Scholarly article on topic 'Improved concrete properties to resist the saline water using environmental by-product'

Improved concrete properties to resist the saline water using environmental by-product Academic research paper on "Civil engineering"

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Abstract of research paper on Civil engineering, author of scientific article — Mohamed Anwar, Mahmoud Roushdi

Abstract This paper investigates the influence of using environmental by-product materials (silica fume and fly ash) in concrete on the chloride ion permeability of concrete. Nine concrete mixtures were designed to have the same degree of workability and air content with water/cementitious material ratio of 0.4. The studied parameters include the main fresh and hardened concrete properties such as slump, air content, unit weight, compressive strength, tensile strength, flexural strength, static Young's modulus, and dynamic elastic modulus. Concrete samples were kept in water for 28 days, then immersed in artificial sea water for 5 months. The total and soluble chloride contents were measured through the concrete using the potentiometric titration analysis. The obtained test results indicated that the use of ternary systems in concrete improved the different characteristics of the product concrete and showed a significant resistance to chloride penetration. The weights of chloride in mix 9 (10% silica fume and 25% fly ash) at depths from the concrete surface to 30mm were less than the weights of control mix 1 (100% ordinary Portland cement) by about 60%. Further, the ternary systems can be used in concrete industry with considerable proportions.

Academic research paper on topic "Improved concrete properties to resist the saline water using environmental by-product"

Water Science

Water Science -

ScienceDirect

X NWRC I

Water Science 27 (2014) 30-38

journal homepage: www.elsevier.com/locate/wsj

Improved concrete properties to resist the saline water using

environmental by-product

Mohamed Anwara, Mahmoud Roushdib*

a National Water Research Center (NWRC), Strategic Research Unit, Egypt b National Water Research Center (NWRC), Environment and Climate Changes Research Institute, Egypt

Received 17 September 2013; received in revised form 2 November 2013 Available online 22 February 2014

Abstract

This paper investigates the influence of using environmental by-product materials (silica fume and fly ash) in concrete on the chloride ion permeability of concrete. Nine concrete mixtures were designed to have the same degree of workability and air content with water/cementitious material ratio of 0.4. The studied parameters include the main fresh and hardened concrete properties such as slump, air content, unit weight, compressive strength, tensile strength, flexural strength, static Young's modulus, and dynamic elastic modulus. Concrete samples were kept in water for 28 days, then immersed in artificial sea water for 5 months. The total and soluble chloride contents were measured through the concrete using the potentiometric titration analysis. The obtained test results indicated that the use of ternary systems in concrete improved the different characteristics of the product concrete and showed a significant resistance to chloride penetration. The weights of chloride in mix 9 (10% silica fume and 25% fly ash) at depths from the concrete surface to 30 mm were less than the weights of control mix 1 (100% ordinary Portland cement) by about 60%. Further, the ternary systems can be used in concrete industry with considerable proportions. ©2013 National Water Research Center. Production and hosting by Elsevier B.V. All rights reserved.

Keywords: By-product; Concrete; Portland cement; Fly ash; Silica fume

1. Introduction

Ministry of water resources and irrigation (MWRI) has many large concrete structures projects in the Nile River, irrigation network, and drainage network as new structures or replacement to old ones. Most of the concrete structures in these projects are water structures such as bridges, regulators, barrages, culvers, siphons and aqueducts. Some parts of the concrete of mentioned water structures are embedded in soil contaminated with chlorides and sulfates while, the other parts are exposed to irrigation water or drainage water (immersion in water) which is contaminated with salts.

* Corresponding author. E-mail address: mahmoudroushdi@yahoo.com (M. Roushdi). Peer review under responsibility of National Water Research Center.

Elsevier Production and hosting by Elsevier

1110-4929 © 2013 National Water Research Center. Production and hosting by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016Zj.wsj.2013.12.003

The two most common causes of reinforcement corrosion are (i) localized breakdown of the passive film on the steel by chloride ions and (ii) general breakdown of passivity by neutralization of the concrete, predominantly by reaction with atmospheric carbon dioxide (Batis and Rakanta, 2005). Sound concrete is an ideal environment for steel, but the increased use of deicing salts and the increased concentration of carbon dioxide in modern environments principally due to industrial pollution, has resulted in corrosion of the rebar becoming the primary cause of failure of this material.

