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.

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.

Etude de la résistance au gel de bétons contenant un fluidifiant

1991 ◽  
Vol 18 (4) ◽  
pp. 581-589 ◽  
Author(s):  
Michel Pigeon ◽  
Marcel Langlois
Keyword(s):  
Silica Fume ◽  
Plain Concrete ◽  
Freezing And Thawing ◽  
Freezing Resistance ◽  
Cement Ratio ◽  
Water Cement Ratio ◽  
Freeze Thaw ◽  
Spacing Factor ◽  
Thaw Cycle ◽  
Air Void

There is some controversy about freezing resistance of concrete containing superplasticizers. It has been quite convincingly demonstrated that, in some cases, such admixtures can significantly alter air-void systems in concrete. Some researchers believe, however, that concrete with superplasticizers can resist frost even when the air-void spacing factor is higher than the usual limit of 200 μm. The freeze–thaw cycle resistance tests described in this paper show that with the two types of concrete tested (a plain concrete with a water/cement ratio of 0.50 and a concrete with the same water/cement ratio but containing silica fume), the critical air-void spacing factor value is not significantly affected by the presence of a superplasticizer. When regular concrete is to be exposed to freeze–thaw conditions, the air-void system should meet the usual standards even when a superplasticizer is present. Key words: concrete, freezing and thawing, durability, superplasticizer, spacing factor, silica fume, water–cement ratio. [Journal translation]

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.

Impact of Concrete Placing Method on Air Content, Air-Void System Parameters, and Freeze-Thaw Durability

1996 ◽  
Vol 1532 (1) ◽  
pp. 1-8 ◽  
Author(s):  
Kenneth C. Hover ◽  
Roger J. Phares
Keyword(s):  
Fresh Concrete ◽  
Free Fall ◽  
Hardened Concrete ◽  
Freezing And Thawing ◽  
Freeze Thaw ◽  
System Parameters ◽  
Air Content ◽  
Void System ◽  
Parking Lot ◽  
Air Void

Approximately 76 m3 (100 yd3) of ready-mixed, air-entrained concrete were placed in a parking lot and driveway at the Schwing America Manufacturing facility in White Bear, Minnesota, on June 21, 1994. This concrete was placed by means of a pump, crane and bucket, and truck-mounted conveyor, and came directly from the chute of ready-mix trucks. Pump configurations were used that allowed unrestricted free-fall of the concrete; a kink in the rubber hose at the end of the line created a slight back pressure and slowed the descent of the concrete. After placement, the concrete was consolidated by an immersion vibrator in some locations and struck off with no further consolidation in other locations. Air content of the fresh concrete was measured by ASTM C231 pressure meters at the truck chutes and at the point of placement. Air content and air-void system parameters of the hardened concrete were determined in accordance with ASTM C457. Actual freeze-thaw performance was evaluated by ASTM C666 for concrete sampled from the truck chute and sampled from the pavement after placement by the various methods. Twenty-four tests of the air content of concrete from six successive truckloads of concrete showed that the variation in truck-to-truck air content was frequently greater than the within-truck variation because of different methods of handling the concrete. Tests of the fresh concrete after pumping, conveying, chuting, and free-fall from the concrete bucket showed reduced air content. From analysis of the hardened concrete, it was observed that the air bubbles remaining in the pumped concrete were smaller than in the concrete as delivered. The air-void spacing factor was not significantly altered by pumping. In ASTM C666 freezing and thawing tests, the specimen experiencing the greatest loss of air content as a result of pumping was determined to have the lowest total air content of all specimens tested (before vibration), yet had the highest durability of all specimens tested.

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 Freeze–Thaw Resistance and Air-Void Analysis of Concrete with Recycled Glass–Pozzolan Using X-ray Micro-Tomography

Materials ◽  
2020 ◽  
Vol 14 (1) ◽  
pp. 154
Author(s):  
Marija Krstic ◽  
Julio F. Davalos ◽  
Emanuele Rossi ◽  
Stefan C. Figueiredo ◽  
Oguzhan Copuroglu
Keyword(s):  
Fly Ash ◽  
Pore Structure ◽  
The United States ◽  
Adsorption Method ◽  
X Ray ◽  
Freeze Thaw ◽  
Void System ◽  
Spatial Parameters ◽  
Micro Tomography ◽  
Air Void

