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The effect of type and concentration of activators on flowability and compressive strength of natural pozzolan and slag-based geopolymers
Construction and Building Materials 111 (2016) 337–347
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
The effect of type and concentration of activators on flowability and compressive strength of natural pozzolan and slag-based geopolymers Mohsen Jafari Nadoushan, Ali Akbar Ramezanianpour ⇑ Concrete Technology and Durability Research Center (CTDRc), Department of Civil & Environmental Engineering, Amirkabir University of Technology, Tehran, Iran
h i g h l i g h t s Production of new geopolymer cement using by natural pozzolan and ground granulated blast furnace slag. The effects of different activator types on the flowability and mechanical properties of alkali activated slag. The effects of different level of natural pozzolan on the properties of slag-based geopolymer. Scanning electron microscopy studies of slag-based geopolymer containing natural pozzolan.
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Article history: Received 14 October 2015 Received in revised form 27 December 2015 Accepted 17 February 2016
Keywords: Geopolymer Slag Natural pozzolan Compressive strength Alkaline solution Activator
a b s t r a c t Materials resulting from the alkali activation of GGBF slag show a wide range of workability, compressive strength and permeability. The main objectives of this work are to determine the effects of alkaline solution type and concentration, modulus of sodium silicate, sodium silicate to alkaline solution ratio and natural pozzolan replacement on the workability and mechanical properties of alkali activated GGBF slag. Results reveal that the geopolymer paste specimens containing KOH solution have higher compressive strength when compared with the geopolymer paste specimens containing NaOH solution. The optimum concentration of the alkaline solution is 6–8 molar. It can be concluded that in the presence of 6 and 8 molar alkaline solutions the maximum strength could be reached with 5% and 10% replacement respectively. The optimum range for each factor is suggested based on the different effects of these factors on the compressive strength. Ó 2016 Published by Elsevier Ltd.
1. Introduction Concrete is the most widely used building material in the world which is because of its beauty, appropriate mechanical properties and durability in different environments. The concrete industry is one of the major consumers of natural resources. In Portland cement production process, natural resources which must be remained for next generations are being used. On the other hand Portland cement clinker production is an energy-intensive process. This energy is mostly supplied by fossil fuels which is costintensive in addition to producing a large amount of greenhouse gas emissions, mostly CO2.
⇑ Corresponding author. E-mail addresses: [email protected] (M. Jafari Nadoushan), [email protected]. ir (A.A. Ramezanianpour). http://dx.doi.org/10.1016/j.conbuildmat.2016.02.086 0950-0618/Ó 2016 Published by Elsevier Ltd.
Therefore any reduction in Portland cement clinker usage reduces energy use and CO2 emissions. One possible way to reduce energy consumption and greenhouse gas emissions in concrete industry is the replacement of clinker with supplementary cementitious materials (SCMs) that has been used considerably over past five decades. Various researchers reveal that the replacement of cement with SCMs such as GGBF slag, fly ash, rice husk ash, silica fume and natural pozzolan in the production of concrete improves the mechanical properties and durability of concrete in addition to reducing environmental impacts [1–3]. Nowadays, SCMs such as GGBF slag and fly ash are used up to 70% replacement with Portland cement in concrete, while it is possible to produce geopolymer concrete with only Si and Al rich materials and no Portland cement. Geopolymers are cohesive materials and have three dimensional polymeric chain and ring structure consisting of Si–O–Al–O bonds that are formed by alkali activation of Si and Al rich materials such as natural and artificial
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Fig. 1. Particle size distributions for GGBF slag and pumice.
Table 1 Chemical characteristics of raw materials. Chemical components
GGBF slag
Pumice
Calcium oxide (CaO) (%) Silicon dioxide (SiO2) (%) Magnesium oxide (MgO) (%) Aluminum oxide (Al2O3) (%) Ferric oxide (Fe2O3) (%) Sulphate oxide (SO3) (%) Sodium oxide (Na2O) (%) Potassium oxide (K2O) (%) Titanium dioxide (TiO2) (%) Manganese oxide (MnO) (%) Phosphor pentoxide (P2O5) (%) LOI (%)
36.75 37.21 8.52 11.56 1.01 0.97 0.61 0.70 1.23 0.99 0.03 0.02
7.4 64.9 1.98 12.1 5.2 0.22 2.49 1.88 0.79 .123 0.2 2.5
pozzolans and can be a real alternative to ordinary Portland cement for construction. Highly alkaline solutions are used to induce the silicon and aluminium ions in the raw materials to dissolve and form the geopolymer paste with three steps in the process including: dissolution of any pozzolanic compound, partial orientation of mobile precursors and re-precipitation of the particles from the initial solid phase. It has been found that geopolymer binders can be synthesized by activating natural pozzolans and condensing them with sodium silicate in a highly alkaline environment [4,5]. Geopolymers produced from solid waste as starting material have benefits such as reducing environmental impacts by using lesser amounts of calcium-based minerals, lower manufacturing
temperature, lower fuel consumption and lower greenhouse gas emission in comparison with ordinary Portland cement and provides a route towards the concept of sustainable development. Blast furnace slag is a by-product that is formed during the production of hot metal in blast furnace. If the molten slag is cooled and solidified by rapid water quenching, ground granulated blast furnace (GGBF) slag is formed. When crushed or milled to very fine cement-sized particles, ground granulated blast furnace slag has cementitious properties, which is a suitable replacement with Portland cement. It has been found that GGBF slag-based geopolymer binders can be synthesized by alkali activation of ground granulated blast furnace slag in presence of sodium silicate. The use of GGBF slag as geopolymer binding material requires its preparation involving grinding, alkali activation and hydration [6]. Geopolymer concrete made from granulated blast furnace slag requires less sodium silicate solution in order to be activated. They therefore have a lower environmental impact than geopolymer concrete made from pure metakaolin [7]. Slag-based geopolymer cements are capable of being mixed with a relatively low-alkali activating solution and must cure in a reasonable time under ambient conditions [8]. The physical and mechanical properties of the geopolymer correlated well with the concentration of alkaline solution. Cheng and Chiu [9] used three different KOH concentrations (5, 10 and 15 molar) for alkali activation of GGBF slag. The sample containing 10 M KOH showed the best strength. With increasing KOH concentration to 15 M, the compressive strength decreased which could be due to too much K+ ions in the framework cavities [9]. The calcium in GGBF slag seems to increase the
Fig. 2. XRD patterns of GGBF slag and pumice.
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Fig. 3. SEM micrographs of (a) GGBF slag and (b) pumice.
Table 2 The introduced levels for each factor in phase 1. Factor
Unit
Level 1
Level 2
Level 3
Level 4
Level 5
Alkaline solution type Alkaline solution concentration Modulus of sodium silicate Sodium silicate to alkaline solution
– Mole Molar ratio Weight ratio
NaOH 6 2.1 0
KOH 8 2.33 0.1
– 10 3.13 0.2
– – – 0.3
– – – 0.4
final mechanical strength. This is because the Ca in GGBF slag is available to form C–S–H [10]. Yunsheng et al. [11] manufactured geopolymer by slag and metakaolin and investigated the immobilization behaviours of slag based geopolymer in the presence of Pb and Cu. Through this study, it is concluded that geopolymer containing 50% slag that is synthesized at steam curing (80 °C for 8 h), exhibited higher mechanical strength. Hu et al. [12] prepared three repair materials using cement-based, geopolymeric and geopolymeric containing steel slag binders. The test results showed that the geopolymeric materials had better repair characteristics than cement-based repair materials, and the addition of steel slag could improve significantly the abrasion resistance of geopolymeric repair. As you can see in the literatures, many factors influence the properties of the slag-based geopolymer. Bondar et al. [4] investigated the effect of the alkaline medium on the strength of alkali-activated Taftan natural pozzolan. The results showed that the KOH solutions between 5 and 7.5 M give the highest values for compressive strength. The optimum curing temperature to achieve the highest strength for alkali-activated Taftan pozzolan was 60 °C [5]. This paper describes the effects of different alkaline solution types and concentrations, modulus of sodium silicate, sodium silicate to alkaline solution ratio and natural pozzolan on the flowability and the mechanical properties of the alkali activated GGBF slag. Properties of fresh and hardened geopolymer specimens such as workability and compressive strength were measured. Scanning electron microscopy (SEM) investigations were conducted on the selected mixes.
89.98 lm and the median particle size of 13.48 lm. The raw materials have been analyzed by X-ray fluorescence (XRF) analysis using a Philips PW 1480 instrument. Chemical characteristics of GGBF slag and Taftan pumice are shown in Table 1. X-ray diffraction (XRD) carried out on GGBF slag and pumice by an EQuniox 3000 machine is presented in Fig. 2. The XRD patterns of the raw materials show that all of them are a mixture of minerals with various degrees of crystallization. Crystalline particles were observed in the pumice sample. Two weak peaks in Xray diffraction studies of GGBF slag powder reveal some crystalline components. SEM photographs of both GGBF slag and pumice are presented in Fig. 3. Potassium hydroxide (KOH) and sodium hydroxide (NaOH) pellets have dissolved to produce the 6, 8 and 10 molar alkaline solutions for geopolymer paste production. Sodium silicate (water glass) provided by Iran Silicate Industrial Company in the form of solution with modulus of 2.1, 2.33 and 3.13. The modulus of water glass is the molar ratio of SiO2/Na2O. The water contents of 2.1, 2.33 and 3.13 modulus sodium silicate are 60%, 52% and 58% and their specific gravities are 1.45, 1.56 and 1.45 respectively. Deionized water was used to produce all alkaline solutions. At first, four factors related to strength of GGBF slag-based geopolymer cement paste such as alkaline solution type, alkaline solution concentration (mole), modulus of sodium silicate (molar ratio) and sodium silicate to alkaline solution (weight ratio) have been investigated. The level of each factor and the values of the tested factors chosen based on the previous researches are presented in Table 2. A total of 90 geopolymer paste mixtures were made in this step. The mixture proportions for geopolymer cement paste specimens are summarized in Table 3. The geopolymer cement paste mixtures were prepared with a constant total binder (GGBF slag) content of about 1547 kg/m3 and the activator (alkaline solution + sodium silicate) to binder ratio in the mixes was 0.4. In the next step to find the effect of natural pozzolans on the properties of GGBF slag-based geopolymer cement paste, 9 different replacement levels were considered. The factors and their levels are presented in Table 4. The mixture proportions for GGBF slag-based geopolymer paste specimens containing natural pozzolan are summarized in Table 5. In this step the geopolymer cement paste mixtures were prepared with the optimum modulus of sodium silicate and the optimum ratio of sodium silicate to alkaline solution (2.33 and 0.4 respectively). The activator (alkaline solution + sodium silicate) to binder ratio in the mixes was 0.4.