Chloride ions penetrate through the concrete by a solution diffusion process and are dissolved in pre-existing pore water which is relevant to reinforcing steel corrosion through the following effects: (a) slightly reduce the alkalinity of concrete, (b) increase the electrical conductivity of concrete, and (c) depassivate the steel surface even at high alkaline environment. Chloride ions may enter easily into fresh concrete from the mix components, such as cement, aggregate, mixing water and chemical admixtures, or from chloride contaminates. The chloride ions may penetrate into hardened concrete from external sources such as: curing water, deicing salts, salt spray and sea water. Chloride ions may be present in concrete in several states (Ravindrarajah and Moses, 1993): (a) strongly bound by tricalcium aluminate hydrates (and to a lesser extent by tetracalcium alumino-ferrite hydrates) mainly in the form of calcium chloroaluminate, (b) loosely bound (immobilized by calcium silicate hydrates), and (c) free in solution (water-soluble) in the pore space. Furthermore, migration of chloride ions occurs primarily through diffusion processes and the arbitrary limits of diffusion coefficient fall in range of the order of 10-7 and 10-8 cm2/s (Luca et al., 2007).

Silica fume is a powder by-product resulting from the manufacture of ferrosilicon and silicon metal. It has a high content of glassy of silicon dioxide (SiO2) and consists of very small spherical particles. Because of this, it has been a popular mineral admixture to use in high-strength concrete (Anwar et al., 2013). However, silica fume is expensive compared to Portland cement type I or fly ash. Fly ash is a by-product of coal-burning power plants. It is widely used as a cementitious material and a pozzolanic ingredient in concrete. The use of fly ash in concrete is constantly increasing because it improves the properties of concrete (Xianming et al., 2012).

In recent years, high-strength concrete has increasingly been used in civil engineering work because it has an advantage of reducing the sizes of beams and columns, which are essential in high-rise buildings. According to ACI 363 (ACI, 2000), concrete having a 28 day compressive strength higher than 41 MPa can be considered as high-strength concrete. Generally, high-strength concrete is achieved by using super plasticizer to reduce the water-binder ratio and by using supplementary cementing materials such as silica fume, natural pozzolan, or fly ash in order to create extra strength by pozzolanic reaction. Furthermore, Shannag (2000) used natural pozzolan and silica fume to produce high strength concrete, and it was found that the combination of the two can be used in producing high-strength concrete in the range of 69-85 MPa at 28 days, with medium workability.

Portland cement is the essential binding agent in concrete, which in turn is the most widely used construction material worldwide due to its many advantages, including lower cost (relative to steel, aluminum or polymers), durability and other properties. Materials of natural origin such as volcanic ash, or industrial by-products, like ground granulated blast furnace slag and pulverized fly ash, have been widely used as partial replacement of Portland cement in concrete constructions. The advantages include improved technological properties, low cost and a reduction in the environmental impact through reduction of waste accumulation. Furthermore, the simple replacement of 5% of cement by one of the aforementioned materials can provide a reduction of about 75 x 106tons of CO2 (considering a world production of about 1500 x 106 tons/year with emission of an average 1 kg CO2/kg cement) (Escalante-Garcia and Sharp, 2004).

Silica fume concrete has a high compressive strength, low permeability and good resistance to freeze-thaw cycling (Malhotra and Mehta, 1996). Similar performance enhancements have also been achieved for high volume fly ash and blast furnace slag concretes (Bilodeau et al., 1994). However research on the long-term effects of these supplementary materials on chloride ion diffusivity and corrosion of the reinforcing steel in concrete is limited and needs further investigation. The use of these materials in concrete not only improves the mechanical properties and durability but also uses industry by-products and has, therefore, significant environmental and economic benefits (Qian et al., 2003). One of the main characteristics of green high-performance concrete is using different types of mineral admixtures (fly ash, slag or silica fume) to partially replace Portland cement. When these different reactive mineral admixtures are added into concrete at the same time, they develop their own characteristics with the development of time, so that the physical, mechanical and durability properties of concrete will not be reduced when a large amount of mineral admixtures are added into concrete. For example, in the case of addition of silica fume, slag and fly ash at the same time, silica fume provides main strength amongst these three types of mineral admixtures before 7 days due to its highly early pozzolanic reaction, then, slag begins develop its strong pozzolanic effect. After 28 days, fly ash also gradually exhibits its own properties and provides its contributions to the strength of concrete (Wei et al., 2004).

