thawing

Construction and Building Materials 233 (2020) 117207

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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

Insights into surface crack propagation of cement mortar with different cement fineness subjected to freezing/thawing Hadi Divanedari ⇑, Hamid Eskandari-Naddaf ⇑ Department of Civil Engineering, Hakim Sabzevari University, Sabzevar, Iran

h i g h l i g h t s

g r a p h i c a l a b s t r a c t


The effect of cement fineness on the

crack propagation of cement mortar was investigated.
Insight into a macro to micro-crack was based on changes in macro to micro-properties under F/T cycle.
Microstructural and image analyses were used to explain the crack mechanism from the macro and micro perspective.
Increase of resistance against cracking was due to the better performance of cement with highest fineness.

a r t i c l e

i n f o

Article history: Received 8 June 2019 Received in revised form 12 August 2019 Accepted 9 October 2019

Keywords: Cement fineness Cement mortar Crack detection Image analysis Freeze-thaw

a b s t r a c t As cementitious material freezes and thaws, cracks may expand due to the weakness in the internal structure, the behavior that influences properties and potential applications. Hence, investigation of cement strength, which is affected by cement fineness, is prior to limit the propensity of cracking through the improvement of internal structure as well as the bond between cement paste and aggregate. In this regard, the tests of porosity, flexural, and compressive in macro-level and SEM/XRD/EDX analysis in micro-level were conducted to clarify the effect of cement fineness on variations of macro- and microproperties of cement mortar specimens subjected to different freezing/thawing cycles (50, 100, 150, and 200). The detection and tracking of cracks were also determined using image analysis. Based on experimental evidence, it was found that the influence of fine cement on the porosity and strength properties of cement mortar was greater than coarse cement; this also was clarified by changes of cement paste micro-structure. Moreover, the image analyses showed that the use of fine cement led to a decrease in the crack width, whereas the crack tortuosity to find the path growth was increased. Consequently, cracks behavior was found to correlate with the cement paste micro-structure, whose characteristics relate to the cement fineness. Ó 2019 Elsevier Ltd. All rights reserved.

1. Introduction Concrete structures are subject to various damage mechanisms such as alkali-silica reaction [1], chloride attack [2], and freezing/ ⇑ Corresponding authors. E-mail addresses: [email protected] (H. Divanedari), [email protected], [email protected] (H. Eskandari-Naddaf). https://doi.org/10.1016/j.conbuildmat.2019.117207 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.

thawing (F/T) cycles [3]. From among these damage mechanisms, environmental F/T usually affect surface scaling as well as internal structure damage of cementitious material, and play an important role in the cementitious material deterioration since a large number of macro and micro-cracks are developed in cement paste and interfaces; resulting in a decrease of mechanical properties [4]. For instance, Liu and Li [5] reported that in the process of F/T cycles as circumferential strain occurred in inner structure, it resulted in

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decreasing the strength properties and developing the maximum stress-strain after F/T cycles; these variations can reflect the internal damage of cementitious materials. On the other hand, the inner damages are mainly caused by the water icing during freezecycling within the cement mortar’s pore structure so that some pores disintegrate and develop into larger pore structures. In addition, the development of pore structures can affect the mechanical properties of cement mortar [6]. It is well-known that most of the porosity in cement mortar is associated with that the interfacial transition zone (ITZ) [7]. Therefore, the pore structure in ITZ creates a trajectory for the pore solution circulation, which speeds up the F/T damage in the cement mortar [8,9]. The ITZ deformation is higher as compared to the cement paste due to its porosity and low strength whereby weakens the bond between cement paste and aggregate. As a result, the overall compressive strength of a specimen is affected by ITZ thickness [10,11]. ITZ is a region where often cracks begin and develop in cement mortar [12]. From the study done by Soroushian et al. [13], it is found that as the F/T cycle increases, the number and width of micro-cracks rise. Increasing and developing of micro-cracks in cement mortar cause deterioration in the cement mortar structure. F/T strength of cement mortar depends strongly on the structure of its cement paste; for instance, its pore distribution, porosity, and formed phases. Proper formation of phases can decrease pores structure, and then decrease ITZ thickens as well as cracks formation; consequently, improve the resistance against F/T cycles. It is clear that the hydration process is mainly affected by the component of consuming cement, which depends on different cement fineness. Hence, investigation of the role of cement fineness in properties and crack propagation of cement mortar is one of the main aims in this research. To better understand the development of cracks, there are various techniques. Manual visual inspection is the common technique for crack identifying; whether crack development gradually would decay texture integrity in the cementitious material. ‘‘However, this technique is labor-intensive, costly, and inaccurate, as the results inevitably depend on the inspector’s skill” [14]. In the other studies, different techniques have been widely applied to investigate the damage condition of cementitious materials exposed to F/T cycles; nevertheless, since surface condition significantly affects the measurement accuracy, investigation of deterioration caused by cracking during F/T cycle was scarcely possible via these techniques [15–19]. Among different techniques such as photography cameras, light microscopy, electron microscopy and image analysis that have been used to detect and identify cracks by Ferrara et al. [20,21], image analysis can be used particularly to detect the surface cracks as a powerful one [14,22–24]. To identify crack, a threshold value, which corresponds with a gray intensity scale, can be considered. The original image can be converted to a binary image and applied to find the path of the cracks that is shown by the remaining pixels in image binarization. More details concerning the operating procedure for detection and identification of crack will be presented in Section 3. In this study, the influence of widely different cement fineness on macro- and micro-properties in cement mortar subjected to different F/T cycle has been examined experimentally. For this purpose, the porosity, flexural, as well as compressive strength tests are performed in macro-level, and SEM/XRD/EDX analyses are employed in micro-level. The additional novelty of this study is identifying and tracking cracks in cement mortar after F/T cycle via image analysis. The results will be reported and discussed in details.

cycles, an extensive experimental program was performed. The specimens tested were made with widely different cement fineness in the form of three different types of cement strength class (CSC). This section describes the characteristics materials used in the casting procedure, mix composition (including specimen preparation), set-up and the procedure adopted of the test. 2.1. Materials characterization and mix preparation Three types of Portland CSCs of 32.5, 42.5, and 52.5 MPa according to BS ED 197–1 were used. Cement 32.5 and 42.5 MPa have the lowest fineness and cement 52.5 MPa has the highest fineness. Fig. 1 shows the micro-structural characteristics and phase compositions of each type of cement were quantified by SEM and XRD analysis. Table 1 gives chemical and physical composition of Portland cements. The fine aggregates consisted of local washed mountain sand with a maximum grain size of 4.75 mm, specific gravity of 2.6 and fineness modulus of 2.48 from Sabzevar mines were used. High range water reducing (HRWR) based on a carboxylic ether polymer was applied as a high performance superplasticizer in order to improve workability and increase early and ultimate compressive strengths [25]. All tests were carried out on 54 cement mortar mixtures containing three types of CSC of 32.5, 42.5, and 52.5 MPa, with six water to cement ratios (w/c) of 0.25, 030, 0.35, 0.40, 0.45 and 0.50 and three sand to cement ratios (s/c) of 2.5, 2.75 and 3 by mass. The preparation of the cement mortar mixtures was followed according to ASTM C305 in a standard mortar mixer. To prepare the mixtures, a planetary mixer was applied to mix the raw materials in definite proportions. The amount of the superplasticizer was obtained by a flow of 110 ± 5% in 25 drops of the flow table for each mix design. Mixing was continued until a consistent homogeneous mixture was reached, and then was molded in prismatic 40  40  160 mm3 casts. Specimens were cured for 24 h in the molds (temperature of 23 ± 2 °C and RH >95%). Then, specimens were taken from their molds and cured in a water tank (with a temperature of 23 ± 2 °C) until specimens have reached the time of the experiment. The exact specifications of all 54 cement mortar mixtures are presented in Table 2. 2.2. Test method Three specimens were prepared for each cement mortar mix design, so 162 specimens for porosity and flexural test and 324 specimens for compressive test were conducted in total. The reported results are an average of the obtained results. 2.2.1. Porosity test The procedure of measured porosity was based on weight changes of specimens for each mix design. The main reason because of choosing this method is that the considered pore size in experimental work could be compatible with image analysis in order to obtain more reliable results. This is according to the study by Gong and et al. [26] that reported that the best range of pores radius in the experimental study for image analysis method. To measure the porosity, the specimens were quite dried in an oven at 105 ± 5 °C in order to reach stable weight (Wd). Next, the specimen’s weight under two conditions: saturated in water (Ww) and saturated surface dry (Wssd) was measured. Finally, the weight difference between specimens used to determine the percentage of the specimens’ porosity (P) using the following formula:

2. Experimental study To evaluate the effect of cement fineness on mechanical properties cement mortar and crack behavior when exposure to F/T

P¼

ðW ssd  W d Þ  100% ðW ssd  W w Þ

ð1Þ

3

C2 S

H. Divanedari, H. Eskandari-Naddaf / Construction and Building Materials 233 (2020) 117207

Ca(OH)

C4 AF Ca(OH) 2 CaCo 3

C4 AF

C4 AF C2 S

CaCo 3 C2 S

(a)

200 µm 10

20

30

40

50

60

70

60

70

C2 S

Position [°2 Theta] (Copper (Cu))

C4 AF Ca(OH)2 CaCo3

C4 AF

C4 AF C2 S Ca(OH)2

C2 S CaCo3

(b)

200 µm 10

20

30

40

50

Ca(OH)2

Ca(OH)2 CaCo3

C4 AF

C4 AF

C2 S CaCo3

(c)

C4 AF

C2 S C2 S C4 AF

Position [°2 Theta] (Copper (Cu))

200 µm 10

20

30

40

50

60

70

Position [°2 Theta] (Copper (Cu)) Fig. 1. SEM and X-ray diffraction curves of different CSCs: (a) 32.5, (b) 42.5 and (c) 52.5 MPa.

2.2.2. Flexural test Three-points bending testing setup was conducted according to ASTM C348. A servo control universal testing machine was used with a maximum load capacity of 5 kN load cell attached. An LSPS deflection gauge (Opkon, Turkey) with 10–100 mm gauge length

was employed. The flexural strength (Ff) can be calculated according to the following formula:

Ff ¼

3 Fl  2 w  h2

ð2Þ

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Table 1 Chemical and physical compositions of Portland cements. CSC (MPa)

CSC 32.5 CSC 42.5 CSC 52.5

Chemical analysis (%)

Physical analysis

SiO2

Al2O3

Fe2O3

CaO

MgO

SO3

Na2O

K2O

LOI

F.CaO

C3A

C3S

Specific gravity (ton/m3)

Sieve residue on 90 mm (%)

Blaine fineness (cm2/gr)

20.4 20.2 21

4.56 4.6 4.7

3.4 3.5 3.52

64.12 64 64.18

1.93 1.94 1.93

2.3 2.4 2.53

0.32 0.35 0.32

0.7 0.7 0.65

2.2 2.7 1.2

1.3 1.3 1.2

6.33 6.27 6.5

63.94 64.27 57.85

3.13 3.13 3.15

0.9 0.8 0.1

3000 3050 3600

Table 2 Details of cement mortar mixtures. No.

CSC (MPa)

c (kg)

s/c

w/c

HRWR (ml)

No.

CSC (MPa)

c (kg)

s/c

w/c

HRWR (ml)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

32.5 42.5 52.5 32.5 42.5 52.5 32.5 42.5 52.5 32.5 42.5 52.5 32.5 42.5 52.5 32.5 42.5 52.5 32.5 42.5 52.5 32.5 42.5 52.5 32.5 42.5 52.5

2.85 2.85 2.85 2.67 2.67 2.67 2.5 2.5 2.5 2.85 2.85 2.85 2.67 2.67 2.67 2.5 2.5 2.5 2.85 2.85 2.85 2.67 2.67 2.67 2.5 2.5 2.5

2.5 2.5 2.5 2.75 2.75 2.75 3 3 3 2.5 2.5 2.5 2.75 2.75 2.75 3 3 3 2.5 2.5 2.5 2.75 2.75 2.75 3 3 3

0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35

90 40 40 90 95 90 95 85 50 40 30 30 45 35 40 90 35 35 17 17 12 22 17 17 22 17 30

28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

32.5 42.5 52.5 32.5 42.5 52.5 32.5 42.5 52.5 32.5 42.5 52.5 32.5 42.5 52.5 32.5 42.5 52.5 32.5 42.5 52.5 32.5 42.5 52.5 32.5 42.5 52.5

2.85 2.85 2.85 2.67 2.67 2.67 2.5 2.5 2.5 2.85 2.85 2.85 2.67 2.67 2.67 2.5 2.5 2.5 2.85 2.85 2.85 2.67 2.67 2.67 2.5 2.5 2.5

2.5 2.5 2.5 2.75 2.75 2.75 3 3 3 2.5 2.5 2.5 2.75 2.75 2.75 3 3 3 2.5 2.5 2.5 2.75 2.75 2.75 3 3 3

0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5

7 5 5 10 7 5 15 10 12 3 3 3 3 3 3 3 3 3 2 2 2 2 2 2 2 2 2

Cement strength class = CSC, Cement = c, Sand = s, Water = w, High Range Water Reducer = HRWR.

Where F is maximum flexural force, l is the loading span (100 mm), w and h are the width and height of specimen respectively. 2.2.3. Compressive test The compression test setup was employed according to the ASTM C349 on the portions of prisms broken into flexural specimens with dimensions of 40  40  40 mm3. A servo control universal testing machine was used with a maximum load capacity of 200 kN load cell attached which was equipped with deflection gauges. The compressive strength (Fc) can be calculated according to the following formula:

Fc ¼

F lw

ð3Þ

Where F is the maximum compression force, l and w are the length and width of the specimen respectively.

2.2.5. Weight loss Weight change in specimens after every F/T cycle was measured by an electronic scale with a capacity of 2 kg and an accuracy of ±0.1 g. The percentage weight change based on the initial weight of the specimen (W0) and the weight after n cycles of F/T (Wn) can be calculated using the following formula:

Weight change ¼

ð4Þ

2.2.6. Modulus of elasticity The elastic modulus of specimens was calculated according to the ASTM C469. This test technique determines chord modulus of elasticity (Young’s) based on stress-strain curves using three strain gauges which placed in direction of the major axis of specimens. The elastic modulus (E) was calculated via following formula:

E¼ 2.2.4. Freezing and thawing test F/T test procedure was performed based on ASTM C666 procedure A to determine the resistance of cement mortar specimens and to rapid F/T in water. Specimens were exposed to four different environments and tested after 4 different times of exposure: 50, 100, 150, and 200 cycles. The environment conditions for freezing cycles at 18 °C and thawing at 4 °C with an error temperature of ±1 °C and a frequency cycle of 4 cycles per day were adjusted.

