ASTM C457 Research Articles

An Alternative Test Method for Determining Hardened Air Void Parameters for Concrete Pavement

This research has developed an alternative test method for determining hardened air void parameters that follows ASTM C457 Procedure C, but does not require image analysis software or the required training and skills to develop or use one. Instead, the alternative technique uses a sophisticated microscope that has on-board counting and measuring capabilities, that are easy to use and easy to repeat. The technique was developed and tested on concrete mixtures with four target air void percentages (control at 2%, low at 3 – 5%, medium at 5 – 7%, and high at >8%) and compared to ASTM C457 Procedure A and B. The concrete produced was a conventional pavement mixture, which was a straight cement mixture with a target 3” slump. The results show that the alternative technique is not only just as accurate as the other methods, but it reduces the analysis time, human judgment calls, and the development and maintenance of a sophisticated image analysis program, which are all typical issues with any of the three procedures described in ASTM C457. Additionally, the alternative technique produces all hardened air void parameters that ASTM C457 provides. This study also demonstrates new potential issues that could result in erroneous hardened air void results when following ASTM C457. Lastly, this study provides a detailed description of the equipment necessary to produce the alternative method including a very detailed list of steps required to obtained the hardened air void parameters.

Deep learning based automated segmentation of air-void system in hardened concrete surface using three dimensional reconstructed images

The automated air-void detection methods specified in the ASTM C457 require the aid of contrast enhancement which is time consuming and labor intensive. This study investigated the utilization of three-dimensional (3D) reconstruction and Deep Convolution Neural Network (DCNN) methods to detect the air voids in hardened concrete surfaces without the use of contrast enhancement. The experimental results showed that the DCNN could accurately distinguish air voids from hardened concrete images with the detection accuracy of over 0.9 in only less than a minute. The accuracy rates for air content, specific surface, and spacing factor were 0.92, 0.91, and 0.89, respectively.

Determining the air void efficiency of fresh concrete mixtures with the Sequential air method

The Sequential Air Method (SAM), AASHTO TP 118, is the only test that can quantify the air void volume and spacing in fresh concrete but using the results to design a concrete mixture can be challenging. This work introduces a new tool that uses the outputs from the SAM to determine how different ingredients or changes to the environment impact the volume and spacing of the air void system. This tool is known as the Efficiency Chart. The Efficiency Chart can help producers create more reliable and consistent air void systems that also meet the suggested freeze thaw requirements. The Efficiency Chart is made by using 227 diverse concrete mixtures to establish an upper and lower bound of performance. To show the usefulness of this method several examples are presented to show how different admixtures and cements impact the air void systems. Agreement is shown between the predictions of the Efficiency Chart and the results from a hardened air void analysis (ASTM C457). Because the SAM can evaluate fresh concrete, the concrete industry can use the Efficiency Chart to help design and troubleshoot the air void systems in their concrete mixtures.

Innovative air entraining and air content measurement methods for roller compacted concrete in pavement applications

Roller compacted concrete pavement (RCCP) is a widely used paving infrastructure for regular and heavy duties. The durability against cyclic freezing and thawing in cold regions is an important issue in lifetime performance of RCCPs. The necessity of using air entraining agents to achieve durable RCCP against freezing and thawing cycles is a controversial subject amongst the researchers. The utilization of appropriate air measurement and entraining methods are two other challenges that RCCPs face in practice. In this study, 8 non-air entrained RCCPs have been designated with 3 paste volumes and different water to cement ratios. In addition, an innovative air entraining method has been used to entrain air in RCCP mixtures by incorporating 1.5–1.9 wt% cement weight of air entraining admixture (AEA). Furthermore, an innovative modified volumetric (IMV) method for air content measurement of fresh RCCP mixtures has been suggested and the results compared with the pressure method (ASTM C231) and microscopical analysis based on ASTM C457 (procedure C). Besides, the modified Vebe and compressive strength tests have been conducted to evaluate the fresh and mechanical properties of RCCPs, respectively. The ASTM C666 test method has also been carried out to assess the durability against cyclic freezing and thawing. The results indicate that both suggested air entraining and IMV methods seem to be efficient in air entrainment and air content measurement, respectively. Adding 1% entrained air bubbles by utilizing AEA could lead to 6.34% lower Vebe time. The air entrainment could result in the reduction of compressive strength up to 15.5% and spacing factor down to 96 μm. The effectiveness of air entrainment on frost resistance of RCCPs can be concluded, as well.

