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Beata Łaźniewska-piekarczyk - One of the best experts on this subject based on the ideXlab platform.

Ismail Aiad - One of the best experts on this subject based on the ideXlab platform.

  • influence of time addition of superplasticizers on the rheological properties of fresh cement pastes
    Cement and Concrete Research, 2003
    Co-Authors: Ismail Aiad
    Abstract:

    It is well known that the fluidity and the fluidity loss of fresh cement pastes are affected by the kind and the time of addition of organic Admixtures. The influence of the time addition of two chemical Admixtures, namely, melamine formaldehyde sulfonate (MFS) and naphthalene formaldehyde sulfonate (NFS), on the rheological properties of ordinary Portland and sulfate-resisting cement pastes through the first 120 min of hydration was investigated. The Admixture addition was delayed by 0, 5, 10, 15, 20, and 25 min. Shear stress and apparent viscosity of the cement pastes were determined at different shear rates (3–146 s−1) and hydration times of 30, 60, 90, and 120 min. The concentration of Ca2+ and the combined water content of the cement pastes were determined after 120 min. Yield stress and plastic viscosity values were also determined by using the Bingham model. The results show that an increase in the addition time of the Admixture reduces the shear stress, the yield stress, and the plastic viscosity of the cement pastes at the early ages (15 min) as well as at later early ages (120 min). The optimum delaying time of Admixture addition is found to be 10–15 min. This time does not depend on the cement and superplasticizer type.

Shunsuke Hanehara - One of the best experts on this subject based on the ideXlab platform.

  • interaction between cement and chemical Admixture from the point of cement hydration absorption behaviour of Admixture and paste rheology
    Cement and Concrete Research, 1999
    Co-Authors: Shunsuke Hanehara, Kazuo Yamada
    Abstract:

    Chemical Admixtures can improve the properties of concrete. High performance concrete with high strength, superior fluidity, and self-compactibility can be realized mainly because of chemical Admixtures. Rheological properties of fresh concrete can be strongly affected by the combination of cement and chemical Admixture, method of Admixture addition, or the water-cement ratio. Problems in fluidity, such as stiffening and large slump-loss, occasionally happen under a particular combination of cement and Admixture. These phenomena are generally called incompatibilities between cement and chemical Admixtures. In this study, the interaction between cement and the chemical Admixture types lignin sulfonate, naphthalene sulfonate, melamine sulfonate, amino sulfonate, and polycarboxylate, together with the working factors and mechanisms, are discussed from the viewpoint of cement hydration. Although the polycarboxylate type superplasticizer was considered to have better compatibility in combination with different kinds of cement, the authors show that its compatibility is affected by the amount of alkaline sulfates in cement.

  • effect of Admixture on hydration of cement adsorptive behavior of Admixture and fluidity and setting of fresh cement paste
    Cement and Concrete Research, 1992
    Co-Authors: Hiroshi Uchikawa, Shunsuke Hanehara, Tokuhiko Shirasaka, Daisuke Sawaki
    Abstract:

    The adsorptive behavior of Admixtures and the hydration of cement in the presence of Admixtures were examined and the relationships of them with the physical properties of fresh cement paste including fluidity, variation of fluidity with time and setting time were discussed with the quantitative determination of organic Admixture adsorbed on the cement, and with the observation and determination of the surface microstructure and composition of polished clinker dipped in aqueous solution containing a specified quantity of Admixture by advanced method of surface analysis. In order to prepare the same fluidity of fresh cement paste, mortar and concrete, the required amount of an easily adsorbed Admixture is larger than that of a hard adsorbed one. An Admixture having a functional group producing a complex salt with Ca2+ decreases the concentration of Ca2+ in liquid phase at early age and delays the saturation of Ca2+, which influences the morphology of hydrate produced, causes fluidity loss with time and delays the setting time of cement. The microstructural and compositional estimations of the adsorption layer of Admixture on the surface of clinker minerals by in-lens FESEM, ESCA-imaging, AES and AFM indicates that the Admixture is partially adsorbed to the interstitial phase in a thick layer, forming characteristic three dimensional surface structure.

  • Effect of Admixture on hydration of cement, adsorptive behavior of Admixture and fluidity and setting of fresh cement paste
    Cement and Concrete Research, 1992
    Co-Authors: Hiroshi Uchikawa, Shunsuke Hanehara, Tokuhiko Shirasaka, Daisuke Sawaki
    Abstract:

    The adsorptive behavior of Admixtures and the hydration of cement in the presence of Admixtures were examined and the relationships of them with the physical properties of fresh cement paste including fluidity, variation of fluidity with time and setting time were discussed with the quantitative determination of organic Admixture adsorbed on the cement, and with the observation and determination of the surface microstructure and composition of polished clinker dipped in aqueous solution containing a specified quantity of Admixture by advanced method of surface analysis. In order to prepare the same fluidity of fresh cement paste, mortar and concrete, the required amount of an easily adsorbed Admixture is larger than that of a hard adsorbed one. An Admixture having a functional group producing a complex salt with Ca2+ decreases the concentration of Ca2+ in liquid phase at early age and delays the saturation of Ca2+, which influences the morphology of hydrate produced, causes fluidity loss with time and delays the setting time of cement. The microstructural and compositional estimations of the adsorption layer of Admixture on the surface of clinker minerals by in-lens FESEM, ESCA-imaging, AES and AFM indicates that the Admixture is partially adsorbed to the interstitial phase in a thick layer, forming characteristic three dimensional surface structure.

