Construction and Building Materials 25 (2011) 933–938

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Construction and Building Materials

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Effect of copper slag as a fine aggregate on the propertiesof cement mortars and concrete

Khalifa S. Al-Jabri *, Abdullah H. Al-Saidy, Ramzi TahaDepartment of Civil and Architectural Engineering, College of Engineering, Sultan Qaboos University, PO Box 33, Al Khodh, Post Code 123, Oman

a r t i c l e i n f o a b s t r a c t

Article history:Received 17 January 2010Received in revised form 26 April 2010Accepted 19 June 2010

Keywords:ConcreteCement mortarCopper slagWaste materialIndustrial by-productsStrengthDurability

0950-0618/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.conbuildmat.2010.06.090

* Corresponding author. Tel.: +968 2414 1333; fax:E-mail address: aljabri@squ.edu.om (K.S. Al-Jabri).

An experimental investigation was conducted to study the effect of using copper slag as a fine aggregateon the properties of cement mortars and concrete. Various mortar and concrete mixtures were preparedwith different proportions of copper slag ranging from 0% (for the control mixture) to 100% as fine aggre-gates replacement. Cement mortar mixtures were evaluated for compressive strength, whereas concretemixtures were evaluated for workability, density, compressive strength, tensile strength, flexuralstrength and durability. The results obtained for cement mortars revealed that all mixtures with differentcopper slag proportions yielded comparable or higher compressive strength than that of the control mix-ture. Also, there was more than 70% improvement in the compressive strength of mortars with 50% cop-per slag substitution in comparison with the control mixture. The results obtained for concrete indicatedthat there is a slight increase in density of nearly 5% as copper slag content increases, whereas the work-ability increased significantly as copper slag percentage increased compared with the control mixture. Asubstitution of up to 40–50% copper slag as a sand replacement yielded comparable strength to that ofthe control mixture. However, addition of more copper slag resulted in strength reduction due to theincrease in the free water content in the mix. Also, the results demonstrated that surface water absorp-tion decreased as copper slag content increases up to 50% replacement. Beyond that, the absorption rateincreased rapidly and the percentage volume of the permeable voids was comparable to the control mix-ture. Therefore, it is recommended that up to 40–50% (by weight of sand) of copper slag can be used as areplacement for fine aggregates in order to obtain a concrete with good strength and durabilityrequirements.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

It was well recognised for many years the beneficial utilisationof some industrial by-products in improving the properties of freshand hardened concrete. By-products such as pulverised fuel ash,silica fume and ground granulated blast furnace slag (ggbfs) areadded in different proportions to concrete mixes as either a partialsubstitute to Portland cement or as admixtures. Concrete preparedwith such materials showed improvement in workability anddurability compared to normal concrete and has been used in theconstruction of power and chemical plants and under-water struc-tures. Use of some waste materials has been well documented indesign specifications. New by-products and waste materials arebeing generated by various industries, dumping or disposal ofthese materials causes environmental and health problems. There-fore, recycling of waste materials a great potential in concreteindustry.

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+968 2441 3416.

Copper slag is an industrial by-product material produced fromthe process of manufacturing copper. It has been estimated thatapproximately 24.6 million tons of slag are generated from theworld copper industry [1]. In the Sultanate of Oman, approxi-mately 60,000 tons of copper slag are produced every year byOman Mining Company. Although copper slag is widely used inthe sand blasting industry and in the manufacturing of abrasivetools, the remainder is disposed of without any further reuse orreclamation. Copper slag possesses mechanical and chemicalcharacteristics that qualify the material to be used in concrete asa partial replacement for Portland cement or as a substitute foraggregates. For example, copper slag has a number of favourablemechanical properties for aggregate use such as excellent sound-ness characteristics, good abrasion resistance and good stability[1]. Also, copper slag exhibits pozzolanic properties since it con-tains a low CaO content and other oxides such as Al2O3, SiO2, andFe2O3. Use of copper slag in the concrete industry as a replacementfor cement and/or fine aggregates can has the benefits of reducingthe costs of disposal and helps protecting the environment.

