Hydration of multi-component cements containing cement clinker, slag, calcareous fly ash and limestone

Calcareous fly ashes are high-potential reactive supplementary cementitious materials, which present an interesting alternative to slowly reacting siliceous fly ashes and to slags, which availability is more and more limited. Themain factor against an accurate qualification and a wide use of calcareous fly ashes in cement is their significant and inherent heterogeneity and variability. Current techniques often fail to characterize the dominant, most reactive, amorphous fraction of the ashes. As a result these fly ashes have not been researched much and many aspects of their reactivity in cement remain ill understood. These include the phase assemblages, microstructure development, strength and performance in aggressive environments. This thesis focuses first on the characterization of the calcareous fly ashes. A new technique based on SEM-EDS full element mapping was developed to identify and characterize the different glassy components in fly ash. This technique was further developed to track the consumption of the individual anhydrous fly ash glasses in hydrating cement paste. A detailed study using synthetic glasses was carried out to investigate the factors influencing glass reaction in cement. Dissolution experiment in alkaline solution and the consumption of the glasses in paste indicated that the key factors of the glass reactivity are the fineness and the degree of depolymerisation of the glass structure. The latter was determined from the chemical composition of glass. The detailed knowledge of the fly ash reaction and the amounts of the elements supplied were linked the phase assemblage, notably the composition of the C-S-H, the amount of AFmphases and the maximumamount of limestone that can react in the given system. Matrix development in composite cements was followed and related to macroscopic aspects of strength and permeability. There are many ways to optimize the replacement of clinker with SCMs. This thesis illustrates an approach that attempts to link the micro- and macro- structural properties not only to a particular fly ash or slag but rather to the amounts and reactivity of their constituent glasses. This way a more fundamental and general understanding is gained, which could forma base for a systematic and deliberate research of the composite cements

Toward an indexing approach to evaluate fly ashes for geopolymer manufacture

Variations between fly ashes can lead to significant differences in the geopolymers derived from them, in both microstructural and mechanical properties. This study assesses the effect of physical, crystallographic and chemical characteristics of fly ash on geopolymerisation performance and the strength of the resulting binders. Physical and glass chemistry factors are combined to develop a comprehensive index to evaluate the suitability of fly ashes for the production of high-strength geopolymers. An equation for this index is proposed, developed using five typical low-calcium fly ashes and then validated against a further eight literature datasets, showing a good relationship between the ranking order of the calculated index and the compressive strengths of geopolymer pastes produced with comparable activator and paste workability. This index can be used to screen the source materials, which is of significant value in moving alkali activated cements towards acceptance in practice

Reactivity tests for supplementary cementitious materials: RILEM TC 267-TRM phase 1

A primary aim of RILEM TC 267-TRM: “Tests for Reactivity of Supplementary Cementitious Materials (SCMs)” is to compare and evaluate the performance of conventional and novel SCM reactivity test methods across a wide range of SCMs. To this purpose, a round robin campaign was organized to investigate 10 different tests for reactivity and 11 SCMs covering the main classes of materials in use, such as granulated blast furnace slag, fly ash, natural pozzolan and calcined clays. The methods were evaluated based on the correlation to the 28 days relative compressive strength of standard mortar bars containing 30% of SCM as cement replacement and the interlaboratory reproducibility of the test results. It was found that only a few test methods showed acceptable correlation to the 28 days relative strength over the whole range of SCMs. The methods that showed the best reproducibility and gave good correlations used the R3 model system of the SCM and Ca(OH)2, supplemented with alkali sulfate/carbonate. The use of this simplified model system isolates the reaction of the SCM and the reactivity can be easily quantified from the heat release or bound water content. Later age (90 days) strength results also correlated well with the results of the IS 1727 (Indian standard) reactivity test, an accelerated strength test using an SCM/Ca(OH)2-based model system. The current standardized tests did not show acceptable correlations across all SCMs, although they performed better when latently hydraulic materials (blast furnace slag) were excluded. However, the Frattini test, Chapelle and modified Chapelle test showed poor interlaboratory reproducibility, demonstrating experimental difficulties. The TC 267-TRM will pursue the development of test protocols based on the R3 model systems. Acceleration and improvement of the reproducibility of the IS 1727 test will be attempted as well

