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Robert Cerný - One of the best experts on this subject based on the ideXlab platform.
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kinetics of pozzolanic reaction and carbonation in ceramic lime system thermogravimetry and solid state nmr spectroscopy study
Journal of building engineering, 2020Co-Authors: Martin Keppert, Lenka Scheinherrová, Libor Kobera, Jiří Brus, Magdaléna Doleželová, Robert CernýAbstract:Abstract Waste red-clay ceramic powder (RCC) is a pozzolanic material which is currently not commercially used, but high amount of “brick fraction” of construction and demolition waste may become a source for a cheap pozzolanic additive for Portland cement and lime-based binders. A sort of specific of RCC, compared to other pozzolans, is the higher content of non-reactive minerals. Pozzolanic reaction, taking place in lime-based system, is inevitably accompanied by carbonation of the lime; these two processes are concurrent with respect to the lime consumption. Products of hydration (C–S–H and calcium aluminate hydrate phases) and carbonation (CaCO3) are contributing to the strengthening of the system. The goal of this research has been to evaluate the rate and mechanism of hardening of the RCC – lime mixtures. The relative rate of pozzolanic reaction and carbonation was studied over one-year period in RCC – lime pastes by help of thermal analysis and 23Na, 27Al and 29Si Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy (MAS NMR), accompanied by porosimetry and compressive strength determination. The kinetics of lime conversion to hydration products and CaCO3 was determined by the help of thermogravimetry and described by Jander's equation. The highest rate of pozzolanic reaction, as well as the highest strength, reached mixture of 70% of RCC and 30% of lime; such high effective Pozzolana content is caused by the phase composition of ceramic powder – it contains lower amount of reactive species, compared to metakaolin or other pozzolans. The formation of AlVI hydration products (AFm and AFt phases) took place within initial 3 days in all mixtures, while the content of C–S–H hydrates grown over the whole year of the experiment.
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physical and chemical characterization of technogenic pozzolans for the application in blended cements
Construction and Building Materials, 2018Co-Authors: Martina Zaleska, Milena Pavlikova, Zbysek Pavlik, Ondřej Jankovský, Jaroslav Pokorný, Vratislav Tydlitat, Petr Svora, Robert CernýAbstract:Abstract Technogenic pozzolans present a diverse group of materials. They differ in their origin, chemical and mineralogical composition, granulometry, or amorphous content. However, the analysis of their properties before utilization as supplementary cementitious materials is often insufficient which may lead to unexpected results in some cases. In this paper, a system of physical and chemical techniques for the characterization of technogenic pozzolans is proposed, which takes into account both functional and environmental aspects. The system is hierarchical and consists of three sets of methods which assess consecutively the fundamental physical and chemical prerequisites, reactivity, and performance in a blend with Portland cement. The practical application of the methodology is demonstrated for the example of fly ash from a coal power plant as the most common technogenic pozzolan. Experimental results show that the proposed system has good prerequisites to serve as a good guidance for both research and building practice.
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waste ceramics as supplementary cementitious material characterization and utilization
Applied Reconfigurable Computing, 2014Co-Authors: Martin Keppert, Milena Pavlikova, Jaromir žumar, Anton Trnik, Monika Cachova, Robert CernýAbstract:Materials containing thermally treated clay minerals are well known for their pozzolanity, i.e. ability to react with calcium hydroxide to cementing compounds. Finely ground ceramics have been used as pozzolan since ancient times and nowadays they again attracts attention because of the current effort to utilize waste as secondary raw material. Contrary to other pozzolans (fly ash, metakaolin etc.) ceramics contain not only a reactive phase but also a certain amount of crystalline minerals which do not take part in the hydration process. The paper deals with finely ground ceramic powder generated during production of brick blocks.
Jean Noël Yankwa Djobo - One of the best experts on this subject based on the ideXlab platform.
