Effect of micro air void system on the permeability of latex-modified concretes with ordinary Portland and very early strength cements

2007 ◽  
Vol 34 (8) ◽  
pp. 895-901 ◽  
Author(s):  
K K Yun ◽  
D H Kim ◽  
K J Kim
Keyword(s):  
Image Analysis ◽  
Specific Surface ◽  
Average Distance ◽  
Chloride Permeability ◽  
Air Voids ◽  
Spacing Factor ◽  
Void System ◽  
Early Strength ◽  
Air Void ◽  
The Impact

This study focused on the impact of the micro air void system on the chloride permeability of latex-modified concretes with ordinary Portland and very early strength cements. The micro air void system was analyzed with the image analysis method. The results of this study will help field engineers and researchers gain a better understanding of the chloride permeability characteristics of latex-modified concretes. The results show that the latex-modified concretes made with both Portland and very early strength cements have more micro air voids, ranging 50 to 500 µm, than ordinary concretes. These small air voids decrease the spacing factor, which is defined as half the average distance that unstable water must travel to reach an escape boundary. The specific surface ranges from 8 to 27 mm–1 and the spacing factor ranges from 275 to 602 µm for ordinary Portland and very early strength cement concretes without and with latex modification. The specific surface tends to decrease as the spacing factor increases. The spacing factors of concretes tend to decrease with latex modification and with very early strength cement. It seems clear that the use of polymer latex in concrete can significantly lower the value of the air void spacing factor by entraining a large number of micro air voids (below 100 µm in diameter). Key words: latex-modified concrete (LMC), micro air void system, chloride permeability, image analysis.

Effect of Pumping on Air Characteristics of Conventional Concrete

1996 ◽  
Vol 1532 (1) ◽  
pp. 9-14 ◽  
Author(s):  
M. Lessard ◽  
M. Baalbaki ◽  
P.-C. Aïtcin
Keyword(s):  
Specific Surface ◽  
Freezing And Thawing ◽  
Conventional Concrete ◽  
Freeze Thaw ◽  
Pump Line ◽  
Spacing Factor ◽  
Void System ◽  
The Stability ◽  
Air Void ◽  
Frost Durability

The stability of the air content of concrete during pumping has been the subject of a number of recent investigations. Because increasing volumes of concrete are placed with the aid of pumps and the durability of such concrete to freezing and thawing (ASTM C666) as well as the scaling resistance (ASTM C672) preoccupy engineers, a study concerning the stability of the air-void system of a concrete with 45 to 50 MPa compressive strength was carried out. The slump of the three tested concretes ranged between 85 and 115 mm. Three pumping setups were studied. In the first, the concrete was pumped horizontally; in the second the concrete was pumped upward and then downward. In the third, the vertical setup was used but a reduced section was placed at the end of the pump line, and the concrete was allowed to free fall a short distance. For each pump setup, the concrete was sampled before being placed in the pump and after leaving the pump. The results clearly show that when the concrete is pumped horizontally, the spacing factor (L) and the specific surface of the air-void system are barely altered. On the other hand, after pumping the concrete vertically without a reduced end section, it was impossible to obtain an L less than 230 μm, the maximum spacing factor allowed by Canadian standards (CSA A23.1) to ensure good frost durability. Furthermore, the specific surface of the air bubbles fell to 20 mm−1, which is inferior to the 25-mm−1 value recommended in Canadian standards. By placing a reduced section at the end of the vertical pump line, it was possible to enhance the air-void system but that procedure still fell short of ensuring a system that satisfies the air-void system recommended by Canadian standards to ensure proper frost durability. Although the pumped concrete mixtures did not always satisfy the requirements of CSA A23.1 regarding air-void systems, they satisfied the requirements of ASTM C666 (Procedure A) for resistance to freeze-thaw cycles. Freeze-thaw resistance in the presence of deicing salts was evaluated according to ASTM C672. After 50 frost cycles, all but one concrete exhibited mass losses that were lower than the maximum permissible limit of 0.50 kg/m2 required by BNQ 2621-900, the standard currently enforced in the province of Quebec. Placing a reduced section at the end of the pump line creates a light counterpressure in the descending section of the pump line, which allows the conservation of an acceptable air-void system. Considering the appreciable improvement in the preservation of air-void characteristics when a reduced section was placed at the end of the pump line, it was decided to proceed with further experimental work using four 90-degree elbows placed at the end of the vertically hanging pump line.