Keith and Tarunjit (2013) indicated the benefits of fly ash concrete. They carried out a longer-term chloride ion permeability tests on samples of concrete containing 0,15,30, and 50% fly ash replacing cement. These tests conducted at the Ohio State University, USA. The chloride ion permeability of the fly ash mixes was significantly lower than that of the no fly ash mix, as they concluded. The permeability reduced with increase in percent of fly ash. Increase in curing time from 6 months to 1 year led to about 4.75% reduction in the permeability of the no fly ash mix, while the permeability of the fly ash mixes reduced 30-40% over the same time period. Even at one year of curing, the no fly ash concrete sample had moderate chloride ion penetrability while all the fly ash concrete samples had very low penetrability values. In addition they reported that the high-volume fly ash mixes would be the most durable concrete mixes for preventing corrosion in reinforced concrete structures.

This paper aims to investigate the influence of using ternary cementitious systems containing ordinary Portland cement, silica fume and fly ash on the chloride ion permeability of concrete. As well as, to assess the effect of the replacement percentage of cement by fly ash and silica fume on the properties of concrete.

2. Materials and methods

At this stage it is not clear how the ordinary Portland cement (OPC), silica fume (SF) and fly ash (FA) work together, therefore, this research is carried out to find out how these ternary cementitious systems affect the concrete properties. Nine concrete mixtures are prepared with water/cementitious material and sand/aggregate ratios of 0.4. The chemical admixtures (high performance super plasticizer and air entraining agent) dosages were changed to achieve the required values of slump and air content (the concrete mixtures designed to achieve slump of 10 ±2 cm and air content of 4 ± 1%). The mix proportions of concrete mixtures are listed in Table 1.

Table 1

Mix proportions of the studied concrete mixtures.

Mix no. W (kg/m3) OPC (kg/m3) FA (kg/m3) SF (kg/m3) Sand (kg/m3) Gravel (kg/m3) Ad AE

20 mm 15 mm C% kg/m3 kg/m3

1 410.0 0.0 0.0 680 512 510 0.95 3.895 1.025

2 348.5 61.5 0.0 672 506 504 0.90 3.690 3.075

3 307.5 102.5 0.0 668 503 501 0.80 3.280 3.690

4 389.5 0.0 20.5 677 510 508 0.95 3.895 0.410

5 164 369.0 0.0 41.0 674 508 506 1.00 4.100 0.410

6 328.0 61.5 20.5 670 504 502 0.90 3.690 1.845

7 287.0 102.5 20.5 665 501 499 0.90 3.690 3.280

8 307.5 61.5 41.0 667 502 500 0.90 3.690 1.845

9 266.5 102.5 41.0 662 499 497 0.90 3.690 2.050

W: water; OPC: ordinary Portland cement; FA: fly ash; SF: silica fume; Ad: chemical admixture (high performance super plasticizer, high range water reducing admixture with air entraining agent effect); AE: air entraining agent.

Used silica fume powder has specific surface area of 15.3 m2/g, silicon dioxide (SiO2) of 94.9%, and specific gravity of 2.24. The sand has 2.55 specific gravity, 2.68 of fineness modulus and 1.23% of the water effective absorption. The coarse aggregate is crushed basalt with two sizes, the first size is 15 mm of nominal maximum size and 2.5 specific gravity, while the second size is 20 mm of nominal maximum size and 2.56 specific gravity. The fineness modulus of the coarse aggregate is 6.72. The grading of used fine and coarse aggregate complies with the specifications.

The materials were put into the mixer as follows: first; coarse aggregate followed by sand, then cementitious materials (OPC, FA, and SF are mixed well before putting into the mixer) added to the mixer. The total mixing time is 3 min divided into two stages, starting with 60 s dry mixing and then the required water (mixed with chemical admixture) is added within 30 s, then mixer continues for the next 1.5 min of mixing. After casting, the concrete specimens were compacted by a vibrator. The test specimens were stripped from their molds the day after casting. The specimens were cured in water until the testing time.

