Effects of commercial waxes on asphalt concrete mixtures performance at low and medium temperatures

doi:10.1016/j.coldregions.2006.01.002

Cold Regions Science and Technology

Volume 45, Issue 1, June 2006, Pages 31-41

https://doi.org/10.1016/j.coldregions.2006.01.002 Get rights and content

Abstract

Effects of adding two commercial waxes to three 160 / 220 penetration grade bitumens in asphalt concrete mixtures were studied using tensile stress restrained specimen test (TSRST), dynamic creep test and complex modulus test. Significant physical hardening of binders, observed in binder testing, could not be observed using TSRST. The reason could be that low temperature physical hardening does not have a large effect on fracture properties of the asphalt mix or that TSRST is a non-suitable test for showing these effects. In dynamic creep testing, the smallest strains were recorded for the asphalt mixture containing non-waxy bitumen and FT-paraffin, indicating better resistance to rutting. In complex modulus testing, adding of 6% commercial wax clearly increased the modulus and decreased the phase angle, an effect more pronounced for the mixture containing FT-paraffin compared to the one containing polyethylene wax.

Introduction

Wax in bitumen often has been considered as a negative indication of the quality of bitumen. However, natural wax is part of most bitumens, and commercial waxes are added to bitumen in order to achieve certain properties. This paper deals with such wax modified bitumens in asphalt concrete mixtures, focusing on mechanical properties of the mixtures at low and medium temperatures. Binder rheological effects of wax modification as well as ageing properties of the wax-modified bitumens involved in this study are evaluated more in detail elsewhere (Edwards et al., submitted for publication-a, Edwards et al., submitted for publication-b, Edwards et al., submitted for publication-c).

Factors influencing the effect of waxes in bitumen are chemical composition (source of bitumen) and rheological behaviour of the bitumen as well as content, composition and crystallinity of the wax. The presence of large crystals (macrocrystalline wax) in bitumen for road construction is considered to be most problematic. Nowadays, natural waxes in straight run bitumen generally are microcrystalline and/or amorphous and not particularly harmful with regard to binder properties. Furthermore, increased sensitivity to cracking or plastic deformation in asphalt pavements is not likely to appear due to the occurrence of natural bitumen wax. However, in the case of blown bitumens and/or wax modified bitumens in road construction (frequently used in the US and Canada), the effects on asphalt concrete properties may vary considerably (Hesp, 2004).

Section snippets

Bitumen and wax modifiers

The binder mixtures used in this study were selected from earlier studies concerning rheological effects on bitumens (Edwards et al., submitted for publication-a, Edwards et al., submitted for publication-b) and influence on ageing properties (Edwards et al., submitted for publication-c) due to the addition of commercial waxes. The selection of binder mixtures was limited due to the limited amounts of bitumen available for the preparation of asphalt concrete test slabs.

Three different bitumens

Results and discussion

In the following sections, effects on low and medium temperature performance of asphalt concrete mixtures due to binder modification with FT-paraffin (wax S) or polyethylene wax (PW) are discussed. Some binder test results are summarized in Table 1, Table 2. As already mentioned in the Introduction, binder effects of wax modification are evaluated more in detail elsewhere (Edwards et al., submitted for publication-a, Edwards et al., submitted for publication-b, Edwards et al., submitted for

Conclusions

Effects on low and medium temperature performance of asphalt mixtures due to the addition of FT paraffin (wax S) or polyethylene wax (PW) to three different bitumens containing different amounts of natural wax were evaluated. Based on the results obtained, the following conclusions were drawn.

•
The TSRST fracture temperature of non-waxy bitumen NV was somewhat increased (from − 34 to − 32 °C) from the addition of 6% FT paraffin (wax S) but unchanged from the addition of the same amount of

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Effects of commercial waxes on asphalt concrete mixtures performance at low and medium temperatures

Abstract

Introduction

Section snippets

Bitumen and wax modifiers

Results and discussion

Conclusions

Physical hardening of asphalt binders relative to their glass transition temperatures

Journal of the Transportation Research Board, Transport Research Record

General Technical Construction Specifications for Roads

Physical hardening of paving grade asphalts as related to compositional factors

A new interpretation of time-dependent physical hardening in asphalt based on DSC and optical thermoanalysis

Reversible ageing in asphalt at low temperatures

Final Report