Concrete structures designed to meet blast criteria often require substantial increases in structural system size, weight, and cost when using conventional materials, but using higher strength materials may offer a way to mitigate these increases while achieving desired performance levels. The primary objective of this research is to investigate the performance of a high-strength Portland cement concrete, high-strength low-alloy vanadium (HSLA-V) rebar material combination that meets or exceeds blast resistance criteria while allowing a more efficient structural design than can be achieved using conventional materials. Twelve panels consisting of both single and double mat conventional Grade 60 rebar or HSLA-V rebar in combination with 4 ksi or 15 ksi concrete were tested using the ERDC quasi-static water chamber. Permission to publish this thesis was granted by the Director of the Geotechnical and Structures Laboratory and the U.S. Army Research Laboratory.

The objective of this research was to explore and demonstrate the production andperformance of fiber-reinforced polymer (FRP) rebar manufactured on a continuous threedimensionalbraiding machine for use as reinforcement in concrete structures. Differentconfigurations of fiberglass/epoxy composite cylindrical rebar rods were manufactured,embedded in concrete, and tested in axial tension to identify the relationships betweenmanufacturing parameters and tensile pull-out strength of the rebar. The strength of the bondbetween concrete and FRP rebar was investigated using the pull-out test detailed by ACI 440.3R-12. The rebar was a No. 4 size and produced by combining multiple tows of fiberglass/epoxyprepreg to form the core of cylindrical rods which were consolidated using spirally-woundaramid consolidation fibers. The manufactured rebar was cured at 121°C (250°F) as specified bythe material manufacturer, TCR Composites. Preliminary research performed on carbon/epoxyrebar guided the process of developing a test matrix based on multiple variables. Primaryvariables investigated included the nature of the consolidation fiber material (dry vs prepreg),and the use of sand coating as a secondary process. The rebar samples were cast in 200 mm x200 mm x 200 mm (8.0 in x 8.0 in x 8.0 in) concrete cubes to investigate bond strength. A testfixture was designed and fabricated for use on a universal tensile testing machine. Standard 12.7mm (0.5 in) diameter steel rebar and a commercially comparable fiberglass rebar were alsotested to provide baseline values. Measurements were collected at both the free and loaded endsof the rebar with free-end results being a more accurate presentation of rebar bond stress.Results showed that the bond strength was 6-13% higher for the free-end for rebarconsolidated with a dry tow compared to prepreg tow consolidated rebar. When sand was added,dry tow consolidated sand-coated samples showed higher bond stress in the range of 15-26% forthe free-end than samples consolidated with a dry tow but excluded sand coating. Samplesconsolidated with prepreg tow and coated with sand showed higher bond stress in the range of43-58% for the free-end compared to prepreg tow no-sand coating samples. Overall, for therebar manufactured on the 3-D braiding machine, the prepreg tow consolidated rebar samplesrecorded the highest bond strength values with a maximum average bond stress value of 15.2MPa (2.26 ksi). The dry tow sand consolidated rebar recorded a maximum average bond stressvalue of 11.4 MPa (1.65 ksi). The rebar purchased from American Fiberglass Rebar recorded amaximum average bond stress of 12.0 MPa (1.74 ksi) while the maximum average bond stress ofsteel rebar was 13.1 MPa (1.90 ksi). Results demonstrated that quality composite rebar can bemanufactured using the 3-D braiding machine and that consolidating the rebar with a prepregtow and coating the surface with sand resulted in a rebar which bonded well with concretecompared to commercialized FRP and steel rebar.

