Civil & Environmental Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2753
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Item COMPARISON OF NEUTRON NON DESTRUCTIVE METHOD AND CONVENTIONAL CHEMICAL METHOD FOR CHLORIDE MEASUREMENT IN CONCRETE(2019) Sridhar, Preethi; Amde, Amde M; Livingston, Richard; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The presence of chloride in concrete is a critical issue raising concerns in the construction industry as they promote corrosion of the steel reinforcements, drastically reducing the strength of the structure. The aim of this study is to compare the performance of a neutron-based nondestructive testing method, Prompt Gamma Activation Analysis (PGAA) against the destructive wet chemistry method ASTM C-1152 currently used to determine the chloride concentration in concrete. Two modes of PGAA operation were tested. One was to use PGAA with a slit collimator to measure the chlorides at 2 mm thick cross-section in intact samples. The other was a direct comparison with C-1152 to analyze powdered concrete samples. Concrete was prepared in four batches, in which three batches had added chloride -at nominally 0.2%, 0.1%, 0.01% by weight of cement and the fourth (control) batch has zero added. The PGAA analysis was done at the Cold Neutron PGAA station at NIST and the C1152 testing was done at the National Ready Mixed Concrete Association (NRMCA) laboratory. The intact samples were scanned at three different vertical positions. The PGAA method is capable of detecting Cl at levels corresponding to the corrosion threshold of 0.1-0.2% Cl by weight of cement. The minimum detectable limit for PGAA is below 0.02% Cl by weight of cement and approaches the Cl background contributed by the raw materials, in this case, the cement. The PGAA- measured chlorides concentrations showed excellent linearity after correction for the chloride content in the concrete raw materials, mainly the cement. For the powdered samples, the C1152 and PGAA results were in very good agreement. However, the PGAA data showed much less scatter with an uncertainty as low as 0.3%. The findings of this study indicate that PGAA is a feasible replacement for the C1152 method and since it can be done on intact specimens, it avoids the time-consuming steps of crushing, sieving and nitric acid extraction and can be more cost-effective.Item MONITORING OF CORROSION IN SUBMERGED REINFORCED CONCRETE STRUCTURES USING BIOLOGICAL INDICATORS(2017) Thampi, Jithin; Chang, Peter C; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Corrosion of steel has severe economic impacts on industry and infrastructure. Reinforcement corrosion and subsequent loss of strength is the reason for failures in numerous reinforced concrete structures that leads to billions of dollars in losses. Thus corrosion detection is of great importance. Currently, corrosion detection in existing structures is performed using non-destructive methods, which include ultrasonics, radiography, thermography, and enhanced photographic imaging. Such methods are quick but lack details and can be unreliable. An alternative approach may be measuring conditions like pH that affect corrosion. Lowering of pH can indicate that corrosion can occur. It has also been identified that certain biological factors like bacteria play a major role in corrosion through a process called Microbial Induced Corrosion (MIC). Bacteria accumulate over metal surfaces over time forming biofilms, creating environments favorable for corrosion. This thesis attempts to study the correlation between corrosion of reinforcement steel in concrete and bacterial activities measured at the concrete surface and thereby observe the effectiveness of using bacterial activities to indirectly detect corrosion in the reinforcement steel.Item Determining Strength Capacity of Deteriorated Reinforced Concrete Bridge Substructures(2010) Saad, Timothy; Fu, Chung C; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Corrosion of steel reinforcement is a major factor in the deterioration of highway and bridge infrastructure. Knowing the initiation time of corrosion on a reinforced concrete structure provides a much needed source of information in evaluating the service life of the structure. To find the corrosion initiation time the effects of carbonation and chloride are examined. Furthermore, the different variables that affect the ingress of carbonation and chloride are also examined and analyzed together. Probabilistic modeling and stochastic design of these variables will determine the initiation of corrosion, the amount of corrosion, and the strength loss of the concrete pier. This process will help classify deteriorating structure into the National Bridge Inventory (NBI) condition ratings from the Federal Highway Administration.