The Experts below are selected from a list of 14016 Experts worldwide ranked by ideXlab platform

J. Szwabowski - One of the best experts on this subject based on the ideXlab platform.

  • air entrainment problem in self compacting concrete
    Journal of Civil Engineering and Management, 2009
    Co-Authors: J. Szwabowski, Beata Lazniewskapiekarczyk
    Abstract:

    Abstract According to the actual state of knowledge and in accordance with the PN‐EN 2006–1 norm, it is recommended to use air‐entrainment as a basic way of assuring frost‐resistance of concrete. In case of self‐compacting concrete (SCC), achieving adequate air‐entrainment is a problematic issue because of one of the side‐effects of the functioning of a new generation of Superplasticizers, i.e. excessive air‐entrainment (considerably higher than 2%) in a self‐compacting concrete mix. Thus, in this situation, the dosage of an air‐entraining admixture has to be reduced. It was discovered that the cause of an air‐entrainment effect of Superplasticizers is a decrease of the surface tension value of the liquid phase in paste. In the paper, the problem of air‐entrainment is discussed, formed as a result of the functioning of a superplasticizer on the characteristics both of concrete and a mixture, depending on the content. To verify the influence a superplasticizer and an air‐entraining admixture have on concre...

  • Air‐entrainment problem in self‐compacting concrete
    Journal of Civil Engineering and Management, 2009
    Co-Authors: J. Szwabowski, Beata Lazniewska-piekarczyk
    Abstract:

    Abstract According to the actual state of knowledge and in accordance with the PN‐EN 2006–1 norm, it is recommended to use air‐entrainment as a basic way of assuring frost‐resistance of concrete. In case of self‐compacting concrete (SCC), achieving adequate air‐entrainment is a problematic issue because of one of the side‐effects of the functioning of a new generation of Superplasticizers, i.e. excessive air‐entrainment (considerably higher than 2%) in a self‐compacting concrete mix. Thus, in this situation, the dosage of an air‐entraining admixture has to be reduced. It was discovered that the cause of an air‐entrainment effect of Superplasticizers is a decrease of the surface tension value of the liquid phase in paste. In the paper, the problem of air‐entrainment is discussed, formed as a result of the functioning of a superplasticizer on the characteristics both of concrete and a mixture, depending on the content. To verify the influence a superplasticizer and an air‐entraining admixture have on concre...

  • influence of Superplasticizers on rheological behaviour of fresh cement mortars
    Cement and Concrete Research, 2004
    Co-Authors: J Golaszewski, J. Szwabowski
    Abstract:

    To assure required workability of high performance concrete (HPC), various Superplasticizers are used. Only by using Superplasticizers can rheological properties of HPC mix be adequately adjusted to the methods and conditions of concrete processing. Thus, the key element in efficient workability shaping is the complex knowledge how Superplasticizers influence the rheological properties of fresh concrete in different technological circumstances. In the paper, the methodology and test results of an investigation into the influence of chemically different Superplasticizers on the rheological properties of standard mortars are presented and discussed. The rheological parameters of mortars yield value g, and plastic viscosity h were determined using VISCOMAT PC rotational rheometer. In the research, the influence of the performance of Superplasticizers was investigated taking into account following factors: chemical origin of Superplasticizers (SNF/naphthalene sulfonic acid/, AP/polycarboxylate acid, PC/policarboxylate ester/), superplasticizer dosage, W/C ratio, cement type (CEM I, CEM II and CEM III), cement physical and chemical properties and temperature. The results presented in the paper show that by testing rheological parameters of mortars with rotational viscometer, it is possible to complex and precisely determine the performance of Superplasticizers. On the ground of obtained results, it is possible to optimise the composition of mortars and concretes from workability point of view.