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Natural pozzolan based geopolymers: A review on mechanical, microstructural and durability characteristics
Construction and Building Materials, 2018Co-Authors: Rafia Firdous, Dietmar Stephan, Jean Noël Yankwa DjoboAbstract:Abstract Natural pozzolans are tremendous source of reactive silica and alumina required for geopolymer synthesis as an alternative binder for ordinary Portland cement. They are available at a comparatively low cost and generate a low ecological footprint through their simple extraction. Following review paper summarizes the mechanical and durability characteristics as well as the microstructural properties of natural pozzolan based geopolymers and their potential as binding material. The microstructural characteristics are based on the advanced analytical techniques used so far to understand geopolymerization, the phase composition, mechanical and durability properties evolution. From this review is obvious that significant analytical techniques have been successfully carried out on fresh and hardened natural pozzolan based geopolymer obtained in alkaline medium, which helped to understand underlying chemical reaction and external factors affecting final properties. These analyses have shown that natural pozzolan based geopolymer has potential to be used as sustainable building materials. But, for its large scale utilisation there is need to upscale the manufacturing process at a pilot-plant in order to address the macroscopic challenges that may arise at that level.
Ali Akbar Ramezanianpour - One of the best experts on this subject based on the ideXlab platform.
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Effect of heat treatment on reactivity-strength of alkali-activated natural pozzolans
Construction and Building Materials, 2011Co-Authors: Dali Bondar, Cyril J. Lynsdale, Neil B. Milestone, Nemat Hassani, Ali Akbar RamezanianpourAbstract:Abstract Natural pozzolans can be activated and condensed with sodium silicate in an alkaline environment to synthesize high performance cementitious construction materials with low environmental impact. The nature of the starting materials including mineral composition, chemical composition and crystal structure groups affects the formation of the geopolymer gel phase. In this paper, the pozzolanic activities of five natural pozzolans are studied. From XRD and XRF results, most of the raw materials contain zeolite clay minerals and have a high loss on ignition. Therefore, before use, samples were calcined at 700, 800 and 900 °C, respectively. The improvement in pozzolanic properties was studied following heat treatment including calcinations and/or elevated curing temperature by using alkali solubility and compressive strength tests. The results show that pozzolan containing sodium zeolite clinoptilolite can be used to prepare a moderate to high strength binder by heat treatment and calcinations can impart disorder hornblende as a constituent of pozzolan with no amorphous phase to prepare a moderate strength binder.
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Engineering Properties of Alkali-Activated Natural Pozzolan Concrete
ACI Materials Journal, 2011Co-Authors: Dali Bondar, Cyril J. Lynsdale, Neil B. Milestone, Nemat Hassani, Ali Akbar RamezanianpourAbstract:The development of alkali-activated binders with superior engineering properties and longer durability has emerged as an alternative to ordinary portland cement (OPC). It is possible to use alkali-activated natural pozzolans to prepare environmentally friendly geopolymer cement leading to the concept of sustainable development. This paper presents a summary of an experimental work that was conducted to determine mechanical strength, modulus of elasticity, ultrasonic pulse velocity, and shrinkage of different concrete mixtures prepared with alkali-activated Iranian natural pozzolans—namely Taftan andesite and Shahindej dacite, both with and without calcining. Test data were used for Taftan pozzolan to identify the effects of water-binder ratios (w/b) and curing conditions on the properties of the geopolymer concrete, whereas the influence of material composition was studied by activating Shahindej pozzolan both in the natural and calcined states. The results show that alkali-activated natural pozzolan (AANP) concretes develop moderate-to-high mechanical strength with a high modulus of elasticity and a shrinkage much lower than with OPC.
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Effect of adding mineral additives to alkali-activated natural pozzolan paste
Construction and Building Materials, 2011Co-Authors: Dali Bondar, Cyril J. Lynsdale, Neil B. Milestone, Nemat Hassani, Ali Akbar RamezanianpourAbstract:Natural pozzolans are raw materials from geological deposits with a range of chemical compositions that when combined with suitable alkali activators can be converted to geopolymer cement for concrete production. In this paper the concept of adding mineral additives to enhance the properties of geopolymer cement is introduced. Taftan andesite, a natural Iranian pozzolan, was used to study the effect of adding mineral additives such as kaolinite, lime and other calcined pozzolans on the compressive strength of geopolymer cement under both normal and autoclave curing. Scanning electron microscopy (SEM)/energy dispersive X-ray (EDX) was used to determine the composition of the gel phase in both alkali-activated Taftan pozzolan with and without mineral additions. The work has shown that deficiencies in SiO2, Al2O3 and CaO content in the raw natural pozzolan can be compensated for by adding mineral additives for enhanced properties.