Despite the fact that several studies [2–7] have been reportedon the effect of copper slag replacement on the properties of

0

20

40

60

80

100

120

1052.361.180.60.30.150.075

Sieve size (mm)

% P

assi

ng

Sand

Copper Slag

Grading limits "zone 1"

Fig. 1. Gradation of sand and copper slag.

934 K.S. Al-Jabri et al. / Construction and Building Materials 25 (2011) 933–938

concrete, further investigations are necessary in order to obtain acomprehensive understanding that would provide an engineeringbasis to allow the use of copper slag in concrete. The effect ofcopper slag on the hydration of cement-based materials was inves-tigated by Mobasher et al. [2] and Tixier et al. [3]. Up to 15% copperslag, by weight of cement was used as a Portland cement replace-ment together with up to 1.5% of hydrated lime as an activator forpozzolanic reactions. Results indicated a significant increase in thecompressive strength for up to 90 days of hydration. Also, a de-crease in capillary porosity and an increase in gel porosity were ob-served. Moura et al. [4] reported that copper slag could be apotential alternative to admixtures used in concrete and mortars.The use of slag from copper smelting as a fine aggregate in concretewas also investigated by Akihiko and Takashi [5]. From mortarstrength tests with a cement/slag/water ratio of 1/2/0.55, the ballmilled slag gave a higher strength. The effects of using severaltypes of slag on mortar and concrete reactions, reinforcing steelcorrosion, abrasion, workability and slump, shrinkage, and freezingand thawing characteristics were examined. Copper slag was alsoused by Ayano et al. [6] as a fine aggregate in concrete. They de-scribed the strength, setting time and durability of concrete mix-tures made with copper slag. Al-Jabri et al. [7] studied the effectof copper slag (CS) and cement by-pass dust (CBPD) replacementson the strength of cement mortars. Experimental results indicatedthat the mixture containing 5% CBPD + 95% cement yielded thehighest 90 days compressive strength of 42 MPa in comparisonwith 40 MPa for the mixture containing 1.5% CBPD + 13.5CS + 85% cement. The optimum CS and CBPD to be used was 5%.In addition, it was determined that using CBPD as an activatingmaterial would operate better than using lime. Also, all samplesmet the 3 and 7 days compressive strength specifications require-ments for cement mortars. The fundamental properties of concreteusing copper slag and class II fly ash as fine aggregates were inves-tigated by Ishimaru et al. [8]. It was concluded that up to 20% (involume) of copper slag or class II fly ash as fine aggregates substi-tution can be used in the production of concrete suitable for struc-tures. In order to control the bleeding in concrete mixtures whenincorporating copper slag as fine aggregates, Ueno et al. [9] sug-gested a grading distribution of fine aggregate based on particledensity. The study investigated the maximum size of slag fineaggregate that does not significantly influence the amount ofbleeding and the required plastic viscosity of paste to control theamount of bleeding by the variation of water-to-cement ratios.Al-Jabri et al. [10] investigated the effect of CS and CBPD as partialreplacements for cement on concrete properties. In addition to thecontrol mixture, two different trial mixtures were prepared usingdifferent proportions of CS and CBPD and three water-to-binder ra-tios were studied: 0.5, 0.6 and 0.7. Results showed that 5% copperslag substitution for Portland cement gave a similar strength per-formance as the control mixture, especially at the low water-to-binder ratios of 0.5 and 0.6, while higher copper slag (13.5%)replacement yielded lower strength values. Results also demon-strated that the use of CS and CBPD as partial replacements forPortland cement has a negligible effect on the modulus of elasticityof concrete, especially at the small quantities substitution. Shi et al.[11] presented a comprehensive review on the use of copper slag incement, mortars and concrete. The paper was focused on the char-acteristics of copper slag and its effects on the engineering proper-ties of cement, mortars and concrete. Wu et al. [12] investigatedthe mechanical properties of copper slag reinforced concrete underdynamic compression. Results showed that the dynamic compres-sive strength of copper slag reinforced concrete generally im-proved with the increase in amounts of copper slag used as asand replacement up to 20%, compared with the control concrete,beyond which the strength was reduced. Wu et al. [13] also inves-tigated the mechanical properties of high strength concrete incor-

porating copper slag as a fine aggregate. Results indicated that thestrength of concrete, with less than 40% copper slag replacement,was higher than or equal to that of the control specimen. Themicroscopic view demonstrated that there were limited differ-ences between the control concrete and the concrete with less than40% copper slag content.

