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Synthesis of geopolymer from industrial wastes
Accepted Manuscript Synthesis of geopolymer from industrial wastes Ali Nazari, Research Fellow at Centre for Sustainable Infrastructure, Jay G. Sanjayan, Professor at Centre for Sustainable Infrastructure PII:
S0959-6526(15)00220-6
DOI:
10.1016/j.jclepro.2015.03.003
Reference:
JCLP 5267
To appear in:
Journal of Cleaner Production
Received Date: 6 January 2015 Revised Date:
2 March 2015
Accepted Date: 2 March 2015
Please cite this article as: Nazari A, Sanjayan JG, Synthesis of geopolymer from industrial wastes, Journal of Cleaner Production (2015), doi: 10.1016/j.jclepro.2015.03.003. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Synthesis of geopolymer from industrial wastes Ali Nazari*,a and Jay G. Sanjayanb a) Research Fellow at Centre for Sustainable Infrastructure, Faculty of Science, Engineering
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and Technology, Swinburne University of Technology, Victoria, 3122, Australia b) Professor at Centre for Sustainable Infrastructure, Faculty of Science, Engineering and
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Technology, Swinburne University of Technology, Victoria, 3122, Australia
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* Corresponding author, Tel: +61 3 92148370, Email: [email protected]
ABSTRACT
Aluminium and grey cast iron slags are produced in small industries and in spite of
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blastfurnace slag are considered as wastes. In this work, synthesis possibility of geopolymeric paste and concrete through alkali activation of different mixes of these slags is studied. Workability of the mixtures was achieved immediately after mixing and compressive strength
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tests were conducted on specimens cured at room temperature. Workability of all pastes and concrete specimens were in acceptable range for use in constructions. Maximum compressive
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strength for both paste and concrete specimens was achieved by using silica/alumina weight ratio of 3.0. By increasing the value of parameters of this study including sodium hydroxide concentration, age of curing and silica/alumina weight ratio, more silicon and aluminium ions dissolve from slag mixture into alkali activator and hence, compressive strength increases. It was concluded that among the considered parameters, silica/alumina weight ratio is the most important factor. The results indicated the possibility of production of geopolymers by utilizing appropriate ratios of aluminium slag (alumina source) and grey cast iron slag (silica source). In most related works reported in the literature, an aluminosilicate source or a 1
ACCEPTED MANUSCRIPT mixture of two aluminosilicate sources with defined silica/alumina weight ratio are evaluated for possibility of geopolymerization. In the current study, each alumina and silica is provided from an individual source, and geopolymerization is performed by manipulating
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silica/alumina weight ratio.
Keywords: Slag mixtures; alkali-activated materials; waste management; compressive
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strength; workability
1. Introduction
Emission of greenhouse gases through industrial activities is of major impact on global warming. It is believed that at least 5-7 % of CO2 release to the atmosphere is due to
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the production of ordinary Portland cement (OPC) (Heath et al., 2014). Geopolymers, ecofriendly materials with much lower carbon dioxide (CO2) emissions produced from industrial by-products such as fly ash, slag or metakaolin are considered as the main possible low
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carbon alternative to Portland cement concrete (Flower and Sanjayan, 2007). This has led to significant research activities around the world in geopolymers in recent years. This is
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demonstrated in the number of research publications in this field and shows the enormous efforts by research community around the world in developing alternative concretes to reduce global carbon emissions (Topçu et al., 2014). Based on the research publications, it is evident that Australia is a leader in this field. Australia is also leading the world in the number of field applications where geopolymer concrete has been applied in real world constructions (Shayan et al., 2013). A number of these geopolymer constructions are located in Melbourne as a result of VicRoads’ (Road Authority in Victoria) pioneering position in allowing the use
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ACCEPTED MANUSCRIPT of geopolymer and setting in place the guidelines for the use of geopolymer concrete as detailed by Andrews-Phaedonos (2011 and 2012). Slags from extracting metal processes are conventionally considered as waste materials. However, new insights into their potential capabilities including high porous
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structure (Ismail et al., 2013) and availability of amorphous oxides (Pontikes et al., 2013) make them as a suitable reactive material for incorporating into different concrete mixtures. These mixtures vary from traditional OPC concrete (Otieno et al., 2014) to bitumen concrete
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(Xie et al., 2013) and geopolymer concrete specimens (Puligilla and Mondal, 2013).
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Geopolymer as a construction material, with the main structural framework of aluminosilicate skeleton in comparison with calcium silicate hydrate structure of OPC binders (Kusbiantoro et al., 2013), is produced from silica- and alumina-rich by-products (Ryu et al., 2013). Various types of slags are used individually or as a partial replacement of fly ash to produce geopolymers. Islam et al. (2014) produced lightweight geopolymers by
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using ground granulated blastfurnace slag, palm oil fuel ash, and low calcium fly ash. Nath and Kumar (2013) studied the influence of iron making slag on microstructure and strength
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assessments of fly ash based geopolymers. Pulligilla and Mondal (2013) produced geopolymers by class F fly ash and ground granulated blastfurnace slag. Utilization of
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blastfurnace slag to produce geopolymers is also reported in some other works, for example Yusuf et al., 2014. Ogundiran et al. (2012) studied the solidification/stabilisation and immobilisation of lead smelting slag through its incorporation into coal fly ash-blastfurnace slag based geopolymers. Alex et al. (2013) used zinc slag generated during imperial smelting process to produce geopolymers. Onisei et al. (2012) produced geopolymers using fly ash and primary lead slag. For a comprehensive study on the influence of slag on properties of geopolymers, Rashad (2013) has collected the works conducted on this area. Although blastfurnace slag can be considered as the most convenient precursor for 3
ACCEPTED MANUSCRIPT slag-based geopolymers, the other slags produced from smaller industries can be considered as well. On the other hand, most utilized slags reported in the literature have a high content of lime (CaO). The used aluminosilicate in the current work has a low amount of CaO, which makes it similar to class F fly ashes. In the present study, different ratios of cast iron and
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aluminium slags are considered for production of geopolymers. Cast iron and aluminium slags are silica-rich and alumina-rich sources respectively, and their mixtures may be considered as an aluminosilicate source. Production of geopolymer mixtures from one of
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these sources does not result in high performance geopolymers due to their unsuitable silica
2. Materials and methods
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to alumina weight ratios.
The materials used in this study were aluminium slag, grey cast iron slag, sodium
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silicate solution, sodium hydroxide solution (NaOH), superplasticizer and sands. Mixtures of aluminium and grey cast iron slags were used as aluminosilicate source. Alkali activation of the aluminosilicate source was performed by a mixture of sodium silicate solution and NaOH.
