Influence of fines content on durability of slag cement concrete produced with limestone sand

Construction and Building Materials 111 (2016) 419–428

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Influence of fines content on durability of slag cement concrete produced with limestone sand Ahmet Gokce a,⇑, Cigdem Beyaz a,b, Hakan Ozkan a,c a

Department of Civil Engineering, Yildiz Technical University, Istanbul, Turkey IHI Infrastructure Systems Co., Ltd., Osaka, Japan c OYAK Ready-Mix Concrete Industry Co., A.Sß., Istanbul, Turkey b

h i g h l i g h t s
Effect of limestone sand fines on durability of slag cement concrete was studied.
Statistical analysis was performed to investigate the significance of fines content.
Contribution of fines on durability was more prominent for concretes with higher w/c.
The findings obtained from the field conform with the output of this research.

a r t i c l e

i n f o

Article history: Received 14 September 2015 Received in revised form 26 January 2016 Accepted 22 February 2016

Keywords: Slag cement concrete Crushed limestone sand Fines content Durability Chloride migration coefficient Water permeability under pressure Wenner probe resistivity Abrasion resistance

a b s t r a c t The effectiveness of limestone sand fines (material finer than 0.063 mm) in controlling durability performance of slag cement concrete was investigated in an experimental program. Slag cement concrete specimens incorporating limestone aggregate were produced in two water-cement ratios leading to moderate and high-level durability. Linear regression analysis was applied to evaluate the rates and significance of change in durability performance parameters of concrete at varied levels of fines content ranging between 0 and 15%. Significant relationships between performance parameters (compressive strength, water penetration resistance, chloride migration coefficient, resistivity and abrasion resistance) and fines content were found in statistical analysis depending on the water-cement ratio. Compared to low watercement ratio concrete specimens, the contribution of the fines on durability was more prominent for the concrete mixes with high water-cement ratio. The paper also presents a case-study on durability assessment in an on-going marine infrastructure project involving Izmit Bay Crossing Suspension Bridge. The findings obtained from the field conform with the output of this research. Ó 2016 Elsevier Ltd. All rights reserved.

1. Introduction Ground granulated blast-furnace slag (GGBS) and its effect on the properties of cement based systems has been the topic of a number of studies [1–5]. Slag cements (SC) are traditional binders playing important role for use in a wide field of applications such as construction of marine infrastructures. The beneficial characteristic of slag cements is contribution to production of durable concrete. This has been demonstrated not only by extensive research results but also by long-term practical experience [6–8].

⇑ Corresponding author. E-mail addresses: [email protected], [email protected] (A. Gokce). http://dx.doi.org/10.1016/j.conbuildmat.2016.02.139 0950-0618/Ó 2016 Elsevier Ltd. All rights reserved.

GGBS – ordinary Portland cement (OPC) binder system, SC in combination with limestone powder (LP), Portland-limestone cement (PLC), or OPC-GGBS-LP cementitious system have been widely practiced for development of engineered concrete mix designs for enhanced durability [9–28]. However, limestone fines (material finer than 0.063 mm) are sometimes directly introduced into concrete as a natural part of crushed aggregate in variable quantities. Having a certain amount of these fines is helpful in concrete in improving cohesiveness and preventing bleeding. Furthermore, aggregates that are totally free from these fines are not normally desirable [29]. Meanwhile, crucial concerns have existed in global concrete society about the presence of excessive quantities of fines in the crushed sand: High fines content tends to increase the water demand in a concrete mix and can impair the aggregate cement paste bond. It is also considered that excessive

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quantities of fines are capable of adversely affecting workability, pumpability, setting and hardening, and durability characteristics of concrete [29–31]. The fines content in aggregates used for the production of concrete is generally limited by most standards worldwide [32–40]. These limits appear to be somewhat arbitrary and it is quite frequently possible to design concrete mixes to accommodate appreciable fines contents of the aggregate, particularly when using admixtures [29]. A considerable work has been undertaken on the optimization of powder content, filler systems and their proportions, or aggregate skeletons [41–50]. However, it appears that the effectiveness of crushed limestone sand fines in controlling durability performance of slag cement concrete is not systematically investigated with respect to fines content. In summary, there is a lack of information on the effects of fines content on durability performance of slag cement concrete. The concrete technologists and practitioners need more clear-cut information on understanding the role of crushed limestone sand fines in concrete, especially for specific applications where use of tailor-made concrete mix designs are required. The research reported herein provides the results from systematic laboratory experiments establishing the link between a range of fines contents and durability performance of concrete. Another significant contribution relates to providing the evidence for the remarkably beneficial effect of high fines content on performance in an ongoing concrete marine infrastructure project, which is presented as a case study with 100-year service life requirement.

