Int. Conference on Sustainable Structural Concrete, 15-18 Sept 2015, La Plata, Argentina.

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EFFECT OF COPPER SLAG AS SUPPLEMENTARY CEMENTITIOUS MATERIAL (SCM) IN ULTRA HIGH PERFORMANCE MORTAR (UHPM)

Romy S. Edwin (1, 2) *, Mieke De Schepper (1), Elke Gruyaert (1), Nele De Belie (1) (1) Magnel Laboratory for Concrete Research, Faculty of Engineering and Architecture, Department of Structural Engineering, Ghent University (2) Faculty of Engineering, Halu Oleo University, Kendari, Indonesia * romysuryaningrat.edwin@UGent.be Abstract

This research investigates the use of copper slag as supplementary cementitious materials (SCM) in ultra high performance mortar (UHPM). Two secondary slag types from a plant in Belgium were utilized as SCM and were classified as a quickly cooled granulated copper slag (QCS) and a slowly cooled broken copper slag (SCS). Both materials were ground intensively using a planetary ball mill. A low water-to-binder ratio of 0.15 was chosen for the UHPM in this study. Various mortar and cement paste samples were produced with increasing copper slag content from 0 to 20 wt% in steps of 5 wt%. Particle size distribution (PSD) and specific surface area (SSA) of the copper slag were assessed using laser diffraction and the Blaine permeability test, respectively.

The results obtained, showed that the strength of mortars with different copper slag proportions was comparable to or even better than the control mixture at 90 days. The increased fineness of the copper slag enhances the mortar strength. Using isothermal calorimetry it was found that the addition of copper slag slows down the hydration of the cement pastes.

1. INTRODUCTION Rapid growth in the construction industry increases the demand for sustainable and high

quality building materials. This creates a challenge to compose high-performance materials which are competitive from both an environmental and an economic viewpoint. On the one hand, large volumes of by-products from the mining industry are jeopardizing the environment by the need for landfilling sites. On the other hand, the availability of natural resources is decreasing due to a large consumption in the cement and concrete production. A possible breakthrough in order to preserve the environment can be sought in exploiting by-products within cement and concrete production.

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Besides mill tailing, copper slag is one of the by-product materials from the copper smelting. In Indonesia, around 400,000 tons of copper slag are produced per year by Freeport Company and Newmont Company [1]. In Belgium, about three million tons of slag are produced by the copper industry every year [2]. In Europe, approximately 40 million tonnes of slag were generated by the European metal industry according to Euroslag data in 2004 [3]. Since this material needs a large area for landfilling, of which the availability is insufficient, and to avoid problems related to the leaching of heavy metal and other harmful elements, it would be interesting to upgrade these ‘waste’ products in high-value applications.

Ultra high performance mortar (UHPM) is a mortar with an extremely low water-to-binder ratio, a high binder content and a high strength equal or greater than 150 MPa. In recent years, ultra high performance concrete (UHPC) has been successfully applied in prestressed concrete beams used in bridges with large span lengths and columns in high rise buildings, etc. However, by far the application of mortar is limited in construction projects to building block wall elements and repair of concrete building elements and highway bridges. Regarding the latter, in the USA, the costs for maintenance and repair of this concrete needs 4 billion dollars annually [4]. In order to reduce the high cost of mortar and achieve UHPM with extremely high strength performance, copper slag waste material can be used as supplementary cementitious materials (SCMs). The availability of pozzolanic components in copper slag is an interesting phenomenon to study within UHPM.

Within the cement and concrete industry, copper slag can be used as cementitious material. Looking into literature, it is seen that most researchers use rather low replacement levels up to 15 wt% [5-10]. Their conclusion is that the effect of using copper slag on compressive strength is limited and only in some cases small improvements were noticed. Some researchers used activators such as cement by-pass dust and/or lime, which had no effect [8], a limited effect [6] or improved the long term strength development [8]. In the latter, a blended cement was studied using 15% copper slag and 1.5% lime as activator. They observed a prolonged strength gain after 28 days, up to 90 days, which was absent for the control mixture with no copper slag and lime. In Tixier et al. [5] a positive effect on the compressive strength from adding copper slag was noticed. This copper slag was well crystallized and the fineness of the copper slag was comparable to the one of cement. The latter was not the case for the copper slag used in De Schepper et al. [11] see Figure 1. In this study replacement levels up to 60 wt% in steps of 10 wt% were tested and the contribution of the ground copper slag to the hydration degree of the cement paste was found negligible.