ðW 0  W n Þ  100% ðW 0 Þ

ðS2  S1 Þ ðe2  0:000050Þ

ð5Þ

Where S2 is stress corresponding to 40% of maximum load, S1 is the stress corresponding to a longitudinal strain of 0.00005, and e2 is the longitudinal strain related to S2. 2.2.7. Micro-structural test Scanning electron microscopy (SEM) was performed to obtain the microscopic morphology of specimens before and after F/T,

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and it provides visual identification of micro-structure of cement hydration and gives a suitable possibility about the evaluation of micro-cracks. SEM was carried out on specimens by a scanning electron microscope (TESCAN VEGA3, Czech) with an accelerating voltage of 20 kV and also it was equipped with energy-dispersive X-ray spectroscopy (EDX) to investigate the elemental behavior. In order to prepare specimens, a small piece of cement mortar was cut off from each mixture, then pieces were quite dried in a vacuum oven with the temperature of 50 °C for 24 h. Afterward, the surface of the pieces was coated with a thin layer of silver to provide a conductive surface for SEM imaging. X-ray diffraction (XRD) was employed to evaluate the effect of CSC on the hydration products of cement paste. XRD analysis was performed to detect changes of phase compositions of different cement types and identification of crystalline phases of cement pastes. For this purpose, the specimens need to be milled into powder (<50 lm). The XRD (Rigaku Ultima IV, Japan) measurements with a copper radiation, Cu Ka (wavelength k = 1.5406 Å) operating at the tube voltage and tube current of 40 kV and 40 mA respectively. Data was collected in measurable angular rotation (2h) from 5 to 70°. 3. Image analysis Image analysis was used by Digital Surf MountainsMap software [27] to identify and quantify characteristics of the cracks created in the cement mortar specimens under the applied load. The images taken by the camera had a maximum resolution of 13 megapixels and 24 bit RGB color depth with 5 Phase Detection Auto Focus (PDAF) in order to provide quick and accurate focusing by every frame detection and give a sharper photo. Each individual image mapped a region of 3.25  5 mm, providing a resolution of 3120  4160 pixels which was considered sufficient for this investigation. In the below subsections, the different aspects of employed procedures are described, the processing and analysis of the images. 3.1. Image binarization In order to binary images, several processes need to be performed on the images obtained (color images) to prepare the images for image analysis. Initially, it is necessary to calculate the weight of the pixel values for color images to convert to grayscale (GS) values in the range of zero (black) to 255 (white). As a result of this process, the color images are converted to GS images that this process has been done by Digital Surf MountainsMap software. In the next process, GS image can be converted into a binary

Original image

3.2. Image processing Image processing process was carried out on the tacked images by a microscope equipped with a digital camera over computercontrolled along the pathway of original crack and subsidiary cracks in the form of the branching or running parallel to the original crack. Images arranged beside together in such a way to determine the precise location of each image and to obviate probability of the duplicated overlapping area. Using this feature, each crack in the general picture was reconstructed through merging approximately 40 images. As an illustration, a full-length crack achieved through image reconstruction is displayed in Fig. 3a. The binary images obtained from process of the color images illustrates merely the real crack pattern containing noise in order to facilitate the analysis of the crack characteristics. The image processing included three major operations: thresholding, cleaning, and filtering have been performed by Digital Surf MountainsMap software. The threshold-setting operation carried out according to an introduced example threshold of the impregnated crack area. Then, the crack area threshold was manually adjusted to specify the exact boundary between the crack and the cement matrix. Fig. 3c displays the output of the threshold-setting operation in the highlighted area of the crack showed in Fig. 3b. It is found that the binary image was still poorly defined and needed a cleaning process to remove existing noise in the background picture after the crack threshold area. The last operation is filtering to remove the large particles in the background related to the pores via manual removal. Fig. 3d shows the output of cleaning and filtering operation on the binary image.

Grayscale image

[A]

[B]

1000 µm

image in the form of white and black particles via the image binarization technique. In the binary image preparation process, each pixel value of the GS images are compared to a threshold value; if this value is lower than the pixel value, it is considered as a pixel value of one (white) otherwise as zero (black). For better understanding, Fig. 2 as a schematic picture illustrates the operations performed in this process to obtain the binary image. For instance, when a threshold value obtained from the average of pixel values is lower than the corresponding pixel values, they in binarization results in A are tagged with one (white), whereas the labels zero (black) from results in B are indicating that the threshold value is higher than the pixel values. Binarization can be distinguished from other techniques that are applied to determine the threshold [28–30]. These differences can be involved in binarization parameters, such as the surface amount that threshold calculation is done by the sensitivity that controls the threshold calculation from the pixel values.

Binary image [A] Pixel value: 125 Threshold value: 119 Binary result: 1 [B] Pixel value: 57 Threshold value: 91 Binary result: 0

Fig. 2. Schematic demonstration of image binarization.

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3.3. The crack width determination By observing the crack propagation in cementitious materials, it is found that they are mainly irregular and continuously change their growth direction. Hence, tracking and accurate detecting of a crack is still a facing problem in many previous studies [31]; because the accuracy is largely dependent on the image resolution and threshold GS identification in boundary areas with a change from a phase to another phase. For example, in one of this studies [32], image analysis was used to determine the crack width through the length of the equal segments in the perpendicular direction of the force, leading to the path creation of cracks in the binary image. Also, results explained that when the crack path changes, due to various factors such as facing with aggregates, and becomes high tortuosity, the crack width would be overestimated. An additional issue induces when branching-related multiple

cracks coexist. Crack-branching can be observed as the bifurcation of one crack, mainly the main crack, into two or more cracks or as micro-cracks smaller than the main crack. Therefore, the creation of crack-branching can be directly relevant to the crack width. In order to compare cracks, it is necessary to define a certain equivalent crack width for different specimens. Hence, in this study, pores considered for crack propagation analysis were in the range of 1– 10,000 mm. This selection range is based on the study by Gong et al. [26] that investigated the best range of pores radius for image analysis technique. The utilized images were acquired in each 0.1 sec during loading time to track crack tortuosity. Each crack is analyzed based on the GS value. Further, binarization images, defined in Sections 3.1 and 3.2, that can cover extant defects in previous studies because of adopted approach in this study not only is based on change direction of each point to other points but also accordingly to GS value of each point.

(b) Zoomed-in region highlighted in (a)

(c) Binary image after thresholding

(a) Original image

(d) Image after cleaning and filtering

Fig. 3. A representative example of the pre-processing image.

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is required for good characteristics of cement materials. Hence, in next subsections, due to the massive number of figures for all the mix designs, the results for that containing s/c of 2.75 are presented.

4. Results and discussion 4.1. Macro-structural evaluation 4.1.1. Porosity The results of porosity in cement mortar specimens with different ratios of w/c, s/c, and numbers of F/T cycles as well as CSCs are given in Figs. 4–6. From these figures, it is observed that the porosity rises with an increase in the numbers of F/T cycles. In comparison to lower F/T cycles, a considerable increase in porosity values is observed for 100 F/T cycles and higher ones, which is due to the increase in pores in the high number of cycles [33]. For instance, in Fig. 4c the porosity values of mixing design with w/c of 0.25 for cycles of 0, 50, 100, 150, and 200 is 4.8%, 5%, 5.5%, 6.8%, and 9%, respectively. On the other hand, comparing the porosity values in Figs. 4–6 at each w/c and F/T cycles showed that the porosity of cement mortar mix design with CSC of 52.5 MPa is lower than the porosity of CSC in 32.5 MPa and 42.5 MPa. This suggests that the CSC has notable effects on the porosity. From these figures, it can be observed that as the w/c increases, the porosity values rise. It can be also seen that the minimum porosity belongs to w/c of 0.25. The other effective parameter is the s/c in which the variation has resulted in different changes in the porosity; the porosity reduces with the increase of s/c from 2.5 to 2.75 and then rises with the increase of s/c from 2.75 to 3. Accordingly, it can be concluded that the cement mortar containing s/c of 2.75, w/c of 0.25, and CSC of 52.5 MPa has the minimum porosity, which

(a)

4.1.2. Weight loss percentage The trend of weight changes for cement mortar mix designs subjected to different F/T cycles with s/c of 2.75 as well as w/c of 0.25 (a), 0.35 (b), and 0.45 (c) are shown in Fig. 7. It is known that increasing w/c of mix designs because of increase in water content and the presence of more void spaces during F/T cycles leads to entrap water in these spaces, increase the volume, and produce a force on the surface of the materials. Accordingly, in Fig. 7, it can be seen that an increase in w/c from 0.25 to 0.45 causes an increase in weight change percentage. Besides, the increase in F/T cycles can induce damage and weight loss of specimens. For example, a mix design containing CSC of 32.5 MPa with w/c of 0.25 has a notable increase of almost triple in weight loss with an increase of 50– 200 F/T cycles (see Fig. 7a). This fact is similar to the results reported by other studies [34,35]. Moreover, in a constant mix design merely the increase of CSC from 32.5 MPa to 52.5 MPa induce a significant decrease in weight loss percentage of specimens, indicating the connection between materials that lead to more resistance to the degradation and scaling of specimens. For instance, in Fig. 7c, in 200 F/T cycles it can be seen that weight loss decreases by approximately 45% when CSC increases from 32.5 MPa to 52.5 MPa.

