Did you know that concrete recycling is still a new, emerging industry? Although there are already plenty of uses for recycled concrete, researchers and businesses are constantly exploring new possibilities.
We’re always keeping our finger on the pulse (and looking for ways to make our own contributions!) so thought we’d share a summary of new concrete recycling developments and research we’ve come across recently.
Scan through the summaries or click through to read more details on the project or research…
World’s First Fully Recycled Concrete Building
Global building sector giant, Holcim, are constructing a 220-unit social housing complex outside of Paris in France. The building, called Recygénie, is being touted as the world’s first fully recycled concrete building, using a custom concrete made with Holcim’s ECOCycle technology. All the components inside the building (cement, aggregates, and water) consist of recycled waste materials.
We’re sure the industry will be watching this project with interest and hope that it opens up future possibilities for using recycled concrete in new buildings!
Logan City Council recently adopted the Institute of Public Works Engineering Australia’s (IPWEA) specification for recycled crushed concrete material, with amendments. They undertook two successful trials, using crushed concrete as a road base material for low traffic volume roads. The council gained valuable insights, identified significant cost savings, and found compaction results to be satisfactory.
Hopefully this means we’ll see more local councils experimenting with and adopting crushed concrete as a more eco-friendly, green option for road bases in the near future.
Blending Nano-Silica With Recycled Cement Fines
Results from one research study indicated that after adding nano-silica to cement blended with recycled concrete powder, the cement was able to set more quickly, and had a higher hydration heat and early hydration rate. Plus, the addition of nano-silica was found to compensate for the mechanical strength loss of mortar that uses recycled cement powder to supplement cement materials, and helped to refine the pore size.
What’s this mean? Well… it means we’re one step closer to potentially incorporating recycled concrete powders into new concrete structures on a more broad scale. Hopefully with the right blend of materials, scientists will figure out how to get the best properties and a reliable outcome.
Researchers experimented with carbonating recycled concrete fines in water to see whether this product can absorb CO2 (as this capability has been observed in recycled concrete aggregates) and whether carbonation could enhance its mechanical properties. They found that the carbonated fines had a significantly high pozzolanic reactivity, which means that it would have potential to be reused as a supplementary material in cement mixes. This is a pretty cool finding because before going through this process, the concrete fines absorbed water too easily to be used for new concrete production. And of course, it’s another way to capture and store carbon dioxide, which is important when you consider the amount of CO2 released from the concrete production process.
Researchers theorised that adding crushed waste glass to concrete, along with recycled concrete aggregates would help to improve issues with workability (due to recycled concrete’s porosity and rough texture, which leads to high water absorption and friction). Their test results predicted that 20% waste glass with 30% recycled concrete aggregates would improve workability to a certain point (as glass does not absorb water from the concrete mix), and that combining these materials could help to improve the concrete’s mechanical performance — although further research is needed to determine how to improve the the resulting concrete’s tensile capacity.
Note: workability refers to how easy the concrete is to mix, transport, place, and compact.
In any case, we’re very interested to hear how two recycled materials might be combined to create more sustainable concrete products!
The Use of Recycled Concrete Aggregates in Asphalt Mixtures
This literature review looked at recent studies on using recycled concrete aggregates in asphalt mixtures as an alternative to natural aggregates. They found that the biggest barrier is recycled concrete’s moisture susceptibility — and once this is addressed with treatments and the right mixes, recycled aggregates will be a promising candidate to replace natural aggregates to produce sustainable, high quality asphalts in future.
What Impacts the Cost of Concrete Made Using Recycled Aggregates?
This study looked at the factors affecting the price of recycled concrete (that is, concrete that is made using recycled aggregates). They found that major factors included the cost to sell the recycled aggregate, the proportion of recycled aggregate substitutions, the water-to-cement ratio, the amount of cement used, the use of supplementary cementitious materials, the use of admixtures, production and installation costs, transportation costs, quality control measures, indirect costs, mandatory regulations, voluntary guidelines, population growth, and economic growth.