Figure 1: Particle size distribution by laser diffraction of the copper slag (mQCS) and cement

(CEM I 52.5 N) used in De Schepper et al. [11]

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2. MATERIALS AND METHODS

2.1 Materials The copper slag used in this research was a secondary slag from a Belgian recycling plant.

This slag was produced by using waste materials such as copper wires, dust from tin production, old television and radiators from cars as raw materials to generate copper, lead, tin and nickel. The secondary slag was classified as a quickly cooled granulated copper slag (QCS) and a slowly cooled broken copper slag (SCS).

Besides copper slag, an undensified silica fume (type 940U, Elkem) was used as SCM. As cement, a CEM I 52.5 N-HS/NA (low C3A) was used throughout all experiments. An overview of the chemical composition of the binders is given in given in Table 1.

Table 1: Chemical composition of the applied binders determined by XRF analysis [wt%]

Material QCS SCS Cement Silica fume CaO SiO2 Al2O3 Fe2O3 MgO Na2O K2O SO3

7.1 25.9 5.9 45.5 0.8 0.8 0.2 0.4

5.2 29.3 3.2 50.7 0.5 2.0 n/a 0.2

63.7 20.9 3.6 5.2 0.8 0.2 0.6 3.0

0.6 94.2 1.0 0.5 0.7 1.0 1.1 0.3

Table 2 depicts the mortar compositions used in this research. A very low water-to-binder

ratio (w/b: 0.15) was chosen in order to produce ultra high performance mortar (UHPM). To obtain the desired workability, a polycarboxylate ether (Glenium 51, 35 wt%) was used. The mortars were made with copper slag contents varying between 0 and 20 wt% in steps of 5 wt%. For all mortars, a quartz sand (type M31, Sibelco) with a d50 of 0.31 mm was used.

Table 2: The UHPM mixtures with copper slag

Material Control 5% CS 10% CS 15% CS 20% CS CEM I 52.5 N HS/NA Copper slag Silica fume (940 U) Sand M31 Glenium 51 35% solid Water

(g) (g) (g) (g) (g) (g)

8750

218.75962.50

40163.99

831.2543.75

218.75962.50

40163.99

787.5087.50

218.75962.50

40163.99

743.75 131.25 218.75 962.50

40 163.99

700175

218.75962.50

40163.99

2.2 Methods

2.2.1 Grinding process Before using the copper slag as SCM, both QCS and SCS were intensively ground using a

planetary ball mill. A short duration (3 times during 4 minutes at 300 rpm) (SCS I; QCS I) and long duration (5 times during 12 minutes at 300 rpm) (SCS II; QCS II) were chosen in

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order to obtain two levels of fineness to assess the effect of fineness on the reactivity of the copper slag.

The particle size distribution of copper slag and silica fume obtained by laser diffraction is given in Figure 2. To disperse the materials, isopropanol was used since it does not react with copper slag and cement. To avoid agglomeration, the copper slag and cement were put in a sonication bath for 5 minutes before the measurement. In case of silica fume, distilled water was used as dispersant. In order to obtain well de-agglomerated silica fume, this material was sonicated in two steps. At first, the solution containing silica fume and water was put in an ultrasonic bath for 5 minutes to de-agglomerate the particles. After this, 10% superplasticizer by weight of silica fume was added followed by sonication for 15 minutes prior to measurement. An overview of the parameters used to determine the PSD of the SCMs by laser diffraction can be seen in Table 3.