The properties of hardened concrete were measured by means of destructive and non-destructive tests. Com-pressive strength and tensile strength are performed via the destructive tests, while the static young's modulus

and dynamic elastic modulus were carried out via the non-destructive ones. The compressive strength (cylinder of 10 cm diameter and height 20 cm) was measured at 3, 7, 28, 90, and 180 days after concrete casting while the tensile strength (cylinder of 15 cm diameter and height 30 cm), static young's modulus (cylinder of 10 cm diameter and height 20 cm), and dynamic elastic modulus (prism of 10 cm x 10 cm x 40 cm) were measured only at 28 days.

After curing procedure, the concrete specimens (prism of 10 cm x 10 cm x 40 cm) immersed in artificial sea water (5% NaCl) for 5 months. Total and soluble chloride ions contents were measured through the concrete samples after 1, 3, 5 months of NaCl immersion. The total chloride content is obtained by removing the chloride from a sample by titration analysis. On the other hand, the water soluble chloride content is determined by immersion of the sample in hot water. The potentiometric titration has been used to measure total and soluble contents of sodium chloride as percentage by total weight of concrete. This was conducted at 0-10,10-20,20-30, and 30-40 mm depths from surface of specimen after 1, 3, and 5 months of chloride immersion while the chloride contents were measured at 30-40 and 40-50 mm depths from surface of specimens after 5 months only. The powdered samples were analyzed for their soluble and total chloride content by the titration method.

3. Results and discussion

3.1. Properties of fresh concrete

The measured values of slump and air content are listed in Table 2 and they fall within the designed rang, i.e., all measured values are 10 ± 2 cm and 4 ± 1% for the slump and air content, respectively. The results of unit weight of concrete change according to the type of used cementitious materials. This is attributed to the difference in the specific gravity of the cementitious materials and air content.

From the mix proportions of the concrete mixtures, it is noticed that fly ash mixtures need high dose of the air entraining agent to achieve the designed values while silica fume mixtures need low dose of the air entraining agent. Concerning the super plasticizer, silica fume mixtures need higher dose than those of fly ash ones. The mixtures that include ternary systems of fly ash and silica fume show that both silica fume and fly ash compensate each other regarding the dose of air entraining agent and super plasticizer.

3.2. Properties of hardened concrete

The compressive strength values of concrete were measured up to age of 180 days while tensile strength, static Young's modulus, and dynamic elastic modulus measured at age of 28 days. The measured properties of hardened concrete are summarized in Table 3.

However, a comparison of the results in Table 3 provides an indication of fly ash and silica fume contributions in the ternary blends. The compressive strengths of silica fume concrete (mixes 4 and 5) are higher than those of all studied mixes at all ages. The control mix (OPC) shows higher strengths than those of mix 2 (15% FA) at ages 7 and 28 days, while the results of ages 3, 90 and 180 days of mix 2 indicate a lower compressive strength compared with the control mix. Mix 3 of fly ash shows lower compressive strengths than those of the control concrete at all ages due to the effect of high replacement percent (25%) of fly ash. The mixes of ternary systems show lower compressive strength than those of OPC mix (control mix) at age 3 days. Moreover, mix 7 (25% FA and 5% SF) give a compressive strength lower than the control mix at ages 7,28, 90 and 180. On the other hand, mix 6(15% FA and 5% SF) give a compressive strength higher than the control mix at ages 7, 28, 90 and 180.

The obtained results are also confirmed with Thomas et al. (1999) who reported that the combination of Portland cement, silica fume and fly ash in a ternary cement system should result in a number of synergistic effects, some of which are obvious or intuitive, as follows: (a) silica fume compensates for low early strength of concrete with low CaO fly ash, (b) fly ash increases long-term strength development of silica fume concrete, and (c) the relatively low cost of fly ash offsets the increased cost of silica fume. The obtained data show that binary cementitious blends of Portland cement and silica fume offers significant advantages over plain Portland cement. Moreover, the ternary cementitious systems of Portland cement, silica fume (5-10%), and fly ash (15-25%) show satisfactory compressive strength especially at ages of 28 and 90 days.

Table 2

Properties of fresh concrete mixtures.