The main objective of this study was to investigate the effect ofusing copper slag as a partial and/or full replacement for sand inmortars and normal concrete. The study consisted of the followingtasks:

1. Investigate the effect of copper slag replacement as a fine aggre-gate on the compressive strength of cement mortars at differentcuring periods.

2. Evaluate the effect of copper slag replacement on the workabil-ity and density of concrete.

3. Conduct compressive, tensile and flexural strength testing onconcrete mixtures.

4. Assess the durability of concrete made with copper slag by con-ducting initial surface absorption and total absorption tests.

2. Materials

2.1. Cement

The cement used in this study was ordinary Portland cement (OPC) produced byOman Cement Company. This cement is the most widely used one in the construc-tion industry in Oman.

2.2. Coarse and fine aggregates

Coarse aggregates (i.e. 20 mm and 10 mm) and fine sand were taken from anearby crusher in Al-Khoudh Area. These are the aggregates typically used in nor-mal concrete mixtures in Oman. The gradation test conducted on the fine sandand copper slag showed that they met specifications requirements for concretesand (Fig. 1).

2.3. Copper slag

Copper slag used in this work was brought from Oman Mining Company, whichproduces an annual average of 60,000 tons. In preparation of cement mortars, thesand and copper slag particles used were those passing 850 lm and retained on600 lm according to OS26-1981 [14]. The copper slag was ground in the laboratoryinto a fine powder to the required size following the procedure described by Al-Jab-ri et al. [7]. Sieve analysis test was conducted in accordance with BS 882 [15] onthree samples of copper slag in order to determine the particle size distributionand to compare with the gradation requirements for concrete sand (Fig. 1). Bothsand and copper slag have comparable gradations, which satisfy grading limit,Zone 1.

K.S. Al-Jabri et al. / Construction and Building Materials 25 (2011) 933–938 935

3. Experimental study

3.1. Mix design

3.1.1. Cement mortarsTo study the effect of copper slag substitution as a replacement for fine aggregates

on the strength of cement mortars, specimens were prepared with different percent-ages of copper slag (by weight). The percentages of copper slag added were as follows:0% (for the control mix), 20%, 40%, 50%, 60%, 80%, and 100%. Fifteen cubes(70 mm � 70 mm � 70 mm) were cast for each mixture and three samples each weretested after 3, 7, 28, 56 and 90 days of curing. The main purpose for keeping the sam-ples for longer curing periods of 56 and 90 days is to observe any detrimental effectfrom the use of copper slag as fine aggregates on the compressive strength of concrete.

The quantities of materials (Table 1) used in each mortar cube were selectedaccording to OS26-1981 [14] using a water-to-cement ratio of 0.4. The specifiedcube compressive strength values for cement mortars are 15 N/mm2 and23 N/mm2 at 3 and 7 days, respectively based on OS26-1981 recommendations.

3.1.2. Concrete mixturesConcrete mixtures with different proportions of copper slag used as a partial or

full substitute for fine aggregates were prepared in order to investigate the effect ofcopper slag substitution on the strength and durability of normal concrete. Eightconcrete mixtures were prepared with different proportions of copper slag. The pro-portions (by weight) of copper slag added to concrete mixtures were as follows: 0%(for the control mix), 10%, 20%, 40%, 50%, 60%, 80%, and 100%. The control mixture(with 0% copper slag and 100% sand) was designed to have a target 28 day compres-sive strength of 45 N/mm2, using a water-to-binder ratio of 0.5. Batch quantities areshown in Table 2.

To determine the unconfined compressive strength of concrete, six cubes(150 mm � 150 mm � 150 mm) were cast for each mixture, and three sampleswere tested after 7 and 28 days of curing. Three 150 mm diameter by 300 mmheight cylinders were prepared for each mixture to determine the tensile strengthof concrete. They were tested after 28 days of curing. Also, to determine the flexuralstrength (modulus of rupture) for each mixture, three 100 mm � 100 mm �500 mm prisms were cast and tested after 28 days of curing.

