Reinforced concrete (RC) bridge decks are exposed to chlorides from deicing salts. Chloride ingress in RC initiates corrosion of the reinforcing steel. The high costs of corrosion have sparked interest in service life design of bridge decks. This thesis characterized the exposure conditions of Virginia, including temperature and surface chloride concentration, as well as Virginia concrete mix properties, including initial chloride concentration and chloride migration coefficient. The service life estimations for a case study bridge in Virginia from three service life models were compared. The first model is based on the fib Bulletin 34 Model Code for Service Life Design, the second is a finite element solution of the fib Bulletin, and the third accounts for a time-, temperature-, moisture-, and concentration-dependent apparent diffusion coefficient. A sensitivity analysis was completed on the three models showing that the most important variables in these models are the aging coefficient and surface chloride concentration. Corresponding life cycle cost analyses were completed for plain and corrosion resistant reinforcing steel. This thesis showed that the error function solution underestimates chloride ingress. The life cycle cost analysis of plain and corrosion resistant reinforcing steels show that overestimation of service life leads to underestimation of life cycle costs. / Master of Science

Chloride induced corrosion of steel in concrete is one of the major forms of deterioration mechanisms found in reinforced concrete bridges. Early age corrosion damage reduces the lifespan of the bridges, which results in heavy economic losses. Research has been conducted to identify economic solutions for significantly delaying and/or preventing corrosion damage. Considering the amount of steel reinforcement used in bridge decks, the influence of as constructed parameters including clear spacing between top and bottom reinforcement bars, ratio of cathode to anode areas, and presence of stay-in-place forms on corrosion activity needs to be evaluated. The influence of the as constructed parameters have been studied using different corrosion assessment methods including resistivity, half-cell potential, linear polarization, chloride content, moisture content, and visual inspection. This study included the clear spacing distances between the anode and cathode of 51, 76, and 102 mm (2, 3, and 4-inch), number of cathodes as 1 and 2, and the presence and absence of stay-in-place forms. Data up to 15 months were taken from a previous study by Smolinski and integrated into the current study period of 35 to 45 months. A trend line may be established to illustrate the changes which took place over the missing time period, from approximately 15 to 35 months, since the specimens were maintained in controlled environment. Analysis of the data showed that there is a significant difference between the spacing values (2, 3, and 4-inch) through all forms of evaluations. Regarding the other parameters, no significant difference was identified. Variations in resistivity with increasing spacing, even when the water-cement ratio was kept at 0.50, maybe the result of the difference in unit consolidation between the clear spacing specimens. Thus, the corrosion mechanism observed in this study may be resistivity-controlled. Also, autopsy showed that corrosion on the top bars was in general agreement with the measured corrosion activity. The bottom bars had no visible corrosion and the chloride had not penetrated to the bottom bars, regardless of the separation distance between the top and bottom bars. For this laboratory study, the measurements showed that macrocell corrosion influence on the total corrosion was insignificant. / Master of Science

Pressure is mounting in the concrete industry to adopt eco-efficient methods to reduce CO₂ emissions. Portland cement (PC), an essential concrete ingredient, is responsible for over two-thirds of the embodied energy of the concrete, generating about 8% of global greenhouse gas emissions. Extraction and transportation of aggregates and raw materials that comprise concrete mixes are also directly linked to their embodied energy; thus, recycled concrete aggregates (RCA) have been proposed as a promising alternative to increase sustainability in new construction. In this context, many studies have been conducted over the past decades on the properties of RCA concrete. Recent studies have shown that suitable fresh (i.e., flowability) and short-term hardened (i.e., compressive strength) properties might be achieved when the unique microstructural features of RCA are accounted for in the mix-design process of the recycled concrete. However, manufacturing RCA from construction demolition waste (CDW) or returned concrete (RC) presents its unique challenges. Amongst others, the variation in the source