Recycling mine waste to improve the acid resistance of cement-based composites for underground structures

• Author / Creator

  Wu, Linping

• Cement-based composites are widely used in underground structures for various applications, such as tunnel lining, mine backfilling, and grouting. However, cement-based composites are highly susceptible to attack by sulfuric acid that can be naturally generated around underground structures through a biogenetical and chemical process. This sulfuric acid attack not only significantly reduces the service life of cement-based underground structures, but also leads to an extremely high cost for the maintenance and rehabilitation of the structures. Hence, cement-based composites should be made in a way that is more durable against the sulfuric acid attack. Among all the methods in improving the acid resistance of cement-based composites, the use of pozzolanic materials that can be sourced from local mine waste has shown great potential.
  The main objective of this thesis is to systematically explore the potential of three types of pozzolanic materials (fly ash, metakaolin and silica fume) that can be recycled from local mine waste in improving the acid resistance of cement-based composites. These three materials were first used as admixtures to replace ordinary Portland cement (OPC) at various dosages. The results showed that the addition of pozzolans in OPC mortar could reasonably improve the acid resistance. In particular, the mixture with 5% silica fume showed the lowest mass loss after sulfuric acid immersion. Then the performance of silica fume and nano-silica was compared. The silica fume was found to be more effective in enhancing the properties of OPC mortar regarding the volume of permeable voids, compressive strength, and acid resistance. After that, the acid resistance of metakaolin-based geopolymers was explored when calcium aluminate cement (CAC) was added. It was found that the addition of CAC drastically improved the acid resistance due to the reduced permeable voids and increased neutralization capacity. Additionally, as fibers are a common component in cement-based materials for underground structures, a green and sustainable nanofiber (cellulose nanocrystals) was introduced in the OPC system to improve the acid resistance. This nanofiber was found to improve the compressive strength and the acid resistance of OPC mortar. At last, based on previous experimental data, a predictive model was proposed to forecast the deterioration of cement-based materials by considering both mixture design and testing conditions. The proposed Bayesian optimized support vector regression model was able to accurately predict the mass change and compressive strength of mortar samples under a sulfuric acid attack.
  Overall, this thesis explores the potential of pozzolanic materials in improving the acid resistance of cement-based composites. The research findings provide an effective way to mitigate the sulfuric acid attack of cement-based underground structures and an innovative way of recycling mine waste.

• Subjects / Keywords

  • acid resistance
  • underground structure
  • mine waste

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-zw8z-p159

• License

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