Performance Related Approach to the Use of Recycled Aggregates in Concrete

A new report launched by WRAP (Waste & Resources Action Programme) provides detailed technical information on the performance of recycled aggregates in concrete. The research demonstrates that blending 20% recycled aggregate with natural aggregate does not have a negative impact on concrete performance. WRAP hopes this report will help the UK construction industry optimise the use of recycled aggregates in another key construction application.

The report was commissioned by WRAP, major aggregate producers and other stakeholders to overcome existing barriers to the use of standard recycled aggregates in concrete rather than being limited to those containing only crushed concrete. The research was carried out by the highly respected Concrete Technology Unit at Dundee University, who undertook a testing regime to establish recycled aggregate quality and performance.

A total of 125 concrete mixes were cast and tested using a number of different aggregates including natural aggregate, crushed concrete, crushed brick, combinations of brick and crushed concrete, and recycled aggregates sourced from recycling plants in the “as produced” condition. Tests were carried out to determine: cube strength, flexural strength, elastic modulus, drying shrinkage, initial surface absorption, carbonation resistance, chloride ingress, freeze/thaw attack, abrasion, sulphate attack and leaching.

The research produced general guidance supporting the wider use of recycled aggregates in concrete as well as grouping aggregate particle composition into three classes of recycled aggregate suitable for different applications:

• class A - recycled aggregates for use in a wide range of concrete including marine environments;
• class B – covering most combinations of natural and recycled aggregate and suitable for most ‘moderate’ exposure conditions; and
• class C – those aggregates suitable for only the ‘mildest’ exposure conditions.
  

John Barritt, Technical Advisor for Aggregates at WRAP and who played a valuable role in contributing to the steering committee for the project, commented: “This project report provides the technical detail required to increase the use of recycled aggregate in concrete, giving industry greater confidence and informing future revisions to the concrete standard.

“There is an increasing demand from clients requiring products with recycled content, which has created a growing demand for concrete produced with recycled aggregates. The recent development of washing plants producing quality recycled aggregates is increasing the availability of these aggregates and WRAP will be working closely with aggregates producers and end users to assist in the sustainable use of resources for the production of aggregates to be used in concrete.”