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Sands were used as aggregates in geopolymer concrete specimens.
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Aluminium slag was fine enough and subjected to crushing for only one hour by a jar mill. Grey cast iron slag was rough and at first, was broken to small pieces by hammer. The as-received slags are shown in Fig. 1. After that, the slag powder was jar-milled by stainless steel balls for four hours. The slag powder to stainless steel balls weight ratio was 7:10, where the ball sizes varied between 4 and 10 mm. When the powders became fine, to avoid agglomeration, 2 wt% of methanol was added to the powder as surfactant. The milling speed was 100 rpm. The average particle size of aluminium and grey cast iron slags were 13 and 18 µm respectively. Fig. 2 illustrates the particle size distribution pattern for both aluminium and 4
ACCEPTED MANUSCRIPT grey cast iron slags after milling process obtained by the ASTM C115 / C115M-10e1 standard (2010). Table 1 shows the chemical composition of both slags obtained by ARL 8410 XRF spectrometer.
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NaOH flakes were dissolved in distilled water to achieve different concentrations of 8, 12 and 16 M. As-received sodium silicate with the chemical composition in accordance to Table 1 was mixed by cooled-down NaOH solutions with the constant weight ratio of 2.5:1. The resultant mixture is called alkali activator and was introduced to the cementitious
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mixtures after cooling at room temperature for 4 h. To increase the workability of the
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mixtures, 1wt% of the alkali activator was replaced by polycarboxylate superplasticizer, which has been demonstrated to be suitable for low calcium aluminosilicate sources (Nematollahi and Sanjayan, 2014).
Locally available natural sands with the particle size less than 2 mm and specific
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gravity of 2.72 g/cm3 were used as aggregates in geopolymer concrete specimen. The weight percentage of aggregates in concrete specimens was 70. Fig. 3 shows particle size distribution of sand particles obtained by the ASTM C136-06 (2006) standard.
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In total, four different slag mixtures were used. The selected aluminium slag to grey
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cast iron slag ratios were 20:80, 30:70, 60:40, and 50:50. For geopolymer pastes, the only cementitious material was slags mixture while for geopolymer concrete, the cementitious materials were slags mixture and aggregates. The cementitious mixtures were dry-mixed for one minute to attain the maximum possible homogeneity. Alkali activator was mixed by cementitious materials and stirred for five minutes. Alkali solution to slags mixture weight ratio for all specimens was 0.35. Sample designation and mixture proportions have been given in Table 2. Workability and compressive strength of specimens were acquired as characteristics 5
ACCEPTED MANUSCRIPT of specimens. Slumps of the fresh mixtures were evaluated immediately after mixing completion to determine the workability of the mixtures in accordance to the ASTM C143/ C143M-12 (2012) standard. Cubic specimens with the dimension of 50 × 50 × 50 mm3 were used to determine compressive strength in accordance to the ASTM C109/ C109M-13 (2013)
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standard. Specimens were poured into the moulds in one layer and vibrated for 45 s to reduce air bubbles. Subsequently, specimens were left in their moulds for 24 hours of pre-curing, while were covered by a polyester sheet to reduce carbonation. After de-moulding, specimens
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were cured for 1, 7 and 28 days at room temperature. Against with fly ash-based geopolymers, which require oven curing for specific time (Hanjitsuwan et al., 2013), slag-
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based geopolymers are capable to cure at room temperature. Geopolymers are supposed to gain their strength within few days of curing and evaluation of their strength at 1 and 7 days of curing should be enough. However, since 28-day compressive strength of concrete specimens is of high importance, this age is examined in this study as well. The reported
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compressive strength results were the average values of three trials. Fig. 4 illustrates a specimen under compressive strength testing.
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Microstructure of specimens was studied using a VEGA TESCAN scanning electron
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microscopy (SEM) apparatus in secondary electron mode.
3. Results and discussion
The analysis methods for evaluating the performance of geopolymer paste and
concrete in this study were workability of fresh mixtures, compressive strength of hardened specimens and electron microscopy. Results arisen from different geopolymeric mixtures are presented separately in this section.
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3.1. Workability
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Fig. 5 and Fig. 6 display the workability of geopolymeric paste and concrete specimens respectively. Workability of both paste and concrete samples are in medium range, suitable for various applications in this range. For example, according to EN 206-1 (2013)
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code, 10-40 mm slump value belongs to S1 which is suitable roller compacted concrete or
and hand-placed pavements.
3.2. Compressive strength
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interlocking paving block productions. 50-90 mm slump value is for S2 appropriate for floors
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Compressive strength of the geopolymeric paste and concrete specimens at 1, 7 and 28 days of curing has been illustrated in Fig. 7 and Fig. 8. For both geopolymeric paste and concrete, by increasing the age of curing, the compressive strength increases as well.
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Additionally, the compressive strength of concrete specimens is much higher in comparison
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with their corresponding paste showing the importance of utilizing aggregates in the suggested mixtures. The minimum strength is 19.8 MPa for geopolymeric paste with NaOH concentration of 8 M and silica/alumina (SiO2/Al2O3) weight ratio of 1.6 at 1 day of curing. The maximum strength is 72.3 MPa for geopolymeric concrete with NaOH concentration of 16 M and SiO2/Al2O3 weight ratio of 3.0 at 28 days of curing. Porous slags result in high strengths because of their degree of reaction and higher content of amorphous materials (Oh et al, 2010). It is worthwhile to note that most slags researched in the literature have a high Ca content, so whether it is the desirable blastfurnace slag or the undesirable metallurgical or 7
ACCEPTED MANUSCRIPT steel slags, the gel that forms is Ca-based and hence of a calcium-(sodium)-alkali-silicatehydrate [C-(N)-A-S-H] nature. That is not the case here, as both slags used are very low in Ca, so that the classical N-A-S-H phase is anticipated to form. In fact, the gel formed here is expected to be similar to that formed from silicate activation of Class F fly ash. However, the
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ash sometimes reacts slower so that room temperature curing is not possible.
