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Johann Plank - One of the best experts on this subject based on the ideXlab platform.
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Adsorbed Conformations of PCE Superplasticizers in Cement Pore Solution Unraveled by Molecular Dynamics Simulations
Scientific Reports, 2017Co-Authors: Tsuyoshi Hirata, Johann Plank, Alex Lange, Paulo Branicio, Jianwei Zheng, Michael SullivanAbstract:The conformations of polycarboxylate ether (PCE) type superplasticizer polymers adsorbed on the surface of MgO in Cement Pore Solution are simulated by molecular dynamics (MD). Three types of PCEs commonly applied to concrete are simulated, namely a methacrylate type PCE (PCEM- P ), an allyl ether type PCE (PCEA- P ), and an isoprenyl ether type PCE (PCEI- P ) with ethylene oxide (EO) unit numbers ( P ) of 25, 34 and 25, respectively. It is observed that the adsorbed layer thickness is inversely proportional to the experimentally measured adsorbed amount at the initial paste flow of 26 ± 0.5 cm. Simulation results indicate that the adsorbed layer thickness is sensitive to the initial polymer orientations against the model MgO surface. I.e., polymer molecules initially placed parallel/perpendicularly against the MgO surface gradually forms a train shaped or a loop and tail adsorption profile, respectively. As a result, the loop and tail shaped conformation gives a higher layer thickness.
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atomistic dynamics simulation to solve conformation of model pce superplasticisers in water and Cement Pore Solution
Advances in Cement Research, 2017Co-Authors: Tsuyoshi Hirata, Johann Plank, Alex Lange, Paulo Branicio, Jianwei Zheng, Yoshikazu Tomike, Michael B SullivanAbstract:The working mechanism of polycarboxylate ether (PCE) type superplasticisers in concrete was studied from the point of view of conformational changes of the polymer simulated by molecular dynamics in pure water and Cement Pore Solution. Three typical types of PCEs, namely a methoxy polyethyleneglycol monomethacrylate–sodium methacrylate copolymer (PCEM), a polyethyleneglycol mono allyl ether–sodium maleate copolymer (PCEA) and a polyethyleneglycol mono (3-methyl-3-butenyl) ether–sodium acrylate copolymer (PCEI) were investigated using large-scale atomistic molecular dynamics simulations. It was observed that the PCE polymers which possess negatively charged backbones were stretched in water due to electrostatic repulsion. However, they were found to be significantly shrunken and distorted in synthetic Cement Pore Solution, depending on the polyethylene glycol (PEG) density along the backbone, resulting in the aggregation of PEG side chains due to the salting-out effect.
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impact of welan gum stabilizer on the dispersing performance of polycarboxylate superplasticizers
Cement and Concrete Research, 2016Co-Authors: E Uzer, Johann PlankAbstract:Welan gum, a microbial biopolymer produced via fermentation, represents a common stabilizer (VMA) for highly dispersed concretes such as e.g. self-compacting concrete (SCC). Here, interaction between welan gum and two methacrylate ester-based polycarboxylate (PCE) superplasticizers was studied. It was found that the stabilizing effect of welan gum solely derives from its strong viscosifying effect on the aqueous phase of concrete (i.e. Cement Pore Solution). The dispersing effectiveness of PCE is negatively influenced by this increased viscosity. A mechanistic study revealed that the stabilizer does not adsorb on Cement and that it does not reduce adsorption of PCE. Thus, no competitive adsorption between the two admixtures occurs. This behavior differentiates welan gum from copolymerized VMAs based on AMPS® which adsorb on Cement and can perturb PCE adsorption. When formulating SCC with welan gum as stabilizer, its dosage should be kept as low as possible to preserve the fluidity provided by PCE.
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contribution of non adsorbing polymers to Cement dispersion
Cement and Concrete Research, 2016Co-Authors: Alex Lange, Johann PlankAbstract:Abstract It has been noticed recently that at low w/c ratios (≤ 0.30), non-adsorbed polycarboxylate (PCE) polymers can contribute as well to Cement dispersion. This study aimed at defining more specifically the structural requirement for such non-adsorbing polymers. For this purpose, a Cement paste (w/c = 0.30) containing a conventional MPEG PCE superplasticizer was admixed with additional quantities of a polyester polymer prepared via homopolymerization of MPEG methacrylate ester macromonomer, the macromonomer used in the homopolymerization, and the polyethylene glycol contained in the macromonomer. It was found that when admixed individually, all three polymers do not adsorb on Cement and cannot fluidize the paste but enhance dispersion and fluidity significantly when combined with the PCE superplasticizer. A potential explanation is that the non-adsorbing polymers act as lubricants between Cement, which are particularly densely packed at low w/c ratios. The Pore fluid loaded with non-adsorbed polymer exhibits superior lubrication compared to pristine Cement Pore Solution.