of RCA and the presence of damage due to several deterioration mechanisms causes major concern. Due to the presence of reactive aggregates in many quarries in Canada, alkali-silica reaction (ASR) is one of the most common deterioration mechanisms. The durability and long-term performance of RCA concrete are not fully understood and should be further investigated, especially in regards to a) the potential of further (secondary) deterioration of recycled concrete bearing coarse and fine alkali-silica reactive aggregates b) the impact of the severity of the initial reaction on mechanical properties and kinetics of expansion in recycled concrete and c) the impact of using sound and alkali-silica reaction (ASR) affected RCA on the chloride diffusivity (and thus corrosion initiation) of concrete. This work aims to appraise the durability performance of RCA concrete made of 100% coarse RCA, particularly two families of RCA selected (i.e., returned concrete RCA, demolished concrete RCA) to represent waste currently being generated. Furthermore, two types of reactive aggregates are selected to investigate the impact of the source of the reaction (i.e. reactive coarse aggregate as original virgin aggregate - OVA and reactive sand within the residual mortar - RM) within the RCA. ASR is the distress mechanism used to introduce damage to the manufactured RCA. A new mix design technique was used to produce recycled concrete mixtures to increase eco-efficiency, improve fresh-state properties, and reduce cement use in RCA concrete. In conclusion, the initial reaction's location and severity significantly impact the compressive strength, SDT parameters, chloride diffusion rate, and shear strength of concrete specimens. Specifically, the location of the initial reaction can influence the distribution and extension of damage within the various parts of recycled concrete, while the severity of the initial reaction can affect the overall integrity of the aggregates as well as the availability of silica and alkalis for secondary reaction. These results demonstrate the importance of assessing the severity of the initial reaction and its source in order to ensure the durability and long-term performance of recycled concrete made with reactive RCA.

No description available.

Modeling of chloride-induced deterioration of bridge decks by using Fick's Second Law of diffusion was performed. The objective of this study is to select suitable input parameters for the model to estimate the service life of bridge decks. Five bridge decks, one in each of the following states, Virginia, Florida, New Jersey, New York, and Minnesota were evaluated. Data collection process involved visual inspections, damage surveys, corrosion testing including continuity, one-point resistivity, four-point resistivity, half-cell potentials, and three-electrode linear polarization, reinforcement cover depths, chloride samples. The Virginia bridge deck was built with epoxy-coated reinforcement as top reinforcement mat and black bar as the bottom mat. The Florida bridge is a segmental prestressed box girder structure built with black bar. The New Jersey bridge deck was overlaid with latex modified concrete. The New York bridge deck, which was built in 1990, is six inch concrete topping over prestressed adjacent box beams structure with epoxy-coated bar in the negative moment area. The Minnesota bridge was rebuilt in 1984. The deck was rebuilt with epoxy coated reinforcing steel in the top and bottom mats. The probabilistic Fickian model requires reinforcement cover depths, surface chloride concentration, chloride initiation concentration, and diffusion coefficients as input parameters. The chloride initiation concentration was input via parametric bootstrapping, while the other parameters were input as simple bootstrapping. Chloride initiation concentration was determined from the chloride concentration at the reinforcement bar depths. The modeling results showed that the deterioration of the Virginia bridge deck was corrosion controlled and the bridge will undergo increasingly severe damage in the future. Florida bridge deck is not undergoing corrosion and will not experience corrosion damage within 100 years. New Jersey bridge deck's service life has been most likely extended by the overlay. Deterioration of the New York bridge was not corrosion controlled, but was related to longitudinal cracking of the topping at match lines of adjacent box beams. Minnesota bridge deck is delaminated and contained a large number of cracks that should be included in service life modeling; otherwise the service life estimate is underestimated. In addition to service life corrosion performance modeling, analyses were conducted on the relationships and interrelations of resistivity, corrosion potential, corrosion current and chloride at the reinforcing bar depth. / Ph. D.

