The University of Auckland received funding of $88,435 from Hoe ki angitū - the NZ Transport Agency Innovation Fund to carry out laboratory research and testing of low carbon, locally sourced material to potentially replace cement in concrete.
This project was in response to one of the Fund’s round one challenges - Accelerating the use of recycled materials and sustainable practices.
The objective of the project was to evaluate a range of different cement mixes comprised of NZ-sourced volcanic material (pumice and tephra). Testing and research considered the properties of the raw volcanic materials, as well as the concrete mixes made with these materials. This primarily involved considering the workability and strength and the environmental impacts of these materials against commonly used international standards.
The project involved sourcing pumice and tephra from commercial suppliers in the central North Island, finely grinding them and preparing six different concrete mixes with these materials. Some pH testing (relevant to the concrete’s protection of reinforcing steel against corrosion) and workability testing was also carried out.
The key findings of the project were that workability of the concrete was able to be preserved at up to a 20% replacement level and that additives may have been able to preserve workability at a higher level. A small fall in the pH level was noted, but it remained within an acceptable range. Compressive strength, flexural strength and density of hardened concrete generally fell with increasing levels of volcanic materials. Tephra generally performed better than pumice. However, at low levels of use of volcanic materials the strength and density remained within specifications, and concrete made with higher levels of volcanic materials would still be suitable for a range of uses where strength is less critical.
The next steps are to further investigate cement made with more finely ground volcanic materials, carefully consider the water demand, which influences workability, and investigate the durability of concrete made with volcanic materials.
Read the full report here:
| Ranatunga, K.S,, del Rey Castilllo, E. (2024). Investigation of low-carbon concrete mixes for roading infrastructure [PDF, 1.5 MB]. The University of Auckland |
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