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semi-lightweight concretes
Construction and Building Materials 25 (2011) 2507–2518
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Effect of basic pumice on morphologic properties of interfacial transition zone in load-bearing lightweight/semi-lightweight concretes _ Mustafa Ayhan a,⇑, Hatice Gönül b, Ismail Ag˘a Gönül b, Askeri Karakusß a a b
Department of Mining Engineering, Engineering Faculty, Dicle University, 21280 Diyarbakir, Turkey Department of Architecture, Architecture Faculty, Dicle University, 21280 Diyarbakir, Turkey
a r t i c l e
i n f o
Article history: Received 19 January 2010 Received in revised form 8 October 2010 Accepted 13 November 2010 Available online 23 December 2010 Keywords: Concrete Basic pumice Interfacial transition zone Morphology
a b s t r a c t The objective of this research is to determine the effect of basic pumice on morphologic properties of interfacial transition zone in load-bearing lightweight/semi-lightweight concretes. In this respect, it has been researched how the chemical and physical structure and the volumetric ratio of basic pumice affected the following three morphologic properties of interfacial transition zone: compactness, width and physical adherence. In accordance with the stated purpose, 15 concrete serials with various properties were produced using basic pumice as aggregate and 670 images were taken from the samples collected from these serials via scanning electron microscope (SEM). Semi-analytical detections were performed based on non-generalizing numeric data obtained in conclusion of the determination of grain limits in these images and comments on visual analysis. In accordance with these detections, it has been concluded that the basic pumice has a high level of potential to contribute to the morphologic properties of interfacial transition zone. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Concrete is one of the materials with wide area of usage in construction. Ayhan et al. [1] have stated that concrete is a heterogeneous material consisting of aggregate, interfacial transition zone (ITZ) and cement paste (Fig. 1). The most important properties differentiating ITZ from cement paste are the porosity ratio and crystals with greater size than the cement paste. Morphologic properties of ITZ have significant influence on compressive strength and elasticity module of concrete. Although the cement paste and the aggregate have dense structures, weak ITZ functioning as a bridge significantly influences concrete – a composite construction material – as it influences the tension transmission. According to Yeg˘inobalı, compressive strength of cement paste and aggregate used in ordinary concrete is above 100 MPa. However, the compressive strength of concrete produced using these materials is 20–40 MPa. The reason of this is ITZ. Therefore, most of the researches conducted in order to increase strength are intended to strengthen ITZ [3]. In load-bearing concretes, the morphologic properties of ITZ are of greater importance. The aggregate to be used in the production of such concretes have a great effect on the morphologic properties of ITZ. Aggregate with different properties may be used in the production of load-bearing concretes. Load bearing ordinary concrete
⇑ Corresponding author. Tel.: +90 412 2488403; fax: +90 412 2488405. E-mail address: [email protected] (M. Ayhan). 0950-0618/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2010.11.083
may be produced using ordinary aggregate and load-bearing lightweight or semi-lightweight concrete may be produced using lightweight aggregate. Load-bearing lightweight/semi-lightweight concretes were initially produced using artificial lightweight aggregates. Later on, along with the development of plasticizer admixtures, loadbearing lightweight/semi-lightweight concretes were started to be produced with natural lightweight aggregates [4]. According to Mehta and Monteiro, artificial lightweight aggregates gave very successful results in concrete production. However, artificial lightweight aggregates are not economic and ecologic materials since the production of artificial lightweight aggregate requires energy consumption, causes nonrenewable resource consumption and increases the cost of structure [2,5]. Therefore, the number of researches and practices regarding the use of natural lightweight aggregates in the production of load-bearing lightweight/semilightweight concrete should increase. One of the natural lightweight aggregates is pumice. Pumices are divided into two groups as acidic and basic. Since lightness and heat conductivity generally gain importance in scientific researches and practices, emphasis was placed on acidic pumice that is superior to ‘‘basic pumice (BP)’’. Therefore, there are very few researches conducted regarding this material. Lack of scientific data regarding BP was observed in application as well. Material with limited information on behavior in concrete was not used so much [4]. In all reports of Eurolightcon, it has been emphasized that the ‘‘insulation’’ performance of concrete should be taken into consideration following the ‘‘load bearing’’ performance in the production
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[6–22]. No research analyzing the ITZ in BPC was conducted. The developments in materials area were obtained upon understanding the microstructure of materials and through changing this structure. In this regard, the findings obtained from this research are expected to make a major contribution and to be guide. 2. Method 2.1. Production of BPC serials
Fig. 1. Schematic illustration of microstructure of concrete [2].
of load-bearing lightweight/semi-lightweight concrete. In literature, the load bearing performance of BP is recognized to be superior to acidic pumice [4]. Therefore, it has been deemed necessary to research the ITZ performance to be obtained using BP in the production of load-bearing lightweight/semi-lightweight concrete. The objective of this research is to determine the effect of BP on the morphologic properties of ITZ in load-bearing lightweight/ semi-lightweight concretes. In this regard, it has been researched how the chemical and physical structure and the volumetric ratio of BP affected the following three morphologic properties of ITZ:
In accordance with the purpose stated within this research, 15 different BPC serials were produced. The properties of cement used in the production of BPC serials were given in Table 1, the physical properties of aggregates were given in Table 2, and the chemical content ratios of BP were given in Table 3. ‘‘Absolute volume method’’ suggested in ACI 213R-03 [23] was used for determining the mixture ratios of BPC series. According to this method, water must be impregnated to the lightweight aggregates before using them in production. There are two main aims of this application: first is to prevent lightweight aggregate that has a rougher surface than normal aggregate obstructing the concrete mixing operation, second is to prevent an improper hydration arisen from lightweight aggregate impregnating the concrete water. For these reasons, in the production of BPC serials, sand dried to reach the oven dry density was used in this state and BP dried to reach the oven dry density was used after 0.5 h (depending on the concrete production conditions and the properties of materials that were used in the production) water was impregnated. Material mixture ratios were designed to obtain high strength BPC and the production of BPC serials was initiated after the 7 days trial samples were tested for strength. In order to determine the effect of volumetric ratio of BP on morphologic properties of ITZ, BP with three different volumetric ratios (40%, 50% and 60%) was used in the produced BPC serials. In order to determine the effect of BP on concretes with different ‘‘water/cement (W/C)’’ ratios, three different W/C ratios (30%, 37.5%
Table 3 The chemical content ratios of BP used in the production of BPC serials.
