The Experts below are selected from a list of 5154 Experts worldwide ranked by ideXlab platform
John L Provis - One of the best experts on this subject based on the ideXlab platform.
-
Chloride binding and mobility in sodium carbonate-Activated Slag pastes and mortars
Materials and Structures, 2017Co-Authors: Susan A Bernal, Oday H. Hussein, John L ProvisAbstract:This study evaluates the chloride binding capacity and the migration of chloride in sodium carbonate-Activated Slag cements and mortars. The effect on chloride mobility and binding of adding a calcined layered double hydroxide (CLDH) to the binder mix was also assessed. Significantly improved durability characteristics can be achieved for sodium carbonate-Activated Slag mortars by the addition of small fractions of CLDH, as a consequence of a higher degree of reaction, higher chloride binding capacity, and the refined pore structures present in these modified materials, in comparison with alkali-Activated cements produced without CLDH. The addition of CLDH enables the production of sodium carbonate-Activated Slag cements with notably reduced chloride ingress compared to silicate Activated Slag cements.
-
The interfacial Transition Zone in alkali-Activated Slag Mortars
Frontiers in Materials, 2015Co-Authors: Rackel San Nicolas, John L ProvisAbstract:The interfacial transition zone (ITZ) is known to strongly influence the mechanical and transport properties of mortars and concretes. This paper studies the ITZ between siliceous (quartz) aggregates and alkali Activated Slag binders in the context of mortar specimens. Backscattered electron images (BSE) generated in an environmental scanning electron microscope (ESEM) are used to identify unreacted binder components, reaction products and porosity in the zone surrounding aggregate particles, by composition and density contrast. X-ray mapping is used to exclude the regions corresponding to the aggregates from the BSE image of the ITZ, thus enabling analysis of only the binder phases, which are segmented into binary images by grey level discrimination. A distinct yet dense ITZ region is present in the alkali-Activated Slag mortars, containing a reduced content of unreacted Slag particles compared to the bulk binder. The elemental analysis of this region shows that it contains a (C,N)-A-S-H gel which seems to have a higher content of Na (potentially deposited through desiccation of the pore solution) and a lower content of Ca than the bulk inner and outer products forming in the main binding region. These differences are potentially important in terms of long-term concrete performance, as the absence of a highly porous interfacial transition zone region is expected to provide a positive influence on the mechanical and transport properties of alkali-Activated Slag concretes.
-
Water content modifies the structural development of sodium metasilicate-Activated Slag binders
2015Co-Authors: Susan A Bernal, Rackel San Nicolas, J.s.j. Van Deventer, John L ProvisAbstract:The effect of modifying the water content of an alkali - Activated Slag binder was assessed, in terms of the kinetics of reaction and the structural development of the material. There is not a s ystematic correlation between the water content of the mix and the rate of reaction, indicating that there is an optimal value that favours dissolution of the Slag and precipitation of reaction products. A h igher water content reduce d the crystallinity and density of the reaction products, especially at advanced age. Small changes in the water content can have a significant impact on the compressive strength development of alkali - silicate Activated Slag mortars, suggesting that when producing materials base d on alkali - Activated binders , it is essential to carefully control the water content.
-
Thermodynamic modelling of alkali-Activated Slag cements
Applied Geochemistry, 2015Co-Authors: Rupert J. Myers, Susan A Bernal, Barbara Lothenbach, John L ProvisAbstract:This paper presents a thermodynamic modelling analysis of alkali-Activated Slag-based cements, which are high performance and potentially low-CO2 binders relative to Portland cement. The thermodynamic database used here contains a calcium (alkali) aluminosilicate hydrate ideal solid solution model (CNASH_ss), alkali carbonate and zeolite phases, and an ideal solid solution model for a hydrotalcite-like Mg–Al layered double hydroxide phase. Simulated phase diagrams for NaOH- and Na2SiO3-Activated Slag-based cements demonstrate the high stability of zeolites and other solid phases in these materials. Thermodynamic modelling provides a good description of the chemical compositions and types of phases formed in Na2SiO3-Activated Slag cements over the most relevant bulk chemical composition range for these cements, and the simulated volumetric properties of the cement paste are consistent with previously measured and estimated values. Experimentally determined and simulated solid phase assemblages for Na2CO3-Activated Slag cements were also found to be in good agreement. These results can be used to design the chemistry of alkali-Activated Slag-based cements, to further promote the uptake of this technology and valorisation of metallurgical Slags.
