The project analysed the technical and economic viability of replacing some natural aggregates with recycled ones from construction and demolition waste in the industrial manufacture for prefabricated concrete products.
The aim is to obtain prefabricated concrete products which, because of their technical, aesthetic and environmental characteristics and cost, have a real chance of an advantageous position in the market for these products.
The objectives of the project were as follows:
- To check the compatibility of recycled aggregates in an industrial process to make prefabricated concrete products.
- To determine the need for pre-treatment of the aggregates.
- To identify the maximum acceptable dose of aggregates.
- To detect possible changes in the manufacturing process and associated modifications (practices, equipment, additives, etc.).
- To check the differences in the parameters characterising the manufactured items.
- To study the economic viability of the use of recycled aggregates in making prefabricated products.
Recycled ceramic and concrete aggregates.
Work was done with different proportions of recycled ceramic and concrete aggregates. The results obtained demonstrated the close relationship between the % weight of those aggregates incorporated in the prefabricated products and the compression strength, resistance to abrasion and wear and water absorption of the items.
Finally, it was possible to develop a line of prefabricated concrete items with recycled aggregates to meet the relevant specifications.
The project’s main conclusions were as follows:
- The replacement of the coarse fraction of the aggregate (gravel) is viable from a technical point of view, although care must be taken over:
- The presence of fines, which can alter the degree of water absorption.
- The water content of the material what it is used, to ensure the concrete sets without difficulties.
- That the water-cement ratio is not affected.
- Replacing the fine fraction (sand or gravel) with recycled aggregates is not advisable, as it can lead to problems with water absorption.
- The maximum established dose of recycled aggregate in a prefabricated concrete product will vary depending on the type of piece to be made and the aggregate to be replaced.
- The pieces recommended by the manufacturers are:
- Non-reforced pieces (kerbs, slabs, cobbles, ordinary blocks, etc.).
- Vertical closure plates although, in future, the material could be used in any prefabricated product, as far as the market allows.