Fig. 7 shows the compressive strength of the geopolymeric pastes at different curing ages. At all ages and NaOH concentrations, the maximum and minimum compressive
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strengths are attainable by SiO2/Al2O3 weight ratio of 3.0 and 1.6 respectively. It has been
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reported that different SiO2/Al2O3 weight ratios alter the mechanisms of geopolymeric reactions depending on the curing ages (Sagoe-Crentsil and Weng, 2007). The compressive strength of specimens with SiO2/Al2O3 weight ratios of 4.7 and 2.1 is a value between these intervals. For the specimen with NaOH concentration of 8 M the difference between strength values has a regular pattern. By increasing the concentration of NaOH to 12 and 16 M, the
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compressive strength of specimens with SiO2/Al2O3 weight ratio of 4.7, 3.0 and 2.1 approaches together, especially at later ages. This indicates that for this system, NaOH
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concentration has a key role on compressive strength of specimens with SiO2/Al2O3 weight ratio of more than 2. When the concentration of NaOH increases, dissolution of silicon ion
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(Si4+) and aluminium ion (Al3+) from the cementitious mixture becomes easier and more geopolymeric reactions occurs (Hanjitsuwan et al., 2014; De Vargas et al., 2011). This is more evident at later ages because the reaction between cementitious mixture and alkali activator in geopolymeric pastes with high concentration of NaOH may be retarded. It has been suggested that formation of some complex compounds reduces the kinetic of aluminosilicate reactions (Riahi and Nazari, 2012). This phenomenon mainly depends on the thickness of the sections and is more evident in the specimen’s centre. For the whole SiO2/Al2O3 ratios and at any ages of curing, regardless of SiO2/Al2O3 8
ACCEPTED MANUSCRIPT ratio of 1.6 and 28 days of curing age, the compressive strength increases by raising the NaOH molarity. At higher SiO2/Al2O3 ratios, the difference between the compressive strength of specimens with high (12 and 16 M) and medium (8 M) NaOH concentrations at 7 days of curing age is considerable. However, at 28 days of curing age, the compressive
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strengths are close. From the economical viewpoint and for regular constructions, it may be better to use lower concentrations and later ages. This is beneficial for slag-based geopolymers, which can be made by in-situ production. This is in spite of fly ash-based ones
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that are made as ready-to-use parts in factories.
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Fig. 8 illustrates the compressive strength of the geopolymeric concrete specimens at different curing ages. Same as geopolymeric pastes, the highest compressive strength of specimens at every age of curing is related to those with SiO2/Al2O3 weight ratio of 3.0. Although specimens with SiO2/Al2O3 weight ratio of 1.6 revealed a reasonable compressive strength at NaOH concentration of 8 M, by increasing the concentration to 12 and 16 M, they
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show the minimum compressive strength at all ages. As the figure shows, there is a considerable difference between the strength of the specimen with SiO2/Al2O3 weight ratio of
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3.0 by the other specimens at 28 days of curing age and all NaOH concentrations. For NaOH concentration of 8 M, this difference for SiO2/Al2O3 weight ratios of 4.7, 2.1 and 1.6 is +20.8,
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+8.70 and +13.5 % respectively. For NaOH concentration of 12 M, this difference for SiO2/Al2O3 weight ratios of 4.7, 2.1 and 1.6 is +9.00, +12.7 and +20.1 % respectively. Finally, for NaOH concentration of 16 M, this difference for SiO2/Al2O3 weight ratios of 4.7, 2.1 and 1.6 is +13.7, +14.8 and +30.3 % respectively. Although for geopolymeric pastes high NaOH concentration retards geopolymeric reactions, in concrete form, the paste is distributed between the aggregates and hence, the thickness of the paste sections is not high to retard the reactions (Riahi and Nazari, 2012). On the whole, the best compressive strength for geopolymeric paste and concrete specimens is achieved by utilizing SiO2/Al2O3 weight ratio 9
ACCEPTED MANUSCRIPT of 3.0. The results obtained from this study show the possibility of using these geopolymers in construction technology. Collins and Sanjayan (1999) were one of the first authors who
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indicated the ability of using alkali-activated slags in construction. They used blastfurnace slag as aluminosilicate source and achieved compressive strength values up to 60 MPa. This is while compressive strength of their examined OPC concrete is up to 50 MPa. Wang et al. (2014) have acquired compressive strength of up to 80 MPa for their alkali-activated slags.
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Comparison between compressive strength of geopolymers in this study and the literature
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show that those in this study fall within the acceptable range. The normal compressive strength of a concrete specimen for using in construction technology should be determined by using American Concrete Institute (ACI) codes. According to ACI 318 and 322 codes, a concrete specimen for residential purposes must have a compressive strength of at least 4500 psi (31 MPa). All of the geopolymer concrete mixtures studied in this paper are therefore
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appropriate for construction application not only when compared with OPC concrete but with
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available alkali-activated slags.
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3.3. Microstructure
SEM micrograph of fracture surface of specimens has been illustrated in Fig. 9.
SiO2/Al2O3 weight ratio for microstructures in Fig. 9a and Fig. 9b is 3.0, in Fig. 9c and Fig. 9d is 4.7, in Fig. 9e and Fig. 9f is 2.1 and in Fig. 9g and Fig. 9h is 1.6. Fig. 9a, Fig. 9c, Fig. 9e and Fig. 9g show microstructure of specimens with NaOH concentration of 8 M and Fig. 9b, Fig. 9d, Fig. 9f and Fig. 9h show that of specimens with NaOH concentration of 16 M. As it is obvious, concentration of NaOH has not a major effect on microstructure of specimens. This can, for example, be seen when Fig. 9a and Fig. 9b are compared. The pastes in these 10
ACCEPTED MANUSCRIPT two figures are similar and seem dense. For SiO2/Al2O3 weight ratios of 4.7 (Fig. 9c and Fig. 9d) and 2.1 (Fig. 9e and Fig. 9f), paste is still dense but some particles are separated from the paste indicating crack branching in weak points. A propagating crack can branch to the weak phases and accelerate fracture of a specimen and hence, decrease compressive strength. The
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weakest paste is seen in Fig. 9g and Fig. 9h with SiO2/Al2O3 weight ratio of 1.6. The paste here is not homogeneous and some coarse geopolymeric particles are observed separated
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from the paste. This is especially more evident for NaOH concentration of 8 M (Fig. 9g).
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5. Conclusions
Compressive strength and workability of the geopolymeric paste and concrete specimens made from different ratios of aluminium and grey cast iron slags were studied. Four different ratios of grey cast iron slag to aluminium slag were considered including
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80/20, 70/30, 60/40 and 50/50. By considering the amount of SiO2 in sodium silicate, SiO2/Al2O3 ratios of specimens were 4.7, 3.0, 2.1 and 1.6. Concentrations for NaOH solutions were 8, 12 and 16 M. Compressive strength of specimens was attained at 1, 7 and 28 days of
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curing, where their suitability for casting were examined on fresh mixes by workability tests.
