Investigations on the influence of fly ash on the formation and stability of artificially entrained air voids in concrete

2008 ◽  
Vol 42 (2) ◽  
pp. 227-240 ◽  
Author(s):  
F. Spörel ◽  
S. Uebachs ◽  
W. Brameshuber
Keyword(s):  
Fly Ash ◽  
Air Voids ◽  
Entrained Air

scholarly journals Sulphate resistance of air entrained mortars with admixture of fly ashes

2015 ◽  
Vol 14 (1) ◽  
pp. 043-052
Author(s):  
Monika Jaworska
Keyword(s):  
Fly Ash ◽  
Sulfate Attack ◽  
Fly Ashes ◽  
Air Voids ◽  
Blended Cements ◽  
Low Calcium ◽  
Entrained Air ◽  
Sem Studies

The effects of entrained air on sulphate resistance of fly ash blended cements mortars long term immersed in Na2SO4 solution were investigated. The expansion strains and decrease in strength of air entrained mortars were faster than those of non-air entrained ones. It was found with SEM and XRD analyses that ettringite and gypsum were the main sulfate attack products. The SEM studies of mortars microstructure showed that the highest amount of ettringite observed occurred in air voids partially filled with this phase. The sulphate resistance of AE and nAE mortars containing high or low calcium fly ash blended cements was significantly higher compared to plain OPC mortar.

scholarly journals The Effect of Fly Ash Microspheres on the Pore Structure of Concrete

Minerals ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 58 ◽  
Author(s):  
Elzbieta Haustein ◽  
Aleksandra Kuryłowicz-Cudowska
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Total Content ◽  
Spherical Particles ◽  
Hardened Concrete ◽  
Image Analysis System ◽  
Micro Computed Tomography ◽  
Concrete Technology ◽  
Air Voids ◽  
X Ray

The fly ash microspheres (FAMs) formed during the mineral transformation stage in coal combustion are hollow spherical particles with a density less than water. This paper presents the results of X-ray micro-computed tomography and an automatic image analysis system of the porosity in the structure of hardened concrete with microspheres. Concrete mixtures with ordinary Portland cement and two substitution rates of cement by microspheres—5% and 10%—are investigated. For all considered mixes, a constant water/binder ratio (w/b) equal to 0.50 was used. The distribution of the air voids and the compressive strength of the concrete were tested after 28 days. With the increasing mass of cement replacement by FAMs, the compressive strength decreases after 28 days. The total volume of the air voids in hardened concrete with fly ash microspheres tested by X-ray varies from 5.1% to 7.4%. The closed pores constitute more than 80% of the total content of air pores. The study proves that the use of microspheres grains with specific dimensions has a significant impact on concrete porosity. Their application in concrete technology can be an alternative aeration solution for fresh concrete mixes and an effective method for utilization.

scholarly journals Effect of entrained air voids on the microstructure and mass transport properties of concrete

2011 ◽  
Vol 41 (10) ◽  
pp. 1067-1077 ◽  
Author(s):  
H.S. Wong ◽  
A.M. Pappas ◽  
R.W. Zimmerman ◽  
N.R. Buenfeld
Keyword(s):  
Mass Transport ◽  
Transport Properties ◽  
Air Voids ◽  
Entrained Air

scholarly journals Influence of the fly ash and the prior freezing and thawing on the sulphate resistance of cement mortars

2018 ◽  
Vol 174 ◽  
pp. 02004
Author(s):  
Julia Marczewska
Keyword(s):  
Fly Ash ◽  
Cement Composites ◽  
Sulphate Attack ◽  
Freezing And Thawing ◽  
Natural Conditions ◽  
Air Voids ◽  
Cement Mortars ◽  
Reduction Of Energy Consumption ◽  
Reduction Of Co2 ◽  
By Products

The use of fly ash for the production of cement is a typical example of the utilization of by-products (waste) from various fields of production in construction, a significant reduction of CO2 emissions and reduction of energy consumption. However, in order to be able to determine the suitability of this additive in construction, it is necessary to examine the durability of cement composites with fly ash in various, often complicated, destructive environments. There are known publications regarding the durability of concretes with fly ash in individual environments. However, in natural conditions, several destructive environments are common at the same time. The article presents an attempt to reproduce natural conditions. This paper presents the results of sulphate expansion tests of air-entrained (AE) and non-air-entrained (nAE) Portland and fly ash cement mortars subjected to prior freezing and thawing. Despite significant strains experienced during freeze-thaw cycles, unlike the non-air-entrained Portland cement mortars, the non-air-entrained mortars made of fly ash cement did not exhibit any significant expansion when exposed to Na2SO4. For 17 months no expansion was found in the air-entrained mortars made of either of the cement types when immersed in Na2SO4solution after freezethaw cycles. The results of the SEM and EDS analyses showed that gypsum and ettringite were the sulphate attack products in all the mortars. The highest amounts of ettringite were found in air voids.

