Image processing methods have been widely used in civil engineering recently. Image
processing is reproducing the processes people got via their own vision system by digitizing.
The aim of this study is to define air void values of different concrete specifies with image
processing methods. With this purpose seven different concrete series have been produced by
using different water/cement rates. Physical and mechanical tests have been applied on the
samples acquired. Additively air void ratios have been calculated after section images obtained
from hardened concrete surfaces are processed. Relations between the results obtained as a
result of image processing method and pressure resistance values of the acquired concrete
samples have been examined.
Consequentially it has been observed that air void values in the concrete obtained by using
image processing techniques may be estimated with a high correlation

Başyiğit, Celalettin

Kılınçarslan, Şemsettin

Çomak, Bekir

Epoka University

2nd International Balkans Conference on Challenges of Civil Engineering, BCCCE, 23-25 May 2013, Epoka University, Tirana, Albania495Estimated the amount of air void in concrete using image processingtechniqueCelalettin Başyiğit1, Bekir Çomak2, Şemsettin Kılınçarslan31 Civil Engineering Department& Faculty of Engineering, Süleyman Demirel University, Türkiye2 Civil Engineering Department& Faculty of Technology, Düzce University, Türkiye3Civil Engineering Department& Faculty of Engineering Süleyman Demirel University, TürkiyeAbstractImage processing methods have been widely used in civil engineering recently. Imageprocessing is reproducing the processes people got via their own vision system by digitizing.The aim of this study is to define air void values of different concrete specifies with imageprocessing methods. With this purpose seven different concrete series have been produced byusing different water/cement rates. Physical and mechanical tests have been applied on thesamples acquired. Additively air void ratios have been calculated after section images obtainedfrom hardened concrete surfaces are processed. Relations between the results obtained as aresult of image processing method and pressure resistance values of the acquired concretesamples have been examined.Consequentially it has been observed that air void values in the concrete obtained by usingimage processing techniques may be estimated with a high correlation.IntroductionIt is an inevitable factor that materials forming the concrete should have good quality,proper material rates should be used; fitting, densification and cure processes of concrete shouldbe applied perfectly in order to obtain concrete, the most popular construction material, in agood quality. Even if concrete which is in touch with outside and has water in its voids has verygood quality, it cannot show adequate resistance against iterant freezing-resolution phenomena[1]. Theoretically, minimum water amount necessary for hydration in Portland cement isapproximately 25% of the cement’s weight. Added water after this process is necessary forpenetrability and compressibility and adding water more than necessary reduces concrete’squality by increasing porosity of hardened concrete. As a result additional water which is used inthe concrete mixture comes up as air void in a hardened concrete [2]. Entrapped air voids arevoids which are included involuntarily (by itself) in the concrete and in arbitrary forms andwhich range arbitrary while mixing and placing fresh concrete. Air voids entrapped in a firmlyfixed concrete are generally less than 2% [3]. There may be a relation between entrapped airvoids which are greater than entrained air voids. And in air contents greater than 5% in the2nd International Balkans Conference on Challenges of Civil Engineering, BCCCE, 23-25 May 2013, Epoka University, Tirana, Albania496concrete, pressure resistance and strength reduce significantly due to increasing discontinuity,voids and reducing mechanical sticking between paste and large aggregates [4].There are several methods for finding entrapped air content in the concrete. Volumemethod or pressure method is used in order to define air amount in fresh mix concrete. Airentrainment meters are used for measuring air amount in fresh mix concrete. In addition airamount can be measured by unit weight method [3]. New methods have been tried formeasuring air parameters in fresh mix concrete. By means of AVA (airvoidanalyzer) distributionof entrained air voids may be found when the concrete is fresh [5]. Air parameter measurementsin hardened concrete are applied according to ASTM C 457 standards. The test is applied byobserving air voids in the prepared plane concrete surface via the condenser. In this standardcalculating air parameters in the concrete takes a long time [3]. New methods exist in order todefine air voids automatically. In RapidAir 457 system, which is one of them, plane concretesurface is prepared in private so air voids seems white and the other surface seems black.Surface which is prepared with system video camera is scanned and air parameters are foundthanks to computer [6]. Besides image processing techniques are began to be used in defining airamount in the hardened concrete thanks to rapid developments in computer technology andimage processing techniques [7-18].In the study seven different concrete types have been obtained by using 7 different W/Cratios which could change between 0.79 and 0.37 in order to define air amount in the hardenedconcrete. Arial ratio of air voids and air void number have been calculated from the imageswhich are obtained from hardened concrete surfaces. Relations between results acquired byimage processing technique and pressure resistance of produced concrete samples have beenexamined.  