Table 2 Controlled gradations of crushed limestone sand. Crushed sand (percent passing)

Controlled gradations adjusted according to target fines contents (percent < 0.063 mm)

4 2 1 0.5 0.25 0.125 0.063

98 61 28 23 14 11 9

100 60 29 21 6 1 0

100 60 29 21 8 4 3

100 60 29 21 11 8 6

100 60 29 21 13 11 9

100 60 29 21 16 14 12

100 60 29 21 18 18 15

Table 3 Properties of blast furnace slag cement.a

a

2. Experimental

Sieve size (mm)

Chemical properties

Physical properties

Compound

(% weight)

Test

Result

CaO SiO2 Al2O3 Fe2O3 MgO SO3 Na2O K2O Cl LOI IR

48.18 32.59 8.68 1.97 3.58 1.76 0.35 0.81 0.0209 1.27 0.37

Specific gravity Specific surface (cm2/g) Setting time (min)

2.94 5240 Initial: 170 Final: 235 243.6

Heat of hydration (kJ/g) Mechanical properties Compressive strength (MPa)

2-day: 12.4 7-day: 20.8 28-day: 34.9

Tested by Turkish Cement Manufacturers’ Association laboratory.

2.1. Materials and methodology The effectiveness of crushed limestone sand fines (particle size fraction which passes the 0.063 mm sieve) in controlling durability performance of slag cement concrete was investigated in an experimental program. Aggregates consisted of two crushed coarse fractions (4–12 mm and 12–22 mm) and a crushed sand (0– 4 mm) with the origin of micritic limestone from Cerkesli quarry near Istanbul. The properties of the aggregates as received from the quarry are summarized in Table 1. The crushed limestone sand was rich in powder fraction with fines content of 9.0%. Since the aim of this investigation was to assess the effects of fines content on durability performance of concrete, the crushed limestone sand supplied from the quarry in original grading was processed at laboratory to obtain the fraction <0.063 mm in 6 different percentages: 0%, 3%, 6%, 9%, 12% and 15% by weight. Crushed limestone sand in oven-dry state was first separated into several fractions (0.125–0.5 mm, 0.5–2.0 mm and 2.0–4.0 mm) by dry sieving to eliminate the coarse particles above 0.125 mm. The remaining fine fraction between 0 and 0.125 mm was then screened through a 0.063 mm sieve by wet washing. The fractions >0.063 mm including coarse aggregates were also rigorously washed to eliminate the fines remained after dry sieving. In the final stage of laboratory processing, fines <0.063 mm and other fractions of crushed limestone sand were recombined in appropriate proportions to achieve target fines contents. Table 2 gives controlled gradations prepared in order to achieve nominal fines contents in comparison with that of original crushed sand. The methylene blue test (MB) was performed for each crushed sand gradation. MB value was determined as 0.25 with no change in different fines contents. Blast furnace slag cement (CEM III/B (S) 32.5 N) with slag content of 68% was used in production of the slag cement concretes. The cement complied with BS/ EN 197-1. The properties of the cement are presented in Table 3. Two types of chemical admixtures were pretested to determine the optimum type for concrete production; a new generation superplasticizer based on modified phosphonate and a polycarboxylic ether based superplasticizer. The compatibility of chemical admixture and blast furnace slag cement was basically assessed with flow behavior

Table 1 Properties of crushed limestone aggregates as received from the quarry. Property

Specific gravity Water absorption (%) Fines content (%) Los Angeles coefficient (%) Methylene blue value

Crushed sand

2.69 0.9 9 – 0.25

Coarse aggregate 4–12 mm

12–22 mm

2.71 0.4 1

2.72 0.3 0.4 29

–

–

of cement pastes. The slump retention characteristics of the concrete mixes were investigated through laboratory trials. The superplasticizer based on modified phosphonate gave the best performance with optimum dosage in relation to desired consistency and slump retention behavior and was selected to use in the production of concrete mixes. 2.2. Design and production of the concrete mixes The experimental methodology of the conducted research is linked to concrete mix design works of Izmit Bay Crossing Suspension Bridge Project. As a design requirement of the project specification, maximum water-cement ratio was stipulated as 0.40. The concrete mix designer was required to define a target watercement ratio that needed to be at least 0.02 lower than the required maximum value. Therefore water-cement ratio of job mix design was selected as 0.38 to comply with service life design procedure. The major aim of this research work is to substantiate the possibility of using properly selected crushed sand even with high fines content in tailor-made concrete mix of durability structures with service life requirement beyond 100 years. For this reason, the same water-cement ratio practiced in the field was studied in the systematic laboratory research. In order to understand the effect of fines content on durability performance of slag cement concrete with ordinary water-cement ratio, another series of concrete mixes were designed with +0.20 water-cement ratio. As a result, two series of concrete mixes were designed with water-cement ratios of 0.38 and 0.58 representing different quality levels. One series consisted of 6 mixes incorporating the same volume of crushed limestone sand with fines contents of 0%, 3%, 6%, 9%, 12% and 15% by weight. In total, 12 concrete mixes were proportioned to systematically investigate the role of fines content in durability performance of slag cement concretes. The mix proportions are given in Table 4. Each percent increment of fines content corresponds to 0, 27, 55, 81, 110 and 137 kg powder material introduced by crushed limestone sand. The concrete mixes had a constant workability by adjusting slump to 180 ± 30 mm with varying dosages of superplasticizer. The molds were compacted using a vibrating table. They were then covered with wet burlap for 24-h to harden. The concrete specimens were cured in lime-saturated water at a temperature of 20 ± 2 °C until testing age.