2. Experimental programs 2.2. Mixing procedure and specimen preparation 2.1. Material and mixture proportion Two raw materials containing GGBF slag and natural pozzolan used throughout this work to be activated as geopolymer cement. GGBF slag with a specific surface area of 3383 cm2/g and a mean particle size of 25.97 lm was obtained. Taftan pumice pozzolan with a specific surface area of 5074 cm2/g and a mean particle size of 22.24 lm was obtained. Specific surface of pumice is greater than specific surface of GGBF slag. The specific gravity of GGBF slag and pumice are 2.79 and 2.54 g/cm3 respectively. The cumulative particle size distributions (PSD) for GGBF slag and pumice are shown in Fig. 1. GGBF slag has a particle size of 1% larger than 86.46 lm and the median particle size of 18.35 lm and pumice has a particle size of 1% larger than
KOH or NaOH pellets were added to the deionized water to provide the 6, 8 and 10 M potassium and sodium hydroxide solutions and were cooled. Geopolymer cement pastes were prepared by adding potassium and sodium hydroxide solutions to the raw materials and blending for 2 min. Then, the sodium silicate was added and mixed for 2 more minutes to form geopolymer paste. The resulting geopolymer paste was transferred to the plexiglass moulds of 20 20 20 mm dimensions. Geopolymer cement pastes specimens were compacted by external vibration to reduce entrapped air and kept protected after casting to avoid water evaporation. At first 24 h the specimens were kept in the room temperature. After 24 h specimens were removed from the mould and cured in the special plastic bags at 23 ± 2 °C. Rapid drying should be avoided to eliminate shrinkage cracking.
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Table 3 Slag-based geopolymer paste mixtures, flowability and compressive strength. Col. Mix
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73
Based material AS
Na6-WG2.1-0 GGBF slag Na6-WG2.1-0.1 Na6-WG2.1-0.2 Na6-WG2.1-0.3 Na6-WG2.1-0.4 Na6-WG2.33-0 Na6-WG2.33-0.1 Na6-WG2.33-0.2 Na6-WG2.33-0.3 Na6-WG2.33-0.4 Na6-WG3.13-0 Na6-WG3.13-0.1 Na6-WG3.13-0.2 Na6-WG3.13-0.3 Na6-WG3.13-0.4 Na8-WG2.1-0 Na8-WG2.1-0.1 Na8-WG2.1-0.2 Na8-WG2.1-0.3 Na8-WG2.1-0.4 Na8-WG2.33-0 Na8-WG2.33-0.1 Na8-WG2.33-0.2 Na8-WG2.33-0.3 Na8-WG2.33-0.4 Na8-WG3.13-0 Na8-WG3.13-0.1 Na8-WG3.13-0.2 Na8-WG3.13-0.3 Na8-WG3.13-0.4 Na10-WG2.1-0 Na10-WG2.1-0.1 Na10-WG2.1-0.2 Na10-WG2.1-0.3 Na10-WG2.1-0.4 Na10-WG2.33-0 Na10-WG2.33-0.1 Na10-WG2.33-0.2 Na10-WG2.33-0.3 Na10-WG2.33-0.4 Na10-WG3.13-0 Na10-WG3.13-0.1 Na10-WG3.13-0.2 Na10-WG3.13-0.3 Na10-WG3.13-0.4 K6-WG2.1-0 K6-WG2.1-0.1 K6-WG2.1-0.2 K6-WG2.1-0.3 K6-WG2.1-0.4 K6-WG2.33-0 K6-WG2.33-0.1 K6-WG2.33-0.2 K6-WG2.33-0.3 K6-WG2.33-0.4 K6-WG3.13-0 K6-WG3.13-0.1 K6-WG3.13-0.2 K6-WG3.13-0.3 K6-WG3.13-0.4 K8-WG2.1-0 K8-WG2.1-0.1 K8-WG2.1-0.2 K8-WG2.1-0.3 K8-WG2.1-0.4 K8-WG2.33-0 K8-WG2.33-0.1 K8-WG2.33-0.2 K8-WG2.33-0.3 K8-WG2.33-0.4 K8-WG3.13-0 K8-WG3.13-0.1 K8-WG3.13-0.2
NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH
Molarity Modulus SS to AS Activator to pozz. Flow of geopolymer Compressive strength (MPa) of SS paste (%) 3 days 7 days 14 days 21 days 28 days 91 days 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 8 8 8 8 8 8 8 8 8 8 8 8 8
2.1 2.1 2.1 2.1 2.1 2.33 2.33 2.33 2.33 2.33 3.13 3.13 3.13 3.13 3.13 2.1 2.1 2.1 2.1 2.1 2.33 2.33 2.33 2.33 2.33 3.13 3.13 3.13 3.13 3.13 2.1 2.1 2.1 2.1 2.1 2.33 2.33 2.33 2.33 2.33 3.13 3.13 3.13 3.13 3.13 2.1 2.1 2.1 2.1 2.1 2.33 2.33 2.33 2.33 2.33 3.13 3.13 3.13 3.13 3.13 2.1 2.1 2.1 2.1 2.1 2.33 2.33 2.33 2.33 2.33 3.13 3.13 3.13
0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2
0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4
40 65 150 160 160 40 55 65 90 140 40 50 55 58 60 5 50 143 160 160 5 48 145 150 150 5 10 120 123 125 35 40 130 130 140 35 100 105 110 115 35 35 95 100 115 20 20 100 135 150 20 15 95 125 140 20 15 60 85 90 35 105 160 160 160 35 100 140 155 160 35 20 50
21.70 31.41 57.79 71.04 61.87 21.70 38.12 56.40 70.17 83.61 21.70 35.51 60.39 69.89 85.27 21.97 35.03 48.60 73.71 63.30 21.97 50.22 51.79 55.46 68.60 21.97 35.84 57.66 64.20 72.56 39.37 59.33 61.78 66.35 69.85 39.37 45.03 59.46 60.48 67.72 39.37 43.67 61.59 64.31 57.96 31.01 45.96 57.41 85.35 87.38 31.01 49.73 68.15 76.26 77.93 31.01 46.18 54.52 82.49 59.13 42.58 53.90 66.17 65.05 67.64 42.58 65.34 66.67 74.71 78.12 42.58 41.42 64.46
24.27 33.33 80.88 74.13 82.11 24.27 51.15 63.39 80.90 85.08 24.27 43.58 67.30 79.76 87.63 26.91 42.13 55.54 84.13 81.38 26.91 59.68 68.38 69.03 84.06 26.91 50.33 71.34 72.91 76.78 43.63 65.68 76.22 77.65 85.74 43.63 52.28 62.89 76.11 80.97 43.63 56.40 71.67 72.46 70.13 50.72 55.32 70.23 89.55 91.70 50.72 58.67 87.56 99.26 86.21 50.72 54.60 54.76 92.32 72.15 54.43 67.41 81.28 83.33 85.40 54.43 67.08 84.29 91.97 94.51 54.43 52.80 71.40
36.07 54.09 84.11 92.83 99.02 36.07 57.32 74.13 83.32 98.23 36.07 43.90 98.13 98.28 120.85 32.38 54.48 80.43 87.14 99.80 32.38 63.35 91.31 92.09 94.27 32.38 56.58 87.05 89.23 82.13 45.11 72.43 76.65 85.73 90.40 45.11 55.91 71.78 80.81 86.94 45.11 59.14 75.96 78.62 74.23 64.20 72.58 98.44 101.19 101.25 64.20 68.97 94.20 99.68 113.31 64.20 60.99 75.46 93.00 107.77 60.07 76.23 92.08 83.13 105.36 60.07 86.17 92.63 94.66 95.11 60.07 62.17 89.37
44.19 61.14 109.88 113.19 118.72 44.19 64.58 87.28 97.83 141.43 44.19 61.22 102.44 99.02 125.63 38.31 59.27 81.35 87.82 100.99 38.31 72.50 99.85 104.36 110.46 38.31 59.32 87.19 88.94 87.25 58.29 79.66 87.57 91.19 97.70 58.29 60.68 80.91 83.74 93.65 58.29 75.71 80.41 87.38 85.71 64.80 74.37 106.93 113.75 115.49 64.80 70.75 104.28 111.31 126.70 64.80 61.28 75.60 100.22 115.11 64.92 79.99 112.39 117.07 122.56 64.92 86.56 114.36 115.18 118.95 64.92 66.25 93.51
46.79 62.81 97.72 118.10 121.36 46.79 73.10 117.10 133.69 145.22 46.79 63.43 112.03 120.00 126.26 49.42 66.10 85.12 100.48 104.20 49.42 77.89 111.63 111.94 113.86 49.42 61.27 88.48 92.86 96.20 59.53 85.43 95.32 104.44 106.81 59.53 62.17 82.91 101.25 102.51 59.53 76.56 91.91 104.83 91.74 67.99 84.13 103.01 118.09 118.22 67.99 75.68 104.59 126.47 127.42 67.99 70.91 84.69 103.21 116.17 69.38 81.86 114.65 118.12 123.16 69.38 96.26 117.11 123.76 139.31 69.38 70.23 93.81
65.28 78.57 100.44 123.12 127.43 65.28 96.11 121.95 139.03 145.77 65.28 83.51 115.43 125.32 131.60 64.37 88.73 95.05 107.47 108.96 64.37 93.88 104.87 107.87 122.62 64.37 68.11 101.45 108.69 116.07 60.07 91.78 98.25 107.07 116.54 60.07 95.82 104.57 105.16 115.72 60.07 83.46 92.68 112.72 96.61 70.04 109.18 113.10 120.67 141.19 70.04 115.95 140.68 153.25 162.67 70.04 85.56 88.90 110.83 124.77 87.11 94.78 127.42 141.11 144.63 87.11 110.25 132.14 149.75 169.41 87.11 87.62 119.12
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74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90
Based material AS
K8-WG3.13-0.3 K8-WG3.13-0.4 K10-WG2.1-0 K10-WG2.1-0.1 K10-WG2.1-0.2 K10-WG2.1-0.3 K10-WG2.1-0.4 K10-WG2.33-0 K10-WG2.33-0.1 K10-WG2.33-0.2 K10-WG2.33-0.3 K10-WG2.33-0.4 K10-WG3.13-0 K10-WG3.13-0.1 K10-WG3.13-0.2 K10-WG3.13-0.3 K10-WG3.13-0.4
KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH
Molarity Modulus SS to AS Activator to pozz. Flow of geopolymer Compressive strength (MPa) of SS paste (%) 3 days 7 days 14 days 21 days 28 days 91 days 8 8 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10
3.13 3.13 2.1 2.1 2.1 2.1 2.1 2.33 2.33 2.33 2.33 2.33 3.13 3.13 3.13 3.13 3.13
0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4
0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4
80 100 5 115 123 125 128 5 110 113 115 115 5 75 80 85 100
64.61 63.57 41.93 56.24 51.13 63.83 63.63 41.93 62.32 54.58 53.55 52.37 41.93 57.24 45.89 59.58 53.06
82.33 71.94 47.18 57.72 72.75 83.69 68.68 47.18 65.80 71.11 73.58 72.46 47.18 61.34 67.39 77.47 74.30
103.09 114.22 60.23 71.99 72.55 89.87 85.38 60.23 70.70 75.30 80.29 75.41 60.23 76.93 78.10 95.69 93.13
107.59 117.00 67.88 75.55 80.47 87.17 93.60 67.88 78.48 79.37 101.40 90.83 67.88 77.41 82.42 97.62 95.11
117.99 134.76 67.15 76.28 80.57 103.86 113.59 67.15 81.10 87.53 109.07 102.76 67.15 80.31 92.53 99.89 96.39
137.47 169.08 72.09 90.42 105.40 127.44 128.57 72.09 86.70 123.17 133.73 125.28 72.09 87.00 106.55 116.70 107.53
AS: alkali solution, SS: sodium silicate. 2.3. Testing procedure Flowability of the fresh geopolymer paste was determined by ASTM C 1437 which consists of measuring the increase in average base diameter of the paste mass, expressed as a percentage of the original base diameter [13]. Geopolymer paste cubes of 20 20 20 mm dimensions were cast for compressive strength. They were tested for compressive strength after 3, 7, 14, 21, 28 and 91 days maintained in the sealed curing. The specimens were wrapped and insulated in a special plastic bag to prevent evaporation and left at room temperature until the age of the test. Three samples for each formulation were measured for the compressive strength according to ASTM C109 [14]. The loading rate of compression machine and its capacity are 1.5 kN/S and 200 kN respectively. The microstructure of the geopolymer pastes was studied by using scanning electron microscope (SEM): Philips XL30. For scanning electron microscopy studies, selected geopolymer paste samples cured 3 and 28 days were used. A cubic form paste was cut into 10 mm squares which had one flat side. The samples were dried and coated with gold.