Deep learning-based automated image segmentation for concrete petrographic analysis

The standard petrography test method for measuring air voids in concrete (ASTM C457) requires a meticulous and long examination of sample phase composition under a stereomicroscope. The high expertise and specialized equipment discourage this test for routine concrete quality control. Though the task can be alleviated with the aid of color-based image segmentation, additional surface color treatment is required. Recently, deep learning algorithms using convolutional neural networks (CNN) have achieved unprecedented segmentation performance on image testing benchmarks. In this study, we investigated the feasibility of using CNN to conduct concrete segmentation without the use of color treatment. The CNN demonstrated a strong potential to process a wide range of concretes, including those not involved in model training. The experimental results showed that CNN outperforms the color-based segmentation by a considerable margin, and has comparable accuracy to human experts. Furthermore, the segmentation time is reduced to mere seconds.

Macro Photography as an Alternative to the Stereoscopic Microscope in the Standard Test Method for Microscopical Characterisation of the Air-Void System in Hardened Concrete: Equipment and Methodology.

The determination of the parameters that characterize the air-void system in hardened concrete elements becomes crucial for structures under freezing and thawing cycles. The ASTM C457 standard describes some procedures to accomplish this task, but they are not easy to apply, require specialised equipment, such as a stereoscopic microscope, and result in highly tedious tasks to be performed. This paper describes an alternative procedure to the modified point-count method that is described in the Standard that makes use of macro photography. This alternative procedure uses macro-photographic images that can be obtained with a quite standard photo camera and it is successfully applied to a large set of samples and presents some advantages over the traditional method, since the required equipment is less expensive and provides a more comfortable and less tedious procedure for the operator.

Determining the air-void distribution in fresh concrete with the Sequential Air Method

A new approach is presented to determine the air void size and spacing in fresh air entrained concrete by measuring the change in response of the concrete to a series of sequential pressures. This information is used to calculate a parameter called the Sequential Air Method (SAM) Number. Comparisons are made to hardened air void analysis (ASTM C457) from laboratory and field tests for 303 mixtures as well as rapid freeze-thaw testing (ASTM C666) for 68 mixtures to the SAM Number with over 85% agreement. Furthermore, the SAM Number showed a higher correlation to rapid freeze-thaw testing than current recommendations for the Spacing Factor. The variability of the SAM Number is compared to other direct and indirect measurements of air void size and spacing. Finally, several applications of the method are discussed along with guidance on how to specify the method.

Comparison of spacing factors as measured by the air-void analyzer and ASTM C457

ABSTRACTThe Kansas Department of Transportation (KDOT) began using the Air-Void Analyzer (AVA) in 2001 and first incorporated an AVA spacing factor requirement into paving specifications beginning in late 2002. In 2005, a statewide investigation to evaluate the AVA and specifications began with the collection of 100-mm diameter hardened concrete samples taken at or near locations where the spacing factor was determined with the AVA. The hardened concrete samples were tested to determine the spacing factor in accordance with ASTM C457, a well-established test method used to determine spacing factors in hardened concrete. A total of 270 data pairs were collected to evaluate KDOT’s current use of the AVA and ASTM C457 tests and to determine if a correlation (either direct or pass-fail criteria) exists between spacing factors obtained with the two methods. Results of the study indicate that average spacing factors obtained with the AVA were 1.67 times higher than average spacing factors determined using ASTM C457. A strong direct correlation was not identified between the two test methods although pass-fail criterion that limits agency risk of accepting concrete with an inadequate air-void system was identified.

Characterisation of air-void systems in concrete

The air-void system in both fresh and hardened states for different concrete mixes was measured and characterised using the methods presented in ASTM C231 and ASTM C457 respectively. The mix variables included two water/binder (w/b) ratios (0·33 and 0·45), one replacement level of Portland cement with slag cement (50%) and a range of air contents achieved through the use of different air-entraining agents. Consistent results were obtained on duplicate specimens using the two testing procedures. The cumulative size distribution of the air voids estimated from chord length measurement was satisfactorily represented by an S-shaped function from which the differential distribution can be derived. The importance of air-void fineness on the spacing was clearly illustrated by the small variation in Powers' spacing factor when large air bubbles were included.

