The renovation of concrete structures has become popular and necessary in Hong Kong. Innovative cement based repairing materials are needed to be developed due to the limitations of conventional repairing materials. For instance, polymer-modified cementitious mortar and resin-based mortar are common materials as patch repair for concrete structures. However, drying shrinkage of these repair materials can promote further corrosion of steel reinforcement. Fiber-reinforced plastic (FRP) has an excellent performance in structural renovation. However, it can fail under high temperature. Because of this, expansive mortar and fire-resistant cement matrix are needed. Magnesium Oxychloride Cement (MOC) may be a good candidate to be utilized as innovative material because it can harden in air and...[ Read more ]

The renovation of concrete structures has become popular and necessary in Hong Kong. Innovative cement based repairing materials are needed to be developed due to the limitations of conventional repairing materials. For instance, polymer-modified cementitious mortar and resin-based mortar are common materials as patch repair for concrete structures. However, drying shrinkage of these repair materials can promote further corrosion of steel reinforcement. Fiber-reinforced plastic (FRP) has an excellent performance in structural renovation. However, it can fail under high temperature. Because of this, expansive mortar and fire-resistant cement matrix are needed. Magnesium Oxychloride Cement (MOC) may be a good candidate to be utilized as innovative material because it can harden in air and has very high bond strength with other substances, as well as excellent fire resistance.

The objective of this research is to develop Magnesium Oxychloride Cement (MOC) as repairing material of concrete structures. The thesis will firstly discuss some key factors affecting the material properties of MOC. Secondly, two applications of MOC, patch repair mortars and fiber reinforced cement developed in this research, will be introduced. Their mechanical behaviors and effectiveness have been systematically studied.

The bond strength of MOC is high enough to rehabilitate the damaged concrete structures. Carbon fiber reinforced cement (CFRC) can increase the flexural capacity of reinforced concrete beams by bonding externally on the bottom surface of concrete. The flexural capacity of RC beams can be enhanced by about 30%.

The experimental results show that the dosage of Potassium Dihydrogen Phosphate, the amount of fly ash replacement, molar ratios of magnesium oxide and magnesium chloride, the activity of magnesium oxide and the water content can influence both early and long term behaviors of MOC such as setting times, water resistance, compressive strength, expansion capability, hydrated phases and bond strength. Therefore, the design and construction guidelines should be strictly followed.