2.3. Test procedure and data analysis The laboratory tests were performed at the age of 28-day. Three replicates were tested and averaged for each experiment. Compressive strength was tested on 150  150  150-mm cylinder specimens in accordance with BS EN 123903:2009 [51].

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A. Gokce et al. / Construction and Building Materials 111 (2016) 419–428 Table 4 Concrete mixes designed for test program. Mixture No.

1 2 3 4 5 6 7 8 9 10 11 12

Fines Content (%)

W/C

Code

Materials (kg/m3) Water

LS-H-00 LS-H-03 LS-H-06 LS-H-09 LS-H-12 LS-H-15 LS-L-00 LS-L-03 LS-L-06 LS-L-09 LS-L-12 LS-L-15

0 3 6 9 12 15 0 3 6 9 12 15

0.58 0.58 0.58 0.58 0.58 0.58 0.38 0.38 0.38 0.38 0.38 0.38

160 161 161 161 161 161 142 142 142 142 141 141

Cement

280 280 280 280 280 280 380 380 380 380 380 380

Aggregate

HRWR

Fine (0–4 mm)

Coarse (4–12 mm)

Coarse (12–22 mm)

915 915 915 915 915 915 915 915 915 915 915 915

519 519 519 519 519 519 495 495 495 495 495 495

517 517 517 517 517 517 492 492 492 492 492 492

2.61 2.61 2.61 2.61 2.61 2.80 3.57 3.57 3.57 3.57 5.32 5.32

LS: Limestone; H: High water-cement ratio (0.58); L: Low water-cement ratio (0.38); HRWR: High range water reducer. Resistance against chloride migration was determined by non-steady migration technique in accordance with Nordic standard NT BUILD 492 [52]. The specimens with a diameter of 100 mm and a thickness of 50 mm, sliced from cast cylinders were used in the tests. The applied voltage was 60 V (DC) and depending on the resistance of the concrete against migration of the chloride ions, the test duration was programmed to 24 or 48 h. After terminating the test, the sample was split and exposed to AgNO3 solution. The chloride penetration depths were measured when the white silver chloride precipitation on the split surface was clearly visible. The chloride migration coefficient was then calculated employing the following equation;

Dnssm ¼

rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi! 0:0239ð273 þ TÞL ð273 þ TÞLxd xd  0:0238 U2 ðU  2Þt

ð1Þ

where Dnssm: non-steady-state migration coefficient, 1012 m2/s; U: absolute value of the applied voltage, V; T: average value of the initial and final temperatures in the anolyte solution, °C; L: thickness of the specimen, mm; xd: average value of the penetration depths, mm; t: test duration, h. Depth of water penetration under pressure was measured in accordance with BS EN 12390-8:2009 [53]. A water pressure of 500 kPa (5 bar) was applied on 150  150  150-mm cubic specimens for 72 h. After the pressure has been applied for the specified time, the specimen was removed from the equipment and split in half, perpendicular to the face on which the water pressure was applied. Water penetration profile was marked on split face of the specimens. The maximum depth of penetration under the test area was measured and recorded to the nearest mm. Wenner probe resistivity [54,55] was measured on the diametral line of 100mm diameter  200-mm high cylindrical specimens. In Wenner probe resistivity technique, four equally spaced electrical probes were used with the two applying low-frequency alternating current (I) while the voltage drop (V) between the two inner probes was measured. The resistivity (q) of the concrete, for a semi-infinite geometry is then given by;

Resistiv ityðqÞ ¼ 2pa

V I

ð2Þ

where a is the contact spacing of the probes used (3.5 cm). Abrasion resistance was determined on 70  70  70-mm cube specimens according to the Böhme test as detailed in BS EN 1338:2003 [56]. In this test, cubes were placed on the Böhme disc abrader, on the test track of which standard abrasive (artificial corundum) was spread, the disc was rotated and the specimen was subjected to an abrasive load of (294 ± 3) N for 16 cycles, each consisting of 22 revolutions. The abrasive wear after 16 cycles was calculated as the mean loss in specimen volume V, from the equation;

V¼

m R

ð3Þ

where V is the loss in volume after 16 cycles in cubic centimeters, m is the loss in mass after 16 cycles in grams and R is the density of the specimen. In this study, a linear regression analysis was performed to evaluate the trend and statistical significance of the observed results, using software called SPSS Statistics 20. The statistical analysis involved in answering if the assigned independent variable (fines content) predicts the value of dependent variable (each observed performance parameter) with a validated regression model. The analysis of variance (ANOVA) procedure was used for testing the statistical validity and significance of the derived linear regression model.

