Mechanical-impermeability properties and environmental degradation of SBS-modified (asphalt and emulsified asphalt) chip seals and FYT-I coating

The effectiveness of waterproof bonding layers is crucial for bridge deck pavements. This study evaluates the mechanical properties, impermeability and economic benefits of three materials: SBS-modified asphalt chip seal, SBS-modified emulsified asphalt chip seal and FYT-I waterproof coating. Under the optimal ratio (1.5 kg/m² asphalt + 6 kg/m² aggregate), SBS-modified asphalt chip seal exhibits superior performance, with shear strength of 0.61 MPa and bonding strength of 0.49 MPa, higher than those of emulsified asphalt chip seal (0.54 MPa shear, 0.45 MPa bonding) and FYT-I (0.57 MPa shear, 0.47 MPa bonding). Shear strength increases linearly with shear rate, rising by 18%–30% relative to 5 mm/min level. This material shows the highest stability due to aggregate interlocking. Environmental testing reveals strength reductions of over 70% at 60°C and nearly 50% under freeze–thaw cycles. Despite such degradation, it maintains the lowest permeability coefficient of 3.36×10−5 cm/s under standard conditions. Although salt freeze–thaw raises permeability by 94%, its high elasticity and aggregate interlocking ensure favorable impermeability. Economic analysis shows that this chip seal has the lowest life-cycle cost, that the emulsified one balances cost and constructability, and that FYT-I coating has the highest long-term cost, offering reference for engineering material selection.