Evaluation of the Critical Air-Void System Parameters for Freeze-Thaw Resistant Ternary Concrete Using the Manual Point-Count and the Flatbed Scanner Methods

Abstract This research was conducted to verify whether the semi-automatic method of air-void system characterization (using a flatbed scanner) could be used in lieu of the manual (ASTM C457) method. This research objective was accompanied by evaluating the critical air-void system parameters required to ensure freeze-thaw resistance of ternary concrete containing ordinary portland cement (OPC), 20 % of fly ash (FA), and 5 % of silica fume (SF). It was observed that, due to adverse effect of high superplasticizer dosage on air-void system quality (particularly on specific surface), the majority of high slump ternary mixtures exhibited poor freeze-thaw resistance, even if spacing factor was below the 0.20 mm recommended value. However, when the ternary mixtures were prepared with slump below the limit commonly specified for bridge deck applications (190 mm), the critical air-void system parameters of the OPC/FA/SF concrete were comparable to those typically associated with adequate quality air-void system in conventional concrete. Furthermore, since the critical value of specific surface was independent of slump (i.e., superplasticizer dosage), specific surface appeared to be more objective and reliable predictor of freeze-thaw resistance than spacing factor. When comparing the semi-automatic and manual methods of air-void system characterization, a reasonably strong agreement was obtained for such parameters as air content, void frequency, and spacing factor. Although the results of these methods did not match perfectly, the data suggested that the flatbed scanner technique could be efficiently used for discerning between freeze-thaw durable and non-durable concretes.

Evaluation of Two Automated Methods for Air-Void Analysis of Hardened Concrete

Abstract Air-void analysis of hardened concrete is typically performed according to ASTM C457–09 [“Standard Test Method for Microscopical Determination of Parameters of Air-Void System in Hardened Concrete,“ Annual Book of ASTM Standards, Vol. 4.2, ASTM International, West Conshohocken, PA], which can be tedious to perform and is operator subjective. Several alternative automated methods have been proposed, two of which are the Rapid Air 457 and the scanner method developed at Michigan Technological University. In each of these methods, images are collected from contrast enhanced surfaces of polished concrete, and image analysis is performed to calculate air-void system parameters. In this research, 22 concrete samples were examined using these two methods, the air-void system parameters were compared to those obtained from the ASTM C457 standard, and the precision of the results was compared to the recommendations of ASTM standard. It was concluded that the total air content and the spacing factor of the air voids measured by Rapid Air 457 and the scanner method were comparable to the air content and the spacing factor measured according to the standard manual method. Considering the fact that the automated image systems could detect air voids smaller in diameter than those typically seen by an operator, it was found that if these small air voids are counted, calculated spacing factors are smaller than those calculated by the manual method. If small diameter air voids are removed from the analysis, then spacing factors agree fairly well with those calculated by ASTM C457 from stereo-optical microscopy.

Assessing the Durability of Engineered Cementitious Composites Under Freezing and Thawing Cycles

Abstract This paper reports the durability performance of non-air-entrained engineered cementitious composites (ECC) when subjected to freezing and thawing cycles. ECC is a newly developed, high-performance, fiber-reinforced, cementitious composite with substantial benefits both in terms of high ductility under uniaxial tensile loading and improved durability due to intrinsically tight crack width of less than 100 μm. To evaluate the frost durability of ECC, freezing and thawing testing in accordance with ASTM C666 Procedure A was conducted. The mass loss, pulse velocity change, and flexural parameters (ultimate deflection and flexural strength) of specimens subjected to freezing and thawing cycles were determined in the test. In addition, air-void parameters, in accordance with ASTM C457, modified point count method, and pore size distribution obtained by mercury intrusion porosimetry technique were studied. To analyze the influence of micro-fibers and high tensile strain capacity on the freezing and thawing durability of ECC, all of the above-mentioned properties were also investigated for a control ECC matrix (ECC without fibers). After 210 cycles of freezing and thawing, the control ECC matrix specimens were severely deteriorated, requiring removal from the test, but still exhibited better performance than the conventional non-air-entrained concrete, which would fail at much earlier cycles. On the other hand, ECC with fibers without air-entrainment had excellent resistance to cycles of freezing and thawing with minimal reduction in ultimate tensile strength and ductility. The observed superior frost durability of ECC over control ECC matrix in terms of lower weight loss, pulse velocity change, and higher flexural load and ductility can be attributed to the following reasons: Increase of pore volume larger than approximately 0.30 μm in diameter, intrinsically high tensile ductility and strength due to the presence of micro-poly-vinyl-alcohol fibers.

