The increasing use of deicing salts has caused the accelerated deterioration of bridge decks due to cracking and spalling from chloride induced corrosion of steel reinforcement. One method being considered as a possible corrosion abatement measure is the removal of chloride contaminated concrete and the chemical treatment of the partially exposed rebar through ponding and/or placement of chemically treated mortar. Reinforced concrete specimens were cast and subjected to repeated exposure to NaCl solution. Half-cell potential, corrosion rate, and chloride ion concentration measurements were conducted until the indication of active reinforcement corrosion. Chloride contaminated concrete was removed to the rebar level through a grooving process. The grooves were chemically treated through solution pondings and backfilling with treated mortar. Seventeen treatments and combination of treatments were evaluated including corrosion inhibitors, polymer sealers, and a possible chloride ion scavenging mineral. The treatment effects were monitored using half-cell potential and corrosion rate measurements. In addition, mortar cubes were cast containing various treatment concentrations and were subsequently tested for compressive strength and change in resistivity over time. Based on the electrochemical and mortar cube measurements, DCI (calcium nitrite) when applied as a ponding and mortar treatment, was determined most effective in abating corrosion after concrete removal. In addition, Alox 901, Cortec 1337, Cortec 1609, sodium tetraborate, and Zinc borate were also found effective in mitigating rebar corrosion after concrete removal; however, both the borate compounds cause set retardation of portland cement. These chemicals were recommended as candidate treatments for further evaluation in both large-scale and field experimentation. / Master of Science

This dissertation investigates the level of acid‐resistance of concrete degradation. Concrete specimens obtained from four mixtures (M1, M2, M3 and M4) were prepared with calcareous, siliceous and a blend of calcareous and silica sand; and then, tested in low (30 g/l) and highly (200 g/l) concentrated sulphuric acid solutions. To this end, an architecture of artificial neural networks (ANNs) was implemented to predict the performance of concrete specimens due to sulphuric acid solutions. Neural networks were composed with one hidden layer for one input and output layer. Nine input parameters were: cement composition, proportions of coarse and fine aggregates, water content, and compressive strength, weight loss of concrete, time impacting corrosion, acid concentration and sulphur concentration. Thickness expansion and concrete conductivity are used as output targets to evaluate the degree of deterioration. In this study, the learning through ANNs from training data sets have been proved to be better than measured data. Excellent results were found with a coefficient of determination (R2 ) of 0.9989, 0.9999, 0.9989 and 0.9998, respectively for the four mixtures M1, M2, M3 and M4 using siliceous aggregate. Also, the results show that two ANN models performed with both the thickness (expansion) and the electrical conductivity can successfully learn the prediction of concrete corrosion. In both low and highly concentrated sulphuric acid condition, the model thickness was more accurate in predicting concrete corrosion compared to the model conductivity. The lowest error in neural networks was provided by the mixture (M2) for the concrete using siliceous aggregate. For this purpose, the root mean squared error (RMSE) and the average absolute error (AAE) were of 0.0049 and 0.0048 % respectively. / College of Engineering, Science and Technology / M. Tech. (Chemical Engineering)

A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy, Johannesburg, 2017 / Many reinforced concrete (RC) structures in inland environment deteriorate early due to carbonation-induced corrosion of their reinforcement. In some cases, the deterioration is visible within a few years of construction in the form of cover concrete cracking. This is widely accepted as one of the limit state indicators in defining the end of functional service life for existing RC structures undergoing corrosion. Many of the currently available service life prediction models are incapable of providing realistic service life estimates of RC structures beyond the corrosion initiation stage. Therefore, the need to incorporate the corrosion initiation and propagation stages in a comprehensive durability prediction approach has been receiving much research attention. In this research, empirical models were developed for predicting carbonation rate and the amount of steel radius loss required to initiate a first visible crack in concretes exposed to Johannesburg environment. The experimental data for the models were obtained from investigations of carbonation-induced reinforcement corrosion, which were explored in three phases; (i) concrete early-age durability and strength characteristics (ii) carbonation rate of different concrete mixes exposed to the natural inland environment (iii) amount of steel radius loss required to initiate the first visible crack on the pre-carbonated cover concretes exposed to an unsheltered environment. The experimental variables for the earlyage durability and strength tests were; water/binder ratio (w/b) and binder type; w/b, binder type, initial moist curing duration and exposure conditions are the experimental variables for the carbonation rate test. Cover depth, reinforcement diameter, binder type and w/b variables were considered for the corrosion cracking test. The results showed that an improvement in concrete quality (binder type, w/b ratio and extending the initial moist curing duration) and increment in cover thickness improved the durability of the RC structures exposed to the natural inland environment. Based on the trends in the observed experimental results, models to predict carbonation rate and the amount of steel radius loss required to initiate cover cracking in concrete were developed. The proposed models’ predictions are more closer to the measured values and compared well with the predictions of some previous models which indicate their respective predictive applications. They provide a general basis for durability analysis of RC structures in inland environment and can serve as basis for condition assessment of existing structures in the inland environment. Engineers can appreciate the consequences of design options on the service life of RC structures, while owners of RC structures can have information about how long their RC structures may last before any repair is envisaged / XL2018