As a result, it has been observed that air voids in the concrete obtained by usingimage processing techniques may be estimated with a high correlation.Materials and methodMaterialsWithin the context of experimental studies aggregates which were provided from a stonecrusher plant in Güneykent, Isparta and broken in four different sizes were used in concretemanufacture. CEM I 42,5 R Portland cement was used as a binding material in concretemanufacture.MethodPreparation of experiment samplesConcrete mixtures were prepared according to TS 802 (2009). Aggregate’s biggest particlesize was selected as 16mm. Aggregate granulation stays in the 4th religion as indicated in TS 802(2009) [19]. Granulometry of the mixture was selected in such a way that 30% was 8-16 mm,30% was 4-8 mm, 10% was 2-4 mm and 30% was 0-2 mm. W/C ratio changed from 0.79, 0.69,0.61, 0.54, 0.47, 0.42 to 0.37. Prepared fresh concretes were poured into cube blocks whosesizes were 100x100x100 mm by applying vibration in the vibration table. Table 1 showsmaterial amounts in 1 m3 concrete for each line and concrete codes according to concrete mixcalculation.2nd International Balkans Conference on Challenges of Civil Engineering, BCCCE, 23-25 May 2013, Epoka University, Tirana, Albania497Table1 Theoretical material amounts in 1m3 concrete (Kg)Code W/C Water Cement Aggregate 0-2 mm (30%)Aggregate 2-4 mm (10%)Aggregate 4-8 mm (30%)Aggregate 8-16 mm (30%)N1 0.79 222 281.0 550.1 183.4 540.1 540.1N2 0.69 222 321.7 539.2 179.7 529.4 529.4N3 0.61 222 363.9 527.9 176.0 518.4 518.4N4 0.54 222 411.1 515.3 171.8 506.0 506.0N5 0.47 222 472.3 499.0 166.3 489.9 489.9N6 0.42 222 528.6 484.0 161.3 475.2 475.2N7 0.37 222 600.0 464.9 155.0 456.5 456.5Four concrete samples were produced for each series and three each of them were used forpressure resistance for 28 days and one of them was used in order to get its section images. Theconcretes were produced in compliance with the standards and samples were waited in thecuring pool until the day when experiments would be carried out. Experiments of visibleporosity, water absorption, ultrasonic pulse velocity and pressure resistance were carried out inthe obtained samples.Preparation of the samples for image processingConcrete samples whose sizes were 100×100×100 mm and which were waited in curingfor 28 days were separated into 4 slices by means of a specimen cutting machine. Their sizeswere 20mm, 30mm, 30 mm and 20 mm and each one of them were vertical to concrete pouringdirection. One surface apiece was obtained from the section surface of pieces numbered 1 and 4and two surfaces apiece were obtained from the pieces numbered 2 and 3. In total 6 surfaceswere obtained.A mechanism comprising of tripod, Conan EOS450D digital camera, cube light and lightswas built for getting digital images of section surfaces (Figure 1). Images of the concretesurfaces cut by using 12.2 megapixel digital camera were obtained via the mechanism. After thesurfaces of the samples were dried, their jpg spanned images having 4272×2848 pixel sizes,which were in RGB color mode, were obtained. All of the imaging shoots on the concretesamples were performed in the same height and light environment on the sample surface.Figure 1 Mechanism built for getting digital images2nd International Balkans Conference on Challenges of Civil Engineering, BCCCE, 23-25 May 2013, Epoka University, Tirana, Albania498Image processing stepsObtained section images were pretreated and their image sizes were kept to be in the samesize owing to open-source coded UTHSCSA Image Tool (Version 3) and image processinganalysis were performed with the following processes via mentioned program.Images in the same sizes were transformed from RGB color mode to 8 bit grey levelimages. Colorful images (RGB- Red, Green, Blue) were transformed to grey toned form byusing equation (1) [20].BGRGr *114.0*587.0*299.0  (1)Where,Gr : Grey color value in each pixel,R : Red color value in each pixel,G : Green color value in each pixel,B : Blue color value in each pixel.Grey level images may get color values from 0 to 225. Value 0 represents black, value 128represents grey and value 255 represents white color [20]. Figure 2 shows an image transformedinto grey level. Histograms of grey level images were removed and so various data about imagewas removed from histogram.Afterwards, images were transformed into doubled (binary) images. In binary images eachpixel has value 0 or 1. 