scholarly journals Development of the Measuring Techniques for Estimating the Air Void System Parameters in Concrete Using 2D Analysis Method

Materials ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 428
Author(s):  
Agnieszka Molendowska ◽  
Jerzy Wawrzeńczyk ◽  
Henryk Kowalczyk
Keyword(s):  
Concrete Surface ◽  
Equivalent Diameter ◽  
Air Voids ◽  
System Parameters ◽  
Air Content ◽  
Image Prior ◽  
Void System ◽  
Scanned Image ◽  
Air Void ◽  
The Impact

The purpose of the present study was to determine the impact of image quality on the results of air void system parameters determination in air-entrained concretes. The focus was on technical aspects related to the preparation of the scanned image of the concrete surface, which was then subjected to 2D surface analysis. Image processing aimed at separating joined voids and removing various types of defects in aggregate and cement mortar. The specific surface of the voids was determined with the air void equivalent diameter or perimeter as the calculation basis. Applying the Schwartz–Saltykov method, the 3D distribution of the air voids was reconstructed based on 2D measurements. On this basis, the micro-air content A300 was determined. The results of the 2D method were compared with the results of determinations carried out using the linear traverse (1D) method according to EN 480-11. The tests confirm the need to correct the image prior to measurements. Comparative tests showed good agreement between the air void system parameters determined using the 2D analysis and the EN 480-11 chord length counting method.

The effect of calcium salts on air-void structure in air-entrained concrete – a statistical and simulated study

2017 ◽  
Vol 24 (4) ◽  
pp. 591-598
Author(s):  
Yong Ge ◽  
Qinfei Li ◽  
Yunsheng Zhang ◽  
Deqing Xie ◽  
Paulo J.M. Monteiro
Keyword(s):  
Water Solution ◽  
Average Distance ◽  
Hardened Concrete ◽  
Index Test ◽  
Calcium Salts ◽  
Spacing Factor ◽  
Void System ◽  
Air Void ◽  
Random Parking ◽  
Air Entrained Concrete

AbstractThis paper analyzed the air-void system in air-entrained concrete in the presence of calcium salts and developed a new approach method, random “parking” method, for studying it. The foam index test studied indicated that the introduction of calcium salts did result in a drop in foaming power at 0.5 min, but the foam ability after 60 min was enhanced in surfactant-water solution. The Powers spacing factor in the air-entrained hardened concrete decreased gradually in the presence of CaCl2 or Ca(NO3)2. The probability density function of air-void distribution showed that the air-void size in air-entraining concrete was reduced with the addition of CaCl2 and Ca(NO3)2. The random parking method developed herein was compared with the experimental Powers spacing factor, and the concept of the alternative spacing factor, defined as the average distance between the surfaces of the two nearest air voids in concrete, was used. It was indicated that the alternative spacing factor is in close proximity to the experimental Powers spacing factor.

scholarly journals Additional Porosity as a Side Effect of Polycarboxylate Addition and Its Influence on Concrete’s Scaling Resistance

Materials ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 316
Author(s):  
Aneta Nowak-Michta
Keyword(s):  
Pore Structure ◽  
Side Effect ◽  
Freeze Thaw ◽  
Concrete Mixtures ◽  
Spacing Factor ◽  
Void System ◽  
Variable Content ◽  
Air Void ◽  
The Impact ◽  
Scaling Resistance