3. Results and discussions 3.1. Workability The flow of GGBF slag-based geopolymer fresh pastes are presented in Table 3. It is shown in Fig. 4 that the flowability of GGBF slag-based geopolymer pastes containing KOH is higher than the identical NaOH. Despite the fact that, because of more molar mass, in the same molarity, KOH solution contains lower water in comparison with NaOH. Fig. 5 demonstrates the flow of the fresh geopolymer pastes containing different types of sodium silicate with different contents. In the presence of sodium or potassium hydroxide, adding the sodium silicate largely enhances the workability of GGBF slag-based geopolymer paste. The sodium silicate solution improves the dissolution of raw material in alkaline environment and more dissolved raw materials result in higher workability. As shown in Fig. 5, increasing of sodium silicate to alkaline solution ratio from 0 to 0.4 results in the increase of the flow of GGBF slag-based geopolymer paste, keeping other parameters constant. Water content is the most effective factor on the flow of the fresh geopolymer paste. Generally, more water leads to higher flowability. The water contents of 2.1, 2.33 and 3.13 modulus sodium silicate are 60%, 52% and 58% respectively. Therefore 2.1 ratio sodium silicate results in maximum workability (see Fig. 5). It was considered that 50% flow (equilibrium 150 mm flow diameter) is the minimum value suitable for geopolymer paste that can easily be worked and placed in the mould. It is found that the mixtures with no sodium silicate and sodium silicate/ alkaline solution of 0.1 have very poor workability and cannot be cast easily.
3.2. Compressive strength The compressive strength of the GGBF slag-based geopolymer paste specimens are presented in Table 3. The highest compressive strength was obtained for Na6-WG2.33-0.4 and K8-WG2.33-0.4 at 28 and 91 days of curing respectively (145.22 MPa and 169.41 MPa). This result indicates that the optimum value of modulus of sodium silicate and sodium silicate to alkaline solution are 2.33 and 0.4 respectively. Generally due to more compaction, the pastes with more workability could have more compressive strength. But it is not the only significant factor. Results in Fig. 6 indicate the compressive strength of Na8WG2.33-0.4 at different ages of curing. As expected, the compressive strength of the geopolymer pastes developed with the curing time. After 3 days of curing, GGBF slag-based geopolymers obtained more than 52% of its final compressive strength which increased to 87% at 28 days of curing. Rapid strength gain rate of geopolymer makes it an ideal material for repairing concrete structures. 3.2.1. Effects of the alkaline solution type on the compressive strength The alkaline solution causes the dissolution of the raw materials. The alkaline solution must be carefully selected because their composition has different impacts on the properties of fresh geopolymer paste and development of the mechanical properties in the hardened geopolymer. Two mostly used alkaline solutions in geopolymer formation are NaOH and KOH. The type of alkaline solution plays an important role on the dissolution rate. As been demonstrated in Fig. 7 for example, the GGBF slag-based geopolymer paste specimens containing potassium hydroxide had higher compressive strength at various ages up to 91 days when compared with the specimens containing sodium hydroxide. For example at 91 days of curing, the mean compressive strength of GGBF slag-based geopolymer specimens containing potassium hydroxide is 16.1% higher than that for specimens containing sodium hydroxide. The ionic size of Na+ is 116 pm while ionic size of K+ is 152 pm. The larger K+ favours the formation of larger silicate oligomers with which Al (OH) 4 prefers to bind. Therefore, in KOH solutions more geopolymer precursors exist which result in better setting and stronger compressive strength of the geopolymers than in the case of NaOH [15]. 3.2.2. Effects of the alkaline solution concentration on the compressive strength Fig. 8 illustrates the effect of alkaline solution concentration on compressive strength of GGBF slag-based geopolymer paste in
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Table 4 The introduced levels for each factor in phase 2. Factor
Unit
Level 1
Level 2
Level 3
Level 4
Level 5
Level 6
Level 7
Level 8
Level 9
Alkaline solution type Alkaline solution concentration Slag replacement with natural pozzolan
– Mole Weight %
NaOH 6 0
KOH 8 5
– – 10
– – 15
– – 20
– – 25
– – 50
– – 75
– – 100
Table 5 Slag-based with natural pozzolan geopolymer paste mixtures, flowability and compressive strength. Col.
Mix
Based material
AS
Molarity
Slag replacement with pumice (%)
Flow (%)
91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126
Na6-WG2.33-P0 Na6-WG2.33-P5 Na6-WG2.33-P10 Na6-WG2.33-P15 Na6-WG2.33-P20 Na6-WG2.33-P25 Na6-WG2.33-P50 Na6-WG2.33-P75 Na6-WG2.33-P100 Na8-WG2.33-P0 Na8-WG2.33-P5 Na8-WG2.33-P10 Na8-WG2.33-P15 Na8-WG2.33-P20 Na8-WG2.33-P25 Na8-WG2.33-P50 Na8-WG2.33-P75 Na8-WG2.33-P100 K6-WG2.33-P0 K6-WG2.33-P5 K6-WG2.33-P10 K6-WG2.33-P15 K6-WG2.33-P20 K6-WG2.33-P25 K6-WG2.33-P50 K6-WG2.33-P75 K6-WG2.33-P100 K8-WG2.33-P0 K8-WG2.33-P5 K8-WG2.33-P10 K8-WG2.33-P15 K8-WG2.33-P20 K8-WG2.33-P25 K8-WG2.33-P50 K8-WG2.33-P75 K8-WG2.33-P100
GGBF slag + pumice
NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH
6 6 6 6 6 6 6 6 6 8 8 8 8 8 8 8 8 8 6 6 6 6 6 6 6 6 6 8 8 8 8 8 8 8 8 8
0 5 10 15 20 25 50 75 100 0 5 10 15 20 25 50 75 100 0 5 10 15 20 25 50 75 100 0 5 10 15 20 25 50 75 100
140 150 140 130 128 125 110 50 5 138 140 130 125 120 118 105 25 0 145 160 150 145 140 135 110 90 10 135 135 130 125 120 115 100 20 0
Compressive strength (MPa) 3 days
7 days
14 days
21 days
28 days
91 days
68.52 67.95 73.20 76.14 77.01 65.33 37.25 19.05 0.00 63.13 63.86 64.04 64.29 59.92 46.23 45.03 10.92 0.00 54.61 78.84 66.14 53.40 52.24 57.71 46.90 17.63 0.00 51.60 55.55 55.76 53.92 45.67 57.67 40.43 19.23 0.00
83.79 81.31 87.98 87.49 80.09 66.67 43.54 22.25 1.25 74.57 91.11 79.47 80.41 79.89 58.35 44.55 17.03 1.26 71.02 98.47 91.47 89.13 88.83 62.66 54.47 26.79 1.21 82.09 90.40 82.69 74.98 70.85 61.19 56.51 28.29 1.26
107.32 111.69 115.76 115.45 112.37 85.49 54.74 28.67 2.44 80.87 102.36 101.13 95.59 95.63 58.53 51.71 24.49 1.23 97.99 112.78 109.75 108.04 108.59 83.31 80.83 41.68 3.57 89.23 92.04 95.49 81.68 79.47 71.24 57.55 36.67 2.43
110.86 123.76 131.73 129.96 120.77 87.50 65.97 41.05 3.74 89.70 114.22 113.18 106.62 106.04 75.76 58.64 39.11 2.51 99.46 142.32 126.16 123.15 122.79 97.03 91.20 54.67 7.50 91.33 120.40 122.26 113.30 112.20 85.43 74.19 49.71 3.71
114.37 131.75 136.22 133.75 120.83 88.89 80.93 52.17 6.27 101.18 120.69 123.12 112.78 113.18 77.67 61.98 42.94 3.01 121.94 147.08 140.40 134.33 120.64 116.84 100.84 55.75 8.06 118.08 121.90 123.76 115.84 115.57 89.81 79.61 55.99 4.14
126.32 148.29 145.99 143.90 132.95 129.68 99.22 73.74 21.36 110.29 131.15 135.56 128.13 125.35 123.43 88.34 43.11 12.60 122.26 159.36 151.38 147.77 139.10 130.32 118.36 90.87 39.71 120.10 136.57 140.39 133.92 132.92 130.25 89.79 87.05 26.42
AS: alkali solution.