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Workability of the whole specimens fell within the acceptable range for casting paste and concrete mixtures. By increasing the age of room temperature curing, the compressive strength of specimens increased. It was concluded that slag-based geopolymer can be suitably synthesized at room temperature. Specimens with SiO2/Al2O3 weigh ratio of 3.0 revealed higher strengths. The strength of specimens with SiO2/Al2O3 weigh ratios of 2.1 and 4.7 in most cases were close. Because of high required mechanical work for preparing grey cast iron slags, specimens with SiO2/Al2O3 weigh ratio of 2.1 and 3.0 can be the most appropriate mixture proportions. Specimens with NaOH concentration of 16 M revealed higher strength 11
ACCEPTED MANUSCRIPT especially at 28 days of curing. Specimens at early ages have relatively similar strengths. It was concluded that higher concentrations causes the formation of complex compounds retard the geopolymerization process. At later ages, because of the suitable amount of Si4+ and Al3+ dissolved from slag mixture into alkali activator with 16 M NaOH concentration,
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geopolymeric reaction completes and higher strengths are attained. Aluminium and grey cast iron slags are alumina- and silica-rich sources respectively. All conducted works on geopolymers indicate the necessity of providing aluminosilicate from one source. In this
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study, successful synthesis of geopolymers demonstrates the capability of binary blended mixtures for use as aluminosilicate sources. Its superiority can be manipulating SiO2/Al2O3
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weight ratios to achieve the desired properties.
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ACCEPTED MANUSCRIPT Table 1. Chemical composition of fly ashes and sodium silicate (Wt.%) which were utilized in this work. Grey cast iron slag
Sodium silicate
SiO2
8.35
63.6
34.5
Al2O3
60.8
2.68
-
Fe2O3
2.35
17.3
CaO
5.21
1.45
SO3
2.84
0.48
Na2O
2.75
2.08
13.1
K2O
0.80
0.31
-
Cr2O3
0.14
Cl
2.35
V2O5
0.05
La & Lu
0.30
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Aluminium slag
-
-
-
1.32
-
0.08
-
0.62
-
8.89
0.84
-
0.12
0.59
-
0.10
0.06
-
0.09
6.27
-
1.82
0.04
-
CuO
1.05
0.12
-
H2O
-
-
52.4
L.O.I.
1.99
1.68
-
TiO2 P2O5 MnO
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ZnO
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MgO
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0.48
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ACCEPTED MANUSCRIPT Table 2. Sample designation and their characteristics which were produced in this work. NaOH concentrati on (M)
SiO2 conten t of binder (Kg/m 3 )
Al2O3 conten t of binder (Kg/m 3 )
SiO2/Al2 O3 weigh ratio of binder
2.9
10.3
8
1187
254
4.7
733
293
10.3
12
1187
254
4.7
0
733
293
10.3
16
1187
254
4.7
1326.3
0
729
292
10.2
8
1084
356
3.0
568.4
1326.3
0
729
292
10.2
12
1084
356
3.0
G6
568.4
1326.3
0
729
292
10.2
16
1084
356
3.0
G7
754
1131
0
725
290
10.2
8
981
457
2.1
G8
754
1131
0
725
290
10.2
12
981
457
2.1
G9
754
1131
0
725
290
10.2
16
981
457
2.1
G10
937.6
937.6
0
721
289
10.1
8
879
556
1.6
G11
937.6
937.6
0
721
289
10.1
12
879
556
1.6
G12
937.6
937.6
0
721
289
10.1
16
879
556
1.6
G13
108.5
434.2
1948
209
83.5
2.90
8
338
72
4.7
G14
108.5
434.2
1948
209
83.5
2.90
12
338
72
4.7
G15
108.5
434.2
1948
209
83.5
2.90
16
338
72
4.7
G16
162.6
379.3
1945
208
83.4
2.90
8
310
102
3.0
G17
162.6
G18
162.6
380.9
1523.6
0
733
G2
380.9
1523.6
0
G3
380.9
1523.6
G4
568.4
G5
EP 379.3
1945
208
83.4
2.90
12
310
102
3.0
379.3
1945
208
83.4
2.90
16
310
102
3.0
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G19
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G1
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Aluminiu m slag
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Superplastici zer
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Quantities of materials (Kg/m3) Grey Aggre Sodiu NaO cast iron gates m H slag silicat e
Sample designati on
216.4
324.6
1942
208
83.2
2.90
8
282
131
2.1
216.4
324.6
1942
208
83.2
2.90
12
282
131
2.1
216.4
324.6
1942
208
83.2
2.90
16
282
131
2.1
269.9
269.9
1938
207
83.0
2.90
8
253
160
1.6
G23
269.9
269.9
1938
207
83.0
2.90
12
253
160
1.6
G24
269.9
269.9
1938
207
83.0
2.90
16
253
160
1.6
G20 G21 G22
18
ACCEPTED MANUSCRIPT 3 cm
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3 cm
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EP
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Fig. 1. As received materials a) aluminium slag and b) grey cast iron slag which were used in this study.
19
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EP
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Fig. 2. Particle size distribution of aluminium and grey cast iron slags after milling are shown in terms of their cumulative percentage.
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Fig. 3. Particle size distribution of fine aggregates is shown as their cumulative percentage.
21
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Fig. 4. Compressive strength of a specimen is being tested.
22
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(a)
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(b)
(c) Fig. 5. Workability of fresh geopolymer mixtures has been given at different concentrations of NaOH; a) geopolymer paste, b) geopolymer concrete, and c) percentage of reduction in workability due to incorporating aggregates. 23
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(a)
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(b)
(c) Fig. 6. Workability of fresh geopolymer mixtures has been given at different SiO2/Al2O3 weight ratios; a) geopolymer paste, b) geopolymer concrete, and c) percentage of reduction in workability due to incorporating aggregates. 24
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(a)
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(b)
(c) Fig. 7. Effect of curing age on compressive strength of the geopolymeric pastes has been shown at different SiO2/Al2O3 weight ratios.
25
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(a)
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(b)
(c) Fig. 8. Effect of curing age on compressive strength of the geopolymeric concrete specimens has been shown at different SiO2/Al2O3 weight ratios.
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(b)
(c)
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(a)
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(e)
(f)
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(d)
(g)
(h)
Fig. 9. Microstructure of a) G1, b) G3, c) G4, d) G6, e) G7, f) G9, g) G10 and h) G12 specimens show different features.
27
ACCEPTED MANUSCRIPT Geopolymers were synthesised by different mixtures of aluminium and grey cast iron slags.
