Glass in bituminous materials
The requirements for aggregates for bituminous materials are defined in Volume 1 of the 'Manual of Contract Documents for Highway Works' issued by the Highways Agency. Other than grading requirements, the properties required of such materials are as follows:
- Foreign Material
Foreign materials (wood, plastic, metal etc.) are limited to no more than 1% by mass. This is unlikely to present a problem for glass processed for recycling, since quality requirements strictly limit levels of such material. - Ten-Percent Fines Value
The required ten-percent fines value for aggregate for bituminous materials is extremely high. For this reason it is unlikely that glass alone would satisfy this requirement. However, combined with other aggregate materials, it is highly likely that satisfacory results can be obtained. - Aggregate Impact Value
The aggregate impact value of aggregates is determined by measuring the reduction in particle size of a sample of material subjected to ten blows from a testing machine. As for the ten-percent fines value, it is likely that combinations of glass and other aggregate materials would best satisfy the requirements of 'Specification for Highway Works'. - Soundness
The soundness of an aggregate material is a measure of its resistance to weathering, and is measured by assessing the reduction in particle size after repeated exposure to a solution of magnesium sulfate. On drying this compound is precipitated in pores within the material which creates stresses that may lead to fracture.
A pre-requisite for poor performance in the soundness test requires that water can permeate into the material. Water absorption of glass (being completely non-porous) is negligible, and so the material fares well under soundness testing.
