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Development of mixture design of heat resistant alkali-activated aluminosilicate binder-based adhesives
Construction and Building Materials 149 (2017) 248–256
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Development of mixture design of heat resistant alkali-activated aluminosilicate binder-based adhesives Pavel Krivenko ⇑, Oleg Petropavlovsky, Hrygorii Vozniuk V.D.Glukhovsky Scientific Research Institute for Binders and Materials, Kiev National University of Construction and Architecture, Ukraine
h i g h l i g h t s Thermo-resistant adhesives are based on alkali-activated aluminosilicate binders. Reaction products of the formulated binders are represented by zeolites. The adhesives are intended for work at high temperatures (up to 900 °C).
a r t i c l e
i n f o
Article history: Received 28 February 2017 Received in revised form 11 May 2017 Accepted 15 May 2017
Keywords: Adhesive Alkaline activation Aluminosilicate Binder Heat resisting Zeolite
a b s t r a c t The study was aimed at producing adhesives with improved thermo-mechanical properties and environmental friendliness and heath safety using alkali-activated aluminosilicate binders in order to meet today’s requirements. A relationship between phase composition of the reaction products after hardening in normal conditions and heating has been established and properties of the formulated alkali-activated aluminosilicate binders and adhesives based on them have been determined. Optimization of binder composition in terms of strength characteristics after hardening and heating has been performed using a two level factorial experiment design with three factors. The results of the study suggested showing that high performance properties of the binders could be provided through a proper choice of optimal ratios of sodium and potassium gel and crystalline structures (zeolites) that were capable to smooth dehydration and following recrystallization into anhydrous compounds of the nepheline and leicite types. These anhydrous compounds determine thermal stability of the resulted artificial stone under action of high temperatures (up to 900 °C). The study held allowed to establish optimal ratios of oxides: [(0.5–0.75)Na2O + (0.25–0.5)K2O]/Al2O3 = 1; SiO2/Al2O3 = 4; H2O/Al2O3 = 12. The developed adhesives exhibit high values of thermo-mechanical characteristics in the conditions of use temperatures reaching 900 °C (adhesion strength – 0.92 to 1.6 MPa, compressive strength up to 68 MPa, coefficient of liner thermal expansion up to 8.51 10 6 C 1, residual adhesion strength up to 88%, shrinkage up to 1.72%). The developed adhesives have been tried on a pilot scale and used in commercial-scale production of fire resistant structures such as lift doors and frames, as well as tried in bonding heat insulation boards to boilers with surface temperatures over 500 °C. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction With consideration of today’s requirements with regard to adhesives, these are: reduced energy consumption in production, high workability (easiness-in-work) in application, high performance properties (good adhesion to various materials, ability to
⇑ Corresponding author. E-mail addresses: [email protected] (P. Krivenko), petropavlovskii@ mail.ru (O. Petropavlovsky), [email protected] (H. Vozniuk). http://dx.doi.org/10.1016/j.conbuildmat.2017.05.138 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.
harden not only in normal conditions but at high temperatures, combination of high strength and thermo-resistance at use temperatures up to 900 °C), as well as health safety and environmental friendliness, an assumption was put forward that the best solution to meet these requirements could be adhesives based on alkaliactivated aluminosilicate binders [1]. Starting 1957, the Scientific Research Institute for Binders and Materials has been involved in the works on development of inorganic polymers based on alkaline – alkaline earth metal compounds [2]. Studies on directed synthesis of alkaline – alkaline earth aluminosilicate hydrates which at
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the moment of formation and crystallization are able to expose binding properties have been taken as theoretical bases [3]. According to the classification proposed in [4], the alkaliactivated aluminosilicate binders belong to the first class of alkali-activated cements – geocements, basic composition of hydration products of which is represented by alkaline and alkaline earth aluminosilicate hydrates – analogs of natural minerals of the zeolite and feldspathoid types [5–7], which are themselves inorganic polymers with three-dimensional framework structure [8]. The geocement-based materials are capable to polycondensation and can acquire quickly a required form at low temperatures (within a few hours at 30 °C and a few minutes at 140 °C), thus predetermining a possibility to use them as thermo-reactive resins. They exhibit high rigidity, weather resistance and ability to withstand high temperatures [9]. With consideration of the data on stability of phase transformations in the alkali-activated aluminosilicate binders when heated [10] and the experience collected from their use in various applications connected with service in high temperature conditions [11–15]. Since previous attempts did not satisfy completely the current needs, the purpose of the study was to develop adhesives from the alkali-activated aluminosilicate binders for high temperature uses with higher characteristics and to check their efficiency in pilot and industrial application.
Fig. 1. X-ray patterns of the constituent materials: 1 – kaolin, 2 – metakaolin (R – kaolinite, Q – b - quartz), 3 – amorphous silica.
2. Materials and testing
reaction products of the formulated binders. The ratios of oxides which would allow to synthesize zeolites of the required composition have been taken with account of recommendations given in [16–20]. Quartz sand and chamotte fines (both composed of fractions 0.14 and 0.315 mm)(both in quantities from 90 to 110% of binder mass) as well as mica (commercial product– ‘‘Mika 40”) (0–10% of binder mass) were used as fillers.
2.1. Constituent materials
2.2. Examination and testing techniques
The alkali-activated aluminosilicate binders were prepared using metakaolin with fineness of 8500 cm2/g (specific surface by Blaine) as an aluminosilicate constituent and amorphous silica with fineness of 8000 cm2/g (by Blaine) as a siliceous constituent. When required, in order to accelerate hardening process in airdry conditions a ground granulated blast-furnace slag (ggbs) with fineness of 4000 cm2/g (by Blaine) in quantities up to 10% of binder mass was added. Chemical composition of the constituents according to the product data sheets of the suppliers is given in Table 1. Soluble sodium silicate (silicate modulus Ms = 2.8 and density q = 1400 ± 10 kg/m3) was used as an alkaline component. Sodium and potassium hydroxides were added, when required. According to X-ray powder diffraction data (Fig. 1, Curve 1), phase composition of the metakaolin is represented by X-ray amorphous substance, kaolinite relicts (low intensity peaks with d = 0.712, 0.357, 0.261) and b-quartz (d = 0.424, 0.334, 0.187). The X-ray patterns of the amorphous silica showed high degree of its amorphization (Fig. 1, Curve 3). The alkali-activated aluminosilicate binders of the composition Me2O-Al2O3-SiO2-H2O varying in ratios of constituent oxides: Na2O/Al2O3 = 0.5 –1, R2O/Al2O3 = 0.25 –0.5 at (Na2O + K2O)/ Al2O3 = 1, SiO2/Al2O3 = 3 –5 and H2O/Al2O3 = 10 –14 have been chosen. Gels of aluminosilicate composition varying in ratios of basic structure- forming oxides have been synthesized in order to study
