Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2007. / Bonded overlays are increasingly used in concrete and reinforced concrete repair and rehabilitation applications, despite the high probability of interfacial debonding. Reasons for such failures include inefficient substrate surface preparations, inappropriate overlay materials, poor curing conditions and time dependent influences. The introduction of engineered cement-based composite (ECC) as an overlay or repair material, does not only address durability aspects but also structural performance. The associated ductility of the material induces a high performance aspect where applied. It is crucial to execute reliable design methods, especially at interfacial level, in order to harness the ductility at hand. The fact of the matter is that through identifying the required performance, one can engineer an optimal bond through implementation of reliable substrate surface preparation techniques (SSPT’s). ECC is a material which exhibits ductile mechanical behaviour. The material matrix is reinforced with synthetic fibres, in the case of this study, poly vinyl alcohol (PVA) fibres were used. The introduction of fibres induces strain-hardening behaviour when in tension. Strain-hardening occurs from the first crack onwards and is accompanied by ductile behaviour, due to a multiple cracking phenomenon. Multiple cracking continues until the increased tensile load incurs localising of an existing crack. The literature study investigates bond properties and bond model parameter test methods. A review of composite design, mainly concrete to concrete, in local and international codes discloses design specifications towards calculating interfacial shear bonds. The interfacial transition zone (ITZ) between the aggregate and cement matrix of concrete is used to define the interfacial bond characteristics and processes. The next step is to investigate a variety of interfacial shear and tensile test methods, in order to implement the most suitable tests.

Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Plastic shrinkage cracking (PSC) is the cracking caused by the early age shrinkage of concrete within the first few hours after the concrete has been cast. It results in unsightly surface cracks that serve as pathways whereby corroding agents can penetrate the concrete which shortens the expected service life of a structure. PSC is primarily a problem at large exposed concrete surfaces for example bridge decks and slabs placed in environmental conditions with high evaporation rates. Most precautionary measures for PSC are externally applied and aimed to reduce the water loss through evaporation. The addition of a low dosage of polymeric fibres to conventional concrete is an internal preventative measure which has been shown to reduce PSC. The mechanisms involved with PSC in conventional and low volume fibre reinforced concrete (LV-FRC) are however not clearly understood. This lack of knowledge and guidance leads to neglect and ineffective use of preventative measures. The objective of this study is to provide the fundamental understanding of the phenomena of PSC. To achieve the objective, an in depth background study and experiments were conducted on fresh conventional concrete and LV-FRC. The three essential mechanisms required for PSC are: 1→ Capillary pressure build-up between the particles of the concrete is the source of shrinkage. 2→ Air entry into a concrete initiates cracking. 3→ Restraint of the concrete is required for crack forming. The experiments showed the following significant findings for conventional and LV-FRC: PSC is only possible once all the bleeding water at the surface has evaporated and once air entry has occurred. The critical period where the majority of the PSC occurs is between the initial and final set of concrete. Any preventative measure for PSC is most effective during this period. The bleeding characteristics of a mix have a significant influence on PSC. Adding a low volume of polymeric fibres to concrete reduces PSC due to the added resistance that fibres give to crack widening, which increases significantly from the start of the critical period. The fundamental knowledge gained from this study can be utilized to develop a practical model for the design and prevention of PSC in conventional concrete and LV-FRC. / AFRIKAANSE OPSOMMING: Plastiese krimp krake (PSK) is die krake wat gevorm word a.g.v. die vroeë krimping van beton binne die eerste paar ure nadat die beton gegiet is. Dit veroorsaak onooglike oppervlak krake wat dien as kanale waardeur korrosie agente die beton kan binnedring om so die dienstydperk van die struktuur te verkort. Dit is hoofsaaklik ʼn probleem by groot blootgestelde beton oppervlaktes soos brug dekke en blaaie wat gegiet is in klimaat kondisies met hoë verdamping tempo’s. Meeste voorsorgmaatreëls vir PSK word ekstern aangewend en beperk die water verlies as gevolg van verdamping. Die byvoeging van ʼn lae volume polimeriese vesels is ʼn interne voorsorgmaatreël wat bekend is om PSK te verminder. Die meganismes betrokke ten opsigte van PSK in gewone beton en lae volume vesel versterkte beton (LV-VVB) is vaag. Die vaagheid en tekort aan riglyne lei tot nalatigheid en oneffektiewe aanwending van voorsorgmaatreëls. Die doel van die studie is om die fundamentele kennis oor die fenomeen van PSK te gee. Om die doel te bereik is ʼn indiepte agtergrond studie en eksperimente uitgevoer op gewone beton en LV-VVB. Die drie meganismes benodig vir PSK is: 1→ Kapillêre druk tussen die deeltjies van die beton is die hoof bron van krimping. 2→ Lugindringing in die beton wat krake inisieer. 3→ Inklemming van die beton is noodsaaklik vir kraakvorming. Die eksperimente het die volgende noemenswaardige bevindinge opgelewer: PSK is slegs moontlik indien al die bloeiwater van die beton oppervlakte verdamp het en indien lug die beton ingedring het. Die kritiese periode waar die meerderheid van die PSK plaasvind is tussen die aanvanklike en finale set van die beton. Enige voorsorgmaatreël vir PSK is mees effektief gedurende die periode. Die bloei eienskappe van ʼn meng het ʼn noemenswaardige effek op die PSK. Die byvoeging van ʼn lae volume polimeriese vesels tot beton verminder die PSK deur die addisionele weerstand wat die vesels bied teen die toename in kraakwydte. Die weerstand vergroot noemenswaardig vanaf die begin van die kritiese periode. Die fundamentele kennis wat in die studie opgedoen is, kan gebruik word vir die ontwikkeling van ʼn praktiese model vir die ontwerp en verhoed van PSK in gewone beton en LV-VVB.

