Date of Award
Open Access Thesis
Civil and Environmental Engineering
A sizeable portion of the civil infrastructure is made from concrete. An estimate shows that about 7 billion cubic meters of concrete is made annually worldwide. With the deterioration of the infrastructure due to aging or external factors, significant monetary and technological investment is needed for condition evaluation, maintenance and repair. Two areas that account for a considerable portion of this investment are condition evaluation for maintenance of corroded concrete structures and mortar patching for repair and rehabilitation.
The primary method of evaluation of a structure is by visual inspection. But this method is limited as some crucial areas in a structure are either completely inaccessible or very difficult to access. Monitoring corrosion in the prestressing strands of post-tensioned [PT] concrete structures is one such example. In post-tensioned concrete structures, the prestressing reinforcement is located deep within the structure and is difficult to access. The reinforcement in these structures when exposed to chlorides starts to corrode and the inaccessibility of the prestressing reinforcement makes condition evaluation much more difficult. Under such circumstances a structural health monitoring [SHM] method is needed to aid in the condition evaluation. Acoustic emission [AE] is one such SHM method that has the ability to evaluate the structure to improve maintenance procedures on post-tensioned concrete structures.
In the first part of the thesis, long term corrosion monitoring studies were performed on specimens representing internal and external post-tensioned methods of construction of concrete structures. Corrosion was induced by adding additional chlorides in the grout mix or by performing wet-dry cycling of NaCl solution. The corrosion process in each specimen was monitored by two acoustic emission R6i sensors and an embedded silver chloride reference electrode for half cell potential [HCP] measurements. Appropriate filters were developed to minimize noise in the AE data and the filtered AE data was validated by HCP measurements. Results also indicate that intensity analysis is a very helpful technique in quantifying the degree of damage in the specimens.
In the second part of this thesis, studies are focused on repair and rehabilitation. The majority of the small to medium scale repair work in concrete structures is done by patch working that uses regular cement mortar doped with additives. These additives help to enhance the properties of regular mortar such as strength, durability, shrinkage, and curing time. Some examples of such additives are ground granulated blast furnace slag [GGBS], silica fume, magnesium, fly ash, or other polymeric additives such as styrene butadiene, polyvinyl acetate, and acrylics. Cement in the mortar is replaced with these additives by about 10 - 20% by weight to achieve enhanced properties, making the patch works expensive.
Dopamine hydrochloride, commonly known as dopamine, is a non-toxic organic biopolymer that has shown promise as a polymeric additive for patch repair work. A preliminary investigation was performed on dopamine doped cement mortars for patch repair work. To evaluate the effect of dopamine on properties of cement mortar, two inch cubes were cast and tested in compression. One of the biggest advantages of dopamine is that while most polymeric additives replace cement by 10 - 20%, dopamine is required only in very minute quantities of 0.05% weight of cement making the patch work very inexpensive. Results also indicate that dopamine is able to enhance the strength, load-deformation behavior and curing time of regular cement mortar.
Appalla, A.(2013). Assessing Corrosion Damage in Post -Tensioned Concrete Structures Using Acoustic Emission & A Preliminary Investigation Of Biopolymer Doped Cement Mortar for Use in Structural Restoration. (Master's thesis). Retrieved from http://scholarcommons.sc.edu/etd/2354