Compactness. Width. Physical adherence. Concrete produced using BP could be defined as ‘‘load-bearing lightweight concrete’’ or ‘‘load-bearing semi-lightweight concrete’’. These definitions are limited with the unit weight value of concrete. Therefore, the importance of aggregate having an influential role on the determination of concrete properties was taken into consideration and such concretes were defined as ‘‘basic pumice concretes (BPC)’’ in this research. There are many researches in which ITZ was analyzed in concretes produced using ordinary and artificial lightweight aggregates
The chemical content of BP used in the production of BPC serials
Ratios (%)
SiO2 (total) Insoluble residue Al2O3 Fe2O3 CaO MgO SO3 Ignition loss Na2O K2O
45.06 59.53 13.34 12.80 12.05 7.41 0.36 1.01 2.88 1.32
Table 1 The properties of cement used in the production of BPC serials [4]. (Normal early strength pure portland cement that is appropriate to TS EN 197-1 standard.) Strength properties
Physical properties
2 days compressive strength 7 days compressive strength 28 days compressive strength
31.0 MPa 39.5 MPa 46.5 MPa
Chemical properties
Density (g/cm3) Prize setting (h) Prize ending (h) Volume constancy (mm) Specific surface area (cm2/g)
3.12 2.15 3.35 1.2 3395
Insoluble residue (%) SO3 (%) Cl (%) Ignition loss (%)
0.55 2.38 0.0085 2.65
Table 2 The physical properties of aggregates used in the production of BPC serials [4]. Aggregates used in the production of BPC serials
Physical properties Maximum aggregate size (mm)
River sand (fine aggregate) BP (coarse aggregate)
4 16
Particle-size distribution
Bulk density (mg/m3)
Moisture content (%)
Particle density (mg/m3)
All distributions are ideal for ASTM C 330
1.707
1.96
2.538
2.538
–
0.864
0.89
1.819
10.884
10
Water absorption ratio (24 h) (%)
Shape index
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M. Ayhan et al. / Construction and Building Materials 25 (2011) 2507–2518 Table 4 The mixture ratios of produced BPC serials. Produced BPC series
1 2 3 4 5 6. 7 8 9 10 11 12 13 14 15
KS4037.5 KS5037.5 KS6037.5 KS4045 KS5045 KS6045 S40-1 S401.25 S401.50 S50-1 S501.25 S501.50 S60-1 S601.25 S601.50
Mixture ratios Volumetric ratio of BP within the whole aggregate (%)
Water/ cement ratio (W/C) (%)
Hyper plasticizer/ cement (HP/C) ratio – amount in 1 m3 concrete (%) – (kg)
Amount of cement (kg)
Volume of cement (dm3)
Amount of BP (kg)
Volume of BP (dm3)
Amount of river sand (kg)
Volume of river sand (dm3)
Net mixture water + amount of hyper plasticizer (kg)
Amount of saturation water of BP (kg)
Amount of saturation water of river sand (kg)
40
37.5
–
500
160.256
474.834
260.898
994.019
391.346
187.5
35.280
14.910
50
37.5
–
500
160.256
593.542
326.122
828.350
326.122
187.5
44.100
12.425
60
37.5
–
500
160.256
712.250
391.346
662.681
260.898
187.5
52.920
9940
40
45
–
500
160.256
447.534
245.898
936.869
368.846
225
33.256
14.053
50
45
–
500
160.256
559.417
307.372
780.725
307.372
225
41.565
11.711
60
45
–
500
160.256
671.300
368.846
624.580
245.898
225
49.880
9370
40 40
30 30
1.00–5.00 1.25–6.25
500 500
160.256 160.256
502.134 502.134
275.898 275.898
1051.169 1051.169
413.846 413.846
150 150
37.310 37.310
15.768 15.768
40
30
1.50–7.50
500
160.256
502.134
275.898
1051.169
413.846
150
37.310
15.768
50 50
30 30
1.00–5.00 1.25–6.25
500 500
160.256 160.256
627.670 627.670
344.872 344.872
876 876
344.872 344.872
150 150
46.640 46.640
13.140 13.140
50
30
1.50–7.50
500
160.256
627.670
344.872
876
344.872
150
46.640
13.140
60 60
30 30
1.00–5.00 1.25–6.25
500 500
160.256 160.256
753.20 753.20
413.846 413.846
700.780 700.780
275.898 275.898
150 150
55.960 55.960
10.510 10.510
60
30
1.50–7.50
500
160.256
753.20
413.846
700.780
275.898
150
55.960
10.510
and 45%) were used in the produced BPC serials. In order to produce BPC serials with 30% W/C ratio, hyper plasticizer Glenium ACE 32 with polycarboxylate origin manufactured by YKS for prefabricated elements in compliance with TS EN 934-2 was used. These serials were produced using three different hyper plasticizer/cement (HP/C) ratios (1%, 1.25% and 1.5%). The mixture ratios of produced BPC serials were given in Table 4. Considering the fact that cement paste and BP may interact within the process, the produced BPC serials were retained in the laboratory under normal ambient conditions for one year in order to determine the long term performances. Furthermore, based on the anticipation that the hydration development could be observed much better in cracks in the concrete, the BPC serials were subjected to bending test at the end of 90 days. 2.2. Sample collection from BPC serials The morphologic properties of ITZ in concretes could be determined in micro levels through images obtained using scanning electron microscope (SEM). The samples, from which SEM images were taken, collected in the form of cubes of 50 mm from the end portion where the crack width is minimum in BPC serials of 100 100 500 mm (Fig. 2). These cube samples with large sizes were reduced twice to 10 25 50 mm using diamond tip SAW. The cut samples were polished, wiped with methyl alcohol to stop the hydration development, coated with gold to reduce conductivity and dried in an oven.
2.3. Taking SEM images from samples The planes for which images were taken from the samples were determined according to the concrete cast direction. SEM images were generally taken from the planes of samples perpendicular to concrete cast direction in the studies within the literature. However, in this research, SEM images were taken from the planes of samples parallel to concrete cast direction considering the bleeding fact. Two types of images could be taken from SEM device. One of these images is called ‘‘Scatter Electron Image (SEI)’’ and the other is ‘‘Backscatter Electron Image (BSEI)’’. SEI is the image with higher quality reflecting three-dimension effect more. Therefore, SEI is preferred to determine the morphologic properties. BSEI is a type of image based on the principle to be sensitive to atomic numbers of elements. The phases with low atomic numbers appear in dark colors, whereas, the phases with high atomic numbers appear in light colors and bright [24]. In this research, both types of images taken from ‘‘LEO 440’’ SEM device were used. Thirty-eight (2 19) images were taken in total from two different areas of each sample. The location, type, magnification ratio and number of images taken from each area of each sample were given in Fig. 3. Thus, 570 (38 15) samples in total were taken from all samples. Apart from these images taken from all samples regarding ITZ that takes place over the BP, 100 images were taken from the samples belonging only to two BPC serials (KS50-45 and S40-1) regarding ITZ that
Fig. 2. The location of samples from which SEM images were taken.
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Fig. 3. The location, type, magnification ratio and number of images taken from each area of each sample.
takes place under the BP. From these images taken within the scope of the research (670), the images taken from the locations where the bleeding was high because of the abnormal formations or the close aggregates were not taken into consideration.
2.4. Analysis method of SEM images Semi-analytical detections were performed based on non-generalizing numeric data obtained in conclusion of the determination of grain limits in these images and comments on visual analysis. This analysis method is frequently referred in the researches within the literature for the analysis of SEM images [4,6,7,9–22].
3. Findings and discussion 3.1. The effect of chemical structure of BP on the morphologic properties of ITZ Three main hydration products are generated as a result of cement hydration. These are ‘‘CSH’’, ‘‘CH’’ and ‘‘AFT’’ crystals. According to Ug˘urlu, more water than the amount required for cement hydration is added to concrete due to the treatable mixture preparation obligation. After the concrete is paved, the coarse grains tend to move downwards in order to equilibrate and due to gravity, whereas, the water not included in hydration process (yet) tend to move upwards. Water unable to flow under coarse aggregate grains is retained here [25]. Due to this occurrence called bleeding, W/C ratio of ITZ is greater than the W/C ratio of cement paste. The fact that W/C ratio of ITZ is greater causes the amount of water not undergoing hydration with cement and thus the porosity ratio to be greater. When the W/C ratio of concrete is increased, the porosity ratio of ITZ will also increase as the bleeding will increase. Increase of porosity ratio causes a decrease in compactness and increase in
width of ITZ. Furthermore, in consequence of the increase in porosity ratio, the physical adherence will decrease since the contact surface of aggregate and ITZ paste will decrease. Even in the event of using aggregate that will increase the physical adherence in terms of surface texture and grain form, the desired physical adherence cannot be obtained when the W/C ratio is high. Certain aggregates cause the hydration process to take longer time by reacting with cement paste due to their chemical structures. In this case, secondary hydration products are generated and the cavities among crystals are filled. This development causes a decrease in the width of ITZ. ITZ that is looser from cement paste at the beginning becomes more compact within the process and its density comes close to the density of cement paste. In rare cases, its density may exceed the density of cement paste [26–28]. In consequence of the decrease in porosity ratio, the adherence will
Fig. 5. The largest unhydrated clinker particle in ITZ (KS40-37.5/BSEI).
Fig. 4. The developed hydration products in ITZ cracks (a: S60-1.25/SEI, b: KS60-45/SEI).
M. Ayhan et al. / Construction and Building Materials 25 (2011) 2507–2518
increase since the contact surface of aggregate and ITZ paste will increase. In this regard, the chemical structure of aggregate to be used in the production of concrete considerably affects the hydration development. Three-hundred and sixty days after the production of BPC serials the images taken from the cracks formed in ITZ since the produced BPC serials are subjected to bending test at the end of 90 days, suggest that the hydration development would continue
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in BPC after the 90th day (Fig. 4). This indicates that the real performances of concretes produced using aggregates with high ‘‘Si’’ contents as BP may be determined only within the process. Image of the largest unhydrated clinker particle that has been determined in this research in ITZ was given in Fig. 5. This image was taken from the BPC serial ‘‘KS40-37.5’’ which is the lowest slump concrete serial produced without admixtures. Accordingly, the size of unhydrated clinker particle is about 3 lm. This value
Fig. 6. General structure of CSH crystals in ITZ (a: S60-1.50/SEI, b: KS60-45/SEI).
Fig. 7. Examples indicating the ratio of CSH crystals in all hydration products in ITZ (a: KS50-45/SEI, b: S50-1.25/SEI).
Fig. 8. General forms of CH crystals in ITZ (a: KS40-45/SEI, b: KS50-45/SEI).