Solid-state nuclear magnetic resonance spectroscopy of cements

Cement is the ubiquitous material upon which modern civilisation is built, providing long-term strength, impermeability and durability for housing and infrastructure. The fundamental chemical interactions which control the structure and performance of cements have been the subject of intense research for decades, but the complex, crystallographically disordered nature of the key phases which form in hardened cements has raised difficulty in obtaining detailed information about local structure, reaction mechanisms and kinetics. Solid-state nuclear magnetic resonance (SS NMR)spectroscopy can resolve key atomic structural details within these materials and has emerged as a crucial tool in characterising cement structure and properties. This review provides a comprehensive overview of the application of multinuclear SS NMR spectroscopy to understand composition–structure–property relationships in cements. This includes anhydrous and hydrated phases in Portland cement, calcium aluminate cements, calcium sulfoaluminate cements, magnesia-based cements, alkali-activated and geopolymer cements and synthetic model systems. Advanced and multidimensional experiments probe 1 H, 13 C, 17 O, 19 F, 23 Na, 25 Mg, 27 Al, 29 Si, 31 P, 33 S, 35 Cl, 39 K and 43 Ca nuclei, to study atomic structure, phase evolution, nanostructural development, reaction mechanisms and kinetics. Thus, the mechanisms controlling the physical properties of cements can now be resolved and understood at an unprecedented and essential level of detail

A new quantification method based on SEM-EDS to assess fly ash composition and study the reaction of its individual components in hydrating cement paste

Calcareous fly ashes are high-potential reactive residues for blended cements, but their qualification and use in concrete are hindered by heterogeneity and variability. Current characterization often fails to identify the dominant, most reactive, amorphous fraction of the ashes. We developed an approach to characterize ashes using electron microscopy. EDS element composition of millions of points is plotted in a ternary frequency plot. A visual analysis reveals number and ranges of chemical composition of populations: silicate, calcium-silicate, aluminosilicate, and calcium-rich aluminosilicate. We quantified these populations in four ashes and followed their hydration in two Portland-ash systems. One ash reacted at a moderate rate: it was composed of 70 vol.% of aluminosilicates and calcium-silicates and reached 60% reaction at 90 days. The other reacted faster, reaching 60% at 28 days due to 55 vol.% of calcium-rich aluminosilicates, but further reaction was slower and 15 vol.% of phases, the silica-rich ones, did not react

Characterization of fly ashes by a novel method in the scanning electron microscope

Copyright © 2019 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. In this paper, we show a new technique to characterize fly ashes using scanning electron microscopy (SEM). Chemical composition of millions of points is measured by SEM-energy dispersive X-ray spectroscopy and plotted in a ternary frequency plot. This new and straightforward way of displaying microscope data makes it easy to understand and assess the number, the approximate chemical composition, and the relative proportions of populations that constitute the fly ash. For quantitative characterization of the raw fly ash, these populations are grouped as predominantly silicate, calcium-silicate, aluminosilicate, and calciumrich aluminosilicate. The same technique is then used to track these anhydrous fly ash fractions in blended cements during hydration and thus provide crucial information on the reactivity of different glasses in cementitious systems

Fly ash as an assemblage of model Ca-Mg-Na-aluminosilicate glasses

Model Ca-Mg-Na-aluminosilicate glasses based on compositions found in a calcareous fly ash were synthesised and their reactivity assessed in NaOH solution and in Portland cement paste. It was found that the reactivity followed the same trend in both systems and that the reaction of the glasses in pastes was very similar to that of the components of similar composition in the real fly ash. This finding indicates that the reactivity of glass in cement can be directly linked to the chemical composition of the glass. Further, when the reactivity of the glasses was normalized to their surface area, it was found that there exists a strong correlation with the NBO/T, the ratio of non-bridging oxygens and tetrahedral ions in the glass

Systems of building influence on the environment comparison – Geoenergetics Laboratory of Drilling, Oil and Gas Faculty AGH-UST contribution to evaluation methodology

