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

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

published_or_final_version / abstract / Civil Engineering / Doctoral / Doctor of Philosophy

Damage to reinforced concrete bridges due to carbonation and chloride induced corrosion is widespread in South Africa and prone in environments where carbon dioxide is at high levels as well as in marine environments where chlorides are present. Performance specifications are therefore essential in order that structural concrete can be designed and constructed to the required standards ensuring that the long term durability can be maintained. This dissertation includes a review of SANRAL‘s current durability specifications. The specifications are critiqued in terms of the testing methodology followed as well as strength and environmental exposure considerations, and recommendations are made for improving the specifications. The literature review, outlines the background to both carbonation and chloride induced corrosion to reinforced concrete bridges , considering the fundamental causes of deterioration of concrete caused by carbonation and chloride ingress and repair costs during their service life. The South African Durability Index tests are presented and reviewed, in particular the laboratory testing apparatus and procedures. In addition, the index tests are compared with durability test methods currently being used internationally. The background and previous durability specifications used in South Africa on road bridges as well as details of research into specifications to ensure durable concrete with specific emphasis on curing of concrete is summarised. The indications are that performance based specifications for concrete on bridge structures internationally follow similar criteria to the specifications currently being adopted by SANRAL. Both performance and prescriptive specifications used usually depend on the risk that a constructor needs to carry. Importantly both cement extenders to ensure long term durability and penalties are applied in performance based durability. SANRAL‘s current durability specifications are reviewed and both the negatives and positives are presented for the various sections. Amendments to the Committee of Land Transport Officials (COLTO) standard specifications are recommended address shortcomings. The latest project specifications used on SANRAL contracts incorporating target requirements for cover and oxygen permeability are evaluated. These impose penalties if targets are not achieved, while limits are placed on chloride conductivity values for various blended binders. Data is also included for the sorptivity index values on the five projects which may analysed and target values can be set and implemented in future. Descriptions of the five projects with regard to durability specifications, their environmental exposure condition and concrete mix designs are presented. Five projects in KwaZulu-Natal, are used as case studies for durability tests and specifications. The only distinct difference in the specifications is that the three projects commencing in 2006 and early in 2007 had the target values for water sorptivity whereas for the project, sorptivity values are only reported on. Durability index testing results at each of the sites from the trial panels, additional test cubes (cast for coring and testing of durability indexes) as well as coring and testing from the bridge structures are presented. A major change is coring and testing of samples from trial panels and additional test cubes on the site instead of coring of the structure. The information is drawn together and relationships are determined between the various durability indexes as well as to strength. It is evident that the quality of concrete as constructed in the structure which is reflected by the durability index results is different to that produced in the test cubes and trial panels. It is deduced that while more care is being taken to produce quality concrete on the sites, certain aspects of the specifications need revision in order to remove confusion as well as to ensure that the concrete in the structure meets the target requirements. Finally it is noted that climate change is having an impact on design of bridge infrastructure, and while the surveys undertaken at Ethekwini and Msunduzi Municipalities shows that carbon dioxide levels being recorded are still average levels, worldwide there has been an increase in CO2 levels and further modifications to specifications in future may be required. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.

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

Weathering steel has been a primary construction material for bridges in the United States. Notches caused by corrosion are observed on the flange of steel I-beams. These notches reduce the cross section area of the structure and are threats to bridge safety. A606-04 Type 4 cold rolled weathering steel samples were studied in this thesis to understand the effect of notches that caused by corrosion. Weathering steel samples were in the shape of plates, which simulated flange of I-beams. The plate samples were notched across their surfaces by applying electrical current through an electrochemical circuit composed of an anode, a cathode and electrolyte. Sixteen samples were notched and cut into appropriate shape for fatigue testing. S-N (Stress-Number of cycles to failure) diagram established from fatigue data indicated that the fatigue strength decreased below AASHTO category B. Weibull analysis was also performed to understand the reliability distribution. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2014. / FAU Electronic Theses and Dissertations Collection

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

This study presents and illustrates a methodology to calculate the capacity of an existing reinforced concrete bridge under a non-conventional blast load due to low and intermediate pressures. ATBlast program is used to calculate the blast loads for known values of charge weight and stand off distance. An excel spreadsheet is generated to calculate ultimate resistance, equivalent elastic stiffness, equivalent elastic deflection, natural period of the beam, the maximum deflection, and the maximum rotation in the support for a simple span solid slab and T-Beam bridges. The allowable rotation could be taken as to two degrees. Naval Facility Engineering Command (NAVFAC) approach was adopted, where the inputs were material properties, span length, and area of reinforcement. The use of the Fiber Reinforced Polymer for increasing the capacity of an existing bridge is also presented in this study. Parametric studies were carried out to evaluate the performance of the solid slab and T-Beam bridges under the assumed blast load. / by Firas A. Abdelahad. / Thesis (M.S.)--Florida Atlantic University, 2008. / Includes bibliography. / Electronic reproduction. Boca Raton, FL : 2008 Mode of access: World Wide Web.

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.

Chloride ions present in the marine atmosphere contained in marine aerosols is investigated for a relationship with chloride that accumulated into concrete. Chloride profiles are conducted on several concrete mixes containing fly ash, silica fume, and slag, with water to cementitious ratios of 0.35, 0.41, and 0.47. The chloride accumulation in concrete samples exposed to the environment is investigated with relation to the chloride deposition from the marine atmosphere measured via the wet candle test. Results indicate a possible relationship for the total accumulated chloride in the concrete with the accumulated chloride deposition (wet candle). Over the exposure periods, concrete specimens with 50% slag addition and 0.47 w/cm had the lowest average rates of chloride accumulation for deposition under 100 g/m2day. Chloride accumulation was lower in concrete containing 20% fly ash and 8% silica fume with 0.35 w/cm for chloride deposition rates over 200 g/m2day. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2014. / FAU Electronic Theses and Dissertations Collection