Choice of examination and testing techniques was determined by intended use of the adhesives. Phase composition of the constituent materials and that of the alkali-activated aluminosilicate binder reaction products were identified with the help of set of physico-chemical examination techniques, these were: X-ray powder diffraction, differentialthermal analyses, scanning electron microscopy and infrared spectroscopy. X-ray powder diffraction analysis was done using a diffractometer DRON-2 M on powder samples. The patterns were acquired from the angles 2H = 10 to 60° at speed of counter rotation of 2°/min. The X-ray phases were identified using ICDD–PDF2 database (Reliese 2000) after the formulated binders hardened for 28 days in air-dry conditions and after treatment at 80 °C. Scanning electron microscopic examination of the resulted microstructure was done using a microscope REMMA – 101A by a method of copper replica in accordance with the procedure described in [21]. Identification of the reaction products was done using the data given in [22] after the formulated binders hardened for 28 days in air-dry conditions and after treatment at 80 °C. Infrared spectroscopy was done using an infrared spectrophotometer IKS-40 with application of standard procedure by grinding a sample to fine powder and mixing of the powder in vaseline oil with KBr and placing into a cell, after this a spectrum was taken within the range of 400–4000 cm 1. An accuracy of measurement of oscillation frequencies of adsorption was ±0.5%. Identification
Table 1 Chemical composition of constituent materials according to the product data sheets. Constituent material
Kaolin Metakaolin Amorphous silica Ground granulated blast-furnace slag (ggbs)
Mass percentage of oxides and chemical elements SiO2
Al2O3
Fe2O3
TiO2
CaO
MgO
K2O
Na2O
S
Al
C
SO3
LOI
48.40 53.16 92.2 38.28
37.27 43.19 0.94 6.52
0.43 0.76 0.25 –
0.29 0.73 – –
0.25 0.51 1.49 45.46
0.05 Traces – 0.24
Traces 0.74 Traces –
Traces 0.25 0.36 –
– – 0.08 1.89
– – 0.23 –
– – 1.5 –
0.13 0.13 – –
13.18 <0.49 2.87 –
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of the molecular structure was done on adsorption spectra in accordance with the data given in [17,23]. Fineness of the powders was measured on a Blaine apparatus (EN 196-6). Viscosity of the formulated binders and adhesives based on them was measured on Suttard viscometer (GOST 23789). Compressive strength of the formulated binders was determined on cubes 20 20 20 mm. Strength of the adhesives in uniform tearing was determined on the bonded specimens ‘‘heat insulation material – concrete” as a ratio of fracture areas, depending upon type of bonding – adhesion, cohesion or mixed type to a total square area of the adhesive joint [24]. Adhesion strength of the alkali-activated aluminosilicate binder-based adhesives used for bonding various materials: concrete tiles (30 40 80 mm and 100 100 15 mm) from cement – sand (1:3) mortar with compressive strength of 48 to 52 MPa determined in accordance with [16], basalt insulation boards (trade name – ‘‘Firerock”), basalt fibre fabric, aluminium foil and steel sheets was determined. Heat resistance of the adhesives was determined on the bonded specimens ‘‘concrete – heat insulation board” which were first heated to 200 ± 5 °C and kept for 2 h at this temperature, then allowed to cool in high humidity conditions (R.H. = 90. . .95%) at 20 °C for 2 h. The adhesion strength in non-uniform tearing was tested after 10, 25, 50 cycles. Thermal resistance of the adhesives after heating at 900 °C was determined on the bonded specimens ‘‘ceramics – ceramics” and expressed as a value of residual adhesion strength. Also, strength in uniform tearing was tested. The specimens were heated at a rate of 200 °C/hr and cured at 900 °C for 4 h. Cooling of the specimens followed cooling of the test oven. Coefficient of linear thermal expansion (CLTE) of the adhesives based on formulated binders was determined in accordance with the procedure described in the National Standard of the USSR GOST 15173-70 after hardening for 28 days in air-dry conditions. Shrinkage of the binders after heating at 900 °C was measured and expressed as changes in linear dimensions of the cube specimens (20 20 20 mm). Planning and set-up of the experiments, as well as numerical treatment of the results was done using the software ‘‘Statistica” [25].
3. Results and discussion 3.1. Binders A two level factorial experiment design with three factors was used to establish a relationship between composition of the formulated binder and its properties. The ratios of oxides: SiO2/Al2O3 varying between 3 and 5 and at ratio of alkali metal oxides (mNa2O + nK2O)/Al2O3 = 1, where: m = 0.5 –1 and n = 0.25–0.5, respectively, were taken as variables. Using the results of tests (Table 2) a conclusion was drawn that the binders of the following chemical composition [(0.5–0.75) Na2O + (0.25–0.5)R2O]Al2O3(3–4)SiO2(9.9–12)H2O exhibited enhanced physico – mechanical properties during hardening in air-dry conditions and at 80 °C. Also, a conclusion was drawn that the formulated binders exhibited mechanical strength of 38. . .63 MPa, had the lower values of modulus of elasticity (18. . .27 GPa, being an evidence of the higher elasticity under loading. After heating at 900 °C they showed good residual strength (49–60%) and high shrinkage (15–20%). A conclusion was drawn that the higher content of potassium oxide in the binder the higher binder strength and that the higher
content of sodium oxide the lower is modulus of elasticity. The binders in which sodium (analcime) and potassium (zeolite ZK-14) aluminosilicate hydrate compounds with various activity and degree of structural order during hardening in air-dry conditions and after treatment at 80 °C were synthesized (Figs. 2 and 3) have been chosen as the binders of optimal composition. The results of study showed that the binder compositions with potassium oxide, not depending upon curing conditions, were characteristic of the quicker structure formation due to strengthening of translational motion of the nearest water molecules in the presence of potassium ions and accelerated formation of the aluminosilicate gels. This was confirmed by the X-ray patterns with corresponding peaks (Fig. 2a), as well as presence of more clearly expressed valence oscillations in the IR-spectrograms (Fig. 3a). These spectrograms were characteristic of formation of nuclei of initial structure of alkaline aluminosilicate hydrate compounds. The process of sodium analcime and potassium analcime (zeolite ZK-14) structure formation tended to accelerate after treatment at 80 °C (Fig. 3b). These reaction products are responsible for high physico-mechanical properties of the formulated binders [26]. A smooth transition of the above hydrous products into anhydrous ones of the nepheline and leicite types was found to take place after heating at 900 °C (Fig. 4). Judging by the values of residual strength and shrinkage of the formulated binders after heating at 900 °C a conclusion could be drawn that optimal field of their composition could be reached with the following ratios of oxides: [(0.25–0.5)K2O + (0.5–0.75)] Na2O/Al2O3 = 1, SiO2/Al2O3 = 4, H2O/Al2O3 = 11.8–12.0 and that they were characterized by optimal ratios of the structure – forming aluminosilicate hydrate phases capable to smooth recrystallization into anhydrous phases of the nepheline and leicite types. In order to accelerate strength gain in air-dry conditions and to bind ions of alkali metal a set of additional studies on modification of the binder of optimal composition (0.75Na2O + 0.25R2O)Al2O34SiO212H2O by addition of ground granulated blast-furnace slag was done. The addition of slag gave rise to strength gain, especially in early ages, as well as allowed to increase physico - mechanical and thermo-mechanical properties: the compressive strength had increased by 20%, adhesion strength – by 5%, residual strength– by 23% and shrinkage of the artificial stone after heating at 900 °C had decreased by 14% (Fig. 5). As it follows from [10,12], the reaction products of the binders containing slag are represented by low-basic calcium silicate hydrate of the CSH(B) composition and sodium-calcium silicate hydrate of the pectolite type, which bind sodium ions, and zeolite structures. After heating at 900 °C, the structure is represented by leicite, nepheline and wollastonite, the latter acts as reinforcement. All above allowed to choose optimal compositions of the binder in the system Na2O-K2O-Al2O3-SiO2-H2O, direction and character of structure formation to provide the required physicomechanical and workability properties, allowing to use them in adhesive joints with potential use temperatures reaching 900 °C.
