The Experts below are selected from a list of 2010 Experts worldwide ranked by ideXlab platform
Moises Frias - One of the best experts on this subject based on the ideXlab platform.
-
characterization of ceramic based construction and demolition waste use as pozzolan in cements
Journal of the American Ceramic Society, 2016Co-Authors: Eloy Asensio, Moises Frias, Cesar Medina, Maria Isabel Sanchez De RojasAbstract:Depending on its composition and properties, construction and demolition waste (C&DW) may be used today as recycled aggregate to manufacture more eco-efficient concrete, for drainage or as a sub-base in roads and on occasion as a decorative or esthetic element in pedestrian pathways in parks and landscaped grounds. In Spain, 54% of C&DW is ceramic-based (CB-C&DW). Since the use of such waste as recycled aggregate is not envisaged in Spanish legislation, it is presently stockpiled in landfills, an environmentally, technically, and economically detrimental procedure. The CB-C&DW recycled at 12 Spanish waste management plants was assessed to determine the feasibility of its use as an alternative to Pozzolans such as silica fume and fly ash presently added to cement during manufacture. The proportion of ceramic-based material contained in this recycled waste varied from plant to plant. The effect of the ceramic-based material content on the chemical and mineralogical composition, morphology, and pozzolanic activity of CB-C&DW was explored in a more exhaustive study of two types of waste, one with 20 and the other with 100% ceramic-based material content. In light of its chemical and mineralogical composition, morphology and lime fixation capacity, this type of C&DW was found to be apt for use as a pozzolan, and hence as a valid alternative for manufacturing more eco-efficient cements.
-
mineralogy and microstructure of hydrated phases during the pozzolanic reaction in the sanitary ware waste ca oh 2 system
Journal of the American Ceramic Society, 2016Co-Authors: Cesar Medina, Moises Frias, Isabel Saez F Del Bosque, Eloy Asensio, Isabel Sanchez M De RojasAbstract:Despite technological improvements in its production process, the sanitary ware industry inevitably generates a certain volume of discards, products whose quality is not up to standard. The present paper is the first to scientifically explore clay-based sanitary ware waste (SW) with a view to its valorization as an addition in the design of new, more environmentally friendly cements. The focus is on characterization of the waste and its pozzolanicity, as well as the structural and microstructural changes taking place in the pozzolan/Ca(OH)2 system in the first 90 d of reaction. The findings show that pozzolanicity in clay-based waste is comparable to the activity observed in silica fume (SF) and higher than that found in other clay-based materials and fly ash (FA). The microstructural study of the clay-based waste/Ca(OH)2 system, in turn, reveals that the proportion of C–S–H gels rises with hydration time. These gels are characterized by long mean chain lengths (MCL) and low Ca/Si ratios. The intrinsic characteristics of this thermally activated clay-based waste qualify it as a type Q Pozzolans as defined in the European cement standards, making it apt for use in the manufacture of CEM II, IV, and V cements.
-
the effect of binary pozzolan mix on the mineralogical changes in the ternary activated paper sludge fly ash ca oh 2 system
Construction and Building Materials, 2013Co-Authors: Moises Frias, R Garcia, Vigil R De La Villa, Ernesto VillarAbstract:Abstract This paper presents for the first time the influence of mixing different thermally activated paper sludges (APS) and fly ash (FA) on the pozzolanic reaction kinetics in APS–FA–Ca(OH) 2 systems as a previous step to manufacture the future commercial ternary blended cements. In this study, two paper sludge wastes from different origins and activation conditions (laboratory (LS) and industrial (IS) scale) have been investigated, once mixed with fly ash at a ratio of 1:1 by weight. The results indicated that binary blends of Pozzolans exhibited a high pozzolanic activity, showing that the hydrated phases produced during the pozzolanic reaction depend on the origin and activation conditions of clay wastes. At all times of reaction, the predominant phase turn out to be the LDH structures when LS pozzolan was used; meanwhile for the IS pozzolan the C 4 A C ¯ H 12 along with the LDH were the main phases during the first 28 days.