To evaluate the durability of concrete mixtures, three 150 mm � 150 mm �150 mm cubes were prepared to determine surface absorption after 28 days of cur-ing. Also, three specimens 10 cm � 10 cm � 4 cm with an average weight of 1 kgwere cut from the prisms to determine percentage of voids in concrete.

3.2. Sample preparation

Cement mortar samples were compacted in three layers using a vibrating table.After 24 h, specimens were removed from the moulds and cured in a water tank forlater testing at 3, 7, 28, 56 and 90 days.

Concrete specimens were prepared and compacted as required by ASTM C192-98 [16]. The required amounts of coarse aggregate, fine aggregate, cement, water,and copper were weighed in separate buckets. The materials were mixed in accor-dance with ASTM C192-98. The slump of the fresh concrete was determined to en-sure that it would be within the designed value. After 24 h, specimens wereremoved from the moulds and cured in a water tank for 7 and 28 days of curing.

3.3. Testing procedure

After curing, the following tests were carried out on the concrete specimens:

Table 1Batch quantities per cube for cementmortars.

Material Weight (g)

Cement 185Sand 555Water 74

Table 2Batch quantities (kg/m3) for concrete mixtures (w/b = 0.5).

Component Weight (kg)

Water 207Cement 416Fine aggregate 72110 mm aggregate 33820 mm aggregate 790

� Compressive strength test was conducted on cement mortar samples at 3, 7, 28,56, and 90 day of curing in accordance with BS 1881: Part 116 [17] using a load-ing rate of 1.25 kN/s;� 7 and 28 day cube compressive strength test was conducted in accordance with

BS 1881: Part 116 [17] using a loading rate of 2.5 kN/s;� 28 day cylinder tensile (splitting) strength test was done in accordance with

ASTM C496-96 [18] using a loading rate of 2 kN/s;� 28 day flexural strength test was conducted in accordance with ASTM C78-94

[19] using a simple beam with third point loading at a loading rate of 0.2 kN/s;� the initial surface absorption test was conducted in accordance with BS 1881:

Part 208 [20]; and� the permeable voids contents were determined as per ASTM C642-97 [21].

4. Results and discussion

4.1. Materials’ characterization

Tests were conducted to determine the chemical composition,specific gravity and water absorption of copper slag and sand[22]. Results presented in Table 3 show that copper slag has alow CaO content compared with ordinary Portland cement, whichindicates that copper slag on its own can not be used as a cemen-titious material. But copper slag has high concentrations of silica,alumina and iron oxides, which suggests that copper slag couldhave the potential to produce high quality pozzolans.

Results from specific gravity and water absorption tests (Table3) revealed that copper slag has a specific gravity of 3.4 which ishigher than that of sand (2.77), whereas the water absorption val-ues for copper slag and sand were about 0.2% and 1.4%, respec-tively. This suggests that concrete produced with large copperslag substitution would have larger density values than concreteproduced with sand alone. On the other hand, due to its low waterabsorption it is expected that the free water content in concretemixtures will increase as copper slag content increases. This willlead to an increase in the workability of concrete mixtures contain-ing high copper slag percentages

4.2. Effect of copper slag replacement on the strength of cementmortars

The measured compressive strength values for different mix-ture proportions are presented in Table 4. The test results indicatethat all specimens yielded a higher compressive strength thanspecifications requirements of 15 and 23 MPa for cement mortarsafter 3 and 7 days, respectively. For all mixtures, as the curing per-iod increases the compressive strength will increase and the gain

Table 3Chemical composition and physical properties of ordinary Portland cement (OPC),copper slag (CS) and sand.

Component OPC (%) CS (%) Sand

SiO2 20.85 33.05 –Al2O3 4.78 2.79 –Fe2O3 3.51 53.45 –CaO 63.06 6.06 –MgO 2.32 1.56 –SO3 2.48 1.89 –K2O 0.55 0.61 –Na2O 0.24 0.28 –TiO2 0.25 0 –Mn2O3 0.05 0.06 –CI 0.01 0.01 –Loss on ignition 1.75 0 –IR 0.21 0 –CuO 0 0.46 –Al2O3 + SiO2 + Fe2O3 29.14 89.29 –

Specific gravity 3.15 3.4 2.77Absorption (%) – 0.17 1.36

Table 4Average compressive strength of cement mortars at different curing ages.