3.2. Adhesives Depending upon intended use temperatures of the adhesives from the formulated binder of the composition (0.75Na2O + 0.25R2O)Al2O34SiO212H2O) the following materials: quartz sand, chamotte fines (fractions: 0.14 and 0.315 mm) and mica were added as fillers. Preliminary studies allowed to show that the adhesive formulations containing binder and filler as 1:1 (quartz sand for the adhe-
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P. Krivenko et al. / Construction and Building Materials 149 (2017) 248–256 Table 2 Physico-mechanical properties and curing conditions vs. ratio of oxides of the binder. Nos
Ratio of oxides
Curing conditions at 80 °C (12 h)
28 days in air-dry conditions (20 °C)
1 2 3 4 5 6 7 8 9
Na2O + K2O Al2O3
SiO2 Al2O3
Rcomp., MPa
Rres., 900 °C,%
Shrinkage, 900 °C,%
Rcomp., MPa
Rres., 900 °C,%
Shrinkage, 900 °C,%
0.5 + 0.5 0.75 + 0.25 1+0 0.5 + 0.5 0.75 + 0.25 1+0 0.5 + 0.5 0.75 + 0.25 1+0
3 3 3 4 4 4 5 5 5
52.5 50.6 45.5 42.2 38.5 34.1 22.5 21.8 20.5
46 44 41 52 49 44 57 53 48
27.8 28.9 30.1 19.3 20.2 22.0 17.4 18.2 19.2
62.1 58.7 49.4 63.2 59.4 45.3 28.2 26.7 23.4
54 49 45 60 56 51 62 56 53
20.5 22.4 25.1 15.6 16.5 18.3 15.1 16.9 17.5
Fig. 2. X-ray patterns of the binders of optimal composition after 28 days of hardening in air-dry conditions (a) and after treatment at 80 °C (b): 1 – (0.5Na2O + 0.5R2O) Al2O33SiO29.9H2O; 2 – (0.5Na2O + 0.5R2O)Al2O34SiO211.8H2O; 3 – (0.75Na2O + 0.25R2O)Al2O33SiO210.2H2O; 4 – (0.75Na2O + 0.25R2O)Al2O34SiO212H2O Designation: A – analcime, R – kaolinite, Q – quartz, T – trona, Z – zeolite ZK-14.
Fig. 3. IR spectra of the binders after hardening in air-dry conditions (a) and after treatment at 80 °C: 1 – (0.5Na2O + 0.5R2O)Al2O33SiO29.9H2O; 2 – (0.5Na2O + 0.5R2O)Al2O34SiO211.8H2O; 3 – (0.75Na2O + 0.25R2O)Al2O33SiO210.2H2O; 4 – (0.75Na2O + 0.25R2O)Al2O34SiO212H2O.
sives with use temperatures up to 500 °C or chamotte fines with use temperatures of up to 900 °C) showed optimal workability of the adhesives (values of viscosity measured by Suttard viscometer were 150. . .160 mm) and maximal adhesion strength (1.10 to
1.21 MPa) at values of shrinkage of 1.65 to 1.70 mm/m after 180 days of hardening. The binder formulations containing slag exhibited the higher values of physico - mechanical properties and shrinkage deformations of the adhesives based on them are lower (0.24 to 0.37 mm/m against 1.7). Optimization of fillers in the adhesives based on the binder of the (0.75Na2O + 0.25R2O)Al2O34SiO212H2O) composition with use temperatures up to 900 °C was done using a fractional factorial three level experimental design and the following parameters were studied: the influence of proportions between fillers (chamotte fines and mica) on workability and physico- mechanical properties of the adhesives after hardening in air-dry conditions and thermomechanical properties after heating at 900 °C. In order to meet the requirement of optimal workability properties of the adhesives (viscosity below 160 mm). Quantities of fillers were chosen with account of the results of the preliminary held study (chamotte fines – 90 to 110% and mica – 0 to 10% of binder mass). Using the results obtained on workability (viscosity) and physico-mechanical properties (adhesion strength, residual adhesion strength, coefficient of linear thermal expansion, shrinkage after heating) of the adhesives the equation of regression were obtained and isoparametric diagrams were plotted (Fig. 6).
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Fig. 4. X-ray patterns (a) and photomicrographs (b) of the binders of optimal composition after heating at 900 °C: 1 – (0.5Na2O + 0.5R2O)Al2O34SiO211.8H2O; 2 – (0.75Na2O + 0.25R2O)Al2O34SiO212H2O. Designation: L – leicite, N – nepheline. Magnification X1000.
Fig. 5. Physico-mechanical and thermo-mechanical properties of the formulated binders vs. curing conditions and quantities of slag additive: compressive strength (a), adhesion strength (b), shrinkage after heating at 900 °C (c), residual strength (d): 1 – reference composition (without slag additive); 2 – composition with slag (5% by mass); 3 – composition with slag (10% by mass).
Analyzing the results suggested to conclude that optimal adhesive with 100% content of chamotte fines and mica – 5% of the binder mass allowed to produce high workability (viscosity by Suttard – 152 mm) and physico-mechanical properties (adhesion strength – 0.92 MPa, coefficient of linear thermal expansion – 8.5110 6 °C 1, residual adhesion strength – 88%, 1.72% after heating at 900 °C). In values of coefficient of linear thermal expansion a possibility was established to use the formulated adhesives for bonding various materials. Above all, the formulated adhesives can be used for lining and repair of high-temperature zones of chimneys and chimneys themselves as fire resistant materials,
for making heat insulation of equipment working at high temperatures, for fire protection of metal structures etc. The results of failure mode identification of the adhesive bonded specimens ‘‘concrete – basalt insulation board Firerock – glass fabric” in non- uniform tearing, which is used for protection of surfaces of concrete structures from high temperatures and inner surfaces of industrial smokestacks with use temperatures of 200 °C, are given in Fig. 7. Quartz sand was used as filler. The results of failure mode identification of the adhesive joints of the bonded ‘‘basalt insulation board Firerock – metal (aluminium foil, steel sheet)” with use temperatures of 500 °C and
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Fig. 6. Isoparametric diagrams showing how the below listed properties of the adhesives, these are:a) viscosity (mm); b) adhesion strength (MPa); c) coefficient of linear thermal expansion (10 6 °C 1); d) residual adhesion strength after heating at 900 °C (MPa); e) compressive strength (MPa); f) shrinkage after heating at 900 °C (%), vary depending upon quantity of mica and chamotte fines.
Fig. 7. Percentage of failure of the adhesive bonded specimens ‘‘concrete – basalt insulation board Firerock – glass fabric” in non- uniform tearing after cyclic heating vs. number of cycles: a) ‘‘concrete – basalt insulation board Firerock”; b) ‘‘basalt insulation board Firerock – glass fabric”.
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Fig. 8. Percentage of failure of the adhesive bonded specimens ‘‘basalt insulation board – metal sheet” in non- uniform tearing after cyclic heating vs. age and number of cycles: a) ‘‘basalt insulation board Firerock – steel sheet” after heating at 900 °C; b) ‘‘basalt insulation board Firerock – aluminium foil” after heating at 500 °C.