(b) 18

18

15

Porosity (%)

12 9

12 9 6

6

200

200

3 0.5

0.45

w/c

0.5

100 0.4

0.35

0.25

100

0.45

0.4

F-T cycles

50 0.3

150

3

150

0.35

w/c

0

50 0.3

0.25

F-T cycles

0

(c) 18 15

Porosity (%)

Porosity (%)

15

12 9 6

200 150

3 0.5

0.45

w/c

100 0.4

0.35

50 0.3

0.25

F-T cycles

0

Fig. 4. Porosity vs. w/c and number of F/T cycles for mixtures with s/c = 2.5 and different CSCs: a) 32.5, b) 42.5 and c) 52.5 MPa.

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H. Divanedari, H. Eskandari-Naddaf / Construction and Building Materials 233 (2020) 117207

(b)

18

18

15

15

Porosity (%)

Porosity (%)

(a)

12 9

12 9 6

6

200 150

3 0.5

0.45

3 0.5

100 0.4

w/c

0.35

F-T cycles

50 0.3

0.25

200 150 0.45

100 0.4

0.35

w/c

0

50 0.3

0.25

F-T cycles

0

(c) 18

Porosity (%)

15 12 9 6

200 150

3 0.5

0.45

100 0.4

0.35

w/c

50 0.3

0.25

F-T cycles

0

Fig. 5. Porosity vs. w/c and number of F/T cycles for mixtures with s/c = 2.75 and different CSCs: a) 32.5, b) 42.5 and c) 52.5 MPa.

4.1.3. Change of elastic modulus In this subsection, the elasticity modulus is presented for the same mix designs of the previous subsection under different F/T cycles. The elastic modulus decreases in lower CSC due to an increase in porosity of specimens (see Fig. 8). Also, in all the mix designs, it can be seen that the increase of F/T cycles causes the decrease in elastic modulus; this fact confirms the similar results of other studies [36,37]. Furthermore, with the decrease of CSC, a similar trend is observed for specimens subjected to F/T cycles. For example, the elastic modulus changes for mix designs with w/c ratio of 0.25 after 100 F/T cycles are almost 7, 9, and 11 GPa as well as CSC as 32.5, 42.5, and 52.5 MPa, respectively. This trend exhibited further reduction with the increase in F/T cycles for other specimens with the same mix designs of different CSC.

4.1.4. Flexural load-deflection behavior Fig. 9 shows the variability effect of CSC and F/T cycles on flexural behavior specimen with w/c of 0.45 and s/c of 2.75. It should be noticed that the load-deflection curves generally have no descending branches. This means that the tested cement mortar specimens failed quickly after reaching their maximum loadcarrying capacity. It is observed that as F/T cycles decrease, the specimens’ load capacity increases accompanied by an increase in deflection limit; this is close to the conclusion reached in previous research [38,39]. On the other hand, Fig. 9 illustrates the variability effect of CSC on load capacity. As it appears clearly in these figures, as the CSC increases the load capacity and deflection limit significantly rises. The reason for this is that mix designs with

higher CSC (52.5 MPa) lead to the formation of the denser composition as compared to the other two CSCs. 4.1.5. Compressive load-deflection behavior The load-deflection curve of cement mortar specimens under compressive load is presented in Fig. 10; this curve show the influence of CSC and F/T cycles for w/c of 0.45 and s/c of 2.75. It can be seen that the trend of specimens’ compressive behavior is almost similar to specimens’ flexural behavior. It is obvious that the compressive load capacity of specimens decreases with the increase in the number of F/T cycles. Comparing the compressive loaddeflection indicated that the curves of the mixture with CSC 52.5 MPa, is higher than the mixtures with CSC of 32.5 and 42.5 MPa. This suggests that the CSC can enhance the compressive load capacity of cement mortar specimens, which is similar to the result as reported in previous studies [40–42]. On the other hand, comparing the compressive load capacity values with flexural load capacity values, it is clearly obvious that compressive load values are higher than flexural load values. From these results, it is evident that the maximum load capacity is obtained in the mixture with CSC of 52.5 MPa. 4.2. Micro-structural evaluation 4.2.1. SEM/XRD/EDX analyses Figs. 11 and 12 present the SEM images of the cement paste samples in order to investigate the effect of different CSCs of 32.5, 42.5, and 52.5 MPa (a–c) vis-a-vis different F/T cycles: 0,

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(b) 26 24 22 20 18 16 14 12 10 8 6 4

Porosity (%)

Porosity (%)

(a)

200 150 0.5

0.45

26 24 22 20 18 16 14 12 10 8 6 4 0.5

100 0.4

0.35

w/c

0.25

0.45

100 0.4

F-T cycles

50 0.3

200 150 50

0.35

0.3

w/c

0

0.25

F-T cycles

0

Porosity (%)

(c) 26 24 22 20 18 16 14 12 10 8 6 4

200 150 0.5

0.45

100 0.4

F-T cycles

50

0.35

0.3

w/c

0.25

0

Fig. 6. Porosity vs. w/c and number of F/T cycles for mixtures with s/c = 3 and different CSCs: a) 32.5, b) 42.5 and c) 52.5 MPa.

Number of F/T cycles

100

150

Number of F/T cycles

(b) 200

50

0

0

-1

-1

Weight change (%)

Weight change (%)

50

-2

-3 -4 -5

-6 -7 -8 -9

100

150

CSC 52.5

CSC 42.5

CSC 32.5

100

150

200

-1

-2

-3 -4 -5 -6

-8

50 0

-7 w/c=0.25, s/c=2.75

Number of F/T cycles

(c) 200

Weight change (%)

(a)

-2 -3 -4 -5

-6 -7

w/c=0.35, s/c=2.75 CSC 52.5

-9

CSC 42.5

CSC 32.5

-8

w/c=0.45, s/c=2.75 CSC 52.5

CSC 42.5

CSC 32.5

-9

Fig. 7. Weight changes vs. number of F/T cycles for mixtures with different CSCs, s/c = 2.75 and w/c: a) 0.25, b) 0.35 and c) 0.45.

100, 150, and 200 (I–IV) for w/c of 0.25 and 0.45, respectively. According to XRD analysis of cement type, Figs. 11 and 12, when CSC increases from 32.5 MPa to 52.5 MPa, due to the high percentage of the involved efficient elements in the hydration process, more hydration products, and a denser mixture are formed. It can be observed that when the CSC is increased, the cement paste internal structure is improved so that the interface and microcracks are formed and filled due to a large amount of calcium hydroxide (CH) and calcium-silicate-hydrate (C-S-H) gel. Therefore, the density of the cement paste with CEM 52.5 MPa is higher as compared to those mixtures with two other CSCs. Moreover, the

SEM images illustrate that the deterioration rate of the microstructure cement paste depends on the number of F/T cycles. From figures for each CSC, it can be seen that with the increase in F/T cycles, the samples are subjected to force by alternating cycles, leading to the creation and growth of micro-cracks such that the pore size increases gradually. This observation in two other types of CSCs illustrates the main difference; an increase in the CSC reduces the damage of samples, such as the number of microcracks and pores (see Fig. 11 for comparison). Nevertheless, in most samples, the degradation by F/T cycles is characterized by the gradual formation of micro-cracks in the cement paste. In addi-

H. Divanedari, H. Eskandari-Naddaf / Construction and Building Materials 233 (2020) 117207

16

CSC 32.5

CSC 42.5

14

(b)

CSC 52.5

w/c=0.25, s/c=2.75

12 10 8 6 4 2

16

CSC 32.5

CSC 42.5

14

(c)

CSC 52.5

w/c=0.35, s/c=2.75

Modulus of elasticity (GPa)

Modulus of elasticity (GPa)

(a)

Modulus of elasticity (GPa)

10

12 10 8 6 4 2

16

0

50

100

150

CSC 42.5

CSC 52.5

w/c=0.45, s/c=2.75

12 10 8 6 4 2 0

0

0

CSC 32.5

14

0

200

50

100

150

0

200

Number of F/T cycles

Number of F/T cycles

50

100

150

200

Number of F/T cycles

Fig. 8. Elastic modulus vs. number of F/T cycles for mixtures with different CSCs, s/c = 2.75 and w/c: a) 0.25, b) 0.35 and c) 0.45.