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is nine times smaller than the values [5,18,21] obtained from high strength concretes manufactured using ordinary aggregate. This indicates that ‘‘internal cure’’ [26–28] occurred along with the use of BP even in lowest slump concrete serials and that the hydration development is very strong due to the chemical interaction between BP and cement paste.
The fact that the hydration development in the produced BPC is very strong and positively affected the structure of crystals that are hydration products in ITZ. It has been determined that the CSH crystals in ITZ were formed in a structure almost undistinguishable from the aggregate (Fig. 6). In SEM images, these structures were defined by the help of capil-
Fig. 9. Examples indicating the ratio of CH crystals in all hydration products in ITZ (a: KS50-45/SEI, b: S50-1.25/SEI).
Fig. 10. AFT and AFM crystals detected rarely in ITZ (a: S40-1.25/SEI, b: KS40-37.5/SEI).
Fig. 11. Examples regarding the general compactness level of ITZ in BPC (a: KS60-45/SEI, b: S40-1.50/SEI).
M. Ayhan et al. / Construction and Building Materials 25 (2011) 2507–2518
lar voids that are more in ITZ compared to the cement paste. As the ratio of CSH crystals with compact and dense structures increases in all hydration products, the porosity ratio of ITZ decreases. In the previous researches [2,5,29], this ratio was reported to be about 50% in concretes produced using ordinary aggregate. However in this research, this ratio was observed to be far above 50% in all BPC serials. This ratio was determined to be higher in BPC serials with low W/C ratio (Fig. 7). Due to their forms and large sizes, CH crystals cause the formation of cavities in ITZ. CH crystals are generally in the form of hexagonal-plate. In this research, it has been determined that the CH crystals – different from the forms defined in literature – are in prismatic forms close to cube three sizes of which are not different from each other (Fig. 8). In concretes produced using ordinary aggregate, the ratio of CH crystals in all hydration products is about 25% [2,5,29]. However in this research, this ratio was observed to be far below 50% in all BPC serials. This ratio was determined to
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be lower in BPC serials with low W/C ratio (Fig. 9). The measurement differentiation between three sizes of CH crystals and the decrease of ratio in hydration products caused a decrease in the porosity ratio of ITZ. AFT crystals are determined based on their acicular structures. There are many cavities around these crystals due to that structure. In respect of their structures, the increase in ratio causes the increase in porosity ratio of ITZ. In concretes produced using ordinary aggregate, the ratio of AFT crystals in all hydration products is about 15–20% [2,5,29]. The AFT crystals formed at the beginning of hydration process convert into AFM crystals within the process. Among hundreds of image taken from the concretes analyzed in this research, AFT and AFM crystals were determined only in few of these images (Fig. 10). AFT crystals were detected only in a few low slump concretes. This was caused by the fact that there was not adequate amount of water for AFT crystals to convert into AFM crystals during the hydration development process. Rarely
Fig. 12. Examples in which the ITZ was defined as ‘‘very compact’’ in high strength concretes produced using ordinary aggregate [10].
Fig. 13. The fact that the ITZ width under the BP is more than the ITZ width over it is due to bleeding (KS50-37.5/SEI).
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Fig. 14. The changing of morphologic properties of ITZ based on HP/C ratio (a, b: S60-1/SEI, BSEI; c, d: S60-1.25/SEI, BSEI; e, f: S60-1.50/SEI, BSEI).
Fig. 15. The cavity forms and sizes of BP used in the research.
M. Ayhan et al. / Construction and Building Materials 25 (2011) 2507–2518
detected AFM crystals suggest that they form a compact structure with CSH crystals during the process due to the fact that the AFT crystals are rare at the beginning of the process and that the hydration development is very strong. The formation of hydration crystals in a manner to decrease the porosity ratio of ITZ has positively affected the morphologic properties of ITZ (compactness, width and physical adherence). Examples regarding the general compactness level of ITZ in BPC were given in Fig. 11. One of these examples is (a) the BPC serial with W/C ratio of 45% and the other one is (b) the BPC serial with W/C ratio of 30%. In Fig. 12, examples [10] in which the ITZ was defined as ‘‘very compact’’ in high strength concretes produced using ordinary aggregate were given. As shown in the figures, both ITZ’s
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in BPC feature more compact structures compared to ITZ in high strength concretes produced using ordinary aggregates. The formation of hydration crystals in a manner to decrease the porosity ratio of ITZ has caused the width of ITZ to decrease and the physical adherence to increase because of the increased contact surface of BP and ITZ paste. Due to bleeding, it has been determined that the ITZ width under the BP is more than the ITZ width over it (Fig. 13). The morphologic properties of ITZ in BPC serials with high W/C ratios were determined to be in good condition as well (Figs. 11 and 12). However, as the W/C ratio of BPC serials decreases, the hydration crystals were formed in a manner to decrease the porosity ratio of ITZ more. Therefore, the morphologic properties of ITZ
Fig. 16. Connected and unconnected cavities of BP used in the research (a: S40-1.50/SEI, b: S60-1/SEI).
Fig. 17. Interlocking zones in BP (a: KS60-45/SEI, b: S50-1.50/SEI, c: S50-1.25/SEI, d: S60-1/SEI).
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were determined to be in better conditions in BPC serials with lowest W/C ratio (30%) within the scope of the research. Within these BPC serials, the morphologic properties of ITZ in the serials with HP/C ratio of 1.25% were determined to be in better conditions (Fig. 14). 3.2. The effect of physical structure of BP on the morphologic properties of ITZ The cavities of BP used in this research are generally in circular forms. The cavity size was determined to be between 100 and 250 lm in general and to reach up to 1 mm. Despite being proportionally rare, connected cavities in ellipse and amorphous forms were determined as a result of interlaced circles (Figs. 15 and 16). The cavity structure of BP used in crushed forms in the production of concrete is important as it affects the surface morphology and thus, the physical adherence of ITZ. The entrance of paste into the bays of aggregate in physical adherence and immerse of aggregate asperities into paste cause
interlocking in the form of pinning [25]. The interlocking zones in BP are given in Fig. 17. Since the surface bays and asperities of BP are much more compared to the bays and asperities of artificial lightweight aggregate, the size of interlocking zones detected in the produced BPC is larger than the size of interlocking zones of high strength concretes produced using artificial lightweight aggregate. The size of largest interlocking zone in high strength concretes produced using artificial lightweight aggregate was about 15 lm [6], whereas, the average size in the produced BPC was determined to be about 200 lm. The size of the largest interlocking zone detected in the produced BPC is 600 lm (Fig. 17a). Due to the connected cavities of BP, it has been determined that the ITZ paste infiltrates to BP and the hydration products developed in these cavities. These formations are to be defined apart from the formations defined as ‘‘interlocking zones’’. These zones were defined as infiltration zones in the research (Fig. 18). No such formation was mentioned in the researches conducted regarding ordinary and artificial lightweight aggregates.
Fig. 18. The infiltration zones in BP and the hydration products developed in these zones (a: S50-1.50/SEI, b: KS50-45/SEI, c: KS60-45/BSEI, d, e: S50-1.50/SEI, f: S50-1.50/ BSEI).
M. Ayhan et al. / Construction and Building Materials 25 (2011) 2507–2518
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Fig. 19. The changing of morphologic properties of ITZ based on volumetric ratio of BP (a, b: KS40-45/SEI, BSEI; c, d: KS50-45/SEI, BSEI; e, f: KS60-45/SEI, BSEI).
The interlocking and infiltration zones in BP have increased the physical adherence of ITZ. It is obvious that ordinary and artificial lightweight aggregates will not allow a physical adherence at this level due to their physical structures. 3.3. The effect of volumetric ratio of BP on the morphologic properties of ITZ Within the scope of the research, BPC serials with the same W/C ratio were produced in which the volumetric ratio of BP within the whole aggregate was 40%, 50% and 60%. The compactness of ITZ has decreased and the width has increased in BPC serials with high volumetric ratios of BP. Furthermore, in consequence of the decrease in the contact surface of BP and ITZ in these BPC serials, the physical adherence has also decreased (Fig. 19). The reason for this situation could be explained as follows: in the production of BPC serials, sand dried to reach the oven dry density was used in this state and BP
dried to reach the oven dry density was used after 0.5 h water was impregnated. The amount of saturation water of sand has been added to the mixture water. Saturation water amounts are not taken into consideration in W/C ratios. In BPC serials in which the sand used in dry form has decreased, the mixture water has intensified around BP that used after the water impregnation, the bleeding has increased, and the W/C ratio and the porosity ratio of ITZ have increased. In this regard, it has been determined that the morphologic properties of ITZ are in better conditions in the BPC serials in which BP was used at the lowest volumetric ratio (40%).