Table 3 Comparative physico-mechanical and thermo-mechanical properties of the adhesives based on the formulated binders and similar products. Property
Prototype 1 (fireclay bonded chamotte refractory, commercial product)
Prototype 2 (mineral binder bonded refractory, commercial product)
Formulated adhesive
Flexural strength (28 days), MPa Compressive strength (28 days), MPa Adhesion strength to fireclay brick of fireplace, MPa Shelf life (retention time), h Thickness of layer, mm Beginning of service life (readiness-to-use), h Drying shrinkage,% Softening point, at °C
0.69 2.28 0.21 6 2 to 3 48 2.5 1400
>4 >12 >0.4 1 3 to 10 72 0.4 1300
8.5 68 1.15 1 to 2 0.5 to 10 48 0.37 >1000
900 °C, respectively, intended for protection of metal structures from action of high temperatures, are given in Fig. 8. The above results suggested to draw a conclusion that with time during service in high temperature conditions the adhesion strength did not change and failure took place in the substrate material and not of the adhesive. 3.3. Case studies and examples of commercial scale production Analyzing the obtained results of the study of the formulated adhesives in various adhesive joints with various use temperatures suggested to draw a conclusion about their efficiency in making heat insulation of industrial equipment (fire stop doors, fire resistant boxes, lifts, walls of boilers, pipelines, smokestacks), heat insulation of chimneys and industrial equipment working at high temperatures. Comparison of the formulated adhesives with best market analogs of adhesives for masonry, repair and heat insulation of kilns and chimneys from ceramic and fire resistant bricks showed that the formulated adhesives were characteristic of the compressive strength by 5.6 times, adhesion strength – by 2.8 times and thermal resistance (by 1.1–2.7 times higher compared to those of the ceramic-type adhesives listed below) (Table 3). A potential industrial application of the developed adhesives is for making heat insulation of industrial boilers. Among many advantages of the formulated adhesives such as ecological friendliness, incombustibility, absence of hazardous gases release under exposure of high temperatures, durability, low cost, is simplicity of its preparation and application: the adhesives may be produced in practice on any site, in required quantities with the use of a simple manual mixing equipment such as an electric drill with a mixing mouth piece (Fig. 9). The adhesives based on the formulated binders have been tried in bonding heat insulation materials to each other, heat insulation materials to structural elements of geometrically complicated shape, for impregnating basalt-fibre cords intended for sealing
holes in heat insulation. In this concrete application, the use was made of the composition designed with ground quartz sand as filler, which was applied with a help of injection-pistol into the holes of width 0 to 4 mm and with the help of a putty- knife into the holes of width 4 to 20 mm (Fig. 9). Above, the adhesives were tried in fire resistant heat insulating system from basalt fibre materials and used in commercial scale production of fire resistant doors, since all other earlier used adhesives did not meet strict requirements applied to fire- resistant doors of lift shafts. Commercial -scale use of these doors was launched by the Company OTIS, Ukraine. The adhesives were tried in bonding different materials: basalt cardboard, rigid heat insulating boards to each other and bonding them with steel and aluminium foil. The prepared adhesive was applied using a stainless steel putty- knife uniformly in thin layers (in thicknesses of 2 to 3 mm for basalt boards and basalt cardboards, in thicknesses of 1.0. . .1.5 mm for bonding basalt cardboard and steel and aluminium sheets), to surface of the heat insulating material (in case of bonding two heat insulating materials or in case of aluminium foil) or to surface of steel plate. The adhesive for gluing aluminium foil, after preparation and before application, was allowed to mature for 24 h. The works on bonding materials were done at temperatures of surrounding environment between + 5 °C and + 30 °C and temperature of the adhesive 20 ± 5 °C. After the materials were bonded together, they were kept at 40 ± 5 °C for 12 h, or at 20 ± 5 °C for 24 h, or at 10 ± 5 °C for 48 h that were required for solidification of the adhesive. Maturing of the ready products was done after placing them on pallets. Testing of fire resistance of the doors of lift shafts under procedure set up in the Russia’s Standard (GOST) 30247.2-97 held by the National Fire Safety Research Institute of the Russian Federation resulted in granting the fire safety certificates for conformity with fire rating EI-60 as per European Standard EN 13501-2:2007 + AI:2009 IDT. The obtained values were two times higher than the EN specified values.
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Fig. 9. Preparation and application of the adhesive.
4. General conclusions The results of the study showed a possibility to obtain binders in the system Na2O-K2O-Al2O3-SiO2-H2O with properties required for thermo-resistant adhesives by changing ratios of the constituent oxides: SiO2/Al2O3, R2O/Al2O3, H2O/Al2O3, K2O/Na2O in order to optimize their composition and contents of gel and crystalline structure-forming phases. The addition of potassium oxide to the composition of the alkali-activated aluminosilicate binder was found to play a positive role by increasing reactivity of the constituents and synthesis of zeolite phases with the increased degree of structure selfordering providing higher physico- mechanical and thermomechanical properties of the adhesive. A conclusion was drawn that the binders with the following ratios of the following oxides [(0.25–0.5)K2O + (0.5–0.75)Na2O]/ Al2O3 = 1, SiO2/Al2O3 = 4, H2O/Al2O3 = 11.8–12.0 create, in the process of hardening, conditions for synthesis of such reaction products that ensure high physico-mechanical properties. Phase composition of the reaction products is represented by analcime and zeolite ZK-14 which provide optimal ratio between gel and crystalline phases. A conclusion was drawn that optimal compositions of the binders exhibit compressive strength of 38–63 MPa, adhesion strength to concrete – 1.65–1.78 MPa and residual strength of 49–60% and shrinkage of 15.6–20.2% (after heating at 900 °C). Behaviour of the reaction products of the formulated binders within the temperature range of 20 to to 900 °C was studied and a conclusion was drawn that high values of residual strength and lower shrinkage after heating at 900 °C could be attributed to smooth processes of recrystallization of hydrous phases into anhydrous ones of the nepheline and leicite type. The optimal compositions of the adhesives prepared with quartz sand and chamotte fines exhibit the following characteristics: viscosity measured on Suttard viscometer- 150–180 mm; shelf life (retention time) – 45 to 90 min; adhesion strength – 0.92 to 1.6 MPa. The coefficient of linear thermal expansion (8.43 to 8.65)10 6 °C 1, was under the ranges of the requirements for majority of building materials, thus allowing to provide high thermo-mechanical characteristics of bonded materials in the conditions of temperatures (up to 500 °C and up to 900 °C), depending upon filler type. The adhesives for repair and making lining of ovens and chimneys made from ceramic and fire resistant bricks exhibit compressive strength of 68 MPa, adhesion strength of 1.15 MPa, residual strength – 87%, shrinkage of 1.72 mm/m after heating at 900 °C.
The adhesives have been brought into commercial scale production of lift portals and frames and heat insulation of boilers and other equipment working at high temperatures.
Acknowledgements The authors would like to acknowledge financial support of the Ministry of Education and Science of Ukraine (Fundamental research project ‘‘Physico- chemical bases for regulation of structure formation process and properties of the mineral alkaline aluminosilicate binder as adhesive for the use in ecologically safety wood products for various use” (Reg. No 0117U004842).
References [1] R.K. Iler, The Chemistry of Silica: Solubility, Polymerization, Colloid and Surface Properties, and Biochemistry, Wiley, 1979, ISBN 978-0-471-02404-0. [2] V.D. Glukhovsky, Soil Silicates. Gosstroyizdat USSR, 1959. [3] P.V. Krivenko, J.V. Skurchinskaya, O.A. Brodko, G.B. Zheludkov, Alkaline aluminosilicate polymers, in: Proc. of III International Scientific Conference. ‘‘Materials for building constructions” ICMB 94, Dnepropetrovsk, 1994, pp. 13– 15. [4] P.V. Krivenko, Alkaline cements: terminology, classification, fields of application, Stroitelnye Materialy i Konstruktsii (Building Materials and Constructions) 1 (1995) 23–24. [5] P.V. Krivenko, Alkaline cements, in: Proc. of the First International Conference ‘‘Alkaline Cements and Concretes”. Scientific-Research Institute for Binders and Materials named after V D Glukhovsky, Kyiv, 1994, pp. 11–129. [6] Geopolymer-based Composites”, W. M. Kriven, in, vol. 5, Ceramics and Carbon Matrix Composites, edited by Marina Ruggles-Wrenn. Part of an 8 volume set of books entitled Comprehensive Composite Materials II, Peter Beaumont and Carl Zweben, Co-editors-in-chief. Published by Elsevier, Oxford, UK, in press, 2017. [7] Skurchinskaya, Zh.V. Synthesis of analogues of natural minerals to produce an artificial stone (PhD Thesis), Lvov, 1973. [8] E. James, Harry R. Mark, Allcock Robert West. Inorganic Polymers, Oxford University Press, 2005. [9] Davidovits J. Geopolymer Chemistry and Applications/ Davidovits J. Geopolymer Institute 02100 Saint-Quentin, France, 2th edition. – 2008. [10] V.D. Glukhovsky, E.A. Starchevskaya, P.V. Krivenko, Study of silicate formation in a mixture of clay, quartz sand and soda, J. Ukrainian Chem. J. 35 (4) (1969) 433–435. [11] P.V. Krivenko, G.Y. Kovalchuk, Directed synthesis of alkaline aluminosilicate minerals in a geocement matrix, J. Mater. Sci. 42 (9) (2007) 2944–2952. [12] P.V. Krivenko, S.G. Guzii, L. Bodnarova, J. Valek, R. Hela, J. Zach, Effect of thickness of the intumescent alkali aluminosilicate coating on temperature distribution in reinforced concrete, J. Build. Eng. 8 (2016) 14–19, http://dx.doi. org/10.1016/j.jobe.2016.09.003. [13] P.V. Krivenko, S.G. Guzii, Aluminosilicate coating with enhanced heat- and corrosion resistance, J. Appl. Clay Sci. 73 (1) (2013) 65–70, http://dx.doi.org/ 10.1016/j.clay.2012.10.010. [14] P. Krivenko, G. Kovalchuk, Achieving a heat resistance of cellular concrete based on alkali activated fly ash cements, J. Mater. Struct. 48 (3) (2014) 599– 606, http://dx.doi.org/10.1617/s11527-014-0479-0.