R. Talero - One of the best experts on this subject based on the ideXlab platform.
-
synergic effect of friedel s salt from pozzolan and from opc co precipitating in a chloride solution
Construction and Building Materials, 2012Co-Authors: R. TaleroAbstract:Abstract Two prior papers on this subject have shown, with XRD and SEM techniques, that almost all pozzolanic additions can induce the rapid formation of Friedel’s salt in quantities in keeping with the reactive alumina, Al 2 O 3 r - (tetra- or penta-coordinated alumina) content of the pozzolan. The formation rate of Friedel’s salt of pozzolan origin has also been shown to be higher than the rate in the slower forming compound, whose origin is the C 3 A in OPC. Consequently, the plate-like hexagonal crystals are smaller and less perfectly shaped in fast- than in slow-forming Friedel’s salt. To describe the inter-relationships between these two non-expansive processes, a terminological analogy is drawn between the rapid and slow formation of Friedel’s salt and drug interaction. A common development in the treatment of certain diseases, drug interaction may be quantitative or qualitative and, depending on the end result, is typed under one of the following headings: additive synergy , partial antagonism , competitive antagonism , potentiating synergy , non-competitive antagonism or physiological and functional antagonism . Borrowing from this classification, the present study sought to determine whether the joint formation of Friedel’s salt from pozzolan and from OPC in a common chloride solution is synergic , additive, antagonistic or able to invert the expected outcome. To this end, 14 binders, 2 PC (1 OPC and 1 SRPC) and 12 blended cements containing 20% or 30% of one of six Pozzolans, were analysed with XRD technique. Water resistance, capillary absorption and total porosity were also determined, along with the chemical composition and physical properties of some cement tested. The experimental results showed that fast- and slow-forming Friedel’s salt precipitated in a common chloride solution not separately but inter-dependently and the closer the pozzolan particles were to the cement particles, the greater was that inter-dependence. Moreover, the joint precipitation – co-precipitation – of the Friedel’s salt from the Al 2 O 3 r - present in Pozzolans and the Friedel’s salt from the C 3 A present in OPC was, to use drug interaction terminology, consistently more synergic than additive . Furthermore, depending on the parameter considered and from a purely technological point of view, the practical implications of the Synergic Effect (SE) between the two types of Friedel’s salt were always beneficial. The experimental results showed, in addition, that the pozzolanic activity of three of the Pozzolans tested, C, M1 and M0 specially, once again proved to be more specific than generic in chloride and water environments. This would induce speedier chloride hydration of all or part of the C 3 A in the OPC fraction than when the OPC was hydrated without the pozzolan. Moreover, the Friedel’s salt from the Al 2 O 3 r - in these Pozzolans was the chief direct and indirect cause of the SE , in conjunction with the Friedel’s salt from the C 3 A in PC, due to their very specific pozzolanic activity in such chloride media. In contrast, when the pozzolan used was silica fume (SF), its pozzolanic activity is not also more specific than generic for the same result but for the contrary result, that is, SF is unspecific for the same result.
-
co precipitation of ettringite of rapid and slow formation consequence expansive synergic effect its demonstration by mortars and concretes
Materiales De Construccion, 2011Co-Authors: R. TaleroAbstract:Several prior papers have shown that enough Pozzolans can bring about rapid formation ettringite (from its Al 2 O 3 r- ). It has likewise been found that the formation rate of this ettringite is higher than the of slower forming ettringite originating from OPC (from its C 3 A). In this context: What type of effect will they ultimately produce? Addition? Synergism? Antagonism? or perhaps Inversion of final expansive action?. To reply to these questions, 4 PC and 12 blended cements containing 20%, 30% or 40% metakaolin, were tested using the ASTM C 452-68, EN 196-1 and RT-86:ΔL tests and also concrete specimens. The experimental results have shows that the joint precipitation in a common sulfate medium, of ettringite from pozzolan and from OPC, was always more synergic than additive , and the technical consequences of the Expansive Synergic Effect may be classified as beneficial, adverse or indifferent according to its sulfates content in excess is more or less adequate.