The objective of this research was to explore and demonstrate the production andperformance of fiber-reinforced polymer (FRP) rebar manufactured on a continuous threedimensionalbraiding machine for use as reinforcement in concrete structures. Differentconfigurations of fiberglass/epoxy composite cylindrical rebar rods were manufactured,embedded in concrete, and tested in axial tension to identify the relationships betweenmanufacturing parameters and tensile pull-out strength of the rebar. The strength of the bondbetween concrete and FRP rebar was investigated using the pull-out test detailed by ACI 440.3R-12. The rebar was a No. 4 size and produced by combining multiple tows of fiberglass/epoxyprepreg to form the core of cylindrical rods which were consolidated using spirally-woundaramid consolidation fibers. The manufactured rebar was cured at 121C (250F) as specified bythe material manufacturer, TCR Composites. Preliminary research performed on carbon/epoxyrebar guided the process of developing a test matrix based on multiple variables. Primaryvariables investigated included the nature of the consolidation fiber material (dry vs prepreg),and the use of sand coating as a secondary process. The rebar samples were cast in 200 mm x200 mm x 200 mm (8.0 in x 8.0 in x 8.0 in) concrete cubes to investigate bond strength. A testfixture was designed and fabricated for use on a universal tensile testing machine. Standard 12.7mm (0.5 in) diameter steel rebar and a commercially comparable fiberglass rebar were alsotested to provide baseline values. Measurements were collected at both the free and loaded endsof the rebar with free-end results being a more accurate presentation of rebar bond stress.Results showed that the bond strength was 6-13% higher for the free-end for rebarconsolidated with a dry tow compared to prepreg tow consolidated rebar. When sand was added,dry tow consolidated sand-coated samples showed higher bond stress in the range of 15-26% forthe free-end than samples consolidated with a dry tow but excluded sand coating. Samplesconsolidated with prepreg tow and coated with sand showed higher bond stress in the range of43-58% for the free-end compared to prepreg tow no-sand coating samples. Overall, for therebar manufactured on the 3-D braiding machine, the prepreg tow consolidated rebar samplesrecorded the highest bond strength values with a maximum average bond stress value of 15.2MPa (2.26 ksi). The dry tow sand consolidated rebar recorded a maximum average bond stressvalue of 11.4 MPa (1.65 ksi). The rebar purchased from American Fiberglass Rebar recorded amaximum average bond stress of 12.0 MPa (1.74 ksi) while the maximum average bond stress ofsteel rebar was 13.1 MPa (1.90 ksi). Results demonstrated that quality composite rebar can bemanufactured using the 3-D braiding machine and that consolidating the rebar with a prepregtow and coating the surface with sand resulted in a rebar which bonded well with concretecompared to commercialized FRP and steel rebar.

No description available.

It is well known that crack spacings and widths can be reduced with the addition of steel fibres to a concrete mix. However, test data for the tensile behaviour of steel fibre reinforced concrete members containing conventional steel reinforcement (R/FRC members) are scarce relative to those of reinforced concrete (RC) specimens and fibre reinforced concrete (FRC) specimens without reinforcing bars. In this research program, uniaxial tension tests were conducted on 12 RC and 48 R/FRC specimens in order to observe cracking and tension stiffening behaviour. The parameters under observation were fibre volumetric content, fibre length and aspect ratio, conventional reinforcement ratio and steel reinforcing bar diameter. ‘Dog-bone’ tension tests and bending tests were also performed in order to determine tensile material properties. It was discovered that currently available crack spacing formulae significantly overestimate the average stabilized crack spacing for R/FRC; therefore, an improved crack spacing model was developed and proposed.

It is well known that crack spacings and widths can be reduced with the addition of steel fibres to a concrete mix. However, test data for the tensile behaviour of steel fibre reinforced concrete members containing conventional steel reinforcement (R/FRC members) are scarce relative to those of reinforced concrete (RC) specimens and fibre reinforced concrete (FRC) specimens without reinforcing bars. In this research program, uniaxial tension tests were conducted on 12 RC and 48 R/FRC specimens in order to observe cracking and tension stiffening behaviour. The parameters under observation were fibre volumetric content, fibre length and aspect ratio, conventional reinforcement ratio and steel reinforcing bar diameter. ‘Dog-bone’ tension tests and bending tests were also performed in order to determine tensile material properties. It was discovered that currently available crack spacing formulae significantly overestimate the average stabilized crack spacing for R/FRC; therefore, an improved crack spacing model was developed and proposed.