Mix No. Mix type Compressive strength (MPa)

3 days 7 days 28 days 56 days 90 days

1 Control (100% S) 22 23.3 24.6 25.3 272 20% CS + 80% S 22.1 29 31 34.7 363 40% CS + 60% S 22.1 30.6 39.8 40 424 50% CS + 50% S 20.3 30 42.7 44.5 50.35 60% CS + 40% S 23 28 39.2 42 47.86 80% CS + 20% S 23.1 26.8 35 40.1 44.87 100% CS + 0% S 20.8 23.3 26.1 32 35.5

S: sand; CS: copper slag.

936 K.S. Al-Jabri et al. / Construction and Building Materials 25 (2011) 933–938

of strength is more rapid in the early curing days (i.e. 3, 7 and28 days).

Table 4 also indicates that all mixtures yielded comparable orhigher compressive strength than the control mixture (100% sand)for all curing ages. Furthermore, as copper slag content increasesthe compressive strength of cement mortars increases up to 50%substitution of copper slag. Beyond that, the compressive de-creased with an increase in copper slag content. However, Mixture#7 with 100% copper slag gave a higher strength than the controlmixture. Mixture #4 with 50% copper slag yielded the highest aver-age 28 day compressive strength of 42.7 N/mm2, almost 74% high-er than the compressive strength of the control mix. For longercuring periods (i.e. 56 and 90 days), most of the samples showedno detrimental effect (i.e. a strength reversal) when using copperslag. Although all mixtures yielded a higher compressive strengththan the control mixture, it can be said that the replacement of50% copper slag as a sand replacement will give the highest com-pressive strength with more than 70% improvement in mortar’sstrength.

4.3. Effect of copper slag replacement on the density and workability ofnormal concrete

Table 5 presents slump values as measurement for the work-ability of fresh concrete, and concrete density for all mixtures withdifferent proportions of copper slag. The test results indicate thatthere is a substantial increase in the workability of concrete as cop-per slag content increases. The measured slump for the controlmixture with 100% sand was 65.5 mm, while the measured slumpfor the concrete mixture with 100% copper slag substitution (Mix-ture #8) was 200 mm. This significant increase in the workabilitywas due to the low water absorption characteristics of copper slagcompared with sand, where more free water remains in the con-crete matrix after hydration. However, segregation and bleedingwere observed in concrete mixtures with high copper slag contents(Mixtures #7 and #8). This observation is in line with similar

Table 5Strength of concrete at 7 and 28 days of curing.

Mix No. Mix type Density (kg/m3) Slum

1 Control (100% S) 2524 65.52 10% CS + 90% S 2515 803 20% CS + 80% S 2540 804 40% CS + 60% S 2550 1105 50% CS + 50% S 2560 1306 60% CS + 40% S 2601 1657 80% CS + 20% S 2597 1908 100% CS + 0% S 2653 200

Fcu = cube compressive strength, Ft = tensile strength, Fcr = flexural strength, S = sand, CSa Cured at 7 days.b Cured at 28 days.

observations from other studies [8,9], where it has been reportedthat concrete with fine slag aggregates have a tendency to exhibita larger amount of bleeding because of their high density and/ormuch water content for a given slump of concrete.

Also, the density of concrete (Table 5) slightly increased as cop-per slag content increases. Density of concrete was increased by al-most 5% (for Mixture #8), which is attributed to the high specificgravity of copper slag.