This investigation presents results of the temperature effect on durability properties (resistivity and diffusivity) and compressive strength of concrete with pozzolans, and the effect of pozzolanic admixtures on microstructure and chemical compositions of concrete pore solution. ... Temperature dependence of electrical resistivity and chloride diffusivity was studied by dynamic temperature tests. Accelerated curing regimes involving curing concrete specimens in 35À C lime water with different durations were tested. Compressive strength test, resisivity measurement and rapid chloride migration (RCM) tests were performed. A leaching method was used to measure pH and conductivity of concrete pore solution. ... The accelerated curing regimes were found to increase the compressive strength and resistance to chloride ion penetration at short-term and long-term. With the developed correlation between resistivity and migration coefficients, it is possible to employ the resistivity measurement as an alternative or replacement of the RCM test to evaluate resistance of chloride ion penetration of concrete. Pozzolanic admixtures were found to decrease both pH and conductivity of concrete pore solution as the replacement ratio increased. Moreover, the migration coefficients were found to be greatly correlated to the microstructure properties of concrete, such as porosity, formation factor and tortuosity. / by Yanbo Liu. / Thesis (Ph.D.)--Florida Atlantic University, 2012. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.

Prevention of the corrosion of steel reinforcement embedded in concrete is a constant challenge in engineering. A study of concrete surface resistivity versus elevation of partially immersed reinforced concrete structures in a marine splash zone has been developed and correlations made between concrete quality and chloride diffusion, i.e., aggressive ion permeability. A conditioning procedure was developed in which the concrete moisture content is increased by direct contact with fresh water for several days. The electrical resistivity of concrete is known to be primarily a function of the degree of water saturation. Correlations between field obtained concrete surface resistivity values versus chloride diffusivity, and between normalized resistivity measured on cores obtained from the field versus chloride diffusivity has been established. The resistivity values were measured on structures with different concrete mixes and various ages. / by Andres M. Suarez-Solano. / Thesis (M.S.C.S.)--Florida Atlantic University, 2009. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web.

The purpose of this study was to investigate the performance to chloride penetration of specimens made with three base compositions (three different supplementary cementitious materials) and water to cementitious ratios of 0.35, 0.41, or 0.47. The specimens were subjected to bulk diffusion test or full immersion. The mixes were exposed to 0.1 M, 0.6 M, or 2.8 M sodium chloride solution for different periods of time. Also, partially immersed specimens were exposed to indoor and outdoor exposures (tidal, splash, barge). Chloride concentration profiles were obtained and the apparent diffusion coefficient was calculated. The skin effect was found only on some chloride profiles exposed to 0.1 M sodium chloride solution. The chloride binding capacity was calculated; specimens with 20% Fly Ash and 8% Silica Fume had the highest binding capacity (70.99%). The apparent diffusivity coefficient was found to be dependent on the curing regime as well as the water to cement ratio. The correlation between effective resistivity and apparent diffusion coefficient was determined. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2014. / FAU Electronic Theses and Dissertations Collection

This research is aimed at investigating the corrosion durability of polyolefin fiber-reinforced fly ash-based geopolymer structural concrete (hereafter referred to as GPC, in contradistinction to unreinforced geopolymer concrete referred to as simply geopolymer concrete), where cement is completely replaced by fly ash, that is activated by alkalis, sodium hydroxide and sodium silicate. The durability in a marine environment is tested through an electrochemical method for accelerated corrosion. The GPC achieved compressive strengths in excess of 6,000 psi. Fiber reinforced beams contained polyolefin fibers in the amounts of 0.1%, 0.3%, and 0.5% by volume. After being subjected to corrosion damage, the GPC beams were analyzed through a method of crack scoring, steel mass loss, and residual flexural strength testing. Fiber reinforced GPC beams showed greater resistance to corrosion damage with higher residual flexural strength. This makes GPC an attractive material for use in submerged marine structures. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2013.