  • INFLUENCE OF CEMENT AND SUPERPLASTICIZER ON RHEOLOGICAL PROPERTIES OF MORTARS
    Brittle Matrix Composites 7, 2003
    Co-Authors: Jacek Gołaszewski, J. Szwabowski
    Abstract:

    ABSTRACT Effectiveness of superplasticizer is an effect of complex system of factors connected mainly with concrete components properties, concrete composition and concreting conditions. From among these factors the key role for the superplasticizer effectiveness plays interaction of cement and superplasticizer. Selection of cement - superplasticizer system determines also workability of fresh concrete and thus also possibility of performing of HPC. In the paper methodology and results of the investigation into the influence of different Superplasticizers on the rheological properties of modified, for the sake of superplasticizer addition and W/C ratio, standard mortars (according PN EN 196—1:1996) with different cements are presented. The rheological parameters of these mortars, yield value and plastic viscosity were determined using a rheometrical methods. In the research program the influence of following factors: chemical origin of Superplasticizers (SNF, SMF, PC and PE Superplasticizers), cement composition (cements of different C3A, Na2Oeq and SO3 content) and cement specific surface, superplasticizer dosage and W/C ratio were investigated. On the basis of test results the relationships between cement and superplasticizer properties and rheological properties of cement mortars were defined and discussed. These relationships in form of mathematical models can be used in workability shaping process to select optimal cement - superplasticizer system.

Robert J. Flatt - One of the best experts on this subject based on the ideXlab platform.

  • Effect of Polymer Structure on the Sulfate-Polycarboxylate Competition
    2009
    Co-Authors: Jörg Zimmermann, Christina Hampel, Christophe Kurz, Lukas Frunz, Robert J. Flatt
    Abstract:

    This paper describes how outstanding concrete performances are achieved nowadays using polycarboxylate-type Superplasticizers. Nevertheless high performing Superplasticizers are often sensitive to the cement used and in particular the cement sulfate content. Laboratory studies have shown that sulfates strongly influence the performance of superplasticizer because they inhibit polymer absorption which causes a reduction in flow properties of cementitious materials. This seems to have led to the belief that this phenomenon is generally true for polycarboxylates. In fact, it depends very much on the detailed polymer structure. In this study, the sulfate sensitivity of polymers with systematically varied polymer structures has been measured through paste experiments and the influence of different polymer structures on the sulfate sensitivity will be discussed.

  • design and function of novel Superplasticizers for more durable high performance concrete superplast project
    Cement and Concrete Research, 2008
    Co-Authors: Yves F. Houst, Paul Bowen, Francois Perche, Robert J. Flatt, Annika Kauppi, Pascal Borget, Laurent Galmiche, Jeanfrancois Le Meins, Francoise Lafuma, Irene Schober
    Abstract:

    In this article we shall describe our quest and ultimate success in furthering our understanding of the action of Superplasticizers on the rheology of cement and concrete. By specifically producing Superplasticizers with varied architectures, we have been able to show the important structural features of the macromolecules that lead to a successful superplasticizer or water reducing agent. Both polycarboxylate and lignosulfonate polymers have been investigated. Using both non-reactive model MgO powders, three different types of cement blends, the adsorption behaviour and the effect on the rheological properties of these two important superplasticizer families have been used to further develop a conceptual model for superplasticizer — cement behaviour. This paper will deal mainly with the conceptual model, the materials and methods used to asses the polymer adsorption behaviour and rheological properties of the systems studied. We shall briefly describe the adsorption of the polymers onto the different surfaces and their influence on surface charge and rheology and the influence of the various ionic species found in cement pore solutions that may influence polymer-cement affinity. The key factors are shown to be the effective adsorbed polymer thickness and the induced surface charge which can be influenced by the polymer architecture, the pore solution composition and the initial particle surface charge.

  • a simplified view on chemical effects perturbing the action of Superplasticizers
    Cement and Concrete Research, 2001
    Co-Authors: Robert J. Flatt, Yves F. Houst
    Abstract:

    Abstract Understanding and quantifying effects of Superplasticizers in concrete is a complex task. Even for nonreactive systems, such as ceramic suspensions, the stabilizing effects of dispersants are a subject of ongoing research. In cementitious systems, hydration reactions can perturb the behavior of suspensions. In this article, we propose three categories to describe the interactions and state of the Superplasticizers with the cement suspensions. The first part would be consumed by intercalation, coprecipitation or micellization, i.e., by the formation of an organo-mineral phase (OMP). A second part of the polymer could be adsorbed onto the surface of particles and help disperse cement agglomerates. The third part consists of the excess superplasticizer neither consumed nor adsorbed and which remains dissolved in the aqueous phase. Thus, at equal dosage, a cement with a larger degree of consumption (Part 1) could have a lower surface coverage and consequently poorer workability (for cements otherwise equal: specific surface, composition, etc.), unless an excess of superplasticizer is added to ensure saturation. Differentiating consumption from adsorption is essential for correct interpretation of experimental data, a fact that is not yet appreciated often enough and to which this paper attempts to draw larger attention.