0 cycle (a) CSC 32.5 MPa w/c = 0.45

100 cycles

150 cycles

200 cycles

(c)(c) CSC 52.552.5 MPaMPa CSC w/cw/c = = 0.45

2

33

0

0.5

1

1.5

Deflection (mm) 3

Load (kN)

1

0

Load (kN)

50 cycles 44

Load (kN)

Load (kN)

3

22

(b) CSC 42.5 MPa w/c = 0.45

2

11

1

0 0

0.5

1

1.5

00 00

0.2 0.2

Deflection (mm)

0.4 0.4

0.6 0.6

0.8 0.8

1

1

1.21

Deflection (mm)

Fig. 9. Comparison of flexural behavior for mixtures with different CSCs, w/c = 0.45 and s/c = 2.75.

tion, Figs. 11 and 12 indicate that the defects as cracks and pores are mostly observed when the w/c increases from 0.25 to 0.45. This can be since the water increase more than requirement limit, induces the more empty space formation that weakens the cement paste structure. This result confirmed by other studies [43,44] that had explained if the freezing process is rapid, water has little chance to redistribute itself through the mixture and results in freezes in the form of almost uniform ice crystals. Nonetheless, these crystals can still destruct the cement paste and deteriorate the connections between the cement paste and aggregates. Consequently, comparison of the SEM images indicates that the highest resistance to F/T cycles is exhibited in CEM 52.5 MPa considering texture improvement in cement past. Fig. 13 shows the XRD curves obtained from cement paste with CSCs of (a) 32.5, (b) 42.5, and (c) 52.5 MPa to better understand the influence of different types of CSC on the hydrated cement paste structure. For this purpose, two representative components in the cement (C2S and C4AF) and two hydration products (Ca(OH)2

and CaCO3) are evaluated. The reason for choosing these two compounds from cement and cement hydrate is that other studies [45,46] pointed to the important role of these two compounds in the hydration process and the formation of cement paste so that Thomas and Jennings [45] reported that the hydration products such as calcium hydroxide and calcium sulfoaluminate form C2S and C4AF that those occupy about 15% and 20% of the volume of a normal Portland cement paste. Fig. 13 indicates that the peak intensity of C2S and C4AF at the angle 2h of 29.41° and 34.37° respectively increase with the rise in CSC. These changes in cement components confirm the role of CSC in improving the formation of cement paste through hydration products such as Ca(OH)2 and CaCO3. These hydration products increase significantly with increasing CSC from 32.5 MPa to 52.5 MPa. For instance, XRD diffraction shows that CSC of 52.5 MPa has a higher amount of C2S and thereby Ca(OH)2 as compared to other CSCs. Based on the XRD result, it can be concluded that hydration reaction would be extended as cement strength develops, resulting in an increase

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0 cycle

Load (kN)

80

50 cycles

100 cycles

150 cycles

200 cycles

100

(a) CSC 32.5 MPa w/c=0.45

(c) CSC 52.5 MPa w/c=0.45

60 80

40

0 0

0.5

1

1.5

2

2.5

3

3.5

Deflection (mm)

Load (kN)

80

Load (kN)

20 60

40

(b) CSC 42.5 MPa w/c=0.45

60 20

40 20

0

0 0

0.5

1

1.5

2

2.5

3

3.5

0

0.5

Deflection (mm)

1

1.5

2

2.5

3

Deflection (mm)

Fig. 10. Comparison of compressive behavior for mixtures with different CSCs, w/c = 0.45 and s/c = 2.75.

in hydration products of cement paste; this is in line with the obtained results of XRD cement. On the other hand, compounds containing calcium silicate are the most abundant and important components in Portland cement, which contribute most development to cement paste strength in different ages [47]. Fig. 14 shows the results of the EDX spectra. The elemental maps of aluminum (Al), magnesium (Mg), silicon (Si), and calcium (Ca) were performed via the SEM-EDX elemental mapping on the test region of sample with CSC of 52.5 MPa, s/c of 2.75, and w/c of 0.25 subjected to 200 F/T cycles. The spatial distribution of the above four main elements is mapped in various colors. The nonuniform distributions of the mentioned elements indicate different hydration products. 4.2.2. Deterioration mechanism of ITZ Fig. 15 shows the deterioration mechanism of ITZ structure under various conditions. In Fig. 15a, it is shown that typically, some pores and micro-cracks are developed in the ITZ structure of the original sample. The cracks can emerge between pores in the ITZ. Gradually as the width goes broader, the main crack in the ITZ develops along the length direction due to loading. As can be observed in Fig. 15b, there are a large number of new cracks that appear in the ITZ structure because of the ice expansion force and shrinkage of cement paste during F/T cycles. Besides, the ITZ thickness increases due to F/T cycles [11]. The results can be confirmed by the micrograph observation, shown in Fig. 16. This figure illustrates the effect of CSC and F/T cycles on the ITZ thickness. The formation of the ITZ region depends on two well-known phenomena of wall effect and growth sided. The wall effect occurs near the aggregates, and the growth sided includes spaces away from aggregate [48]. The results show that the ITZ thickness value decreases by increasing the CSC. It can also be observed that the ITZ thickness increases by the addition of F/T cycles. For instance, the maximum ITZ thickness of cement mortar specimens with CSC of 32.5, 42.5, and 52.5 MPa at cycle 0 is 90.16 mm, 71.57 mm, and 59.11 mm, respectively. After adding

F/T cycles (200 cycles) the maximum ITZ thickness increases to 113.36 mm, 86.16 mm, and 69.67 mm at CSC of 32.5, 42.5, and 52.5 MPa. The increase percentages in maximum ITZ thickness for three CSCs are about 25%, 20%, and 18%. The differences obtained for the ITZ thickness of cement mortar can be associated with the hydration process; with alternation of CSC types, the contribution of any CSC changes in cement hydration. 4.3. Comparative analysis of influence of CSC on width and propagation of cracks under F/T cycles Usually, the micro-crack grows in the regions, where the strain value is great, and its propagation develops along relative great strain regions. Figs. 17–19 show the surface morphology of cement mortar specimens during loading until the ultimate load. In these figures, the crack propagation tracking is detected for mixtures with the highest strength against F/T cycles in different CSCs of 32.5, 42.5, and 52.5 MPa. When the loading increases, it can be seen that the main micro-crack is generated on the surface of cement mortar specimen. Also, the cracks mainly begin on the lowest middle section of the cement mortar specimen. As shown in Fig. 17, by increasing the load on the specimen, the damage region of cement mortar specimen changes significantly in the form of an obvious damage band caused by cracking. In addition, the length of the crack propagates gradually in the specimen depth as the loading increases to ultimate load. The crack region color close to increasingly bright reddish shows the cracking damage degree gradually deepens. However, at first glance, it seems that the crack propagation pattern is the same for all specimens, a closer look indicates notable differences between the behaviors and characteristics of specimen cracks. A major difference is visible in the path of the main crack so that mixture with low CSC displays a single crack almost vertical to the specimen surface (Fig. 17). Moreover, branching-cracks are generally spread around the main crack. This phenomenon often occurs in specimens with more pores. In this study, the mixture with CSC

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(I) Cycle 0

(I) Cycle 0

(I) Cycle 0

Pore Pore Micro-crack Pore

(II) Cycles 100

(II) Cycles 100

(II) Cycles 100

Micro-crack

Micro-crack

Micro-crack Pore

Pore Pore

(III) Cycles 150

(III) Cycles 150

(III) Cycles 150

Micro-crack

Micro-crack

Micro-crack

Pore

Pore

Pore

(IV) Cycles 200

(IV) Cycles 200

(IV) Cycles 200

Micro-crack

Pore

Pore

Pore Micro-crack

Micro-crack

(a) CSC 32.5 MPa

(b) CSC 42.5 MPa

(c) CSC 52.5 MPa

Fig. 11. SEM images of samples with s/c = 2.75, w/c = 0.25 and different CSCs subjected to different F/T.