3. Results and discussion 3.1. Compressive strength Mechanical strength is a simple and consistent indicator in the assessment of the fines content effect on performance of slag cement concrete. Table 5 summarizes the statistical data including the validity test results of the regression model. The trends of compressive strength versus fines content are compared in Fig. 1 for the water-cement ratios studied. The compressive strength ranged from 65 to 75 MPa and 34–46 for the water-cement ratios of 0.38 and 0.58, respectively. The trend explained by the linear regression model revealed that the compressive strength does not appear to depend on fines content of crushed limestone sand for low water-cement ratio concretes (R2 = 0.0002). A slope that is highly close to zero means that compressive strength changes arbitrarily as the fines content changes with certain increments (pvalue = 0.982). The concretes with higher water-cement ratio were noticeably responsive to fines content in terms of strength gain (R2 = 0.863). The adequacy of the calculated regression model is viewed as strong for only the concrete series with water-cement ratio of 0.58 (p-value = 0.007). The results showed that low water-cement ratio slag cement concrete tends to suppress the positive effect of the fines on compressive strength observed in that of high water-cement ratio. This is explained by the presence of blast furnace slag in high volumes that facilitates an excellent refinement of the pore system in low water-cement ratio system. The concrete with less dense microstructure accommodating larger pore size and pore volume seems to effectively benefit from higher fines content in terms of strength gain. The physical presence of the fines (<0.063 mm) of crushed limestone sand with increasing amounts might have led to an overall reduction in the porosity of the system facilitating gradual increase in compressive strength. Moosberg-Bustnes et al. reported that concrete with

Table 5 Results of regression analysis (linear model) for compressive strength. Model Summary

W/C = 0.38

W/C = 0.58

R-Square Regression equation

0.0002 YCST = 0.008  FC + 70.776

0.863 YCST = 0.663  FC + 35.662

Significance of the regression model (ANOVA) F-value 0.001 p-value* 0.982

25.185 0.007

YCST: Predicted (dependent) compressive strength; FC: Fines content (predictor as independent variable). * p-value < 0.05 depicts that the model is statistically significant.

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A. Gokce et al. / Construction and Building Materials 111 (2016) 419–428

migration coefficient was greater for the concretes with watercement ratio of 0.58 (R2 = 0.727). However, the chloride migration coefficients of the concrete mixtures were <5  1012 m2/s regardless of water-cement ratio and fines content as illustrated in Fig. 2. A significant difference was not found in level of chloride migration coefficient of slag cement concrete when the water-cement ratio was increased from 0.38 to 0.58. As reported by van der Wegen et al. [57], the level of chloride migration coefficient strongly depends on binder type. For ordinary Portland cement, chloride migration coefficient is strongly influenced by water-binder ratio. For slag cement this influence turned out to be less pronounced. When referring to their correlation in the range of water-binder ratios between 0.38 and 0.58, chloride migration coefficient is predicted within a band of 5  1012 m2/s and 30  1012 m2/s for ordinary Portland cement concrete, whereas a quite narrow range between 3  1012 m2/s and 6  1012 m2/s is anticipated for slag cement concrete (>50% slag), respectively. This is due to the fact that slag cements generally seem to facilitate denser structure and prevents concrete from moisture uptake and ion penetration even at not extremely high level of water-binder ratio (w/ c = 0.60).

80.0

Compressive Strength (MPa)

70.0

R² = 0.0002 60.0

50.0

R2 = 0.863 40.0 W/C=0.38 W/C=0.58

30.0

Linear (W/C=0.38) Linear (W/C=0.58) 20.0 0

3

6

9

12

15

18

Fines Content (%) Fig. 1. Effect of fines content on compressive strength of slag cement concrete.