The corrosion study in actual concrete structures is a subject enough discussed as much in the academic ambience as in the professional one. The subject is relevant due the numberless pathology cases of corrosion in structural concrete that are reported, almost daily, in the technical sphere. Nevertheless, few are the studies on this phenomenon in structural concrete of the first half of the 20th century. Is common sense that these structures were executed in a different way from the actual, and its behavior in front of corrosion may be differentiated, however, little are the studies that analyze the behavior of these structures in front of this pathology. This dissertation, based on bibliographical study and author s experience, look for not only analyze the concrete structure characteristics of the first half of 20th century and its influence on the rebar corrosion, as also propose a methodology for its detection. The proposition of this theme is based in fact that many execution and calculus methods were enough different from the actual concerning the concrete structures. The sodium chloride and calcium chloride addition in concrete, with purpose to accelerate the set and curing of concrete, the use of wooden pins as spacers are some characteristics showed in this work. As conclusion, is proposed an evaluation methodology which permits analyze such structures under the optics of its peculiar characteristics, aiming at the rebar corrosion. / O estudo da corrosão em estruturas de concreto armado atuais é um assunto bastante discutido tanto no meio acadêmico, como no profissional. O tema reveste-se desta importância devido aos inúmeros casos de patologias de corrosão em estruturas de concreto armado que são reportados, quase diariamente, ao meio técnico. No entanto, pouco se tem estudado a respeito desse fenômeno em estruturas de concreto armado da primeira metade do século XX. É senso comum que essas estruturas foram executadas de forma diferente das atuais e que seu comportamento frente à corrosão pode ser diferenciado; no entanto, são poucos os estudos que analisam o comportamento desse tipo de estrutura frente a essa patologia. Este trabalho, tendo por base um estudo bibliográfico e a experiência do autor, busca não só analisar as características das estruturas de concreto armado da primeira metade do século XX e suas influências sobre a corrosão das armaduras, como também propor uma metodologia para sua detecção. A proposição desse tema baseia-se no fato de que muitos métodos de execução e cálculo eram bastante diferentes dos atuais no que concerne a estruturas de concreto armado. A adição de cloreto de sódio e cloreto de cálcio no concreto, com a finalidade de acelerar a pega e a cura do concreto, e o uso de tarugos de madeira como espaçadores são algumas das características mostradas neste trabalho. Como conclusão é proposta uma metodologia de avaliação que permita analisar tais estruturas sob a ótica de suas características particulares, com vistas à corrosão da armadura.

<p>Embedded plates are used to support the external attachments such as heavy piping, brackets, sprinkler systems, or other equipment in nuclear power plants. The plates are welded with deformed reinforcing bars or deformed wires and anchored to reinforced concrete walls. The ACI code (ACI 318-19/ACI 349-13) provides design equations to calculate the anchor strength in concrete under tension load. These empirical equations are based on experiments conducted on headed studs, hooked bars, headed bolts, and adhesive anchors. With the lack of experimental data and code provisions on straight deformed reinforcing bars or deformed wires used as anchors, it is believed that anchoring bars with the embedment length as per code prescribed development length will provide sufficient strength to transfer tensile forces to the concrete, ignoring other failure modes such as concrete breakout. </p> <p>In this study, eight large scale group anchor tests were performed to evaluate their concrete breakout strength as per ACI 349-13. The test specimens were made with deformed reinforcing bar anchors (DRAs) and deformed wire anchors (DWAs). The tests included the effect of different bar types, bar sizes, and anchor spacings on the breakout capacities of such connections. The mean average back-calculated effective <i>k </i>value is 33.25 for DRAs and 36.26 for DWAs. The experimental study confirms that the axial tension capacity of embedded plates anchored to concrete using deformed reinforcing bars or deformed wires can be limited by concrete breakout strength.</p>

