Practical Notes
! NOTE: IRC SP 79:2008 — revised directly to 2023, no 2019 edition
! SMA requires fibre stabilizer — without it, the high binder content drains down during transport.
! Gap-graded means more coarse aggregate, less fine — creates stone-on-stone contact for excellent rutting resistance.
! SMA is specified for all new expressways and heavy traffic NH corridors in India.
! Ensure rigorous quality control on aggregate gradation, especially for the 2.36 mm sieve, as it significantly impacts SMA's drainage and stability.
! The higher binder content requires careful temperature control during mixing and compaction to avoid binder drainage.
! Fibers are crucial for preventing binder drain-down during mixing and transport. Ensure uniform dispersion.
! SMA's high stiffness and low air voids demand specialized compaction techniques. Avoid over-compaction.
! The drainage characteristic of SMA is a key advantage, but it necessitates proper design of sub-base and base layers to manage the infiltrated water effectively.
! Use a superpave or modified binder if the design traffic and climatic conditions warrant enhanced performance beyond conventional bitumen.
! Adequate mineral filler is essential for creating a stable mastic that binds the coarse aggregate skeleton.
! The 'stone-on-stone' contact is the fundamental principle of SMA; any deviation can compromise its performance. Visually inspect the mix for this.
! Site personnel must be well-trained on the specific handling and placement requirements of SMA, as it differs from conventional mixes.
! During compaction, monitor mat temperature closely. If it drops too low, it can lead to poor interlock and density.
! Consider the source and quality of cellulose fibers; they must be properly treated to prevent moisture absorption.
! The selection of aggregates with high PSV is paramount for skid resistance, especially on high-speed corridors like expressways managed by NHAI.
! For PMGSY roads where this premium mix might be considered for critical sections, ensure the contractor has proven experience with SMA.
! The design mix needs to be validated with actual site materials to ensure it meets the desired performance criteria before full-scale production.
! Regularly check the calibration of asphalt mixing plants to ensure accurate binder and fiber addition, critical for SMA's success.