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McNally, Ciaran
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McNally, Ciaran
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McNally, Ciaran
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Now showing 1 - 10 of 13
- PublicationWavelet analysis of bender element signals(Institution of Civil Engineers/Thomas Telford Publishing, 2012-03-01)
; ; Accurate determination of shear wave arrival time using bender elements may be severely affected by a combination of near field effects and reflected waves. These may mask the first arrival of the shear wave, making its detection difficult in the time domain. This paper describes an approach for measuring the shear wave arrival time through analysis of the output signal in the time-scale domain using a multi-scale wavelet transform. The local maxima lines of the wavelet transform modulus are observed at different scales and all singularities are mathematically characterised, allowing subsequent detection of the singularity relating to the first arrival. Examples of the use of the approach on typical synthetic and experimental bender element signals are also supplied, and these results are compared to those from other time and frequency domain approaches. The wavelet approach is not affected by near field effects and instead is characterised by a relatively consistent singularity related to the shear wave arrival time, across a range of frequencies and noise levels.1497Scopus© Citations 25 - PublicationDomain size as a parameter for studying the potential alkali-silica reactivity of chert-bearing aggregates(Institution of Civil Engineers, 2004-05)
; ; ; The presence of chert or flint in aggregates used for concrete manufacture has long been a source of concern in the context of alkali-silica reactivity. The global in-service performance of chert and flint-bearing aggregates, however, varies from innocuous to deleterious. This could be due to variations in the degree of crystallinity of the silica, which influences potential reactivity. Chert occurs in significant Irish sources of aggregate used for concrete, yet no cases of deleterious expansion have been reported in the Republic of Ireland to date. Many of these sources fail to conclusively demonstrate innocuous behaviour in the laboratory expansion tests despite satisfactory in-service behaviour. A previous X-ray diffraction study, employing quartz crystallinity index, had indicated a significant difference between Irish Carboniferous cherts and English Cretaceous flints. This paper reports a further study of crystallinity, correlated with mortar bar expansion tests, but employing both quartz crystallinity index and domain size in the characterisation of crystallinity. The influence of chert content was also studied. Twenty-three Irish aggregate sources were sampled, and petrographic analysis revealed that 17 of these contained chert. Three flint-bearing aggregates, from sources in England that had demonstrated alkali-silica reactivity, were also sampled. Chert and flint were extracted from the aggregate samples by a petrographer experienced in the field of concrete technology. Twenty-six distinct samples were successfully extracted from 13 of the Irish and the three English sources. X-ray diffraction testing confirmed the previous findings (using the quartz crystallinity indices) that the Irish cherts are,more crystalline than the English flints. Domain size determination, however, showed that the difference in crystallinity of the national sets was less than that anticipated. The influence of chert content is advanced as a hypothesis to explain the apparent reactivity of Irish cherts in screening tests. The potential value of combining domain size and chert content determination in helping to classify aggregate reactivity is advanced for cases where in-service behaviour is in significant conflict with findings from standard laboratory tests.1079Scopus© Citations 9 - PublicationDevelopment of a recycled polymer modified binder for use in stone mastic asphaltThe number of commercial vehicles using Irish roads has increased considerably in recent years, leading to higher demands being placed on pavement materials and increased use of polymer modified bitumens. This has also coincided with significant changes in Governmental policy which has produced large increases in Irish recycling rates. Improved recycling levels are set to provide Ireland with a new challenge: to find potential uses for the large quantities of recycled polymer that are becoming available. Towards this end, the potential of developing a recycled polymer modified binder was investigated. The polymers most commonly recycled in Ireland were identified and sourced from industry. Fundamental bitumen tests were conducted to assess the effect of the recycled polymer and a mixing methodology developed. It was found that the addition of 4% recycled HDPE into a pen grade binder produced the most promising results, and the mixing process was then optimised with respect to mixing parameters and binder additives. A developmental recycled binder was produced and compared in performance tests to binders currently used in road construction practice. Results obtained from wheel track and fatigue tests show that although the binder does not deliver equivalent performance levels to a proprietary polymer modified binder, it does out-perform traditional binders used in stone mastic asphalt. Recommendations are offered on the further development of the recycled polymer modified binder to achieve the standards currently required.
