Concrete is the second most utilized material worldwide after water and it is widely used in the construction industry. However, its production has a significant environmental footprint, hence, attempts to make the material eco-friendlier are of great importance.
A new study, recently published in the Journal Construction and Building Materials, was conducted by scientists from the University of British Columbia (UBC) in Canada. It suggests that a proportion of the natural aggregates used in concrete production can be replaced by recycled aggregates. This will not only preserve the natural deposits but it will also help reduce the waste of the construction industry that ends up in landfills. “We live in a world where we are constantly in search of sustainable solutions that remove waste from our landfills. A number of countries around the world have already standardized the use of recycled concrete in structural applications, and we hope our findings will help Canada follow suit," Prof. Shahria Alam, co-author of the study and co-director of the Green Construction Research and Training Centre at the University of British Columbia, stated.
The authors of the study state that recycled aggregates can be readily used in concrete production but they are not utilized in large scale projects due to 3 main causes:
- Uncertainties regarding their properties
- High porosity
- Inadequate in-situ tests and studies
The team conducted a detailed study to assess the performance of concrete made of recycled aggregates. In particular, a building foundation and a sidewalk were evaluated in a 5-year period. Firstly, concrete deriving from demolitions was collected from a landfill and was thoroughly inspected to exclude any impurities. Then, the concrete was placed into a jaw crusher from which the recycled aggregates were produced. Those aggregates were tested by a sieve analysis so that they complied with building regulations. Concrete mixtures consisting of different proportions of recycled aggregates were produced and were utilized in the aforementioned structures 5 years ago.
The findings of the study suggest that the recycled concrete has similar strength and durability to the conventional one. It obtains the required uniaxial compressive strength (UCS) within 28 days and constantly strengthens with time.
In particular, when targeting a compressive strength of 25 MPa, the concrete mixture may consist of 20%-30% recycled aggregates. Moreover, when the proportion of recycled aggregates is 30%, the concrete mixture obtains quicker its strength compared to conventional concrete.
When it comes to long-term performance, tests conducted both 2 and 5 years after the completion of the building and the sidewalk suggest that recycled concrete presents adequate mechanical properties. Moreover, exposure to harsh weather conditions that were confronted in the foundation did not affect the performance of the material.
Nevertheless, the study mentions that 2 mixtures consisting of 50% and 70% recycled aggregates, respectively, presented relatively reduced strength at 120 days but this is probably caused by the presence of water in the pores of the recycled aggregates that is consumed over time, hence, this effect decays.
Click here to find the study published on November 30, 2020
Additional source: UBC