32.5 MPa, has created the crack rapidly in the straight pathway (see Fig. 17) due to pore structure with the formation of the first crack and quick connection between pores, which is similar to the result as reported in previous study [49]. In contrast, the CSC increase, as it results from macro test and SEM images analysis, reduces porosity and increases strength; whereby more tortuosity of the cracks to find a pathway for move in the specimen depth is resulted. This fact was confirmed by Edvardsen [50] who claimed that the hydration products can increase the resistance against cracking through blocking the products in the pore structure. Con-

sequently, by comparing the figures for different cements can be clearly observed that the cracking pattern is different so that the specimens with the higher cement fineness (CSC 52.5 MPa) in Fig. 19 compared to ones with the lower cement fineness (CSC 32.5 MPa) in Fig. 17 experience more tortuosity in order to find the cracking path in the specimen depth due to the increase in cement paste strength. Another important difference is crack width. As shown in Figs. 17–19 the cracks widths are smaller in specimens containing CSC 52.5 MPa as compared with two others comprising CSC 42.5

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(I) Cycle 0

(I) Cycle 0

(I) Cycle 0 Pore

Pore Pore

(II) Cycles 100

(II) Cycles 100

(II) Cycles 100

Pore Micro-crack

Pore

Micro-crack Micro-crack

Pore

(III) Cycles 150

(III) Cycles 150

(III) Cycles 150

Micro-crack

Pore Micro-crack Pore Pore Micro-crack

(IV) Cycles 200

(IV) Cycles 200

(IV) Cycles 200 Pore

Micro-crack Pore Pore

Micro-crack Micro-crack

(a) CSC 32.5 MPa

(b) CSC 42.5 MPa

(c) CSC 52.5 MPa

Fig. 12. SEM images of samples with s/c = 2.75, w/c = 0.45 and different CSCs subjected to different F/T.

and 32.5 MPa. The increase in the CSC from CSC 32.5 MPa (cycle 0 from Fig. 17) to CSC 52.5 MPa (cycle 0 from Fig. 19) induces an increase in cement mortar strength that leads to a decrease up to 25% in the crack width of normal specimen. This can be mainly due to the better connection between cement paste and aggregate in the specimens containing higher CSC. On the other hand, it can be seen that with the increase of F/T cycles and loading the tortuosity and crack width increase, which is similar results to other studies [13,51]. This increase in crack width is higher for low CSC

(see Figs. 17-19 to compare). Accordingly, curves height-crack width indicate the significant influence of CSC on crack width in specimen depth so that the increase of CSC from 32.5 MPa to 52.5 MPa encourages to increase the cement mortar bonding and resistance to opening, and thereby a decrease in crack width. In addition, Fig. 20 shows crack propagation of cement mortar under ultimate compressive load during different F/T cycles for different CSC. As shown in Fig. 20a, the number of cracks and crackbranching in specimens containing CSC 32.5 MPa is higher than

H. Divanedari, H. Eskandari-Naddaf / Construction and Building Materials 233 (2020) 117207

CaCo3 C2 S

14

10

20

CaCo3 Ca(OH)

C4 AF

Ca(OH)2 C4 AF C2 S

(a)

40

30

XRD diffraction peak

60

50

Compound

Height

Position (°2θ)

Ca(OH) 2

80.85

34.37

CaCO 3

118.15

29.41

C4AF

80.85

34.37

C 2S

118.15

29.41

70

CaCo3 C2 S

Position [°2 Theta] (Copper (Cu))

10

20

30

40

XRD diffraction peak

C4 AF

CaCo3 Ca(OH)

C2 S Ca(OH) C4 AF

(b)

50

60

Compound

Height

Position (°2θ)

Ca(OH) 2 CaCO 3 C4AF C 2S

88.46 254.65 90.69 254.65

34.37 29.41 34.37 29.41

70

10

20

30

40

XRD diffraction peak

C2 S

C4 AF

Ca(OH)2 C4 AF

(c)

CaCo3 C2 S Ca(OH)2

CaCo3 C2 S

Position [°2 Theta] (Copper (Cu))

50

60

Compound

Height

Position (°2θ)

Ca(OH) 2 CaCO 3 C4AF C 2S

201.19 360.04 97.47 360.04

34.37 29.41 34.37 29.41

70

Position [°2 Theta] (Copper (Cu)) Fig. 13. X-ray diffraction pattern of cement paste samples with w/c = 0.25, s/c = 2.75 and different CSCs: a) 32.5, b) 42.5 and c) 52.5 MPa.

ones containing other two cement types, 42.5 and 52.5 MPa (Fig. 20b and c). This could be since the specimens with low CSC include the more pores that cause more cracks. Moreover, the

specimens exposed to F/T cycles under pressure load indicate that increasing the number of the cycles, caused by the internal structure weakening of cement mortar, leads to more deterioration in

H. Divanedari, H. Eskandari-Naddaf / Construction and Building Materials 233 (2020) 117207

15

Al

Mg

Ca

Si

Fig. 14. EDX analysis of backscattered electron micrograph and EDX mapping of sample with CSC 52.5 MPa, s/c = 2.75 and w/c = 0.25 subjected to 200F/T cycles.

Original thickness

Aggregate

ITZ

Mortar matrix

(a)

Second thickness

Aggregate

ITZ

Mortar matrix

(b) Original crack

Original pore

New crack New pore

Fig. 15. Deterioration mechanism of ITZ, (a): original specimen, (b): specimen under F/T cycle.

specimens than normal so that specimens containing CSC 32.5 MPa, in different cycles under compression, in some areas face with overall destruction. Note that the specimens containing higher CSC have a high strength against cracking due to a denser texture in cement paste. In contrast, the specimens containing lower CSC cause a fast failure of the specimens by increasing the number of micro-cracks and their quick connection. As a result of Fig. 20, the number of major and branch cracks along with the intensity of damage to the specimens increases with the increasing number of cycles and decreasing cement strength.

Fig. 21 shows a comparison between reference crack widths based on GS pixel values of the original image for specimens with different cement types of 32.5, 42.5, and 52.5 MPa on respectively the red, blue, and green lines between two points of A and B. The distance between these two points shows the change of GS values with that of matter essence on survey location. Generally, it is observable that the location and crack widths are detected accurately. Moreover, Fig. 21 shows that the reference width for the specimen with CSC of 32.5 MPa is more than two other types of cement, 42.5 and 52.5 MPa. This result confirms the obtained

16

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(I) Cycle 0

(I) Cycle 0

(I) Cycle 0

Aggregate Mortar matrix Aggregate Mortar matrix

Mortar matrix

Aggregate

(II) Cycles 200

(II) Cycles 200

Aggregate

(II) Cycles 200

Aggregate Aggregate Mortar matrix Mortar matrix

Mortar matrix

(a) CSC 32.5 MPa

(b) CSC 42.5 MPa

(c) CSC 52.5 MPa

Fig. 16. ITZ thickness for mixtures with different CSCs.

