Assessing durability of geopolymer concrete mortar for sewer pipe coating

Assessing durability of geopolymer concrete mortar for sewer pipe coating

Alkali-activated geopolymer (GP) is emerging as a promising alternative to Ordinary Portland Cement (OPC) in addressing microbial-induced concrete corrosion (MICC) of concrete structures in aggressive sewerage environments. However, identifying an effective binder formulation for GP to combat aggressive MICC remains a challenge, highlighting the need for developing sustainable repair materials. This study conducted extensive experimental studies to assess the long-term performance and durability of low calcium-based geopolymer mortar under simulated typical aggressive sewer conditions. Class F fly ash (FA) serves as the sole precursor for GP mortar. The approach included developing, characterising, and selecting optimal low-calcium FA-only geopolymer (FAGP) mortar mixes, evaluating bond strength to typical sewer pipe substrates, investigating acid resistance in terms of macro and microstructural evolution, and ultimately assessing FAGP degradation mechanism and longterm performance under hostile typical sewer conditions. The results demonstrate that FAGP mortar, with appropriate adjustments, can achieve sprayable consistency structural mortar comparable to standard OPC repair mortar. Material compatibility and adhesion properties of FAGP mortar surpass the standard OPC, regardless of substrate conditions. The holistic approach of assessing the deterioration of FAGP qualitatively and quantitatively demonstrated that acid exposure caused no substantial changes to the microstructural properties, corroborating the results for mass and cross-sectional analysis. FAGP retained 30% of its mechanical integrity under highly aggressive sewer conditions, whereas OPC failed to endure beyond the initial phase of the exposure period. The phase alterations and the resultant functional groups in the acid-exposed FAGP indicated new formations. However, these formations appeared to impede the acid reaction, thereby slowing the corrosion process compared to OPC. Despite the corrosion process intensifying with prolonged exposure duration, FAGP exhibited excellent acid resistance relative to OPC, regardless of the sewer conditions. This comprehensive evaluation confirms the feasibility of using geopolymers as repair materials in sewer rehabilitation, demonstrating their high acid resistance, durability, and long-term performance under aggressive conditions.

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