presence of different amount of 3.13 modulus sodium silicate. As been demonstrated in Fig. 8 the optimum concentration of alkaline solution is 8 molar. Increasing the alkaline solution concentration from 8 to 10 M results in reduction of compressive strength of the GGBF slag-based geopolymer pastes. The increase in molarity of alkaline solution causes lower workability, lower compressive strength, more cost and increase in the efflorescence risk. In this work, the efflorescence has been seen in the specimens containing KOH 10 M. Because of the reduction of alkaline solution in mixtures, increasing the sodium silicate to alkaline solution ratio causes reduction in efflorescence. Lower molarity and lower amount of alkaline solution in mixtures lead to lower efflorescence. 3.2.3. Effects of sodium silicate to alkaline solution ratio on the compressive strength The activating solution can contain a supplementary source of silica such as sodium silicate, to promote geopolymerization phases. It has been demonstrated in Fig. 9 that the presence of sodium silicate in the GGBF slag-based geopolymer paste results in increasing the compressive strength. It is clear that increasing the sodium silicate to alkaline solution ratio from 0 to 0.3 causes
the increase in the compressive strength about 100% whereas increasing from 0.3 to 0.4 has a slight effect on enhancement of the compressive strength. Sodium silicate promotes the compressive strength of GGBF slag-based geopolymer paste in two ways: (1) the sodium silicate solution improves the dissolution rate of Si and Al; (2) because the Al–O bonds are weaker than Si–O bonds [16] in the raw material, Al dissolves rapidly in alkali solution. Therefore if Si ion is provided prior to being available through dissolution of raw material, it can increase the degree of geopolymerization and improves the mechanical properties. 3.2.4. Effects of modulus of sodium silicate on the compressive strength The two most important properties of sodium silicate solution in geopolymer paste production are its modulus (SiO2:Na2O) and amounts. It has been demonstrated in Fig. 9 that the optimum modulus of sodium silicate for compressive strength is 2.33. 3.2.5. Effects of natural pozzolan replacement on the compressive strength In many researches one raw material is combined with a liquid activator in order to develop geopolymer [4,9]. In this study, com-
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Fig. 4. Flow of GGBF slag-based geopolymer pastes containing NaOH and KOH.
Fig. 5. Flow of fresh geopolymer paste containing NaOH 8 M with different types of sodium silicate and sodium silicate contents.
Fig. 6. Compressive strength of Na8-WG2.33-0.4 at different ages of curing up to 91 days.
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Fig. 7. Compressive strength of GGBF slag-based geopolymer pastes containing NaOH and KOH after 91 days of curing.
Fig. 8. The effect of alkaline solution (KOH) concentration on compressive strength of GGBF slag-based geopolymer paste after 91 days of curing.
Fig. 9. Compressive strength of GGBF slag-based geopolymer pastes containing NaOH 6 M in the presence of different types of sodium silicate and sodium silicate contents after 91 days of curing.
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Fig. 10. Flow of the fresh geopolymer paste containing NaOH 6 M and 8 M and KOH 6 M and 8 M with different types of sodium silicate and sodium silicate contents.
Fig. 11. The effect of GGBF slag replacement with pumice on compressive strength after 91 days of curing.
bination of GGBF slag and natural pozzolan was used to produce geopolymer paste. The effect of different amounts of GGBF slag replacement with pumice on the flowability of fresh geopolymer paste is demonstrated in Fig. 10. Generally, 5% of GGBF slag replacement with pumice results in maximum flow of the geopolymer paste. The flow of the geopolymer paste reduces about 24% by 50% GGBF slag replacement with pumice. With increase in pumice replacement level from 50% to 75%, the flow of GGBF slag-based geopolymer decreases about 60%. Also the geopolymer paste with 100% pumice as a raw material is sticky, with high viscosity and hardly could be cast in the mould. All mentioned observations are because of the higher amount of specific surface area of pumice than GGBF slag (5074 cm2/g vs 3383 cm2/g) which causes more water demand to reach constant flowability. The flowability of fresh geopolymer paste containing KOH is higher than NaOH if other factors are fixed. For the GGBF slag-based geopolymer with pumice, flowability decreased with the increase in molarity of alkaline solution (see Fig. 10). As been mentioned in Section 3.1 water content plays an important role in the flowability of the fresh geopolymer paste. Water content decreases with the increase in molarity of the alkaline solution and leads to higher viscosity. The effect of GGBF slag replacement with pumice after 91 days of curing on the compressive strength of geopolymer paste is shown in Fig. 11. It can be concluded that in the presence of 6 M and 8 M alkaline solutions, the maximum strength could be reached with 5% and 10% replacement respectively.
3.3. SEM investigation Fig. 12 shows SEM micrographs of the selected geopolymer pastes in 3 and 28 days of curing. Fig. 12(a) shows that there are some non-reacted GGBF slag particles (S) in sample after 3 days of curing. It has been concluded from Fig. 12(e–h) that the GGBF slag particle has been completely transferred into the geopolymer phase (G) after 28 days of curing and forms a dense structure. 4. Conclusions As seen in this paper GGBF slag-based geopolymer paste can be produced through room temperature. From the results obtained in this investigation, the following conclusions are drawn: 1. The flowability of GGBF slag-based geopolymer pastes containing KOH is higher than identical NaOH. The flow of the geopolymer paste reduces by more than 5% GGBF slag replacement with pumice. 2. The presence of sodium silicate in the GGBF slag-based geopolymer paste largely enhances the workability and results in increasing the compressive strength. The optimum modulus of sodium silicate and optimum ratio of sodium silicate to alkaline solution are 2.33 and 0.4 respectively. 3. The GGBF slag-based geopolymer paste specimens containing potassium hydroxide had higher compressive strength at various ages up to 91 days when compared with the specimens containing sodium hydroxide.
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(e)
(a)
G G
(b)
(f)
(c)
(g)
S
(d)
(h)
Fig. 12. SEM micrograph of (a and e) Na6-WG2.33-P0, (b and f) Na6-WG2.33-P10, (c and g) K6-WG2.33-P0, (d and h) K6-WG2.33-P10. (a, b, c and d: after 3 days geopolymerisation and e, f, g and h: after 28 days geopolymerisation), S: GGBF slag and G: geopolymer.
4. The optimum concentration of alkaline solution is 6–8 molar. 5. It can be concluded that in the presence of 6 M and 8 M alkaline solutions the maximum strength could be reached with 5% and 10% replacement respectively.
References [1] A.A. Ramezanianpour, A. Kazemian, M.A. Moghaddam, F. Moodi, A.M. Ramezanianpour, Studying effects of low-reactivity GGBFS on chloride
resistance of conventional and high strength concretes, Mater. Struct. (July 2015). [2] A.A. Ramezanianpour, M. Mahdikhani, Gh. Ahmadibeni, The effect of rice husk ash on mechanical properties and durability of sustainable concretes, Int. J. Civil Eng. (2009) 83–91. [3] A.A. Ramezanianpour, M. Jafari Nadooshan, M. Peydayesh, Effect of a new composite cement containing volcanic ash and limestone on mechanical properties and salt scaling resistance of concrete, J. Mater. Civil Eng. (2013). [4] D. Bondar, C.J. Lynsdale, N.B. Milestone, N. Hassani, A.A. Ramezanianpour, Effect of type, form, and dosage of activators on strength of alkali-activated natural pozzolans, Cem. Concr. Compos. 33 (2011) 251–260.
M. Jafari Nadoushan, A.A. Ramezanianpour / Construction and Building Materials 111 (2016) 337–347 [5] D. Bondar, Alkali activation of Iranian natural pozzolans for producing geopolymer cement and concrete: a dissertation submitted to University of Sheffield in fulfilment of the requirements for the degree of Doctor of Philosophy, UK, 2009. [6] W. Mozgawa, J. Deja, Spectroscopic studies of alkaline activated GGBF slag geopolymers, J. Mol. Struct. (2009) 434–441. [7] G. Habert, J.B. d’Espinose de Lacaillerie, N. Roussel, An environmental evaluation of geopolymer based concrete production: reviewing current research trends, J. Cleaner Prod. 19 (2011) 1229–1238. [8] Joseph Davidovits, Application of Ca-based geopolymer with blast furnace slag, a review, in: 2nd International Slag Valorisation Symposium, Leuven, 2011. [9] T.W. Cheng, J.P. Chiu, Fire-resistant geopolymer produced by granulated blast furnace slag, Miner. Eng. 16 (2003) 205–210. [10] Jae Eun Oh, Paulo J.M. Monteiro, Ssang Sun Jun, Sejin Choi, Simon M. Clark, The evolution of strength and crystalline phases for alkali-activated ground blast furnace slag and fly ash-based geopolymers, Cem. Concr. Res. 40 (2010) 189–196.
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[11] Zhang Yunsheng, Sun Wei, Chen Qianli, Chen Lin, Synthesis and heavy metal immobilization behaviors of slag based geopolymer, J. Hazard. Mater. 143 (2007) 206–213. [12] Shuguang Hu, Hongxi Wang, Gaozhan Zhang, Qingjun Ding, Bonding and abrasion resistance of geopolymeric repair material made with steel slag, Cem. Concr. Compos. 30 (2008) 239–244. [13] ASTM, C1437: standard test method for flow of hydraulic cement mortar, Annual Book of ASTM Standards, vol. 04.01, American Society for Testing and Materials, United States, 2001. [14] ASTM, C109: standard test method for compressive strength of hydraulic cement mortars, Annual Book of ASTM Standards, vol. 04.02, American Society for Testing and Materials, United States, 2001. [15] H. Xu, J.S.J. Van Deventer, The geopolymerisation of alumino-silicate minerals, Int. J. Miner. Process. 59 (2000) 247–266. [16] L. Fernandez-Carrasco, A. Fernandez Jimenez, A. Palomo, Alkali activation of pozzolan-cement aluminate cement mixtures, in: 12th International Congress on the Chemistry of Cements, 2007.