Mix no. OPC (%) FA (%) SF (%) Slump (cm) Air content (%) Unit weight (tons/m3)

1 100 0 0 11.1 3.6 2.398

2 85 15 0 11.3 4.5 2.359

3 75 25 0 10.0 3.3 2.334

4 95 0 5 11.4 4.0 2.381

5 90 0 10 10.8 4.9 2.372

6 80 15 5 11.2 4.1 2.381

7 75 25 5 10.7 3.6 2.347

8 70 15 10 10.6 4.1 2.347

9 65 25 10 9.7 3.3 2.339

From Table 3, it is seems that there is a data scatter of tensile strength of the studied concrete mixtures. However, mix 3 (25% FA) shows the lowest tensile strength due to the effect of using large replacement percent of fly ash; while mix 8 (15% and 10% SF) shows the highest tensile strength. Also, the results of the static elastic modulus are affected by the change in the type of supplementary cementing materials as well as the replacement percent. Furthermore, mix 9 (25% and 10% SF) shows lower static elastic modulus than that of control mix while mixes 4 and 5 (5% and 10% SF) show higher static elastic modulus than that of control mix as listed in Table 3. The dynamic elastic modulus values of tested concrete indicate slight differences due to the change in the combination of the cementitious materials. However, mix 3 (25% FA) shows the lowest values of dynamic elastic modulus at all testing ages.

Table 3

Properties of hardened concrete mixtures.

Property Age (day) Mix 1 Mix 2 Mix 3 Mix 4 Mix 5 Mix 6 Mix 7 Mix 8 Mix 9

3 396 362 308 456 457 381 286 351 304

7 468 484 434 579 608 493 429 491 426

Compressive strength (kg/cm2) 28 669 678 613 803 819 765 560 704 632

90 777 734 717 917 934 842 718 765 755

180 802 742 726 880 913 885 780 846 854

Tensile strength (kg/cm2) 28 49.2 46.9 41.1 49.7 50.6 50.4 48.8 52.1 48.0

Dynamic elastic modulus (x 105 kg/cm2) 28 4.24 4.19 3.93 4.32 4.33 4.23 4.00 4.12 3.99

Static elastic modulus (x 105 kg/cm2) 28 2.99 2.98 2.86 3.47 3.09 2.89 2.89 2.82 2.81

3.3. Chloride ion content

Table 4 and Figs. 1-3 show the results of the total and soluble chloride ion contents for the studied mixes as percentage by weight of concrete after 1, 3, and 5 months at depths from the surface to 30 mm. The results indicate that there were large reductions in the total and soluble chloride as the depth of concrete zones surveyed increased. Also, the results indicate that the first 10 mm of the specimens provides little barrier to chloride penetration and underscores the importance of concrete cover to the reinforcement.

Furthermore, the effect of ternary cementitious systems with regard to chloride penetration tended to be more noticeable as the type of cementitious materials and their replacement percent changed as clarified in Table 4 and Figs. 1-3. Also, The second and third zones (i.e., 10-20 mm and 20-30 mm) of tested concrete of ternary cementitious system indicate lower values of chloride contents than those of the OPC concrete. The rates of increase in chloride contents with time in the case of OPC concrete are larger than those of concrete of ternary cementitious system.

Marusin (1989) mentioned that the corrosion threshold limit for soluble chloride ion concentration in normal weight reinforced concrete is about 0.03% by weight of concrete. The soluble chloride contents for all the tested samples after 5 months at the depth 20-30 mm concrete are lower than the above mentioned limits for corrosion threshold. Ternary cementitious mixtures have lower soluble chloride content, which leads to conclude that using concrete containing ternary cementitious systems may reduce the depth of cover needed to protect the reinforcing steel. Gaynor (1987)

Table 4

Total and soluble chloride contents of different mixes (depths from 0 to 30 mm).