4. Conclusions In accordance with the findings obtained from this research, the following determinations were performed regarding the affect of BP on the morphologic properties of ITZ:
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Due to its chemical structure, BP has caused a very strong hydration development (the size of unhydrated clinker particle was determined to be about 3 lm) within a long process by reacting with the cement paste. The fact that the hydration development is very strong has caused the formation of hydration crystals in a manner to decrease the porosity ratio of ITZ. This has positively affected the morphologic properties of ITZ (compactness, width and physical adherence). ITZ in BPC has been structured in a more compact form compared to ITZ in high strength concretes produced using normal aggregate, also the width has decreased and the physical adherence has increased as the contact surface of BP and ITZ paste has increased. Due to bleeding, it has been determined that the ITZ width under the BP is more than the ITZ width over it. The morphologic properties of ITZ in BPC serials with high W/C ratios were determined to be in good condition as well. However, as the W/C ratio of BPC serials decreases, the hydration crystals were formed in a manner to decrease the porosity ratio of ITZ more. Therefore, the morphologic properties of ITZ were determined to be in better conditions in BPC serials with lowest W/C ratio (30%) within the scope of the research. Within these BPC serials, the morphologic properties of ITZ in the serials with HP/C ratio of 1.25% were determined to be in better conditions. Since the surface bays and asperities of BP are much more compared to the bays and asperities of artificial lightweight aggregate, the size of interlocking zones in the produced BPC is much larger (the largest is 600 lm) than the size of interlocking zones (the largest is 15 lm) of high strength concretes produced using artificial lightweight aggregate. Furthermore, due to the existing connected cavities of BP (rare in terms of ratio), it has been determined that the ITZ paste infiltrates to BP and the hydration products developed in these cavities. These zones were defined as ‘‘infiltration zones’’ in the research. No such formation was mentioned in the researches conducted regarding ordinary and artificial lightweight aggregates. The interlocking and infiltration zones in BP caused the formation of a physical adherence level which could not be obtained through the use of ordinary and artificial lightweight aggregates. The compactness of ITZ has decreased and the width has increased in BPC serials with high volumetric ratios of BP. Furthermore, in consequence of the decrease in the contact surface of BP and ITZ in these BPC serials, the physical adherence has also decreased. In this regard, it has been determined that the morphologic properties of ITZ are in better conditions in the BPC serials in which BP was used at the lowest volumetric ratio (40%). In accordance with the above-mentioned semi-analytic detections, BP has a potential to make high level of contribution to the morphologic properties of ITZ. The fact that high performance from BPC serials with high W/C ratios such as 37.5% and 45% has been obtained in terms of the studied properties supports this determination. However, the fact that the highest performance has been obtained from the BPC serial with W/C ratio of 30%, HP/C ratio of 1.25% and BP volumetric ratio of 40% indicates that higher level of performances could be obtained from BPC serials that would be produced in different mixture ratios. Therefore, it is believed that the researches associating numerically the morphologic properties of ITZ in BPC serials with production components, with each other, hydration products and the load bearing properties of concrete will be beneficial.
Acknowledgments We thank to Dicle University Coordinator of Scientific Researches (DÜBAP) which provided funding, YKS Industry Co. which helped us procure hyper-plasticizer additives, Mardin Cement Industry and Trade Co. which helped us procure cement and BP, and valuable employees thereof. References _ ve Karakusß A. Güneydog˘u Anadolu Bölgesindeki [1] Ayhan M, Gönül H, Gönül IA, bazik pomza kaynakları ile üretilen yüksek dayanımlı betonlarda ara yüzey bölgesinin morfolojik özellikleri ve beton özellikleri ile ilisßkisi. Dicle Üniversitesi Bilimsel Arasßtırma Projeleri (DÜBAP), 04-MF-34 nolu Arasßtırma Projesi, Diyarbakır; 2008. [2] Mehta PK, Monteiro PJM. Concrete, microstructure, properties and materials. Mc-Graw-Hill: New York; 2005. [3] Yeg˘inobalı A. Çimento ve çimento esaslı malzemenin geleceg˘i. Yapı _ Malzemesinin Geleceg˘i – Yapı Malzemesi Kurultayı, Istanbul; 2003. [4] Gönül H. Bazalt skoriasının tasßıyıcı yarı hafif beton üretiminde kullanımı. Doktora Tezi, Gazi Üniversitesi Fen Bilimleri Enstitüsü, Ankara; 2008. [5] Monteiro PJM. The structure and properties of civil engineering materials. Berkeley: Department of Civil and Environmental Engineering, University of California; 2003. [6] Lo TY, Cui HZ. Effect of porous lightweight aggregate on strength of concrete. Mater Lett 2004;58:916–9. [7] Maage M et al. Structural LWAC specification and guideline for materials and production. European Union, EuroLightCon, Document BE96-3942/R14. Gouda; 2000 [ISBN: 90 376 0108 1]. [8] Li G, Zhao Y, Pang SS, Li Y. Effective Young’s modulus estimation of concrete. Cem Concr Res 1999;29:1455–62. [9] Basheer L, Basheer PAM, Long AE. Influence of coarse aggregate on the permeation, durability and the microstructure characteristics of ordinary portland cement concrete. Constr Build Mater 2005;19:682–90. [10] Tam VWY, Gao XF, Tam CM. Microstructural analysis of recycled aggregate concrete produced from two-stage mixing approach. Cem Concr Res 2005;35:1195–203. _ Transition zone in high performance concrete [11] Vivekanandam K, Patnaikuni I. during hydration. Cem Concr Res 1997;27:817–23. [12] Lo Y, Gao XF, Jeary AP. Microstructure of pre-wetted aggregate on lightweight concrete. Build Environ 1999;34:759–64. [13] Tasong WA, Lynsdale CJ, Cripps JC. Aggregate-cement paste interface. Part I: influence of aggregate geochemistry. Cem Concr Res 1999;29:1019–25. [14] Chan WWJ, Wu CML. Durability of concrete with high cement replacement. Cem Concr Res 2000;30:865–79. [15] Elsharief A, Cohen MD, Olek J. Influence of aggregate size, water cement ratio and age on the microstructure of the interfacial transition zone. Cem Concr Res 2003;33:1837–49. [16] Li G. A new way to increase the long-term bond strength of new-to-old concrete by the use of fly ash. Cem Concr Res 2003;33:799–806. [17] Poon CS, Shui ZH, Lam L. Effect of microstructure of ITZ on compressive strength of concrete prepared with recycled aggregates. Constr Build Mater 2004;18:461–8. [18] Elsharief A, Cohen MD, Olek J. Influence of lightweight aggregate on the microstructure and durability of mortar. Cem Concr Res 2005;35:1368–76. [19] Gao JM, Qian CX, Liu HF, Wang B, Li L. ITZ microstructure of concrete containing GGBS. Cem Concr Res 2005;35:1299–304. [20] Ye G, Breugel KV, Fraaij ALA. Three-dimensional microstructure analysis of numerically simulated cementitious materials. Cem Concr Res 2003;33:215–22. [21] Diamond S. The microstructure of cement paste and concrete – a visual primer. Cem Concr Compos 2004;26:919–33. [22] Diamond S. The patch microstructure in concrete: the effect of superplasticizer. Cem Concr Res 2006;36:776–9. [23] American Concrete Institute, ACI 213R-03. Guide for structural lightweight aggregate concrete. Michigan: ACI; 2003. p. 1–38. [24] Sahu S, Badger S, Thaulow N, Lee RJ. Determination of water–cement ratio of hardened concrete by scanning electron microscopy. Cem Concr Compos 2004;26:987–92. [25] Ug˘urlu A. Agrega – çimento hamuru bag˘ı üzerine, 2. Ulusal Kırmatasß _ Sempozyumu, Istanbul; 1999. p. 213–28. [26] Holm TA, Bremner TW. State-of-the-art report on high-strength, highdurability structural low-density concrete for applications in severe marine environments, ERDC/SL TR-00-3 (TR INP-00-2), Washington; 2000. [27] Sveindottir EL et al. LWAC material properties, state-of-the-art, European Union, EuroLightCon, Document BE96-3942/R2, Gouda; 1998. [28] Liao KY, Chang PK, Peng YN, Yang CC. A study on characteristics of interfacial transition zone in concrete. Cem Concr Res 2004;34:977–89. [29] Fernández RDH, Alonso JM, Abella FM, Barrios MH. Ageing of concrete in dams. Switzerland: ICOLD European Club; 2004.