Elena Fabiola Ruíz Ledesma - One of the best experts on this subject based on the ideXlab platform.

  • increased durability of concrete made with fine recycled concrete aggregates using Superplasticizers
    Materials, 2016
    Co-Authors: F Cartuxo, Jose Ramon Jimenez, J De Brito, Luis Evangelista, Elena Fabiola Ruíz Ledesma
    Abstract:

    This paper evaluates the influence of two Superplasticizers (SP) on the durability properties of concrete made with fine recycled concrete aggregate (FRCA). For this purpose, three families of concrete were tested: concrete without SP, concrete made with a regular superplasticizer and concrete made with a high-performance superplasticizer. Five volumetric replacement ratios of natural sand by FRCA were tested: 0%, 10%, 30%, 50% and 100%. Two natural gravels were used as coarse aggregates. All mixes had the same particle size distribution, cement content and amount of superplasticizer. The w/c ratio was calibrated to obtain similar slump. The results showed that the incorporation of FRCA increased the water absorption by immersion, the water absorption by capillary action, the carbonation depth and the chloride migration coefficient, while the use of Superplasticizers highly improved these properties. The incorporation of FRCA jeopardized the SP's effectiveness. This research demonstrated that, from a durability point of view, the simultaneous incorporation of FRCA and high-performance SP is a viable sustainable solution for structural concrete production.

  • rheological behaviour of concrete made with fine recycled concrete aggregates influence of the superplasticizer
    Construction and Building Materials, 2015
    Co-Authors: F Cartuxo, Jose Ramon Jimenez, J De Brito, Luis Evangelista, Elena Fabiola Ruíz Ledesma
    Abstract:

    Abstract This paper evaluates the influence of two Superplasticizers (SP) on the rheological behaviour of concrete made with fine recycled concrete aggregates (FRCA). Three families of concrete were tested: family C0 made without SP, family C1 made with a regular superplasticizer and family C2 made with a high-performance superplasticizer. Five replacement ratios of natural sand by FRCA were tested: 0%, 10%, 30%, 50% and 100%. The coarse aggregates were natural gravels. Three criteria were established to design the concrete mixes’ composition: keep the same particle size distribution curves, adjust the water/cement ratio to obtain a similar slump and no pre-saturation of the FRCA. All mixes had the same cement and SP content. The results show that the incorporation of FRCA significantly increased the shrinkage and creep deformation. The FRCA’s effect was influenced by the curing age. The reference concrete made with natural sand stabilizes the creep deformation faster than the mixes made with FRCA. The incorporation of superplasticizer increased the shrinkage at early ages and decreased the shrinkage at 91 days of age. The regular superplasticizer did not improve the creep deformation while the high-performance superplasticizer highly improved this property. The incorporation of FRCA jeopardized the SP’s effectiveness. This study demonstrated that to use FRCA and superplasticizer for concrete production it is necessary to take into account the different rheological behaviour of these mixes.

Johann Plank - One of the best experts on this subject based on the ideXlab platform.

Lucia Ferrari - One of the best experts on this subject based on the ideXlab platform.

  • multi method approach to study influence of Superplasticizers on cement suspensions
    Cement and Concrete Research, 2011
    Co-Authors: Josef Kaufmann, Lucia Ferrari, Frank Winnefeld, Johann Plank
    Abstract:

    Abstract Superplasticizers are widely used in concrete processing to increase the rheological properties of hardening pastes. In this study, different techniques (rheology, adsorption, atomic force microscopy—AFM, and ζ-potential) are used to characterize the impact of polycarboxylate-ether based superplasticizer (PCE) on particle suspensions. Results obtained with two cements and two inert powders (MgO and calcite) show that superplasticizer efficiency is strongly influenced by polymer architecture and by the ionic species present in solution. Additionally, experiments performed with AFM and ζ-potential contributed to characterize dispersion forces exerted by Superplasticizers at the solid–liquid interface. The application of plateau AFM-tips coated with platinum reveals that dispersion forces depends on the presence of ions in solution, and that multilayer formation occurs with certain superplasticizer types. A further conclusion includes the idea that the PCE has a lubricating effect between adjacent particles and PCE increases surface wettability.