The objective of this research was to investigate the effects of twisted steel micro rebar (TSMR) fibers on 1) the mechanical properties of concrete used in bridge deck construction and 2) the early cracking behavior of concrete bridge decks. This research involved the evaluation of four newly constructed bridge decks through a series of laboratory and field tests. At each location, one deck was constructed using a conventional concrete mixture without TSMR, and one was constructed using the same conventional concrete mixture with an addition of 40 lb of TSMR per cubic yard of concrete. Regarding laboratory testing, the conventional and TSMR beam specimens exhibited similar average changes in height after 4 months of shrinkage testing. The electrical impedance measurements did not indicate a notable difference between specimens comprising concrete with TSMR and those comprising conventional concrete. Although no notable difference in behavior between conventional and TSMR specimens was apparent before initial cracking, the toughness of the TSMR specimens was substantially greater than that of the conventional concrete specimens. Regarding field testing, sensors installed in the bridge decks indicated that the addition of TSMR does not affect internal concrete temperature, moisture content, or electrical conductivity. The average Schmidt rebound number varied little between the TSMR decks and conventional decks; therefore, the stiffness of the TSMR concrete was very similar to that of conventional concrete. Distress surveys showed that the conventional decks exhibited notably more cracking than the TSMR decks. The TSMR fibers exhibited the ability to limit both crack density and crack width. For all of the decks, chloride concentrations increased every year as a result of the use of deicing salts on the bridge decks during winter. However, the chloride concentrations for samples collected over cracked concrete increased more rapidly than those for samples collected over non-cracked concrete. Although TSMR fibers themselves do not directly affect the rate at which chloride ions penetrated cracked or non-cracked concrete, the fibers do prevent cracking, which, in turn, limits the penetration of chloride ions into the decks. Therefore, the use of TSMR would be expected to decrease the area of a bridge deck affected by cracking and subsequent chloride-induced corrosion damage and thereby increase the service life of the bridge deck.

Com o envelhecimento das estruturas de concreto armado, ficou evidente sua deterioração num período de tempo muito menor do que o previsto, pois sempre foram consideradas construções de elevada vida útil. Entre os fenômenos de maior gravidade para a sua estabilidade estrutural está a corrosão das armaduras de aço. Visando melhorar o desempenho das construções, aumentando a vida útil e diminuindo custos com manutenção, esta dissertação propõe o desenvolvimento de um vergalhão com melhor resistência à corrosão, de microestrutura dual-phase. O objetivo principal foi propor uma rota de produção viável, agregando o mínimo de custo possível, de forma a se obter um produto competitivo. A simulação da produção do vergalhão, desde o refino na aciaria, passando por tratamento térmico e propriedades mecânicas, foi realizada com auxílio da termodinâmica computacional, através do software FactSage. A simulação consistiu de três etapas: 1) determinação das temperaturas A1 e A3 e janelas de tratamento térmico; 2) cálculo das propriedades mecânicas a partir de modelos empíricos; 3) comportamento das inclusões durante o refino, durante a solidificação e durante a laminação. O estudo das inclusões é importante porque os aços simulados possuem alto teor de silício (de 1% a 2,5% em massa), podendo precipitar óxidos sólidos nos moldes de lingotamento contínuo. O estudo termodinâmico apontou que a produção de vergalhões com aços dual-phase com alto teor de silício é possível e sugere-se a fabricação pela seguinte rota: aciaria elétrica convencional, com ajuste final do teor de silício após a desoxidação e adição de alumínio controlada para obter inclusões com 15% a 25% de Al2O3, ajuste da escória, rica em CaO, de maneira a obter inclusões favoráveis ao lingotamento contínuo e laminação, e após o último passe de laminação, têmpera por resfriamento em água online (Thermex/Tempcore). / With the aging of reinforced concrete structures, their premature wearing became evident. Among the phenomena of greater severity to the structural stability of buildings is the corrosion of the steel rebar. To improve the performance of these structures, increase their service life and reduce maintenance costs, this work proposes the development of a rebar with better corrosion resistance, with a dual-phase microstructure. The main objective was to propose a viable production route, which adds the least possible cost, so as to obtain a competitive product. The thermodynamic simulation of the rebar manufacturing, from steelmaking to heat treatment and mechanical properties was carried out with the aid of computational thermodynamics using the FactSage software. The simulation consisted of three steps: 1) determining the temperatures A1 and A3 and the heat treatment windows; 2) calculating the mechanical properties from empirical models; 3) analyzing the behavior of inclusions during refining, solidification and hot-rolling. The study of the inclusion system is important because the simulated steels have high silicon content (from 1% to 2.5% by weight) and solid oxides may precipitate in the continuous casting molds. As a result of the study, it was found that the production of rebars with dual-phase microstructure and high silicon content is possible and the manufacturing route proposed is as follows: conventional electric steelmaking, with final adjustment of the silicon content after deoxidation and controlled addition of aluminum to obtain inclusions with 15% to 25% of Al2O3, refining slag rich in CaO, in order to obtain inclusions favorable to continuous casting and hot-rolling, and direct water quenching after the final rolling step (Thermex / Tempcore processes).