0 represents black and 1 represent white. Each pixel takes up 1 bit inthose images. Binary images are generally used in showing finger prints, architectural plans andwritten texts [21]. Threshold value chosen visually by the user is applied for the image totransform into binary form (Black-White). The threshold may differ from image to image.Basyigit et al. (2012), in their study, calculated air voids, aggregate and cement matrixpercentages from section images by using image processing technique [9]. They accepted greycolor value which was from 0 to 63 as air void. As a result of their analysis they indicated thatthreshold value they identified represents aggregate, cement and air amount in the concrete mixsuccessfully. Therefore, threshold value which would be applied for defining air void within thecontext of the study was chosen as 64 for equation (2) (Figure 3).Color (x,y) <64, 0, “Black”Color (x,y) = (2)Color (x,y) >64, 1, “White”Figure 2. Grey level image Figure 3. Doubled (Binary) image2nd International Balkans Conference on Challenges of Civil Engineering, BCCCE, 23-25 May 2013, Epoka University, Tirana, Albania499By virtue of equation 2, the part having air voids from section images were transformed intoblack and the other parts were transformed into white color. Areal ratio of the voids in thesection and void number were calculated on binary images.FindingsTable 2 shows experiment results belonging to obtained concrete serials.Table 2 Hardened concrete experiment resultsConcreteCodes W/CAveragecompressivestrength(MPa)Averageultrasonicvelocity(km/s)Averagewaterabsorption(%)Porosity(%)N1 0.79 24.0 4.25 5.18 11.75N2 0.69 27.1 4.33 5.29 11.95N3 0.61 34.0 4.10 4.58 10.31N4 0.54 36.0 4.70 4.38 9.96N5 0.47 44.8 4.40 4.04 9.24N6 0.42 48.7 4.30 4.00 9.14N7 0.37 53.2 4.48 3.49 8.04When examining Table 2 it is observed that pressure resistance of the concretes increasesas W/C ratio decreases, according to the results of ultrasonic pulse velocity quality of N4 codedconcrete is perfect and quality of other concretes are good.When examining water absorption ratios, it is seen that the highest value belongs to N2series concrete with 5.29 % and the lowest value belongs to N7 with 3.49%. It is seen that waterabsorption value falls as W/C ratio decreases. Water absorption amount of the concrete dependsupon the pores’ situation in the concrete and aggregate as much as porosity. In other words if thepores are half-open or completely closed, the concrete will absorb less water. If the pores in theconcrete or aggregates are open, they will have water absorption competency as much asporosity rate [22]. When porosity values are examined, it is observed that water absorption ratiosof concrete series have values from 5.29% to 3.48% while porosity values of the same seriesrange from 11.95% to 8.04%. As it is seen, water absorption ratios are nearly as much half ofvisible porosities. It may be conferred that nearly 50% of the pores in the series comprises ofhalf-open or completely closed.Table 3 shows the results obtained as a result of image processing.Table 3 Image processing resultsConcreteCodesSectionalSurfaceTotalAirVoidsThe ratioof thetotal areaof thesectionvoid area(%)ConcreteCodesSectionalSurfaceTotalAirVoidsTheratioof thetotalareaof thesection2nd International Balkans Conference on Challenges of Civil Engineering, BCCCE, 23-25 May 2013, Epoka University, Tirana, Albania500voidarea(%)N11 168 0.33N51 997 0.382 207 0.13 2 203 0.833 78 0.22 3 377 0.424 149 0.15 4 355 0.515 271 0.13 5 99 0.79Mean 174.60 0.19 6 305 0.65StandardDev. 71.37 0.09Mean 389.33 0.60N21 151 0.38 StandardDev. 315.19 0.192 170 0.27N61 NA 1.763 95 0.32 2 1399 0.584 137 0.18 3 3526 1.205 118 0.19 4 350 1.126 30 0.13 5 1928 0.78Mean 116.83 0.25 6 1366 1.08StandardDev. 49.84 0.09Mean 1713.80 1.09N31 47 0.08 StandardDev. 1162.97 0.402 649 0.30N71 1782 0.833 98 0.46 2 388 0.954 181 0.37 3 835 1.035 147 0.36 4 467 0.886 96 0.35 5 1691 2.95Mean 203.00 0.32 6 173 0.68StandardDev. 223.31 0.13Mean 889.33 1.22N41 123 0.21 StandardDev. 690.70 0.862 557 0.723 49 0.134 158 0.565 118 0.146 552 0.66Mean 259.50 0.40StandardDev. 231.23 0.27When table 3 was examined it was seen that the lowest air void percentage in terms of itsaverages was obtained from N1 coded concrete and the highest air void percentage was obtainedfrom N7 coded concrete.2nd International Balkans Conference on Challenges of Civil Engineering, BCCCE, 23-25 May 2013, Epoka University, Tirana, Albania501Conclusions and suggestionsBy using the method in this paper void amounts of various concretes may be defined andcompared. 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Estimated the amount of air void in concrete using image processing technique

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Estimated the amount of air void in concrete using image processing technique

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