Unbound Aggregates and Hydraulically Bound Mixtures

Unbound aggregates and Hydraulically Bound Materials

Delivered crushed rock materials, recycled aggregates and drainage gravels are all produced to a specification and in order to confirm a delivery is in order loads are sampled at regular intervals to enable laboratory testing for compliance.

Primarily the sieve analysis (grading) and the moisture content are confirmed as these have the most immediate effect on the works into which the material is to be incorporated.

Sieve Analysis

Sieve analysis or “Grading” is the process of splitting a sample of unbound material into the various decreasing sizes to identify the range of particles and thereby the material’s likely characteristics. Using a set of calibrated sieves, a graphical representation known as a Particle Size Distribution graph or PSD for short can be established which can be used to classify an in-situ material or confirm compliance of a bought in processed material.

This test is therefore an integral part of quality control regimes in civil engineering works. Grading analysis for classification purposes is carried out to BS 1377-2 and for aggregate compliance is carried out to BS EN 933-1. In both cases the sieve sets are dictated by the specification for the aggregate, as-raised materials will need to be classified according to Table 6/1 of Series 600 of the Specification for Highway Works Volume 1 whereas processed aggregates each have a specification according to the required use. This will be different for drainage materials, concrete aggregates and sub bases for instance.