Now showing 1 - 10 of 14
  • Publication
    Assessment of ultrasonic signals to determine the early age properties of concretes incorporating secondary cementitious materials
    Secondary cementitious materials (SCMs) such as ground granulated blast-furnace slag (GGBS) are used in increasing quantities in concrete practice internationally. While these materials offer benefits such as reduced CO2 and a more dense microstructure, they also have drawbacks in terms of slower initial gain of strength. There are significant financial implications associated with this, as it can lead to delays in the construction process. Key to overcoming this challenge is the development of a methodology to assess the early-age stiffness development in concretes manufactured using GGBS. This paper presents the results of a study into the application of ultrasonic sensors to assess the early age concrete stiffness. A novel wavelet-based approach is used to overcome the difficulties associated with wave reflections and classical wave theory is used to determine the concrete small-strain stiffness based on P and S wave velocities. It was found that the results are largely in agreement with those obtained using standard strength testing, suggesting potential practical applications of this method.
  • Publication
    The performance of Irish aggregates in the 'ultra-accelerated test' for alkali-aggregate reactivity with particular reference to chert content
    Irish aggregates have a satisfactory history of service regarding alkali-aggregate reaction despite containing significant amounts of chert and use for a period in conjunction with cements of high alkali level. An investigation was conducted of the performance in the draft RILEM ‘ultra-accelerated mortar-bar test’ of 23 individual aggregates and 14 combinations found in Irish practice. An X-ray diffraction study was also carried out. Definitive expansion limits have yet to be finalised but a value of 0.15% after 14 days immersion has been suggested as the innocuous/deleterious threshold and 0.25% expansion is suggested as the lower limit for reactive aggregates. Despite their satisfactory history of use, almost half of the aggregates tested individually and one third of the combinations exceeded the innocuous/deleterious threshold value. However, the lower limit for reactive aggregates was reached by only four individual aggregates and by one of the combinations. The X-ray diffraction study revealed the presence of well-crystallised quartz, confirming the likelihood that the aggregates would not be reactive. The highest expansions were recorded in samples from argillaceous limestones and those containing small amounts of greywacke and chalcedonic chert. As expected, there was no correlation between chert content and degree of expansion. It is concluded that most Irish cherts are unreactive; that the draft mortar-bar test returns pessimistic results and is therefore a suitable screening test but could not be used universally for definitive assessment unless national expansion limits could be agreed in the place of use; and that X-ray diffractometry may be used in conjunction with the rapid screening test to assist early judgement on likely reactivity.
  • Publication
    Domain size as a parameter for studying the potential alkali-silica reactivity of chert-bearing aggregates
    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
  • Publication
    Numerical Model for Quantifying Degree of Hydration in Concrete Mixes with Reduced CO2 Footprint
    The widespread application of innovative cementitious combinations in concrete raises the need for more comprehensive investigation of the resulting concrete properties. Early age behaviour is a major factor to be addressed, and tools are required for quantifying the hydration state of concrete members, particularly at early-ages. Numerical models can potentially be used in mass concrete construction to predict and prevent possible thermal crack formation. They also provide an indirect means for characterizing development of the hydration reaction in concrete. The latter can then be utilised in modelling and predicting secondary concrete properties, such as diffusion coefficient. This is gaining increasing importance as we harness the ability to develop innovative combinations. The cement industry is estimated to be responsible for about 7% of the carbon dioxide generated globally. As such, reducing the amount of CO2 emitted during cement production is a key issue if the construction industry is to fully participate in sustainable development. Under the terms of the Kyoto Protocol Emissions Trading Scheme it is also potentially profitable for cement companies to reduce their CO2 emissions. By using blended cement instead of ordinary Portland cement, it is possible to lower the share of clinker in cement, resulting in reduced CO2 and energy emissions. In Ireland, CEM II now accounts for over 80% of the Irish cement production portfolio. GGBS is a by-product of steel industry and a common replacement for cement. When compared to Portland cement it has a reduced CO2 footprint and concretes containing GGBS are less prone to deterioration due to aggressive chemical attacks. Its use has the potential to produce more durable concrete with increased service life, lower maintenance costs and a lower carbon footprint, increasing the sustainability of concrete construction. The aim of the current study is to use numerical models to quantify the development of heat of hydration when mixtures of CEM II and GGBS are utilised. Experiments were conducted where the temperature profiles in 4 different mixes of concrete (CEM II with 0%, 30%, 50% and 70% GGBS) are recorded. This was achieved by casting 6 identical concrete samples from each mix, with thermocouples embedded to record the internal temperature of the mix at regular time steps. Temperature changes of the mix are then used to quantify the heat evolved, based on the principles of heat transfer. To account for the combined effect of time and temperature on hydration development, activation energy of the mix is used, along with the equivalent age maturity method. Total heat of hydration is determined based on the composition and amount of cementitious materials. It has long been accepted that the liberated heat of hydration, divided by the total available heat of hydration is a good measure of the degree of hydration. The experimental data describing hydration development with equivalent age are then used to calibrate the exponential formulation presenting the S-shaped hydration curve. Values of β, τ, and αu (the hydration parameters) are obtained for each mix, from the results of multivariate non-linear regression analysis. Comments on the use of this method in quantifying concrete hydration are then made.
  • Publication
    Biochemical attack on concrete in wastewater applications : a state of the art review
    The 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.
  • Publication
    Development of calcium sulfate - ggbs - Portland cement binders
    Binders 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
  • Publication
    Performance of concrete incorporating GGBS in aggressive wastewater environments
    Concrete 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
  • Publication
    Reactivity assessment of aggregates : the role of chert crystallinity
    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.
  • Publication
    A study of the influence of slag alkali level on the alkali-silica reactivity of slag concrete
    Ground 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
  • Publication
    Application of Bologna cycle programme structures and the European credit transfer system to Irish civil engineering programmes
    (Taylor & Francis, 2020-03-30) ;
    The 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.
      113Scopus© Citations 2