published_or_final_version / abstract / Civil Engineering / Master / Master of Philosophy

published_or_final_version / abstract / Civil Engineering / Master / Master of Philosophy

The high cost of repairing reinforced or prestressed concrete structures due to steel corrosion has driven engineers to look for solutions. Much research has been conducted over the last two decades to evaluate the use of Fiber Reinforced Polymers (FRPs) in concrete structures. Structural engineering researchers have been testing FRP to determine their usability instead of steel for strengthening existing reinforced concrete structures, reinforcing new concrete members, and for prestressed concrete applications. The high strength-to-weight ratio of FRP materials, especially Carbon FRP (CFRP), and their non-corrosive nature are probably the most attractive features of FRPs. In this study, an experimental program was conducted to investigate the flexural behavior of prestressed concrete beams pre-tensioned with CFRP strands. The bond characteristics were examined by means of experimentally measuring transfer length, flexural bond length, and bond stress profiles. A total of four rectangular beams pre-tensioned with one 0.5-in. diameter CFRP strand were fabricated and tested under cyclic loading for five cycles, followed by a monotonically increasing load until failure. In investigating bond properties, the experimental results were compared to the equations available in the literature. The results from the four flexural tests showed that the main problem of CFRP strands, in addition to their liner-elastic tensile behavior, was lack of adequate bonding between FRP and concrete. Poor bonding resulted in early failure due to slippage between FRPs and concrete. As a result, a new technique was developed in order to solve the bonding issues and improve the flexural response of CFRP prestressed concrete beams. The new technique involved anchoring the CFRP strands at the ends of the concrete beams using a new "steel tube" anchorage system. It was concluded that the new technique solved the bond problem and improved the flexural capacity by about 46%. A computer model was created to predict the behavior of prestressed beams pre-tensioned with CFRP. The predicted behavior was compared to the experimental results. Finally, the experimental results were compared to the behavior of prestressed concrete beams pre-tensioned with steel strands as generated by the computer model. The CFRP beams showed higher strength but lower ductility.

The objective of this research is to determine if the deflection equations currently adopted in ACI 440.1r-15 and previously ACI 440.1r-06 accurately reflect the flexural behavior of an overreinforced Basalt Fiber Reinforced Polymer (BFRP) concrete beam. This was accomplished with experimental, analytical and numerical models. The experiment consisted of two beams doublyreinforced with BFRP rebar. A three-point flexural test on beams with a 30 in. clear span was performed and the deflections were recorded with a dial gauge and LVDT system. This data was compared to the equations from ACI 440.1r-06, ACI 440.1r-15, Branson’s equation and a numerical model created in ANSYS Mechanical APDL. Experimental results show a stiffer beam than expected when compared to the four predictive models for deflection. This can be due to the level of over-reinforcement and the small clear-span to depth ratio. Further research should be conducted to determine the cause for the additional stiffness. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2017. / FAU Electronic Theses and Dissertations Collection

