Start main page content

Witsies cement their ideas to minimise construction waste

- Wits University

Two engineering students used their final year projects to study the possibilities of using rubble clay-brick masonry as part of the sand in fresh concrete.

Lepogo Maleka and Kgadimo Mohlatlole in the School of Civil and Environmental Engineering conducted research on the sustainability of cement and concrete construction materials. The students’ projects investigated if construction waste can be recycled to create concrete.

The findings indicated that crushed brick rubble can be used to replace a part of the sand to make competent concrete, which is stronger than concrete made with the more energy-intensive crushed rock aggregate.

Mohlatlole, who hopes to be one of the best engineers in the field one day, says using construction waste for concrete reduces landfill space, thereby making it environmentally friendly.

“One of the benefits of using clay brick as fine aggregate in concrete is that it gains more strength compared to normal andesite concrete,  is less energy-consuming than virgin andesite sand, and , it is easier to access clay brick than crushed rock aggregate,” says Mohlatlole.

Lepogo Maleka and Kgadimo Mohlatlole

Maleka says the strength of clay brick has great benefits for the building of structures that require high strength concrete.

“Greater concrete strength can be achieved without the use of crushed rock aggregate. The high strength can be attributed somewhat to the clay material found in the brick rubble, which produces pozzolanic reactions when the fine particles of the crushed clay-brick rubble react with cement products,” she says.

Rubble concrete is also suitable due to the scarcity of aggregates. “In the past, aggregates were found from natural sand and also manufactured by crushing rocks as, at that time, it was thought that they were in abundance, which currently is not the case. Aggregates have reached a point of scarcity and the more we dig to supply more and more of these aggregates, the more degraded the environment becomes. Thus, instead of removing more aggregates from the environment, it is beneficial to reuse rubble in the production of fresh concrete,” says Maleka.

The pair was part of a global online workshop attended by 600 people from 13 countries, sharing knowledge and research on recycling construction materials. Their research and findings contributed to a global study on minimising construction waste.

Maleka, who aspires to be a structural engineer says the workshop was highly informative and revealed the economic and environmental benefits of using concrete made from rubble.

“The online workshop was one of the most informative workshops on the recycling and demolition of construction waste that I have ever attended. It was an honour to be part of the collaboration in studying the durability and engineering properties of new concrete made with rubble as aggregate. It was interesting to learn how broad the study of recycling construction and demolition waste is,” she says.

New concrete made with construction rubble

Mohlatlole, the only undergraduate student at the workshop, is now motivated to take his research further. “I am proud to know that my contribution to the global study will help other researchers from different disciplines who will do similar projects in the future, and it is also contributing to the research on recycling construction materials, which is something that will help in keeping our environment safe and sustainable.”

Professor Yunus Ballim and Professor Janina Kanjee in the School at Wits supervised their project. Ballim was impressed with the findings of the students, which will be valuable for the construction industry.

“The students’ results are exciting and hold good promise for reducing the amount of construction rubble that ends up on our waste disposal sites, as well as for producing more sustainable and good quality new concretes into the future,” he said.

Mohlatlole expressed gratitude to his supervisors who made his project enjoyable and encouraged him to further his studies.