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[15] V. Petranek, L. Nevrivova, D. Zezulova, S. Guziy, Thermal insulating materials for energy storage application, J. Adv. Mater. Res. 911 (2014) 30–35, http://dx. doi.org/10.4028/www.scientific.net/AMR.911.30. [16] Lovat V.C. Rees, S. Chandrasekhar, Formation of zeolite from the system Na2OAl2O3-SiO2-H2O in alkaline medium (pH >10), J. Zeolites 13 (7) (1993) 524– 533. [17] D.W. Breck, Zeolite Molecular Sieves: Structure, Chemistry, and Use, Wiley, 1973. [18] R.M. Barrer, D.A. Langley, Synthesis of a zeolite mineral with chabazite-like sorptive properties, J. Chem. Soc. 3804–3817 (1958). [19] R.M. Barrer, Hydrothermal chemistry of silicates. Part X. A partial study of the field CaO-Al2O3-SiO2-H2O, J. Chem. Soc. 4684 (1964) 35.
[20] R.M. Barrer, R.W. Bullitude, I.S. Kerr, Some properties of, and a structural scheme for, the harmotome zeolites, J. Chem. Soc. 1521 (1959) 49. [21] B. Fultz, J.M. Howe, Transmission Electron Microscopy and Diffractometry of Materials, Springer-Verlag, Berlin Heidelberg, 2013. [22] E. Karapuzov, G. Luts, X. Gerold, Dry Building Mixes, Tekhnika Publish, 2000. [23] I.I. Plusnina, Infrared Spectra of Silicates, Moscow State University Publish, 1967. [24] R.A. Kardashev, Structural Glues, Khimija (Chemistry) Publish, 1980. [25] V. Borovikov, Statistica: Art of Computer Data Analysis. For Professionals, Piter, 2003. [26] Ch. Baerlocher, D.H. Olson, W.M. Meier, Atlas of Zeolite Framework Types (Formerly: Atlas of Zeolite Structure Types), Elsevier Science, 2001.
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Development of mixture design of heat resistant alkali-activated aluminosilicate binder-based adhesives Pavel Krivenko ⇑, Oleg Petropavlovsky, Hrygorii Vozniuk V.D.Glukhovsky Scientific Research Institute for Binders and Materials, Kiev National University of Construction and Architecture, Ukraine
h i g h l i g h t s Thermo-resistant adhesives are based on alkali-activated aluminosilicate binders. Reaction products of the formulated binders are represented by zeolites. The adhesives are intended for work at high temperatures (up to 900 °C).
a r t i c l e
i n f o
Article history: Received 28 February 2017 Received in revised form 11 May 2017 Accepted 15 May 2017
Keywords: Adhesive Alkaline activation Aluminosilicate Binder Heat resisting Zeolite
a b s t r a c t The study was aimed at producing adhesives with improved thermo-mechanical properties and environmental friendliness and heath safety using alkali-activated aluminosilicate binders in order to meet today’s requirements. A relationship between phase composition of the reaction products after hardening in normal conditions and heating has been established and properties of the formulated alkali-activated aluminosilicate binders and adhesives based on them have been determined. Optimization of binder composition in terms of strength characteristics after hardening and heating has been performed using a two level factorial experiment design with three factors. The results of the study suggested showing that high performance properties of the binders could be provided through a proper choice of optimal ratios of sodium and potassium gel and crystalline structures (zeolites) that were capable to smooth dehydration and following recrystallization into anhydrous compounds of the nepheline and leicite types. These anhydrous compounds determine thermal stability of the resulted artificial stone under action of high temperatures (up to 900 °C). The study held allowed to establish optimal ratios of oxides: [(0.5–0.75)Na2O + (0.25–0.5)K2O]/Al2O3 = 1; SiO2/Al2O3 = 4; H2O/Al2O3 = 12. The developed adhesives exhibit high values of thermo-mechanical characteristics in the conditions of use temperatures reaching 900 °C (adhesion strength – 0.92 to 1.6 MPa, compressive strength up to 68 MPa, coefficient of liner thermal expansion up to 8.51 10 6 C 1, residual adhesion strength up to 88%, shrinkage up to 1.72%). The developed adhesives have been tried on a pilot scale and used in commercial-scale production of fire resistant structures such as lift doors and frames, as well as tried in bonding heat insulation boards to boilers with surface temperatures over 500 °C. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction With consideration of today’s requirements with regard to adhesives, these are: reduced energy consumption in production, high workability (easiness-in-work) in application, high performance properties (good adhesion to various materials, ability to
⇑ Corresponding author. E-mail addresses: [email protected] (P. Krivenko), petropavlovskii@ mail.ru (O. Petropavlovsky), [email protected] (H. Vozniuk). http://dx.doi.org/10.1016/j.conbuildmat.2017.05.138 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.
harden not only in normal conditions but at high temperatures, combination of high strength and thermo-resistance at use temperatures up to 900 °C), as well as health safety and environmental friendliness, an assumption was put forward that the best solution to meet these requirements could be adhesives based on alkaliactivated aluminosilicate binders [1]. Starting 1957, the Scientific Research Institute for Binders and Materials has been involved in the works on development of inorganic polymers based on alkaline – alkaline earth metal compounds [2]. Studies on directed synthesis of alkaline – alkaline earth aluminosilicate hydrates which at
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the moment of formation and crystallization are able to expose binding properties have been taken as theoretical bases [3]. According to the classification proposed in [4], the alkaliactivated aluminosilicate binders belong to the first class of alkali-activated cements – geocements, basic composition of hydration products of which is represented by alkaline and alkaline earth aluminosilicate hydrates – analogs of natural minerals of the zeolite and feldspathoid types [5–7], which are themselves inorganic polymers with three-dimensional framework structure [8]. The geocement-based materials are capable to polycondensation and can acquire quickly a required form at low temperatures (within a few hours at 30 °C and a few minutes at 140 °C), thus predetermining a possibility to use them as thermo-reactive resins. They exhibit high rigidity, weather resistance and ability to withstand high temperatures [9]. With consideration of the data on stability of phase transformations in the alkali-activated aluminosilicate binders when heated [10] and the experience collected from their use in various applications connected with service in high temperature conditions [11–15]. Since previous attempts did not satisfy completely the current needs, the purpose of the study was to develop adhesives from the alkali-activated aluminosilicate binders for high temperature uses with higher characteristics and to check their efficiency in pilot and industrial application.
Fig. 1. X-ray patterns of the constituent materials: 1 – kaolin, 2 – metakaolin (R – kaolinite, Q – b - quartz), 3 – amorphous silica.
2. Materials and testing
reaction products of the formulated binders. The ratios of oxides which would allow to synthesize zeolites of the required composition have been taken with account of recommendations given in [16–20]. Quartz sand and chamotte fines (both composed of fractions 0.14 and 0.315 mm)(both in quantities from 90 to 110% of binder mass) as well as mica (commercial product– ‘‘Mika 40”) (0–10% of binder mass) were used as fillers.