Cycles 100

20 10 0

40 30 20 10

1

2

3

4

5

Crack width (mm)

6

7

40 30 20 10 0

0 0

Cycles 200

Height (mm)

30

Cycles 150

Height (mm)

40

Height (mm)

Height (mm)

Cycle 0

0

1

2

3

4

5

6

7

Crack width (mm)

8

40 30 20 10 0

0

1

2

3

4

5

6

Crack width (mm)

7

8

0

1

2

3

4

5

6

7

8

9

Crack width (mm)

Fig. 17. Comparison of crack propagation and crack width under different F/T cycles using image analysis for mixture with w/c = 0.25, s/c = 2.75 and CSC 32.5 MPa.

results in Fig. 20. In addition, it is found that the gray pixel values in non-crack areas, set relatively in the same phase compared to the neighbor regions with cracks, are higher in specimens contain-

ing cement 52.5 MPa than those of other types. This is because these areas are related to cement paste as cement hydration products. Thus, CSC is considered to be effective in the formation of dif-

17

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40

20 10 0 1

2

3

4

5

20 10

6

40

40

30

30 20 10 0

0 0

Cycles 200

Height (mm)

30

Height (mm)

Height (mm)

40

Height (mm)

Cycles 150

Cycles 100

Cycle 0

0

1

2

Crack width (mm)

3

4

5

6

30 20 10 0

0

7

1

2

3

4

5

6

7

8

0

1

2

Crack width (mm)

Crack width (mm)

3

4

5

6

7

8

Crack width (mm)

Fig. 18. Comparison of crack propagation and crack width under different F/T cycles using image analysis for mixture with w/c = 0.25, s/c = 2.75 and CSC 42.5 MPa.

Cycle 0

Cycles 100

20 10 0

40

30 20 10 0

0

1

2

3

4

Crack width (mm)

5

40

Height (mm)

30

Height (mm)

40

Height (mm)

Height (mm)

40

Cycles 200

Cycles 150

30 20 10 0

0

1

2

3

4

5

Crack width (mm)

6

30 20 10 0

0

1

2

3

4

5

Crack width (mm)

6

0

1

2

3

4

5

6

7

Crack width (mm)

Fig. 19. Comparison of crack propagation and crack width under different F/T cycles using image analysis for mixture with w/c = 0.25, s/c = 2.75 and CSC 52.5 MPa.

ferent reference cracks widths so that CSC has a significant influence on the connection between constituents in cementitious materials.

5. Conclusions The main results obtained in this research can be summarized as follows:


Porosity and weight loss decreased with the increase in cement fineness, and the resulting modulus of elasticity and loadcarrying capacity increased. This trend in F/T cycling was reversed.
Denser texture was formed using the fine cement (CSC 52.5 MPa) so that the interface and micro-cracks due to a large amount of CH and C-S-H gel were formed and filled. Moreover, the SEM images illustrated that the deterioration rate depends on w/c and F/T cycles so that increase of these factors induced

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H. Divanedari, H. Eskandari-Naddaf / Construction and Building Materials 233 (2020) 117207

(I) Cycle 0

(II) Cycles 100

(III) Cycles 150

(IV) Cycles 200

(a) CSC 32.5 MPa (I) Cycle 0

(II) Cycles 100

(III) Cycles 150

(IV) Cycles 200

(b) CSC 42.5 MPa (I) Cycle 0

(II) Cycles 100

(III) Cycles 150

(IV) Cycles 200

(c) CSC 52.5 MPa Fig. 20. Comparison of crack propagation under compressive ultimate load during F/T cycles for mixture with w/c = 0.25, s/c = 2.75 and different CSCs: a) 32.5, b) 42.5 and c) 52.5 MPa.

the more formation of empty spaces and finally growth of micro-cracks. Also, micro-structure observations showed that effective compounds of fine cement in hydration reaction led to not only more increase in hydration products but also decrease in ITZ thickness.
Characterized crack behavior obtained from the image analysis showed that crack pattern under flexural load was approximately similar for all the specimens, i.e., a single main crack. Nonetheless, to find a trajectory for growth, tortuosity of the cracks changed significantly in depth of different specimens so that, in those with coarse cement,

propagated quickly in a straight trajectory; while with increased cement fineness, tortuosity of the cracks increased.
The cracks width significantly decreased with the increase in cement fineness. Moreover, the cracking pattern under ultimate compressive load was indicative of the highest number of micro-cracks in the specimen with coarse cement (CSC 32.5 MPa) compared to fine cement (CSC 52.5 MPa). These results can be generalized for different F/T cycles. Using image analysis, it was found that surface and cement paste cracking is more prominent in specimens with coarse cement.

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H. Divanedari, H. Eskandari-Naddaf / Construction and Building Materials 233 (2020) 117207

A

B

A

B A

(a) CSC 32.5 MPa

(b) CSC 42.5 MPa CSC 32.5 MPa

B

(c) CSC 52.5 MPa

CSC 42.5 MPa

CSC 52.5 MPa

250 Reference width Reference width Reference width

Gray pixel value

200

150

100

50

0 0

15

30

45

60

75

90

105

120

135

150

165

180

195

210

225

Pixel location Fig. 21. A comparative analysis of reference crack widths for specimens with different CSCs.

Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgement The authors appreciate the support for this investigation by thecentral laboratory of Hakim Sabzevari University (member of network of Iranian science laboratories-NISL). References [1] G. Giaccio, M.C. Torrijos, C. Milanesi, R. Zerbino, Alkali–silica reaction in plain and fibre concretes in field conditions, Mater. Struct. 52 (2) (2019) 31. [2] R.P. Borg, E. Cuenca, E.M. Gastaldo Brac, L. Ferrara, Crack sealing capacity in chloride-rich environments of mortars containing different cement substitutes and crystalline admixtures, J. Sustain. Cem. Based Mater. 7 (3) (2018) 141–159. [3] K.Z. Hanjari, P. Utgenannt, K. Lundgren, Experimental study of the material and bond properties of frost-damaged concrete, Cem. Concr. Res. 41 (3) (2011) 244–254. [4] J. Cao, D. Chung, Damage evolution during freeze–thaw cycling of cement mortar, studied by electrical resistivity measurement, Cem. Concr. Res. 32 (10) (2002) 1657–1661. [5] H.-K. Liu, J. Li, Constitutive law of attacked concrete, J. Build. Mater. 6 (2011) 007.

[6] L. Liu, X. Wang, J. Zhou, H. Chu, D. Shen, H. Chen, et al., Investigation of pore structure and mechanical property of cement paste subjected to the coupled action of freezing/thawing and calcium leaching, Cem. Concr. Res. 109 (2018) 133–146. [7] K.L. Scrivener, A.K. Crumbie, P. Laugesen, The interfacial transition zone (ITZ) between cement paste and aggregate in concrete, Interface Sci. 12 (4) (2004) 411–421. [8] A. Cwirzen, V. Penttala, Aggregate–cement paste transition zone properties affecting the salt–frost damage of high-performance concretes, Cem. Concr. Res. 35 (4) (2005) 671–679. [9] J. Lizarazo-Marriaga, C. Higuera, P. Claisse, Measuring the effect of the ITZ on the transport related properties of mortar using electrochemical impedance, Constr. Build. Mater. 52 (2014) 9–16. [10] P.R. Rangaraju, J. Olek, S. Diamond, An investigation into the influence of interaggregate spacing and the extent of the ITZ on properties of Portland cement concretes, Cem. Concr. Res. 40 (11) (2010) 1601–1608. [11] E. Sicat, F. Gong, T. Ueda, D. Zhang, Experimental investigation of the deformational behavior of the interfacial transition zone (ITZ) in concrete during freezing and thawing cycles, Constr. Build. Mater. 65 (2014) 122–131. [12] I. Maruyama, H. Sasano, M. Lin, Impact of aggregate properties on the development of shrinkage-induced cracking in concrete under restraint conditions, Cem. Concr. Res. 85 (2016) 82–101. [13] P. Soroushian, M. Elzafraney, Damage effects on concrete performance and microstructure, Cem. Concr. Compos. 26 (7) (2004) 853–859. [14] H. Kim, E. Ahn, S. Cho, M. Shin, S.-H. Sim, Comparative analysis of image binarization methods for crack identification in concrete structures, Cem. Concr. Res. 99 (2017) 53–61. [15] V. Penttala, Surface and internal deterioration of concrete due to saline and non-saline freeze–thaw loads, Cem. Concr. Res. 36 (5) (2006) 921–928. [16] H. Hornain, J. Marchand, A. Ammouche, J. Commène, M. Moranville, Microscopic observation of cracks in concrete—A new sample preparation technique using dye impregnation, Cem. Concr. Res. 26 (4) (1996) 573–583.