260 kg cement, 50% filler and a water-cement ratio of 0.81 has 9.6 MPa higher compressive strength than that of the concrete without filler. It was similarly concluded that the strengthening effect of filler on concrete paste derives from the improvement of the pore structure. The amount of small pores increases at the same time as the number of large pores decreases. Based on the results, it seems that the concrete strength can be increased not only necessarily through excessive cement contents, but via improved particle packing [46]. Bederina et al. also investigated the influence of limestone filler content on the strength of concrete with water-cement ratio of 0.60. The strength of the concretes with cement – limestone paste system displayed increasing trend for quantities of limestone filler >30% as a result of modification in the nature of hydrates. Furthermore, the hardened cement paste and interfacial transition zone showed few or no microcrack features affecting mechanical behavior adversely [48].

3.3. Water penetration resistance under pressure Water penetration resistance of concrete is one of the key performance indicators in assessment of durability. The effect of fines content of crushed limestone sand on mean water penetration depths and related statistical data including the validity test results of the regression model are presented in Table 7 and Fig. 3. Similar to the behavior observed in strength gain, the influence of the crushed limestone sand fines is less pronounced in resistance of low water-cement ratio concrete against water penetration under pressure. The calculated linear regression model is not sufficiently sound (R2 = 0.319, p-value > 0.05) meaning that the water penetration depth does not significantly depend on fines content of crushed limestone sand. The measured water penetration depths lie in the range of 5–9 mm indicating that this series of concrete are almost inherently watertight thanks to outstanding contribution of high volume slag (68.4%) and low water-cement ratio (<0.40) in building up highly densified microstructure. On

5.00 W/C=0.38

3.2. Resistance against chloride migration A significant relationship between chloride migration coefficient and fines content was observed in regression analysis. Table 6 summarizes the statistical data including the validity test results of the regression model. The significance and adequacy of the calculated regression models is viewed as strong for both watercement ratios (p-value < 0.05). The reduction rate of chloride

Table 6 Results of regression analysis (linear model) for chloride migration coefficient. Model Summary

W/C = 0.38

W/C = 0.58

R-Square Regression equation

0.895 YCMC = 0.062  FC + 2.242

0.727 YCMC = 0.104  FC + 4.360

Significance of the regression model (ANOVA) F-value 34.011 p-value* 0.004

10.653 0.031

YCMC: Predicted (dependent) chloride migration coefficient; FC: Fines content (predictor as independent variable). * p-value < 0.05 depicts that model is statistically significant.

Chloride Migration Coefficient (10¯¹² m²/s)

4.50

W/C=0.58 Linear (W/C=0.38)

4.00 Linear (W/C=0.58) 3.50

3.00

R2 = 0.727

2.50

2.00

1.50

R2 = 0.895 1.00 0

3

6

9

12

15

18

Fines Content (%) Fig. 2. Effect of fines content on chloride migration coefficient of slag cement concrete.

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A. Gokce et al. / Construction and Building Materials 111 (2016) 419–428 Table 7 Results of regression analysis (linear model) for water penetration resistance.

Table 8 Results of regression analysis (linear model) for Wenner probe resistivity.

Model Summary

W/C = 0.38

W/C = 0.58

Model Summary

W/C = 0.38

W/C = 0.58

R-Square Regression equation

0.319 YWPD = 0.157  FC + 9.095

0.901 YWPD = 0.157  FC + 9.095

R-Square Regression equation

0.672 YRSV = 17.638  FC + 863.381

0.771 YRSV = 13.086  FC + 585.524

36.258 0.004

Significance of the regression model (ANOVA) F-value 8.198 p-value* 0.046

Significance of the regression model (ANOVA) F-value 1.870 p-value* 0.243

YWPD: Predicted (dependent) water penetration depth; FC: Fines content (predictor as independent variable). * p-value < 0.05 depicts that model is statistically significant.

YRSV: Predicted (dependent) resistivity; FC: Fines content (predictor as independent variable). * p-value < 0.05 depicts that model is statistically significant.

30

1200 W/C=0.38 W/C=0.58 Linear (W/C=0.38) Linear (W/C=0.58)

W/C=0.38 W/C=0.58 25

1100 Linear (W/C=0.38)

R2 = 0.672

Linear (W/C=0.58) 20

Resistivity (Ohm.m)

Depth of Water Penetration (mm)

13.465 0.021

15

R2 = 0.901 10

1000

900

800

R2 = 0.771

R2 = 0.319 5

700

0 0

3

6

9

12

15

18

Fines Content (%) Fig. 3. Effect of fines content on water penetration depth of slag cement concrete.

the other hand, water penetration depth of high water-cement ratio concretes noticeably depends on the fines content of crushed limestone sand ranging between 12 and 27 mm (R2 = 0.901). The calculated regression model has strong validity for the concrete series with water-cement ratio of 0.58 (p-value = 0.004). The highest water penetration depth was observed on the specimens incorporating the crushed limestone sand with minimum fines content. The resistance to water penetration under pressure was substantially improved by gradual increase of fines content. The crushed limestone sand with fines content of 15% physically introduced 137 kg more pore filling powder material in comparison with that of minimum fines content. This clear result demonstrates that the use of such high fines crushed limestone sand in concrete is possible for even better durability owing to its merit in facilitating superior blocking performance in concrete against penetration of water or attack of other aggressive solutions. 3.4. Wenner probe resistivity Wenner probe resistivity technique is considered as a practical tool for determining the durability potential of concrete. The results obtained from resistivity measurements and their statistical model analysis are presented in Table 8 and Fig. 4. The inconsistency in the change of resistivity with fines content results can be explained with intrinsic variability of the test procedure. As pointed out in a previous study [58], Eq. (2) assumes that the concrete behaves as a homogeneous medium, but it is not. The current distribution when using a Wenner probe is non-uniform and therefore the

600 0

3

6

9

12

15

18

Fines Content (%) Fig. 4. Effect of fines content on Wenner probe resistivity of slag cement concrete.

resistivity measurement tends to be representative of the concrete region located roughly between two center potential probes. However, a significant positive relationship between resistivity values and fines content was observed for both series of concretes with different water-cement ratios (p-values < 0.05). The behavior was in contrast to trend in chloride migration coefficient that reduced with increasing fines content. Fig. 5 shows the relationship between chloride migration coefficient and Wenner probe resistivity values. It is easily observed that the governing parameter in both performance criteria is the water-cement ratio. However, it is also interesting to see that there is a meaningful transition between high water-cement ratio and low water-cement ratio series in the effect of fines content. The durability performance of high water-cement ratio (0.58) concrete incorporating crushed limestone sand with fines content of 15% remarkably approaches to that of low watercement ratio (0.38) concrete incorporating crushed limestone sand with fines content of 0%. This finding strongly implies that high amount of fines (15% corresponds to 137 kg fines per cubic meter) in crushed limestone sand functions as an effective pore filling powder material phase that significantly close the gap in durability performance between the slag cement concretes with watercement ratios of 0.38 and 0.58.

3.5. Abrasion resistance For particular types of constructed facilities such as roads and hydraulic structures, abrasion resistance is a vital property to

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A. Gokce et al. / Construction and Building Materials 111 (2016) 419–428

30.00 0%

4.5

W/C=0.38

4

28.00

R2 = 0.009

W/C=0.58

3.5 15%

3

0%

2.5 2

15%

1.5 1 0.5 0 500

750

1000

1250

Resistivity (Ohm.m) Fig. 5. Chloride migration coefficient versus resistivity relationships with increasing fines content.

Loss in Volume - Böhme Test (cm3/50cm 2)

Chloride Migration Coefficient (10¯¹² m²/s)

5

26.00 24.00

R² = 0.691

22.00 20.00 18.00 16.00

W/C=0.38 14.00

W/C=0.58 Linear (W/C=0.38)

12.00

Linear (W/C=0.58) 10.00

achieve long-term durability. Excluding uneven test results obtained from the concrete series belonging to water-cement ratio of 0.58, it is found that the abrasion loss was not dependent on fines content of crushed limestone sand as shown in Table 9 and Fig. 6. In general, slightly higher resistance to wear was displayed by the concrete series of low water-cement ratio. Ghafoori and Diawara [59] also showed that an increase in unit binder content or decrease in water-binder ratio produced a denser and stronger concrete surface, thus resulting in a higher resistance to wear for the silica fume concretes. When rates of change and trending are evaluated with statistical analysis, the regression model is valid (p-value < 0.05), but the response of the abrasion resistance to the fines content ranges in a narrow range (24.1–25.5 cm3/50 cm2) for the concrete series of low water-cement ratio. The regression analysis of the concrete series of high water-cement ratio does not depict a valid and statistically significant model (pvalue = 0.858). It is supposed that three replicates tested in accordance with Böhme abrasion method were not sufficient for a sound interpretation of the results. Shackel and Shi [60] similarly pointed out that the abrasion resistance should be reported as a statistic based on the results of not <10 replicates for an alternative testing protocol. Consequently, additional replicates are needed to obtain data by counting the intrinsic variability of the applied test procedure for the future works.

4. Practical implications In this section, feedback from field experience belonging to ongoing Izmit Bay Crossing Suspension Bridge Project is presented in order to demonstrate the performance of engineered concrete mixtures using high fines crushed limestone sand. Izmit Bay

Table 9 Results of regression analysis (linear model) for abrasion resistance. Model Summary

W/C = 0.38

W/C = 0.58

R-Square Regression equation

0.691 YABR = 0.083  FC + 25.486

0.009 YABR = 0.037  FC + 26.501

Significance of the regression model (ANOVA) F-value 8.924 p-value* 0.040

0.036 0.858

YABR: Predicted (dependent) abrasion loss; FC: Fines content (predictor as independent variable). * p-value < 0.05 depicts that model is statistically significant.