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
The effect of type and concentration of activators on flowability and compressive strength of natural pozzolan and slag-based geopolymers Mohsen Jafari Nadoushan, Ali Akbar Ramezanianpour ⇑ Concrete Technology and Durability Research Center (CTDRc), Department of Civil & Environmental Engineering, Amirkabir University of Technology, Tehran, Iran
h i g h l i g h t s Production of new geopolymer cement using by natural pozzolan and ground granulated blast furnace slag. The effects of different activator types on the flowability and mechanical properties of alkali activated slag. The effects of different level of natural pozzolan on the properties of slag-based geopolymer. Scanning electron microscopy studies of slag-based geopolymer containing natural pozzolan.
a r t i c l e
i n f o
Article history: Received 14 October 2015 Received in revised form 27 December 2015 Accepted 17 February 2016
Keywords: Geopolymer Slag Natural pozzolan Compressive strength Alkaline solution Activator
a b s t r a c t Materials resulting from the alkali activation of GGBF slag show a wide range of workability, compressive strength and permeability. The main objectives of this work are to determine the effects of alkaline solution type and concentration, modulus of sodium silicate, sodium silicate to alkaline solution ratio and natural pozzolan replacement on the workability and mechanical properties of alkali activated GGBF slag. Results reveal that the geopolymer paste specimens containing KOH solution have higher compressive strength when compared with the geopolymer paste specimens containing NaOH solution. The optimum concentration of the alkaline solution is 6–8 molar. It can be concluded that in the presence of 6 and 8 molar alkaline solutions the maximum strength could be reached with 5% and 10% replacement respectively. The optimum range for each factor is suggested based on the different effects of these factors on the compressive strength. Ó 2016 Published by Elsevier Ltd.
1. Introduction Concrete is the most widely used building material in the world which is because of its beauty, appropriate mechanical properties and durability in different environments. The concrete industry is one of the major consumers of natural resources. In Portland cement production process, natural resources which must be remained for next generations are being used. On the other hand Portland cement clinker production is an energy-intensive process. This energy is mostly supplied by fossil fuels which is costintensive in addition to producing a large amount of greenhouse gas emissions, mostly CO2.
⇑ Corresponding author. E-mail addresses: [email protected] (M. Jafari Nadoushan), [email protected]. ir (A.A. Ramezanianpour). http://dx.doi.org/10.1016/j.conbuildmat.2016.02.086 0950-0618/Ó 2016 Published by Elsevier Ltd.
Therefore any reduction in Portland cement clinker usage reduces energy use and CO2 emissions. One possible way to reduce energy consumption and greenhouse gas emissions in concrete industry is the replacement of clinker with supplementary cementitious materials (SCMs) that has been used considerably over past five decades. Various researchers reveal that the replacement of cement with SCMs such as GGBF slag, fly ash, rice husk ash, silica fume and natural pozzolan in the production of concrete improves the mechanical properties and durability of concrete in addition to reducing environmental impacts [1–3]. Nowadays, SCMs such as GGBF slag and fly ash are used up to 70% replacement with Portland cement in concrete, while it is possible to produce geopolymer concrete with only Si and Al rich materials and no Portland cement. Geopolymers are cohesive materials and have three dimensional polymeric chain and ring structure consisting of Si–O–Al–O bonds that are formed by alkali activation of Si and Al rich materials such as natural and artificial
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Fig. 1. Particle size distributions for GGBF slag and pumice.
Table 1 Chemical characteristics of raw materials. Chemical components
GGBF slag
Pumice
Calcium oxide (CaO) (%) Silicon dioxide (SiO2) (%) Magnesium oxide (MgO) (%) Aluminum oxide (Al2O3) (%) Ferric oxide (Fe2O3) (%) Sulphate oxide (SO3) (%) Sodium oxide (Na2O) (%) Potassium oxide (K2O) (%) Titanium dioxide (TiO2) (%) Manganese oxide (MnO) (%) Phosphor pentoxide (P2O5) (%) LOI (%)
36.75 37.21 8.52 11.56 1.01 0.97 0.61 0.70 1.23 0.99 0.03 0.02
7.4 64.9 1.98 12.1 5.2 0.22 2.49 1.88 0.79 .123 0.2 2.5
pozzolans and can be a real alternative to ordinary Portland cement for construction. Highly alkaline solutions are used to induce the silicon and aluminium ions in the raw materials to dissolve and form the geopolymer paste with three steps in the process including: dissolution of any pozzolanic compound, partial orientation of mobile precursors and re-precipitation of the particles from the initial solid phase. It has been found that geopolymer binders can be synthesized by activating natural pozzolans and condensing them with sodium silicate in a highly alkaline environment [4,5]. Geopolymers produced from solid waste as starting material have benefits such as reducing environmental impacts by using lesser amounts of calcium-based minerals, lower manufacturing
temperature, lower fuel consumption and lower greenhouse gas emission in comparison with ordinary Portland cement and provides a route towards the concept of sustainable development. Blast furnace slag is a by-product that is formed during the production of hot metal in blast furnace. If the molten slag is cooled and solidified by rapid water quenching, ground granulated blast furnace (GGBF) slag is formed. When crushed or milled to very fine cement-sized particles, ground granulated blast furnace slag has cementitious properties, which is a suitable replacement with Portland cement. It has been found that GGBF slag-based geopolymer binders can be synthesized by alkali activation of ground granulated blast furnace slag in presence of sodium silicate. The use of GGBF slag as geopolymer binding material requires its preparation involving grinding, alkali activation and hydration [6]. Geopolymer concrete made from granulated blast furnace slag requires less sodium silicate solution in order to be activated. They therefore have a lower environmental impact than geopolymer concrete made from pure metakaolin [7]. Slag-based geopolymer cements are capable of being mixed with a relatively low-alkali activating solution and must cure in a reasonable time under ambient conditions [8]. The physical and mechanical properties of the geopolymer correlated well with the concentration of alkaline solution. Cheng and Chiu [9] used three different KOH concentrations (5, 10 and 15 molar) for alkali activation of GGBF slag. The sample containing 10 M KOH showed the best strength. With increasing KOH concentration to 15 M, the compressive strength decreased which could be due to too much K+ ions in the framework cavities [9]. The calcium in GGBF slag seems to increase the
Fig. 2. XRD patterns of GGBF slag and pumice.
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Fig. 3. SEM micrographs of (a) GGBF slag and (b) pumice.
Table 2 The introduced levels for each factor in phase 1. Factor
Unit
Level 1
Level 2
Level 3
Level 4
Level 5
Alkaline solution type Alkaline solution concentration Modulus of sodium silicate Sodium silicate to alkaline solution
– Mole Molar ratio Weight ratio
NaOH 6 2.1 0
KOH 8 2.33 0.1
– 10 3.13 0.2
– – – 0.3
– – – 0.4
final mechanical strength. This is because the Ca in GGBF slag is available to form C–S–H [10]. Yunsheng et al. [11] manufactured geopolymer by slag and metakaolin and investigated the immobilization behaviours of slag based geopolymer in the presence of Pb and Cu. Through this study, it is concluded that geopolymer containing 50% slag that is synthesized at steam curing (80 °C for 8 h), exhibited higher mechanical strength. Hu et al. [12] prepared three repair materials using cement-based, geopolymeric and geopolymeric containing steel slag binders. The test results showed that the geopolymeric materials had better repair characteristics than cement-based repair materials, and the addition of steel slag could improve significantly the abrasion resistance of geopolymeric repair. As you can see in the literatures, many factors influence the properties of the slag-based geopolymer. Bondar et al. [4] investigated the effect of the alkaline medium on the strength of alkali-activated Taftan natural pozzolan. The results showed that the KOH solutions between 5 and 7.5 M give the highest values for compressive strength. The optimum curing temperature to achieve the highest strength for alkali-activated Taftan pozzolan was 60 °C [5]. This paper describes the effects of different alkaline solution types and concentrations, modulus of sodium silicate, sodium silicate to alkaline solution ratio and natural pozzolan on the flowability and the mechanical properties of the alkali activated GGBF slag. Properties of fresh and hardened geopolymer specimens such as workability and compressive strength were measured. Scanning electron microscopy (SEM) investigations were conducted on the selected mixes.
89.98 lm and the median particle size of 13.48 lm. The raw materials have been analyzed by X-ray fluorescence (XRF) analysis using a Philips PW 1480 instrument. Chemical characteristics of GGBF slag and Taftan pumice are shown in Table 1. X-ray diffraction (XRD) carried out on GGBF slag and pumice by an EQuniox 3000 machine is presented in Fig. 2. The XRD patterns of the raw materials show that all of them are a mixture of minerals with various degrees of crystallization. Crystalline particles were observed in the pumice sample. Two weak peaks in Xray diffraction studies of GGBF slag powder reveal some crystalline components. SEM photographs of both GGBF slag and pumice are presented in Fig. 3. Potassium hydroxide (KOH) and sodium hydroxide (NaOH) pellets have dissolved to produce the 6, 8 and 10 molar alkaline solutions for geopolymer paste production. Sodium silicate (water glass) provided by Iran Silicate Industrial Company in the form of solution with modulus of 2.1, 2.33 and 3.13. The modulus of water glass is the molar ratio of SiO2/Na2O. The water contents of 2.1, 2.33 and 3.13 modulus sodium silicate are 60%, 52% and 58% and their specific gravities are 1.45, 1.56 and 1.45 respectively. Deionized water was used to produce all alkaline solutions. At first, four factors related to strength of GGBF slag-based geopolymer cement paste such as alkaline solution type, alkaline solution concentration (mole), modulus of sodium silicate (molar ratio) and sodium silicate to alkaline solution (weight ratio) have been investigated. The level of each factor and the values of the tested factors chosen based on the previous researches are presented in Table 2. A total of 90 geopolymer paste mixtures were made in this step. The mixture proportions for geopolymer cement paste specimens are summarized in Table 3. The geopolymer cement paste mixtures were prepared with a constant total binder (GGBF slag) content of about 1547 kg/m3 and the activator (alkaline solution + sodium silicate) to binder ratio in the mixes was 0.4. In the next step to find the effect of natural pozzolans on the properties of GGBF slag-based geopolymer cement paste, 9 different replacement levels were considered. The factors and their levels are presented in Table 4. The mixture proportions for GGBF slag-based geopolymer paste specimens containing natural pozzolan are summarized in Table 5. In this step the geopolymer cement paste mixtures were prepared with the optimum modulus of sodium silicate and the optimum ratio of sodium silicate to alkaline solution (2.33 and 0.4 respectively). The activator (alkaline solution + sodium silicate) to binder ratio in the mixes was 0.4.