8025Scopus© Citations 172 - PublicationBiochemical attack on concrete in wastewater applications : a state of the art reviewThe costs associated with the provision and maintenance of drinking water and wastewater infrastructure represents a significant financial demand worldwide. Maintenance costs are disproportionately high, indicating a lack of adequate durability. There remains a lack of consensus on degradation mechanisms, the performance of various cement types, the role of bacteria in the corrosion process associated with wastewater applications and testing methodologies. This paper presents a review of the literature, outlining the various research approaches undertaken in an effort to address this problem. The findings of these varying approaches are compared, and the different strategies employed are compiled and discussed. It is proposed that a key step in advancing the understanding of the associated deterioration mechanism is a combined approach that considers the interaction between biological and chemical processes. If this can be achieved then steps can be taken to establishing a performance-based approach for specifying concrete in these harsh service conditions.
8269 - PublicationDevelopment of calcium sulfate - ggbs - Portland cement bindersBinders manufactured using a blend of gypsum, ground granulated blast furnace slag and Portland cements are technically viable and possess considerable environmental and economic advantages when compared to binders manufactured using Portland cement alone. As such, the evaluation of binders made from these materials offers a promising research focus in the quest to produce technically sound, environmental and economical binders for specialist uses as an alternative to traditional concrete binders of higher carbon footprint. The aim of the test programme was to investigate the viability of a series of binders designed to fulfil particular user needs while having significantly decreased carbon footprints. Two distinct series of binders were designed; the dominant ingredient in the first was calcium sulfate while in the second it was ggbs. Potential applications for both series of binders were considered and the strength development of each binder was analysed. In addition, the effect of water on the gypsum-based binders was analysed, as was the sulfate resistance of the ggbs-based binder. The results of the laboratory tests carried out were varied. For the calcium sulfate-based binders, those manufactured using anhydrite II as the dominant ingredient were found to achieve highest strengths. However these binders were found to be particularly susceptible to moisture-induced deterioration. For the ggbs-based binders, it was found that the early strength development was improved by the addition of small quantities of anhydrite II and gypsum. The strengths and sulfate resistance at later ages remained unaffected. These binders may have significant potential in situations where early strength development is a requirement.
4244Scopus© Citations 60 - PublicationPerformance of concrete incorporating GGBS in aggressive wastewater environmentsConcrete is traditionally used as the main component of wastewater facilities. The sulfate and acidic environment presents significant challenges. Supplementary cementitious materials (SCM) such as GGBS are being used in increasing quantities in concrete and have been shown to provide concrete with increased durability in this particular environment. They have traditionally been used with CEM I, but in recent years a shift in concrete practice has led to the introduction of CEM II cements with reduced CO2 footprint and obvious environmental and economic benefits. However, the change in cement chemistry associated with using CEM II and GGBS must also be accounted for in concrete specifications for aggressive environments. This has particular importance when concrete is exposed to elevated sulfate and sulfuric acid environments, such as that associated with water and wastewater treatment. The performance of CEM II/A-L cements with varying amounts of GGBS was evaluated through a series of tests conducted to determine their durability characteristics in respect of sulfate attack and sulfuric acid attack. As a benchmark, samples were also tested using CEM I cement, CEM I with GGBS, and a sulfate resistant Portland cement. Results have shown that for all cases, the addition of GGBS resulted in considerable reductions in sulfate induced expansion relative to samples using CEM I or CEM II binders alone. A slight improvement in performance relative to sulfate resisting Portland cement (SRPC) binders was also observed. However in respect of the sulfuric acid environment the regime proved too harsh and ultimately resulted in the early failure of all samples. Some difference in performance was noted, but this was not considered noteworthy. The influence of pH and acid type was studied. The conclusions were that the concretes tested cannot adequately address the durability threat to all parts of wastewater infrastructure over a significant life span due to the extraordinarily harsh nature of this form of attack.