0

3

6

9

12

15

18

Fines Content (%) Fig. 6. Effect of fines content on abrasion loss of slag cement concrete.

Crossing Suspension Bridge will be a 2682 m long structure located at the eastern end of Marmara Sea with the main span of 1550 m making it the world’s fourth longest suspension bridge when completed in 2016 [61]. The owner of the project required a minimum service life of 100 years as the key durability requirement and this was implemented in the design of this mega-infrastructure project. The durability design philosophy of the project is based on facilitating a functional barrier against chloride ingress in any structural bridge member under exposure of marine environment as conceptually defined in Table 10. The scope of this case study is limited to the North side bridge elements shown in Fig. 7, where the structural concrete was produced with the same source of constituent materials used in the experimental part presented in Section 2. The South site bridge elements were cast with a different concrete mixture designed with crushed stone aggregate supplied from another quarry. Constituent materials and mix proportions were selected such as to satisfy the long-term durability requirement of the owner. The only additional constituent material used in project mix design was a natural sand containing dominantly quartz minerals and quartz rich rock fragments. The combined fine aggregate fraction of the project mix design consisted of 52% of crushed limestone sand and 48% of natural sand. There were several technical reasons to use natural sand in the mixture. Some of them were linked to fresh state performance of structural concrete. A minimum 3-h slump retention, easy pumpability, superior compactability and high quality finished surfaces were some of the important benefits of natural sand inclusion in the mixture. Natural sand particles smaller than 0.5 mm size also played a significant role in densification of microstructure in combination with the high fines crushed sand. The representative gradation of the blended sand is given in Table 11. The amount of fines (<0.063 mm) in crushed limestone sand was 10.4%, whereas natural sand contained only 0.9% of fines. The fines content of blended sand resulted in 5.8% herein. Among the alternative binder systems, CEM III/B slag cement was chosen as the best binder in achieving the lowest chloride migration coefficient, highest density and low porosity in the structural concrete of the project. This tailor made concrete mixture was designed with water-cement ratio of 0.38 and unit binder content of 380 kg/m3.

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A. Gokce et al. / Construction and Building Materials 111 (2016) 419–428 Table 10 Design solution for long-term durability (>100-year) of Izmit Bay Crossing Bridge [61]. Exposure zone

Structures

Design solution for achieving 100-year service life of Izmit Bay Crossing Suspension Bridge

Submerged Splash/spray/ tidal Atmospheric Buried zone

Caisson shaft and caissons Plinths and tie beams

Sufficient concrete cover thickness per specific element

Maximum chloride migration coefficient at 28 maturity days: 3  1012 m2/s

Side-span and transition piers, anchorage Side-span and transition piers, anchorage, bored piles

North Tower plinths and e beam Side-span pier Anchorage

Transion pier

Fig. 7. Izmit Bay crossing suspension bridge structures under exposure of marine environment.

selected constituent materials and mix proportions in accordance with the standards and norms satisfying the Designer’s requirements. Following the laboratory tests, the trial castings were performed to verify fulfilment of concrete performance in accordance with Designer’s requirements at an industrial scale. In the first stage of the industrial trials, 1 m3 concrete blocks were cast to determine optimum mixing time, transportation time and pumpability. In the second stage, full scale trial castings for caisson and anchorage were performed to make the final demonstration of concreting process including execution of the proposed construction method (i.e. internal cooling) and workmanship prior to start-up of actual concrete works at site [61]. In production testing, chloride migration coefficient was determined once per 1000 m3 of concrete at the age of 28 maturity days. The sampling was done from the truck mixers delivered to the site. Three cylindrical specimens were made and cured in chloride free water with a temperature 20 °C until testing. The in-situ chloride

The service life requirement of Izmit Bay Suspension Bridge has been fulfilled by development of a highly dense and impermeable structural concrete. This was assured by; i. facilitating an appropriate design covering engineered material solutions (proper selection of constituent materials, tailor made mixture design, cover thickness calculation based on a model code for Service Life Design [62], surface protection, etc.), ii. proper execution (transport, placement, compaction and curing of concrete mixture), iii. monitoring chloride migration coefficient and other decisive performance parameters of structural concrete from beginning to the end of production phase at site. An extensive pre-testing program was carried out for verification of fresh, hardening and hardened concrete performance with

Table 11 Representative gradation of individual and combined sands. Percent passing (%) Sieve size (mm) Crushed sand (52%) Natural sand (48%) Combined sand

31.5 100 100 100

22 100 100 100

16 100 100 100

8 100 100 100

4 100 100 100

2 84 99 91

1 54 99 76

0.5 38 97 66

0.25 22 15 19

0.125 15 1 8

0.063 10.4 0.9 5.8

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Chloride migration coefficient (×12-12 m2 /s)