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Compressive strength and workability were conducted to evaluate performance criteria.
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Green geopolymers with suitable properties are achievable by using these waste materials.
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S0959-6526(15)00220-6
DOI:
10.1016/j.jclepro.2015.03.003
Reference:
JCLP 5267
To appear in:
Journal of Cleaner Production
Received Date: 6 January 2015 Revised Date:
2 March 2015
Accepted Date: 2 March 2015
Please cite this article as: Nazari A, Sanjayan JG, Synthesis of geopolymer from industrial wastes, Journal of Cleaner Production (2015), doi: 10.1016/j.jclepro.2015.03.003. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Synthesis of geopolymer from industrial wastes Ali Nazari*,a and Jay G. Sanjayanb a) Research Fellow at Centre for Sustainable Infrastructure, Faculty of Science, Engineering
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and Technology, Swinburne University of Technology, Victoria, 3122, Australia b) Professor at Centre for Sustainable Infrastructure, Faculty of Science, Engineering and
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Technology, Swinburne University of Technology, Victoria, 3122, Australia
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* Corresponding author, Tel: +61 3 92148370, Email: [email protected]
ABSTRACT
Aluminium and grey cast iron slags are produced in small industries and in spite of
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blastfurnace slag are considered as wastes. In this work, synthesis possibility of geopolymeric paste and concrete through alkali activation of different mixes of these slags is studied. Workability of the mixtures was achieved immediately after mixing and compressive strength
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tests were conducted on specimens cured at room temperature. Workability of all pastes and concrete specimens were in acceptable range for use in constructions. Maximum compressive
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strength for both paste and concrete specimens was achieved by using silica/alumina weight ratio of 3.0. By increasing the value of parameters of this study including sodium hydroxide concentration, age of curing and silica/alumina weight ratio, more silicon and aluminium ions dissolve from slag mixture into alkali activator and hence, compressive strength increases. It was concluded that among the considered parameters, silica/alumina weight ratio is the most important factor. The results indicated the possibility of production of geopolymers by utilizing appropriate ratios of aluminium slag (alumina source) and grey cast iron slag (silica source). In most related works reported in the literature, an aluminosilicate source or a 1
ACCEPTED MANUSCRIPT mixture of two aluminosilicate sources with defined silica/alumina weight ratio are evaluated for possibility of geopolymerization. In the current study, each alumina and silica is provided from an individual source, and geopolymerization is performed by manipulating
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silica/alumina weight ratio.
Keywords: Slag mixtures; alkali-activated materials; waste management; compressive
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strength; workability
1. Introduction
Emission of greenhouse gases through industrial activities is of major impact on global warming. It is believed that at least 5-7 % of CO2 release to the atmosphere is due to
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the production of ordinary Portland cement (OPC) (Heath et al., 2014). Geopolymers, ecofriendly materials with much lower carbon dioxide (CO2) emissions produced from industrial by-products such as fly ash, slag or metakaolin are considered as the main possible low
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carbon alternative to Portland cement concrete (Flower and Sanjayan, 2007). This has led to significant research activities around the world in geopolymers in recent years. This is
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demonstrated in the number of research publications in this field and shows the enormous efforts by research community around the world in developing alternative concretes to reduce global carbon emissions (Topçu et al., 2014). Based on the research publications, it is evident that Australia is a leader in this field. Australia is also leading the world in the number of field applications where geopolymer concrete has been applied in real world constructions (Shayan et al., 2013). A number of these geopolymer constructions are located in Melbourne as a result of VicRoads’ (Road Authority in Victoria) pioneering position in allowing the use
2
ACCEPTED MANUSCRIPT of geopolymer and setting in place the guidelines for the use of geopolymer concrete as detailed by Andrews-Phaedonos (2011 and 2012). Slags from extracting metal processes are conventionally considered as waste materials. However, new insights into their potential capabilities including high porous
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structure (Ismail et al., 2013) and availability of amorphous oxides (Pontikes et al., 2013) make them as a suitable reactive material for incorporating into different concrete mixtures. These mixtures vary from traditional OPC concrete (Otieno et al., 2014) to bitumen concrete
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(Xie et al., 2013) and geopolymer concrete specimens (Puligilla and Mondal, 2013).
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Geopolymer as a construction material, with the main structural framework of aluminosilicate skeleton in comparison with calcium silicate hydrate structure of OPC binders (Kusbiantoro et al., 2013), is produced from silica- and alumina-rich by-products (Ryu et al., 2013). Various types of slags are used individually or as a partial replacement of fly ash to produce geopolymers. Islam et al. (2014) produced lightweight geopolymers by
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using ground granulated blastfurnace slag, palm oil fuel ash, and low calcium fly ash. Nath and Kumar (2013) studied the influence of iron making slag on microstructure and strength
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assessments of fly ash based geopolymers. Pulligilla and Mondal (2013) produced geopolymers by class F fly ash and ground granulated blastfurnace slag. Utilization of
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blastfurnace slag to produce geopolymers is also reported in some other works, for example Yusuf et al., 2014. Ogundiran et al. (2012) studied the solidification/stabilisation and immobilisation of lead smelting slag through its incorporation into coal fly ash-blastfurnace slag based geopolymers. Alex et al. (2013) used zinc slag generated during imperial smelting process to produce geopolymers. Onisei et al. (2012) produced geopolymers using fly ash and primary lead slag. For a comprehensive study on the influence of slag on properties of geopolymers, Rashad (2013) has collected the works conducted on this area. Although blastfurnace slag can be considered as the most convenient precursor for 3
ACCEPTED MANUSCRIPT slag-based geopolymers, the other slags produced from smaller industries can be considered as well. On the other hand, most utilized slags reported in the literature have a high content of lime (CaO). The used aluminosilicate in the current work has a low amount of CaO, which makes it similar to class F fly ashes. In the present study, different ratios of cast iron and
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aluminium slags are considered for production of geopolymers. Cast iron and aluminium slags are silica-rich and alumina-rich sources respectively, and their mixtures may be considered as an aluminosilicate source. Production of geopolymer mixtures from one of
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these sources does not result in high performance geopolymers due to their unsuitable silica
2. Materials and methods
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to alumina weight ratios.
The materials used in this study were aluminium slag, grey cast iron slag, sodium
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silicate solution, sodium hydroxide solution (NaOH), superplasticizer and sands. Mixtures of aluminium and grey cast iron slags were used as aluminosilicate source. Alkali activation of the aluminosilicate source was performed by a mixture of sodium silicate solution and NaOH.
