High Friction Surfacing

In the UK, CD236 Surface course materials for construction, part of the Design Manual for Roads and Bridges, gives the requirements for the use of surfacing materials.

Tables 3.2a and 3.2b of CD236 define the circumstances in which HFS should be used based on the type of surfacing, the required skid resistance measured using SCRIM, the site category and the volume of commercial vehicles per lane the road experiences per day.

CD236 defines HFS as ‘specialised high friction surfacing conforming to clause 924 of the Specification for Highway Works (MCHW1)’.

Clause 924 requires that both the HFS system and the installer have HAPAS or equivalent product acceptance scheme certification. These schemes have a requirement that a system meets strict laboratory determined test requirements and undergoes a two year road trial where its performance in use is assessed. The requirements for HFS systems under the HAPAS scheme operated by the British Board of Agrement (BBA) are available here, whilst the installer requirements under the scheme are here.

Types of HFS System

There are several different types of high friction surfacing. The main difference is that some systems are applied hot and others at ambient temperatures, leading to the generic terms ‘hot-applied’ and ‘cold-applied’.

Cold-applied systems

Cold-applied systems comprise two or more chemical components including at least one liquid. When blended, a cure or hardening process is instigated. This blended binder is spread onto the substrate and aggregate is scattered onto it to excess whilst still wet. The binder curing process adheres the aggregate and, once complete, excess aggregate can be swept off for re-use. There are different types of chemistry within the cold-applied HFS systems but the fundamental method of installation is the same.

Hot-applied systems

Hot-applied systems employ resin binder and a graded blend of calcined bauxite and finer aggregates and are pre-mixed at the factory. When heated on site, they become molten, are installed using the screed method and harden upon cooling.