-
comparative and semi quantitative xrd analysis of friedel s salt originating from pozzolan and portland cement
Construction and Building Materials, 2011Co-Authors: R. Talero, Viviana Fátima Rahhal, Lidia Natalia Trusilewicz, A Delgado, C Pedrajas, R Lannegrand, Raul Mejia, Silvio Delvasto, F A RamirezAbstract:Abstract The Friedel’s salt (Fs) is often formed when reinforced concrete is attacked by chlorides from marine environmental and/or thaw salts. In this investigation, a semi-quantitative analysis and study of the Fs (2θ range = 11.16–11.34°) in the solid phase of the Frattini test was made by XRD analysis. For this purpose, two Portland cements (PC) P1 (14% C3A) and PY6 ( 1. All the Pozzolans exhibited different pozzolanic activity depending on the mineralogical composition of the Portland cement with which they were tested, although such differences were attributable more to their Al 2 O 3 r - (%) content than to their SiO 2 r - (%) content for the case of the Pozzolans A, C, M1 and M0 specially. Thus, M0, M1, C and A Pozzolans mainly, tend to sustain [OH−] content and react readily with Ca2+. On the contrary, for the SF and D Pozzolans was due to their SiO 2 r - (%) content only, which react with both, Ca2+ and OH− ions, in the same way. But despite what the physical state of D pozzolan is like SF, vitreous mainly and its SiO 2 r - content as well (practically), the size and shape of their respective particles (“frustules” for D, empty, perforated sheaths) are totally different, and as a consequence, their respective behaviour in the Frattini test has been different as well. 2. In this investigation, the Friedel’s salt (Fs) owns its formation to two different origins: the C3A of PC and to the reactive alumina, Al 2 O 3 r - , of Pozzolans which reaction with chloride ions, pointing the latter as a preferential (see point 3); but it is also possible C4AF reactivity involved at later ages. 3. The role of the reactive alumina, Al 2 O 3 r - , and reactive silica, SiO 2 r - , (vitreous and/or amorphous fractions of the pozzolanic additions) during the Friedel’s salt formation has been specified and, as a result, the formation rate of Fs from Al 2 O 3 r - of pozzolan turns out to be notably higher than the formation rate of Fs from C3A of PC. For this reason, both have been termed rapid forming Fs or Fs-rf and slow forming Fs or Fs-lf, respectively, but in any case, topochemical mechanism with prior dissolution must be preponderant over through-solution mechanism. 4. The Friedel’s salt formation in all the PC/pozzolan blends have coincided quantitatively in the vast majority of the cases with the respective reactive alumina, Al 2 O 3 r - (%), content of each pozzolan. The number of these coincidences was greater for the PY6 blends, due to its C3A practical absence in these samples, since its presence in the P1 blends can stimulate directly, non-directly, but above all, indirectly the chemical reaction of the C3A hydration with NaCl solutions (3.75% and 3.00% in this study) and influence like that in the velocity of the compound formation: Fs. 5. The physical state of the reactive alumina, Al 2 O 3 r - , in C natural pozzolan must be more amorphous than vitreous, resembling metakaolin more than fly ash. That notwithstanding, pozzolan composition must have conditioned the water/cementitious material ratios obtained for their respective P1 and PY6 blended cements (a finding that could be used in the future for speedy, easy, reliable, reproducible and inexpensive characterization of natural and artificial Pozzolans, and logically for this purpose, its previous physics-chemical analysis, Frattini test at 2 and/or 7 and/or 28 days-age and/or mechanical strengths will also be previously needed), as well as its specific pozzolanic activity.
-
expansive synergic effect of ettringite from pozzolan metakaolin and from opc co precipitating in a common plaster bearing solution part ii fundamentals explanation and justification
Construction and Building Materials, 2011Co-Authors: R. TaleroAbstract:Abstract In Part I, already published about this topic, Expansive Synergic Effect (ESE) between both types of ettringite was shown by means of cement pastes and mortars. In this Part II, ESE will also be shown by means of cement mortars and concretes, but above all, will be explained and justified. For this purpose, the same cementitious materials (OPC, SRPC and metakaolin, MK) plus OPC P-31, silica fume, SF, and diatomite, D, the same blended cements plus the corresponding POZC of SF and D, and the same ASTM C 452-68 test than in Part I were used, and specimens of the most significant types of cement were made for ASTM C 452-68 testing, and once again, several direct and indirect physical, chemical and mechanical strengths parameters were measured, as follows: increase in length, ΔL (%), and pozzolanic activity index of Pozzolans. In parallel, concrete specimens also were prepared with (15.05% or 45.16%) and without excess gypsum, and the following parameters were measured: compressive strength and indirect tensile strength (“brazilian” test). Finally, other complementary determinations were specific physical properties, chemical analysis of some cement tested and SEM-EDX analysis of ettr-rf and ett-lf formed. The experimental results have once again shown that, the joint precipitation in the same plaster-bearing solutions – co-precipitation – of the ettringite from the Al 2 O 3 r - present in Pozzolans, and the ettringite from the C3A present in OPC, was, to use drug interaction terminology, always more synergic than additive. Furthermore, depending on the parameter considered and from a purely technological point of view, the practical implications of Expansive Synergic Effect (ESE) between the two types of ettringite can be classified as beneficial, adverse or indifferent (for more detail, see Abstract in Part I). On the other hand, the experimental results have also shown that the pozzolanic activity of MK has proved to be once again more specific than generic in gypsum and water environments, prompting greater or lesser but speedier gypsum hydration of all or part of the C3A (than of the C3S) content of the OPC fraction than when the OPC in question was hydrated in the same manner but without MK, and as a result, a stronger or weaker ESE, being moreover, the ett-rf from the Al 2 O 3 r - in MK its chief direct and indirect cause in conjunction with the ettringite from the C3A in PC, due to its very specific pozzolanic activity in such gypsum media; and when it was hydrated with SF – in this case, with at least 20% of such pozzolan SF – gypsum-mediated hydration of the C3A was obstructed, thereby confirming that, as expected, this pozzolan protects its corresponding POZC from gypsum attack, that is, its pozzolanic activity is not also more specific than generic for the same result but for the contrary result, that is, SF is unspecific for the same result.