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Sands were used as aggregates in geopolymer concrete specimens.
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Aluminium slag was fine enough and subjected to crushing for only one hour by a jar mill. Grey cast iron slag was rough and at first, was broken to small pieces by hammer. The as-received slags are shown in Fig. 1. After that, the slag powder was jar-milled by stainless steel balls for four hours. The slag powder to stainless steel balls weight ratio was 7:10, where the ball sizes varied between 4 and 10 mm. When the powders became fine, to avoid agglomeration, 2 wt% of methanol was added to the powder as surfactant. The milling speed was 100 rpm. The average particle size of aluminium and grey cast iron slags were 13 and 18 µm respectively. Fig. 2 illustrates the particle size distribution pattern for both aluminium and 4
ACCEPTED MANUSCRIPT grey cast iron slags after milling process obtained by the ASTM C115 / C115M-10e1 standard (2010). Table 1 shows the chemical composition of both slags obtained by ARL 8410 XRF spectrometer.
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NaOH flakes were dissolved in distilled water to achieve different concentrations of 8, 12 and 16 M. As-received sodium silicate with the chemical composition in accordance to Table 1 was mixed by cooled-down NaOH solutions with the constant weight ratio of 2.5:1. The resultant mixture is called alkali activator and was introduced to the cementitious
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mixtures after cooling at room temperature for 4 h. To increase the workability of the
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mixtures, 1wt% of the alkali activator was replaced by polycarboxylate superplasticizer, which has been demonstrated to be suitable for low calcium aluminosilicate sources (Nematollahi and Sanjayan, 2014).
Locally available natural sands with the particle size less than 2 mm and specific
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gravity of 2.72 g/cm3 were used as aggregates in geopolymer concrete specimen. The weight percentage of aggregates in concrete specimens was 70. Fig. 3 shows particle size distribution of sand particles obtained by the ASTM C136-06 (2006) standard.
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In total, four different slag mixtures were used. The selected aluminium slag to grey
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cast iron slag ratios were 20:80, 30:70, 60:40, and 50:50. For geopolymer pastes, the only cementitious material was slags mixture while for geopolymer concrete, the cementitious materials were slags mixture and aggregates. The cementitious mixtures were dry-mixed for one minute to attain the maximum possible homogeneity. Alkali activator was mixed by cementitious materials and stirred for five minutes. Alkali solution to slags mixture weight ratio for all specimens was 0.35. Sample designation and mixture proportions have been given in Table 2. Workability and compressive strength of specimens were acquired as characteristics 5
ACCEPTED MANUSCRIPT of specimens. Slumps of the fresh mixtures were evaluated immediately after mixing completion to determine the workability of the mixtures in accordance to the ASTM C143/ C143M-12 (2012) standard. Cubic specimens with the dimension of 50 × 50 × 50 mm3 were used to determine compressive strength in accordance to the ASTM C109/ C109M-13 (2013)
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standard. Specimens were poured into the moulds in one layer and vibrated for 45 s to reduce air bubbles. Subsequently, specimens were left in their moulds for 24 hours of pre-curing, while were covered by a polyester sheet to reduce carbonation. After de-moulding, specimens
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were cured for 1, 7 and 28 days at room temperature. Against with fly ash-based geopolymers, which require oven curing for specific time (Hanjitsuwan et al., 2013), slag-
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based geopolymers are capable to cure at room temperature. Geopolymers are supposed to gain their strength within few days of curing and evaluation of their strength at 1 and 7 days of curing should be enough. However, since 28-day compressive strength of concrete specimens is of high importance, this age is examined in this study as well. The reported
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compressive strength results were the average values of three trials. Fig. 4 illustrates a specimen under compressive strength testing.
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Microstructure of specimens was studied using a VEGA TESCAN scanning electron
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microscopy (SEM) apparatus in secondary electron mode.
3. Results and discussion
The analysis methods for evaluating the performance of geopolymer paste and
concrete in this study were workability of fresh mixtures, compressive strength of hardened specimens and electron microscopy. Results arisen from different geopolymeric mixtures are presented separately in this section.
6
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3.1. Workability
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Fig. 5 and Fig. 6 display the workability of geopolymeric paste and concrete specimens respectively. Workability of both paste and concrete samples are in medium range, suitable for various applications in this range. For example, according to EN 206-1 (2013)
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code, 10-40 mm slump value belongs to S1 which is suitable roller compacted concrete or
and hand-placed pavements.
3.2. Compressive strength
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interlocking paving block productions. 50-90 mm slump value is for S2 appropriate for floors
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Compressive strength of the geopolymeric paste and concrete specimens at 1, 7 and 28 days of curing has been illustrated in Fig. 7 and Fig. 8. For both geopolymeric paste and concrete, by increasing the age of curing, the compressive strength increases as well.
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Additionally, the compressive strength of concrete specimens is much higher in comparison
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with their corresponding paste showing the importance of utilizing aggregates in the suggested mixtures. The minimum strength is 19.8 MPa for geopolymeric paste with NaOH concentration of 8 M and silica/alumina (SiO2/Al2O3) weight ratio of 1.6 at 1 day of curing. The maximum strength is 72.3 MPa for geopolymeric concrete with NaOH concentration of 16 M and SiO2/Al2O3 weight ratio of 3.0 at 28 days of curing. Porous slags result in high strengths because of their degree of reaction and higher content of amorphous materials (Oh et al, 2010). It is worthwhile to note that most slags researched in the literature have a high Ca content, so whether it is the desirable blastfurnace slag or the undesirable metallurgical or 7
ACCEPTED MANUSCRIPT steel slags, the gel that forms is Ca-based and hence of a calcium-(sodium)-alkali-silicatehydrate [C-(N)-A-S-H] nature. That is not the case here, as both slags used are very low in Ca, so that the classical N-A-S-H phase is anticipated to form. In fact, the gel formed here is expected to be similar to that formed from silicate activation of Class F fly ash. However, the
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ash sometimes reacts slower so that room temperature curing is not possible.