Zagadnienie zrównoważonego budownictwa, z powodu nieustającego wzrostu cen surowców mineralnych oraz energii, stało się poważnym wyzwaniem naukowym, zajmując coraz więcej miejsca w pracach badawczych jednostek naukowych na całym świecie. Istnieje duża liczba metod określania oddziaływania budynku na środowisko oraz wzajemnego porównywania obiektów budowlanych. W pracy przedstawiono kilka najbardziej znanych metod (programów) oceny oddziaływania budynku na środowisko. Opisano również zbiór norm, które powstały w celu normalizacji metod kompleksowej oceny oddziaływania budynku na środowisko. Porównano dwa najpopularniejsze programy: British Establishment Environmental Assessments Method (BREEAM) i Leadership in Energy and Environmental Design (LEED). W artykule zaprezentowany został model oceny środowiskowej budynków, który został opracowany w Laboratorium Geoenergetyki Wydziału Wiertnictwa Nafty i Gazu AGH, na podstawie aktualnie istniejących metodyk, przede wszystkim programów E-Audyt i BREEAM. Model ten poszerzono o zagadnienia, które nie występowały w aktualnie stosowanych programach, a które dotyczą propozycji wynikających ze specyfiki pracy podziemnych magazynów ciepła. Podsumowano również realizację projektu badawczego, który miał za zadanie określić efektywność magazynowania ciepła w górotworze z zastosowaniem otworowych wymienników ciepła różnej konstrukcji. Zaproponowano nowe rozwiązania z branży geologiczno-energetycznej, które zdaniem autorów, powinny zostać ujęte w metodach kompleksowej oceny budynku, szczególnie w polskich warunkach klimatycznych.Due to rising prices of mineral resources and energy, sustainable development in construction industry became an important scientific problem. Recently, sustainable building engineering problem is the base of research for many scientific and development centers. There is a lot of methods of labeling buildings’ influence on the environment and comparing building objects. Several of them were presented in this article and the best-known Building Establishment Environmental Assessments Method (BREEAM) and Leadership in Energy and Environmental Design (LEED) were compared. The set of standards that were elaborate in order to standardize the methods of a comprehensive assessment of the environmental impact of the building were also submitted. In addition, the article presented model of environmental assessment of building, that was developed in Laboratory of Geoenergetics at Faculty of Drilling, Oil and Gas AGH-UST, based on currently existing systems, in particular E-audit and BREEAMprograms. This model was expanded to cover issues that are not used in currently applied programs, and which concern the proposals arising from the operation of underground heat storages. The research project, that was designed to determine the advisability of heat storage in the ground was summarize. New solutions connected with geological and energetic fields of science were proposed. According to the authors, these ideas should be applied for complex evaluation of the building, especially in polish climate conditions

Properties and pozzolanic reactivity of flash calcined dredging sediments

Dredging of ports, harbours and waterways generates vast amounts of sediments that find few applications and need to be disposed of. In the port of Antwerp, Belgium, each year 450.000 t (dry matter) of dredging sediments are mechanically dewatered and stockpiled. This paper investigates flash calcination of the clay-rich dredged sediments as a sustainable solution to develop novel pozzolanic supplementary cementitious materials (SCM) for blended cement. The dredging sediments were mainly comprised of clay minerals (2:1 clays and kaolinite), quartz, calcium carbonates and an amorphous phase. Sulfur and chloride contents were relatively low. Flash calcination at 820, 865 and 905°C reduced the total organic carbon fraction but did not alter the content of chloride and sulfate. The clay minerals in the dredged sediments were entirely dehydroxylated and calcium carbonates were largely decarbonated by the calcination treatment. Part of the CaO released in the decomposition of the calcium carbonates reacted with the dehydroxylated clays to form the main reactive amorphous component at 45- 51 mass%. Another part of the CaO reacted with sulfate to form around 2 mass% of anhydrite. Electron microscopy showed that the Ca-rich reactive material partly consisted of spherical particles indicative for melt formation. Melt formation and sintering were more extensive at higher calcination temperatures (865 and 905°C); they did not change the particle size distribution significantly, but led to a remarkable reduction in the BET specific surface area and related particle surface roughness. The calcined dredging sediments clearly demonstrated a pozzolanic reactivity superior to that of Class F fly ash, which demonstrates their high potential as a new pozzolanic SCM for the production of low-CO2 blended cements.publisher: Elsevier articletitle: Properties and pozzolanic reactivity of flash calcined dredging sediments journaltitle: Applied Clay Science articlelink: http://dx.doi.org/10.1016/j.clay.2016.04.019 content_type: article copyright: © 2016 Elsevier B.V. All rights reserved.status: publishe