Dali Bondar - One of the best experts on this subject based on the ideXlab platform.
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Effect of heat treatment on reactivity-strength of alkali-activated natural pozzolans
Construction and Building Materials, 2011Co-Authors: Dali Bondar, Cyril J. Lynsdale, Neil B. Milestone, Nemat Hassani, Ali Akbar RamezanianpourAbstract:Abstract Natural pozzolans can be activated and condensed with sodium silicate in an alkaline environment to synthesize high performance cementitious construction materials with low environmental impact. The nature of the starting materials including mineral composition, chemical composition and crystal structure groups affects the formation of the geopolymer gel phase. In this paper, the pozzolanic activities of five natural pozzolans are studied. From XRD and XRF results, most of the raw materials contain zeolite clay minerals and have a high loss on ignition. Therefore, before use, samples were calcined at 700, 800 and 900 °C, respectively. The improvement in pozzolanic properties was studied following heat treatment including calcinations and/or elevated curing temperature by using alkali solubility and compressive strength tests. The results show that pozzolan containing sodium zeolite clinoptilolite can be used to prepare a moderate to high strength binder by heat treatment and calcinations can impart disorder hornblende as a constituent of pozzolan with no amorphous phase to prepare a moderate strength binder.
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Engineering Properties of Alkali-Activated Natural Pozzolan Concrete
ACI Materials Journal, 2011Co-Authors: Dali Bondar, Cyril J. Lynsdale, Neil B. Milestone, Nemat Hassani, Ali Akbar RamezanianpourAbstract:The development of alkali-activated binders with superior engineering properties and longer durability has emerged as an alternative to ordinary portland cement (OPC). It is possible to use alkali-activated natural pozzolans to prepare environmentally friendly geopolymer cement leading to the concept of sustainable development. This paper presents a summary of an experimental work that was conducted to determine mechanical strength, modulus of elasticity, ultrasonic pulse velocity, and shrinkage of different concrete mixtures prepared with alkali-activated Iranian natural pozzolans—namely Taftan andesite and Shahindej dacite, both with and without calcining. Test data were used for Taftan pozzolan to identify the effects of water-binder ratios (w/b) and curing conditions on the properties of the geopolymer concrete, whereas the influence of material composition was studied by activating Shahindej pozzolan both in the natural and calcined states. The results show that alkali-activated natural pozzolan (AANP) concretes develop moderate-to-high mechanical strength with a high modulus of elasticity and a shrinkage much lower than with OPC.
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Effect of adding mineral additives to alkali-activated natural pozzolan paste
Construction and Building Materials, 2011Co-Authors: Dali Bondar, Cyril J. Lynsdale, Neil B. Milestone, Nemat Hassani, Ali Akbar RamezanianpourAbstract:Natural pozzolans are raw materials from geological deposits with a range of chemical compositions that when combined with suitable alkali activators can be converted to geopolymer cement for concrete production. In this paper the concept of adding mineral additives to enhance the properties of geopolymer cement is introduced. Taftan andesite, a natural Iranian pozzolan, was used to study the effect of adding mineral additives such as kaolinite, lime and other calcined pozzolans on the compressive strength of geopolymer cement under both normal and autoclave curing. Scanning electron microscopy (SEM)/energy dispersive X-ray (EDX) was used to determine the composition of the gel phase in both alkali-activated Taftan pozzolan with and without mineral additions. The work has shown that deficiencies in SiO2, Al2O3 and CaO content in the raw natural pozzolan can be compensated for by adding mineral additives for enhanced properties.