4.4. Effect of copper slag replacement on the strength of normalconcrete

The effect of copper slag substitution as a fine aggregate on thestrength of concrete is given in Table 5, which presents the average7- and 28 day cube compressive strength, the average 28 day ten-sile strength and the average 28 day flexural strength of concrete.The unconfined compressive strength values of concrete mixtureswith different proportions of copper slag cured at 7 and 28 daysare also plotted in Fig. 2. The test results indicate that for mixturesprepared using up to 60% copper slag replacement, the compres-sive strength of concrete is comparable to the strength of the con-trol mix with 100% sand. However, for mixtures with 80% and 100%copper slag (i.e. Mixtures #7 and #8), the compressive strength de-creased rapidly below the strength of the control mixture. Mixture#4 with 40% copper slag content yielded the highest 28 day com-pressive strength of 47.1 N/mm2 compared with 45 N/mm2 forthe control mixture, whereas the lowest compressive strength of34.8 N/mm2 was obtained for Mixture #7 with 80% copper slag.Here, the compressive strength yielded by Mixture #7 is almost22% lower than that of the control mix. This reduction in compres-sive strength for concrete mixtures with high copper slag contentsis due to the increase in the free water content that results fromthe low water absorption characteristics of copper slag in compar-ison with sand. This causes a considerable increase in the workabil-ity of concrete and, thus, reduces concrete strength as shown inTable 5. Also, Fig. 2 shows that the compressive strengths for dif-ferent concrete mixtures at 7 and 28 days of curing were consistentwhere 80% of 28 day concrete strength was achieved after 7 days ofcuring.

Wu et al. [12,13] observed that, after examining the microstruc-ture of concrete specimens with different copper slag contents,that the strength improvement with 40% substitution was mainlyattributed to the physical properties of copper slag. Copper slaghas a better compressibility than sand, which can partially relievethe stress concentration, if the sand is still as the dominant fineaggregate holding the concrete matrix together. Also, the angularsharp edges of copper slag particles can improve the cohesion ofthe concrete matrix. It is known that the sand has good abrasionproperties because of its rough surface, which can improve thecohesion between cement paste and coarse aggregate. However,

p (mm) Strength (MPa)

(Fcu)a (Fcu)b (Ft)b (Fcr)b

36.2 45.0 3 7.738.8 46.0 3.5 7.240.2 47.0 3.7 7.238.7 47.1 3.8 6.538.1 47.0 4.1 7.337.7 46.0 3.6 6.327.8 34.8 3.6 7.229 35.1 3.4 5.9

= copper slag.

0

5

10

15

20

25

30

35

40

45

50

1 2 3 4 5 6 7 8

Mix No.

7-day

28-day

Com

pres

sive

Str

engt

h (N

/mm

2 )

Fig. 2. Cube compressive strength of concrete at 7 and 28 days of curing.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 30 60 90 120 150

Time(Minutes)

100%S+0%CS

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60%S+40%CS

50%S+50%CS

40%S+60%CS

20%S+80%CS

0%S+100%CS

Flow

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2 .s)

Fig. 3. Surface water absorption of concrete versus time for different concretemixtures.

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l/m2 .

s)

K.S. Al-Jabri et al. / Construction and Building Materials 25 (2011) 933–938 937

the abrasion properties of sand is weakened with time after yearsof weathering causing sand particles to have rounded edges, whichare detrimental to the interlocking properties of composite materi-als. The angular sharp edges of copper slag particles have the abil-ity to compensate to some extent the adverse effects of sand and,thus, further improve the cohesion of concrete. On the other hand,the glassy surface texture of copper slag particles has a negative ef-fect on the cohesion. Also, the low absorption properties of copperslag can leave excess water in concrete, which can cause excessivebleeding at higher copper slag content. This results in the forma-tion of internal voids and capillary channels in the concrete, caus-ing a reduction in its quality. Therefore, the strength of concretewith lower copper slag contents can be improved by the positiveeffect of copper slag, whereas if copper slag content exceeds 40%,the strength of concrete can be decreased substantially with areduction in cohesion governed by copper slag.

Also it is worth mentioning that there was more than 70%improvement in the compressive strength of mortars (Table 4)with 50% copper slag replacement, whereas there is a slight in-crease of 4.4% in the compressive strength of concrete (Table 5)with 50% copper slag replacement. This difference in the strengthimprovement between cement mortars and concrete may beattributed to the bonding between the particles within the cementpaste. Furthermore, coarse aggregates are introduced in concretemixtures, which could contribute to the different behaviour ob-served for the same mixture in mortars and concrete. The in-creased porosity in concrete weakens the bond between theconcrete components, which is one of determining factors for thestrength of concrete.