Fig. 7 shows the compressive strength of the geopolymeric pastes at different curing ages. At all ages and NaOH concentrations, the maximum and minimum compressive
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strengths are attainable by SiO2/Al2O3 weight ratio of 3.0 and 1.6 respectively. It has been
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reported that different SiO2/Al2O3 weight ratios alter the mechanisms of geopolymeric reactions depending on the curing ages (Sagoe-Crentsil and Weng, 2007). The compressive strength of specimens with SiO2/Al2O3 weight ratios of 4.7 and 2.1 is a value between these intervals. For the specimen with NaOH concentration of 8 M the difference between strength values has a regular pattern. By increasing the concentration of NaOH to 12 and 16 M, the
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compressive strength of specimens with SiO2/Al2O3 weight ratio of 4.7, 3.0 and 2.1 approaches together, especially at later ages. This indicates that for this system, NaOH
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concentration has a key role on compressive strength of specimens with SiO2/Al2O3 weight ratio of more than 2. When the concentration of NaOH increases, dissolution of silicon ion
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(Si4+) and aluminium ion (Al3+) from the cementitious mixture becomes easier and more geopolymeric reactions occurs (Hanjitsuwan et al., 2014; De Vargas et al., 2011). This is more evident at later ages because the reaction between cementitious mixture and alkali activator in geopolymeric pastes with high concentration of NaOH may be retarded. It has been suggested that formation of some complex compounds reduces the kinetic of aluminosilicate reactions (Riahi and Nazari, 2012). This phenomenon mainly depends on the thickness of the sections and is more evident in the specimen’s centre. For the whole SiO2/Al2O3 ratios and at any ages of curing, regardless of SiO2/Al2O3 8
ACCEPTED MANUSCRIPT ratio of 1.6 and 28 days of curing age, the compressive strength increases by raising the NaOH molarity. At higher SiO2/Al2O3 ratios, the difference between the compressive strength of specimens with high (12 and 16 M) and medium (8 M) NaOH concentrations at 7 days of curing age is considerable. However, at 28 days of curing age, the compressive
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strengths are close. From the economical viewpoint and for regular constructions, it may be better to use lower concentrations and later ages. This is beneficial for slag-based geopolymers, which can be made by in-situ production. This is in spite of fly ash-based ones
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that are made as ready-to-use parts in factories.
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Fig. 8 illustrates the compressive strength of the geopolymeric concrete specimens at different curing ages. Same as geopolymeric pastes, the highest compressive strength of specimens at every age of curing is related to those with SiO2/Al2O3 weight ratio of 3.0. Although specimens with SiO2/Al2O3 weight ratio of 1.6 revealed a reasonable compressive strength at NaOH concentration of 8 M, by increasing the concentration to 12 and 16 M, they
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show the minimum compressive strength at all ages. As the figure shows, there is a considerable difference between the strength of the specimen with SiO2/Al2O3 weight ratio of
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3.0 by the other specimens at 28 days of curing age and all NaOH concentrations. For NaOH concentration of 8 M, this difference for SiO2/Al2O3 weight ratios of 4.7, 2.1 and 1.6 is +20.8,
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+8.70 and +13.5 % respectively. For NaOH concentration of 12 M, this difference for SiO2/Al2O3 weight ratios of 4.7, 2.1 and 1.6 is +9.00, +12.7 and +20.1 % respectively. Finally, for NaOH concentration of 16 M, this difference for SiO2/Al2O3 weight ratios of 4.7, 2.1 and 1.6 is +13.7, +14.8 and +30.3 % respectively. Although for geopolymeric pastes high NaOH concentration retards geopolymeric reactions, in concrete form, the paste is distributed between the aggregates and hence, the thickness of the paste sections is not high to retard the reactions (Riahi and Nazari, 2012). On the whole, the best compressive strength for geopolymeric paste and concrete specimens is achieved by utilizing SiO2/Al2O3 weight ratio 9
ACCEPTED MANUSCRIPT of 3.0. The results obtained from this study show the possibility of using these geopolymers in construction technology. Collins and Sanjayan (1999) were one of the first authors who
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indicated the ability of using alkali-activated slags in construction. They used blastfurnace slag as aluminosilicate source and achieved compressive strength values up to 60 MPa. This is while compressive strength of their examined OPC concrete is up to 50 MPa. Wang et al. (2014) have acquired compressive strength of up to 80 MPa for their alkali-activated slags.
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Comparison between compressive strength of geopolymers in this study and the literature
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show that those in this study fall within the acceptable range. The normal compressive strength of a concrete specimen for using in construction technology should be determined by using American Concrete Institute (ACI) codes. According to ACI 318 and 322 codes, a concrete specimen for residential purposes must have a compressive strength of at least 4500 psi (31 MPa). All of the geopolymer concrete mixtures studied in this paper are therefore
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appropriate for construction application not only when compared with OPC concrete but with
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available alkali-activated slags.
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3.3. Microstructure
SEM micrograph of fracture surface of specimens has been illustrated in Fig. 9.
SiO2/Al2O3 weight ratio for microstructures in Fig. 9a and Fig. 9b is 3.0, in Fig. 9c and Fig. 9d is 4.7, in Fig. 9e and Fig. 9f is 2.1 and in Fig. 9g and Fig. 9h is 1.6. Fig. 9a, Fig. 9c, Fig. 9e and Fig. 9g show microstructure of specimens with NaOH concentration of 8 M and Fig. 9b, Fig. 9d, Fig. 9f and Fig. 9h show that of specimens with NaOH concentration of 16 M. As it is obvious, concentration of NaOH has not a major effect on microstructure of specimens. This can, for example, be seen when Fig. 9a and Fig. 9b are compared. The pastes in these 10
ACCEPTED MANUSCRIPT two figures are similar and seem dense. For SiO2/Al2O3 weight ratios of 4.7 (Fig. 9c and Fig. 9d) and 2.1 (Fig. 9e and Fig. 9f), paste is still dense but some particles are separated from the paste indicating crack branching in weak points. A propagating crack can branch to the weak phases and accelerate fracture of a specimen and hence, decrease compressive strength. The
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weakest paste is seen in Fig. 9g and Fig. 9h with SiO2/Al2O3 weight ratio of 1.6. The paste here is not homogeneous and some coarse geopolymeric particles are observed separated
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from the paste. This is especially more evident for NaOH concentration of 8 M (Fig. 9g).
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5. Conclusions
Compressive strength and workability of the geopolymeric paste and concrete specimens made from different ratios of aluminium and grey cast iron slags were studied. Four different ratios of grey cast iron slag to aluminium slag were considered including
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80/20, 70/30, 60/40 and 50/50. By considering the amount of SiO2 in sodium silicate, SiO2/Al2O3 ratios of specimens were 4.7, 3.0, 2.1 and 1.6. Concentrations for NaOH solutions were 8, 12 and 16 M. Compressive strength of specimens was attained at 1, 7 and 28 days of
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curing, where their suitability for casting were examined on fresh mixes by workability tests.