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Effect of basic pumice on morphologic properties of interfacial transition zone in load-bearing lightweight/semi-lightweight concretes _ Mustafa Ayhan a,⇑, Hatice Gönül b, Ismail Ag˘a Gönül b, Askeri Karakusß a a b
Department of Mining Engineering, Engineering Faculty, Dicle University, 21280 Diyarbakir, Turkey Department of Architecture, Architecture Faculty, Dicle University, 21280 Diyarbakir, Turkey
a r t i c l e
i n f o
Article history: Received 19 January 2010 Received in revised form 8 October 2010 Accepted 13 November 2010 Available online 23 December 2010 Keywords: Concrete Basic pumice Interfacial transition zone Morphology
a b s t r a c t The objective of this research is to determine the effect of basic pumice on morphologic properties of interfacial transition zone in load-bearing lightweight/semi-lightweight concretes. In this respect, it has been researched how the chemical and physical structure and the volumetric ratio of basic pumice affected the following three morphologic properties of interfacial transition zone: compactness, width and physical adherence. In accordance with the stated purpose, 15 concrete serials with various properties were produced using basic pumice as aggregate and 670 images were taken from the samples collected from these serials via scanning electron microscope (SEM). Semi-analytical detections were performed based on non-generalizing numeric data obtained in conclusion of the determination of grain limits in these images and comments on visual analysis. In accordance with these detections, it has been concluded that the basic pumice has a high level of potential to contribute to the morphologic properties of interfacial transition zone. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Concrete is one of the materials with wide area of usage in construction. Ayhan et al. [1] have stated that concrete is a heterogeneous material consisting of aggregate, interfacial transition zone (ITZ) and cement paste (Fig. 1). The most important properties differentiating ITZ from cement paste are the porosity ratio and crystals with greater size than the cement paste. Morphologic properties of ITZ have significant influence on compressive strength and elasticity module of concrete. Although the cement paste and the aggregate have dense structures, weak ITZ functioning as a bridge significantly influences concrete – a composite construction material – as it influences the tension transmission. According to Yeg˘inobalı, compressive strength of cement paste and aggregate used in ordinary concrete is above 100 MPa. However, the compressive strength of concrete produced using these materials is 20–40 MPa. The reason of this is ITZ. Therefore, most of the researches conducted in order to increase strength are intended to strengthen ITZ [3]. In load-bearing concretes, the morphologic properties of ITZ are of greater importance. The aggregate to be used in the production of such concretes have a great effect on the morphologic properties of ITZ. Aggregate with different properties may be used in the production of load-bearing concretes. Load bearing ordinary concrete
⇑ Corresponding author. Tel.: +90 412 2488403; fax: +90 412 2488405. E-mail address: [email protected] (M. Ayhan). 0950-0618/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2010.11.083
may be produced using ordinary aggregate and load-bearing lightweight or semi-lightweight concrete may be produced using lightweight aggregate. Load-bearing lightweight/semi-lightweight concretes were initially produced using artificial lightweight aggregates. Later on, along with the development of plasticizer admixtures, loadbearing lightweight/semi-lightweight concretes were started to be produced with natural lightweight aggregates [4]. According to Mehta and Monteiro, artificial lightweight aggregates gave very successful results in concrete production. However, artificial lightweight aggregates are not economic and ecologic materials since the production of artificial lightweight aggregate requires energy consumption, causes nonrenewable resource consumption and increases the cost of structure [2,5]. Therefore, the number of researches and practices regarding the use of natural lightweight aggregates in the production of load-bearing lightweight/semilightweight concrete should increase. One of the natural lightweight aggregates is pumice. Pumices are divided into two groups as acidic and basic. Since lightness and heat conductivity generally gain importance in scientific researches and practices, emphasis was placed on acidic pumice that is superior to ‘‘basic pumice (BP)’’. Therefore, there are very few researches conducted regarding this material. Lack of scientific data regarding BP was observed in application as well. Material with limited information on behavior in concrete was not used so much [4]. In all reports of Eurolightcon, it has been emphasized that the ‘‘insulation’’ performance of concrete should be taken into consideration following the ‘‘load bearing’’ performance in the production
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[6–22]. No research analyzing the ITZ in BPC was conducted. The developments in materials area were obtained upon understanding the microstructure of materials and through changing this structure. In this regard, the findings obtained from this research are expected to make a major contribution and to be guide. 2. Method 2.1. Production of BPC serials
Fig. 1. Schematic illustration of microstructure of concrete [2].
of load-bearing lightweight/semi-lightweight concrete. In literature, the load bearing performance of BP is recognized to be superior to acidic pumice [4]. Therefore, it has been deemed necessary to research the ITZ performance to be obtained using BP in the production of load-bearing lightweight/semi-lightweight concrete. The objective of this research is to determine the effect of BP on the morphologic properties of ITZ in load-bearing lightweight/ semi-lightweight concretes. In this regard, it has been researched how the chemical and physical structure and the volumetric ratio of BP affected the following three morphologic properties of ITZ:
In accordance with the purpose stated within this research, 15 different BPC serials were produced. The properties of cement used in the production of BPC serials were given in Table 1, the physical properties of aggregates were given in Table 2, and the chemical content ratios of BP were given in Table 3. ‘‘Absolute volume method’’ suggested in ACI 213R-03 [23] was used for determining the mixture ratios of BPC series. According to this method, water must be impregnated to the lightweight aggregates before using them in production. There are two main aims of this application: first is to prevent lightweight aggregate that has a rougher surface than normal aggregate obstructing the concrete mixing operation, second is to prevent an improper hydration arisen from lightweight aggregate impregnating the concrete water. For these reasons, in the production of BPC serials, sand dried to reach the oven dry density was used in this state and BP dried to reach the oven dry density was used after 0.5 h (depending on the concrete production conditions and the properties of materials that were used in the production) water was impregnated. Material mixture ratios were designed to obtain high strength BPC and the production of BPC serials was initiated after the 7 days trial samples were tested for strength. In order to determine the effect of volumetric ratio of BP on morphologic properties of ITZ, BP with three different volumetric ratios (40%, 50% and 60%) was used in the produced BPC serials. In order to determine the effect of BP on concretes with different ‘‘water/cement (W/C)’’ ratios, three different W/C ratios (30%, 37.5%
Table 3 The chemical content ratios of BP used in the production of BPC serials.