3 2.5 2 1.5 1 0.5 0 14-Aug-13

3-Oct-13

22-Nov-13

11-Jan-14

2-Mar-14

21-Apr-14

10-Jun-14

30-Jul-14

Date of concrete casting North Anchorage Massive Part

North Transition Pier Piles

North Triangular Piers

North Side Span Pier and Transition Pier

North Plinths

North Tie-beam Top Slab

Fig. 8. Achieved chloride migration coefficients in construction phase of North-side bridge structures.

migration coefficient was also determined by testing cores from the permanent structures as required in project technical specification [63]. The concrete mix design successfully delivered a very dense and low permeability concrete meeting the project requirements. Fig. 8 illustrates the chloride migration coefficient data obtained in chronological order. Low water-cement ratio slag cement concrete mixture enriched with high fines crushed limestone sand revealed chloride migration coefficients below maximum permissible limit of 3  1012 m2/s. The results also showed a continual improvement in performance of cast concrete in terms of hindering migration of chloride ion. This was considered to be related to the continuous improvement in material supply, manufacturing process and execution techniques (compaction, curing, etc.) at the site. Based on the production test results, the initiation period of the chloride-induced reinforcement corrosion is not predicted to be <100 years. This mega-scale field application demonstrated that properly selected and good quality crushed sand with high fines content would significantly contribute the performance of engineered concretes. 5. Conclusions This study was carried out in order to better understand the influence of fines content on durability performance of slag cement concrete produced with crushed limestone sand. Linear regression analysis has been used to evaluate the response of investigated performance parameters and their rates of change with respect to fines content. Based on the results of this study the following conclusions are drawn: 1. Compressive strength was not dependent on fines content of crushed limestone sand for low water-cement ratio concrete mixes, whereas the mixes with higher water-cement ratio were noticeably responsive to fines content in terms of strength gain. The concrete with less dense microstructure seems to benefit from higher fines content of crushed limestone sand effectively. 2. A significant relationship between chloride migration coefficient and fines content was observed in analysis of experimental results. The reduction rate of chloride migration coefficient was greater for the concretes with water-cement ratio of 0.58. 3. The regression model analysis result depicts that the influence of the crushed limestone sand fines on resistance against water penetration under pressure is not significant for low water-cement

ratio concrete mixes. On the other hand, water penetration depth of high water-cement ratio concrete mixes noticeably depended on the fines content of crushed limestone sand. 4. A significant positive relationship between resistivity values and fines content was observed for both series of concretes with different water-cement ratios. The correlation between chloride migration coefficient and Wenner probe resistivity values showed that there is a meaningful transition between high water-cement ratio and low water-cement ratio series by the effect of fines content. This finding strongly implies that high amount of fines (137 kg per cubic meter) in crushed limestone sand functions as an effective pore filling powder material phase that significantly close the gap in durability performance between the slag cement concretes with water-cement ratios of 0.38 and 0.58. 5. A valid regression model has been derived for the abrasion resistance of the concrete series with low water-cement ratio, but the response of the abrasion resistance to the fines content lies in a narrow range (24.1–25.5 cm3/50 cm2). The regression analysis of the concrete series of high water-cement ratio does not depict a valid and statistically significant model. It is supposed that three replicates tested in accordance with applied abrasion test method were not sufficient for interpretation of the results. Additional tests are needed to obtain data by counting the intrinsic variability of the test procedure for the future works. 6. The data from the ongoing Izmit Bay Crossing Suspension bridge project justified the substantial performance of tailor made job mix design in achieving the long-term (>100 years) durability requirement with great functionality of fines in crushed limestone sand. Slag cement and engineered sand gradation providing high amount of fines appear to be an appropriate material solution in achieving long-term durability performance requirement of tailor made concrete structures. While CEM III/B facilitates highly dense structural concrete at low water cement ratio, high amounts of fines in crushed limestone sand secondarily refine the microstructure controlling desired transport properties.

Acknowledgements The authors wish to thank NOMAYG JV, Nurol-Ozaltin-MakyolAstaldi-Yuksel-Gocay for their permission to publish field feedback

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from Izmit Bay Crossing Suspension Bridge Project. The authors are grateful for collaboration of IHI Infrastructure Systems Co., Ltd., EPC Contractor of the Project, COWI A.S. as IHI’s designer, STFA, Sezai Turkes Feyzi Akkaya Insaat A.S, as sub-contractor of IHI for substructure works, ITU-Marmaray Laboratory, and OYAK ReadyMix Concrete Industry Co. AS. Thanks also to all YTU students who carried out the experimental works of this research.

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