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role of pvoh and kaolin on colloidal stability of liquid and powder eva and sb latexes in Cement Pore Solution
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2013Co-Authors: Stefan Baueregger, Margarita Perello, Johann PlankAbstract:The influence of polyvinylalcohol (PVOH) and kaolin on the stability of an ethylene–vinylacetate (EVA) and a carboxylated styrene–butadiene (SB) latex copolymer in synthetic Cement Pore Solution (SCPS) was investigated by photometric turbidity measurements. The dispersions were prepared from liquid EVA/SB latexes or re-dispersible powders (RDPs) obtained by spray drying of the mother liquor with PVOH and kaolin. Colloidal properties of the EVA and SB latex particles were captured by dynamic light scattering (DLS), environmental scanning electron microscopy (ESEM), zeta and streaming potential measurements. The amount of PVOH sorbed onto SB particles was quantified via total organic carbon (TOC) method. It was found that in water, EVA particles generally coagulate and settle with time as a consequence of their nonionic character. In contrast, dispersions of the anionic styrene–butadiene latex show high stability due to repulsion from the pressure of their counter ions clouds. In synthetic Cement Pore Solution, however, the liquid SB latex becomes unstable and shows strong coagulation as a consequence of calcium interaction. Surprisingly, the corresponding SB re-dispersible powder is much more stable in SCPS and exhibits only slight sedimentation. The enhanced stability is attributed to a surface coating of the SB powder particles with a film of PVOH during spray drying. The PVOH coating embeds some of the carboxylate groups located on the surface of the SB powder, as evidenced by a reduced anionic charge density. This way, interaction with calcium is weakened and precipitation via latex–calcium complexation is much reduced. Consequently, addition of PVOH/kaolin during the spray drying of latex polymers not only prevents coalescence and caking of the powder particles, but also enhances their colloidal stability in Cementitious systems.
Bjarne Osbaeck - One of the best experts on this subject based on the ideXlab platform.
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thermal stability and pozzolanic activity of raw and calcined mixed layer mica smectite
Applied Clay Science, 2000Co-Authors: Emil Makovicky, Bjarne OsbaeckAbstract:Abstract Samples of synthetic mixed-layer mica/smectite were calcined at 560°C, 760°C and 960°C. Chemical, physical and mineralogical properties of both untreated and calcined samples, before and after being mixed with Ca(OH) 2 in the presence of simulated Cement Pore Solution, were studied in detail. Technological properties such as rheology and compressive strength of the clay mortars were also studied. The investigation indicates that the mixed-layer mica/smectite is a fairly good pozzolanic material and calcination is an effective approach to improve its pozzolanic activity. Dehydration and dehydroxylation of the sample at 560°C increase its pozzolanic activity considerably. Calcination from 560°C to 760°C does not cause further significant improvement, whereas calcination at 960°C again increases the compressive strength of the mortars to 113% (compared to the reference ordinary Portland Cement (OPC) mortar). Most of six studied standard clay minerals are compositionally suitable to be used as pozzolanic materials. The common reaction products of clays and Cement are CSH and C 4 AH x . The untreated clay minerals with stable layer structures have low pozzolanic activity and have negative effects on the compressive strength. Particle sizes of pozzolanic materials of calcined clay minerals and some other artificial pozzolans correlate well with the compressive strength of their Cement mortars.
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thermal treatment and pozzolanic activity of na and ca montmorillonite
Applied Clay Science, 1996Co-Authors: Emil Makovicky, Bjarne OsbaeckAbstract:Abstract Samples of both untreated and calcined (at about 730, 830 and 930°C) Na- and Ca-montmorillonite, before and after having reacted with Ca(OH) 2 in the presence of simulated Cement Pore Solution, were studied with XRD, SEM, EPMA and for chemical solubility. The reaction rate of the mixtures was monitored by a chemical shrinkage test. Technological properties of the (un) calcined montmorillonite-Cement mortars were studied with theological properties and compressive strength tests after reaction for 2, 7, 28 and 91 days. The study indicates that the montmorillonites are fairly good pozzolanic materials and calcination substantially improves their pozzolanic activity. A clear optimum calcination temperature is 830°C for both Na- and Ca-montmorillonite.