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[17] T. Suzuki, T. Shiotani, M. Ohtsu, Evaluation of cracking damage in freezethawed concrete using acoustic emission and X-ray CT image, Constr. Build. Mater. 136 (2017) 619–626. [18] D. Smyl, R. Rashetnia, A. Seppänen, M. Pour-Ghaz, Can electrical resistance tomography be used for imaging unsaturated moisture flow in cement-based materials with discrete cracks?, Cem. Concr. Res. 91 (2017) 61–72. [19] M. Jin, L. Jiang, M. Lu, N. Xu, Q. Zhu, Characterization of internal damage of concrete subjected to freeze-thaw cycles by electrochemical impedance spectroscopy, Constr. Build. Mater. 152 (2017) 702–707. [20] L. Ferrara, T. Van Mullem, M.C. Alonso, P. Antonaci, R.P. Borg, E. Cuenca, et al., Experimental characterization of the self-healing capacity of cement based materials and its effects on the material performance: a state of the art report by, COST Action SARCOS WG2 167 (2018) 115–142. [21] E. Cuenca, L. Ferrara, Self-healing capacity of fiber reinforced cementitious composites. State of the art and perspectives, KSCE J. Civ. Eng. 21 (2017). [22] C.G. Berrocal, I. Löfgren, K. Lundgren, N. Görander, C. Halldén, Characterisation of bending cracks in R/FRC using image analysis, Cem. Concr. Res. 90 (2016) 104–116. [23] E. Cuenca, A. Tejedor, L. Ferrara, A methodology to assess crack-sealing effectiveness of crystalline admixtures under repeated cracking-healing cycles, Constr. Build. Mater. 179 (2018) 619–632. [24] H. Kim, E. Ahn, M. Shin, S.-H. Sim, Crack and noncrack classification from concrete surface images using machine learning, Struct. Health Monit. (2018). 1475921718768747. [25] A. Shah, S. Khan, R. Khan, I. Jan, Effect of high range water reducers (HRWR) on the properties and strength development characteristics of fresh and hardened concrete, Iran. J. Sci. Technol. Trans. Civil Eng. 37 (C) (2013) 513. [26] F. Gong, D. Zhang, E. Sicat, T. Ueda, Empirical estimation of pore size distribution in cement, mortar, and concrete, J. Mater. Civ. Eng. 26 (7) (2013) 04014023. [27] M. Map, Software (Digital Surf, Besançon, France). http://www.digitalsurf.fr/ en/index.html. [28] J. Sauvola, M. Pietikäinen, Adaptive document image binarization, Pattern Recogn. 33 (2) (2000) 225–236. [29] C. Wolf, J.-M. Jolion, Extraction and recognition of artificial text in multimedia documents, Formal Pattern Anal. Appl. 6 (4) (2004) 309–326. [30] K. Khurshid, I. Siddiqi, C, Faure, N. Vincent, Comparison of Niblack inspired Binarization methods for ancient documents. Document Recognition and Retrieval XVI: International Society for Optics and Photonics, 2009, p. 72470U. [31] Husain SI, Ferguson PM. Flexural crack width at the bars in reinforced concrete beams. 1968. [32] C. Qi, J. Weiss, J. Olek, Characterization of plastic shrinkage cracking in fiber reinforced concrete using image analysis and a modified Weibull function, Mater. Struct. 36 (6) (2003) 386–395. [33] H. Wu, Z. Liu, B. Sun, J. Yin, Experimental investigation on freeze–thaw durability of Portland cement pervious concrete (PCPC), Constr. Build. Mater. 117 (2016) 63–71. [34] X-c Qin, S-p Meng, D-f Cao, Y-m Tu, N. Sabourova, N. Grip, et al., Evaluation of freeze-thaw damage on concrete material and prestressed concrete specimens, Constr. Build. Mater. 125 (2016) 892–904.

[35] F. Shahrajabian, K. Behfarnia, The effects of nano particles on freeze and thaw resistance of alkali-activated slag concrete, Constr. Build. Mater. 176 (2018) 172–178. [36] W. Tian, N. Han, Evaluation of damage in concrete suffered freeze-thaw cycles by CT technique, J. Adv. Concr. Technol. 14 (11) (2016) 679–690. [37] K. Li, Durability Design of Concrete Structures: Phenomena, Modeling, and Practice, John Wiley & Sons, 2017. [38] Y.-R. Zhao, L. Wang, Z.-K. Lei, X.-F. Han, Y.-M. Xing, Experimental study on dynamic mechanical properties of the basalt fiber reinforced concrete after the freeze-thaw based on the digital image correlation method, Constr. Build. Mater. 147 (2017) 194–202. [39] S. Xu, X. Cai, Mechanics behavior of ultra high toughness cementitious composites after freezing and thawing, J. Wuhan Univ. Technol. Mater. Sci. Ed. 25 (3) (2010) 509–514. [40] H. Eskandari-Naddaf, R. Kazemi, Experimental evaluation of the effect of mix design ratios on compressive strength of cement mortars containing cement strength class 42.5 and 52.5 MPa, Procedia Manuf. 22 (2018) 392–398. [41] H. Eskandari-Naddaf, R. Kazemi, ANN prediction of cement mortar compressive strength, influence of cement strength class, Constr. Build. Mater. 138 (2017) 1–11. [42] A. Kargari, H. Eskandari-Naddaf, R. Kazemi, Effect of cement strength class on the generalization of Abrams’ law, Struct. Concr. 20 (1) (2019) 493–505. [43] R. Polat, The effect of antifreeze additives on fresh concrete subjected to freezing and thawing cycles, Cold Regions Sci. Technol. 127 (2016) 10–17. [44] B. Pang, Z. Zhou, X. Cheng, P. Du, H. Xu, ITZ properties of concrete with carbonated steel slag aggregate in salty freeze-thaw environment, Constr. Build. Mater. 114 (2016) 162–171. [45] J. Thomas, H. Jennings, The science of concrete, Northwestern Education 14 (2008) 08. [46] T. Matschei, B. Lothenbach, F.P. Glasser, The role of calcium carbonate in cement hydration, Cem. Concr. Res. 37 (4) (2007) 551–558. [47] H. Jennings, J.J. Thomas, Materials of Cement Science Primer, Northwestern University Infrastructure Technology Institute, 2009. [48] P. Vargas, O. Restrepo-Baena, J.I. Tobón, Microstructural analysis of interfacial transition zone (ITZ) and its impact on the compressive strength of lightweight concretes, Constr. Build. Mater. 137 (2017) 381–389. [49] K. Yang, M. Zhong, B. Magee, C. Yang, C. Wang, X. Zhu, et al., Investigation of effects of Portland cement fineness and alkali content on concrete plastic shrinkage cracking, Constr. Build. Mater. 144 (2017) 279–290. [50] C. Edvardsen, Water permeability and autogenous healing of cracks in concrete, Mater. J. 96 (4) (1999) 448–454. [51] A. Carpiuc-Prisacari, M. Poncelet, K. Kazymyrenko, F. Hild, H. Leclerc, Comparison between experimental and numerical results of mixed-mode crack propagation in concrete: Influence of boundary conditions choice, Cem. Concr. Res. 100 (2017) 329–340.