Compactness. Width. Physical adherence. Concrete produced using BP could be defined as ‘‘load-bearing lightweight concrete’’ or ‘‘load-bearing semi-lightweight concrete’’. These definitions are limited with the unit weight value of concrete. Therefore, the importance of aggregate having an influential role on the determination of concrete properties was taken into consideration and such concretes were defined as ‘‘basic pumice concretes (BPC)’’ in this research. There are many researches in which ITZ was analyzed in concretes produced using ordinary and artificial lightweight aggregates
The chemical content of BP used in the production of BPC serials
Ratios (%)
SiO2 (total) Insoluble residue Al2O3 Fe2O3 CaO MgO SO3 Ignition loss Na2O K2O
45.06 59.53 13.34 12.80 12.05 7.41 0.36 1.01 2.88 1.32
Table 1 The properties of cement used in the production of BPC serials [4]. (Normal early strength pure portland cement that is appropriate to TS EN 197-1 standard.) Strength properties
Physical properties
2 days compressive strength 7 days compressive strength 28 days compressive strength
31.0 MPa 39.5 MPa 46.5 MPa
Chemical properties
Density (g/cm3) Prize setting (h) Prize ending (h) Volume constancy (mm) Specific surface area (cm2/g)
3.12 2.15 3.35 1.2 3395
Insoluble residue (%) SO3 (%) Cl (%) Ignition loss (%)
0.55 2.38 0.0085 2.65
Table 2 The physical properties of aggregates used in the production of BPC serials [4]. Aggregates used in the production of BPC serials
Physical properties Maximum aggregate size (mm)
River sand (fine aggregate) BP (coarse aggregate)
4 16
Particle-size distribution
Bulk density (mg/m3)
Moisture content (%)
Particle density (mg/m3)
All distributions are ideal for ASTM C 330
1.707
1.96
2.538
2.538
–
0.864
0.89
1.819
10.884
10
Water absorption ratio (24 h) (%)
Shape index
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M. Ayhan et al. / Construction and Building Materials 25 (2011) 2507–2518 Table 4 The mixture ratios of produced BPC serials. Produced BPC series
1 2 3 4 5 6. 7 8 9 10 11 12 13 14 15
KS4037.5 KS5037.5 KS6037.5 KS4045 KS5045 KS6045 S40-1 S401.25 S401.50 S50-1 S501.25 S501.50 S60-1 S601.25 S601.50
Mixture ratios Volumetric ratio of BP within the whole aggregate (%)
Water/ cement ratio (W/C) (%)
Hyper plasticizer/ cement (HP/C) ratio – amount in 1 m3 concrete (%) – (kg)
Amount of cement (kg)
Volume of cement (dm3)
Amount of BP (kg)
Volume of BP (dm3)
Amount of river sand (kg)
Volume of river sand (dm3)
Net mixture water + amount of hyper plasticizer (kg)
Amount of saturation water of BP (kg)
Amount of saturation water of river sand (kg)
40
37.5
–
500
160.256
474.834
260.898
994.019
391.346
187.5
35.280
14.910
50
37.5
–
500
160.256
593.542
326.122
828.350
326.122
187.5
44.100
12.425
60
37.5
–
500
160.256
712.250
391.346
662.681
260.898
187.5
52.920
9940
40
45
–
500
160.256
447.534
245.898
936.869
368.846
225
33.256
14.053
50
45
–
500
160.256
559.417
307.372
780.725
307.372
225
41.565
11.711
60
45
–
500
160.256
671.300
368.846
624.580
245.898
225
49.880
9370
40 40
30 30
1.00–5.00 1.25–6.25
500 500
160.256 160.256
502.134 502.134
275.898 275.898
1051.169 1051.169
413.846 413.846
150 150
37.310 37.310
15.768 15.768
40
30
1.50–7.50
500
160.256
502.134
275.898
1051.169
413.846
150
37.310
15.768
50 50
30 30
1.00–5.00 1.25–6.25
500 500
160.256 160.256
627.670 627.670
344.872 344.872
876 876
344.872 344.872
150 150
46.640 46.640
13.140 13.140
50
30
1.50–7.50
500
160.256
627.670
344.872
876
344.872
150
46.640
13.140
60 60
30 30
1.00–5.00 1.25–6.25
500 500
160.256 160.256
753.20 753.20
413.846 413.846
700.780 700.780
275.898 275.898
150 150
55.960 55.960
10.510 10.510
60
30
1.50–7.50
500
160.256
753.20
413.846
700.780
275.898
150
55.960
10.510
and 45%) were used in the produced BPC serials. In order to produce BPC serials with 30% W/C ratio, hyper plasticizer Glenium ACE 32 with polycarboxylate origin manufactured by YKS for prefabricated elements in compliance with TS EN 934-2 was used. These serials were produced using three different hyper plasticizer/cement (HP/C) ratios (1%, 1.25% and 1.5%). The mixture ratios of produced BPC serials were given in Table 4. Considering the fact that cement paste and BP may interact within the process, the produced BPC serials were retained in the laboratory under normal ambient conditions for one year in order to determine the long term performances. Furthermore, based on the anticipation that the hydration development could be observed much better in cracks in the concrete, the BPC serials were subjected to bending test at the end of 90 days. 2.2. Sample collection from BPC serials The morphologic properties of ITZ in concretes could be determined in micro levels through images obtained using scanning electron microscope (SEM). The samples, from which SEM images were taken, collected in the form of cubes of 50 mm from the end portion where the crack width is minimum in BPC serials of 100 100 500 mm (Fig. 2). These cube samples with large sizes were reduced twice to 10 25 50 mm using diamond tip SAW. The cut samples were polished, wiped with methyl alcohol to stop the hydration development, coated with gold to reduce conductivity and dried in an oven.
2.3. Taking SEM images from samples The planes for which images were taken from the samples were determined according to the concrete cast direction. SEM images were generally taken from the planes of samples perpendicular to concrete cast direction in the studies within the literature. However, in this research, SEM images were taken from the planes of samples parallel to concrete cast direction considering the bleeding fact. Two types of images could be taken from SEM device. One of these images is called ‘‘Scatter Electron Image (SEI)’’ and the other is ‘‘Backscatter Electron Image (BSEI)’’. SEI is the image with higher quality reflecting three-dimension effect more. Therefore, SEI is preferred to determine the morphologic properties. BSEI is a type of image based on the principle to be sensitive to atomic numbers of elements. The phases with low atomic numbers appear in dark colors, whereas, the phases with high atomic numbers appear in light colors and bright [24]. In this research, both types of images taken from ‘‘LEO 440’’ SEM device were used. Thirty-eight (2 19) images were taken in total from two different areas of each sample. The location, type, magnification ratio and number of images taken from each area of each sample were given in Fig. 3. Thus, 570 (38 15) samples in total were taken from all samples. Apart from these images taken from all samples regarding ITZ that takes place over the BP, 100 images were taken from the samples belonging only to two BPC serials (KS50-45 and S40-1) regarding ITZ that
Fig. 2. The location of samples from which SEM images were taken.
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Fig. 3. The location, type, magnification ratio and number of images taken from each area of each sample.
takes place under the BP. From these images taken within the scope of the research (670), the images taken from the locations where the bleeding was high because of the abnormal formations or the close aggregates were not taken into consideration.
2.4. Analysis method of SEM images Semi-analytical detections were performed based on non-generalizing numeric data obtained in conclusion of the determination of grain limits in these images and comments on visual analysis. This analysis method is frequently referred in the researches within the literature for the analysis of SEM images [4,6,7,9–22].
3. Findings and discussion 3.1. The effect of chemical structure of BP on the morphologic properties of ITZ Three main hydration products are generated as a result of cement hydration. These are ‘‘CSH’’, ‘‘CH’’ and ‘‘AFT’’ crystals. According to Ug˘urlu, more water than the amount required for cement hydration is added to concrete due to the treatable mixture preparation obligation. After the concrete is paved, the coarse grains tend to move downwards in order to equilibrate and due to gravity, whereas, the water not included in hydration process (yet) tend to move upwards. Water unable to flow under coarse aggregate grains is retained here [25]. Due to this occurrence called bleeding, W/C ratio of ITZ is greater than the W/C ratio of cement paste. The fact that W/C ratio of ITZ is greater causes the amount of water not undergoing hydration with cement and thus the porosity ratio to be greater. When the W/C ratio of concrete is increased, the porosity ratio of ITZ will also increase as the bleeding will increase. Increase of porosity ratio causes a decrease in compactness and increase in
width of ITZ. Furthermore, in consequence of the increase in porosity ratio, the physical adherence will decrease since the contact surface of aggregate and ITZ paste will decrease. Even in the event of using aggregate that will increase the physical adherence in terms of surface texture and grain form, the desired physical adherence cannot be obtained when the W/C ratio is high. Certain aggregates cause the hydration process to take longer time by reacting with cement paste due to their chemical structures. In this case, secondary hydration products are generated and the cavities among crystals are filled. This development causes a decrease in the width of ITZ. ITZ that is looser from cement paste at the beginning becomes more compact within the process and its density comes close to the density of cement paste. In rare cases, its density may exceed the density of cement paste [26–28]. In consequence of the decrease in porosity ratio, the adherence will
Fig. 5. The largest unhydrated clinker particle in ITZ (KS40-37.5/BSEI).
Fig. 4. The developed hydration products in ITZ cracks (a: S60-1.25/SEI, b: KS60-45/SEI).
M. Ayhan et al. / Construction and Building Materials 25 (2011) 2507–2518
increase since the contact surface of aggregate and ITZ paste will increase. In this regard, the chemical structure of aggregate to be used in the production of concrete considerably affects the hydration development. Three-hundred and sixty days after the production of BPC serials the images taken from the cracks formed in ITZ since the produced BPC serials are subjected to bending test at the end of 90 days, suggest that the hydration development would continue
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in BPC after the 90th day (Fig. 4). This indicates that the real performances of concretes produced using aggregates with high ‘‘Si’’ contents as BP may be determined only within the process. Image of the largest unhydrated clinker particle that has been determined in this research in ITZ was given in Fig. 5. This image was taken from the BPC serial ‘‘KS40-37.5’’ which is the lowest slump concrete serial produced without admixtures. Accordingly, the size of unhydrated clinker particle is about 3 lm. This value
Fig. 6. General structure of CSH crystals in ITZ (a: S60-1.50/SEI, b: KS60-45/SEI).
Fig. 7. Examples indicating the ratio of CSH crystals in all hydration products in ITZ (a: KS50-45/SEI, b: S50-1.25/SEI).
