CoMSIRU research spotlights potential for a greener construction industry
CoMSIRU is making remarkable headway with its research on the use of recycled materials from construction and demolition waste (C&DW) as aggregate in concrete. As it stands, little research on the topic is available. The team at CoMSIRU, as part of an international initiative, aims to fill this knowledge gap and assist the local construction industry.
Professor Hans Beushausen of CoMSIRU explains: "Construction and demolition materials are typically labelled as 'waste' and perceived as inferior. We are looking at changing this notion by researching not only how recycled aggregates can be used instead of conventional stone and sand but also how they can actually add extra value to the concrete mix."
Studies and tests are being undertaken at CoMSIRU's laboratories in Cape Town, and the data is shared with CoMSIRU's international collaborators at IIT Madras (India), BAM (Berlin, Germany) and Universidade de São Paulo (Brazil).
The ongoing research at CoMSIRU falls into three broad categories:
- The use of C&DW as fine aggregates; investigating the short- and long-term effects of fine C&DW aggregates on fresh and hardened properties of concrete and durability;
- The use of recycled crushed concrete fines (RCCF) as supplementary cementitious materials (SCMs) and their effect on concrete properties and durability; and
- The life cycle analysis (LCA) of concretes made from C&DW.
Philemon Arito, a post-doctoral fellow at CoMSIRU, says that research on C&DW in concrete to date mainly focuses on its use as coarse aggregates. Only limited studies are available on the use of C&DW as fine aggregate, fine fillers and supplementary cementitious materials (SCMs). The need for this line of research is self-evident: "Construction and demolition waste makes up about 20% of the total general waste stream in South Africa. Approximately 518 000 m3 of C&DW is dumped in municipal landfills in Cape Town alone. That's equivalent to filling up the entire Cape Town Stadium seven metres in height – or 140 Olympic-size swimming pools – every year," says Arito. "As much as 40% thereof could be recycled and re-used in construction."
The use of SCMs in the Western Cape has declined, partly attributed to a limited supply of locally available SCMs and, if available, the SCMs fluctuating properties. As a result, local contractors have been forced to avoid SCMs altogether or source them non-locally at high costs. Therefore, there is a need to identify and exploit alternative, non-conventional and locally available SCMs and fine aggregates that are environmentally friendly, cost-effective, and can sustain the future demand for concrete.
The potential benefits are extensive. "In the light of the rising demand for concrete, depleting resources of traditional, extracted aggregates and the sprawling landfills endangering our ecosystems, we can offer the construction industry sustainable alternatives that have a lesser impact on the environment. So yes, we are looking at scalable, long-term solutions. As an added benefit, the re-use of C&DW could translate to significant cost savings and efficient management of solid waste", Arito explains.
CoMSIRU's work is hands-on and along the entire value chain: for example, the researchers crush demolition waste and sieve it into standard sand sizes and grading, perform microstructural investigations, and perform service life modelling of concretes with the recycled aggregates.
The CoMSIRU team anticipates that the insights from the studies will inform practitioners' codes of practice and technical guidelines on the use of C&DW in concrete. It will also provide useful technical and environmental data that engineers, contractors and regulatory agencies can deploy to evaluate the suitability of C&DW in concrete.