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Workability of the whole specimens fell within the acceptable range for casting paste and concrete mixtures. By increasing the age of room temperature curing, the compressive strength of specimens increased. It was concluded that slag-based geopolymer can be suitably synthesized at room temperature. Specimens with SiO2/Al2O3 weigh ratio of 3.0 revealed higher strengths. The strength of specimens with SiO2/Al2O3 weigh ratios of 2.1 and 4.7 in most cases were close. Because of high required mechanical work for preparing grey cast iron slags, specimens with SiO2/Al2O3 weigh ratio of 2.1 and 3.0 can be the most appropriate mixture proportions. Specimens with NaOH concentration of 16 M revealed higher strength 11
ACCEPTED MANUSCRIPT especially at 28 days of curing. Specimens at early ages have relatively similar strengths. It was concluded that higher concentrations causes the formation of complex compounds retard the geopolymerization process. At later ages, because of the suitable amount of Si4+ and Al3+ dissolved from slag mixture into alkali activator with 16 M NaOH concentration,
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geopolymeric reaction completes and higher strengths are attained. Aluminium and grey cast iron slags are alumina- and silica-rich sources respectively. All conducted works on geopolymers indicate the necessity of providing aluminosilicate from one source. In this
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study, successful synthesis of geopolymers demonstrates the capability of binary blended mixtures for use as aluminosilicate sources. Its superiority can be manipulating SiO2/Al2O3
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weight ratios to achieve the desired properties.
References
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Alex, T. C., Kalinkin, A. M., Nath, S. K., Gurevich, B. I., Kalinkina, E. V., Tyukavkina, V. V., & Kumar, S. (2013). Utilization of Zinc Slag through Geopolymerization:
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Influence of Milling Atmosphere. International Journal of Mineral Processing, 123, 102-107. Andrews-Phaedonos, F. “Geopolymer “green” concrete: reducing the carbon
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ACCEPTED MANUSCRIPT Table 1. Chemical composition of fly ashes and sodium silicate (Wt.%) which were utilized in this work. Grey cast iron slag
Sodium silicate
SiO2
8.35
63.6
34.5
Al2O3
60.8
2.68
-
Fe2O3
2.35
17.3
CaO
5.21
1.45
SO3
2.84
0.48
Na2O
2.75
2.08
13.1
K2O
0.80
0.31
-
Cr2O3
0.14
Cl
2.35
V2O5
0.05
La & Lu
0.30
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Aluminium slag
-
-
-
1.32
-
0.08
-
0.62
-
8.89
0.84
-
0.12
0.59
-
0.10
0.06
-
0.09
6.27
-
1.82
0.04
-
CuO
1.05
0.12
-
H2O
-
-
52.4
L.O.I.
1.99
1.68
-
TiO2 P2O5 MnO
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ZnO
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MgO
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0.48
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SiO2 conten t of binder (Kg/m 3 )
Al2O3 conten t of binder (Kg/m 3 )
SiO2/Al2 O3 weigh ratio of binder
2.9
10.3
8
1187
254
4.7
733
293
10.3
12
1187
254
4.7
0
733
293
10.3
16
1187
254
4.7
1326.3
0
729
292
10.2
8
1084
356
3.0
568.4
1326.3
0
729
292
10.2
12
1084
356
3.0
G6
568.4
1326.3
0
729
292
10.2
16
1084
356
3.0
G7
754
1131
0
725
290
10.2
8
981
457
2.1
G8
754
1131
0
725
290
10.2
12
981
457
2.1
G9
754
1131
0
725
290
10.2
16
981
457
2.1
G10
937.6
937.6
0
721
289
10.1
8
879
556
1.6
G11
937.6
937.6
0
721
289
10.1
12
879
556
1.6
G12
937.6
937.6
0
721
289
10.1
16
879
556
1.6
G13
108.5
434.2
1948
209
83.5
2.90
8
338
72
4.7
G14
108.5
434.2
1948
209
83.5
2.90
12
338
72
4.7
G15
108.5
434.2
1948
209
83.5
2.90
16
338
72
4.7
G16
162.6
379.3
1945
208
83.4
2.90
8
310
102
3.0
G17
162.6
G18
162.6
380.9
1523.6
0
733
G2
380.9
1523.6
0
G3
380.9
1523.6
G4
568.4
G5
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1945
208
83.4
2.90
12
310
102
3.0
379.3
1945
208
83.4
2.90
16
310
102
3.0
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G19
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Aluminiu m slag
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Superplastici zer
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Quantities of materials (Kg/m3) Grey Aggre Sodiu NaO cast iron gates m H slag silicat e
Sample designati on
216.4
324.6
1942
208
83.2
2.90
8
282
131
2.1
216.4
324.6
1942
208
83.2
2.90
12
282
131
2.1
216.4
324.6
1942
208
83.2
2.90
16
282
131
2.1
269.9
269.9
1938
207
83.0
2.90
8
253
160
1.6
G23
269.9
269.9
1938
207
83.0
2.90
12
253
160
1.6
G24
269.9
269.9
1938
207
83.0
2.90
16
253
160
1.6
G20 G21 G22
18
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Fig. 1. As received materials a) aluminium slag and b) grey cast iron slag which were used in this study.
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Fig. 2. Particle size distribution of aluminium and grey cast iron slags after milling are shown in terms of their cumulative percentage.
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Fig. 3. Particle size distribution of fine aggregates is shown as their cumulative percentage.
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Fig. 4. Compressive strength of a specimen is being tested.
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(c) Fig. 5. Workability of fresh geopolymer mixtures has been given at different concentrations of NaOH; a) geopolymer paste, b) geopolymer concrete, and c) percentage of reduction in workability due to incorporating aggregates. 23
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(c) Fig. 6. Workability of fresh geopolymer mixtures has been given at different SiO2/Al2O3 weight ratios; a) geopolymer paste, b) geopolymer concrete, and c) percentage of reduction in workability due to incorporating aggregates. 24
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(c) Fig. 7. Effect of curing age on compressive strength of the geopolymeric pastes has been shown at different SiO2/Al2O3 weight ratios.
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(c) Fig. 8. Effect of curing age on compressive strength of the geopolymeric concrete specimens has been shown at different SiO2/Al2O3 weight ratios.
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(b)
(c)
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(e)
(f)
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(g)
(h)
Fig. 9. Microstructure of a) G1, b) G3, c) G4, d) G6, e) G7, f) G9, g) G10 and h) G12 specimens show different features.
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Compressive strength and workability were conducted to evaluate performance criteria.
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Green geopolymers with suitable properties are achievable by using these waste materials.
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