Fig. 8. General forms of CH crystals in ITZ (a: KS40-45/SEI, b: KS50-45/SEI).
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is nine times smaller than the values [5,18,21] obtained from high strength concretes manufactured using ordinary aggregate. This indicates that ‘‘internal cure’’ [26–28] occurred along with the use of BP even in lowest slump concrete serials and that the hydration development is very strong due to the chemical interaction between BP and cement paste.
The fact that the hydration development in the produced BPC is very strong and positively affected the structure of crystals that are hydration products in ITZ. It has been determined that the CSH crystals in ITZ were formed in a structure almost undistinguishable from the aggregate (Fig. 6). In SEM images, these structures were defined by the help of capil-
Fig. 9. Examples indicating the ratio of CH crystals in all hydration products in ITZ (a: KS50-45/SEI, b: S50-1.25/SEI).
Fig. 10. AFT and AFM crystals detected rarely in ITZ (a: S40-1.25/SEI, b: KS40-37.5/SEI).
Fig. 11. Examples regarding the general compactness level of ITZ in BPC (a: KS60-45/SEI, b: S40-1.50/SEI).
M. Ayhan et al. / Construction and Building Materials 25 (2011) 2507–2518
lar voids that are more in ITZ compared to the cement paste. As the ratio of CSH crystals with compact and dense structures increases in all hydration products, the porosity ratio of ITZ decreases. In the previous researches [2,5,29], this ratio was reported to be about 50% in concretes produced using ordinary aggregate. However in this research, this ratio was observed to be far above 50% in all BPC serials. This ratio was determined to be higher in BPC serials with low W/C ratio (Fig. 7). Due to their forms and large sizes, CH crystals cause the formation of cavities in ITZ. CH crystals are generally in the form of hexagonal-plate. In this research, it has been determined that the CH crystals – different from the forms defined in literature – are in prismatic forms close to cube three sizes of which are not different from each other (Fig. 8). In concretes produced using ordinary aggregate, the ratio of CH crystals in all hydration products is about 25% [2,5,29]. However in this research, this ratio was observed to be far below 50% in all BPC serials. This ratio was determined to
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be lower in BPC serials with low W/C ratio (Fig. 9). The measurement differentiation between three sizes of CH crystals and the decrease of ratio in hydration products caused a decrease in the porosity ratio of ITZ. AFT crystals are determined based on their acicular structures. There are many cavities around these crystals due to that structure. In respect of their structures, the increase in ratio causes the increase in porosity ratio of ITZ. In concretes produced using ordinary aggregate, the ratio of AFT crystals in all hydration products is about 15–20% [2,5,29]. The AFT crystals formed at the beginning of hydration process convert into AFM crystals within the process. Among hundreds of image taken from the concretes analyzed in this research, AFT and AFM crystals were determined only in few of these images (Fig. 10). AFT crystals were detected only in a few low slump concretes. This was caused by the fact that there was not adequate amount of water for AFT crystals to convert into AFM crystals during the hydration development process. Rarely
Fig. 12. Examples in which the ITZ was defined as ‘‘very compact’’ in high strength concretes produced using ordinary aggregate [10].
Fig. 13. The fact that the ITZ width under the BP is more than the ITZ width over it is due to bleeding (KS50-37.5/SEI).
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Fig. 14. The changing of morphologic properties of ITZ based on HP/C ratio (a, b: S60-1/SEI, BSEI; c, d: S60-1.25/SEI, BSEI; e, f: S60-1.50/SEI, BSEI).
Fig. 15. The cavity forms and sizes of BP used in the research.
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detected AFM crystals suggest that they form a compact structure with CSH crystals during the process due to the fact that the AFT crystals are rare at the beginning of the process and that the hydration development is very strong. The formation of hydration crystals in a manner to decrease the porosity ratio of ITZ has positively affected the morphologic properties of ITZ (compactness, width and physical adherence). Examples regarding the general compactness level of ITZ in BPC were given in Fig. 11. One of these examples is (a) the BPC serial with W/C ratio of 45% and the other one is (b) the BPC serial with W/C ratio of 30%. In Fig. 12, examples [10] in which the ITZ was defined as ‘‘very compact’’ in high strength concretes produced using ordinary aggregate were given. As shown in the figures, both ITZ’s
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in BPC feature more compact structures compared to ITZ in high strength concretes produced using ordinary aggregates. The formation of hydration crystals in a manner to decrease the porosity ratio of ITZ has caused the width of ITZ to decrease and the physical adherence to increase because of the increased contact surface of BP and ITZ paste. Due to bleeding, it has been determined that the ITZ width under the BP is more than the ITZ width over it (Fig. 13). The morphologic properties of ITZ in BPC serials with high W/C ratios were determined to be in good condition as well (Figs. 11 and 12). However, as the W/C ratio of BPC serials decreases, the hydration crystals were formed in a manner to decrease the porosity ratio of ITZ more. Therefore, the morphologic properties of ITZ
Fig. 16. Connected and unconnected cavities of BP used in the research (a: S40-1.50/SEI, b: S60-1/SEI).
Fig. 17. Interlocking zones in BP (a: KS60-45/SEI, b: S50-1.50/SEI, c: S50-1.25/SEI, d: S60-1/SEI).
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were determined to be in better conditions in BPC serials with lowest W/C ratio (30%) within the scope of the research. Within these BPC serials, the morphologic properties of ITZ in the serials with HP/C ratio of 1.25% were determined to be in better conditions (Fig. 14). 3.2. The effect of physical structure of BP on the morphologic properties of ITZ The cavities of BP used in this research are generally in circular forms. The cavity size was determined to be between 100 and 250 lm in general and to reach up to 1 mm. Despite being proportionally rare, connected cavities in ellipse and amorphous forms were determined as a result of interlaced circles (Figs. 15 and 16). The cavity structure of BP used in crushed forms in the production of concrete is important as it affects the surface morphology and thus, the physical adherence of ITZ. The entrance of paste into the bays of aggregate in physical adherence and immerse of aggregate asperities into paste cause
interlocking in the form of pinning [25]. The interlocking zones in BP are given in Fig. 17. Since the surface bays and asperities of BP are much more compared to the bays and asperities of artificial lightweight aggregate, the size of interlocking zones detected in the produced BPC is larger than the size of interlocking zones of high strength concretes produced using artificial lightweight aggregate. The size of largest interlocking zone in high strength concretes produced using artificial lightweight aggregate was about 15 lm [6], whereas, the average size in the produced BPC was determined to be about 200 lm. The size of the largest interlocking zone detected in the produced BPC is 600 lm (Fig. 17a). Due to the connected cavities of BP, it has been determined that the ITZ paste infiltrates to BP and the hydration products developed in these cavities. These formations are to be defined apart from the formations defined as ‘‘interlocking zones’’. These zones were defined as infiltration zones in the research (Fig. 18). No such formation was mentioned in the researches conducted regarding ordinary and artificial lightweight aggregates.
Fig. 18. The infiltration zones in BP and the hydration products developed in these zones (a: S50-1.50/SEI, b: KS50-45/SEI, c: KS60-45/BSEI, d, e: S50-1.50/SEI, f: S50-1.50/ BSEI).
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Fig. 19. The changing of morphologic properties of ITZ based on volumetric ratio of BP (a, b: KS40-45/SEI, BSEI; c, d: KS50-45/SEI, BSEI; e, f: KS60-45/SEI, BSEI).
The interlocking and infiltration zones in BP have increased the physical adherence of ITZ. It is obvious that ordinary and artificial lightweight aggregates will not allow a physical adherence at this level due to their physical structures. 3.3. The effect of volumetric ratio of BP on the morphologic properties of ITZ Within the scope of the research, BPC serials with the same W/C ratio were produced in which the volumetric ratio of BP within the whole aggregate was 40%, 50% and 60%. The compactness of ITZ has decreased and the width has increased in BPC serials with high volumetric ratios of BP. Furthermore, in consequence of the decrease in the contact surface of BP and ITZ in these BPC serials, the physical adherence has also decreased (Fig. 19). The reason for this situation could be explained as follows: in the production of BPC serials, sand dried to reach the oven dry density was used in this state and BP
dried to reach the oven dry density was used after 0.5 h water was impregnated. The amount of saturation water of sand has been added to the mixture water. Saturation water amounts are not taken into consideration in W/C ratios. In BPC serials in which the sand used in dry form has decreased, the mixture water has intensified around BP that used after the water impregnation, the bleeding has increased, and the W/C ratio and the porosity ratio of ITZ have increased. In this regard, it has been determined that the morphologic properties of ITZ are in better conditions in the BPC serials in which BP was used at the lowest volumetric ratio (40%).