A side effect of using modified polycarboxylates to liquefy a concrete mix is additional pores in the concrete. They change the air void system in hardened concretes, and can be used to evaluate the freeze–thaw resistance of concretes. The purpose of this study is to determine the impact of the abovementioned quantitative and qualitative parameters on the freeze–thaw resistance of concretes. The research program was performed on eight sets of air-entraining and non-air-entraining concretes with a variable content of superplasticizer based on modified polycarboxylates. The basic composition of and air-entraining admixture content in the air-entraining concrete mixtures were held constant. Pore structure tests were performed according to EN 480-11. Scaling resistance was determined according to PKN-CEN/TS 12390-9. The results showed that as the content of modified polycarboxylates increased, the pore structure was adversely affected, and, consequently, the air void parameters deteriorated. At the same time, the freeze–thaw resistance of the non-air-entraining concretes decreased. The pores sizes also changed. As the fluidity increased, the specific surface area decreased, and, consequently, the spacing factor increased. The air-entraining concretes, despite the deterioration in the pore structure due to the modified polycarboxylates, were found to be very good quality concretes after 56 freeze–thaw cycles in the presence of 3% NaCl.

scholarly journals Environmental Assessment of Frost-resistant Concrete with Superabsorbent Polymers

2020 ◽  
Vol 63 (2) ◽  
pp. 43-62
Author(s):  
Gui Li ◽  
Marianne Tange Hasholt ◽  
Ole Mejlhede Jensen
Keyword(s):  
Environmental Impact ◽  
Concrete Strength ◽  
Significant Loss ◽  
Strength Increase ◽  
Life Cycle Assessment Methodology ◽  
Void System ◽  
Strength And Durability ◽  
Air Entraining Agents ◽  
Air Void ◽  
The Impact

AbstractAir-entraining agents (AEA) are normally used to improve the frost resistance of concrete. However, it is not possible to accurately control the air void system in concrete with AEA. Thus, a significant loss of concrete strength is caused by over-dosing voids, and this increases the environmental impact from concrete structures. Superabsorbent polymer (SAP) can also be used to produce frost-resistant concrete. Compared to AEA, it can be used to precisely engineer the air void structure of concrete, promote cement hydration, and mitigate self-desiccation cracks. In this study, life cycle assessment methodology is applied to evaluate the overall environmental impact of frost-resistant concrete based on AEA and SAP, respectively. The results illustrate that frost-resistant concrete with SAP has a lower environmental impact than frost-resistant concrete with AEA if the strength and durability of concrete are considered in the defined functional unit. In addition, frost-resistant concrete with SAP reduces the environmental burdens of the vertical elements such as columns, but it increases the environmental load of the horizontal elements such as slabs, where the strength increase cannot be utilized. Moreover, the inventory data for AEA and SAP can affect the impact assessment results.

Precision of the air void characteristics measurement by ASTM C 457: results of an interlaboratory test program

1996 ◽  
Vol 23 (5) ◽  
pp. 1118-1128 ◽  
Author(s):  
François Saucier ◽  
Richard Pleau ◽  
Daniel Vézina
Keyword(s):  
Test Method ◽  
Interlaboratory Study ◽  
Hardened Concrete ◽  
Probability Of Error ◽  
Air Content ◽  
Spacing Factor ◽  
Interlaboratory Test ◽  
Void System ◽  
Concrete Production ◽  
Air Void

Since 1993, the Quebec Department of Transportation requires all its concrete suppliers to demonstrate that their concrete satisfies the requirements of the CSA A23.1 standard as regards the maximum spacing factor of the air void system. This new requirement raises questions about the reproducibility of the ASTM C 457 test method. An interlaboratory study was carried out to verify if the variability of the test method is sufficiently low to allow reliable decisions on the acceptance or rejection of in-place hardened concrete. A total of 18 operators from 13 different laboratories microscopically examined the six concrete slabs used for the study. It is concluded that the average reproducibility coefficient of variation is 14.4% for the total air content measurement and 14.2% for the spacing factor measurement. Considering these results, the probability that the measured value of the spacing factor exceeds the mandatory limit of 230 μm on a concrete production containing an air void system with a spacing factor of 170 μm (the target value proposed in the CSA A23.1 M-94 standard) is less than 0.7% (a probability of error of about 1%, 5%, or 10% is typical of most quality control test methods). Key words: concrete, air content, air void measurement, spacing factor, ASTM C 457 standard, interlaboratory study, freeze–thaw durability.