Valeria Corinaldesi - One of the best experts on this subject based on the ideXlab platform.

  • combined effect of expansive shrinkage reducing and hydrophobic Admixtures for durable self compacting concrete
    Construction and Building Materials, 2012
    Co-Authors: Valeria Corinaldesi
    Abstract:

    Abstract This paper presents the results of an investigation carried out to develop white self-compacting concretes (SCCs) especially devoted to durable architectural structures. In fact, shrinkage-free SCC mixtures were studied, obtained by combining CaO-based expansive agent and shrinkage reducing Admixture. Also a hydrophobic Admixture was added to SCC in order to preserve the white surface from the growth of micro-organisms as well as to increase concrete durability. Rheological tests were carried out on cement pastes, as well as on fresh SCCs, containing the three Admixtures in order to study their influence (alone or in combination) on cement paste and concrete rheology. Also thermogravimetric analysis was carried out on cement pastes in order to evaluate the influence of various Admixtures on portlandite solubility. Hardened SCCs were characterized by means of compression tests, free dying shrinkage, and restrained expansion measurements.

Francisca Puertas - One of the best experts on this subject based on the ideXlab platform.

  • effect of polycarboxylate ether Admixtures on calcium aluminate cement pastes part 2 hydration studies
    Industrial & Engineering Chemistry Research, 2013
    Co-Authors: M.m. Alonso, Marta Palacios, Francisca Puertas
    Abstract:

    In part 1, the effect of different polycarboxylate ether (PCE) Admixtures with Portland-based binder (OPC) and calcium aluminate cement (CAC) pastes has been studied; indicating a low CAC–PCEs compatibility. In this part, 2, the effect of PCE Admixtures with different molecular structure on the hydration and microstructural development of CAC pastes has been studied. The findings showed that the PCE Admixtures used retarded CAC hydration and this effect is independent of the Admixture carboxylate/ester ratio. The results obtained have proven that the presence of PCE Admixtures in OPC and CAC pastes does not modify the nature of hydrates formed. However, in CAC pastes, the presence of PCE Admixture has an important effect on the amount of hydrates generated, it being 45% lower at the same time than in CAC pastes without Admixture.

  • Compatibility between polycarboxylate-based Admixtures and blended-cement pastes
    Cement & Concrete Composites, 2012
    Co-Authors: M.m. Alonso, Marta Palacios, Francisca Puertas
    Abstract:

    Abstract Compatibility between three structurally different PCEs and four commercial cements: one non-blended cement and three blended cements, was studied by adsorption, zeta potential, rheological and calorimetric methods. According to the adsorption curve results, the higher the percentage of carboxylates groups in the Admixture, the more intensely it is adsorbed on cement pastes. Moreover, Admixtures were shown to be adsorbed by the additions as well, being most effectively adsorbed in limestone. From the rheological point of view, the optimum carboxylate group/ester group ratio for the Admixtures used in the present study was found to range from 0.7 to 1.2. The fluidizing effect of the Admixtures on cement pastes is conditioned by the presence of mineral additions. Despite the low adsorption rates of the Admixtures in slag-blended cements, the inclusion of PCEs generated the steepest declines in the rheological parameters. The delay of Admixtures on cement hydration intensifies with rising PCE dosage. This Admixture-mediated retarding effect was also observed to vary depending on the nature of the addition, and was most intense in slag-blended cement.

  • polycarboxylate superplasticiser Admixtures effect on hydration microstructure and rheological behaviour in cement pastes
    Advances in Cement Research, 2005
    Co-Authors: Francisca Puertas, Marta Palacios, H Santos, S Martinezramirez
    Abstract:

    A study was conducted on the effect of a polycarboxylate (PC) Admixture on the mechanical, mineralogical, microstructural and rheological behaviour of Portland cement pastes. It was observed that the presence of PC Admixture retards the initial cement hydration reactions, although this effect may be offset by possible increased diffusion in later stages. Additionally, the PC Admixtures produce a few alterations in the structure and composition of the formed C—S—H gel. The addition of 1% PC Admixture in the pastes generates a higher percentage of silicate bridge (Si Q2 units) mainly at 2 days. The Admixture used in this study induced microstructural modifications in the pastes which slightly reduced the porosity; however the Admixture did not affect the mechanical strength of the pastes at either 2 or 28 days of hydration. Finally, from the results of the rheological studies it was concluded that a low dosage of PC led to a substantial reduction (over 70%) in the yield stress.