-
Performance of Metakaolin and Portland Cements in Ettringite Formation as Determined by ASTM C 452-68: Kinetic and Morphological Differences
Cement and Concrete Research, 2005Co-Authors: R. TaleroAbstract:Abstract In this study, the results of prior XRD and Le Chatelier–Ansttet test experiments were re-verified in terms of a relative parameter, the Length Growth Rate, Vcl(=Δ L (%)/day). For this purpose ASTM C 452-68 testing was conducted for 2 years on 40 cements, 10 Portland cements–6 OPCs and 4 SRPCs–and 30 blended cements containing 20%, 30% and 40% metakaolin (M pozzolan). ASTM C 452-68 specimens were manufactured with all cements and their daily length growth rate was calculated by dividing the measured increase in length, Δ L (%), by the number of days lapsing since the preceding measurement. Additional experiments were also run: chemical analysis, XRD and SEM analysis of ettringites and tests to determine specific properties of some cements tested. The results have once again borne out that: (a 1 ) The formation rate of the ettringite deriving from the reactive alumina, Al 2 O 3 r − , present in Pozzolans is considerably higher than the rate for ettringite forming from the C 3 A (and, logically, much higher than for C 4 AF ettringite) present in OPC. Owing to this, these ettringites were termed: “rapid formation” ( ett-rf ), “slow formation” ( ett-lf ) and “very slow formation” ( ett-vlf ʺ) ettringites, respectively. (b 1 ) The foregoing directly affects the size of the respective crystals, which are much smaller in ett-rf than in ett-lf . These results have also shown that: (a 2 ) In a gypsum and water environment (ASTM C 452-68 specimens), the pozzolanic reactions involving the reactive alumina, Al 2 O 3 r − , present in Pozzolans take place during the first 28 days of age–and, sometimes, even during the first 7 days (this occurred for most POZCs prepared with this M pozzolan and PC)–, and ettringite from both, Al 2 O 3 r − and C 3 A, origin, are the reaction products in all cases. (b 2 ) Ett-rf and ett-lf formation does not take place independently from one another, but inter-dependently or in a joint way or interactive way. Consequently, both ettringites appear, to a greater or lesser extent, when dealing with gypsum and water environments. Nevertheless, the reaction products are closer to ett-rf than to ett-lf , when more M pozzolan is added (40%) and vice versa (20%), and in any case, topochemical mechanism with prior dissolution must be preponderant over through-solution mechanism. (b 3 ) According to ASTM C 150-95 standard, the optional physical requirement to characterize SRPCs is Δ L 14 days ≤0.040%. Unlike the requirement formerly used, i.e., Δ L 28 days ≤0.054%, this requirement “predicts” rather than “assures” the most probable behaviour of a PC under gypsum attack. Moreover, if the results of the tests set out in standards EN 196-1, EN 196-3, EN 196-5 and EN 450 and/or ASTM C 311-94b, mainly, are positive, the ASTM C 452-68 test can be validly used to characterize and differentiate at 28 days, POZCs prepared with M pozzolan–or any other natural or artificial (fly ash) pozzolan–, which would give rise to low, moderate or high sulfate resistance. The only requisite in this regard would be to establish suitable standard and chemical–physical requirements and specifications.
Robert Cerný - One of the best experts on this subject based on the ideXlab platform.