Este trabalho apresenta um estudo para a previsão de comportamento quanto à fissuração e seu controle pelo uso das fibras de aço, em elementos de superfície de concreto restringidos, ou seja, submetidos às tensões de tração induzidas pela retração restringida. Neste estudo, foi desenvolvido um método analítico para calcular o consumo de um determinado tipo de fibra de aço em função do potencial de retração da matriz de concreto e da máxima abertura de fissura, determinada em função de parâmetros de durabilidade e aceitabilidade sensorial. Posteriormente, foram realizados ensaios para caracterização do potencial de fissuração de matrizes de concreto utilizadas em obras de elementos de superfície, onde testou-se um método de estimativa das tensões induzidas por retração restringida no concreto, no momento da primeira fissura. Na etapa final do trabalho, foi realizado um programa experimental, com a construção de pistas de concreto reforçado com fibras de aço (CRFA), com consumos de fibras de 10 kg/m3, 30 kg/m3 e 60 kg/m3, construídas sobre bases com duas condições de restrição: superfície desempenada e superfície jateada com exposição dos agregados. A fissuração destas pistas, nas primeiras idades, foi monitorada através da medida da abertura e do comprimento das fissuras. Com os resultados desta etapa experimental, foi realizada uma retroanálise do método onde concluiu-se que a consideração de valores característicos na previsão da resistência à tração do concreto era um ajuste necessário e coerente com a observação prática. Com o ajuste, os resultados experimentais de abertura de fissura ficaram dentro da faixa de previsibilidade do método, considerando um intervalo de confiança de 90%. Com o desenvolvimento deste método, buscou-se contribuir para a aplicação do CRFA no controle da fissuração por retração restringida de elementos de superfície, ampliando a fronteira do conhecimento no aspecto da escolha e dosagem da fibra para um determinado desempenho esperado quanto à fissuração. / This work presents a study for crack prediction and use of steel fibers to crack control in concrete surface elements submitted to tension stress induced by restrained shrinkage. In this study, a method was developed where a certain steel fiber type could be quantified, as function of concrete matrix shrinkage potential and maximum crack width, determined from human sensorial and durability criteria. Afterwards, an experimental program was done in order to characterize the crack potential of concrete matrices commonly used in surface elements. In this program, a method to predict tension stress induced by restrained shrinkage, at first crack moment, was tested. In the final step of this work, another experimental program was done, where steel fiber reinforced concrete (SFRC) tracks were built, with fiber contents of 10 kg/m3, 30 kg/m3 and 60 kg/m3, over substrates with two restriction conditions: smooth surface and rough surface, with exposition of surface aggregates. Lengths and widths of the early age shrinkage cracks in the tracks were monitored. The results obtained in this program were useful to analyze the method, adjusting it with the consideration of characteristic values in prediction of tension strength. With this adjust, experimental crack width results were more compatible with 90% confidence interval for crack width values predicted by the method. With this study, the goal was the contribution to use SFRC in the control of restrained shrinkage cracks in surface elements, amplifying the knowledge border in the aspect of fiber selection and proportioning, for a determined and expected performance in terms of crack width.

Laboratory experiments were conducted to observe, document and evaluate the mechanical behavior of Fiber Reinforced Concrete after being submitted to five different environments for 8 months. The specimens were molded and reinforced with synthetic fibers with a composition similar to that used for dry-cast concrete. Four different types of fibers with different composition were used. The fibers were mixed with the concrete to create the samples and the samples were exposed to different environmental conditions. Some of these environments were meant to increase degradation of the interface fiber-concrete to simulate longevity and imitate harsh environments or marine conditions. The environments consisted of: a high humidity locker (laboratory conditions), submerged in the Intracoastal Waterway in a barge (SeaTech), a wet/dry cycle in seawater immersion simulating a splash/tidal zone, low pH wet/dry seawater immersion cycle and samples submerged in calcium hydroxide solution. The latter three were in an elevated temperature tank (87-95°F) to increase degradation process. The specimens were monitored weekly and the environments were controlled. Then, specimens were evaluated using different mechanical testing as the Indirect Tensile (IDT) test method, compressive strength according to ASTM standards. Results of testing were documented and observed in this study for further understanding of mechanical properties of Fiber Reinforced concrete. Forensic observation of fiber distribution after the IDT tests were also performed. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

Not available / text

Rehabilitation and maintenance of the aging transportation infrastructure are of major concern in the Province of Ontario. A large portion of this work is related to the durability of highway bridges around the province. One of the weakest points in a bridge structure from a durability aspect is the expansion joints that can allow harmful elements, such as road salts and contaminants to leak down from the road surface and attack the supporting structure of the bridge. Although expansion joints can be eliminated in the design of a new bridge, such as in an integral abutment bridge, this requires major changes to the supports and structure of the bridge, making it impractical for retrofitting existing bridges. One effective alternative is the replacement of a traditional expansion joint with a link slab. A link slab is a concrete slab used in place of an expansion joint to make the bridge deck continuous while keeping the supporting girders simply supported [1]. Link slabs must be able to resist large force effects both in bending and direct tension while minimizing cracking [2], one solution is to use the high tensile and flexural strength properties of an ultra-high performance fibre-reinforced concrete (UHPFRC) [3]. The UHPFRC mixtures are often proprietary and expensive. The purpose of this research was to evaluate the potential of using common fibre types with standard concrete ingredients in a fibre-reinforced concrete (FRC) as an alternative to UHPFRC in a link slab. Using a selection of macro fibres commonly used in slab on grade applications for crack control, an optimized FRC mixture was developed following the principals established by Rossi and Harrouche [4]. This mixture was then used with a variety of fibre types to evaluate the structural and durability properties of the FRC. Testing was conducted for fresh mixture properties, compressive, tensile and flexural strength as well as freezing and thawing resistance, linear shrinkage, environmental and salt exposure along with other durability tests. Results showed that the concrete mixture used for an FRC link slab should consist of; an equal ratio of fine and coarse aggregate by weight and a higher than normal percentage of cement paste, for optimal workability and a dosage of 1.5% by volume of macro steel fibres. Hooked-end steel fibres resulted in the best performance increase to the FRC of the six fibre types tested. Results also showed that reinforcing cage for an FRC link slab should be designed to ensure that fibres can evenly reach all areas of the link slab form to give homogeneous fibre distribution. Although the FRCs created did not perform to the high level of a UHPFRC, these results show a consistent and effective FRC can be created, for use in a link slab with common fibres and standard concrete materials to provide a less expensive and more widely available FRC link slab than UHPFRC.