Characterization of entrained air voids in cement paste with scattered ultrasound

The microstructure of air voids in both air-entrained and non air-entrained paste, mortar, and concrete has been studied at different ages (5 min to 60 days) in order to understand how air-entrained voids form in portland-cement systems. Scanning electron micrographs of air voids are presented for different ages. The solidification process of portland-cement paste and mortar was frozen at different ages using a low temperature scanning electron microscope and freeze drying. At very early ages the air voids show thin shells made of very fine particles. The packing of the cement grains behind the air void varies, depending on the water-to-cement ratio. Air voids appear to have the same interface with the cement paste matrix as aggregates. No readily visible difference was found between entrapped and entrained air voids.

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Effect of Salt Admixtures on Air Content in Fresh Air-Entrained Concretes

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.477.211 ◽

2011 ◽

Vol 477 ◽

pp. 211-215

Author(s):

Qin Fei Li ◽

Yong Ge ◽

Wen Cui Yang ◽

Jie Yuan ◽

Ji Shou Yu

Keyword(s):

Cement Paste ◽

Fresh Concrete ◽

Foam Stability ◽

Air Voids ◽

Air Content ◽

Foaming Power ◽

Entrained Air

Combined with the foam stability of air-entraining admixtures (AEAs), the effect of salt admixtures (including CaCl2, Ca(NO3)2, Na2SO4 and NaNO2) on morphology of air-voids in cement paste with a couple kinds of air-entraining admixtures (including SJ-2 and DH-9) was examined by means of SEM. In accordance with foam stability and the morphology, air content of fresh concrete was studied and analyzed more deeply. The results pointed out that these salts mitigated the foam stability of SJ-2 solution, and the deteriorated effect of CaCl2 and Ca(NO3)2 was more obvious. By contrast, these salts seemed to make no difference to the foam stability, but CaCl2 and Ca(NO3)2 reduced the foaming power of DH-9 solution. The walls of air voids in cement paste without using AEAs were compact. Differently, it was a distinct shell that formed around most of the entrained air voids with AEAs. This shell connected with capillary pores. For SJ-2 mixed, the air content of fresh air-entrained concretes was decreased by CaCl2 and Ca(NO3)2, but was enhanced by Na2SO4 and NaNO2; for DH-9 mixed, with the increasing usage of CaCl2, Ca(NO3)2, Na2SO4 or NaNO2, the air content was rising gradually.

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The morphology of entrained air voids in hardened cement paste generated with different anionic surfactants

Cement and Concrete Composites ◽

10.1016/j.cemconcomp.2008.02.003 ◽

2008 ◽

Vol 30 (7) ◽

pp. 566-575 ◽

Cited By ~ 33

Author(s):

H.N. Atahan ◽

C. Carlos ◽

S. Chae ◽

P.J.M. Monteiro ◽

J. Bastacky

Keyword(s):

Cement Paste ◽

Anionic Surfactants ◽

Hardened Cement ◽

Hardened Cement Paste ◽

Air Voids ◽

Entrained Air

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Characterization of Entrained Air Voids Using Scattered Ultrasound

10.1063/1.2184679 ◽

2006 ◽

Cited By ~ 2

Author(s):

W. Punurai

Keyword(s):

Air Voids ◽

Entrained Air

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Modelling Pore Structure of Cement Based Material According to Continuous Network System

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.578-579.1531 ◽

2014 ◽

Vol 578-579 ◽

pp. 1531-1537

Author(s):

Sung In Hong ◽

Joon Woo Park ◽

Young Hee Jung ◽

Ki Yong Ann

Keyword(s):

Pore Structure ◽

Cement Paste ◽

Mercury Intrusion Porosimetry ◽

Cement Matrix ◽

Network System ◽

Air Voids ◽

Mercury Intrusion ◽

Entrapped Air ◽

Entrained Air

In this study, a modified pore structure of cement based material with respect to a path for ingressive ions was established. Of pores in a concrete, gel pores and other entrapped air voids were excluded from modelling the pore structure as no interests are given due to the ions immobilization of cement paste media. To setup the pore structure, the linear traverse method (LTM) was used to distribute air voids along the traverse line in a hexahedron cement paste structure, followed by including entrained air voids to fill up the least space of the cement matrix and making a network of the air voids through capillary pores at the variation in the diameters. Then the mercury intrusion porosimetry (MIP) was used to iteratively approach an accordance rate with calculated one from the above way to get into appropriate convergence value. As a result, for the OPC specimen the developed model shows a somewhat relevant value of 42.4 % of the accordance rate compared to empirical one and 64.24 of the ratio of ionic path to original distance within a concrete.

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Characterization of the damage of a chemically degraded cement paste

Materials and Structures ◽

10.1617/14225 ◽

2005 ◽

Author(s):

E. Guillon

Keyword(s):

Cement Paste

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Characterization of high strength cement paste with pristine graphite and heptane-graphite emulsion

10.21838/uhpc.2016.110 ◽

2016 ◽

Cited By ~ 1

Author(s):

Aileen Vandenberg ◽

Daniel Massucci ◽

Steven Woltornist ◽

Douglas Adamson ◽

Kay Wille

Keyword(s):

Cement Paste ◽

High Strength

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Quantitative Characterization of Hydration of Cement Pastes by Rietveld Phase Analysis and Thermoanalysis

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.539.19 ◽

2013 ◽

Vol 539 ◽

pp. 19-24 ◽

Cited By ~ 1

Author(s):

Yong Qi Wei ◽

Wu Yao

Keyword(s):

Phase Analysis ◽

Cement Paste ◽

Rietveld Method ◽

X Ray Diffraction ◽

Scanning Calorimetry ◽

Quantitative Characterization ◽

Cement Pastes ◽

Hydration Mechanism ◽

Spot Check

The quantitative characterization of hydration of cement pastes has always been one of focuses of researchers’ attention. Rietveld phase analysis (RPA), a combination of quantitative X-ray diffraction (QXRD) and the Rietveld method, supplies a tool of an enormous potential for that. Although a few of related researches were conducted by RPA, the reported attention was not paid to the neat cement paste with a low w/c ratio. Therefore, this work aimed at the quantitative study on hydration of such a cement paste chiefly by this method, meanwhile, cooperated with the hyphenated technique of thermogravimetry with differential scanning calorimetry (TG-DSC), as a spot check. Results indicated that RPA was a reliable method in quantitatively characterizing hydration of cement pastes, and gave a clear decription of evolution of all main crystal phases in cement pastes; and that the evolution of monosulphate(Afm_12) was also able to be tracked quantitatively. This will help to understand better the hydration mechanism of cement pastes, as well as to investigate quantitatively effects of mineral and chemical admixtures on hydration of composite cementitious systems.

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