Path building materials

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In most path construction projects you will need to find suitable construction materials for the base and surface layers.

type1

Construction materials used to build paths are called 'aggregates'. Aggregates are generally from natural, recycled or industry waste by-product materials used in construction, which are described by size, angularity, etc. Aggregates are generally sold as mixtures of different particle sizes, where each one is designed for a specific purpose. Aggregate mixtures, are generally described either as traditional mixtures, (20mm down to dust) or standardised mixtures based on the Department of Transports ' Specification for Highway Works (SHW) (Type 1 granular sub base). Aggregates are also defined by compliance to British Standards (BS) or European Norms (EN) standards.

Aggregate mixture sizes are determined by standard range of sieve sizes used for sieving during the materials production at a quarry. Standard sieve sizes are: 80mm, 62.5mm, 40mm, 32mm, 20mm, 16mm, 14mm, 10mm, 8mm, 6.3mm, 4mm, 2.8mm, 2mm and up to 0.063mm.

Under European Norms standards, aggregate mixtures are determined by the size of sieve that the aggregate does not fit through (lower range d) and the size of sieve that all aggregate must pass through (upper range D). The standard formulea used to write a European Norm aggregate mixture is d/D. For example, Type 1 granular sub base is specified as 0/32.

Following the SHW specifications, aggregate mixtures consist of several aggregate sizes mixed together in known proportions, with size distributions described by the meaning of 'grading', as follows:

  • 'Well graded' - contains a good range of different particle sizes in the aggregate mixture which allows it to naturally interlock, forming a strong solid mass once compacted

  • 'Uniformly graded' - contains mostly particle sizes of the same size in the aggregate mixture which interlock less when compacted, leaving plenty of voids

Aggregates used for path construction are generally of high quality. If won 'as dug' aggregates or recycled aggregates are locally available, these materials should be considered first, before quarried aggregates. Such aggregates depend on availability and suitability, but if a particular type of material is required it must be specified clearly. Before using these aggregates, obtain a sample to check it out, and test it to ensure it will perform to your requirements, before purchasing.

Making the grade

In many parts of Scotland naturally occurring deposits of glacial material lie beneath the soil, which can be won and used to build the base layer and, in some circumstances, the surface layer if suitable. Materials that are found on site are called ‘as dug’, which is won from excavated pits called ‘borrow pits’. Make sure that you get permission to dig borrow pits first.

excavator working at borrow pit

Looking for suitable materials in a borrow pit...

A simple material test can be used to decide on whether the materials on site are likely to be suitable, or if recycled or quarried aggregates will need to be transported-in to site. You can do a simple test to check the suitability of on-site materials before using them.

For further information about the use of locally won as dug material for lowland path construction, where the material didn't work, read the case study 'The Use of Locally Won As Dug Materials at Oatridge College'.

Using local as dug or recycled aggregates that may be highly variable in quality and not suitable for a path, choosing commercially available aggregates produced to the Department of Transports 'Specification for Highway Works' specifications, is a safe and better option, as minimum standards in grading and material quality are monitored.

Find out about the different types of aggregates used to construct the base layer here.

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