A Novel Approach to Characterize Entrained Air Content in Pervious Concrete

Abstract The current pervious concrete placed in cold climates generally contains air entrainment but, unlike traditional concrete, the evaluation of entrained air is not performed. This paper presents results from a study that characterized the entrained air voids in pervious concrete using a RapidAir system. The RapidAir system is an automatic device that determines the air void properties of hardened concrete according to ASTM C457, “Standard Test Method for Microscopical Determination of Parameters of the Air-Void System in Hardened Concrete.” Two types of aggregates, i.e., crushed limestone and rounded river gravel (pea gravel), and two types of air entraining agents, i.e., natural and synthetic, were used. The air entrainment dosage rates varied from zero to double the manufacturer’s recommended dosage. Compressive strength, tensile strength, and freeze-thaw durability (ASTM C666A) of the pervious concrete were tested. The results show that use of air entrainment improves workability of pervious concrete, thus reducing the overall porosity and increasing unit weight of the pervious concrete. The strength and freeze-thaw durability also increases with the level of entrained air in pervious concrete.

Hardened Concrete Air Void Analysis with a Flatbed Scanner

Digital images collected from a polished concrete surface with a flatbed scanner are used to quantify air void characteristics. The surface is scanned a total of three times. Between the first and second scans, the surface is stained with phenolphthalein to color the cement paste pink. Between the second and third scans, the surface is painted black, and white powder is pressed into depressions left by air voids. The images collected from the three scans are aligned and input into a classification scheme to yield an output image. Each pixel in the output image is categorized as air void, cement paste, or aggregate. By digitally applying a grid of points and a series of lines to the output image, a modified point count is automatically performed according to ASTM C457, Standard Test Method for Microscopical Determination of Parameters of the Air-Void System in Hardened Concrete. A comparison is made between results obtained by an automatic analysis of the digital output image and results obtained by a manual analysis of the surface with an optical microscope.

Freeze-Thaw Durability of Concrete with Ground Waste Tire Rubber

Used tires represent an increasingly serious environmental problem in the United States. This study examines the freeze-thaw durability of concrete with ground waste tire rubber. Various percentages of rubber, by weight of cement, were added to a control concrete mixture. To evaluate the freeze-thaw durability of these “rubcrete” mixtures, freeze-thaw tests in accordance with ASTM C666 Procedure A and microscopic analyses in accordance with ASTM C457 Procedure B, were conducted. Results show that the rubcrete mixtures with 10 and 15 percent rubber by weight of cement are freeze-thaw durable. Results of the microscopic analysis indicate that properties such as air content and spacing factors are difficult to determine accurately because of the problems associated with polishing of the rubcrete specimens.

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

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.

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

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 samp...

Durabilité au gel-dégel et résistance à l'écaillage des pavés de béton

Tests results described in this paper show that it is quite easy to produce concrete paving blocks with excellent resistance to freezing–thawing cycles in water. Good resistance to frost-associated scaling in the presence of deicing salts is, however, much more difficult to obtain; and the problem is particularly difficult to analyse because two types of tests gave very different results. A freezing test in the presence of a saline solution (ASTM C672) showed positive influence of certain parameters (such as finer material), but freezing tests in a brine bath (ACNOR CAN3 A231.2 M85) did not show influence of any variable. In addition, the high number of compacting voids made it very difficult to interpret measurements of air-void characteristics made by examining ground sections under an optical microscope (ASTM C457). Key words: concrete paving blocks, scaling resistance, deicing salts, freezing–thawing cycles, air-void spacing factor. [Journal translation]

Strength and durability of concretes containing 50% Portland cement replacement by fly ash and other materials

Results are presented from an investigation on the compressive strength and durability of concretes containing substitute materials at a 50% replacement level (by mass) of Portland cement. Seven fly ashes (sub-bituminous, bituminous, and lignitic), together with limestone and an inert material (silica flour), were used as replacement materials. Durability studies included freeze–thaw testing (ASTM C666A), scaling resistance (ASTM C672), and abrasion resistance (ASTM C944). The air void system was assessed using the modified point count method of ASTM C457. The results indicate that although concretes with a 50% replacement level of cementitious material did not perform as well as the control concretes with no replacement, such concretes were able to meet minimum durability requirements. As anticipated, air-entrainment is the overriding factor that allows concrete to meet freeze–thaw durability requirements. In the context of this study, compressive strength does not appear to be a significant factor in freeze–thaw durability. Results indicated that concretes with compressive strengths of less than 10 MPa will still pass the freeze–thaw test, provided an adequate air void system is in place. Abrasion resistance tends to increase with compressive strength but not in all the cases. Key words: concrete, fly ash, compressive strength, durability, mineral admixtures.