Experimental Investigation on the Influence of Water-Cement Ratio on Air-Void Parameters of Cement Concrete

2013 ◽  
Vol 771 ◽  
pp. 29-33
Author(s):  
Jin Xi Zhang ◽  
Chao Wang ◽  
Ming Yang Guo ◽  
Mao Cheng Ma
Keyword(s):  
Experimental Investigation ◽  
Hardened Concrete ◽  
Cement Concrete ◽  
Marked Rise ◽  
Air Voids ◽  
Cement Ratio ◽  
Water Cement Ratio ◽  
Influence Of Water ◽  
Air Void ◽  
The Impact

This paper studies the effect of water-cement ratio [w/ on the air-void parameters of cement concrete, which has a significant influence on the durability of concrete. Based on the experimental investigation, it is found that the impact on the air content of hardened concrete due to different water-cement ratio is not great. Test results also indicate that with the increase of water-cement ratio, the spacing factors also experienced a marked rise, and the mean diameters as well as the specific areas of air voids evidently increased or declined, respectively, which may lead to an adverse effect on the frost resistance of concrete.

scholarly journals Image-based Restoration of the Concrete Void System Using 2D-to-3D Unfolding Technique

2020 ◽  
Author(s):  
Yu Song ◽  
Chuanyue Shen ◽  
Robbie Damiani ◽  
David Lange
Keyword(s):  
Air Entrainment ◽  
Void Size ◽  
Essential Information ◽  
Air Voids ◽  
Freeze Thaw ◽  
Void System ◽  
Void Structure ◽  
Unfolding Analysis ◽  
Air Void ◽  
2D To 3D

Hardened air void analysis provides essential information of concrete freeze-thaw durability based on the size and spacing of air voids in the material. As the physical freeze-thaw experiment is time-consuming and costly, the characteristics of concrete air voids are often deemed as a proxy of the freeze-thaw performance. This analysis is typically done by measuring the 2D air void intersections on polished samples, but the current interpretation of the 2D void characters does not accurately represent the actual void structure in 3D. To solve this problem, a 2D-to-3D unfolding technique has been proposed in the field of stereology. However, the unfolding analysis is known to be sensitive to several factors, such as void population and size along with a binning scheme, where improper unfolding can considerably bias the prediction of the actual concrete void system. This study investigates the optimal strategy of conducting the unfolding analysis for concrete. The investigation is carried out on both idealized void systems to interrogate the influence of the critical factors individually, and real concrete samples with varying levels of air entrainment to assess the concrete-specific impacts. The concrete void system is studied based on a stereological model emulating the intersected 3D air voids on the surface of polished concrete. The results highlight that, for unfolding concrete voids, logarithmic binning scheme is far more accurate to linear binning. The low unfolding error of the concrete samples indicates that the proposed methodology enables an accurate restoration of 3D void size distribution.

Béton produit en bétonnière mobile et en usine conventionnelle : comparaison des caractéristiques du réseau de bulles d'air

1988 ◽  
Vol 15 (3) ◽  
pp. 306-314
Author(s):  
Gaston Larose ◽  
Michel Pigeon
Keyword(s):  
Key Words ◽  
Laboratory Tests ◽  
Fresh Concrete ◽  
Mobile Unit ◽  
Freeze Thaw ◽  
Air Content ◽  
Spacing Factor ◽  
Void System ◽  
Concrete Mixer ◽  
Air Void

The durability of concrete to freeze-thaw cycles is dependent upon the existence of an adequate air-void system. There are very few studies on the air-void system of field concretes. Laboratory tests have proven that the air content measurement on the fresh concrete is not sufficient to judge the aptitude of the air-void system to protect the concrete from frost damage.This paper is a comparison of the air-void systems of field concretes produced in either a conventional plant or a mobile unit the use of which is becoming more and more frequent. The concretes produced in the conventional plant generally had sufficient air-void systems for air contents in the usual range (5–7%). The mobile unit showed that a slightly higher air content (8%) was needed to produce an adequate air-void system. Key words: concrete, mobile concrete-mixer, air-void systems, air-entraining agent, spacing factor, surface area, air content.

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