-
distinctive microstructural features of aged sodium silicate Activated Slag concretes
Cement and Concrete Research, 2014Co-Authors: Rackel San Nicolas, Susan A Bernal, Ruby Mejia De Gutierrez, Jannie S J Van Deventer, John L ProvisAbstract:Abstract Electron microscopic characterisation of 7-year old alkali-Activated blast-furnace Slag concretes enabled the identification of distinct microstructural features, providing insight into the mechanisms by which these materials evolve over time. Backscattered electron images show the formation of Liesegang-type ring formations, suggesting that the reaction at advanced age is likely to follow an Oswald supersaturation–nucleation–depletion cycle. Segregation of Ca-rich veins, related to the formation of Ca(OH)2, is observed in microcracked regions due to the ongoing reaction between the pore solution and available calcium from remnant Slag grains. A highly dense and uniform interfacial transition zone is identified between siliceous aggregate particles and the alkali Activated Slag binders, across the concretes assessed. Alkali-Activated Slag concretes retain a highly dense and stable microstructure at advanced ages, where any microcracks induced at early ages seem to be partially closing, and the remnant Slag grains continue reacting.
Susan A Bernal - One of the best experts on this subject based on the ideXlab platform.
-
Chloride binding and mobility in sodium carbonate-Activated Slag pastes and mortars
Materials and Structures, 2017Co-Authors: Susan A Bernal, Oday H. Hussein, John L ProvisAbstract:This study evaluates the chloride binding capacity and the migration of chloride in sodium carbonate-Activated Slag cements and mortars. The effect on chloride mobility and binding of adding a calcined layered double hydroxide (CLDH) to the binder mix was also assessed. Significantly improved durability characteristics can be achieved for sodium carbonate-Activated Slag mortars by the addition of small fractions of CLDH, as a consequence of a higher degree of reaction, higher chloride binding capacity, and the refined pore structures present in these modified materials, in comparison with alkali-Activated cements produced without CLDH. The addition of CLDH enables the production of sodium carbonate-Activated Slag cements with notably reduced chloride ingress compared to silicate Activated Slag cements.
-
Water content modifies the structural development of sodium metasilicate-Activated Slag binders
2015Co-Authors: Susan A Bernal, Rackel San Nicolas, J.s.j. Van Deventer, John L ProvisAbstract:The effect of modifying the water content of an alkali - Activated Slag binder was assessed, in terms of the kinetics of reaction and the structural development of the material. There is not a s ystematic correlation between the water content of the mix and the rate of reaction, indicating that there is an optimal value that favours dissolution of the Slag and precipitation of reaction products. A h igher water content reduce d the crystallinity and density of the reaction products, especially at advanced age. Small changes in the water content can have a significant impact on the compressive strength development of alkali - silicate Activated Slag mortars, suggesting that when producing materials base d on alkali - Activated binders , it is essential to carefully control the water content.
-
Thermodynamic modelling of alkali-Activated Slag cements
Applied Geochemistry, 2015Co-Authors: Rupert J. Myers, Susan A Bernal, Barbara Lothenbach, John L ProvisAbstract:This paper presents a thermodynamic modelling analysis of alkali-Activated Slag-based cements, which are high performance and potentially low-CO2 binders relative to Portland cement. The thermodynamic database used here contains a calcium (alkali) aluminosilicate hydrate ideal solid solution model (CNASH_ss), alkali carbonate and zeolite phases, and an ideal solid solution model for a hydrotalcite-like Mg–Al layered double hydroxide phase. Simulated phase diagrams for NaOH- and Na2SiO3-Activated Slag-based cements demonstrate the high stability of zeolites and other solid phases in these materials. Thermodynamic modelling provides a good description of the chemical compositions and types of phases formed in Na2SiO3-Activated Slag cements over the most relevant bulk chemical composition range for these cements, and the simulated volumetric properties of the cement paste are consistent with previously measured and estimated values. Experimentally determined and simulated solid phase assemblages for Na2CO3-Activated Slag cements were also found to be in good agreement. These results can be used to design the chemistry of alkali-Activated Slag-based cements, to further promote the uptake of this technology and valorisation of metallurgical Slags.
