Overview
Hydraulically bound materials (HBM) are are mixtures that set and harden by hydraulic reaction. They include Cement Stabilised Material (CBM) (i.e. mixtures based on the fast setting and hardening characteristics of cement). They also include hydraulically bound mixtures based on slow setting and hardening binders made from industrial by-products such as PFA (Fly ash bound material) and blastfurnace slag (Slag bound materials).
HBM has potential to be used in a range of paving and non-paving applications. Use of HBM and RSA in HBM offers the following general advantages:
- HBM construction is well known and versatile in terms of availability of plant and materials.
- HBM can be produced by “mix-in-plant” or “mix-in-place” equipment.
- Plant for laying and compaction of HBM is similar to that required for laying and compacting other paving materials such as unbound layers or bituminous bound products.
- Some HBM mixtures allow the re-use of materials available on site (e.g. soil, demolition wastes) with savings on imported primary material (avoiding the Aggregates Levy) and disposal costs (avoiding sending materials to landfill).
- HBM has proven energy saving benefits. ETSU General Information Report 49 illustrates the energy benefits of using HBM. These include the significant energy savings associated with the use of a cold mix technology and utilisation of by products such as pfa and slag. You can also download the CO2 Emissions Estimator Tool to check the CO2 savings associated with using HBM.
- HBM assists in winning work by meeting or exceeding client requirements for “green” procurement.
Hydraulically bound material is used in a wide range of applications, including:
Paving applications
- Major roads
- Minor roads and paving (e.g. paths)
- Heavy duty paving
- Reinstatement of openings, as clarified by the HAUC - Advice Note 1
Non-paving application
- Erosion protection
- Liners
- Piling platforms
- Hydraulically bound fill in embankments and for structures such as dams
Case studies include:
Hydraulically bound mixture utilising pulverized fuel ash in the New Mill Dam construction
Hydraulically bound mixture utilising pulverized fuel ash at Rainbow terminal, Immingham Docks
Lime modified, cement stabilised Weald Clay for sub-base for construction of A27 Polegate Bypass
The use of Pulverized-fuel ash as a binder for the A259 Ramsgate Harbour approach road in Kent
Lime modified, cement stabilised alluvial deposits for piling platforms (Genome Campus Extension)
Hydraulically bound material can use a high proportion of RSA. No recycled or secondary aggregate is specifically precluded as a component of HBM by the Specification for Highway Works. The materials suitable for use in HBM are listed below (adapted from Sherwood, 1994):
High Potential
- China clay sand, recycled concrete aggregates, air-cooled blastfurnace slag, GBS*, burnt colliery spoil, PFA*, spent oil shale, recycled asphalt, other road arisings, slate aggregate, incinerator bottom ash aggregates (IBAA)
Medium Potential
- Unburnt colliery spoil, general demolition waste
Low Potential
- basic oxygen (BOS) slag, electric arc furnace (EAF) slag
*can be used as 'aggregate' or as part of the binder
Detailed information on use of hydraulically bound materials is provided in the Specification for Highway Works Series 600 and 800. Aggregates should comply with BS EN 13242+A1. The mixture including water shall comply with BS EN 14227.
Further advice is presented in CIRIA Report 573 'Guide to ground treatment' and the WRAP guidance documents:
