The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Hao Pang - One of the best experts on this subject based on the ideXlab platform.
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study on the dispersion adsorption and early hydration behavior of cement pastes containing multi armed polycarboxylate superplasticizers
Journal of Dispersion Science and Technology, 2020Co-Authors: Kun Wang, Jianheng Huang, Hao Pang, Hao Huang, Linxia Song, Yangyang ZhaoAbstract:Multi-armed polycarboxylate superplasticizers (SPCEs) were prepared via esterification-copolymerization in aqueous media from various polyols (including glycerol, xylitol and mannitol), acrylic aci...
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synthesis and characterization of high performance cross linked polycarboxylate superplasticizers
Construction and Building Materials, 2019Co-Authors: Xiuju Lin, Bing Liao, Jingfei Zhang, Jianheng Huang, Hao PangAbstract:Abstract Cross-linked sustained-release polycarboxylate superplasticizers (SPs) are superior alternative to the comb-type polycarboxylate SPs due to they offer both a high fluidity and a good retention effect for concrete slurry. In this context, a series of cross-linked polycarboxylate superplasticizers were synthesized using acrylic acid, methylallyl polyoxyethylene ether and four different cross-linkers containing ester groups, respectively. The key difference among these four cross-linkers is their molecular weights because they each possessed the different ethoxy content. The fluidity and fluidity retention tests, adsorption performance and scanning electron microscope tests showed that the cross-linked superplasticizers offered good dispersing effects and excellent slump performance. Excitingly, the maximum flow reached up to 394 mm at a water-cement ratio of 0.35 and this high fluidity could be simultaneously maintained for 2 h, which facilitated concrete transport over long distances, therefore improving the practical workability of concrete. Furthermore, it was found that the superplasticizers derived from cross-linkers with higher ethoxy group contents provided cement paste samples with improved fluidity. Evaluation of the hydration heat and setting time demonstrated that the cross-linked polycarboxylate superplasticizers could delay the hydration of cement and the final setting time had been extended by 4 h in comparation with blank samples. After 3, 7 and 28 d, the compressive strength of the cement mortar was improved with increases of molecular weight of the cross-linker in the cross-linked superplasticizers due to the elevation of ethoxy content.
Francisca Puertas - One of the best experts on this subject based on the ideXlab platform.
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Adsorption of PCE and PNS Superplasticisers on cubic and orthorhombic C3A. Effect of sulfate
Construction and Building Materials, 2015Co-Authors: M.m. Alonso, Francisca PuertasAbstract:C3A is the most highly reactive phase in clinker and the one with the greatest affinity for superplasticiser admixtures. The amount of C3A in cement, the sulfate content in the medium and the type and amount of admixture largely determine paste, mortar and concrete rheology. Many unknowns remain, however, around the effect of SP structure on admixture adsorption onto (cubic or orthorhombic) C3A polymorphs. Isotherms were found for polycarboxylate ether and naphthalene-based admixture adsorption onto synthetic cubic and orthorhombic C3A to determine that effect, given their different structure and nature. The impact of sulfates on adsorption was also explored. The conclusion drawn was that admixture structure and sulfate content in the media were the factors with the greatest impact on adsorption onto cubic C3A. Orthorhombic C3A was observed to react more intensely to the presence of sulfate and consequently to have less affinity for the admixtures. In the presence of soluble sulfates the addition of Superplasticisers was shown to retard the appearance of the main cubic-C3A calorimetric signal more effectively when admixture-sulfate competition was more intense. The presence of SP admixtures has no impact on the peak heat flow time in orthorhombic-C3A hydration. The affinity of this polymorph for sulfates is so high that admixture adsorption is much smaller than observed in cubic-C3A. Therefore, the SPs have a scant effect on orthorhombic-C3A hydration.
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viscosity and water demand of limestone and fly ash blended cement pastes in the presence of Superplasticisers
Construction and Building Materials, 2013Co-Authors: Olga Burgosmontes, M.m. Alonso, Francisca PuertasAbstract:Abstract The rheological behaviour of fresh cement has a direct effect on the microstructural development of mortar and concrete. Inasmuch as the presence of mineral additions impact cement paste rheology and consequently its permanent microstructure and strength, a full understanding of blended cement behaviour should be pursued. The present study addresses the joint effect of mineral additions (limestone and fly ash) and Superplasticisers admixtures on the viscosity and water demand of cement pastes. Cement pastes were prepared with 10, 30 or 50 wt% limestone or fly ash as mineral admixtures. Melamine-, naphthalene- and polycarboxylate-based Superplasticisers were used. Paste rheology was studied in terms of variations in yield stress and viscosity with the solids content and amount of mineral additions added. The strength and microstructure of the blended cement pastes were determined at viscosity values of 1.5 Pa·s. in the presence of Superplasticisers. The findings showed that the Krieger–Dougherty equation could be used to determine the effect of solids content on the apparent viscosity of limestone- and fly ash-blended cement suspensions, as well as the effect of Superplasticisers. Adding less than 30% limestone to cement had no effect on paste rheology: i.e., the w/c ratios for minimum and optimal workability were similar to the ratios for ordinary cement. However, adding fly ash did lower the minimum water demand, and the optimal amount of water needed for suitable fluidity. The inclusion of 10% of either addition raised paste strength, while higher proportions 30 or 50%) had the opposite effect. The use of mineral additions reduced the effectiveness of cement Superplasticisers.