The 28 day tensile strength of concrete is also given in Table 5.The results show that the average tensile strength was within thepermissible values in accordance with the design specifications.For design purposes, the tensile strength can be empirically takenas 0.45

pFcu [23]. The 28 day average flexural strength (modulus of

rupture) values for concrete are presented in Table 4. The resultsindicate that the flexural strength values for all concrete mixtureswere slightly higher than the permissible design values. The flex-ural strength of concrete is normally taken as 0.75

pFcu [23]. The

experimental average flexural strength of concrete was 6.9 N/mm2,compared with 5 N/mm2 calculated from the empiricalrelationship.

0 20 40 50 60 80 100

0

Copper slag content (%)

Fig. 4. Effect of copper slag addition on the surface water absorption for differentconcrete mixtures.

4.5. Effect of copper slag replacement on the durability of normalconcrete

Two tests were conducted to assess the durability of concretemade with copper slag as a fine aggregate substitution. The first

test measures the surface water absorption of concrete [20], whilethe second test measures the percentage of volume of permeablevoids in concrete [21]. The results from the initial surface absorp-tion test are shown in Figs. 3 and 4. Fig. 3 indicates that all mix-tures showed a similar trend of decreasing surface waterabsorption with time. The decrease was generally rapid duringthe first 30 min, which later decreased afterwards up to 120 min.All mixtures yielded flow rate values within the specified limits,which were between 0.05 ml/m2 s and 3.6 ml/m2 s in the first10 min [20].

Also, Fig. 3 demonstrated that Mixture #4 with 40% copper slagreplacement showed the lowest surface water absorption for theentire testing time, while Mixture #8 with 100% copper slagreplacement showed the largest surface water absorption. Fig. 4shows that there is a general decrease in the surface water absorp-tion with an increase in copper slag content up to 40% copper slagsubstitution. Beyond that, absorption increases as copper slag con-tent increases. This is primarily due to the increase in the freewater content leading to more voids created in the hardened con-crete. However, at 120 min, up to 50% replacement of copper slaggave comparable surface water absorption values to the controlmixture with 100% sand.

Fig. 5 shows volume of water permeable void contents for dif-ferent concrete mixtures at 28 day curing. The results show thatthe percentage of permeable voids slightly decreased with an in-

0

24

6

810

12

14

1618

20

0 20 40 50 60 80 100

Copper slag content (%)

Vol

ume

of P

erm

eabl

e V

oids

(%

)

Fig. 5. Water permeable void contents for different concrete mixtures at 28 daycuring.

938 K.S. Al-Jabri et al. / Construction and Building Materials 25 (2011) 933–938

crease in copper slag content up to 40% replacement. Beyond that,the volume of voids increases to become comparable to the controlmixture. Thus, it is recommended that the replacement of 40–50%copper slag (by weight) as a partial replacement for fine aggregateswill produce a concrete with good durability requirements.

5. Conclusions

The following conclusions are drawn regarding the use of cop-per slag as a fine aggregate in cement mortars and concrete:

� For cement mortars, all mixtures with different copper slag pro-portions yielded comparable or higher compressive strengththan the strength of the control mixture. There was more than70% improvement in the compressive strength of mortars with50% copper slag substitution in comparison with the controlmixture.� There is almost 5% increase in the concrete density, when cop-

per slag was used as a sand replacement, whereas the workabil-ity increased substantially with an increase in copper slagcontent. This was attributed to the low water absorption andglassy surface of copper slag.� The compressive, tensile and flexural strength of concrete were

comparable to the control mix using up to 50% copper slag sub-stitution for sand, but they decreased with a further increase incopper slag contents.� The surface water absorption of concrete was reduced with up

to 40% copper slag replacement for sand.� The volume of permeable voids decreased with the replacement

of up to 50% copper slag.� Copper slag, in the range of 40–50%, could potentially replace

sand in concrete mixtures.

Acknowledgment

The authors would like to express their sincere thanks to SultanQaboos University for the financial support provided to performthroughout this project.

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