Mechanism of Settling in Cement Paste

Wheeler, J.

doi:10.1038/2121035a0

Cited by 8 publications

(4 citation statements)

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“…In this case, the segregation of solid particles by gravity-induced settlement has likely played a relevant role in determining the observed plastic shrinkage. Particle settlement has long been recognized as a mechanism that controls the behaviour of fresh cement [43]. This tendency to settling and segregation of samples C2 is related to the intrinsic lower reactivity of this sample, which is characterized by a lower Al 2 O 3 /SiO 2 ratio, indicative of a larger amount of inert phases such as feldspars and quartz, compared to samples C1 and C3 prepared using Clay 1 and Clay 3.…”

Section: Discussionmentioning

confidence: 99%

Assessing the dimensional stability of alkali-activated calcined clays in the fresh state: a time-lapse X-ray imaging approach

Valentini

Mascarin

2021

Mater Struct

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Alkali-activated calcined clays are promising candidates for playing a prominent role in the future construction industry. These binders may achieve excellent mechanical performance, but one issue deserving attention is the proneness to plastic shrinkage and surface cracking. Tackling this issue requires the deployment of laboratory techniques that allow shrinkage-inducing mechanisms to be quantitatively assessed. Here, we demonstrate that time-lapse X-ray imaging can be used to quantify shrinkage immediately after mixing, when the binder is still in its fresh state, with excellent time and space resolution. The numeric quantification of strain is complemented by the real time visual inspection of the displacing sample interface and of the bleed aqueous solution layer that may form. Implementation of this method to a set of alkali-activated cement pastes, prepared by combining calcined clays having different mineralogical composition with sodium silicate activating solutions having different $$\hbox {SiO}_2$$ SiO 2 /$$\hbox {Na}_2\hbox {O}$$ Na 2 O ratios, suggests that two main mechanisms control the early dimensional stability of alkali-activated calcined clays. These mechanisms are: (a) volumetric contraction occurring in response to capillary stress arising from water evaporation and (b) segregation by particle settling, favoured in the water-saturated regime.

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Section: Discussionmentioning

confidence: 99%

Assessing the dimensional stability of alkali-activated calcined clays in the fresh state: a time-lapse X-ray imaging approach

Valentini

Mascarin

2021

Mater Struct

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“…Homogeneity is a prerequisite for a quantification of the water in the samples. Any sedimentation or bleeding of cement paste as reported by various authors (Peng & Jacobsen, 2013;Wheeler, 1966;Wheeler & Chatterji, 1972) leads to a differentiation in the sample and thus to a overdetermined quantification of the free water.…”

Section: Introductionmentioning

confidence: 99%

Quantitative X-ray diffraction of free, not chemically bound water with the PONKCS method

et al. 2018

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The free water in calcined phyllosilicate–water mixtures exhibits a distinctly different behaviour in its X‐ray amorphous scattering contribution as opposed to fly ash– or limestone powder–water mixtures. While fly ash and limestone powder yield a continuous increase in the scattering contribution when water is added, the scattering contribution stagnates for calcined phyllosilicates over a wide range of water addition. There is a direct correlation between the consistency of the sample and the X‐ray amorphous scattering contribution caused by the water. The same correlation can also be found in in situ X‐ray diffraction measurements of hydrating systems. As long as the sample has a pasty consistency, the scattering contribution of the water decreases with progressive reaction. After the transition from fresh paste to final set, there is no further reduction of the X‐ray amorphous scattering contribution caused by the free water, which means that the free water cannot be quantified correctly from this point in time.

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“…Powers [3] as well as Steinour [4] developed the first equations, based on Poiseuille's Law of capillary flow, to determine the initial constant bleeding rate of cement pastes. In order to get a better understanding about the mechanism of settling in cement pastes, Wheeler and Chatterji calculated the density of a sedimenting (bleeding) fresh cement paste by X-ray radiography [5,6]. Using this method, they found that the bleeding process is accompanied by an increase in density of the consolidated cement paste and that a density gradient is formed over the height of the cement paste column.…”

Section: Introductionmentioning

confidence: 99%

The Influence of Bleeding of Cement Suspensions on Their Rheological Properties

2020

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Flowable concretes tend to segregate. The risk of segregation is particularly high when the concrete is vibrated during the compaction process. A well-known segregation phenomenon is the so-called “bleeding”. This is a rise of water to the surface of the freshly poured concrete due to the difference in density between the mixing water and the concrete’s denser solid components (aggregates, cement and additives). This type of segregation occurs particularly within the paste. The focus of this paper is, therefore, on the sedimentation behavior at the microscale of concrete and especially on the influence of this process on rheological properties of the cement paste. In addition to common bleeding tests of cement suspensions using standing cylinders, rheometric measurements were performed on the suspensions during the bleeding process. A measuring procedure was developed for the rheometric measurements of the sedimenting cement suspensions. The rheological properties of the investigated cement suspensions were determined at four specific measuring times and at four specific measuring heights (i.e., positions) each. With this method it could be shown that the cement suspensions are not homogeneous over their height and that bleeding has a great influence on the rheological properties of cement suspension.

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Mechanism of Settling in Cement Paste

Cited by 8 publications

References 0 publications

Assessing the dimensional stability of alkali-activated calcined clays in the fresh state: a time-lapse X-ray imaging approach

Assessing the dimensional stability of alkali-activated calcined clays in the fresh state: a time-lapse X-ray imaging approach

Quantitative X-ray diffraction of free, not chemically bound water with the PONKCS method

The Influence of Bleeding of Cement Suspensions on Their Rheological Properties

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