2.1. Constituent materials
2.2. Examination and testing techniques
The alkali-activated aluminosilicate binders were prepared using metakaolin with fineness of 8500 cm2/g (specific surface by Blaine) as an aluminosilicate constituent and amorphous silica with fineness of 8000 cm2/g (by Blaine) as a siliceous constituent. When required, in order to accelerate hardening process in airdry conditions a ground granulated blast-furnace slag (ggbs) with fineness of 4000 cm2/g (by Blaine) in quantities up to 10% of binder mass was added. Chemical composition of the constituents according to the product data sheets of the suppliers is given in Table 1. Soluble sodium silicate (silicate modulus Ms = 2.8 and density q = 1400 ± 10 kg/m3) was used as an alkaline component. Sodium and potassium hydroxides were added, when required. According to X-ray powder diffraction data (Fig. 1, Curve 1), phase composition of the metakaolin is represented by X-ray amorphous substance, kaolinite relicts (low intensity peaks with d = 0.712, 0.357, 0.261) and b-quartz (d = 0.424, 0.334, 0.187). The X-ray patterns of the amorphous silica showed high degree of its amorphization (Fig. 1, Curve 3). The alkali-activated aluminosilicate binders of the composition Me2O-Al2O3-SiO2-H2O varying in ratios of constituent oxides: Na2O/Al2O3 = 0.5 –1, R2O/Al2O3 = 0.25 –0.5 at (Na2O + K2O)/ Al2O3 = 1, SiO2/Al2O3 = 3 –5 and H2O/Al2O3 = 10 –14 have been chosen. Gels of aluminosilicate composition varying in ratios of basic structure- forming oxides have been synthesized in order to study
Choice of examination and testing techniques was determined by intended use of the adhesives. Phase composition of the constituent materials and that of the alkali-activated aluminosilicate binder reaction products were identified with the help of set of physico-chemical examination techniques, these were: X-ray powder diffraction, differentialthermal analyses, scanning electron microscopy and infrared spectroscopy. X-ray powder diffraction analysis was done using a diffractometer DRON-2 M on powder samples. The patterns were acquired from the angles 2H = 10 to 60° at speed of counter rotation of 2°/min. The X-ray phases were identified using ICDD–PDF2 database (Reliese 2000) after the formulated binders hardened for 28 days in air-dry conditions and after treatment at 80 °C. Scanning electron microscopic examination of the resulted microstructure was done using a microscope REMMA – 101A by a method of copper replica in accordance with the procedure described in [21]. Identification of the reaction products was done using the data given in [22] after the formulated binders hardened for 28 days in air-dry conditions and after treatment at 80 °C. Infrared spectroscopy was done using an infrared spectrophotometer IKS-40 with application of standard procedure by grinding a sample to fine powder and mixing of the powder in vaseline oil with KBr and placing into a cell, after this a spectrum was taken within the range of 400–4000 cm 1. An accuracy of measurement of oscillation frequencies of adsorption was ±0.5%. Identification
Table 1 Chemical composition of constituent materials according to the product data sheets. Constituent material
Kaolin Metakaolin Amorphous silica Ground granulated blast-furnace slag (ggbs)
Mass percentage of oxides and chemical elements SiO2
Al2O3
Fe2O3
TiO2
CaO
MgO
K2O
Na2O
S
Al
C
SO3
LOI
48.40 53.16 92.2 38.28
37.27 43.19 0.94 6.52
0.43 0.76 0.25 –
0.29 0.73 – –
0.25 0.51 1.49 45.46
0.05 Traces – 0.24
Traces 0.74 Traces –
Traces 0.25 0.36 –
– – 0.08 1.89
– – 0.23 –
– – 1.5 –
0.13 0.13 – –
13.18 <0.49 2.87 –
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of the molecular structure was done on adsorption spectra in accordance with the data given in [17,23]. Fineness of the powders was measured on a Blaine apparatus (EN 196-6). Viscosity of the formulated binders and adhesives based on them was measured on Suttard viscometer (GOST 23789). Compressive strength of the formulated binders was determined on cubes 20 20 20 mm. Strength of the adhesives in uniform tearing was determined on the bonded specimens ‘‘heat insulation material – concrete” as a ratio of fracture areas, depending upon type of bonding – adhesion, cohesion or mixed type to a total square area of the adhesive joint [24]. Adhesion strength of the alkali-activated aluminosilicate binder-based adhesives used for bonding various materials: concrete tiles (30 40 80 mm and 100 100 15 mm) from cement – sand (1:3) mortar with compressive strength of 48 to 52 MPa determined in accordance with [16], basalt insulation boards (trade name – ‘‘Firerock”), basalt fibre fabric, aluminium foil and steel sheets was determined. Heat resistance of the adhesives was determined on the bonded specimens ‘‘concrete – heat insulation board” which were first heated to 200 ± 5 °C and kept for 2 h at this temperature, then allowed to cool in high humidity conditions (R.H. = 90. . .95%) at 20 °C for 2 h. The adhesion strength in non-uniform tearing was tested after 10, 25, 50 cycles. Thermal resistance of the adhesives after heating at 900 °C was determined on the bonded specimens ‘‘ceramics – ceramics” and expressed as a value of residual adhesion strength. Also, strength in uniform tearing was tested. The specimens were heated at a rate of 200 °C/hr and cured at 900 °C for 4 h. Cooling of the specimens followed cooling of the test oven. Coefficient of linear thermal expansion (CLTE) of the adhesives based on formulated binders was determined in accordance with the procedure described in the National Standard of the USSR GOST 15173-70 after hardening for 28 days in air-dry conditions. Shrinkage of the binders after heating at 900 °C was measured and expressed as changes in linear dimensions of the cube specimens (20 20 20 mm). Planning and set-up of the experiments, as well as numerical treatment of the results was done using the software ‘‘Statistica” [25].
3. Results and discussion 3.1. Binders A two level factorial experiment design with three factors was used to establish a relationship between composition of the formulated binder and its properties. The ratios of oxides: SiO2/Al2O3 varying between 3 and 5 and at ratio of alkali metal oxides (mNa2O + nK2O)/Al2O3 = 1, where: m = 0.5 –1 and n = 0.25–0.5, respectively, were taken as variables. Using the results of tests (Table 2) a conclusion was drawn that the binders of the following chemical composition [(0.5–0.75) Na2O + (0.25–0.5)R2O]Al2O3(3–4)SiO2(9.9–12)H2O exhibited enhanced physico – mechanical properties during hardening in air-dry conditions and at 80 °C. Also, a conclusion was drawn that the formulated binders exhibited mechanical strength of 38. . .63 MPa, had the lower values of modulus of elasticity (18. . .27 GPa, being an evidence of the higher elasticity under loading. After heating at 900 °C they showed good residual strength (49–60%) and high shrinkage (15–20%). A conclusion was drawn that the higher content of potassium oxide in the binder the higher binder strength and that the higher
content of sodium oxide the lower is modulus of elasticity. The binders in which sodium (analcime) and potassium (zeolite ZK-14) aluminosilicate hydrate compounds with various activity and degree of structural order during hardening in air-dry conditions and after treatment at 80 °C were synthesized (Figs. 2 and 3) have been chosen as the binders of optimal composition. The results of study showed that the binder compositions with potassium oxide, not depending upon curing conditions, were characteristic of the quicker structure formation due to strengthening of translational motion of the nearest water molecules in the presence of potassium ions and accelerated formation of the aluminosilicate gels. This was confirmed by the X-ray patterns with corresponding peaks (Fig. 2a), as well as presence of more clearly expressed valence oscillations in the IR-spectrograms (Fig. 3a). These spectrograms were characteristic of formation of nuclei of initial structure of alkaline aluminosilicate hydrate compounds. The process of sodium analcime and potassium analcime (zeolite ZK-14) structure formation tended to accelerate after treatment at 80 °C (Fig. 3b). These reaction products are responsible for high physico-mechanical properties of the formulated binders [26]. A smooth transition of the above hydrous products into anhydrous ones of the nepheline and leicite types was found to take place after heating at 900 °C (Fig. 4). Judging by the values of residual strength and shrinkage of the formulated binders after heating at 900 °C a conclusion could be drawn that optimal field of their composition could be reached with the following ratios of oxides: [(0.25–0.5)K2O + (0.5–0.75)] Na2O/Al2O3 = 1, SiO2/Al2O3 = 4, H2O/Al2O3 = 11.8–12.0 and that they were characterized by optimal ratios of the structure – forming aluminosilicate hydrate phases capable to smooth recrystallization into anhydrous phases of the nepheline and leicite types. In order to accelerate strength gain in air-dry conditions and to bind ions of alkali metal a set of additional studies on modification of the binder of optimal composition (0.75Na2O + 0.25R2O)Al2O34SiO212H2O by addition of ground granulated blast-furnace slag was done. The addition of slag gave rise to strength gain, especially in early ages, as well as allowed to increase physico - mechanical and thermo-mechanical properties: the compressive strength had increased by 20%, adhesion strength – by 5%, residual strength– by 23% and shrinkage of the artificial stone after heating at 900 °C had decreased by 14% (Fig. 5). As it follows from [10,12], the reaction products of the binders containing slag are represented by low-basic calcium silicate hydrate of the CSH(B) composition and sodium-calcium silicate hydrate of the pectolite type, which bind sodium ions, and zeolite structures. After heating at 900 °C, the structure is represented by leicite, nepheline and wollastonite, the latter acts as reinforcement. All above allowed to choose optimal compositions of the binder in the system Na2O-K2O-Al2O3-SiO2-H2O, direction and character of structure formation to provide the required physicomechanical and workability properties, allowing to use them in adhesive joints with potential use temperatures reaching 900 °C.