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adsorption of superplasticizer admixtures on alkali activated slag pastes
Cement and Concrete Research, 2009Co-Authors: Marta Palacios, Yves F. Houst, Paul Bowen, Francisca PuertasAbstract:Abstract Alkali-activated slag (AAS) binders are obtained by a manufacturing process less energy-intensive than ordinary Portland cement (OPC) and involves lower greenhouse gasses emission. These alkaline cements allow the production of high mechanical strength and durable concretes. In the present work, the adsorption of different superplasticizer admixtures (naphthalene-based, melamine-based and a vinyl copolymer) on the slag particles in AAS pastes using alkaline solutions with different pH values have been studied in detail. The effect of the superplasticizers on the yield stress and plastic viscosity of the AAS and OPC pastes have been also evaluated. The results obtained allowed us to conclude that the adsorption of the superplasticizers on AAS pastes is independent of the pH of the alkaline solutions used and lower than on OPC pastes. However, the effect of the admixtures on the rheological parameters depends directly on the type and dosage of the superplasticizer as well as of the binder used and, in the case of the AAS, on the pH of the alkaline activator solution. In 11.7-pH NaOH-AAS pastes the dosages of the superplasticizers required to attain similar reduction in the yield stress are ten-fold lower than for Portland cement. In this case the superplasticizers studied show a fluidizing effect considerably higher in 11.7-pH NaOH-AAS pastes than in OPC pastes. In 13.6-pH NaOH-AAS pastes, the only admixture observed to affect the rheological parameters is the naphthalene-based admixture due to its higher chemical stability in such extremely alkaline media.
Xiuju Lin - One of the best experts on this subject based on the ideXlab platform.
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synthesis and characterization of high performance cross linked polycarboxylate superplasticizers
Construction and Building Materials, 2019Co-Authors: Xiuju Lin, Bing Liao, Jingfei Zhang, Jianheng Huang, Hao PangAbstract:Abstract Cross-linked sustained-release polycarboxylate superplasticizers (SPs) are superior alternative to the comb-type polycarboxylate SPs due to they offer both a high fluidity and a good retention effect for concrete slurry. In this context, a series of cross-linked polycarboxylate superplasticizers were synthesized using acrylic acid, methylallyl polyoxyethylene ether and four different cross-linkers containing ester groups, respectively. The key difference among these four cross-linkers is their molecular weights because they each possessed the different ethoxy content. The fluidity and fluidity retention tests, adsorption performance and scanning electron microscope tests showed that the cross-linked superplasticizers offered good dispersing effects and excellent slump performance. Excitingly, the maximum flow reached up to 394 mm at a water-cement ratio of 0.35 and this high fluidity could be simultaneously maintained for 2 h, which facilitated concrete transport over long distances, therefore improving the practical workability of concrete. Furthermore, it was found that the superplasticizers derived from cross-linkers with higher ethoxy group contents provided cement paste samples with improved fluidity. Evaluation of the hydration heat and setting time demonstrated that the cross-linked polycarboxylate superplasticizers could delay the hydration of cement and the final setting time had been extended by 4 h in comparation with blank samples. After 3, 7 and 28 d, the compressive strength of the cement mortar was improved with increases of molecular weight of the cross-linker in the cross-linked superplasticizers due to the elevation of ethoxy content.
Johann Plank - One of the best experts on this subject based on the ideXlab platform.
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novel concrete superplasticizers based on phosphate esters
Cement and Concrete Research, 2019Co-Authors: J Stecher, Johann PlankAbstract:Abstract Novel polyphosphate superplasticizers were synthesized by copolymerization reaction between 2-(methacryloyl oxy) ethyl phosphate monomer and the macromonomer polyethylene glycol methacrylate ester at different molar ratios. The synthesized phosphated comb polymers were characterized by size exclusion chromatography and elemental analysis and their dispersing performance in cement was assessed via mini slump tests in cement paste. The phosphated comb polymers exhibited superior dispersing performance over conventional polycarboxylate comb polymers (PCEs), were less retarding on cement and showed comparable robustness against sulfate and clay impurities. These properties can be explained by the high calcium complexing capacity of the phosphate groups. Thus, phosphated comb polymers present a viable alternative to polycarboxylate superplasticizers.
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dispersing performance of superplasticizers admixed to aged cement
Construction and Building Materials, 2017Co-Authors: Markus R Meier, Teepakorn Napharatsamee, Johann PlankAbstract:Abstract A mechanistic study using fresh and aged binary mixtures of C3A (cubic and orthorhombic) and gypsum revealed that the interaction and hence dispersing performance of superplasticizers in aged cement is controlled by two competing processes, one being agglomeration and caking of the binder particles resulting in a decreased specific surface area, and the other process being continuous formation of hydration products, especially of ettringite, which leads to an increase of surface area. The results suggest that the interaction of superplasticizers with aged cement can be positive or negative, depending on the composition of the cement relative to C3A, with negative effects being most prevalent.
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formation of nano sized ettringite crystals identified as root cause for cement incompatibility of pce superplasticizers
2015Co-Authors: Alex Lange, Johann PlankAbstract:Recently, nano materials including nanoclays, nano-TiO2 or nano-sized CSH-PCE seed crystals have gained considerable attention in building materials. It is however frequently overlooked that particularly nano-sized crystals can also form during cement hydration. This study investigates on the early ettringite formation in cement, and on the interaction of polycarboxylate-based superplasticizers with such ettringite. Two different cements and five different polycarboxylate-based superplasticizers were analyzed. It was found that the formation of nano-sized ettringite instigated by common PCE superplasticizers presents the root cause for cement-PCE incompatibility which is frequently observed in concrete exhibiting low water-to-cement ratio. Experiments revealed that PCE superplasticizers act as morphological catalyst and transform common micro-meter sized ettringite into nano-sized crystals (l–200 nm). This effect can cause incompatibility between PCE and cements possessing elevated C3A content (>7 wt.-%) and high amounts of immediately soluble sulfates. The nano-scale ettringite was identified via X-ray diffraction, elemental analysis and thermogravimetry. It can be separated from a cement paste by centrifugation where it appears as a gel-like, viscous top layer. Almost all PCE polymers, independent of their chemical nature, produce particularly small, nano-sized ettringite and thus require exceptionally high dosages with these cements. Such phenomenon is commonly referred to as “cement incompatibility” of PCE. Only one specific molecular structure of PCE was identified which produces micro-meter sized ettringite, therefore requires low dosages.
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influence of the hlb value of polycarboxylate superplasticizers on the flow behavior of mortar and concrete
Cement and Concrete Research, 2014Co-Authors: Alex Lange, Tsuyoshi Hirata, Johann PlankAbstract:Abstract Applicators of mortars and concretes admixed with polycarboxylate superplasticizers routinely observe that at low water-to-cement (w/c) ratios (e.g.
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synthesis and performance of methacrylic ester based polycarboxylate superplasticizers possessing hydroxy terminated poly ethylene glycol side chains
Cement and Concrete Research, 2008Co-Authors: Johann Plank, K Pollmann, Nadia Zouaoui, P R Andres, C SchaeferAbstract:Abstract The synthesis and performance of new methacrylate ester based polycarboxylate superplasticizers is shown. These new superplasticizers possess hydroxy termination of the poly(ethylene glycol) side chains instead of conventional methoxy termination. Properties of the new superplasticizers in cement paste were compared to those of conventional ones. For this comparison, methacrylic acid–poly(ethylene glycol) methacrylate ester copolymers having three different side chain lengths and either hydroxyl or methoxy terminated graft chains were synthesized. For characterization of the superplasticizers, gel permeation chromatography (GPC) as well as anionic charge density determination was carried out. The performance of the polymers in cement was tested by measuring paste flow, adsorption as well as zeta potential. Additionally, retardation of the copolymers possessing side chains of 45 ethylene oxide units was investigated by heat calorimetry. According to the data, macromonomers based on hydroxy terminated poly(ethylene glycol) methacrylate ester chemistry allow to produce superplasticizers of high quality.
Said Kenai - One of the best experts on this subject based on the ideXlab platform.
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effects of granulated blast furnace slag and superplasticizer type on the fresh properties and compressive strength of self compacting concrete
Cement & Concrete Composites, 2012Co-Authors: Othmane Boukendakdji, El-hadj Kadri, Said KenaiAbstract:Abstract This paper presents the results of an experimental investigation carried out to study the effect of granulated blast furnace slag and two types of superplasticizers on the properties of self-compacting concrete (SCC). In control SCC, cement was replaced with 10%, 15%, 20%, and 25% of blast furnace slag. Two types of superplasticizers: polycarboxylate based superplasticizer and naphthalene sulphonate based superplasticizers were used. Tests were conducted for slump flow, the modified slump test, V-Funnel, J-Ring, U-Box, and compressive strength. The results showed that polycarboxylate based superplasticizer concrete mixes give more workability and higher compressive strength, at all ages, than those with naphthalene sulphonate based superplasticizer. Inclusion of blast furnace slag by substitution to cement was found to be very beneficial to fresh self-compacting concrete. An improvement of workability was observed up to 20% of slag content with an optimum content of 15%. Workability retention of about 45 min with 15% and 20% of slag content was obtained using a polycarboxylate based superplasticizer; compressive strength decreased with the increase in slag content, as occurs for vibrated concrete, although at later ages the differences were small.