2. Experimental programs 2.2. Mixing procedure and specimen preparation 2.1. Material and mixture proportion Two raw materials containing GGBF slag and natural pozzolan used throughout this work to be activated as geopolymer cement. GGBF slag with a specific surface area of 3383 cm2/g and a mean particle size of 25.97 lm was obtained. Taftan pumice pozzolan with a specific surface area of 5074 cm2/g and a mean particle size of 22.24 lm was obtained. Specific surface of pumice is greater than specific surface of GGBF slag. The specific gravity of GGBF slag and pumice are 2.79 and 2.54 g/cm3 respectively. The cumulative particle size distributions (PSD) for GGBF slag and pumice are shown in Fig. 1. GGBF slag has a particle size of 1% larger than 86.46 lm and the median particle size of 18.35 lm and pumice has a particle size of 1% larger than
KOH or NaOH pellets were added to the deionized water to provide the 6, 8 and 10 M potassium and sodium hydroxide solutions and were cooled. Geopolymer cement pastes were prepared by adding potassium and sodium hydroxide solutions to the raw materials and blending for 2 min. Then, the sodium silicate was added and mixed for 2 more minutes to form geopolymer paste. The resulting geopolymer paste was transferred to the plexiglass moulds of 20 20 20 mm dimensions. Geopolymer cement pastes specimens were compacted by external vibration to reduce entrapped air and kept protected after casting to avoid water evaporation. At first 24 h the specimens were kept in the room temperature. After 24 h specimens were removed from the mould and cured in the special plastic bags at 23 ± 2 °C. Rapid drying should be avoided to eliminate shrinkage cracking.
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Table 3 Slag-based geopolymer paste mixtures, flowability and compressive strength. Col. Mix
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73
Based material AS
Na6-WG2.1-0 GGBF slag Na6-WG2.1-0.1 Na6-WG2.1-0.2 Na6-WG2.1-0.3 Na6-WG2.1-0.4 Na6-WG2.33-0 Na6-WG2.33-0.1 Na6-WG2.33-0.2 Na6-WG2.33-0.3 Na6-WG2.33-0.4 Na6-WG3.13-0 Na6-WG3.13-0.1 Na6-WG3.13-0.2 Na6-WG3.13-0.3 Na6-WG3.13-0.4 Na8-WG2.1-0 Na8-WG2.1-0.1 Na8-WG2.1-0.2 Na8-WG2.1-0.3 Na8-WG2.1-0.4 Na8-WG2.33-0 Na8-WG2.33-0.1 Na8-WG2.33-0.2 Na8-WG2.33-0.3 Na8-WG2.33-0.4 Na8-WG3.13-0 Na8-WG3.13-0.1 Na8-WG3.13-0.2 Na8-WG3.13-0.3 Na8-WG3.13-0.4 Na10-WG2.1-0 Na10-WG2.1-0.1 Na10-WG2.1-0.2 Na10-WG2.1-0.3 Na10-WG2.1-0.4 Na10-WG2.33-0 Na10-WG2.33-0.1 Na10-WG2.33-0.2 Na10-WG2.33-0.3 Na10-WG2.33-0.4 Na10-WG3.13-0 Na10-WG3.13-0.1 Na10-WG3.13-0.2 Na10-WG3.13-0.3 Na10-WG3.13-0.4 K6-WG2.1-0 K6-WG2.1-0.1 K6-WG2.1-0.2 K6-WG2.1-0.3 K6-WG2.1-0.4 K6-WG2.33-0 K6-WG2.33-0.1 K6-WG2.33-0.2 K6-WG2.33-0.3 K6-WG2.33-0.4 K6-WG3.13-0 K6-WG3.13-0.1 K6-WG3.13-0.2 K6-WG3.13-0.3 K6-WG3.13-0.4 K8-WG2.1-0 K8-WG2.1-0.1 K8-WG2.1-0.2 K8-WG2.1-0.3 K8-WG2.1-0.4 K8-WG2.33-0 K8-WG2.33-0.1 K8-WG2.33-0.2 K8-WG2.33-0.3 K8-WG2.33-0.4 K8-WG3.13-0 K8-WG3.13-0.1 K8-WG3.13-0.2
NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH
Molarity Modulus SS to AS Activator to pozz. Flow of geopolymer Compressive strength (MPa) of SS paste (%) 3 days 7 days 14 days 21 days 28 days 91 days 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 8 8 8 8 8 8 8 8 8 8 8 8 8
2.1 2.1 2.1 2.1 2.1 2.33 2.33 2.33 2.33 2.33 3.13 3.13 3.13 3.13 3.13 2.1 2.1 2.1 2.1 2.1 2.33 2.33 2.33 2.33 2.33 3.13 3.13 3.13 3.13 3.13 2.1 2.1 2.1 2.1 2.1 2.33 2.33 2.33 2.33 2.33 3.13 3.13 3.13 3.13 3.13 2.1 2.1 2.1 2.1 2.1 2.33 2.33 2.33 2.33 2.33 3.13 3.13 3.13 3.13 3.13 2.1 2.1 2.1 2.1 2.1 2.33 2.33 2.33 2.33 2.33 3.13 3.13 3.13
0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2
0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4
40 65 150 160 160 40 55 65 90 140 40 50 55 58 60 5 50 143 160 160 5 48 145 150 150 5 10 120 123 125 35 40 130 130 140 35 100 105 110 115 35 35 95 100 115 20 20 100 135 150 20 15 95 125 140 20 15 60 85 90 35 105 160 160 160 35 100 140 155 160 35 20 50
21.70 31.41 57.79 71.04 61.87 21.70 38.12 56.40 70.17 83.61 21.70 35.51 60.39 69.89 85.27 21.97 35.03 48.60 73.71 63.30 21.97 50.22 51.79 55.46 68.60 21.97 35.84 57.66 64.20 72.56 39.37 59.33 61.78 66.35 69.85 39.37 45.03 59.46 60.48 67.72 39.37 43.67 61.59 64.31 57.96 31.01 45.96 57.41 85.35 87.38 31.01 49.73 68.15 76.26 77.93 31.01 46.18 54.52 82.49 59.13 42.58 53.90 66.17 65.05 67.64 42.58 65.34 66.67 74.71 78.12 42.58 41.42 64.46
24.27 33.33 80.88 74.13 82.11 24.27 51.15 63.39 80.90 85.08 24.27 43.58 67.30 79.76 87.63 26.91 42.13 55.54 84.13 81.38 26.91 59.68 68.38 69.03 84.06 26.91 50.33 71.34 72.91 76.78 43.63 65.68 76.22 77.65 85.74 43.63 52.28 62.89 76.11 80.97 43.63 56.40 71.67 72.46 70.13 50.72 55.32 70.23 89.55 91.70 50.72 58.67 87.56 99.26 86.21 50.72 54.60 54.76 92.32 72.15 54.43 67.41 81.28 83.33 85.40 54.43 67.08 84.29 91.97 94.51 54.43 52.80 71.40
36.07 54.09 84.11 92.83 99.02 36.07 57.32 74.13 83.32 98.23 36.07 43.90 98.13 98.28 120.85 32.38 54.48 80.43 87.14 99.80 32.38 63.35 91.31 92.09 94.27 32.38 56.58 87.05 89.23 82.13 45.11 72.43 76.65 85.73 90.40 45.11 55.91 71.78 80.81 86.94 45.11 59.14 75.96 78.62 74.23 64.20 72.58 98.44 101.19 101.25 64.20 68.97 94.20 99.68 113.31 64.20 60.99 75.46 93.00 107.77 60.07 76.23 92.08 83.13 105.36 60.07 86.17 92.63 94.66 95.11 60.07 62.17 89.37
44.19 61.14 109.88 113.19 118.72 44.19 64.58 87.28 97.83 141.43 44.19 61.22 102.44 99.02 125.63 38.31 59.27 81.35 87.82 100.99 38.31 72.50 99.85 104.36 110.46 38.31 59.32 87.19 88.94 87.25 58.29 79.66 87.57 91.19 97.70 58.29 60.68 80.91 83.74 93.65 58.29 75.71 80.41 87.38 85.71 64.80 74.37 106.93 113.75 115.49 64.80 70.75 104.28 111.31 126.70 64.80 61.28 75.60 100.22 115.11 64.92 79.99 112.39 117.07 122.56 64.92 86.56 114.36 115.18 118.95 64.92 66.25 93.51
46.79 62.81 97.72 118.10 121.36 46.79 73.10 117.10 133.69 145.22 46.79 63.43 112.03 120.00 126.26 49.42 66.10 85.12 100.48 104.20 49.42 77.89 111.63 111.94 113.86 49.42 61.27 88.48 92.86 96.20 59.53 85.43 95.32 104.44 106.81 59.53 62.17 82.91 101.25 102.51 59.53 76.56 91.91 104.83 91.74 67.99 84.13 103.01 118.09 118.22 67.99 75.68 104.59 126.47 127.42 67.99 70.91 84.69 103.21 116.17 69.38 81.86 114.65 118.12 123.16 69.38 96.26 117.11 123.76 139.31 69.38 70.23 93.81
65.28 78.57 100.44 123.12 127.43 65.28 96.11 121.95 139.03 145.77 65.28 83.51 115.43 125.32 131.60 64.37 88.73 95.05 107.47 108.96 64.37 93.88 104.87 107.87 122.62 64.37 68.11 101.45 108.69 116.07 60.07 91.78 98.25 107.07 116.54 60.07 95.82 104.57 105.16 115.72 60.07 83.46 92.68 112.72 96.61 70.04 109.18 113.10 120.67 141.19 70.04 115.95 140.68 153.25 162.67 70.04 85.56 88.90 110.83 124.77 87.11 94.78 127.42 141.11 144.63 87.11 110.25 132.14 149.75 169.41 87.11 87.62 119.12
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74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90
Based material AS
K8-WG3.13-0.3 K8-WG3.13-0.4 K10-WG2.1-0 K10-WG2.1-0.1 K10-WG2.1-0.2 K10-WG2.1-0.3 K10-WG2.1-0.4 K10-WG2.33-0 K10-WG2.33-0.1 K10-WG2.33-0.2 K10-WG2.33-0.3 K10-WG2.33-0.4 K10-WG3.13-0 K10-WG3.13-0.1 K10-WG3.13-0.2 K10-WG3.13-0.3 K10-WG3.13-0.4
KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH
Molarity Modulus SS to AS Activator to pozz. Flow of geopolymer Compressive strength (MPa) of SS paste (%) 3 days 7 days 14 days 21 days 28 days 91 days 8 8 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10
3.13 3.13 2.1 2.1 2.1 2.1 2.1 2.33 2.33 2.33 2.33 2.33 3.13 3.13 3.13 3.13 3.13
0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4
0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4
80 100 5 115 123 125 128 5 110 113 115 115 5 75 80 85 100
64.61 63.57 41.93 56.24 51.13 63.83 63.63 41.93 62.32 54.58 53.55 52.37 41.93 57.24 45.89 59.58 53.06
82.33 71.94 47.18 57.72 72.75 83.69 68.68 47.18 65.80 71.11 73.58 72.46 47.18 61.34 67.39 77.47 74.30
103.09 114.22 60.23 71.99 72.55 89.87 85.38 60.23 70.70 75.30 80.29 75.41 60.23 76.93 78.10 95.69 93.13
107.59 117.00 67.88 75.55 80.47 87.17 93.60 67.88 78.48 79.37 101.40 90.83 67.88 77.41 82.42 97.62 95.11
117.99 134.76 67.15 76.28 80.57 103.86 113.59 67.15 81.10 87.53 109.07 102.76 67.15 80.31 92.53 99.89 96.39
137.47 169.08 72.09 90.42 105.40 127.44 128.57 72.09 86.70 123.17 133.73 125.28 72.09 87.00 106.55 116.70 107.53
AS: alkali solution, SS: sodium silicate. 2.3. Testing procedure Flowability of the fresh geopolymer paste was determined by ASTM C 1437 which consists of measuring the increase in average base diameter of the paste mass, expressed as a percentage of the original base diameter [13]. Geopolymer paste cubes of 20 20 20 mm dimensions were cast for compressive strength. They were tested for compressive strength after 3, 7, 14, 21, 28 and 91 days maintained in the sealed curing. The specimens were wrapped and insulated in a special plastic bag to prevent evaporation and left at room temperature until the age of the test. Three samples for each formulation were measured for the compressive strength according to ASTM C109 [14]. The loading rate of compression machine and its capacity are 1.5 kN/S and 200 kN respectively. The microstructure of the geopolymer pastes was studied by using scanning electron microscope (SEM): Philips XL30. For scanning electron microscopy studies, selected geopolymer paste samples cured 3 and 28 days were used. A cubic form paste was cut into 10 mm squares which had one flat side. The samples were dried and coated with gold.