3.2. Adhesives Depending upon intended use temperatures of the adhesives from the formulated binder of the composition (0.75Na2O + 0.25R2O)Al2O34SiO212H2O) the following materials: quartz sand, chamotte fines (fractions: 0.14 and 0.315 mm) and mica were added as fillers. Preliminary studies allowed to show that the adhesive formulations containing binder and filler as 1:1 (quartz sand for the adhe-
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P. Krivenko et al. / Construction and Building Materials 149 (2017) 248–256 Table 2 Physico-mechanical properties and curing conditions vs. ratio of oxides of the binder. Nos
Ratio of oxides
Curing conditions at 80 °C (12 h)
28 days in air-dry conditions (20 °C)
1 2 3 4 5 6 7 8 9
Na2O + K2O Al2O3
SiO2 Al2O3
Rcomp., MPa
Rres., 900 °C,%
Shrinkage, 900 °C,%
Rcomp., MPa
Rres., 900 °C,%
Shrinkage, 900 °C,%
0.5 + 0.5 0.75 + 0.25 1+0 0.5 + 0.5 0.75 + 0.25 1+0 0.5 + 0.5 0.75 + 0.25 1+0
3 3 3 4 4 4 5 5 5
52.5 50.6 45.5 42.2 38.5 34.1 22.5 21.8 20.5
46 44 41 52 49 44 57 53 48
27.8 28.9 30.1 19.3 20.2 22.0 17.4 18.2 19.2
62.1 58.7 49.4 63.2 59.4 45.3 28.2 26.7 23.4
54 49 45 60 56 51 62 56 53
20.5 22.4 25.1 15.6 16.5 18.3 15.1 16.9 17.5
Fig. 2. X-ray patterns of the binders of optimal composition after 28 days of hardening in air-dry conditions (a) and after treatment at 80 °C (b): 1 – (0.5Na2O + 0.5R2O) Al2O33SiO29.9H2O; 2 – (0.5Na2O + 0.5R2O)Al2O34SiO211.8H2O; 3 – (0.75Na2O + 0.25R2O)Al2O33SiO210.2H2O; 4 – (0.75Na2O + 0.25R2O)Al2O34SiO212H2O Designation: A – analcime, R – kaolinite, Q – quartz, T – trona, Z – zeolite ZK-14.
Fig. 3. IR spectra of the binders after hardening in air-dry conditions (a) and after treatment at 80 °C: 1 – (0.5Na2O + 0.5R2O)Al2O33SiO29.9H2O; 2 – (0.5Na2O + 0.5R2O)Al2O34SiO211.8H2O; 3 – (0.75Na2O + 0.25R2O)Al2O33SiO210.2H2O; 4 – (0.75Na2O + 0.25R2O)Al2O34SiO212H2O.
sives with use temperatures up to 500 °C or chamotte fines with use temperatures of up to 900 °C) showed optimal workability of the adhesives (values of viscosity measured by Suttard viscometer were 150. . .160 mm) and maximal adhesion strength (1.10 to
1.21 MPa) at values of shrinkage of 1.65 to 1.70 mm/m after 180 days of hardening. The binder formulations containing slag exhibited the higher values of physico - mechanical properties and shrinkage deformations of the adhesives based on them are lower (0.24 to 0.37 mm/m against 1.7). Optimization of fillers in the adhesives based on the binder of the (0.75Na2O + 0.25R2O)Al2O34SiO212H2O) composition with use temperatures up to 900 °C was done using a fractional factorial three level experimental design and the following parameters were studied: the influence of proportions between fillers (chamotte fines and mica) on workability and physico- mechanical properties of the adhesives after hardening in air-dry conditions and thermomechanical properties after heating at 900 °C. In order to meet the requirement of optimal workability properties of the adhesives (viscosity below 160 mm). Quantities of fillers were chosen with account of the results of the preliminary held study (chamotte fines – 90 to 110% and mica – 0 to 10% of binder mass). Using the results obtained on workability (viscosity) and physico-mechanical properties (adhesion strength, residual adhesion strength, coefficient of linear thermal expansion, shrinkage after heating) of the adhesives the equation of regression were obtained and isoparametric diagrams were plotted (Fig. 6).
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Fig. 4. X-ray patterns (a) and photomicrographs (b) of the binders of optimal composition after heating at 900 °C: 1 – (0.5Na2O + 0.5R2O)Al2O34SiO211.8H2O; 2 – (0.75Na2O + 0.25R2O)Al2O34SiO212H2O. Designation: L – leicite, N – nepheline. Magnification X1000.
Fig. 5. Physico-mechanical and thermo-mechanical properties of the formulated binders vs. curing conditions and quantities of slag additive: compressive strength (a), adhesion strength (b), shrinkage after heating at 900 °C (c), residual strength (d): 1 – reference composition (without slag additive); 2 – composition with slag (5% by mass); 3 – composition with slag (10% by mass).
Analyzing the results suggested to conclude that optimal adhesive with 100% content of chamotte fines and mica – 5% of the binder mass allowed to produce high workability (viscosity by Suttard – 152 mm) and physico-mechanical properties (adhesion strength – 0.92 MPa, coefficient of linear thermal expansion – 8.5110 6 °C 1, residual adhesion strength – 88%, 1.72% after heating at 900 °C). In values of coefficient of linear thermal expansion a possibility was established to use the formulated adhesives for bonding various materials. Above all, the formulated adhesives can be used for lining and repair of high-temperature zones of chimneys and chimneys themselves as fire resistant materials,
for making heat insulation of equipment working at high temperatures, for fire protection of metal structures etc. The results of failure mode identification of the adhesive bonded specimens ‘‘concrete – basalt insulation board Firerock – glass fabric” in non- uniform tearing, which is used for protection of surfaces of concrete structures from high temperatures and inner surfaces of industrial smokestacks with use temperatures of 200 °C, are given in Fig. 7. Quartz sand was used as filler. The results of failure mode identification of the adhesive joints of the bonded ‘‘basalt insulation board Firerock – metal (aluminium foil, steel sheet)” with use temperatures of 500 °C and
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Fig. 6. Isoparametric diagrams showing how the below listed properties of the adhesives, these are:a) viscosity (mm); b) adhesion strength (MPa); c) coefficient of linear thermal expansion (10 6 °C 1); d) residual adhesion strength after heating at 900 °C (MPa); e) compressive strength (MPa); f) shrinkage after heating at 900 °C (%), vary depending upon quantity of mica and chamotte fines.