-
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.
-
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.
-
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.
Brian R Strazisar - One of the best experts on this subject based on the ideXlab platform.
-
effect of exposure environment on the interactions between acid gas h2s and co2 and pozzolan amended wellbore cement under acid gas co sequestration conditions
International Journal of Greenhouse Gas Control, 2014Co-Authors: Liwei Zhang, David A Dzombak, David V Nakles, Steven B Hawthorne, David J Miller, Barbara Kutchko, Christina L Lopano, Brian R StrazisarAbstract:Abstract Laboratory experiments were conducted to determine the effect of exposure environment on the integrity of pozzolan-amended Class H cement under geologic acid gas co-sequestration conditions. Cement was exposed to two potential subsurface storage environments: (1) a supercritical mixture of CO2/H2S and (2) a CO2/H2S saturated brine. Results show that cement alteration is dependent on the amount of pozzolan addition. The alteration rate and mechanism also differ for the two exposure scenarios. Cement containing 35% pozzolan amounts by volume (hereafter referred to as 35 vol% pozzolan cement) exposed to the aqueous environment was more vulnerable to alteration, compared with the same pozzolan content cement exposed to a supercritical mixture of CO2/H2S (21 mol% H2S). Specifically, 35 vol% pozzolan cement exposed to the aqueous environment exhibited a higher level of mineral dissolution (e.g., C-S-H, 3CaO·SiO2, 2CaO·SiO2, etc.) and a higher degree of sulfur alteration than the same pozzolan content samples exposed to the supercritical mixture of CO2–H2S (21 mol% H2S). Different from the 35 vol% pozzolan cement, the cement containing 65% pozzolan by volume (hereafter referred to as 65 vol% pozzolan cement) was more susceptible to alteration in the supercritical CO2/H2S (21 mol% H2S) environment, compared with the same pozzolan content cement exposed to the aqueous environment. Increasing the H2S mol% in the supercritical phase from 21 mol% to 40 mol% increased the alteration of cement exposed to both exposure environments. The 65 vol% pozzolan cement was more resistant to H2S and CO2 alteration than the 35 vol% pozzolan cement if the H2S content was high (i.e., 40 mol%), while the 35 vol% pozzolan cement was more resistant to H2S and CO2 alteration than the 65 vol% pozzolan cement if the H2S content was relatively low (i.e., 21 mol%). It was observed that while the two related exposure environments resulted in different degrees of cement alteration, the exposure environments did not result in the formation of different minerals.
-
characterization of pozzolan amended wellbore cement exposed to co2 and h2s gas mixtures under geologic carbon storage conditions
International Journal of Greenhouse Gas Control, 2013Co-Authors: Liwei Zhang, David A Dzombak, David V Nakles, Steven B Hawthorne, David J Miller, Barbara Kutchko, Christina L Lopano, Brian R StrazisarAbstract:Abstract Capture and subsurface co-sequestration of acid gas (a mixture of CO2 and H2S) is a geologic sequestration approach that can reduce the emission of both CO2 and sulfur-containing “sour” gas. To investigate the effects of co-sequestration on pozzolan-amended wellbore cement, samples were mixed, cured and exposed to mixtures of H2S and CO2 under geologic sequestration conditions (50 °C, 15.1 MPa) for various periods of time. The resulting samples were characterized using microscopy, X-ray diffraction, and microhardness testing. These analyses showed significant alteration at the surfaces of pozzolan-amended cement samples after 28 days of exposure to 21 mole% H2S in a mixture with CO2. Results of samples exposed for 28 days also revealed that the samples with higher pozzolan amount (65% pozzolan by volume) allowed faster CO2 and H2S penetrations than those with lower pozzolan amount (35% pozzolan by volume). Analyses showed that there was formation of carbonate species in the interior “core” region of pozzolan-amended cement samples with 65 vol% pozzolan after 28 days of exposure, which was not the case for the samples with 35 vol% pozzolan. In addition, the microhardness test results showed that the rim region of the 35 vol% pozzolan samples exhibited a higher microhardness than that of the core region for the same sample, whereas the different regions of the 65 vol% pozzolan samples exhibited similar microhardness values. In summary, the pozzolan-amended cement samples with 35 vol% pozzolan exhibited better H2S-resisting performance than the samples with 65 vol% pozzolan.
Dali Bondar - One of the best experts on this subject based on the ideXlab platform.
-
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.
-
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.
-
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.
-
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.