1561Scopus© Citations 79 - PublicationA literature review of critical thinking in engineering education(Taylor & Francis, 2019-03-08)
; ; ; ; Developing optimum solutions to engineering problems typically relies on structured and complex thought processes that require evaluation, interpretation and opinion. Well-developed critical thinking (CT) skills are essential for dealing with the multi-dimensional nature of these problems. CT in an engineering context is well reported in teaching and learning academic literature. However, much of this is framed within theoretical and conceptual frameworks. Practical approaches of how CT skills are best promoted in engineering curricula are less common. A state-of-art review of practical interventions that target the development of CT in engineering students is presented. The review draws on 25 selected peer-reviewed journal articles in established engineering databases and focusses on teaching strategies where their effects in promoting CT skills in students are measured. Considerable variability in the reviewed literature was apparent. CT interventions and strategies are often reported, but metrics of their success in enhancing students’ CT is often limited to qualitative, subjective inferences. To more robustly and holistically ensure that CT is clearly embedded in university curricula, there needs to be well-funded research programmes that allow different methods to be developed and trialled over extended periods in higher education engineering programmes.Scopus© Citations 47 338 - PublicationProbability-based assessment of the durability characteristics of concretes manufactured using CEM II and GGBS bindersThis paper presents an overview of an investigation into the durability characteristics of blends of GGBS with CEM II/A Portland cements. The introduction of the Emission Trading Scheme has focussed attention on the carbon footprint arising from concrete construction, leading to many countries employing cementitious binder combinations not previously used. In Ireland for example concrete practice has recently changed to allow the addition of GGBS to CEM II/A cements at the concrete mixer, dependent on these blends providing adequate durability. To demonstrate this performance, specific research was conducted into the influence of GGBS addition on resistance to chloride ingress and carbonation, as well as compressive strength. The data from the testing was then used as input parameters for a number of probabilistic models describing chloride and carbonation related deterioration mechanisms. The influence of GGBS content on the expected service life is determined and compared to other research in this area
883Scopus© Citations 45 - PublicationReactivity assessment of aggregates : the role of chert crystallinity(2005-05)
; A systematic assessment scheme for determining the alkali reactivity of aggregates has been developed for international use. Expansion tests were conducted on Irish aggregates. Aggregates were subjected to a sequence of tests for alkali reactivity: petrographic examination and mortar bar and concrete prism expansion testing. No cases of damaging alkali-silica reaction have been identified to date in Ireland despite the presence of chert in significant commercial sources. Chert-bearing Irish aggregates performed poorly in expansion tests despite an exemplary service record. Chert crystallinity was examined through domain size and quartz crystallinity index. The crystallinity study helped explain the apparently anomalous behavior of the aggregates in tests. A preliminary study of the effect of alkali loading provided confirming evidence. It is suggested that enhanced crystallinity raises the alkali threshold value for reaction to one intermediate between that experienced in practice and in tests.1561 - PublicationThe influence of recycled asphalt pavement on the fatigue performance of asphalt concrete base courses(American Society of Civil Engineers, 2010-06)
; ; ; This paper presents the physical properties of Recycled Asphalt Pavement (RAP) and its influence on the mechanical performance of a binder course asphalt pavement mix. A series of binder course mixes were designed containing varying percentages of RAP. A mix made from only virgin material was selected as the control mix for the investigation. The effect of introducing RAP into the binder course mix was evaluated through a series of laboratory tests including the Marshall test, the indirect tensile stiffness modulus Test, the indirect tensile fatigue test and the water sensitivity test. A Circular Wheel Track (CWT) was developed in order to study the dynamic effects of a rolling wheel travelling over an asphalt pavement. The CWT was commissioned within a temperature controlled room along with a customised data acquisition system. The system involves the testing of rectangular slabs and allows for the investigation of dynamic tensile strain. The laboratory tests have shown that the introduction of RAP to the binder course mix resulted in an improvement in all mechanical properties. In particular, it was found that the mix containing up to 30% RAP, displayed improved fatigue resistance relative to the control mix manufactured from virgin materials.Scopus© Citations 70 2602