Even the construction world must face a path of sustainability that is increasingly important for the environment and for man.

Concrete are construction elements that involve an important consumption of natural resources, in particular the aggregates that compose them, being extracted and made available to the construction sector.

As it happens more and more often in the road and soundproofing sector, where, for example, recycled and ground bituminous sheathing powders of recycled tires are used, also in the field of concrete, the market demand for a more sustainable product is now growing.

The recipes that make up a traditional concrete see the use of natural aggregates, with different granulomentries, a share of cement, water and additives when necessary.

As part of an eco-sustainable approach to the product, various experiments and laboratory tests were carried out which aimed at the complete replacement of the natural aggregate with aggregates consisting of selected industrial and post-consumer waste.

In the family of waste considered in these tests we can include fly ash, which is waste produced during the incineration of municipal solid waste, slag ground blast furnace, which is also a by-product of the incineration operations and a post-consumer plastic product, PET powder, coming from the recycling of water and soft drinks bottles.

Test methodologies

With these three elements, different cement mixtures have been created aimed at obtaining lightened concrete, creating a series of laboratory samples with the aim of testing the compressive strength and the thermal conductivity of composite elements, both with lightened natural aggregates and with various types of aggregates from waste.

The study was promoted with the intention of giving an analytical history to lightweight recycled concrete that can be used, for example, in the construction of lightweight concrete blocks for the construction of non-structural walls.

A series of different mixtures were then created with the corresponding quantity of samples, which were tested by compression and the thermal conductivity of the same was calculated.

The aim was to compare a traditional concrete mix with light natural aggregates with concrete mixes made with aggregates recycled from waste.

Test results

The results showed an average reduction of the compressive strength of the samples composed with the waste aggregates, without PET, of 13.7%, compared to the samples made with natural aggregates, while the blends that contained the PET powder had resistance performances that were further lower than 10%.

However, it was noted that the addition of PET powder had a positive effect on thermal conductivity, compared to samples made up of 100% aggregates from the waste, but lower approximately 22% compared to concrete made with lightened natural aggregates.

Conclusions

Although recycled lightweight concrete has lower mechanical and thermal performance than that produced with natural elements, the need to limit the use of natural resources and that of reducing non-recyclable waste going to landfills could lead to a new awareness in building design and manufacturing.

Automatic translation. We apologize for any inaccuracies. Original article in Italian.