Two duplex stainless steels rebars: UNS32304SS and UNS32101SS, were selected to investigate the corrosion initiation and propagation in reinforced concrete specimens. The investigation is divided in two phases with two different methods to accelerate the transport of chlorides through the concrete and initiate corrosion in a short period of time. After corrosion had initiated and propagated for some time; selected specimens were terminated for visual examination. On specimens selected for autopsy, the rebars in the top row showed corrosion to various degrees. Corrosion had propagated to such extent on the terminated specimens that the specimen showed cracks. Stray current might have caused accelerated corrosion on rebars where corrosion had initiated. Based on chloride concentrations measured at the rebar trace, corrosion initiated: on S32101 rebars on average at 7.9 kg/m3, and S32101 rebars on average at 6.0 kg/m3. The findings suggest that S32304 rebars corroded at a slower than S32101. / by Francisco Gutierrez Tellez. / Thesis (M.S.C.S.)--Florida Atlantic University, 2013. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.

A danificaÃÃo e a falha do concreto sÃo largamente investigadas no ramo da MecÃnica do Dano em Meios ContÃnuos. VÃrios modelos existem na literatura e descrevem muito bem uma variedade de fenÃmenos observados, dependendo de sua complexidade. O principal objetivo deste trabalho à investigar e modelar os efeitos da corrosÃo no dano e falha das propriedades do concreto. Inicialmente, foram feitos ensaios de traÃÃo e de compressÃo em alguns corpos-de- prova intactos sem que tivessem sido submetidos a nenhuma corrosÃo para determinar o comportamento mecÃnico do concreto. Outros foram submetidos a uma cÃmara de corrosÃo acelerada Salt Spray ( durante perÃodos de tempo diferentes) para determinar esse comportamento considerando a corrosÃo. Para o ensaio de traÃÃo, foi desenvolvido um dispositivo composto de peÃas de aÃo, onde se pode realizar esse ensaio de tal maneira a se obter os grÃficos de tensÃo deformaÃÃo utilizando corpos-de-prova cilÃndricos iguais aos usados para a compressÃo. Com esses resultados experimentais, utilizando a MecÃnica do Dano em Meios ContÃnuos, um modelo elÃstico aclopado ao dano à usado para modelar o comportamento do concreto. Em um primeiro estÃgio, a elasticidade isotrÃpica e o dano isotrÃpico ( somente com uma variÃvel escalar D) sÃo usados, mas incluindo-se os efeitos da corrosÃo. Nos resultados, à analisada a evoluÃÃo do dano no concreto em relaÃÃo ao tempo de exposiÃÃo dos corpos-de-prova na cÃmara de corrosÃo acelerada Salt Spray e em funÃÃo dos carregamentos mecÃnicos. / A danificaÃÃo e a falha do concreto sÃo largamente investigadas no ramo da MecÃnica do Dano em Meios ContÃnuos. VÃrios modelos existem na literatura e descrevem muito bem uma variedade de fenÃmenos observados, dependendo de sua complexidade. O principal objetivo deste trabalho à investigar e modelar os efeitos da corrosÃo no dano e falha das propriedades do concreto. Inicialmente, foram feitos ensaios de traÃÃo e de compressÃo em alguns corpos-de- prova intactos sem que tivessem sido submetidos a nenhuma corrosÃo para determinar o comportamento mecÃnico do concreto. Outros foram submetidos a uma cÃmara de corrosÃo acelerada Salt Spray ( durante perÃodos de tempo diferentes) para determinar esse comportamento considerando a corrosÃo. Para o ensaio de traÃÃo, foi desenvolvido um dispositivo composto de peÃas de aÃo, onde se pode realizar esse ensaio de tal maneira a se obter os grÃficos de tensÃo deformaÃÃo utilizando corpos-de-prova cilÃndricos iguais aos usados para a compressÃo. Com esses resultados experimentais, utilizando a MecÃnica do Dano em Meios ContÃnuos, um modelo elÃstico aclopado ao dano à usado para modelar o comportamento do concreto. Em um primeiro estÃgio, a elasticidade isotrÃpica e o dano isotrÃpico ( somente com uma variÃvel escalar D) sÃo usados, mas incluindo-se os efeitos da corrosÃo. Nos resultados, à analisada a evoluÃÃo do dano no concreto em relaÃÃo ao tempo de exposiÃÃo dos corpos-de-prova na cÃmara de corrosÃo acelerada Salt Spray e em funÃÃo dos carregamentos mecÃnicos.

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