3. Results and discussions 3.1. Workability The flow of GGBF slag-based geopolymer fresh pastes are presented in Table 3. It is shown in Fig. 4 that the flowability of GGBF slag-based geopolymer pastes containing KOH is higher than the identical NaOH. Despite the fact that, because of more molar mass, in the same molarity, KOH solution contains lower water in comparison with NaOH. Fig. 5 demonstrates the flow of the fresh geopolymer pastes containing different types of sodium silicate with different contents. In the presence of sodium or potassium hydroxide, adding the sodium silicate largely enhances the workability of GGBF slag-based geopolymer paste. The sodium silicate solution improves the dissolution of raw material in alkaline environment and more dissolved raw materials result in higher workability. As shown in Fig. 5, increasing of sodium silicate to alkaline solution ratio from 0 to 0.4 results in the increase of the flow of GGBF slag-based geopolymer paste, keeping other parameters constant. Water content is the most effective factor on the flow of the fresh geopolymer paste. Generally, more water leads to higher flowability. The water contents of 2.1, 2.33 and 3.13 modulus sodium silicate are 60%, 52% and 58% respectively. Therefore 2.1 ratio sodium silicate results in maximum workability (see Fig. 5). It was considered that 50% flow (equilibrium 150 mm flow diameter) is the minimum value suitable for geopolymer paste that can easily be worked and placed in the mould. It is found that the mixtures with no sodium silicate and sodium silicate/ alkaline solution of 0.1 have very poor workability and cannot be cast easily.
3.2. Compressive strength The compressive strength of the GGBF slag-based geopolymer paste specimens are presented in Table 3. The highest compressive strength was obtained for Na6-WG2.33-0.4 and K8-WG2.33-0.4 at 28 and 91 days of curing respectively (145.22 MPa and 169.41 MPa). This result indicates that the optimum value of modulus of sodium silicate and sodium silicate to alkaline solution are 2.33 and 0.4 respectively. Generally due to more compaction, the pastes with more workability could have more compressive strength. But it is not the only significant factor. Results in Fig. 6 indicate the compressive strength of Na8WG2.33-0.4 at different ages of curing. As expected, the compressive strength of the geopolymer pastes developed with the curing time. After 3 days of curing, GGBF slag-based geopolymers obtained more than 52% of its final compressive strength which increased to 87% at 28 days of curing. Rapid strength gain rate of geopolymer makes it an ideal material for repairing concrete structures. 3.2.1. Effects of the alkaline solution type on the compressive strength The alkaline solution causes the dissolution of the raw materials. The alkaline solution must be carefully selected because their composition has different impacts on the properties of fresh geopolymer paste and development of the mechanical properties in the hardened geopolymer. Two mostly used alkaline solutions in geopolymer formation are NaOH and KOH. The type of alkaline solution plays an important role on the dissolution rate. As been demonstrated in Fig. 7 for example, the GGBF slag-based geopolymer paste specimens containing potassium hydroxide had higher compressive strength at various ages up to 91 days when compared with the specimens containing sodium hydroxide. For example at 91 days of curing, the mean compressive strength of GGBF slag-based geopolymer specimens containing potassium hydroxide is 16.1% higher than that for specimens containing sodium hydroxide. The ionic size of Na+ is 116 pm while ionic size of K+ is 152 pm. The larger K+ favours the formation of larger silicate oligomers with which Al (OH) 4 prefers to bind. Therefore, in KOH solutions more geopolymer precursors exist which result in better setting and stronger compressive strength of the geopolymers than in the case of NaOH [15]. 3.2.2. Effects of the alkaline solution concentration on the compressive strength Fig. 8 illustrates the effect of alkaline solution concentration on compressive strength of GGBF slag-based geopolymer paste in
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Table 4 The introduced levels for each factor in phase 2. Factor
Unit
Level 1
Level 2
Level 3
Level 4
Level 5
Level 6
Level 7
Level 8
Level 9
Alkaline solution type Alkaline solution concentration Slag replacement with natural pozzolan
– Mole Weight %
NaOH 6 0
KOH 8 5
– – 10
– – 15
– – 20
– – 25
– – 50
– – 75
– – 100
Table 5 Slag-based with natural pozzolan geopolymer paste mixtures, flowability and compressive strength. Col.
Mix
Based material
AS
Molarity
Slag replacement with pumice (%)
Flow (%)
91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126
Na6-WG2.33-P0 Na6-WG2.33-P5 Na6-WG2.33-P10 Na6-WG2.33-P15 Na6-WG2.33-P20 Na6-WG2.33-P25 Na6-WG2.33-P50 Na6-WG2.33-P75 Na6-WG2.33-P100 Na8-WG2.33-P0 Na8-WG2.33-P5 Na8-WG2.33-P10 Na8-WG2.33-P15 Na8-WG2.33-P20 Na8-WG2.33-P25 Na8-WG2.33-P50 Na8-WG2.33-P75 Na8-WG2.33-P100 K6-WG2.33-P0 K6-WG2.33-P5 K6-WG2.33-P10 K6-WG2.33-P15 K6-WG2.33-P20 K6-WG2.33-P25 K6-WG2.33-P50 K6-WG2.33-P75 K6-WG2.33-P100 K8-WG2.33-P0 K8-WG2.33-P5 K8-WG2.33-P10 K8-WG2.33-P15 K8-WG2.33-P20 K8-WG2.33-P25 K8-WG2.33-P50 K8-WG2.33-P75 K8-WG2.33-P100
GGBF slag + pumice
NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH KOH
6 6 6 6 6 6 6 6 6 8 8 8 8 8 8 8 8 8 6 6 6 6 6 6 6 6 6 8 8 8 8 8 8 8 8 8
0 5 10 15 20 25 50 75 100 0 5 10 15 20 25 50 75 100 0 5 10 15 20 25 50 75 100 0 5 10 15 20 25 50 75 100
140 150 140 130 128 125 110 50 5 138 140 130 125 120 118 105 25 0 145 160 150 145 140 135 110 90 10 135 135 130 125 120 115 100 20 0
Compressive strength (MPa) 3 days
7 days
14 days
21 days
28 days
91 days
68.52 67.95 73.20 76.14 77.01 65.33 37.25 19.05 0.00 63.13 63.86 64.04 64.29 59.92 46.23 45.03 10.92 0.00 54.61 78.84 66.14 53.40 52.24 57.71 46.90 17.63 0.00 51.60 55.55 55.76 53.92 45.67 57.67 40.43 19.23 0.00
83.79 81.31 87.98 87.49 80.09 66.67 43.54 22.25 1.25 74.57 91.11 79.47 80.41 79.89 58.35 44.55 17.03 1.26 71.02 98.47 91.47 89.13 88.83 62.66 54.47 26.79 1.21 82.09 90.40 82.69 74.98 70.85 61.19 56.51 28.29 1.26
107.32 111.69 115.76 115.45 112.37 85.49 54.74 28.67 2.44 80.87 102.36 101.13 95.59 95.63 58.53 51.71 24.49 1.23 97.99 112.78 109.75 108.04 108.59 83.31 80.83 41.68 3.57 89.23 92.04 95.49 81.68 79.47 71.24 57.55 36.67 2.43
110.86 123.76 131.73 129.96 120.77 87.50 65.97 41.05 3.74 89.70 114.22 113.18 106.62 106.04 75.76 58.64 39.11 2.51 99.46 142.32 126.16 123.15 122.79 97.03 91.20 54.67 7.50 91.33 120.40 122.26 113.30 112.20 85.43 74.19 49.71 3.71
114.37 131.75 136.22 133.75 120.83 88.89 80.93 52.17 6.27 101.18 120.69 123.12 112.78 113.18 77.67 61.98 42.94 3.01 121.94 147.08 140.40 134.33 120.64 116.84 100.84 55.75 8.06 118.08 121.90 123.76 115.84 115.57 89.81 79.61 55.99 4.14
126.32 148.29 145.99 143.90 132.95 129.68 99.22 73.74 21.36 110.29 131.15 135.56 128.13 125.35 123.43 88.34 43.11 12.60 122.26 159.36 151.38 147.77 139.10 130.32 118.36 90.87 39.71 120.10 136.57 140.39 133.92 132.92 130.25 89.79 87.05 26.42
AS: alkali solution.