-
distinctive microstructural features of aged sodium silicate Activated Slag concretes
Cement and Concrete Research, 2014Co-Authors: Rackel San Nicolas, Susan A Bernal, Ruby Mejia De Gutierrez, Jannie S J Van Deventer, John L ProvisAbstract:Abstract Electron microscopic characterisation of 7-year old alkali-Activated blast-furnace Slag concretes enabled the identification of distinct microstructural features, providing insight into the mechanisms by which these materials evolve over time. Backscattered electron images show the formation of Liesegang-type ring formations, suggesting that the reaction at advanced age is likely to follow an Oswald supersaturation–nucleation–depletion cycle. Segregation of Ca-rich veins, related to the formation of Ca(OH)2, is observed in microcracked regions due to the ongoing reaction between the pore solution and available calcium from remnant Slag grains. A highly dense and uniform interfacial transition zone is identified between siliceous aggregate particles and the alkali Activated Slag binders, across the concretes assessed. Alkali-Activated Slag concretes retain a highly dense and stable microstructure at advanced ages, where any microcracks induced at early ages seem to be partially closing, and the remnant Slag grains continue reacting.
-
Natural carbonation of aged alkali-Activated Slag concretes
Materials and Structures, 2014Co-Authors: Susan A Bernal, Ruby Mejía De Gutiérrez, Rackel San Nicolas, John L Provis, Jannie S. J. Van DeventerAbstract:Alkali-Activated Slag concretes stored for 7 years under atmospheric conditions are assessed, and the structural characteristics of naturally carbonated regions are determined. Concretes formulated with a 400 kg/m^3 and water/binder (w/b) ratio between 0.42 and 0.48 present similar natural carbonation depths, although these concretes report different permeabilities after 28 days of curing. The inclusion of increased contents of binder leads to a substantial reduction of the CO_2 penetration in these concretes, so that negligible carbonation depth values (2 mm) are identified in concretes formulated with 500 kg/m^3 of binder. Calcite, vaterite, and natron are identified as the main carbonation products formed in these concretes. These observations differ from the trends which would be expected in comparable ordinary Portland cement-based concretes, which is attributable to the physical (permeability) and chemical properties of alkali-Activated Slag concretes promoting high long-term stability and acceptably slow carbonation progress under natural atmospheric conditions.
Pavel Rovnaník - One of the best experts on this subject based on the ideXlab platform.
-
Comparison of electrical and self-sensing properties of Portland cement and alkali-Activated Slag mortars
Cement and Concrete Research, 2019Co-Authors: Pavel Rovnaník, Patrik Bayer, Ivo Kusák, Pavel Schmid, Lukáš FialaAbstract:Abstract Aluminosilicate-based construction materials are known generally as electrical insulators. The electrical resistivity of cement paste and composites with conductive admixture and the consequent multifunctionality of such materials have been widely studied. Only limited information is provided for other types of aluminosilicate binders. This paper presents a comparison of the electrical properties, especially resistance and capacitance, and consequent self-sensing functionality of Portland cement and alkali-Activated Slag mortars. The results show that alkali-Activated Slag shows enhanced conducting properties due to the presence of mobile hydrated sodium ions and metallic iron microparticles. Although the absolute resistivity of alkali-Activated Slag is quite low, it exhibits sufficient self-sensing properties even without the addition of conductive filler.
-
Electrical Properties of Steel Fibre Reinforced Alkali-Activated Slag Composite
Key Engineering Materials, 2018Co-Authors: Pavel Rovnaník, Ivo KusákAbstract:Alkali-Activated Slag is an alternative binder to the ordinary Portland cement. In order to improve its tensile properties steel fibres as dispersed reinforcement can be used. Since steel is very good conductor it changes the electrical properties of alkali-Activated Slag composite that can have a potential to be used as self-sensing material then. In this study up to 20% of steel fibres by mass of the Slag was added to alkali-Activated Slag mortar and the mechanical properties, electrical resistance, capacitance and microstructure of the composites were investigated. The results showed that the best improvement of both the mechanical and electrical properties can be observed for the composite with 15% of steel fibres.
