Fungal-microbial interactions impacting the physico-chemical and structural integrity of concrete
File(s)
Author(s)
Jiang, Liying
Type
Thesis
Abstract
Filamentous fungi are prevalent in concrete environments, impacting its physico-chemical properties and leading to either fungal-induced deterioration (FID) or self-healing. These opposing effects are facilitated by the unique mycelial structure of fungi, which penetrate the concrete matrix to acquire and transport organic resources and nutrients, as well as their ability to secrete organic acids. Preventing FID and enhancing self-healing are crucial for reducing maintenance costs and promoting sustainable construction materials. This study examined the effects of three common fungal strains in building environment — Aspergillus niger, Cladosporium sphaerospermum, Fusarium oxysporum, and environmental isolates of A. niger and F. oxysporum, on the microstructural properties of mortar, and the chemical (focussing on oxalic acid) and physical mechanisms influencing FID and self-healing of different mortar types and under different environmental conditions.
Aspergillus niger produced oxalic acid, forming a large quantities of bipyramidal calcium oxalate dihydrate (COD) crystals and their large size of aggregates that expand and, coupled with hyphal penetration, cause progressive FID of the mortar outer layers. In contrast, FID induced by C. sphaerospermum is milder, mainly discoloration from melanin release and minor surface spalling due to oxalic or citric acid production. In contrast, F. oxysporum generated tubular-like precipitates and bipyramidal-prism crystals of COD, which, combined with fungal hyphae, filled mortar pores and cracks, promoting self-healing by increasing the mortar mass and reducing mortar porosity. Among all mortar and environmental condition treatments, reducing the water/cement ratio limited FID and increased self-healing processes to the greatest extent, while, the soil environment promoted the most aggressive FID and inhibited self-healing.
This study is the first to identify aggregates of bipyramidal COD and singular bipyramidal-prism COD crystals in mortar samples due to the microstructural effects of filamentous fungi, and the contrasting roles of oxalic acid in FID and self-healing of concrete is first reported.
Aspergillus niger produced oxalic acid, forming a large quantities of bipyramidal calcium oxalate dihydrate (COD) crystals and their large size of aggregates that expand and, coupled with hyphal penetration, cause progressive FID of the mortar outer layers. In contrast, FID induced by C. sphaerospermum is milder, mainly discoloration from melanin release and minor surface spalling due to oxalic or citric acid production. In contrast, F. oxysporum generated tubular-like precipitates and bipyramidal-prism crystals of COD, which, combined with fungal hyphae, filled mortar pores and cracks, promoting self-healing by increasing the mortar mass and reducing mortar porosity. Among all mortar and environmental condition treatments, reducing the water/cement ratio limited FID and increased self-healing processes to the greatest extent, while, the soil environment promoted the most aggressive FID and inhibited self-healing.
This study is the first to identify aggregates of bipyramidal COD and singular bipyramidal-prism COD crystals in mortar samples due to the microstructural effects of filamentous fungi, and the contrasting roles of oxalic acid in FID and self-healing of concrete is first reported.
Version
Open Access
Date Issued
2024-10-31
Date Awarded
01/06/2025
License URL
Advisor
Smith, Stephen R.
Buenfeld, Nick
Pettitt, Tim R.
Publisher Department
Department of Civil and Environmental Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)