In Situ Stabilisation – HBM

  • Client:  KierWSP & Northamptonshire CC
  • Road Class:  Class 4 (0.5msa)
  • Depth:  330 mm
  • Surfacing:  10mm Close Graded
  • Site:  Papley Lane, Lutton
  • Works Type:  In Situ Road Recycling
  • Material:  Hydraulically Bound Material (HBM) H2 Class
  • Specification:  TRL611
In situ mixer before works
Papley Lane was selected for a deep in situ reconstruction due to the significant amount of structural defects along the 1.6km route. Traditional treatments of patching/dressing, overlays or inlays would not have been suitable with the only long term treatment option being reconstruction. As with many evolved roads the site had very little formal construction with a mix of clay bearing granular material beneath. A site investigation, laboratory testing and pavement design service was provided in accordance with TRL611.

During Treatment




As clay was present in the layers to be utilised, a lime pre-treatment was undertaken with stabilisation using conditioned Pulverised Fly Ash (PFA) and Ordinary Portland Cement (OPC) to produce a H2 class CBGM. The inclusion of PFA reduces the risk of reflective cracking commonly associated with cement bound materials by protracting the rate of hardening. This is achieved by utilising the pozzolans available in the PFA to form part of the cementitious binder. The two stage process (Lime and PFA/OPC) was completed in 6 days with a further 2 days surfacing. Quality was monitored by an onsite Technician to ensure compliance with the mix design. Works were completed under a road closure, with a running surface maintained at the end of every shift to allow access to the adjacent properties. Throughout the works access was maintained to properties through careful planning of the closure system.


Process Overview

  1. Initial Pulverisation
  2. Lime Addition
  3. Conditioned PFA/ OPC addition
  4. Grading and Compaction
  5. Application of Curing membrane and Sealing grit
  6. Surfacing


Key Benefits

  • Sustainable Construction
  • Coal Tar Encapsulation
  • Reduced Vehicle Movements
  • Significantly Reduced Cost