-
Differences in Electrical Properties of Portland Cement and Alkali-Activated Slag Mortars
Solid State Phenomena, 2018Co-Authors: Pavel Rovnaník, Ivo Kusák, Maria Míková, Patrik BayerAbstract:Alkali-Activated Slag is known as a building material for more than sixty years and is considered an alternative to Portland cement based binders. Compared to Portland cement it exhibits some superior properties such as higher resistance against chemical attack and exposure to elevated temperatures. Aluminosilicate binders are generally electrical insulators; however, electrical properties of building materials gain the importance in the new field of applications such as self-sensing or self-heating materials. This paper brings a comparison of the electrical properties, especially resistance and capacitance, between Portland cement and alkali-Activated Slag mortars. The measurements revealed that alkali-Activated Slag shows enhanced conducting properties due to the presence of mobile hydrated sodium ions and metallic iron microparticles.
-
Influence of Polymer Admixtures on the Rheological Properties and Heat of Hydration of Alkali Activated Slag Pastes
Solid State Phenomena, 2018Co-Authors: Olesia Mikhailova, Pavel RovnaníkAbstract:The purpose of this study is to investigate the rheological properties of alkali-Activated Slag prepared as a paste modified by various amount of polymer admixtures. Four commercial admixtures VINNAPAS®5023 L, 5111 L, 7016 F and 7220 E were used as polymer admixture in this study. These admixtures were incorporated to alkali Activated Slag pastes in quantities between 0.5 and 2% by mass of Slag. Rheological properties as shear stress and viscosity of fresh pastes were examined by Discovery HR-1. Another main focus of this paper is the effect of selected admixtures on the heat of hydration of an alkali Activated Slag. Results indicate that addition of polymer admixtures affects the viscosity of the pastes and hydration process.
-
Electrical Properties of Alkali-Activated Slag Mortar with Carbon Fibres
Materials Science Forum, 2017Co-Authors: Pavel Rovnaník, Maria Míková, Ivo KusákAbstract:Building materials with enhanced electrical properties gain the importance in the new field of applications such as self-sensing or self-heating materials. In this paper, 3 mm long carbon fibres were used as a conductive admixture to alkali-Activated Slag mortar in order to reduce its resistivity. The amount of carbon fibres was ranging from 0.5 to 4.0% of the Slag mass and the effect of the conductive admixture on the mechanical properties, electrical impedance, specific conductivity, and microstructure of alkali-Activated Slag composite was investigated. Only 0.5% of carbon fibres caused a significant decrease in impedance of alkali-Activated Slag composite and the addition of 4% reduced the impedance by one order of magnitude for low AC frequencies. However, due to problematic dispersion and higher demand of mixing water, the mechanical properties were deteriorated, especially at higher content of carbon fibres.
Francisca Puertas - One of the best experts on this subject based on the ideXlab platform.
-
Alkali-Activated Slag concrete: Fresh and hardened behaviour
Cement and Concrete Composites, 2018Co-Authors: Francisca Puertas, B. González-fonteboa, I. González-taboada, G. Rojo, Manuel Torres-carrasco, M.m. Alonso, F. Martínez-abellaAbstract:The behaviour of fresh and hardened alkali-Activated Slag (AAS) and OPC concretes was compared and the effect of mixing time assessed. OPC and AAS concrete slump and rheological results proved to differ, particularly when the Slag was Activated with waterglass (WG). The nature of the alkaline activator was the key determinant in AAS concrete rheology. Bingham models afforded a good fit to all the OPC and AAS concretes. In OPC and NaOH-Activated AAS concretes, longer mixing had an adverse effect on rheology while improving hardened performance only slightly. In WG-AAS concrete, longer mixing times, improved mechanical properties and also rheological behaviour was enhanced, in which those conditions were required to break down the microstructure. Longer mixing raised thixotropy in OPC and NaOH-Activated AAS concretes, but lowered the value of this parameter in waterglass-Activated Slag concrete.
