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Richardson, Mark G.
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Richardson, Mark G.
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Richardson, Mark G.
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Now showing 1 - 7 of 7
- 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 - 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 - 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 - PublicationA study of the influence of slag alkali level on the alkali-silica reactivity of slag concreteGround granulated blast furnace slag (ggbs), can reduce the alkali load in concrete, despite its relatively high alkali content. Most research has been devoted to the efficacy of slag with an alkali content of less than 1.0% and this is reflected in guidance documents. A comparative assessment was made of the effect, if any, of the alkali level of ggbs on potential alkali-silica reactivity. Expansion tests were performed on a matrix of concrete mixes using Irish normal Portland cement, two slags of differing alkali content, three aggregates and alkali loads of 5 and 6 kg Na2Oeq./m(3). A replacement level of 50% was used throughout. No significant difference in behaviour was apparent, irrespective of aggregate type or alkali load, indicating that the alkali level of the slag is not a contributory factor at the 50% replacement level.
Scopus© Citations 40 1154 - PublicationApplication of Bologna cycle programme structures and the European credit transfer system to Irish civil engineering programmesThe objective of this study was to assess, through a cross-institutional comparison, whether higher education institutions in the Republic of Ireland have responded to Bologna Declaration first- and second-cycle programme restructuring and applied the European Credit Transfer System (ECTS) to similarly-accredited civil engineering programmes in a consistent manner. Assessment strategies were also examined. The predominant programme structure was the pre-Bologna ‘4+1’ structure, demonstrating limited national impact of the principles underpinning the Bologna Declaration cycle concept. The first-cycle programmes differed widely in terms of allocated student workload per ECTS credit as well as in the way that educational outcomes were assessed, which was primarily by written examination. There was no ‘best’ (or consensus) practice for applying the two-cycle programme structure or ECTS workload norms. This lack of national consensus reveals issues that may have relevance in other countries, 20 years after the signing of the Bologna Declaration.
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