Interesting stuff, huh? In particular, it’s interesting how the study noted that the price of recycled concrete was 0-10% higher than virgin concrete, which is a significant barrier to adoption — even with customers being keen to adopt greener materials. This is in stark contrast to our own recycled aggregates, which are significantly cheaper than comparable quarry products.
Properties of Concrete With Different Sized Recycled Concrete Aggregates
Another paper looked at the properties of concrete with different sizes and concentrations of recycled concrete aggregates. They found that 12-20mm aggregates enabled better workability than the 5-12mm aggregates. But the 5-12mm aggregate mixes possessed higher compressive and split-tensile strength, and a higher modulus of elasticity than the 12-20mm aggregate mixes.
This study looked at the properties of concrete pavements made with recycled concrete aggregates compared to pavements made with natural aggregates. Lab study results found that the recycled concrete aggregate option improved the hydraulic properties (reduced soil sealing due to greater permeability) but decreased mechanical properties. However, a field test found that the only significant difference in mechanical properties was the compressive strength, and the sustainable concrete met the Brazilian standard for pervious pavements, as well as international recommendations.
So, if you’re creating a footpath and want/need water to easily penetrate to the soil below, recycled concrete aggregates could be a better choice than quarry gravels.
A study looked at the use of recycled concrete aggregates as a potential microbial carrier for self-healing of concrete cracks. Due to the recycled concrete’s porous nature, it proved to be a viable carrier that retained bacterial viability even during concrete mixing. Where initial crack widths were less than 0.6mm, the recycled concrete + bio-agent mixture was able to self-heal around 84% of the crack area in the first week. Following the self-healing, the compressive strength regain ratio reached 99.5%, and the water tightness regain ratio reached 99.2%.
Using Fine Recycled Concrete in Cement
Researchers looked at the properties of concrete that uses recycled fine aggregates as a partial replacement for cement — and how these properties were impacted if the concrete was recycled and reused multiple times. They used replacement ratios of 10%, 20%, and 30%, then formed the concrete slabs and recycled them three times over. Interestingly, the replacement ratio had a greater impact than the number of times the concrete had been recycled, with the 10-20% recycled ratio surpassing the target strength by up to 21% each time it was recycled.
What Makes Concrete Recycling in Construction Work?
A study looked at the success factors of concrete recycling in Malaysian construction projects. They used research, interviews, and surveys to determine 10 critical success factors, including the availability of uniform standards for concrete waste recycling, stakeholder awareness of concrete recycling, suitable construction waste management plans, government policies that support concrete recycling, good marketing strategies to support concrete recycling, good employee communication, sub-industries with applications for recycled concrete, work method statements making provisions for concrete recycling, positive legislation towards concrete waste recycling, and available concrete recycling infrastructure.
Interestingly, the study found that large enterprises and small-medium enterprises didn’t agree on the success factors! However, the above list is a great starting place for governments and organisations that are looking to encourage better concrete recycling practices in the construction industry.
Meanwhile, we’ve been involved in a little bit of research, ourselves! Civil Engineering Honours students at QUT have been using our donated recycled concrete aggregates to mix and characterise concrete for structural applications in their civil engineering lab.
Although this testing is at undergrad level, the tests performed by the undergrad students in the QUT Civil lab will lead to real insights into the impact of replacing quarried aggregates with Moreton Bay Recycling’s recycled aggregates for same target compressive strength of concrete. The students are batching the recycled aggregates concrete for 25 MPa and 40 MPa concrete strengths and will compare the 28 days strength with the normal weight aggregates concrete obtained from a quarry. These results can be useful for the industry for adopting recycled aggregate concrete for their projects.
In future, QUT anticipates this research will be extended to a higher degree research project and we look forward to sharing any relevant findings when they’re released.
Our Recycled Concrete Is Ready To Go
It’s an exciting time to be in the concrete recycling industry!
Although researchers are exploring a variety of ways to use recycled concrete, there are already plenty of tried and true applications. So if you’re looking for a more sustainable alternative to gravel for drainage, driveways, pathways, hard stand, under slab, or something else… we’ve got you covered.