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Alkali activation of Iranian natural pozzolans for producing geopolymer cement and concrete
2009Co-Authors: Dali BondarAbstract:The challenge for the civil engineering community in the near future will be to realize the building of structures in harmony with the concept of sustainable development, through the use of high performance materials which have low environmental impact and can be produced at reasonable cost. Geopolymers are novel binder materials that could provide a route towards this objective. Although research on geopolymer has advanced, most of the previous research conducted on geopolymers has dealt with pastes and concentrated on the material's chemistry and microstructure. There is little information available concerning the engineering and durability properties of geopolymer concrete and none considering the use of natural pozzolans for production of geopolymer concrete. This investigation has studied the potential of using five natural pozzolans from Iran as geopolymer precursors. Most of the raw materials contain zeolites and clay minerals and have a high loss on ignition. Therefore, trials were made where samples were calcined at 700, 800 and 900°C. The solubility of both the raw and calcined materials in an alkaline solution was used as an indicator for pozzolanic activity. Improvements in pozzolanic properties due to heat treatment and elevated curing temperatures (20, 40, 60, and 80°C) were studied by using alkali solubility, XRD and compressive strength tests. It has been found that geopolymer binders can be synthesized by activating natural pozzolans and condensing them with sodium silicate in a highly alkaline environment. A new model is presented which allows the prediction of the alkali activated pozzolan strength from information on their crystallinity, chemical compositions and alkali solubility. Two types of Iranian natural pozzolans, namely Taftan which can be activated without calcination and Shahindej which was calcined were selected for further activation to study the effect of the alkaline medium on the strength of the alkali-activated natural pozzolan. The effect of the type, form, and concentration (molarities =2.5, 5.0, 7.5, 10.0 M) of the alkaline hydroxide, the modulus of sodium silicate (Si02INa20 ratio =2.1, 2.4, 3.1) and different curing conditions on the geopolymerisation of the above two natural pozzolans were studied. The optimum range and contributions for each factor is suggested based on their effect on compressive strength. An optimum paste formulation has been developed for concrete mixing together with the procedure of addition of the raw materials to the reaction mixture and suitable curing methods for producing the geopolymer concrete derived from them. The properties of this geopolymer concrete in both the fresh and hardened states have been investigated in terms of setting time, workability, air content, compressive strength, splitting tensile strength, static modulus of elasticity, ultrasonic pulse velocity, and drying shrinkage. Studies related to durability such as gas permeability, chloride ion penetration, and sulphate resistance have been undertaken and compared to these for typical OPC concretes. Some problems were encountered in applying the standard concrete durability tests. In this study attempts have been made to determine the relationships between the different properties of geopolymer concrete with its compressive strength and compared to results for ope concrete, to help to explain the differences between alkali-activated natural pozzolan concrete and ope concrete. In the countries which have large resources of natural pozzolan, geopolymer concrete based on alkali activation of these resources can help decrease the energy consumption and environmental impacts involved in using traditional cement pastes.
Rafia Firdous - One of the best experts on this subject based on the ideXlab platform.
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Natural pozzolan based geopolymers: A review on mechanical, microstructural and durability characteristics
Construction and Building Materials, 2018Co-Authors: Rafia Firdous, Dietmar Stephan, Jean Noël Yankwa DjoboAbstract:Abstract Natural pozzolans are tremendous source of reactive silica and alumina required for geopolymer synthesis as an alternative binder for ordinary Portland cement. They are available at a comparatively low cost and generate a low ecological footprint through their simple extraction. Following review paper summarizes the mechanical and durability characteristics as well as the microstructural properties of natural pozzolan based geopolymers and their potential as binding material. The microstructural characteristics are based on the advanced analytical techniques used so far to understand geopolymerization, the phase composition, mechanical and durability properties evolution. From this review is obvious that significant analytical techniques have been successfully carried out on fresh and hardened natural pozzolan based geopolymer obtained in alkaline medium, which helped to understand underlying chemical reaction and external factors affecting final properties. These analyses have shown that natural pozzolan based geopolymer has potential to be used as sustainable building materials. But, for its large scale utilisation there is need to upscale the manufacturing process at a pilot-plant in order to address the macroscopic challenges that may arise at that level.