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thermal treatment and pozzolanic activity of sepiolite
Applied Clay Science, 1996Co-Authors: Emil Makovicky, Bjarne OsbaeckAbstract:Abstract Samples of standard sepiolite were calcined at 370, 570 and 830°C corresponding to the various stages of thermal reaction detected by DTA and TG. Both the raw and calcined samples, before and after being mixed with Ca(OH) 2 in the presence of simulated Cement Pore Solution, were studied with XRD, SEM, EPMA and chemical solubility. The reaction rate of the mixtures was monitored by a chemical shrinkage test. Technological properties of the raw and calcined sepiolite-Cement mortars were studied with theology and compressive strength tests after reaction for 2, 7, 28 and 91 days at 40°C. The results indicated that sepiolite is rather inactive as a pozzolanic material and has high water demand. The calcination to 370 and 570°C does not upgrade it significantly. The most effective calcination temperature is 830°C, which increases the compressive strength of its mortar to 84% of the compressive strength of the reference ordinary Portland Cement (OPC) mortar.
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pozzolanic reactions of six principal clay minerals activation reactivity assessments and technological effects
Cement and Concrete Research, 1995Co-Authors: Bjarne Osbaeck, Emil MakovickyAbstract:Abstract Six standard clays, before and after calcination at 3 or 4 temperatures and being mixed with Ca(OH) 2 [CH] in the presence of simulated Cement Pore Solution, and with ordinary Portland Cement, respectively, were studied in detail. Chemical compositions of most clays conform well to the requirement in ASTM C 618. Water demand of clay-containing mortar varies, depending on the crystal chemistry of raw clays, and on the specific surface area of calcined clays. Measurements of XRD background or alkali soluble Si are rapid methods in evaluation of the pozzolanic activity of clays. Compressive strength of mortars based on the raw clays is affected by structure of clays. Calcination increases the pozzolanic activity of clays and the compressive strength of the Portland Cement — clay mortars. A close correlation exists between compressive strength of mortars and particle size distribution of the dehydroxylated clays. The most common reaction products of clay — CH mixtures are C-S-H 2 and C 4 AH x , while C 2 ASH j8 and C 3 AH 6 were also detected with clays rich in Al.
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thermal stability and pozzolanic activity of calcined kaolin
Applied Clay Science, 1995Co-Authors: Changling He, Emil Makovicky, Bjarne OsbaeckAbstract:Abstract Standard illite (American Clay Society, IMt-1) was calcined at 650,790 and 930°C for 100 minutes. Both the raw and calcined samples, before and after being mixed with Ca(OH) 2 in the presence of simulated Cement Pore Solution, were studied by DTA, TG (for raw illite), XRD, SEM, EMPA and chemical solubility. The reaction rate of the mixtures was monitored by a chemical shrinkage test. Technological properties of the untreated and calcined illite-Cement mortars were studied by theology (flow) and by a compressive strength test after reaction for 2, 7, 28 and 91 days. The current investigation revealed that illite has low pozzolanic activity. Dehydroxylation at 650°C does not upgrade it significantly. Further calcination at 790°C brings about considerable activation but it still does not qualify as a pozzolan. Calcination at 930°C produces the highest pozzolanic activity. Compressive strength of the mortar with 930°C illite is 79% of that of reference ordinary portland Cement.
Emil Makovicky - One of the best experts on this subject based on the ideXlab platform.
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thermal stability and pozzolanic activity of raw and calcined mixed layer mica smectite
Applied Clay Science, 2000Co-Authors: Emil Makovicky, Bjarne OsbaeckAbstract:Abstract Samples of synthetic mixed-layer mica/smectite were calcined at 560°C, 760°C and 960°C. Chemical, physical and mineralogical properties of both untreated and calcined samples, before and after being mixed with Ca(OH) 2 in the presence of simulated Cement Pore Solution, were studied in detail. Technological properties such as rheology and compressive strength of the clay mortars were also studied. The investigation indicates that the mixed-layer mica/smectite is a fairly good pozzolanic material and calcination is an effective approach to improve its pozzolanic activity. Dehydration and dehydroxylation of the sample at 560°C increase its pozzolanic activity considerably. Calcination from 560°C to 760°C does not cause further significant improvement, whereas calcination at 960°C again increases the compressive strength of the mortars to 113% (compared to the reference ordinary Portland Cement (OPC) mortar). Most of six studied standard clay minerals are compositionally suitable to be used as pozzolanic materials. The common reaction products of clays and Cement are CSH and C 4 AH x . The untreated clay minerals with stable layer structures have low pozzolanic activity and have negative effects on the compressive strength. Particle sizes of pozzolanic materials of calcined clay minerals and some other artificial pozzolans correlate well with the compressive strength of their Cement mortars.