Mix no. Depth from surface (mm) 1 Month 3 Months 5-Months

Total (%) Soluble (%) Total (%) Soluble,% Total (%) Soluble (%)

0-10 0.896 0.549 0.844 0.672 1.314 1.140

1 10-20 0.050 0.015 0.041 0.033 0.245 0.201

20-30 0.013 0.007 0.019 0.008 0.019 0.011

0-10 0.656 0.511 1.090 0.830 1.103 0.803

2 10-20 0.014 0.009 0.035 0.025 0.124 0.089

20-30 0.013 0.008 0.017 0.003 0.010 0.004

0-10 0.796 0.653 1.008 0.839 1.060 0.836

3 10-20 0.013 0.011 0.042 0.019 0.160 0.106

20-30 0.008 0.008 0.016 0.005 0.006 0.004

0-10 0.759 0.533 0.776 0.589 1.048 0.847

4 10-20 0.016 0.009 0.011 0.007 0.019 0.012

20-30 0.013 0.002 0.006 0.003 0.008 0.004

0-10 0.703 0.529 0.724 0.645 1.068 0.900

5 10-20 0.013 0.006 0.011 0.006 0.015 0.013

20-30 0.012 0.002 0.005 0.001 0.006 0.004

0-10 0.746 0.545 0.557 0.457 0.885 0.724

6 10-20 0.011 0.005 0.008 0.004 0.022 0.016

20-30 0.005 0.001 0.005 0.003 0.007 0.006

0-10 0.532 0.341 0.681 0.482 0.756 0.562

7 10-20 0.008 0.006 0.012 0.008 0.019 0.011

20-30 0.007 0.002 0.005 0.002 0.007 0.004

0-10 0.491 0.398 0.401 0.345 0.681 0.600

8 10-20 0.012 0.009 0.007 0.003 0.016 0.013

20-30 0.004 0.002 0.007 0.005 0.006 0.008

0-10 0.527 0.341 0.487 0.387 0.582 0.465

9 10-20 0.008 0.003 0.006 0.001 0.019 0.014

20-30 0.008 0.003 0.003 0.001 0.008 0.006

Fig. 1. Total and soluble chloride contents of mixes 1-3.

Soluble surface

Fig. 2. Total and soluble chloride contents of mixes 4-6.

Fig. 3. Total and soluble chloride contents of mixes 7-9.

reported that 0.5-0.75 of penetrated chlorides ions in hardened concrete are soluble in water and free to contribute to corrosion.

The obtained results for all studied mixtures show lower percent of soluble/total chloride than that reported by Gaynor (1987). The mixes containing ternary cementitious systems show lower ratios of soluble/total than those of OPC mix. Anwar and Sakai (2007) reported that concrete of binary cementitious systems (silica fume, blast-furnace, fly ash) indicated lower chloride content than OPC mix as well as lower ratio of soluble/total chloride content, which complies with the obtained results.

Figs. 1-3 indicate that, the binary system (mixes 2-5) results of the total and soluble chloride ion contents were better than the control mix (mix 1) about 20%. Moreover, the ternary system (mixes 6-9) results of the total and soluble chloride ion contents were better than the control mix about 40-60%. Mix 9 (10% SFand 25% FA) gave the best results in terms of total and soluble chloride ion contents at all tested depths.

Table 5 lists the results of the total and soluble chloride ion contents for the studied mixes as percentage by weight of concrete after 5 months at depths from 30 mm to 50 mm. The results indicate that the levels of total and soluble chloride contents were very small for all mixes, nevertheless the results of binary and ternary systems were better than the control mix by 10-50% for different depths after 5 months.

Table 5

Total and soluble chloride contents of different mixes (depths from 30 to 50 mm).

Mix no. Depth from surface (mm) 5-Months Total (%) Soluble (%)

1 30-40 40-50 0.012 0.010 0.008 0.008

2 30-40 40-50 0.007 0.007 0.004 0.004

3 30-40 40-50 0.005 0.007 0.004 0.005

4 30-40 40-50 0.008 0.008 0.005 0.005

5 30-40 40-50 0.008 0.009 0.006 0.008

6 30-40 40-50 0.006 0.007 0.004 0.007

7 30-40 40-50 0.006 0.009 0.005 0.005

8 30-40 40-50 0.009 0.009 0.007 0.007

9 30-40 40-50 0.008 0.008 0.004 0.007

4. Conclusions

Much attention must be given to the development of a new generation of cements incorporating combination of by-product materials in binary and ternary systems. The test results show that ternary blends of Portland cement, silica fume, and fly ash offer significant advantages over binary blends and plain Portland cement. Also, the combination of silica fume and fly ash is complementary: the silica fume improves the early age performance of concrete with the fly ash continuously refining the properties of the hardened concrete as it matures.