A model to determine the time to the End of Functional Service Life (EFSL) for concrete bridge decks in Virginia was developed. The service life of Virginia bridge decks is controlled by chloride-induced corrosion of the reinforcing steel. Monte Carlo resampling techniques were used to integrate the statistical nature of the input variables into the model. This is an improvement on previous deterministic models in that the effect of highly variable input parameters is reflected in the service life estimations. The model predicts the time required for corrosion to initiate on 2% of the reinforcing steel in a bridge deck and then a corrosion propagation time period, determined from empirical data, is added to estimate the EFSL for a given bridge deck or set of bridge decks. Data from 36 Virginia bridge decks was collected in order to validate the service life model as well as to investigate the effect of bridge deck construction specification changes. The bridge decks were separated into three distinct groups: 10 bare steel reinforcement decks â 0.47 water/cement (w/c), 16 Epoxy-Coated Reinforcement (ECR) decks â 0.45 w/c, and 10 ECR decks â 0.45 w/(c+pozzolan). Using chloride titration data and cover depth measurements from the sampled bridge decks and chloride corrosion initiation values determined from the literature for bare steel, service life estimates were made for the three sets of bridge decks. The influence of the epoxy coating on corrosion initiation was disregarded in order to allow direct comparisons between the three sets as well as to provide conservative service life estimates. The model was validated by comparing measured deterioration values for the bare steel decks to the estimated values from the model. A comparison was then made between the three bridge deck sets and it was determined that bridge decks constructed with a 0.45 w/(c+p) will provide the longest service life followed by the 0.47 w/c decks and the 0.45 w/c decks, respectively. From this it can be inferred that the addition of pozzolan to the concrete mix will improve the long-term durability of a bridge deck while a reduction in w/c appears to be of no benefit. / Ph. D.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Natural rice husk ash (RHA) used in concrete contributes to civil construction sustainability. In fact, RHA is considered a residual pollutant and then it is necessary to destine this material correctly. However, it is necessary to investigate the consequences of replacing part of cement by natural RHA to produce concrete for structural purposes. In this context, the aim of this study was to evaluate the concrete durability produced with 15 % of blinder partial replacement by natural RHA in the expansion due to alkali-silica reaction (ASR) and penetration of chloride ion, as well as to suggest preventive measures with the use of mineral additions. In the present study, natural RHA was used as partially replacement of Portland cement. This natural RHA has been obtained without temperature control burning and placed directly into the mixer to suffer self-grinding with aggregates. We investigated the RAS neutralization of natural RHA by the use of cement with mineral additions (CPIIZ, CPIII e CPIV), as well as, we performed additional replacements of part from CPIIZ cement by fly ash (10, 15, 20, 30 and 40 %). We employed accelerated expansion method at 80°C in mortar bars followed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), and long term at 38 °C and accelerated at 60 °C methods in concrete prisms. To investigate concrete resistance in the chloride ion penetration, we used chloride ions penetration method by immersion in saline solution (CPT) of concrete produced with natural RHA and CPIIZ cement added of fly ash (0, 12.75 or 17 %) and water-binder ratios of 0.45, 0.55 and 0.65 were adopted. Analyses of results were based in slope (K ) obtained from the average depths of penetration. In this study, we verified that in mortar bars assay the natural RHA generated expansion above of results allowed by norm in mixtures with standard cement, while CPIIZ cement with addition from 20 % of fly ash showed to mitigate the ASR. These results demonstrated that effect of mitigation of RAS proportionally increased with fly ash addition. Moreover, CPIV cement demonstrated excellence in mitigate the expansive reaction. The SEM analysis identified the characteristic products of ASR in the samples containing natural RHA. XRD analysis showed that the samples of mixtures with higher content of mineral addition showed peaks of calcium hydroxide (CH) with less intensity and mixtures with natural RHA presented greater calcium carbonate content. In relation to concrete prisms molded at 60°C, results showed an increase in expansion for mixture of CPIIZ with natural RHA, but these results remained below of maximum expansion predicted by test. Mixtures of CPII-Z with natural RHA added of 10 and 15% fly ash demonstrated better efficiency in expansion mitigation. In relation to concrete prisms molded at 38°C, the results are