-
Rheology and Setting of Alkali-Activated Slag Pastes and Mortars: Effect of Organic Admixture
ACI Materials Journal, 2008Co-Authors: Marta Palacios, Phillip Frank Gower Banfill, Francisca PuertasAbstract:The rheology of waterglass-(Na 2 O·nSiO 2 ·mH 2 O) and NaOH-Activated Slag pastes and mortars depends on the nature of the alkaline activator used: in waterglass-Activated Slag pastes and mortars, the extensive structural breakdown under shear makes the Herschel-Bulkley model a better fit to the down ramp of the flow curve, whereas NaOH-Activated pastes and mortars, such as portland-cement pastes and mortars, behaved like Bingham fluids. Admixtures were unable to reduce the yield stress of waterglass-Activated Slag pastes, but the inclusion of a naphthalene derivative admixture in NaOH-Activated Slag pastes reduced the yield stress by 80%. The problem of undesirably short setting times for waterglass-Activated Slag mortars and concretes could be overcome by an extended mixing time, giving an initial set of nearly 3 hours.
-
Effect of Carbonation on Alkali‐Activated Slag Paste
Journal of the American Ceramic Society, 2006Co-Authors: Marta Palacios, Francisca PuertasAbstract:Carbonation on waterglass- and NaOH-Activated Slag pastes was analyzed and compared with carbonation in Portland cement pastes to determine possible differences. Thermogravimetry-differential thermal analysis (TG/DTA), Fourier-transform infrared spectrometry, and nuclear magnetic resonance were used to determine the effects on the main reaction products. According to the TG/DTA results, carbonate precipitation following carbonation is much more intense in Portland cement pastes than in alkali-Activated Slag pastes. This may be attributed to the fact that in Portland cement paste both the portlandite and the C–S–H gel can be carbonated, whereas in alkali-Activated Slag pastes, only the C–S–H gel is carbonated directly. In both systems, carbonation leads to the formation of CaCO3, Si-rich C–S–H gel, silica gel, and alumina. The carbonation of waterglass-Activated Slag pastes is not altered by the presence of either of the organic additives used in the study.
-
Alkali-Activated Slag cements: Kinetic studies
Cement and Concrete Research, 1997Co-Authors: Ana Fernández-jiménez, Francisca PuertasAbstract:The kinetics of hydration of alkali-Activated Slag (AAS) have been studied for different temperatures. The alkaline activator used was a mix of water-glass and NaOH solution. The degree of reaction was determined by means of the heat of hydration after the induction period. The reaction mechanism determined for AAS pastes was a diffusion mechanism and their activation energy was 57.6 KJ/mol.
Zuhua Zhang - One of the best experts on this subject based on the ideXlab platform.
-
Chloride binding of alkali-Activated Slag/fly ash cements
Construction and Building Materials, 2019Co-Authors: Jian Zhang, Caijiun Shi, Zuhua ZhangAbstract:Abstract In this study, the effects of Slag/fly ash ratio, Na2O concentration, silicate modulus of activators and water/binder ratio on chloride binding of alkali-Activated Slag/fly ash cements (AACs) are studied, using the binding isotherms. The Langmuir isotherm suits better for chloride adsorption of most of AACs, and the amount of bound chloride is predominantly influenced by the chloride concentration. The Friedel’s salt only presents in alkali-Activated Slag samples after adsorption equilibrium. An appropriate Slag/fly ash ratio could improve the chloride binding capacity due to the physical adsorption of N-A-S-H. The chloride binding of AACs decreases with the increased Na2O concentration but increases with the increased water/binder ratio, which is believed to be related to the OH− concentration in pore solutions.
-
Effect of alkali dosage and silicate modulus on carbonation of alkali-Activated Slag mortars
Cement and Concrete Research, 2018Co-Authors: Zhenguo Shi, Shu Wan, Caijun Shi, Ning Li, Zuhua ZhangAbstract:The long-term durability and their mechanisms of alkali-Activated cement based materials have remained largely elusive. In this paper, carbonation of alkali-Activated Slag (AAS) mortars Activated by NaOH and waterglass with different alkali dosages and silicate moduli has been investigated after exposure to 3 ± 0.2% (v/v) CO2 at 20 ± 2 °C/65 ± 5% RH for 56 days. The results show that carbonation resistance of the AAS mortars increases with increase of not only alkali dosage but also silicate modulus. In addition to the higher pore solution alkalinity and Slag reaction extent, the relatively higher carbonation resistance of the AAS mortars is attributed to the lower porosity and average pore size. The loss of compressive strength for the waterglass Activated Slag mortars after carbonation is due to decalcification of C-A-S-H phase, whereas the carbonation of katoite contributes to the increase of compressive strength of the NaOH Activated Slag mortars.