Combinations of 5-10% silica fume with 15-25% fly ash show satisfactory performance in both fresh and hardened concrete. Such combinations produce concrete with generally good properties especially the resistance to chloride penetration.

Mix 5 (10% SF) is the best mix in terms of compressive strength, tensile strength and elastic modules, while mix 9 (25% FA and 10% SF) is the best mix in terms of chloride resistance.

The obtained results lead to recommend the MWRI introduce the ternary blended cement in the new water structures exposed to saline water.

References

ACI, 2000. State of the Art Report on High-Strength Concrete—Manual of Concrete Practice: Part I. 363R-92. ACI, American Concrete Institute, Detroit.

Anwar, M., Sakai, K., 2007. Chloride ion permeability and sulphate resistance of concrete with ternary cementitious systems. In: CONSEC'07, 5th

International Conference on Concrete under Severe Conditions Environment and Loading, Tours, France. Anwar, M., Roushdi, M., Mustafa, H., 2013. Investigating the usage of environmental by-product materials in concrete for sustainable development.

Australian Journal of Basic and Applied Sciences 7 (9), 132-139. Batis, G., Rakanta, E., 2005. Corrosion of steel reinforcement due to atmospheric pollution. Cement Concrete Composites 27, 269-275. Bilodeau, A., Sivasundaram, V., Painter, K.E., Malhotra, V.M., 1994. Durability of concrete incorporating high-volume fly ash from sources in the

U.S. ACI Matter Journal 91 (1), 3-12. Escalante-Garcia, J., Sharp, J.H., 2004. The chemical composition and microstructure of hydration products in blended cements. Cement Concrete Composites 26 (8), 967-976.

Gaynor, R., 1987. Understanding chloride percentages. In: Corrosion, Concrete, and Chlorides. Steel Corrosion in Concrete: Causes and Restraints, (SP102-11). American Concrete Institute, Detroit, MI, pp. 161-165.

Keith, B., Tarunjit, B., 2013. Prevention of Corrosion in Concrete Using Fly Ash Concrete Mixes, Available from: http://circainfo.ca/pdf/ K.%20Bargaheiser%20-%20Corrosion%20Paper.pdf

Luca, B., Maddalena, C., Pietro, P., 2007. Corrosion behaviour of steel in concrete in the presence of stray current. Corrosion Science 49, 1056-1068.

Malhotra, V.M., Mehta, P.K., 1996. Pozzolanic and Cementious Materials. Advances in Concrete Technology Series, vol. 1. Taylor & Francis Group, Canada.

Marusin, S.L., 1989. Influence of length of moist curing time on weight change behavior and chloride ion permeability of concrete containing silica fume. In: 3rd International Conference on Fly Ash, Silica Fume, Slag, and Natural Pozzolans in Concrete, Trondheim, Norway.

Qian, S., Baldock, B., Qu, D., Bouzoubaa, N., Gu, P., Fournier, B., 2003. Corrosion performance of reinforcing steel in concrete containing supplementary cementing materials. In: NACE Northern Area 2003 Conference, Ottawa, Ontario.

Ravindrarajah, R.S., Moses, P.R., 1993. Effect of binder type on chloride penetration in mortar. In: 4th International Conference on Structural Failure, Durability and Retrofitting, Singapore.

Shannag, M.J., 2000. High strength concrete containing natural pozzolan and silica fume. Cement Concrete Composites 22, 399-406.

Thomas, M.D.A., Shehata, M.H., Shashiprakash, S.G., Hopkins, D.S., Cail, K., 1999. Use of ternary cementitious systems containing silica fume and fly ash in concrete. Cement Concrete Research 29 (8), 1207-1214.

Wei, S., Yunsheng, Z., Sifeng, L., Yanmei, Z., 2004. The influence of mineral admixtures on resistance to corrosion of steel bars in green highperformance concrete. Cement Concrete Research 34 (10), 1781-1785.

Xianming, S., Ning, X., Keith, F., Jing, G., 2012. Durability of steel reinforced concrete in chloride environments: an overview. Construction and Building Materials 30, 125-138.