Figure 2: Particle size distribution of binders

Table 3: Overview of the parameters applied to determine the PSD of the different SCMs by laser diffraction

Optical parameters Copper slag Silica fume Cement I 52,5 N HS/NA

Refractive index Absorption coefficient Obscuration (%) Stirrer rate (rpm) Dispersant RI Sonication times (minutes)

1.731 0.055

10 - 20 1700 1.390

5

1.53 0.001

10 - 20 2000 1.33 20

1.73 0.003 5 – 10 1500 1.39

5 In addition to the PSD by laser diffraction, the fineness of the binders was evaluated by

their specific surface area (SSA) using the Blaine air permeability test according to EN 196-6:2010. To start, the pycnometer method was used to measure the density of all binders. Both the density and SSA of the binders are presented in Table 4.

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Table 4: Density and SSA of the different binders

Materials SCS I SCS II QCS I QCS II CEM I SF Density (g/cm3) 4.066 3.976 3.765 3.761 3.152 2.017 SSA (cm2/g) : Blaine permeability Laser diffraction

1503 1530

3155 3170

- 577

2533 2610

4955 5390

- 80200

2.2.2 Mixing Procedure In the mixing process of UHPC, more energy is needed to get the desired workability and

homogeneity of the mixture, which is considered in both the mixing time and speed of the mixer. A mixer with two speeds (140; 285 rpm) was used. The mixing procedure of UHPM is visualized below in Figure 3.

Figure 3: Mixing procedure

2.2.3 Compressive strength testing After curing in a room at relative humidity of 95±5%, the specimens were tested to

evaluate the compressive strength according to NBN EN 196-1 (2005) at the age of 7, 28, 56, and 90 days. The compressive strength machine was set at a loading speed of 1.5 N/mm2/s and a maximum force of 250 kN.

2.2.4 Isothermal Calorimetry Isothermal calorimetry was carried out at 20°C on cement pastes that were mixed manually

using a small container. After 4 minutes of dry mixing, the water and Glenium 51 were added and mixing continued for another 2 minutes. Afterwards, around 14 g of paste was injected into an ampoule using a modified syringe. The water-to-binder ratio of the cement pastes was 0.214. The main reason of the different water-to-binder ratio between mortar and paste in this research was that a cement paste with w/b of 0.15 cannot be mixed manually to obtain a homogeneous mixture . Moreover, the superplasticizer used in this research was a Glenium 51 with a solid content of 35% which can be diluted using water during the mixing time to adjust the consistency of the paste mixture to the one of the mortar mixture. Similar to the mortars, the cement pastes were made with an increasing copper slag content from 0 wt% to 20 wt% in steps of 5 wt%. More details about the paste composition are given in Table 5.

• Cement + copper slag + silica fume1’

• Sand1’

• Water + superplasticizer1.30'

• Full speed4’

• Manual mixing1’

• Full speed1’

• Normal speed2’

140 rpm

140 rpm

285 rpm

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Table 5: Paste composition

Material Control 5% CS 10% CS 15% CS 20% CS CEM I 52.5 N HS/NA Copper slag Silica fume (940U) Glenium 51 35% solidWater

(g) (g) (g) (g) (g)