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thermal treatment and pozzolanic activity of na and ca montmorillonite
Applied Clay Science, 1996Co-Authors: Emil Makovicky, Bjarne OsbaeckAbstract:Abstract Samples of both untreated and calcined (at about 730, 830 and 930°C) Na- and Ca-montmorillonite, before and after having reacted with Ca(OH) 2 in the presence of simulated Cement Pore Solution, were studied with XRD, SEM, EPMA and for chemical solubility. The reaction rate of the mixtures was monitored by a chemical shrinkage test. Technological properties of the (un) calcined montmorillonite-Cement mortars were studied with theological properties and compressive strength tests after reaction for 2, 7, 28 and 91 days. The study indicates that the montmorillonites are fairly good pozzolanic materials and calcination substantially improves their pozzolanic activity. A clear optimum calcination temperature is 830°C for both Na- and Ca-montmorillonite.
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thermal treatment and pozzolanic activity of sepiolite
Applied Clay Science, 1996Co-Authors: Emil Makovicky, Bjarne OsbaeckAbstract:Abstract Samples of standard sepiolite were calcined at 370, 570 and 830°C corresponding to the various stages of thermal reaction detected by DTA and TG. Both the raw and calcined samples, before and after being mixed with Ca(OH) 2 in the presence of simulated Cement Pore Solution, were studied with XRD, SEM, EPMA and chemical solubility. The reaction rate of the mixtures was monitored by a chemical shrinkage test. Technological properties of the raw and calcined sepiolite-Cement mortars were studied with theology and compressive strength tests after reaction for 2, 7, 28 and 91 days at 40°C. The results indicated that sepiolite is rather inactive as a pozzolanic material and has high water demand. The calcination to 370 and 570°C does not upgrade it significantly. The most effective calcination temperature is 830°C, which increases the compressive strength of its mortar to 84% of the compressive strength of the reference ordinary Portland Cement (OPC) mortar.
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pozzolanic reactions of six principal clay minerals activation reactivity assessments and technological effects
Cement and Concrete Research, 1995Co-Authors: Bjarne Osbaeck, Emil MakovickyAbstract:Abstract Six standard clays, before and after calcination at 3 or 4 temperatures and being mixed with Ca(OH) 2 [CH] in the presence of simulated Cement Pore Solution, and with ordinary Portland Cement, respectively, were studied in detail. Chemical compositions of most clays conform well to the requirement in ASTM C 618. Water demand of clay-containing mortar varies, depending on the crystal chemistry of raw clays, and on the specific surface area of calcined clays. Measurements of XRD background or alkali soluble Si are rapid methods in evaluation of the pozzolanic activity of clays. Compressive strength of mortars based on the raw clays is affected by structure of clays. Calcination increases the pozzolanic activity of clays and the compressive strength of the Portland Cement — clay mortars. A close correlation exists between compressive strength of mortars and particle size distribution of the dehydroxylated clays. The most common reaction products of clay — CH mixtures are C-S-H 2 and C 4 AH x , while C 2 ASH j8 and C 3 AH 6 were also detected with clays rich in Al.
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thermal stability and pozzolanic activity of calcined kaolin
Applied Clay Science, 1995Co-Authors: Changling He, Emil Makovicky, Bjarne OsbaeckAbstract:Abstract Standard illite (American Clay Society, IMt-1) was calcined at 650,790 and 930°C for 100 minutes. Both the raw and calcined samples, before and after being mixed with Ca(OH) 2 in the presence of simulated Cement Pore Solution, were studied by DTA, TG (for raw illite), XRD, SEM, EMPA and chemical solubility. The reaction rate of the mixtures was monitored by a chemical shrinkage test. Technological properties of the untreated and calcined illite-Cement mortars were studied by theology (flow) and by a compressive strength test after reaction for 2, 7, 28 and 91 days. The current investigation revealed that illite has low pozzolanic activity. Dehydroxylation at 650°C does not upgrade it significantly. Further calcination at 790°C brings about considerable activation but it still does not qualify as a pozzolan. Calcination at 930°C produces the highest pozzolanic activity. Compressive strength of the mortar with 930°C illite is 79% of that of reference ordinary portland Cement.
