Environmental effects on the rheological properties of fine warm RAP-foamed bitumen mixtures using SATS conditioning protocol

Diana B Sánchez,Gordon Airey,Silvia Caro,James Grenfell

doi:10.1080/10298436.2019.1679365

Abstract

ABSTRACT This paper uses the Saturation Ageing Tensile Stiffness (SATS) conditioning to evaluate the combined effects of moisture and oxidative ageing on the rheological characteristics of the Fine Aggregate Matrix (FAM) portion of various Foamed Bitumen Mixtures (FBMs) in combination with Reclaimed Asphalt Pavement (RAP) material produced at 90, 120 and 160°C (i.e. half-warm, warm and hot processes, respectively). A reference fine Hot Mix Asphalt (HMA) with RAP – no foamed bitumen – was also manufactured. Their rheological properties were determined through Dynamic Mechanical Analysis (DMA) tests on specimens tested in their unconditioned and after SATS conditioning states. Rheology of the recovered binders of all FAM mixes before and after SATS conditioning was also studied, and rheological parameters were used to link their long-term performance in terms of cracking susceptibility. The results showed an overall increase in the stiffness of the fine mixtures after the conditioning process, mainly due to oxidation of the bitumen. Although the half-warm and warm fine RAP-FBMs exhibited the highest increase in their complex shear modulus after SATS conditioning, rheological analysis of their corresponding binders indicated that their long-term performance in terms of cracking susceptibility might be superior to those of the hot RAP-FBM, and the HMA-RAP fine mixtures.

Highlights

Foamed bitumen is a road construction technique where the bitumen is heated at high temperatures and foamed by combining it with cold water during mixture production
The objective of this study is to evaluate the combined effects of water and oxidative ageing on the linear viscoelastic properties of the Fine Aggregate Matrix (FAM) portion existing within various Foamed Bitumen Mixtures (FBMs) that incorporate 50% fine Reclaimed Asphalt Pavement (RAP) material
We show that there are some differences in the air void content among the fine mixtures, the standard deviations were between 0.48% and 0.66%, which are considered acceptable for the purpose of this study

Summary

Introduction

Foamed bitumen is a road construction technique where the bitumen is heated at high temperatures (i.e. usually between 140 – 160oC) and foamed by combining it with cold water during mixture production. The bitumen presents an increased volume that is up to 20 times its original volume, and lower viscosity than the same bitumen in its liquid state (Csanyi, 1957, Jenkins et al, 2000) These two conditions allow coating of aggregates at lower temperatures than those typically used for Hot Mix. Asphalt (HMA) production with good workability conditions (Mallick et al, 2004). Since only the bitumen is heated at high temperatures, this technique provides significant energy savings compared to traditional HMA (Bowering and Martin, 1976, Jenkins et al, 1999) This process is generally used for stabilisation of various types of materials, which include Reclaimed Asphalt Pavement (RAP) (i.e. cold recycling), and it can be accomplished in a central plant or can be applied on-site. The incorporation of this material in HMA reduces the amount of virgin bitumen and aggregates added to the final mixtures and, contributes to the conservation of natural and non-renewable resources (Copeland, 2011)

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Results

Conclusion