scholarly journals Influence of Fly Ash From Co-Combustion of Coal and Biomass on Scaling Resistance of Concrete / Wpływ Popiołu Lotnego Ze Współspalania Wegla I Biomasy Na Odpornosc Betonu Na Powierzchniowe Łuszczenie

2010 ◽  
Vol 56 (3) ◽  
pp. 239-254 ◽  
Author(s):  
M. Kosior-Kazberuk ◽  
D. Józwiak-Niedzwiedzka
Keyword(s):  
Fly Ash ◽  
Cost Effective ◽  
Hard Coal ◽  
Freezing And Thawing ◽  
Air Voids ◽  
Freeze Thaw ◽  
Industrial Utilization ◽  
Concrete Production ◽  
Fly Ash Utilization

Abstract Industrial utilization of fly ash from various kinds of fuel plays an important role in the environmentally clean and cost effective power production. The primary market for fly ash utilization is as a pozzolanic addition in concrete production. The paper concerns the concretes containing fly ash called Fly Ash from Biomass (FAB) from co-combustion of hard coal and wood biomass (wood chips). Characterization of the fly ash was carried on by means of X-ray diffractometry and E-SEM/EDS analysis. The results of laboratory studies undertaken to evaluate the influence of FAB on concrete resistance to surface scaling due to cyclic freezing and thawing in the presence of NaCl solution were presented. The tests were carried out for concretes containing up to 25% of fly ash related to cement mass. Additionally, the microstructure of air-voids was described. It was concluded that the FAB has significant effect on concrete freeze/thaw durability. The replacement of cement by fly ash from co-combustion progressively transformed the concrete microstructure into less resistant against freeze/thaw cycles and excessive dosage (over 15%) may dangerously increase the scaling.

Microstructure of entrained air voids in concrete, Part I

1991 ◽  
Vol 6 (9) ◽  
pp. 2004-2012 ◽  
Author(s):  
Ahmed I. Rashed ◽  
Robert Brady Williamson
Keyword(s):  
Portland Cement ◽  
Cement Paste ◽  
Fine Particles ◽  
Solidification Process ◽  
Scanning Electron Micrographs ◽  
Air Voids ◽  
Different Ages ◽  
Temperature Scanning ◽  
Entrained Air ◽  
Scanning Electron

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.

scholarly journals Characteristics of Entrained Air Voids in Hardened Concrete with the Method of Digital Image Analysis Coupled with Schwartz-Saltykov Conversion

Materials ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2439
Author(s):  
Teemu Ojala ◽  
Yanjuan Chen ◽  
Jouni Punkki ◽  
Fahim Al-Neshawy
Keyword(s):  
Image Analysis ◽  
Digital Image ◽  
Digital Image Analysis ◽  
Three Dimensional ◽  
Volume Density ◽  
Hardened Concrete ◽  
Air Voids ◽  
Air Content ◽  
Entrained Air ◽  
Number Of Classes

This paper presents the characteristics of air void systems in hardened concrete with the method of digital image analysis (DIA) coupled with Schwartz-Saltykov (SS) conversion. The results indicate that the DIA method coupled with SS conversion estimates the air content with more accuracy than it would without SS conversion; the correlation between air content obtained from the DIA method, and that from the thin section (TS) method is as good as the correlation observed between the pressure saturation (PS) method and the TS method. It was also found that the DIA method shows a better correlation with the TS method when the spacing factor without SS conversion is considered, while both methods show poor correlations when the corresponding specific surface is considered. In addition, it indicates that the peak of three-dimensional size distribution (3-DSD) of air voids after SS conversion falls in smaller voids, and 3-DSD of air voids shifts to a narrow size range, in comparison with the 2-DSD without SS conversion; the shape of the 3-DSD air voids remains constant irrespective of the class widths. Increasing the number of classes can minimise the standard deviation in the estimation, however, it also results in a leap in voids volume density, which will influence the estimation of air content.

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