator—3rd model (MMLS3). The objectives of the experimental design and testing were to evaluate the binder performance, chip seal performance in terms of early loss of chips before chip orientation, punching of the chips into the anionic NME-stabilised base and deformation characteristics of a Cape seal that was hand-laid using an anionic NME slurry without any cement filler. It was shown that that chip seal surfacings can be used at low risk, on a base layer containing materials with fines exceeding 22%. The selection of specific modified binders can reduce risks associated with chip seal surfacings, which can impact construction limitations. The recommended use of elastomer-modified binders on newly constructed or rehabilitated layers, resulting in moisture entrapment, needs to be reconsidered.
Highlights
Surfaced road networks, creating accessibility to markets and reducing transportation costs, have been shown to be a major stimulus for economic growth
For single and double seals with an elastomer-modified binder (S-E1 and S-E2) [11], a maximum of 4% low flash-point solvent (LFS) is recommended, while for a bitumen-rubber (S-R1) [11] binder, a maximum of 8% high flash-point solvent (HFS) is recommended
accelerated pavement testing (APT) on the Cape seal was included as a good indication of possible punching of the large stone size into the anionic new-age modified emulsion (NME)-stabilised base layer, which could result in an associated over-exposure of the slurry with severe bleeding of the bitumen binder visible on the surfacing
Summary
Surfaced road networks, creating accessibility to markets and reducing transportation costs, have been shown to be a major stimulus for economic growth. The introduction of material-compatible anionic NME stabilisation has the advantage that over and above evaporation, water is effectively repelled from the stabilised layer through a chemical reaction between the minerals of the materials and the materialcompatible modifying agent applied to the emulsion This results in accelerated drying of the layer, with an associated accelerated development of compressive and tensile strengths [6,7,8] and a reduced risk of early-life failures. A need was identified to evaluate the early life of thin chip seal surfacings on a pavement constructed with an anionic NME-stabilised base layer using naturally available materials traditionally classified as unsuitable. The digitised twin samples allowed for accurate objective calculations and analyses of the effect of APT loading on each of the different surfacings
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