Guangling Song - One of the best experts on this subject based on the ideXlab platform.
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influence of dissolved oxygen on the corrosion of mild steel in a simulated Cement Pore Solution under supercritical carbon dioxide
Construction and Building Materials, 2021Co-Authors: Jina Feng, Zi Ming Wang, Dajiang Zheng, Guangling SongAbstract:Abstract To understand the influence of oxygen on initiation of the localized corrosion of mild steel in the underground casing/Cement system for carbon capture and sequestration, the corrosion behavior of P110 steel was systematically investigated by means of electrochemical and analytical measurements in a simulated Cement Pore Solution under supercritical carbon dioxide at 80 °C and 10 MPa. With the increasing concentration of dissolved oxygen from
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the localized corrosion of mild steel in carbonated Cement Pore Solution under supercritical carbon dioxide in a simulated geothermal environment
Construction and Building Materials, 2021Co-Authors: Jina Feng, Zi Ming Wang, Dajiang Zheng, Guangling SongAbstract:Abstract Cement carbonation, one of the main causes of the reinforced concrete corrosion, is also inevitable in the geological environment of carbon sequestration, possibly destroying the integrity of well/Cement system. To evaluate the corrosion risk of casing pipe in a geothermal well environment, the corrosion behavior of P110 steel was investigated in carbonated Cement Pore Solutions under carbon dioxide supercritical conditions. It was found that a dense FeCO3 layer was generally formed and it could effectively prevent the steel from corrosion. However, above the threshold concentrations of chloride ion and dissolved oxygen, localized corrosion protrusions could be observed, which might continuously grow larger and higher until its outer shell ruptured during the exposure of the steel substrate in the simulated environment. The expansive growth of the protrusion could be attributed to the active disSolution accelerated by chloride ion at the bottom and the cooperative formation of iron oxide and carbonate in the core region. Such a localized corrosion damage could occur at the casing/Cement interface in practice and may become a fatal threat to casing pipes for carbon sequestration in the oil/gas industry.
Markus Gretz - One of the best experts on this subject based on the ideXlab platform.
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effect of ca2 ions on the film formation of an anionic styrene n butylacrylate latexpolymer in Cement Pore Solution
Advanced Materials Research, 2013Co-Authors: Thomas Pavlitschek, Markus Gretz, Johann PlankAbstract:Several methods were employed to study the time dependent film formation of a self synthesized anionic latex dispersion in water and Cement Pore Solution. First, a model carboxylated styrene/n-butyl acrylate latex dispersion possessing a minimum film forming temperature (MFFT) of 18 °C and a glass transition temperature (Tg) of 30 °C was synthesized via emulsion polymerization. Next, its film forming behaviour was studied at 40 °C, using an ESEM instrument. The analysis revealed that upon removal of water, film formation occurs as a result of particle packing, particle deformation and finally particle coalescence. Film formation is significantly hindered in synthetic Cement Pore Solution. This effect can be ascribed to adsorption of Ca2+ ions onto the surface of the anionic latex particles and to interfacial secondary phases. This layer of adsorbed Ca2+ ions hinders interdiffusion of the macromolecules and subsequent film formation of the latex polymer.
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An ESEM investigation of latex film formation in Cement Pore Solution
Cement and Concrete Research, 2011Co-Authors: Markus Gretz, Johann PlankAbstract:Environmental scanning electron microscopy (ESEM) and complementary methods were employed to study the time dependent film formation of a latex dispersion in water and Cement Pore Solution. First, a model carboxylated styrene/n-butyl acrylate latex dispersion possessing a minimum film forming temperature (MFFT) of 18 {sup o}C was synthesized in aqueous media via emulsion polymerization. Its film forming property was at a temperature of 40 {sup o}C, studied under an ESEM. The analysis revealed that upon removal of water, film formation occurs as a result of particle packing, particle deformation and finally particle coalescence. Film formation is significantly retarded when the latex dispersion is present in Cement Pore Solution. This effect can be ascribed to adsorption of Ca{sup 2+} ions onto the surface of the anionic latex particles and to interfacial secondary phases. This layer of adsorbed Ca{sup 2+} ions hinders interdiffusion of the macromolecules and subsequent film formation of the latex polymer.