25 0 6.25 1.14 6.69

23.75 1.25 6.25 1.14 6.69

22.50 2.50 6.25 1.14 6.69

21.25 3.75 6.25 1.14 6.69

20 5 6.25 1.14 6.69

3. RESULTS

3.1 Compressive strength Figure 4 describes the effect of copper slag replacement on the compressive strength of

mortars at 7, 28, 56 and 90 days. In general, the strength of UHPM at 7 days increases with rising copper slag substitution in the mortar mixture. Nevertheless, the strength increase for UHPM with CS between 7 and 90 days was lower than for the reference mortar. This resulted in a strength at 90 days, which was similar or slightly lower for the UHPM with CS than for the reference UHPM. The compressive strength of mortar for nearly all mixtures achieved more than 140 MPa at 90 days of curing. The highest compressive strength (167 MPa) was achieved for 20% copper slag (SCS II) with a fineness of 3155 cm2/g (ground 5 times during 12 minutes at 300 rpm) at 90 days of curing, however, this value is not significantly different from the strength of the control mixture. The lowest mortar strength at 90 days (120 MPa) was obtained for QCS I at 15% replacement. Nevertheless, the fact that the strength of this mix decreased between 56 and 90 d of age needs further investigation. The increased fineness of the copper slag also seemed to enhance mortar strength. This can be seen in figure 5. It can be observed that the mortar strength with 20% replacement of SCS II increases by 18% compared to SCS I at 90 days of curing. Furthermore, this phenomenon also occurred for UHPM using QCS II at 10% replacement which achieved almost 5% improvement compared to QCS I.

Looking into the literature, the small effect of copper slag as cementitious material in this research regarding to mortar strength was similar as for the copper slag used in De Schepper et al. [10] especially for 20wt% mQCS (QCS which was milled 3 times during 4 min at 300 rpm in a planetary ball mill) which was higher in strength development at early age but lower in strength after 7 days of curing compared to reference mixture. The small improvement of concrete strength using copper slag as cement replacement in combination with activators such as cement by-past dust and lime was also achieved by [5,8]. Comparing the result presented in the current paper with the one of the researchers aforementioned, this phenomenon was caused by insufficient fineness of copper slag used in this study to react with cement to form calcium silicate hydrate during the hydration process. In addition to the insufficient fineness of copper slag, the increase of copper slag content in the mixture also delayed the main hydration peak due to the set-inhibiting properties of heavy metal in copper slag [7]. However, a positive effect of copper slag on the compressive strength was achieved by 20% SCS II. This phenomenon can be explained by the fact that physical properties of copper slag allow it to play role as filler in the interface zone of the mortar matrix and reduces porosity [9, 12]. It is worth mentioning that the contribution of copper slag to an enhanced compressive strength is limited in this research.

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(a) QCS I (b) QCS II

(c) SCS I (d) SCS II

Figure 4: Mortar compressive strength results

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Figure 5: Comparison of the mortar strength of four types of copper slag at 90 days

3.2 Isothermal Calorimetry Figure 6 shows the process of the heat production in function of time for all mixes. It is

clear that the second peak starts after about 40 hours, which is relatively late. The maximum value of the heat production rate during the second peak decreases with increasing copper slag replacement. Moreover, the addition of copper slag substitution tends to delay the hydration, except for low replacement levels. This phenomena is probably caused by heavy metals present in the copper slag [6]. It is assumed that Zn plays a role in the delay of the setting time and hydration process of the cement paste containing copper slag. Using glenium 51 in high dosage also postpones the hydration. This superplasticizer, being a carboxylic ether polymer with long lateral chains, disperses the cement particles delaying the hydration process for UHPM. Nonetheless, the amount of superplasticizer cannot be reduced, since it is needed to get the desired workability due to the low water-to-binder ratio. In ongoing experiments, different superplasticizers which have a less pronounced delaying effect, are used.

The cumulative heat production is shown in Figure 7. It is seen that the highest total heat production is achieved for the mix with 5% copper slag. In addition, in this study, an increase of the copper slag amount above 5%, did not further promote the increase of total heat production of the paste. This can be seen in Figure 7 for QCS I, QCS II, and SCS I. On the other hand, it is observed that the maximum values of the cumulative hydration heat are almost identical for all mixes with SCS II, and comparable to the control. These results suggest that the binder reactions are enhanced by replacement of a small part (5%) of Portland cement by copper slag. Larger replacement levels rather delay the hydration reactions. Nevertheless, the use of finely ground slowly cooled copper slag (SCSII) in replacement levels of up to 20%, allows to reach similar overall reaction degrees after 7 days as in a control mixture with Portland cement as only binder.

This phenomenon is seen in spite of the fact that heavy metal compounds such as Zn, Pb, and Cu in copper slag can postpone the hydration of the clinker in the paste.