presence of different amount of 3.13 modulus sodium silicate. As been demonstrated in Fig. 8 the optimum concentration of alkaline solution is 8 molar. Increasing the alkaline solution concentration from 8 to 10 M results in reduction of compressive strength of the GGBF slag-based geopolymer pastes. The increase in molarity of alkaline solution causes lower workability, lower compressive strength, more cost and increase in the efflorescence risk. In this work, the efflorescence has been seen in the specimens containing KOH 10 M. Because of the reduction of alkaline solution in mixtures, increasing the sodium silicate to alkaline solution ratio causes reduction in efflorescence. Lower molarity and lower amount of alkaline solution in mixtures lead to lower efflorescence. 3.2.3. Effects of sodium silicate to alkaline solution ratio on the compressive strength The activating solution can contain a supplementary source of silica such as sodium silicate, to promote geopolymerization phases. It has been demonstrated in Fig. 9 that the presence of sodium silicate in the GGBF slag-based geopolymer paste results in increasing the compressive strength. It is clear that increasing the sodium silicate to alkaline solution ratio from 0 to 0.3 causes
the increase in the compressive strength about 100% whereas increasing from 0.3 to 0.4 has a slight effect on enhancement of the compressive strength. Sodium silicate promotes the compressive strength of GGBF slag-based geopolymer paste in two ways: (1) the sodium silicate solution improves the dissolution rate of Si and Al; (2) because the Al–O bonds are weaker than Si–O bonds [16] in the raw material, Al dissolves rapidly in alkali solution. Therefore if Si ion is provided prior to being available through dissolution of raw material, it can increase the degree of geopolymerization and improves the mechanical properties. 3.2.4. Effects of modulus of sodium silicate on the compressive strength The two most important properties of sodium silicate solution in geopolymer paste production are its modulus (SiO2:Na2O) and amounts. It has been demonstrated in Fig. 9 that the optimum modulus of sodium silicate for compressive strength is 2.33. 3.2.5. Effects of natural pozzolan replacement on the compressive strength In many researches one raw material is combined with a liquid activator in order to develop geopolymer [4,9]. In this study, com-
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Fig. 4. Flow of GGBF slag-based geopolymer pastes containing NaOH and KOH.
Fig. 5. Flow of fresh geopolymer paste containing NaOH 8 M with different types of sodium silicate and sodium silicate contents.
Fig. 6. Compressive strength of Na8-WG2.33-0.4 at different ages of curing up to 91 days.
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Fig. 7. Compressive strength of GGBF slag-based geopolymer pastes containing NaOH and KOH after 91 days of curing.
Fig. 8. The effect of alkaline solution (KOH) concentration on compressive strength of GGBF slag-based geopolymer paste after 91 days of curing.
Fig. 9. Compressive strength of GGBF slag-based geopolymer pastes containing NaOH 6 M in the presence of different types of sodium silicate and sodium silicate contents after 91 days of curing.
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Fig. 10. Flow of the fresh geopolymer paste containing NaOH 6 M and 8 M and KOH 6 M and 8 M with different types of sodium silicate and sodium silicate contents.
Fig. 11. The effect of GGBF slag replacement with pumice on compressive strength after 91 days of curing.
bination of GGBF slag and natural pozzolan was used to produce geopolymer paste. The effect of different amounts of GGBF slag replacement with pumice on the flowability of fresh geopolymer paste is demonstrated in Fig. 10. Generally, 5% of GGBF slag replacement with pumice results in maximum flow of the geopolymer paste. The flow of the geopolymer paste reduces about 24% by 50% GGBF slag replacement with pumice. With increase in pumice replacement level from 50% to 75%, the flow of GGBF slag-based geopolymer decreases about 60%. Also the geopolymer paste with 100% pumice as a raw material is sticky, with high viscosity and hardly could be cast in the mould. All mentioned observations are because of the higher amount of specific surface area of pumice than GGBF slag (5074 cm2/g vs 3383 cm2/g) which causes more water demand to reach constant flowability. The flowability of fresh geopolymer paste containing KOH is higher than NaOH if other factors are fixed. For the GGBF slag-based geopolymer with pumice, flowability decreased with the increase in molarity of alkaline solution (see Fig. 10). As been mentioned in Section 3.1 water content plays an important role in the flowability of the fresh geopolymer paste. Water content decreases with the increase in molarity of the alkaline solution and leads to higher viscosity. The effect of GGBF slag replacement with pumice after 91 days of curing on the compressive strength of geopolymer paste is shown in Fig. 11. It can be concluded that in the presence of 6 M and 8 M alkaline solutions, the maximum strength could be reached with 5% and 10% replacement respectively.
3.3. SEM investigation Fig. 12 shows SEM micrographs of the selected geopolymer pastes in 3 and 28 days of curing. Fig. 12(a) shows that there are some non-reacted GGBF slag particles (S) in sample after 3 days of curing. It has been concluded from Fig. 12(e–h) that the GGBF slag particle has been completely transferred into the geopolymer phase (G) after 28 days of curing and forms a dense structure. 4. Conclusions As seen in this paper GGBF slag-based geopolymer paste can be produced through room temperature. From the results obtained in this investigation, the following conclusions are drawn: 1. The flowability of GGBF slag-based geopolymer pastes containing KOH is higher than identical NaOH. The flow of the geopolymer paste reduces by more than 5% GGBF slag replacement with pumice. 2. The presence of sodium silicate in the GGBF slag-based geopolymer paste largely enhances the workability and results in increasing the compressive strength. The optimum modulus of sodium silicate and optimum ratio of sodium silicate to alkaline solution are 2.33 and 0.4 respectively. 3. The GGBF slag-based geopolymer paste specimens containing potassium hydroxide had higher compressive strength at various ages up to 91 days when compared with the specimens containing sodium hydroxide.
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(e)
(a)
G G
(b)
(f)
(c)
(g)
S
(d)
(h)
Fig. 12. SEM micrograph of (a and e) Na6-WG2.33-P0, (b and f) Na6-WG2.33-P10, (c and g) K6-WG2.33-P0, (d and h) K6-WG2.33-P10. (a, b, c and d: after 3 days geopolymerisation and e, f, g and h: after 28 days geopolymerisation), S: GGBF slag and G: geopolymer.
4. The optimum concentration of alkaline solution is 6–8 molar. 5. It can be concluded that in the presence of 6 M and 8 M alkaline solutions the maximum strength could be reached with 5% and 10% replacement respectively.
References [1] A.A. Ramezanianpour, A. Kazemian, M.A. Moghaddam, F. Moodi, A.M. Ramezanianpour, Studying effects of low-reactivity GGBFS on chloride
resistance of conventional and high strength concretes, Mater. Struct. (July 2015). [2] A.A. Ramezanianpour, M. Mahdikhani, Gh. Ahmadibeni, The effect of rice husk ash on mechanical properties and durability of sustainable concretes, Int. J. Civil Eng. (2009) 83–91. [3] A.A. Ramezanianpour, M. Jafari Nadooshan, M. Peydayesh, Effect of a new composite cement containing volcanic ash and limestone on mechanical properties and salt scaling resistance of concrete, J. Mater. Civil Eng. (2013). [4] D. Bondar, C.J. Lynsdale, N.B. Milestone, N. Hassani, A.A. Ramezanianpour, Effect of type, form, and dosage of activators on strength of alkali-activated natural pozzolans, Cem. Concr. Compos. 33 (2011) 251–260.
M. Jafari Nadoushan, A.A. Ramezanianpour / Construction and Building Materials 111 (2016) 337–347 [5] D. Bondar, Alkali activation of Iranian natural pozzolans for producing geopolymer cement and concrete: a dissertation submitted to University of Sheffield in fulfilment of the requirements for the degree of Doctor of Philosophy, UK, 2009. [6] W. Mozgawa, J. Deja, Spectroscopic studies of alkaline activated GGBF slag geopolymers, J. Mol. Struct. (2009) 434–441. [7] G. Habert, J.B. d’Espinose de Lacaillerie, N. Roussel, An environmental evaluation of geopolymer based concrete production: reviewing current research trends, J. Cleaner Prod. 19 (2011) 1229–1238. [8] Joseph Davidovits, Application of Ca-based geopolymer with blast furnace slag, a review, in: 2nd International Slag Valorisation Symposium, Leuven, 2011. [9] T.W. Cheng, J.P. Chiu, Fire-resistant geopolymer produced by granulated blast furnace slag, Miner. Eng. 16 (2003) 205–210. [10] Jae Eun Oh, Paulo J.M. Monteiro, Ssang Sun Jun, Sejin Choi, Simon M. Clark, The evolution of strength and crystalline phases for alkali-activated ground blast furnace slag and fly ash-based geopolymers, Cem. Concr. Res. 40 (2010) 189–196.
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[11] Zhang Yunsheng, Sun Wei, Chen Qianli, Chen Lin, Synthesis and heavy metal immobilization behaviors of slag based geopolymer, J. Hazard. Mater. 143 (2007) 206–213. [12] Shuguang Hu, Hongxi Wang, Gaozhan Zhang, Qingjun Ding, Bonding and abrasion resistance of geopolymeric repair material made with steel slag, Cem. Concr. Compos. 30 (2008) 239–244. [13] ASTM, C1437: standard test method for flow of hydraulic cement mortar, Annual Book of ASTM Standards, vol. 04.01, American Society for Testing and Materials, United States, 2001. [14] ASTM, C109: standard test method for compressive strength of hydraulic cement mortars, Annual Book of ASTM Standards, vol. 04.02, American Society for Testing and Materials, United States, 2001. [15] H. Xu, J.S.J. Van Deventer, The geopolymerisation of alumino-silicate minerals, Int. J. Miner. Process. 59 (2000) 247–266. [16] L. Fernandez-Carrasco, A. Fernandez Jimenez, A. Palomo, Alkali activation of pozzolan-cement aluminate cement mixtures, in: 12th International Congress on the Chemistry of Cements, 2007.