not conclusive to 12 months, but mixtures that presented a great expansion were of CPII-Z with natural RHA and 15% fly ash, the CPII-Z with RHA natural and CPII-Z with natural RHA and 10% fly ash, respectively. However, all mixtures had expansion below the maximum limit suggested by the Brazilian standard at 24 months. Through of results CPT, we can conclude that mineral additions provided improvements to the concrete with higher ages due to pozzolanic effect. Moreover, the best results obtained were in trace with lowest water-binder ratios, probably due to increased consumption of cement, which increases the CH amount to interact with the RHA and the fly ash. Therefore, mixtures of Portland cement with fly ash and natural RHA meet the durability of concrete, and also the use of natural RHA would be an important contribution to sustainability and preservation of environment by civil construction. / O emprego de cinza de casca de arroz (CCA) natural no concreto visa contribuir para a sustentabilidade da construção civil, destinando de maneira adequada, esse material que antes seria considerado um resíduo poluente. Porém, é necessária a investigação das consequências em substituir parte do cimento por CCA natural para produzir concreto com finalidade estrutural. Neste sentido, o objetivo deste trabalho foi avaliar a durabilidade de concretos produzidos com teor de 15 % de substituição parcial do aglomerante por CCA natural, frente à expansão devido à reação álcali-sílica (RAS) e à penetração de íons cloretos, assim como, sugerir medidas preventivas através do uso de adições minerais. No presente estudo, a CCA natural foi utilizada em substituição parcial ao cimento Portland no estado em que se encontra ao sair dos fornos de queima (sem controle de temperatura), diretamente na betoneira para sofrer auto-moagem com os agregados. Foi investigada a neutralização das RAS da CCA natural pelo emprego de cimentos com adições minerais (CPIIZ, CPIII e CPIV), assim como foram realizadas as substituições adicionais de parte do cimento CPIIZ por cinza volante (10, 15, 20, 30 e 40 %). Na investigação da RAS foram empregados os métodos de expansão acelerado a 80 °C em barras de argamassa acompanhado pela microscopia eletrônica de varredura (MEV) e difração de raios-X (DRX), e os métodos de longa duração a 38 °C e acelerado a 60 °C em prismas de concreto. Na investigação da resistência a penetração de íons cloretos foi empregado o método de penetração de íons cloretos por imersão em solução salina (EPCI) dos concretos produzidos com CCA natural e cimento CPIIZ adicionados de cinza volante (0; 12,75 ou 17 %) e nas relações água/aglomerante(a/ag) de 0,45; 0,55 e 0,65. A análise dos resultados do EPCI foi realizada com base no coeficiente angular da equação da reta (K ) obtido a partir das profundidades médias de penetração dos períodos investigados. Neste trabalho verificou-se que, no ensaio em barras de argamassa a CCA natural gerou expansão acima do permitido por norma nas misturas com cimento padrão, enquanto o cimento CPIIZ com adição a partir de 20 % de cinza volante se mostrou mitigador da RAS. Através desses resultados pode-se verificar que o efeito mitigador da RAS aumentou proporcionalmente com a adição de cinza volante. Além disso, o cimento CPIV mostrou excelência em mitigar a reação expansiva. A análise de MEV identificou os produtos característicos da RAS nas amostras contendo CCA natural e a DRX verificou que as amostras retiradas das misturas com maior teor de adição mineral apresentaram picos de hidróxido de cálcio (CH) com menor intensidade e ainda, que as misturas com CCA natural apresentaram maior quantidade de carbonato de cálcio. Em relação aos prismas de concreto moldados a 60 °C, os resultados mostraram maior expansão na mistura de CPIIZ com CCA natural, mas ela se manteve abaixo do limite máximo de expansão preconizado pelo ensaio. As misturas de CPII-Z com CCA natural adicionadas de 10 e 15 % de cinza volante mostraram melhor eficiência em mitigar a expansão. Em relação aos prismas de concreto moldados a 38 °C os resultados ainda não são conclusivos aos 12 meses, porém as misturas que apresentaram maior expansão em 12 meses foram as de CPII-Z com CCA natural e 15 % de cinza volante, de CPII-Z com CCA natural e CPII-Z com CCA natural e 10 % de cinza volante, respectivamente, entretanto, todas abaixo do limite máximo de expansão aos 24 meses, preconizado pela norma brasileira. Através das análises dos resultados do EPCI concluiu-se que as adições minerais proporcionaram melhorias ao concreto com maiores idades devido ao efeito pozolânico. Além disso, os melhores resultados obtidos foram nos traços com menor relação a/ag, provavelmente devido ao maior consumo de cimento que aumenta a quantidade de CH para interagir com a CCA e a cinza volante. Portanto, as misturas de cimento Portland com CCA natural e cinza volante atendem aos parâmetros de durabilidade do concreto, e com isso o uso da CCA natural seria um importante contribuinte na sustentabilidade e preservação do meio ambiente pela construção civil.