020406080

100120140160180

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(a) QCS I (b) QCS II

(c) SCS I (d) SCS II

Figure 6: Influence of copper slag addition on the cement hydration

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(a) QCS I (b) QCS II

(c) SCS I (d) SCS II

Figure 7: Total heat production for pastes with copper slag

4. CONCLUSIONS Within this paper the use of copper slag as Supplementary Cementitious Material (SCM) in

Ultra High Performance Mortar (UHPM) was investigated. The following conclusions can be made:

1) The binder reactions in UHPM can be enhanced by replacement of a small part (5%) of Portland cement by copper slag. Larger replacement levels rather delay the hydration reactions. This can be due to the dilution of the clinker content in the paste, to the limited pozzolanic activity of the copper slag, and to heavy metal compounds such as Zn, Pb, and Cu in copper slag.

2) Nevertheless, the use of finely ground slowly cooled copper slag (SCSII) in replacement levels of up to 20%, allows to reach similar overall reaction degrees at 7 days, as in a

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control mixture with Portland cement as only binder. The compressive strength at 7 days is even higher for the mixtures with CS than for the control with OPC. But due to a slower strength development after 7 days of age, similar or slightly lower strengths are obtained for mixes with up to 20% CS as OPC replacement, than for the OPC reference.

3) By increasing the fineness of the copper slag, somewhat higher compressive strengths can be obtained, both for quickly and slowly cooled copper slag.

4) In these experiments, the second peak of heat production occurred about 40 hours after mixing for all mixtures with different copper slag proportions. This delay was mainly caused by the superplasticizer used, being a carboxylic ether polymer with long lateral chains (Glenium 51) which generates cement particles dispersion and delays the hydration process for UHPM.

ACKNOWLEDGEMENTS The author would like to thank the Indonesian Government Scholarship (DIKTI) for

providing the financial support to the PhD research project (2013-2016). Special thanks are addressed to Magnel Laboratory of Ghent University (staff and researchers) for their contribution to this research.

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[4] FHWA-RD-01-156., ‘Corrosion cost and preventive strategies in the United States’, Report by CC Technologies Laboratories, Inc. to Federal Highway Administration (FHWA), Office of Infrastructure Research and Development. 2001.

[5] Tixier. R., Devaguptapu, R, and Mobasher, B., ‘The effect of copper slag on the hydration and mechanical properties of cementitious mixtures’, Cem. Concr. Res. 27 (10) (1997) 1569-1580.

[6] Taha, R., Al-Rawas, A., Al-Jabri, K., Al-Harthy, A., Hassan, H., Al-Oraimi, S., ‘An overview of waste materials recycling in the Sultanate of Oman’, Resources, Conservation and Recycling 41 (4) (2004) 293-306.

[7] Zain, M.F.M., Islam, M.N., Radin, S.S., and Yap, S.G., ‘Cement-based solidification for the safe disposal of blasted copper slag’, Cement and Concrete Composites 26 (7) (2004) 45-851.

[8] Al-Jabri, K.S., Taha, R.A., Al-Hashmi, A., and Al-Harthy, A.S., ‘Effect of copper slag and cement by-pass dust addition on mechanical properties of concrete’, Construction and Building Materials 20 (5) (2006) 322-331.

[9] Shi, C., Meyer, C. and Behnood, A., ‘Utilization of copper slag in cement and concrete’, Resources, Conservation and Recycling 52 (10) (2008) 1115-1120.

[10] Mobasher, B., Devaguptapu, R., and Arino, A.M., ‘Effect of copper slag on the hydration of blended cementitious mixtures’, Materials for the New Millennium, ASCE. (1996).

[11] De Schepper, M., Verle, P., Van Driessche, I., and De Belie, N., ‘Use of secondary slags in completely recyclable concrete’, Journal of Materials in Civil Engineering (2014) (published online)

[12] Moura, W.A., Goncalves, J.P. and Lima, M.B.L., ‘Copper slag waste as a supplementary cementing material to concrete’, Journal of Materials Science 42 (7) (2007) 2226-2230.