4. Conclusions In accordance with the findings obtained from this research, the following determinations were performed regarding the affect of BP on the morphologic properties of ITZ:
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Due to its chemical structure, BP has caused a very strong hydration development (the size of unhydrated clinker particle was determined to be about 3 lm) within a long process by reacting with the cement paste. The fact that the hydration development is very strong has caused the formation of hydration crystals in a manner to decrease the porosity ratio of ITZ. This has positively affected the morphologic properties of ITZ (compactness, width and physical adherence). ITZ in BPC has been structured in a more compact form compared to ITZ in high strength concretes produced using normal aggregate, also the width has decreased and the physical adherence has increased as the contact surface of BP and ITZ paste has increased. Due to bleeding, it has been determined that the ITZ width under the BP is more than the ITZ width over it. The morphologic properties of ITZ in BPC serials with high W/C ratios were determined to be in good condition as well. However, as the W/C ratio of BPC serials decreases, the hydration crystals were formed in a manner to decrease the porosity ratio of ITZ more. Therefore, the morphologic properties of ITZ were determined to be in better conditions in BPC serials with lowest W/C ratio (30%) within the scope of the research. Within these BPC serials, the morphologic properties of ITZ in the serials with HP/C ratio of 1.25% were determined to be in better conditions. Since the surface bays and asperities of BP are much more compared to the bays and asperities of artificial lightweight aggregate, the size of interlocking zones in the produced BPC is much larger (the largest is 600 lm) than the size of interlocking zones (the largest is 15 lm) of high strength concretes produced using artificial lightweight aggregate. Furthermore, due to the existing connected cavities of BP (rare in terms of ratio), it has been determined that the ITZ paste infiltrates to BP and the hydration products developed in these cavities. These zones were defined as ‘‘infiltration zones’’ in the research. No such formation was mentioned in the researches conducted regarding ordinary and artificial lightweight aggregates. The interlocking and infiltration zones in BP caused the formation of a physical adherence level which could not be obtained through the use of ordinary and artificial lightweight aggregates. The compactness of ITZ has decreased and the width has increased in BPC serials with high volumetric ratios of BP. Furthermore, in consequence of the decrease in the contact surface of BP and ITZ in these BPC serials, the physical adherence has also decreased. In this regard, it has been determined that the morphologic properties of ITZ are in better conditions in the BPC serials in which BP was used at the lowest volumetric ratio (40%). In accordance with the above-mentioned semi-analytic detections, BP has a potential to make high level of contribution to the morphologic properties of ITZ. The fact that high performance from BPC serials with high W/C ratios such as 37.5% and 45% has been obtained in terms of the studied properties supports this determination. However, the fact that the highest performance has been obtained from the BPC serial with W/C ratio of 30%, HP/C ratio of 1.25% and BP volumetric ratio of 40% indicates that higher level of performances could be obtained from BPC serials that would be produced in different mixture ratios. Therefore, it is believed that the researches associating numerically the morphologic properties of ITZ in BPC serials with production components, with each other, hydration products and the load bearing properties of concrete will be beneficial.
Acknowledgments We thank to Dicle University Coordinator of Scientific Researches (DÜBAP) which provided funding, YKS Industry Co. which helped us procure hyper-plasticizer additives, Mardin Cement Industry and Trade Co. which helped us procure cement and BP, and valuable employees thereof. References _ ve Karakusß A. Güneydog˘u Anadolu Bölgesindeki [1] Ayhan M, Gönül H, Gönül IA, bazik pomza kaynakları ile üretilen yüksek dayanımlı betonlarda ara yüzey bölgesinin morfolojik özellikleri ve beton özellikleri ile ilisßkisi. Dicle Üniversitesi Bilimsel Arasßtırma Projeleri (DÜBAP), 04-MF-34 nolu Arasßtırma Projesi, Diyarbakır; 2008. [2] Mehta PK, Monteiro PJM. Concrete, microstructure, properties and materials. Mc-Graw-Hill: New York; 2005. [3] Yeg˘inobalı A. Çimento ve çimento esaslı malzemenin geleceg˘i. Yapı _ Malzemesinin Geleceg˘i – Yapı Malzemesi Kurultayı, Istanbul; 2003. [4] Gönül H. Bazalt skoriasının tasßıyıcı yarı hafif beton üretiminde kullanımı. Doktora Tezi, Gazi Üniversitesi Fen Bilimleri Enstitüsü, Ankara; 2008. [5] Monteiro PJM. The structure and properties of civil engineering materials. Berkeley: Department of Civil and Environmental Engineering, University of California; 2003. [6] Lo TY, Cui HZ. Effect of porous lightweight aggregate on strength of concrete. Mater Lett 2004;58:916–9. [7] Maage M et al. Structural LWAC specification and guideline for materials and production. European Union, EuroLightCon, Document BE96-3942/R14. Gouda; 2000 [ISBN: 90 376 0108 1]. [8] Li G, Zhao Y, Pang SS, Li Y. Effective Young’s modulus estimation of concrete. Cem Concr Res 1999;29:1455–62. [9] Basheer L, Basheer PAM, Long AE. Influence of coarse aggregate on the permeation, durability and the microstructure characteristics of ordinary portland cement concrete. Constr Build Mater 2005;19:682–90. [10] Tam VWY, Gao XF, Tam CM. Microstructural analysis of recycled aggregate concrete produced from two-stage mixing approach. Cem Concr Res 2005;35:1195–203. _ Transition zone in high performance concrete [11] Vivekanandam K, Patnaikuni I. during hydration. Cem Concr Res 1997;27:817–23. [12] Lo Y, Gao XF, Jeary AP. Microstructure of pre-wetted aggregate on lightweight concrete. Build Environ 1999;34:759–64. [13] Tasong WA, Lynsdale CJ, Cripps JC. Aggregate-cement paste interface. Part I: influence of aggregate geochemistry. Cem Concr Res 1999;29:1019–25. [14] Chan WWJ, Wu CML. Durability of concrete with high cement replacement. Cem Concr Res 2000;30:865–79. [15] Elsharief A, Cohen MD, Olek J. Influence of aggregate size, water cement ratio and age on the microstructure of the interfacial transition zone. Cem Concr Res 2003;33:1837–49. [16] Li G. A new way to increase the long-term bond strength of new-to-old concrete by the use of fly ash. Cem Concr Res 2003;33:799–806. [17] Poon CS, Shui ZH, Lam L. Effect of microstructure of ITZ on compressive strength of concrete prepared with recycled aggregates. Constr Build Mater 2004;18:461–8. [18] Elsharief A, Cohen MD, Olek J. Influence of lightweight aggregate on the microstructure and durability of mortar. Cem Concr Res 2005;35:1368–76. [19] Gao JM, Qian CX, Liu HF, Wang B, Li L. ITZ microstructure of concrete containing GGBS. Cem Concr Res 2005;35:1299–304. [20] Ye G, Breugel KV, Fraaij ALA. Three-dimensional microstructure analysis of numerically simulated cementitious materials. Cem Concr Res 2003;33:215–22. [21] Diamond S. The microstructure of cement paste and concrete – a visual primer. Cem Concr Compos 2004;26:919–33. [22] Diamond S. The patch microstructure in concrete: the effect of superplasticizer. Cem Concr Res 2006;36:776–9. [23] American Concrete Institute, ACI 213R-03. Guide for structural lightweight aggregate concrete. Michigan: ACI; 2003. p. 1–38. [24] Sahu S, Badger S, Thaulow N, Lee RJ. Determination of water–cement ratio of hardened concrete by scanning electron microscopy. Cem Concr Compos 2004;26:987–92. [25] Ug˘urlu A. Agrega – çimento hamuru bag˘ı üzerine, 2. Ulusal Kırmatasß _ Sempozyumu, Istanbul; 1999. p. 213–28. [26] Holm TA, Bremner TW. State-of-the-art report on high-strength, highdurability structural low-density concrete for applications in severe marine environments, ERDC/SL TR-00-3 (TR INP-00-2), Washington; 2000. [27] Sveindottir EL et al. LWAC material properties, state-of-the-art, European Union, EuroLightCon, Document BE96-3942/R2, Gouda; 1998. [28] Liao KY, Chang PK, Peng YN, Yang CC. A study on characteristics of interfacial transition zone in concrete. Cem Concr Res 2004;34:977–89. [29] Fernández RDH, Alonso JM, Abella FM, Barrios MH. Ageing of concrete in dams. Switzerland: ICOLD European Club; 2004.