Using untreated and nanobubble-treated potable and wastewater in mortar

The construction sector places a significant demand on potable freshwater resources, with more than two billion tonnes of water used each year for producing concrete. The increase in population growth, demand for infrastructure, and climate-induced water scarcity, especially in arid and semi-arid regions such as Southern Africa, adds pressure on the freshwater resources. This points out the importance of investigating alternative water sources that could be used in cement-based materials. These may include non-potable water sources like brackish water, seawater, greywater, and other contaminated waters; however, these normally possess high levels of dissolved salts, organic matter, surfactants, and biological contaminants that may impact cement hydration, strength development, and durability. This illustrates that the treatment of alternative water sources could be required before the water can be used in concrete or mortar. Nanobubble technology is a promising water treatment method. Nanobubbles are tiny gas-filled structures under 200 nanometres with unique physico-chemical properties, including high internal pressure, high stability, large surface area, and enhanced gas-liquid mass transfer efficiency, enabling improved interaction with contaminants. In addition, nanobubbles can encapsulate gases like carbon dioxide, presenting potential for carbon capture within cement-based systems. Despite successful applications in agricultural, industrial, and biomedical fields, the use of nanobubble-treated water in construction materials remains very limited. In this study, untreated and nanobubble-treated wastewater sources were investigated for use as mixing water in the production of mortar. This study investigated the impact of untreated as well as air and CO2 nanobubble-treated water sources on the fresh and hardened properties of mortar. The water sources included potable water, brackish and seawater, and contaminated freshwater, such as detergent, sugar and algae water sources. The results show that untreated contaminated water affects the performance of mortar. Water containing chlorides (brackish and seawater) improved flowability and showed improved early-age strength due to the accelerating hydration effects given by chloride; however, these mixtures are at high risk for reinforcement corrosion. Sugar-contaminated water significantly retarded early-age compressive strength but regained long-term strength. Detergent contamination consistently reduced strength and durability, while algae-contaminated mixtures resulted in low flowability and compressive strength. Brackish and seawater showed lower porosity, whereas freshwater sources resulted in increased porosity, with oxygen permeability within acceptable limits. The introduction of air nanobubbles provided limited improvement in mortar performance and was generally ineffective in saline systems. However, CO₂ nanobubble treatment was more effective, especially in seawater mixtures, where strength development increased. The CO2 nanobubble treatment method also shows potential for capturing CO2 in cement-based systems. However, the long-term durability and corrosion risks should still be considered.

Grantor dc:publisher

Stellenbosch : Stellenbosch University

Year dc:date.issued

2026

Author dc:creator

• Augustyn, Bianca Monique

Advisor dc:contributor.advisor

• Combrinck, Riaan

Language dc:language.iso

en

Repository record dc:identifier.uri

https://scholar.sun.ac.za/handle/10019.1/135571

OAI identifier oai:identifier

oai:scholar.sun.ac.za:10019.1/135571