Recent studies have shown promising potential for using Glass Pozzolan (GP) as an alternative supplementary cementitious material (SCM) due to the scarcity of fly ash and slag in the United States. However, comprehensive studies on the freeze–thaw (FT) resistance and air void system of mixtures containing GP are lacking. Therefore, this study aimed to evaluate GP’s effect on FT resistance and characterize mixtures with different GP contents, both macro- and microscopically. In this study, six concrete mixes were considered: Three mixes with 20%, 30% and 40% GP as cement replacements and two other comparable mixes with 30% fly ash and 40% slag, as well as a mix with 100% Ordinary Portland cement (OPC) as a reference. Concrete samples were prepared, cured and tested according to the ASTM standards for accelerated FT resistance for 1000 cycles and corresponding dynamic modulus of elasticity (Ed). All the samples showed minimal deterioration and scaling and high F/T resistance with a durability factor of over 90%. The relationships among FT resistance parameters, air-pressured method measurements of fresh concretes and air void analysis parameters of hardened concretes were examined in this study. X-ray micro-tomography (micro-CT scan) was used to evaluate micro-cracks development after 1000 freeze–thaw cycles and to determine spatial parameters of air voids in the concretes. Pore structure properties obtained from mercury intrusion porosimetry (MIP) and N2 adsorption method showed refined pore structure for higher cement replacement with GP, indicating more gel formation (C-S-H) which was verified by thermogravimetric analysis (TGA).

Material Characteristics Evaluation of Existing Pre-Stressed Concrete Railroad Ties After Service Period

2018 ◽  
Author(s):  
Aref Shafiei Dastgerdi ◽  
Kyle Riding ◽  
Robert J. Peterman ◽  
B. Terry Beck
Keyword(s):  
Service Life ◽  
High Speed ◽  
Current Status ◽  
Polished Surface ◽  
Material Characteristic ◽  
Freeze Thaw ◽  
Material Characteristics ◽  
Void System ◽  
Different Types ◽  
Air Void

As an important element in track, pre-stressed concrete railroad ties in the high-speed rail industry must meet the safety and performance specifications of high-speed trains. Systematic destructive and non-destructive evaluation of existing concrete ties can lead to a better understanding of the effect of prestressed concrete tie material design on performance and failure within their service life. It has been evident that environmental and climate conditions also have a significant impact on concrete railroad ties, causing various forms of deterioration such as abrasion and freeze-thaw damage. Understanding of the material characteristics that cause failure in different types of existing concrete railroad ties taken from different places is the main focus of this paper. Observing the current status and damages of railroad ties taken from track might give a correlation between the material characteristic and type of distress and cracking seen. Although it has been seen by previous works that effective factors such as air void system and material composition directly affect the performance of concrete ties such as freeze-thaw, material evaluation of existing ties after service life has not been addressed in previous publications. In this research, the authors have investigated the material characteristic such as aggregate and air-void system of existing pre-stressed concrete railroad ties taken from track. However, compressive and splitting tensile strength and fractured surface of samples cored from the ties were acquired. In order to obtain the strength of concrete materials of existing ties, six samples were cored from six different types of ties taken from tracks across the U.S., according to ASTM C42-16, and tested using ASTM C39 and ASTM C496 methods. However, the concrete air-void system (ASTM C457) was measured on saw-cut samples extracted from the ties to evaluate the influence air content and distribution on mechanical properties of the ties. Regarding the history and service life condition of the ties, it seems that material properties of the ties effectively alter the performance of the ties. Aggregate sources used at each location may have different properties such as texture, angularity, and mineralogy, contributing either propagation or resistance in splitting cracking in concrete. Furthermore, the polished surface of samples extracted from the ties show the uniformity and air void system in some ties which demonstrate their superiority in terms of resistance to freeze-thaw damage. Considering the results of this research, comprehensive evaluation of material characteristics might give a better view of existing concrete railroad ties situation, providing a worthwhile background for future tie design considerations.

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.

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.

A laboratory investigation for potential durability of ready-mixed concrete retempered for air content and workability

1976 ◽  
Vol 3 (4) ◽  
pp. 570-577 ◽  
Author(s):  
B. W. Langan ◽  
M. A. Ward
Keyword(s):  
Compressive Strength ◽  
Laboratory Investigation ◽  
Hardened Concrete ◽  
Air Content ◽  
Spacing Factor ◽  
Void System ◽  
Air Void ◽  
Ready Mixed Concrete ◽  
Mixed Concrete

The effects of agitation and retempering on some properties of fresh and hardened concrete are considered.Data are presented on the influence of agitation and retempering with an air-entraining agent on the workability, compressive strength, and air void system in hardened concrete.The results indicate that although agitation reduces air content and increases the spacing factor, the original parameters can be regained by proper retempering. It is shown that any loss in compressive strength due to retempering is accompanied by an increase in potential durability due to the improvement of the air void system.

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