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Winning project – Turning waste rubber into cement substitution

Well-done to the University of the Witwatersrand for winning the property-lead category of the 2020 Student Greenovate Awards for the project, “The Use of Waste Tyre Rubber in the Partial Substitution of Cement Bricks in South Africa”, submitted by Fadheelah Madhi, Shweta Singh and Mpho Mtimkulu. The Greenovate awards are proudly presented by Growthpoint Properties and the Green Building Council of South Africa (GBCSA) and include quantity surveying, construction management and property studies.

For their thesis as part of their honours studies, these female Wits students were inspired by the number of used tyres burned during the “fees must fall” student demonstrations. They decided to do a study to understand what value could be derived from using these tyres in a more useful and environmentally friendly way.

Fadheelah Madhi comments, “Through extensive research we found that tyre waste is a major problem globally and particularly in South Africa, as it is poorly disposed of. It is primarily burnt and illegally dumped in landfills, which results in the release of harsh chemicals, depleted, damaged and unusable land, environmental hazards, fire threats, illness and death.”

Research for alternatives

The team felt that something better should be done with old tyres and decided to concentrate their efforts on testing tyre waste rubber (TWR) in three different forms as a partial substitution in cement bricks. The three different forms of rubber were made into three specimens and tested against a control specimen, manufactured according to standard bricks currently found in South African. The research project followed an experimental approach and was conducted in partnership with SAYCON Developers. The four different specimens were made from scratch, followed by physical and characteristic testing thereafter.

Intensive specimen and aggregate analysis

The cement mixture of each brick specimen varied in aggregate according to the amount of TWR added as a partial substitute in different forms. Each specimen was manufactured four times to allow a brand-new brick to be used for each test. Following these tests, an extensive cost analysis was conducted and the key findings from the study were as follows:

• The use of TWR in cement bricks enhanced the characteristics of a traditional cement brick and proved to be cost effective.
• Not all the TWR brick specimens made were of an acceptable standard or tested better than the traditional cement brick.
• The crumbed rubber cement brick, illustrated the most successful outcome of all the variations of cement bricks incorporated with used rubber.
• A significant difference and improvement were seen in the bonding structure and compressibility, thus rendering TWR a good source of strength and durability.
• Brick flammability increased in 2/3 specimens with TWR
• In comparison with the traditional cement brick, the cement brick incorporated with elongated rubber pieces (specimen 2) produced the weakest characteristics and the cement bricks incorporated with cubed and crumbed rubber pieces (specimen 3 and 4) produced acceptable characteristics.
• Specimen 4 – Crumbed rubber brick was of the highest standard and produced the most desirable characteristics of all specimens
• Specimen 4 was found to be the most cost effective at R2.80 when compared to the market rate of traditional cement bricks of R3.40
• Implementation is possible in South Africa

Conclusive evidence and environmental impact

The team concluded that waste tyre rubber could be used as a partial substitution in cement bricks and by doing so, would have significant environmental benefits. These benefits are listed below.

• Recycling reduces the number of natural resources used
• Decreases pollution
• Recycling of tyre requires less energy than producing new rubber
• Reduces the demand for new natural rubber.
• Partial substitution of natural aggregates means less use of depleting resources.
• In line with SA’s goal to reach a NET ZERO WASTE building country by the end of 2050

Our sincere thanks and congratulations to the team of dynamic women who through this study have not only made a significant environmental finding, but have also demonstrated the level of ingenuity and brilliance in our local females. We salute you!

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