Moisture Sensitivity of Hot Mix Asphalt Concrete Containing Optimal Sulfur Waste Content at Later Ages and a Proposed Engineering Solution for Flexible Pavement Applications

Abstract This study provides a comprehensive evaluation of the performance of hot mix asphalt concrete incorporating sulfur waste (HMAS) as a partial replacement for bitumen binders during extended curing times, aiming to investigate the evolution of strength in asphalt concrete containing sulfur after paving and determine the effect of sulfur waste on the mechanical properties and performance of HMAS at later ages. The optimal binder content in asphalt concrete containing sulfur waste was determined for HMAS mixtures incorporating 30% and 40% sulfur as a replacement for the bitumen binder by weight. The optimal bitumen content used in HMAS using sulfur bitumen binder (SBB) was found to be within the range of 3.15–4.5% for SBB containing 40% sulfur and 3.5-5% for SBB containing 30% sulfur, which is lower than that in HMA without sulfur. Experimental results revealed that the Marshall stability of HMAS consistently increases over time and stabilizes after 14 days, whereas HMA does not exhibit this behavior. Recrystallized sulfur crystals formed a lattice in the pores and binders, reinforcing the structure and increasing the density and stiffness of the HMAS samples after 14 days, which led to improving the mechanical properties of HMAS at later ages. However, HMAS exhibits sensitivity to moisture even at later ages, and HMAS containing 30% sulfur demonstrates higher moisture resistance compared to that containing 40% sulfur. The moisture sensitivity of HMAS containing a high amount of sulfur is attributed to the agglomeration and recrystallization of sulfur crystals in asphalt concrete at later ages. Based on the experimental results, an engineering solution was proposed for using HMAS in flexible pavements to prevent moisture damage. The HMAS layer is sandwiched between two layers of hydrophobic (waterproofing) materials in the flexible pavement structure and the HMAS layer should be placed beneath the wearing course (surface course). The performance calculation of the pavement structure with the HMAS layer demonstrates a superior load-bearing capacity compared to the structure using only HMA. The proposed pavement structure has the potential to incorporate a large amount of sulfur in asphalt concrete pavement, contributing to sustainability in pavement engineering.