Fig. 7. Percentage of failure of the adhesive bonded specimens ‘‘concrete – basalt insulation board Firerock – glass fabric” in non- uniform tearing after cyclic heating vs. number of cycles: a) ‘‘concrete – basalt insulation board Firerock”; b) ‘‘basalt insulation board Firerock – glass fabric”.
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Fig. 8. Percentage of failure of the adhesive bonded specimens ‘‘basalt insulation board – metal sheet” in non- uniform tearing after cyclic heating vs. age and number of cycles: a) ‘‘basalt insulation board Firerock – steel sheet” after heating at 900 °C; b) ‘‘basalt insulation board Firerock – aluminium foil” after heating at 500 °C.
Table 3 Comparative physico-mechanical and thermo-mechanical properties of the adhesives based on the formulated binders and similar products. Property
Prototype 1 (fireclay bonded chamotte refractory, commercial product)
Prototype 2 (mineral binder bonded refractory, commercial product)
Formulated adhesive
Flexural strength (28 days), MPa Compressive strength (28 days), MPa Adhesion strength to fireclay brick of fireplace, MPa Shelf life (retention time), h Thickness of layer, mm Beginning of service life (readiness-to-use), h Drying shrinkage,% Softening point, at °C
0.69 2.28 0.21 6 2 to 3 48 2.5 1400
>4 >12 >0.4 1 3 to 10 72 0.4 1300
8.5 68 1.15 1 to 2 0.5 to 10 48 0.37 >1000
900 °C, respectively, intended for protection of metal structures from action of high temperatures, are given in Fig. 8. The above results suggested to draw a conclusion that with time during service in high temperature conditions the adhesion strength did not change and failure took place in the substrate material and not of the adhesive. 3.3. Case studies and examples of commercial scale production Analyzing the obtained results of the study of the formulated adhesives in various adhesive joints with various use temperatures suggested to draw a conclusion about their efficiency in making heat insulation of industrial equipment (fire stop doors, fire resistant boxes, lifts, walls of boilers, pipelines, smokestacks), heat insulation of chimneys and industrial equipment working at high temperatures. Comparison of the formulated adhesives with best market analogs of adhesives for masonry, repair and heat insulation of kilns and chimneys from ceramic and fire resistant bricks showed that the formulated adhesives were characteristic of the compressive strength by 5.6 times, adhesion strength – by 2.8 times and thermal resistance (by 1.1–2.7 times higher compared to those of the ceramic-type adhesives listed below) (Table 3). A potential industrial application of the developed adhesives is for making heat insulation of industrial boilers. Among many advantages of the formulated adhesives such as ecological friendliness, incombustibility, absence of hazardous gases release under exposure of high temperatures, durability, low cost, is simplicity of its preparation and application: the adhesives may be produced in practice on any site, in required quantities with the use of a simple manual mixing equipment such as an electric drill with a mixing mouth piece (Fig. 9). The adhesives based on the formulated binders have been tried in bonding heat insulation materials to each other, heat insulation materials to structural elements of geometrically complicated shape, for impregnating basalt-fibre cords intended for sealing
holes in heat insulation. In this concrete application, the use was made of the composition designed with ground quartz sand as filler, which was applied with a help of injection-pistol into the holes of width 0 to 4 mm and with the help of a putty- knife into the holes of width 4 to 20 mm (Fig. 9). Above, the adhesives were tried in fire resistant heat insulating system from basalt fibre materials and used in commercial scale production of fire resistant doors, since all other earlier used adhesives did not meet strict requirements applied to fire- resistant doors of lift shafts. Commercial -scale use of these doors was launched by the Company OTIS, Ukraine. The adhesives were tried in bonding different materials: basalt cardboard, rigid heat insulating boards to each other and bonding them with steel and aluminium foil. The prepared adhesive was applied using a stainless steel putty- knife uniformly in thin layers (in thicknesses of 2 to 3 mm for basalt boards and basalt cardboards, in thicknesses of 1.0. . .1.5 mm for bonding basalt cardboard and steel and aluminium sheets), to surface of the heat insulating material (in case of bonding two heat insulating materials or in case of aluminium foil) or to surface of steel plate. The adhesive for gluing aluminium foil, after preparation and before application, was allowed to mature for 24 h. The works on bonding materials were done at temperatures of surrounding environment between + 5 °C and + 30 °C and temperature of the adhesive 20 ± 5 °C. After the materials were bonded together, they were kept at 40 ± 5 °C for 12 h, or at 20 ± 5 °C for 24 h, or at 10 ± 5 °C for 48 h that were required for solidification of the adhesive. Maturing of the ready products was done after placing them on pallets. Testing of fire resistance of the doors of lift shafts under procedure set up in the Russia’s Standard (GOST) 30247.2-97 held by the National Fire Safety Research Institute of the Russian Federation resulted in granting the fire safety certificates for conformity with fire rating EI-60 as per European Standard EN 13501-2:2007 + AI:2009 IDT. The obtained values were two times higher than the EN specified values.
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Fig. 9. Preparation and application of the adhesive.
4. General conclusions The results of the study showed a possibility to obtain binders in the system Na2O-K2O-Al2O3-SiO2-H2O with properties required for thermo-resistant adhesives by changing ratios of the constituent oxides: SiO2/Al2O3, R2O/Al2O3, H2O/Al2O3, K2O/Na2O in order to optimize their composition and contents of gel and crystalline structure-forming phases. The addition of potassium oxide to the composition of the alkali-activated aluminosilicate binder was found to play a positive role by increasing reactivity of the constituents and synthesis of zeolite phases with the increased degree of structure selfordering providing higher physico- mechanical and thermomechanical properties of the adhesive. A conclusion was drawn that the binders with the following ratios of the following oxides [(0.25–0.5)K2O + (0.5–0.75)Na2O]/ Al2O3 = 1, SiO2/Al2O3 = 4, H2O/Al2O3 = 11.8–12.0 create, in the process of hardening, conditions for synthesis of such reaction products that ensure high physico-mechanical properties. Phase composition of the reaction products is represented by analcime and zeolite ZK-14 which provide optimal ratio between gel and crystalline phases. A conclusion was drawn that optimal compositions of the binders exhibit compressive strength of 38–63 MPa, adhesion strength to concrete – 1.65–1.78 MPa and residual strength of 49–60% and shrinkage of 15.6–20.2% (after heating at 900 °C). Behaviour of the reaction products of the formulated binders within the temperature range of 20 to to 900 °C was studied and a conclusion was drawn that high values of residual strength and lower shrinkage after heating at 900 °C could be attributed to smooth processes of recrystallization of hydrous phases into anhydrous ones of the nepheline and leicite type. The optimal compositions of the adhesives prepared with quartz sand and chamotte fines exhibit the following characteristics: viscosity measured on Suttard viscometer- 150–180 mm; shelf life (retention time) – 45 to 90 min; adhesion strength – 0.92 to 1.6 MPa. The coefficient of linear thermal expansion (8.43 to 8.65)10 6 °C 1, was under the ranges of the requirements for majority of building materials, thus allowing to provide high thermo-mechanical characteristics of bonded materials in the conditions of temperatures (up to 500 °C and up to 900 °C), depending upon filler type. The adhesives for repair and making lining of ovens and chimneys made from ceramic and fire resistant bricks exhibit compressive strength of 68 MPa, adhesion strength of 1.15 MPa, residual strength – 87%, shrinkage of 1.72 mm/m after heating at 900 °C.
The adhesives have been brought into commercial scale production of lift portals and frames and heat insulation of boilers and other equipment working at high temperatures.
Acknowledgements The authors would like to acknowledge financial support of the Ministry of Education and Science of Ukraine (Fundamental research project ‘‘Physico- chemical bases for regulation of structure formation process and properties of the mineral alkaline aluminosilicate binder as adhesive for the use in ecologically safety wood products for various use” (Reg. No 0117U004842).
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